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OCR for page 72
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
OCR for page 73
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
OCR for page 74
74
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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 42-43°C (107.6-
109.4°F) with poorer growth at 37°C (98.6°F) and no growth at 25°C
(77°F). 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.
OCR for page 95
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
OCR for page 96
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 58°C
[137°Fl), 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.
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Representative terms from entire chapter:
foodborne disease
