Molecular Detection of Listeria Monocytogenes in Milk and Some Milk Products

Listeria monocytogenes is considered one of the major potential foodborne pathogens which often threaten human health and life. Our study assessed both existence and virulence of L. monocytogenes in raw milk and different milk byproducts in Damietta Governorate, Egypt. One hundred and fifty random samples of raw milk, Kariesh cheese, Domiati cheese, Roomi cheese, yogurt and cream (twenty-five samples for each) were gathered from small retails and various supermarkets at for isolation of L. monocytogenes as well as direct detection of the pathogen in the samples’ using PCR technique that targeting 16S rRNA. Also, the study aimed to investigate the presence of virulence genes; (hly A, inl A, inl B, prf A, plc A) in L. monocytogenes isolates. The PCR findings for direct detection of L. monocytogenes declared that 41 out 150 examined samples were positive to 16S rRNA meanwhile by culture methods L. monocytogenes was recovered from 36 out of 150 examined samples. With regard to detection of virulence genes in isolates, 100% of the isolates (36) harbor inl A gene while 35 isolate (97.2%) harbor hly A gene. It was found that 100% of the samples (41) that were positive to 16S rRNA were also found positive to hly A and inl A genes. plcA gene was not detected in all samples whether directly or in isolates. inlB was detected in 8 out of 41 (19.5%) positive samples directly detected while it was detected in 15 out of 36 (41.6%) of isolates. prfA gene was detected in 25 out of 41 (60.9%) positive samples while it was detected in 20 out of 36 (55.5%) of isolates. Our study revealed that the considerable high isolation of L. monocytogenes among examined raw milk and its byproducts constitutes a potential public health hazard. Usually, PCR is seen as important technique for precise diagnosis of microorganisms rather than the classical cultural methods.