Investigation of antibiotic resistance profiles of Streptococcus uberis isolates isolated from mastitis cases by molecular methods

Mastitis is an infection that causes significant economic losses in dairy cattle farms and is important for public health. In addition to the decrease in milk quality and yield, treatment options are also limited in cases caused by antibiotic-resistant bacteria. Streptococcus uberis is one of the most important factors of mastitis. This study aimed to investigate the presence of S. uberis in 1200 milk samples collected from 300 animals with mastitis in different dairy cattle farms in the Aegean region provinces (İzmir, Manisa, Aydın, Denizli, Kütahya) and to determine the phenotypic and genotypic antibiotic resistance profiles of the isolates. S. uberis was isolated in 22 (7.33%) of the 300 cows from which samples were collected. It was determined that the isolates were phenotypically resistant to tetracycline 77.3%, erythromycin 27.3%, neomycin 22.7%, trimethoprim/sulfamethoxazole 13.6%, and kanamycin 4.5%. Multiple antibiotic resistance was detected in 13.6% of the isolates. As a result of PCR performed to determine genotypic resistance, it was determined that all isolates carried pbp1B and pbp2A, 95.4% carried pbp2B, 77.3% had blaTEM, 63.6% had ermB, 59.1% had tetM, and 22.7% had the gyrA gene region. As a result of the study, it was revealed that S. uberis is the most common streptococcal mastitis agent in the provinces of the Aegean Region and is an effective pathogen in the formation of erectile dysfunction in the region. The high rate of resistance to penicillin and tetracycline, which are widely used in mastitis treatment, confirms the importance of antibiotic resistance, which has become a difficult obstacle to overcome today. Incompatibilities between phenotypic and genotypic resistance profiles suggest that resistance may depend not only on the presence of the gene, but also on gene expression and environmental factors. Therefore, in future studies, gene expression analyses and molecular tests aimed at examining transcription regulation will contribute to reducing phenotypic and genotypic resistance differences.