Molecular Detection of Virulence Genes and Multi-drug Resistance Patterns in Streptococcus Agalactiae in Clinical Bovine Mastitis: Tehran and Alborz Provinces, Iran.

INTRODUCTION: Streptococcus agalactiae is one of the important causes of mastitis in cows. The ability of S. agalactiae to cause disease depends on the production of a large number of virulence factors encoded by different genes. The overuse of antibiotics to treat mastitis can lead to antibiotic resistance. This research was conducted to detect selected virulence genes and assess the antibiotic resistance of S. agalactiae. MATERIALS & METHODS: A total of 30 bacteria that isolated from clinical cases of mastitis and characterized as S. agalactiae by conventional cultural methods was collected from veterinary diagnostic laboratories. Then, these isolates undergo further characterization by detecting virulence genes by molecular methods and antibiotic resistance by disc diffusion method. RESULTS: Of these, 24 samples were confirmed as S. agalactiae through the detection of the two 16S-23S rRNA genes. The disk diffusion method, using a panel of 10 antimicrobial agents, showed a large number of strains resistant simultaneously to six antibiotics. Five virulence genes bac, bca, cylE, hylB, and cfb were screened by polymerase chain reaction (PCR). The cfb and hylB genes were found in 95.83 % of the isolates,while the cylE gene was detected in 29.16% of the isolates. The bca and bac genes were not detected in any of the isolates. The absence of bac and bca genes suggests that they likely have minimal impact on the pathogenesis of S. agalactiae mastitis in dairy cows, while the hylB and cfb genes play a crucial role in this condition. CONCLUSION: The results presented here are one of the first molecular data concerning these five virulence genes in S. agalactiae isolates causing bovine mastitis in the Tehran and Alborz provinces, providing a foundation for the development of diagnostic, preventive, and therapeutic methods.