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Abstract
Two hundred samples of milk and milk products including cream, ice cream, Kareish cheese and Damietta cheese (40 samples each) were collected from Assiut City markets. The samples were examined bacteriologically for enumeration, isolation and identification of enteropathogenic E.coli.
The results revealed that, 12.5% of the examined milk samples were contaminated with E.coli. Moreover, 60% of positive samples had counts of 10- 102 cfu/ml, while 20% contained less than 10 cfu/ml and 20% contained 102-103 cfu/ ml. The isolated strains were serologically identified as O25 (1), O128 (2) and untyped (2).
However, the incidence of E.coli in raw cream samples were 5%. The frequency distribution of the examined samples were 50% less than 10 cfu/g and 50% lies within the range of 10-100 cfu/g. Serological typing of the isolated strains proved to be belonged to O55.
In case of ice cream samples, E.coli could be detected in 17.5% of the examined samples. The highest frequency distribution was 57% which contained less than 10 cfu/g and 43% contained 10-100 cfu/g. Ant. Ok (B) Pool A (2), O126(2), O128(1), O142, (1) and O157 were the isolated strains of E.coli.
20% of the examined Kareish cheese samples were contaminated with E.coli. In addition, 25% of positive samples contained less than 10cfu/g, 50% contained 10-100 cfu/g and 25% contained 102-103 cfu/g. The isolates could be identified as O111 (3), O119 (2), O157(1) and untyped (2). Concerning Damietta cheese, E.coli could not be detected in the examined samples.
In addition, ice cream samples were prepared in the laboratory and incoulated with the previously isolated and identified E.coli O157 strain to yield a concentration of 106 cfu/g (6.4 log cfu/g) to study the fate of E.coli O157 in ice cream samples during storage at freezing (-6ºC) and deep freezing (-18ºC) temperatures. The obtained results pinpoint out that, the survival of E.coli O157 at freezing and deep freezing. There was a reduction in the count during the first three days and returned to increase in the first week. Then, E.coli count started to decrease until the end of the experiment where, the number of the organism become 1.1×104cfu/g (4.04 log cfu/g) and 5.5 ×104cfu/g (4.74 log cfu/g) at freezing and deep freezing storages, respectively.
The public health significance and suggestive measures to improve the keeping quality as well as sanitary conditions of milk and milk products are given.