Molecular Investigation of the Frequency of Listeria Monocytogenes in Raw Milk Samples Collected from Zanjan Province, Iran

Listeria monocytogenes is one of the most important foodborne pathogens that infect various food sources such as raw milk, cheese, ice cream, vegetables, ready-to-eat (RTE) foods, poultry, meat, and fish. Listeria monocytogenes can cause severe diseases such as meningoencephalitis, abortion, and septicemia, with a high mortality rate (30%) in humans. Therefore, the present study was carried out to molecularly investigate the frequency of Listeria monocytogenes in raw milk samples.

In this study, 150 raw milk samples from Zanjan province, Iran, were collected at regular intervals. Pure isolates of Listeria monocytogenes were obtained after enrichment in Buffered Listeria enrichment broth (BLEB), followed by plating onto blood agar and PALCAM agar medium and incubation at 35 °C for 48 hours. A hly gene-based PCR assay was developed to detect the presence or absence of virulence genes in isolated Listeria monocytogenes.

The results showed that only one sample was positive by both real-time and conventional PCR methods. It contained three virulence genes, including hlyA, actA, and prf-A, among the virulence genes studied.

The prevalence of Listeria monocytogenes in Zanjan province was lower than in previous studies, which was attributed to the small number of samples and the sampling season.