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4 Selection of Pathogens as Components of Microbiological Criteria INTRODUCTION Microorganisms as components of microbiological criteria for foods may be grouped into two categories: pathogens, including their harmful toxins, and indicator organisms. Pathogens suitable as components of a criterion are those likely to be found in the food or ingredient which thereby becomes a potential vehicle for its transmission to consumers. Suitable indicator organisms or agents are those whose presence in the food or ingredient indicates: (1) the likelihood that a pathogenks) or harm- ful toxints) of concern also may be present; (2) the likelihood that faulty practices occurred during production, processing, or distribution that may adversely affect the safety and/or the shelf-life of the product; or (3) that the food or ingredient is unsuited for an intended use. Furthermore, ad- equate and practical methods must be available for detection and/or enu- meration of selected pathogens or indicator organisms. Other ancillary factors that relate to the selection of contaminants, as well as other com- ponents of microbiological criteria, are presented elsewhere (see Chapters 2, 3, and 6~. Indicator organisms that may be useful for the purposes indi- cated above are treated in Chapter 5. This chapter deals with the various foodborne pathogens that are of particular concern. Each pathogen is grouped in one of three categories according to the severity of the hazard it may present. The discussion of each organism or group of organisms includes its relative importance, the status of the methodist available for its detection and/or enumeration, and conclusions on suitability of the organism as a component of a micro- biological criterion. 72

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SELECTION OF PATHOGENS 73 PATHOGENS An extensive listing of foodborne diseases and the agents that cause them has been prepared by Bryan (19821. Included in this manual are brief but pertinent summaries of the nature of the organism, incubation period and symptoms of the disease, likely sources and reservoirs of the organisms, the foods most likely involved, and the most useful specimens for laboratory examination. Similar listings with emphasis on only the more commonly occurring and important foodborne diseases also are avail- able (Bryan, 1980a; Sanders et al., 19841. Although the list of foodborne diseases of microbial etiology is long, only about 20 are known to be transmitted by foods with a consequence serious and frequent enough to cause concern relative to microbiological criteria (see listing below). As for the others, either proof of their trans- mission by foods is inconclusive or suspect or they are so infrequently foodborne that their involvement is remote. Table 4- 1 presents a summary of reported foodborne disease outbreaks in the United States during the years 1977-1981 (CDC, 1983~. Similar data are available for Japan (Okabe, 1974), the United Kingdom (Vernon, 1977), and Canada (Health and Welfare Canada, 19811. The number of foodborne disease organisms required to produce disease has been investigated to some extent, largely through feeding studies using healthy adult volunteers. A summary of a series of such studies is given in Table 4-2. Except for Shigella dysenteriae, the results indicate that large numbers were necessary to cause illness in the volunteers. However, it would be imprudent to conclude that small dosages are relatively harm- less. Host parasite susceptibility varies, the more susceptible being infants, the aged, and debilitated persons. Studies in connection with investigations of certain Salmonella foodborne outbreaks indicate that relatively few cells of several serotypes caused illness. A summary of these studies in which the number of cells found in the causative vehicles were quantitated is shown in Table 4-3. Compared to those given in Table 4-2, the numbers are surprisingly low. Assuming that a reasonable serving was consumed, e.g., approximately 3 ounces of chocolate, the number causing illness would approximate 0.6-6 cells of Salmonella eastbourne. A 3-ounce serv- ing of cereal would have contained approximately 600-1,200 cells of Salmonella muenchen. It must be recognized that investigation and reporting of foodborne disease outbreaks are grossly incomplete. For example, about 400-500 outbreaks and 10,000-20,000 cases are reported annually in the United States. The actual incidence, however, may be 100 times or more the reported figures (CDC, 1981a; Hauschild and Bryan, 19801. Although

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76 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA TABLE 4-2 Summary of Various Organisms Found to Induce Illness in Volunteer Feeding Studiesa Number Causing Organism Illnessb Reference Campylobacter jejuni lob 5x 1o2 Steele and McDermott, 1978 Robinson, 1981 Clostridium perfringens type A, heat resistant 108-109 Dische and Elek, 1957 type A, heat sensitive 109 Hauschild and Thatcher, 1967 Escherichia cold 106-10~ DuPont et al., 1971; Ferguson and June, 1952; June et al., 1953; Kirby et al., 1950 Salmonella anatum 105- 108 McCullough and Eisele, 195 la,b Salmonella derby 107 McCullough and Eisele, l951c Salmonella bareilly 105- 1 o6 McCullough and Eisele, 1951 c Salmonella meleagridis 1 o6- 107 McCullough and Eisele, l951a,b Salmonella newport 106 McCullough and Eisele, l951c Salmonella pullorum 109-10 'A McCullough and Eisele, 195 id Salmonella typhi 104- 1 O9 Hornick et al., 1970a,b; DuPont et al., 1970 Shigella flexneri lo2-109 Shaughnessy et al., 1946; DuPont et al., 1969, 1972 Shigella dysenteriae 1o'-104 Levine et al., 1973 Streptococcus faecalis 109- 10~ Sedova, 1970 subsp. Iiquefaciens Vibrio cholerae (unbuffered) 1 08- 1 0 ~ ~Hornick et al., 1 97 1 (buffered) 103-104 Hornick et al., 1971 Vibrio parahaemolyticus (buffered) 1oS-7 Sanyal and Sen, 1974 Yersinia enterocolitica 109 Szita et al., 1973 aAdapted from Bryan (1977). bIn some studies no attempt was made to determine lowest levels. In others, such attempts were made for C. perfringens, V. cholerae., S. typhi, S. anatum, S. meleagridis, S. derby, E. coli, S. faecalis subsp. Iiquefaciens, Y. enterocolitica. Adults were subjects for all studies except for E. cold studies in which some nonadults were included. incomplete, the reporting at current levels through the efforts of the Centers for Disease Control (CDC) and other federal and state agencies does help to provide a continuing assessment of trends in etiologic agents and food vehicles. Furthermore, such efforts contribute to (1) identification and removal of contaminated products from the market, (2) correction of faulty food-handling practices, (3) identification and treatment of human car- riers, and (4) detection of newly emerging agents of foodborne disease. Items (1) and (2) are of particular significance with respect to microbiol- ogical criteria. Many sources of information, those referred to above and others (Bryan, 1972; Riemann and Bryan, 1979; Sours and Smith, 1980), amply justify

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SELECTION OF PATHOGENS 77 TABLE 4-3 Number of Various Organisms Found in Foods Involved as Vehicles in Foodborne Outbreaks Vehicle Strain/Serotype Number Reference Ham S. infantis 23,000/g Angelotti et al., 1961 Frozen egg yolk S. typhimurium 0.6/g CDC, 1967 Carmine dye S. cubana 30,000/0.3 g Lang et al., 196i Protein dietary supplement Spice flavored S. minnesota 11/100 g Andrews and Wilson, 1976 Apricot flavored S. minnesota 13/100 g Chocolate S. eastbourne 1.7/100 g Deibela 0.6/100 g 6/100 g 2/100 g 2.5/g 0.2-0.9/g 7-14/g 113/75 g Cereal S. muenchen Frozen dessert S. typhimurium and (Chiffonade) S. braenderup Raw hamburger S. newport 60-2300/100 g Craven et al., 1975 D'Aoust et al., 1975 Silverstolpe et al., 1962 Armstrong et al., 1970 Fontaine et al., 1978 aR. H. Deibel, Department of Bacteriology, University of Wisconsin, Madison, personal com- munication, 1974. the listing of the organisms and/or toxins given below as being of concern as causative agents of foodborne disease in the United States. The agents are grouped according to the seriousness of the hazard they present when found in food. The grouping parallels that of the International Commission on Microbiological Specifications for Foods (see Chapter 4 and Table 7 of ICMSF, 19741. Some rearrangement within categories was necessary as the scope of the current report is confined to the United States. Severe Hazards: Clostridium botulinum, Shigella, Vibrio cholerae, Salmonella typhi, Salmonella paratyphi A, Salmonella paratyphi B. Sal- monella paratyphi C, Salmonella sendai, Salmonella cholerae-suis, Bru- cella abortus, Brucella melitensis and Brucella suds, Mycobacterium bovis, hepatitis A virus, fish and shellfish toxins, and certain mycotoxins. C. botulinum causes botulism, which frequently results in death. Shiga dysentery, caused by S. dysenteriae, is an example of a disease that, without specific treatment, may result in high mortalities (ICMSF, 19781. While the illness caused by the other three species of Shigella (S. flexneri, S. boydii, S. sonneiJ is usually less severe, considerable variation in se- verity occurs; hence, these species are included. Cholera may be severe and result in death if untreated; however, mild to asymptomatic infections are common. Salmonellae more or less strictly adapted to humans are

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78 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA S. typhi, S. paratyphi A, S. paratyphi B. S. paratyphi C, and S. sendai. These species and S. cholerae-suis (primary host, swine) generally pro- duce a systemic syndrome as opposed to the gastroenteritis caused by other Salmonella (NRC, 19691. Brucellosis and tuberculosis, although now rarely foodborne in the United States, result in serious consequences for those affected. The effects of hepatitis A virus infection may range from asymptomatic to acute liver disease resulting in severe debilitation and even death. Paralytic shellfish poisoning is a severe intoxication that may result in respiratory failure and death. Ciguatera fish poisoning results in gastrointestinal and neurological symptoms with disability lasting sev- eral days, several months, or longer. The disease implications of myco- toxins for man are still not clear; however, aflatoxin is a known carcinogen. Moderate Hazards with potentially extensive spread: Salmonella. pathogenic Escherichia cold (PEC), and Streptococcus pyogenes. Moderate Hazards with limited spread: Staphylococcus aureus, Clostridium perfringens, Bacillus cereus, Vibrio parahaemolyticus, Cox- iella burnetii, Yersinia enterocolitica, Campylobacter fetus subsp. jejuni, Trichinella spiralis, and histamine. The agents listed as "moderate" hazards generally cause illnesses milder than those caused by the agents listed as "severe" hazards. Agents with potential for extensive spread are often initially spread by specific foods; however, secondary spread to other foods commonly occurs from envi- ronmental contamination and cross-contamination within processing plants and food preparation areas including homes. The illness dose for these agents may be low. Agents in the lowest risk group (moderate hazards, limited spread) are found in many foods, usually in small numbers. Generally, illness is caused only when ingested foods contain large numbers of the pathogens, e.g., C. perfringens, or have at some time contained large enough numbers to produce sufficient toxin to cause illness, e.g., S. aureus. Outbreaks are usually restricted to consumers of a particular meal or a particular kind of food, e.g., milk in the instance of C. burnetii. Y. enterocolitica and C. fetus subsp. jejuni are included as moderate hazards although the full importance of these species is not clear, nor are the factors governing secondary spread to other foods. Severe Hazards ClostridFium botulinum The importance of the botulism hazard in foods is well known and needs no further elaboration here. Food containing botulinal toxin in any amount

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SELECTION OF PATHOGENS 79 is unacceptable. Excellent methods are available for detection of C. botulinum and its toxins (AOAC, 19801. They are invaluable for the examination of foods implicated in botulism outbreaks and for other investigational pur- poses. However, the expertise required in application of the methods and in the interpretation of results precludes their use in most laboratories that routinely analyze food. Sampling and testing for purposes of routine sur- veillance of the botulism hazard in foods is ill advised. The probability that the examination of any reasonable size sample of a low-acid canned food contaminated with C. botulinum would result in~detection of the organism is too low to assure the level of safety necessary. Safety of low- acid canned foods must depend primarily on instrumentation and other process assurance mechanisms to be certain that processing has been adequately accomplished and that container integrity has been maintained (FDA, 19791. Control of the botulism hazard in perishable foods must be based on adherence to food-handling practices that will prevent growth of C. botulinum. Shigella The importance and epidemiology of shigellosis as a foodborne disease has been reviewed by Morris (1984) and Bryan (19791. Briefly, Shigella is host-adapted to humans and higher primates. Shigellosis is an infectious disease transmitted most commonly by close person-to-person contact via the fecal-oral route. Poor personal hygiene, inadequate sanitation, and crowded living conditions are important factors in the spread of this dis- ease. Migrant workers often are victims and outbreaks among younger children and others confined in hospital wards are not uncommon. Pro- cessed foods are rarely involved as vehicles of transmission; however, food may be easily contaminated during preparation by infected food handlers, particularly by convalescent carriers. The infectious dose can be as low as 10 organisms. The mere presence of Shigella in a food that will not be subsequently cooked presents a serious hazard. Detection of Shigella in foods is usually done by an enrichment pro- cedure followed by subculturing to a variety of selective/differential media (Morris, 19841. The procedures are useful for the examination of suspect foods in the investigation of outbreaks and should be applied when in- dicated. The method for their detection in foods is not sensitive and quantitation is rarely done. Because processed foods are rarely involved and analytical procedures are relatively insensitive and complicated, routine sampling and testing for Shigella would not be practical in routine surveillance programs. San- itary handling of food prior to serving, strict adherence to good personal

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80 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA hygiene practices, and proper temperature control should be relied upon as effective preventive measures. Vibrato cholerae Cholera is an acute diarrhea! disease caused by V. cholerae. This species includes the strains that cause cholera epidemics (V. cholerae O group 1) and others that are similar to the epidemic strains but have not been associated with epidemic disease; these organisms, now referred to as non- O1 V. cholerae, were formerly referred to as nonagglutinating vibrios (NAGs) or noncholera vibrios (NCVs) (CDC, 1979a). The number of V. cholerae Of and non-O1 infections found in the United States has increased in recent years. Recent outbreaks have been reported from sev- eral states (Blake et al., 1980; CDC, 1979a,b, 19801. Raw oysters and steamed crabs were often epidemiologically associated with infections. V. cholerae O 1 produces an enterotoxin that causes excretion and severe loss of fluid and electrolytes from the body. The mortality rate for severe cases where rapid replacement of fluid and electrolytes is not provided may reach 30-40% (WHO, 19761. Non-O1 V. cholerae infections are characterized by diarrhea, nausea and vomiting, abdominal cramps and fever (Morris et al., 1981), and the symptoms may range from mild to severe. Certain of the non-O1 strains produce a toxin similar to that of Of strains. The pathogenic mechanism for the nontoxigenic strains, how- ever, is not well defined. Detection of V. cholerae in foods (Twedt et al., 1984) requires primary enrichment. Subsequently, subculturing usually is done in selective media. Suspect colonies are confirmed by biochemical and serological procedures and other tests, including a mouse adrenal cell assay for cholera toxin. The method has proven useful in the examination of Moore swabs and gauze filters used in investigations of suspect water areas for presence of V. cholerae (CDC, 1979b). However, it is too insensitive and time-con- suming for routine application to oysters, crabs, and other seafoods in surveillance programs. Further, experience has shown that testing crabs from suspect waters was not an effective and beneficial means of moni- toring such areas (CDC 1979b). Over 2,000 crabs were examined in one such program and V. cholerae was found in none. Thus, microbiological criteria with V. cholerae as the designated contaminant are not indicated. Strict adherence to measures specified under the National Shellfish San- itation Program should be relied upon as the principal means of minimizing the risk of raw oysters, clams, and mussels contaminated with V. cholerae from reaching the consumer. Furthermore, adequate heat treatment of crabmeat before eating and use of good sanitary practices during the

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SELECTION OF PATHOGENS 81 handling of crabmeat before and after heat treatment (especially avoidance of cross-contamination between raw and heated product) should prevail. Salmonella With respect to the establishment and application of microbiological criteria for Salmonella in foods, there is little if any present justification to consider the human-adapted species and S. cholerae-suis mentioned above (see "Pathogens, severe hazards") differently from the other Sal- monella. All are considered pathogenic for human beings and methods for their detection and enumeration are equally applicable; therefore, see the discussion of Salmonella below under "Moderate Hazards." Brucella abortus, Brucella melitensis, Brucella suds, and Mycobacter~um basis Brucellosis and tuberculosis in man are serious diseases often resulting in long-term illness and serious complications. Brucellosis is primarily an occupational disease of workers in the meat-processing and livestock in- dustries. However, since the organisms may be shed in milk from infected animals, the disease may be acquired by drinking raw milk, usually from infected cattle and goats, or by eating fresh cheese made from such raw milk. Similarity M. bovis may be shed in milk from infected cattle and goats and be transmitted to human beings through the milk. The organisms, however, do not survive commercial milk pasteurization processes. The methods for detection of Brucella and Mycobacterium in foods are insensitive and lengthy and are unsuited for routine application to milk or other foods. The likelihood of Brucellosis in man being acquired from milk is remote for several reasons. First, availability of pasteurized milk in the United States is virtually universal. Second, the National Cooperative State/Fed- eral Brucellosis Eradication Program in cattle (USDA, 1982), which has been operative over a period of many years, has reduced the incidence of this disease in cattle to an extremely low level. For example, 11 states are now certified as brucellosis-free and all but 4 of the remaining states are nearly brucellosis-free. Finally, the public has been repeatedly warned of the risk of acquiring milkborne diseases by consuming raw milk. Never- theless a few, some perhaps in ignorance, persist in ignoring the hazards involved. Others, overly impressed by often unwarranted emphasis on attributes of so-called "natural foods", continue to seek out raw milk for their fluid milk needs. Consequently, occasional outbreaks of diseases, including Brucellosis and tuberculosis, do occur through the consumption

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82 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA of raw milk and products such as unripened cheese prepared from raw milk. As part of the brucellosis eradication program, serological techniques are used in testing the milk of dairy cattle to detect Brucella infections. In this circumstance, a microbiological criterion is applicable, effective, and widely applied. Milkborne tuberculosis in the United States is rare, largely due to the reasons stated above for brucellosis. The State/Federal Tuberculosis Erad- ication Program for cattle (USDA, 1981a) has practically eliminated the disease from milking animals. Milk pasteurization has been an effective measure. At one time, the mandatory time-temperature requirements for milk pasteurization were based on those necessary for the destruction of M. tuberculosis; present requirements are even more stringent. Also, ed- ucational programs warning of the hazards of raw milk consumption have contributed to reducing the exposure to infection. While serological methods are used in testing cattle for tuberculosis infection, neither these tests nor cultural methods are applied routinely to milk available for purchase by the public. However, suspect tuberculosis lesions found at time of carcass inspection at slaughter are routinely cul- tured for Mycobacterium. This is an important part of the state/federal eradication program. In this circumstance, a microbiological criterion is appropriate, effective, and routinely applied. viruses Viruses as agents of foodborne disease have been reviewed extensively by Cliver (1979) and Cliver et al. (19841. Hepatitis A, the cause of in- fectious hepatitis, is a virus frequently transmitted to humans by food. The consequences of infection range from asymptomatic Unapparent in- fection) to severe liver involvement and damage, and even death. Infected persons shed large numbers of the virus in the feces several days before onset of symptoms and during the acute stage of infection. Raw or in- adequately cooked shellfish that have been harvested from sewage-polluted waters have been the most frequent food vehicles for transmission. Con- tamination of foods may occur during handling and processing by infected persons during the incubation period of the disease. Viral diarrhea may be transmitted through foods. The agents most com- monly involved resemble the "Norwalk" virus. The severity of the disease however is less than for hepatitis A. Poliomyelitis also may be foodborne. Viruses are detected on the basis of their infectivity; therefore, a sus- ceptible living host must be available for testing. Cell cultures are most frequently used. However, some viruses are difficult to isolate and others

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SELECTION OF PATHOGENS 93 skipjack, and yellow fin tuna with histamine levels of 20 mg or more per 100 g are subject to regulatory action by FDA as being suspect of dete- rioration. The agency will consider regulatory action against any tuna found to contain between 10 and 20 mg of histamine per 100 g when a second indication of decomposition is present (FDA, 1982a). Furthermore, FDA has established on an interim basis a level of 50 mg of histamine per 100 g of tuna as the level of histamine in tuna that it considers a health hazard. This value may be changed after evaluation of additional data (FDA, 1982b). Accordingly, a microbiological criterion with histamine as the designated contaminant is useful when applied as indicated above to prevent deteriorated fish as well as toxic fish from reaching the processor or consumer. The histamine problem in cheese is not of sufficient incidence to justify routine testing for histamine or tyramine. Yersin~a enterocolitica The most common symptoms of Y. enterocolitica infections are gastro- enteritis and terminal ileitis. This organism has been isolated from a wide variety of foods and animals and therefore is of concern as a cause of foodborne illness. Reviews by Lee (1977), Stern and Pierson (1979), and Swaminathan et al. (1982) provide details on Y. enterocolitica as a food- borne pathogen. Current methods for its recovery from food and tests for pathogenicity are provided by Feeley and Schiemann (19841. Currently, members of the species Y. enterocolitica include biochem- ically and serologically diverse strains. In addition to the typical strains of Y. enterocolitica, there are closely related species often referred to as Y. enterocolitica-like bacteria. The species also includes nonpathogenic strains. Recently, it has been proposed to separate the group into four species, i.e., Y. enterocolitica, Y. intermedia, Y. frederiksenii, and Y. kristensenii (Bercovier et al., 1 980; Brenner, 1 9804. Although frequently found in swine and other food animals and often reported as causing illness in humans in many countries, only three doc- umented outbreaks of foodborne illness due to Y. enterocolitica have been reported in the United States. One was due to recontaminated chocolate milk (Black et al., 1978), another to tofu (soybean curd packed in water) (Aulisio et al., 1983), and the third to recontaminated pasteurized milk (CDC, 1982a). Methods for recovery of Y. enterocolitica from foods have been im- proved in recent years; however, no single method is suitable for recovery of all types of this species from various foods. Since not all strains are pathogenic, isolates must be tested for pathogenicity. Primary and sec- ondary or selective enrichment procedures, followed by determination of

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94 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA biochemical and serological characteristics of cultural isolates, are re- quired. Recently, however, a simple method based on reaction of Y. enterocolitica with Congo red has been proposed to differentiate path- ogenic from nonpathogenic strains (Prpic et al., 1983, 19841. If confirmed, this finding will fulfill an important need. In view of the limited occurrence of known foodborne outbreaks of Y. enterocolitica infections and the complexities of recovery methods, the application of microbiological criteria would currently be of little value. Methods, however, are adequate and their use should be encouraged for investigational purposes whenever foodborne outbreaks occur and in sur- veys to determine the incidence of potential pathogenic strains in suspect foods. Campylobacter The nature and significance of Campylobacter as a cause of illness in man were presented in reviews by Doyle (1981) and Bokkenheuser and Mosenthal (19811. The two species pathogenic for humans are C. fetus subsp. jejune and C. fetus subsp. intestinalis. Infections with the sub- species intestinalis rarely are foodborne and have been almost entirely limited to compromised patients such as those afflicted with cirrhosis, diabetes, or cancer. On the other hand, C. fetus subsp. jejuni is recognized as a common cause of gastroenteritis in humans. It is commonly found as a commensal or pathogen in cattle, sheep, fowl, swine, and rodents. In spite of the widespread animal reservoir, few foodborne outbreaks of Campylobacter enterocolitis have been reported in the United States. In those few, raw milk and perhaps undercooked poultry were the principal vehicles of transmission (Bryan, 1983; Park et al., 19841. C. fetus subsp. jejuni has been inappropriately termed thermophilic, as it is neither thermophilic nor heat resistant. However, an outstanding characteristic of C. fetus subsp. jejuni is its growth at 42-43C (107.6- 109.4F) with poorer growth at 37C (98.6F) and no growth at 25C (77F). Also, the organism is microaerophilic and requires an atmosphere of reduced oxygen for growth. Because of its sensitivity to air and the relatively high temperature required for growth, growth of C. fetus subsp. jejuni in foods would be unlikely under ordinary conditions of food han . . ~Taxonomic uncertainty existed over the nomenclature for members of this species. In the eighth edition of "Bergey's Manual" (Buchanan and Gibbons, 1974), they are classified as a single species, C. fetus subsp. jejuni. In the classification by Veron and Chatelain (1973) and in the Approved Lists of Bacterial Names of the International Committee on Systematic Bac- teriology, they are divided into the two species C. jejuni and C. coli.

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SELECTION OF PATHOGENS 95 cling. Until recently, C. fetus subsp. jejuni was not usually sought in foods suspect in gastroenteritis outbreaks. Also, while the animal reser- voirs are well known, little is known of the incidence of this organism in food supplies in general. Methods for detecting C. fetus subsp. jejuni in foods are available (Park et al., 1984~. The following conditions are required for accurate analysis: (1) large sample size, (2) suitable microaerophilic condition, (3) selective broth enrichment, (4) filtration to separate the small filterable campylo- bacters from other nonfilterable organisms in the enrichment cultures, and (5) selective plating agar. Routine analysis of foods for the presence of C. fetus subsp. jejuni at the present is not practical because procedures for its recovery from foods are in a state of rapid development. While published data on the incidence of foodborne Campylobacter enteritis in the United States are limited, unofficial information appears to indicate that campylobacteriosis is more widespread. Sanitary handling, proper cooking, and prevention of tem- perature abuse of sensitive foods and avoidance of consumption of raw milk would be far more effective control measures. While microbiological criteria would not be applicable, surveys to ascertain the incidence of this organism in the general food supply should be encouraged and investi- gations of foodborne gastroenteritis outbreaks should include examination of suspect food for the presence of C. fetus subsp. jejuni. Tr~chinella spiralis This nematode, which infects many species of animals, causes a fre- quently severe parasitic disease, trichinellosis, in humans. The most im- portant source of human infection is inadequately cooked pork. Human infection occurs only when the meat of host animals is eaten raw or in an undercooked state. Several outbreaks of trichinellosis are reported an- nually in the United States. Forty-four outbreaks were reported from 1977 through 1981 (see Table 4-11. For a brief summary of the sources of the parasite and the nature and consequences of infection see Healy and Jur- anek (19791. Symptoms of trichinellosis in humans that occur at time of initial in- vasion include vomiting, diarrhea, and fever. Later, during the phase of parasite distribution to various tissues, joint manifestations, edema, and even myocarditis, encephalitis, and neuritis may occur. The larvae of T. spiralis (trichinellae) in meat can be detected by several methods, including microscopic examination of fresh or digested meat and by enzyme-linked immunosorbent assay (ELISA). While larvae de- tection methods are routinely used in many countries for examination of

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96 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA swine after slaughter, they are not used in the United States as a means of preventing infected meat from reaching the consumer. Rather, the processing procedures specified in USDA regulations for destroying tri- chinellae in infected meat are emphasized by regulatory agencies and others. These procedures thorough cooking of pork (to at least 58C [137Fl), proper meat curing conditions, and specified freezing conditions (USDA, 1973, 1981b) are considered more effective in preventing hu- man infection as well- as less expensive than is routine examination of meat by larvae detection methods. REFERENCES Andrews, W. H., and C. R. Wilson 1976 Salmonella contamination in a protein dietary supplement. Pp. 219-220 in FDA Byliner No. 5. Washington, D.C.: Food and Drug Administration. Angelotti, R., G. C. Bailey, M. J. Foter, and K. H. Lewis 1961 Salmonella infantis isolated from ham in food poisoning incident. Publie Health Reports 76:771-776. AOAC (Association of Offieal Analytical Chemists) 1980 Official Methods of Analysis. 13th Ed. Washington, D.C.: AOAC. APHA (American Publie Health Association) 1970 Recommended Procedures for the Examination of Sea Water and Shellfish. 4th Ed. Washington, D.C.: APHA. Armstrong, R. W., T. Fodor, G. T. Curlin, A. B. Cohen, G. K. Morris, W. T. Martin, and J. Feldman 1970 Epidemic Salmonella gastroenteritis due to contaminated imitation ice cream. Am. J. Epidemiol. 91:300-307. Aulisio, C.C.G., J. T. Stanfield, S. W. Weagant, and W. E. Hill 1983 Yersiniosis associated with tofu consumption. Serological, biochemical and patho- genieity studies of Yersinia enterocolitica isolates. J. Food Prot. 46:226-230, 234. Bagnis, R., S. Chanteau, E. Chungue, J. M. Hurtel, T. Yasumoto, and A. Inoue 1980 Origins of ciguatera fish poisoning: a new dinoflagellate, Gambierdiscus toxicus Adaehi and Fukuyo, definitely involved as a causal agent. Toxieon 18:199-208. Bereovier, H., D. J. Brenner, J. Ursing, A. G. Steigerwalt, G. R. Fanning, J. M. Alonzo, G. P. Carter, and H. H. Mollaret 1980 Characterization of Yersinia enterocolitica sensu stricto. Curr. Microbiol. 4:201-206. Bergdoll, M. S. 1979 Staphylococcal intoxications. Pp. 443-494 in Food-borne Infections and Intoxica- tions. 2nd Ed. H. Riemann and F. L. Bryan, eds. New York: Academic Press. Black, R. E., R. J. Jackson, T. Tsai, M. Medevesky, M. Shayegani, J. C. Feeley, K.J.E. McLeod, and A. W. Wakelee 1978 Epidemic Yersinia enterocolitica infection due to contaminated chocolate milk. N. Engl. J. Med. 298(2):76-79. Blake, P. A., D. T. Allegra, J. D. Snyder, T. J. Barrett, L. McFarland, C. T. Caraway, J. C. Feeley, J. P. Craig, J. V. Lee, N. D. Puhr, and R. A. Feldman 1980 Cholera a possible endemic focus in the United States. N. Engl. J. Med. 302:305- 309. Bokkenheuser, V. D., and A. C. Mosenthal 1981 Campylobacteriosis: A foodborne disease. J. Food Safety 3:127-143.

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SELECTION OF PATHOGENS 97 Brenner, D. J. 1980 Classification of Yersinia enterocolitica. In Yersinia enterocolitica. E. J. Bottone, ed. Boca Raton, Fla.: CRC Press. Bryan, F. L. 1972 Emerging foodborne diseases. I. Their surveillance and epidemiology. J. Milk Food Technol. 35:618-625. 1977 Diseases transmitted by foods contaminated by wastewater. J. Food Prot. 40:45-56. 1979 Infections and intoxications caused by other bacteria. Pp. 211-297 in Food-borne Infections and Intoxications. 2nd Ed. H. Riemann and F. L. Bryan, eds. New York: Academic Press. 1980a Procedures to use during outbreaks of foodborne disease. Pp. 40-51 in Manual of Clinical Microbiology. 3rd Ed. E. H. Lennette, A. Balows, W. J. Hausler, Jr., and J. P. Truant, eds. Washington, D.C.: American Society for Microbiology. 1980b Epidemiology of foodborne diseases transmitted by fish, shellfish and marine crus- taceans in the United States, 1970-1978. J. Food Prot. 43:859-876. 1982 Diseases transmitted by foods A classification and summary. 2nd Ed. Atlanta: Centers for Disease Control. 1983 Epidemiology of milk-borne diseases. J. Food Prot. 46:637-649. Buchanan, R. E., and N. E. Gibbons 1974 Bergey's Manual of Determinative Bacteriology. 8th Ed. Baltimore, Md.: Williams and Wilkins. CDC (Center for Disease Control) 1967 Salmonella Surveillance Report No. 61 (and supplement dated Oct. 23, 1967). Atlanta: Center for Disease Control. 1979a Non-O1 Vibrio cholerae infections Florida. Morb. Mort. Weekly Rpt. 28:571-572, 577. 1979b Vibrio cholerae O-group 1 infections in Louisiana, 1978. EPI-78-102-2. Atlanta: Center for Disease Control. CDC (Centers for Disease Control) 1980 Cholera Florida. Morb. Mort. Weekly Rpt. 29:601. 1981a Foodborne disease outbreaks. Annual Summary 1979. Atlanta: Centers for Disease Control. 1981b Foodborne disease surveillance. Annual Summary 1978 (revised). Reissued February 1981. Atlanta: Centers for Disease Control. 1982a Multi-state outbreak of yersiniosis. Morb. Mort. Weekly Rpt. 31:505-506. 1982b Isolation of E. cold 0157:H7 from sporadic cases of hemorrhagic colitis United States. Morb. Mort. Weekly Rpt. 31:580, 585. 1983 Foodborne disease outbreaks. Annual Summary 1981. Atlanta: Centers for Disease Control. Cliver, D. O 1979 Viral Infections. Pp. 299-342 in Food-Borne Infections and Intoxications, 2nd Ed., H. Riemann and F. L. Bryan, eds. New York: Academic Press. Cliver, D. O., R. D. Ellender, and M. D. Sobsey 1984 Foodborne Viruses. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Craven, P. C., W. B. Baine, D. C. Mackel, W. H. Barker, E. J. Gangarosa, M. Goldfield, H. Rosenfeld, R. Altman, G. Lachapelle, J. W. Davies, and R. C. Swanson 1975 International outbreak of Salmonella eastbourne infection traced to contaminated chocolate. Lancet 1:788-793, April 5. Dale, B., and C. M. Yentsch 1978 Red tide and paralytic shellfish poisoning. Oceans 21:41-49.

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98 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA D'Aoust, J. Y., B. J. Aris, P. Thisdale, A. Durante, N. Brisson, D. Dragon, G. Lachapelle, M. Johnston, and R. Laidley 1975 Salmonella eastbourne outbreak associated with chocolate. Can. Inst. Food Sci. Tech- nol. J. S:181-184. DeSilva, D. P., and M. Poll 1982 Ciguatera-tropical fish poisoning. Annual Yearbook. International Game Fish As- sociation. Dische, F. E., and S. D. Elek 1957 Experimental food poisoning by Clostridium welchii. Lancet 2:71-74. Doyle, M. P. 1981 Campylobacter fetus subsp. jejuni: An old pathogen of new concern. J. Food Prot. 44:480-488. DuPont, H. L., R. B. Hornick, A. T. Dawkins, M. J. Snyder, and S. B. Formal 1969 The response of man to virulent Shigellaflexneri 2a. J. Infect. Dis. 119:296-299. DuPont, H. L., R. B. Hornick, M. J. Snyder, J. P. Libonati, and T. E. Woodward 1970 Immunity in typhoid fever: evaluation of live streptomycin-dependent vaccine. Pp. 236- 239 in Proceedings of 10th Interscience Conference on Antimicrobial Agents and Chemotherapy. G. L. Hobby, ed. Oct. 18-21. DuPont, H. L., S. B. Formal, R. B. Hornick, M. J. Snyder, J. P. Libonati, D. G. Sheahan, E. H. LaBrec, and J. P. Kalas 1971 Pathogenesis of Escherichia cold diarrhea. N. Engl. J. Med. 285: 1-9. DuPont, H. L., R. B. Hornick, M. J. Snyder, J. P. Libonati, S. B. Formal, and E. J. Gangarosa 1972 Immunity in shigellosis. II. Protection induced by oral live vaccine or primary in- fection. J. Infect. Dis. 125:12-16. Edwards, S. T., and W. E. Sandine 1981 Public health significance of amines in cheese. J. Dairy Sci. 64:2431-2438. Enright, J. B. 1961 The pasteurization of cream, chocolate milk and ice cream mixes containing the organism of Q-fever. J. Milk Food Technol. 24:351-355. Enright, J. B., W. W. Sadler, and R. C. Thomas 1956 Observations on the thermal inactivation of the organism of Q-fever in milk. J. Milk Food Technol. 19:313-318. FDA (Food and Drug Administration) 1979 Thermally processed foods packaged in hermetically sealed containers. Code of Fed- eral Regulations 21 CFR 113. 1982a Defect action levels for histamine. Supplementary information. Federal Register 47(178):40487-40488. 1982b FDA Compliance Policy Guide 7108-24. Dockets Management Branch. Rockville, Md.: Food and Drug Administration. Feeley, J. C., and D. A. Schiemann 1984 Yersinia. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. American Public Health Association. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Ferguson, W. W., and R. C. June 1952 Experiments on feeding adult volunteers with Escherichia cold 111, B4, a coliform organism associated with infant diarrhea. Am. J. Hyg. 55:155-169. Fontaine, R. E., S. Arnon, W. T. Martin, T. M. Vernon, E. J. Gangarosa, J. J. Farmer, A. B. Moran, J. H. Silliker, and D. L. Decker 1978 Raw hamburger: An interstate common source of human salmonellosis. Am. J. Ep- idemiol. 107:36-45.

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SELECTION OF PATHOGENS 99 Gangaroso, E. J. 1978 What have we learned from 15 years of Salmonella surveillance? In Proceedings, National Salmonellosis Seminar, Jan. 10-11. Washington, D.C.: U.S. Department of Agriculture. Gilbert, R. S. 1979 Bacillus cereus gastroenteritis. Pp. 495-518 in Food-borne Infections and Intoxi- cations. 2nd Ed. H. Riemann and F. L. Bryan, eds. New York: Academic Press. Harmon, S. M., and C. L. Duncan 1984 Clostridium pe~fringens. In Compendium of Methods for the Microbiological Ex- amination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Harmon, S. M., and J. M. Goepfert 1984 Bacillus cereus. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health As- sociation. Hauschild, A.H.W., and F. S. Thatcher 1967 Experimental food poisoning with heat-susceptible Clostridium pe~fringens type A. J. Food Sci. 32:467-469. Hauschild, A. H. W., and F. L. Bryan 1980 Estimate of cases of food- and waterborne illness in Canada and the United States. J. Food Prot. 43:435-440. Health and Welfare Canada 1981 Foodborne and Waterborne Disease in Canada. Annual Summary 1977. Ottawa: Health Protection Branch, Health and Welfare Canada. 1983a Hemorrhagic colitis in a home for the aged Ontario. Canada Diseases Weekly Report: 9(8):29-32. 1983b Hemorrhagic colitis following the consumption of hamburger Quebec. Canada Dis- eases Weekly Report 9(13):50-51. Healy, G. R., and D. D. Juranek 1979 Parasitic infections. Pp. 343-385 in Food-borne Infections and Intoxications. H. Riemann and F. L. Bryan, eds. New York: Academic Press. Hickman, F. W., J. J. Farmer III, D. G. Hollis, G. R. Fanning, A. G. Steigerwalt, R. E. Weaver, and D. J. Brenner 1982 Identification of Vibrio hollisae sp. nov. from patients with diarrhea. J. Clin. Mi- crobiol. 15:395-401. Hobbs, B. C. 1979 Clostridum perfringens gastroenteritis. Pp. 131-171 in Food-borne Infections and Intoxications. 2nd Ed. H. Riemann and F. L. Bryan, eds. New York: Academic Press. Hornick, R. B., S. E. Greisman, T. E. Woodward, H. L. DuPont, A. T. Dawkins, and M. J. Snyder 1970a Typhoid fever: pathogenesis and immunologic control (I). N. Engl. J. Med. 283:686 691. 1970b Typhoid fever: pathogenesis and immunologic control (II). N. Engl. J. Med. 283:739 746. Hornick, R. B., S. I. Music, R. Wenzel, R. Cash, J. P. Libonati, M. J. Snyder, and T. E. Woodward 1971 The broad street pump revisited: Response of volunteers to ingested cholera vibrios. Bull. N.Y. Acad. Med. 47: 1181-1191.

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100 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA ICMSF (International Commission on Microbiological Specifications for Foods) 1974 Microorganisms in Foods. 2.Sampling for microbiological analysis: Principles and specific applications. Toronto: University of Toronto Press. 1978 Microorganisms in Foods. l .Their significance and methods of enumeration. Toronto: University of Toronto Press. June, R. C., W. W. Ferguson, and M. T. Worfel 1953 Experiments in feeding adult volunteers with Escherichia cold 55, Bs, a coliform organism associated with infant diarrhea. Am. J. Hyg. 57:222-236. Kirby, A. C., E. G. Hall, and W. Coackley 1950 Neonatal diarrhoea and vomiting. Outbreaks in the same maternity unit. Lancet 2:201- 207. Lang, D. J., L. J. Kunz, A. R. Martin, S. A. Schroeder, and L. A. Thomson 1967 Carmine as a source of nosocomial salmonellosis. N. Engl. J. Med. 276:829-832. Lee, W. H. 1977 An assessment of Yersinia enterocolitica and its presence in foods. J. Food Prot. 40:486-489. Levine, M. M., H. L. DuPont, S. B. Formal, R. B. Hornick, A. Takeuchi, E. J. Gangarosa, M. J. Snyder, and J. P. Libonati 1973 PathogenesisofShigelladysenteriaeI(Shiga)dysentery. J. Infect. Dis. 127:261- 270. Marier, R., J. G. Wells, R. C. Swanson, W. Callahan, and I. J. Mehlman 1973 An outbreak of enteropathogenic Escherichia cold foodborne disease traced to imported French cheese. Lancet 2:1376-1378. McCullough, N. B., and C. W. Eisele 1951a Experimental human salmonellosis. I. Pathogenicity of strains of Salmonella melea- gridis and Salmonella anatum obtained from spray-dried whole egg. J. Infect. Dis. 88:278-289. l951b Experimental human salmonellosis. II. Immunity studies following experimental ill- ness with Salmonella meleagridis and Salmonella anatum. J. Immunol. 66:595-608. l951c Experimental human salmonellosis. III. Pathogenicity of strains of Salmonella new- port, Salmonella derby and Salmonella bareilly obtained from spray-dried whole egg. J. Infect. Dis. 89:209-213. l951d Experimental human salmonellosis. IV. Pathogenicity -otst~ns of Salmonella pul- lorum obtained from spray-dried whole egg. J. Infect. Dis. 89:259-265. Mehlman, I. J. 1984 Coliforms, fecal coliforms, Escherichia cold and enteropathogenic E. coli. In Com- pendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Morris, G. K. 1984 Shigella. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Morris, J. G., R. Wilson, B. R. Davis, I. K. Wachsmuth, C. F. Riddle, H. G. Wathen, R. A. Pollard, and P. A. Blake 1981 Non-O Group 1 Vibrio cholerae gastroenteritis in the United States. Clinical, epi- demiologic and laboratory characteristics of sporadic cases. Ann. Intern. Med. 94:656- 658. NRC (National Research Council) 1969 An Evaluation of the Salmonella Problem. Committee on Salmonella. Washington, DC.: National Academy of Sciences.

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SELECTION OF PATHOGENS 101 Okabe, S. 1974 Statistical review of food poisoning in Japan Especially that by Vibrio parahae- molyticus. In Proceedings, International Symposium on Vibrio parahaemolyticus. T. Fujino, G. Sakaguchi, R. Sakazaki, and Y. Takeda, eds. Tokyo: Saikon Publishing. Ormsbee, R. A. 1980 Rickettsiae. Pp. 922-933 in Manual of Clinical Microbiology. 3rd Ed. E. H. Len- nette, A. Balows, W. J. Hausler, Jr., and J. P. Truant, eds. Washington, D.C.: American Society for Microbiology. Oshima, Y., L. J. Buckley, M. Alam, and Y. Shimizu 1977 Heterogeneity of paralytic shellfish poisons. Three new toxins from cultured Gon- youlax tamarensis cells, Mya arenaria and Saxidomas gigantens. Comp. Biochem. Physiol. 57:31-34. Park, C. E., R. M. Smibert, M. J. Blaser, C. Vanderzant, and N. J. Stern 1984 Campylobacter. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health As- sociation. Prpic, J. K., R. M. Robins-Browne, and R. B. Davey 1983 Differentiation between virulent and nonvirulent Yersinia enterocolitica isolates by using Congo red agar. J. Clin. Microbiol. 18:486-490. 1984 Differentiation between virulent and nonvirulent Yersinia enterocolitica isolates by using Congo red agar. Erratum. J. Clin. Microbiol. 19:446. Rice, S. L., R. R. Eitenmiller, and P. E. Koehler 1976 Biologically active amines in food. A review. J. Milk Food Technol. 39:353-358. Riemann, H., and F. L. Bryan, eds. 1979 Food-borne Infections and Intoxications. 2nd Ed. New York: Academic Press. 748 pp. Riley, L. W., R. S. Remis, S. D. Helgerson, H. B. McGee, J. G. Wells, B. R. Davis, R. J. Hebert, E. S. Olcott, L. M. Johnson, N. T. Hargrett, P. A. Blake, and M. L. Cohen 1983 Hemorrhagic colitis associated with a rare Escherichia cold serotype. New. Engl. J. Med. 308:681-685. Robinson, D. A. 1981 Infective dose of Campylobacter jejuni in milk. Br. Med. J. 282:1584. Sanders, A. C., F. L. Bryan, J. C. Olson, Jr., and J. M. Madden 1984 Foodborne illness Suggested approaches for the analysis of foods and specimens obtained in outbreaks. In Compendium of Methods for the Microbiological Exami- nation of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Sanyal, S. C., and P. C. Sen 1974 Human volunteer study on the pathogenicity of Vibrio parahaemolyticus. In Pro- ceedings, International Symposium on Vibrio parahaemolyticus. F. Fujino, G. Sak- aguchi, R. Sakazaki, and Y. Takeda, eds. Tokyo: Saikon Publishing. Sedova, N. N. 1970 Study of the role of enterococci in the etiology of bacterial food poisoning. Vopr. Pitan. 29:82-87. Shaughnessy, H. J., R. C. Olsson, K. Bass, F. Friewer, and S. O. Levinson 1946 Experimental human bacillary dysentery. J. Am. Med. Assoc. 132:362-368. Shimizu, Y. 1979 Developments in the study of paralytic shellfish toxins. In Proceedings of the Second International Conference on Toxic Dinoflagellate Blooms. D. K. Taylor and H. H. Seliger, eds. New York: Elsevier/North Holland.

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102 EVALUATION OF THE ROLE OF MICROBIOLOGICAL CRITERIA Silliker, J. H. 1980 Status of Salmonella Ten years later. J. Food Prot. 43:307-313. Silverstolpe, L., U. Plazikowski, J. Kjellander, and G. Vahlne 1962 An epidemic among infants caused by Salmonella muenchen. J. Appl. Bacteriol. 24: 134- 142. Sours, H. E., and D. G. Smith 1980 Outbreaks of foodborne disease in the United States. 1972-1978. J. Infect. Dis. 142: 122- 125. Steele, T. W., and S. McDermott 1978 Campylobacter enteritis in South Austrialia. Med. J. Austr. 2:404-406. Stern, N. J., and M. D. Pierson 1979 Yersinia enterocolitica: A review of the psychrotrophic water and foodborne pathogen. J. Food. Sci. 44:1736-1742. Stoloff, L. 1984 Toxigenic Fungi. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Swaminathan, B., M. C. Harmon, and I. J. Mehlman 1982 A review: Yersinia enterocolitica. J. Appl. Bacteriol. 52:151-183. Szita, J., M. Kali, and B. Redey 1973 Incidence of Yersinia enterocolitica infection in Hungary. Proceedings, Symposium on Yersinia, Pasteurella and Francisella. In Contributions in Microbiology and Im- munology. Vol. 2. S. Winblad, ed. Basel, Switzerland: Karger. Tatini, S., D. G. Hoover, and R.V.F. Lachica 1984 Methods for the isolation and enumeration of Staphylococcus aureus. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. Twedt, R. M., J. M. Madden, and R. R. Colwell 1984 Vibrio. In Compendium of Methods for the Microbiological Examination of Foods. 2nd Ed. M. L. Speck, ed. Washington, D.C.: American Public Health Association. USDA (U.S. Department of Agriculture) 1973 Treatment of pork products to destroy trichinae. Meat and Poultry Inspection Reg- ulation Part 318. 10:125-131. Washington, D.C.: USDA. 1981 a Bovine Tuberculosis Eradication, Uniform Methods and Rules, effective Jan. 2, 1981. Animal and Plant Health Inspection Service. Washington, D.C.: USDA. 1981b Labeling policy book. Food Safety and Inspection Service: 53. Washington, D.C.: USDA. 1982 Brucellosis Uniform Methods and Rules and Amendment of May, 1982. Animal and Plant Health Inspection Service. Washington, D.C.: USDA. USDHEW (U.S. Department of Health, Education and Welfare) 1965 National Shellfish Sanitation Program, Manual of Operations, Part 1, Sanitation of shellfish growing areas, 1965 revision. Washington, D.C.: Superintendent of Doc- uments. USPHS/FDA (U.S. Public Health Service/Food and Drug Administration) 1978 Grade A Pasteurized Milk Ordinance. 1978 Recommendations. USPHS/FDA Publ. No. 229. Washington, D.C.: U.S. Government Printing Office. Vernon, E. 1977 Food Poisoning and Salmonella infections in England and Wales, 1973-1975. Public Health (UK) 91:225-235.

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SELECTION OF PATHOGENS 103 Veron, M., and R. Chatelain 1973 Taxonomic study of the genus Campylobacter Sebald and Veron and designation of the neotype strain for the type species Campylobacterfetus (Smith and Taylor) Sebald and Veron. Int. J. Syst. Bacteriol. 23:122-134. Voigt, M. N., and R. R. Eitenmiller 1978 Role of histidine and tyrosine decarboxylases and mono- and diamine oxidases in amine build-up in cheese. J. Food Prot. 41:182-186. Voigt, M. N., R. R. Eitenmiller, P. E. Koehler, and M. K. Hamdy 1974 Tyramine, histamine and tryptamine content of cheese. J. Milk Food Technol. 37:377- 381. Wells, J. G., B. R. Davis, I. K. Wachsmuth, L. W. Riley, R. S. Remis, R. Solokow, and G. K. Morris 1983 Laboratory investigation of hemorrhagic colitis outbreaks associated with a rare Esch- erichia cold serotype. J. Clin. Microbiol. 18:512-520. WHO (World Health Organization) 1976 Microbiological aspects of food hygiene. Report on a WHO Expert Committee with participation of FAO. Technical Report Series 578. Geneva, Switzerland: World Health Organization. Withers, N. 1982 Ciguatera fish poisoning. Am. Rev. Med. 33:97-111.