Abstract of research

Bacteriological and Molecular studies of Listeria species in milk and milk products at El-Kaliobia Governorate

1Ashraf, A. Abd El Tawab, 2Ahmed, A. A. Maarouf and 2Zeinab, A.M. Mahdy

Abstract

A total of 200 random samples of raw milk, Fita cheese, Kariesh cheese and ice cream (50 samples each) were collected from small retails and different supermarkets in El-Kaliobia Governorate to estimate the prevalence of Listeria species in such products with special interest to L. monocytogenes. The bacteriological examination of the samples resulted; 13(6.5%) isolates of Listeria species were recovered from 200 samples, includes 10 L. monocytogenes (5.0%) and 3 L. grayi (1.5%). Moreover, the other 4 species (L. ivanovii; L. innocua; L. seeligeri and L. welshimeri) were not isolated from all samples (Listeria strains). The in-vitro antimicrobial sensitivity test showed that the isolated L. monocytogenes were sensitive to amoxicillin; gentamycin; enrofloxacin; kanamycin and ampicillin. While they were resistant to Nalidixic acid, streptomycin and tetracycline. The results of virulence tests for isolated Listeria strains appeared that all of L. monocytogenes strains were virulent strains as all of them were positive to CAMP test; showed narrow zone of β-hemolysis on sheep blood agar and were positive for Anton’s test. Meanwhile, L. grayi strains were non-virulent, as none of them could produce hemolysin (CAMP test negative) and negative for Anton’s test. The PCR results for L. monocytogenes showed that all genes (16S rRNA; inlA; inlB; hlyA and prfA) were detected in five studied strains (100.0%) i.e., all studied strains were L. monocytogenes and all of them were virulent strains.