الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
INTRODUCTION
Cheese has or:casior.ally been implicated in ·-rood poison- ing since the 19th century.
The World Health Organization
<WHO) has described 16 different bacterial into>:ication and 7 viral and rickettsial
diseases caused by ingestion of contaminated dairy products <Kaplan et al.,
1962). The poisoning usually is not reported or publicized unless out break is fairly
large. It is known, however, that a large percentage of all cases reported as ”Food
poisoning” or ”Food infection” actually are staph·y lococcal food poisoning.
Staphylococcal food poisoning is ·the most commonly occurring true food poisoning
which is caused by the ingestion of ·the entrotm:in formed in food during growth of
certain strains of St Of.-”’hyl ococc·us a·w”e·us. The to): in is termed an entroto>:in
because it causes gastroenterities or infla mmation of the lining of the stomach and
intestines.
St.aphylocm::ci can readily multiply in many foods, but in Egypt and warm countries, dairy
products a-.e probably the type of ·food most frequently implicated. Therefore, outbreaks
of cheese-borne staphylococcal enteroto>:in have been reported
<Legler et aL, 1957; Hendrict<s et al., 1959; Allen &
stovall, 1960; Hausler et al., 1960; Zehren and Zehren, 1968b
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and Troller, 1976>.
However, evidences have been accumulated by a number of investigators (Takahashi & Johns, 1959;
Thatcher & Ross, 1960 and Walker et al., 1961} which verity that when S.aureus is present in
significant numbers in raw milk used for cheese at the begining of the process, the organisms will
tend to be concentrated in the curd and also increase in numbers during the manufacturing as
well as persist several weeks during the ripening of the cheeses.
Staphylococci may produce five serological types of entrotoxin; A, B, c, D and E, that differ in
toxicity; most food poisoning is from type A. Staphylococcal enterotoxins
are e;:oproteins that, when ingested, cause the development of a gastroenteric syndrome
characterized by early onset, about
2 to 3 h after ingestion. Some strains produce staphylococ-
cins or micrococcins which may be bacteriostatic or bactericidal to other
staphylococci and certain other bacteria (Gilmour & Rowe, 1990). However, appreciable levels
of enterotoxin are produced only after conside·rable growth of the staphylococcus; usually a
population of at least several millions per milliliter or gram must be attained. Therefore, the
conditions that favor toxin production are those best for growth of staphylococcus.
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Moreover, other kinds of food bacteria, competing with the staphylococcus, may repress its growth
enough to delay or prevent production of toxin. The effectivness of repression varies with the
kinds and nLwiliers of competing organisms, the type of food, temperature and time. It has been
observed that the production of enterotoxin by tr.e staphylococcus is more
likely when competing organisms are absent, few or inhibited for some reasons.
Of all dairy products, cheese is perhaps the most susceptible to S.aureus contamination.
The presence of large numbers of staphylococci in cheese must be due to gross contamination or
to incidental contamination, followed by growth either in milk or cheese or in both. Even with
to-days advances, the product is still largely made by hand in open vats. The cheesemaking process
necessitates maintenance of favorable temperatures for growth of S.aur91.1S, for extended
periods. Contaminatior, of cheese milk with a very small in- oculum of S.aureus (5 CFU/ml>
could cause formation of enterotoxins in cheese, in the absence of starter activity (Ibrahim
et al., 1981b>. The account of S.aur...us present in the cheese is not always a reliable indicator
for likelihood of the presence of enterotoxins because the count could decl- ine rapidly after
production !Ibrahim et al., 1981 a and b).
However, conditions that lead to presence of detectable
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amount of enterotoxin A in Cheddar and Colby cheeses <Tatini et al., 197lb; Zehren & Zehren,
1968a) in Blue, Brick, Mozzarella and Swiss cheeses (Tatini et al., 1973> were identified.
While growth of S.aur9us can occur in other varieties of cheese <Tuckey et al., 1964; Naguib
et al.,
1978; Ahmed et al., 1983 b; Tawfek, 1984; Mahmoud et al.,
1985 and Naguib et al., 1986>, it is not l:nown whether these support enterotoxin production.
In addition, some of the toxigenic staphylococci are very salt-tolerant, growing in sodium
chloride solutions that approach saturation (Frazier, 1967}. Helmy et al., (l975l reported that
S.a 9us tolerated 2.5-15 salt in cheese. Therefore, the assumption that pickled cheese is
a safe product (low pH and high salt} may not be true, and that such cheeses could become a risk to
public health on account of the entrotoxin produced by S.aur9us (Nussinovitch et al.,
1987).
Soft cheeses such as kareish, Tallaga and Domiati are the most popular varieties of cheese in
Egypt. These cheeses, with their high moisture and salt in water phase contents appear to be a
good environment for growth of enteroto>:igenic S.a e s. They could, if contaminated, be a major
cause of food-borne diseases. Cases of food poisoning caused by con-
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sumption of cheese heavily contaminated with staphylococci have been documented (Hendricks et
al., 1959>.
Data concerning the incidence of staphylococcal food poisoning in Egypt are not available,
although existence of enterotoxigenic S.aure in dairy products is recognized
<Ahmed et al., 1978 and Ahmed, 1980}. Si><teen toxigenic strains of S.aure have been
isolated from 100 market samples of Domiati cheese (Abou-Donia et al., 1985a>. Also, toxigenic
strains of S.aurehave been isolated from lOX of market kareish cheese samples, and all of these
strains were thermonuclease and enterotoxin positive (Abou-Donia et al.,
1985 b).
With these facts in view, the present work was planned to study the growth and survival of
different enterotm:igenic strains of S.auretiS in kareish, Tallaga and Domiati cheeses and also
the potential for enterotoxins production in these cheeses.