Determination of the occurrence of plasmid virulence genes (spv) and antibiotic resistance of Salmonella strains isolated from raw milk

The aim of the study was to measure the frequency of occurrence of Salmonella spp. in raw milk, to identify their serotype, as well as to determine their antibiotic resistance and the presence of Salmonella plasmid virulence (spv) genes. Out of 300 bulk tank milk samples, 5.3% were contaminated with Salmonella spp. All strains isolated belonged to the serovar S enteritidis, as confirmed by serotyping and molecular methods. The presence of spv genes was determined by PCR. Spv genes were present, in different patterns, in all strains tested. SpvA gene was present in all isolates (100%), spvB in 56.25%, spvC in 62.5%, spvD in 75%, and spvR in 56.25%. Antibiotic resistance was evaluated according to the NCCLS recommendations. All isolates were sensitive to ciprofloxacin (CIP), gentamicin (GE), and chloramphenicol (CH). Thirteen strains were resistant to ampicillin (AMP), 8 to erythromycin (E), 1 to doxycycline (DO), and 1 to tetracycline (TE). Different frequency of occurrence of the spv genes in Salmonella strains isolated from raw milk demonstrates their high adaptability. As many as 87.5% of isolates showed resistance to at least one of the antibiotics tested.