الفهرس 
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Abstract
In this study, 200 samples (80 raw milk, 60 yoghurt and, 60 cheese) were collected from different places in Assiut city to detect the presence of Lactococcus lactis. All samples were cultured under microaerophilic conditions. Suspected colonies were identified conventionally using standard culture and biochemical methods then confirmed by conventional PCR.
Out of these 200 samples, Lc. lactis was detected in 67.5% of milk, 41.7% of cheese and 33.3% of yoghurt samples by conventional methods.
By PCR, the prevalence of isolated Lc. lactis was 58 isolates (29% of all samples); 57 isolates (28.5% of all samples) were Lactococcus lactis subsp. lactis and one isolate (0.5% of all samples) was Lactococcus lactis subsp. cremoris. The highest frequency of Lc. lactis was found in milk samples (33.8%), followed by cheese samples (28.3%), and the lowest frequency of Lc. lactis was in yoghurt (23.3%). The only isolate of Lc. lactis subsp. cremoris was detected in milk sample.
In this study, the highest antimicrobial activities of Lc. lactis subsp. lactis were observed against MRSA followed by CoNS, then Cl. perfringens but no inhibitory effect was detected against C. jejuni or CR-GNB. Similarly, Lc. lactis subsp. cremoris showed strong inhibitory effect on MRSA and CoNS, but no inhibitory effect on Clostridium perfringens, Campylobacter jejuni or CR-GNB.