Incidence of Salmonella species in Table Eggs and some Egg-based Products
The incidence of Salmonella species was determined in 1050 eggs including balady hen’s eggs, farm hen’s eggs and duck’s eggs (350 eggs each represented by 70 samples as every 5 eggs constitute one sample) and in 90 samples of egg-based products including mayonnaise, cream cake and custard (30 each) were collected from different localities in Assiut city, Egypt. Salmonella was recovered from 8.58, 5.72% of balady hen’s egg shells using Xylose Lysine Deoxycholate (XLD) agar and Salmonella Shigella (SS) agar, respectively and could be isolated from egg content in a percentage of 1.43% by XLD agar. Different serotypes of Salmonella were isolated from shells of balady hen’s eggs including S. typhimurium, S. anatum, S. infantis, S. kentucky while, S. enteritidis was the only serotype that recovered from both shell and content. In case of farm hen’s eggs, S. kentucky and S. infantis could be identified from positive shell and content samples, respectively at same percentage of 1.43% by using XLD agar. On the other hand, Salmonella could not be detected on SS agar from both shell and content of all examined samples. Concerning duck’s eggs 4.29 and 1.43% of shell samples were contaminated with Salmonella by using XLD and SS, respectively. While, 2.86 and 1.43% of examined egg content samples were positive using XLD and SS agar, respectively and S. typhimurium was the predominant serotype which isolated from both shell and content samples. While, S. infantis was recovered from shell only and S. kentucky was isolated from content only. Salmonella species were existed in 2 (6.66%) and 1 sample (3.33%) of the examined cream cake using XLD and SS agar, respectively while, none of the examined custard and mayonnaise samples were positive for Salmonella on both media. S. kentucky, S. shubra and S. enteritidis were isolated from the positive cream cake samples with an equal incidence of 3.33 % for each. Although XLD agar was found to be comparatively better in recovering Salmonella species than SS agar, the two media were found to be complementary to each other for recovering different Salmonella serotypes. Detection of common invA gene in all isolated Salmonella serotypes by PCR assay showed positive amplification of 284 bp fragment specific for the invA gene with total percentage of 100%. Screening of 12 isolates of S. typhimurium and S. enteritidis, which were the most prevalent serotypes in the positive samples for stn, hilA and fimH virulence genes by multiplex PCR revealed varying distribution pattern. The public health hazards and the recommended measures required to prevent contamination of eggs and its based products by Salmonella were discussed.
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