Phenotypic and genotypic evaluation of Listeria monocytogenes strains isolated from fish and fish processing plants

The aim of this study was to perform the phenotypic and genotypic evaluation of Listeria monocytogenes strains isolated from fish and equipment used in fish processing plants. The prevalence of selected gene-encoding virulence factors among L. monocytogenes strains was assessed by multiplex PCR. The genetic (PFGE method) and protein similarities (MALDI-TOF MS technique) of isolates were determined. Their drug resistance (disk-diffusion method and MIC values), serogroup classification (multiplex-PCR), and the ability to co-aggregate with Salmonella enteritidis were also evaluated. Among 37 L. monocytogenes isolates, 36 strains were found, one of which included two genetically identical isolates (PFGE method). In all examined strains, the following genes were found: hlyA, plcB, plcA, inlA, inlB, prfA, iap, and actA. The presence of virulence genes, mpl, and fbpA was confirmed in 32 (88.9%) strains. It was reported that 30 (83.3%) of the strains belonged to serogroup 1/2a-3a. It was also found that the rate of coaggregation with S. enteritidis bacilli was 16.5-36.3%. Among the investigated L. monocytogenes strains, 25 (69.4%) were sensitive to all antibiotics used. Resistance to penicillin was reported most often among strains (n=6, 16.7%). The assessment of L. monocytogenes virulence level is an important aspect for the protection of public health. It was reported that strains isolated from fish contain genes coding for virulence factors and some of them are antibiotic-resistant. In our study, it was found that strains with a high degree of genetic similarity also showed a high degree of similarity at the level of protein profiles.