Prevalence of Virulence Factors and Antimicrobial Resistance of Streptococcus agalactiae and Streptococcus uberis in Ruminant Sub-clinical Mastitic Milk in Iran

Background and Aims: The aim of this study was to determine the virulence and antibiotic resistance properties of Streptococcus agalactiae (S. agalactiae) and Streptococcus uberis (S. uberis) isolated from the ruminant’s sub-clinical mastitic milk in Iran. Materials and Methods: Positive samples in the CMT test were cultured and S. agalactiae and S. uberis have been identified using biochemical tests and polymerase chain reaction (PCR). Virulence and antibiotic resistance genes were studied using PCR. A total of 350 milk samples were collected randomly from 4 major provinces of Iran. We chose 55 bovine, 43 ovine, and 32 caprine herds from these regions. Results: Totally, 34.52% of bovine, 25% of ovine, and 25% of caprine milk samples were found to be contaminated with S. agalactiae and also, 27.38% of bovine, 25% of ovine, and 25% of caprine milk samples were found to be contaminated with S. uberis. The most commonly detected virulence genes of S. agalactiae were cfb (68.75%), scpB and pavA (43.75%). Also, the most commonly detected pathogenic genes of S. uberis were sua and hasB (83.33%), cfu (75.00%) and skc (70.83%). Totally, tetO (89.28%), ermA (82.14%), mefA (73.21%) and tetM (69.64%) were the most common antibiotic resistance genes in Streptococcus isolates. The most resistance were detected against tetracycline (87.5%) and erythromycin (83.92%), respectively. Conclusions: Our results showed that animal milk samples should be controlled, especially in colder seasons of the year in order to study the presences of S. agalactiae and S. uberis.