¹İzmir Bornova Veterinary Control Institute, Department of Bacteriology, TR-35040 İzmir - TÜRKİYE
²Aydın Adnan Menderes University, Faculty of Veterinary Medicine, Veterinary Microbiology Department, TR-09100 Aydın - TÜRKİYE DOI : 10.9775/kvfd.2026.36569 Bovine mastitis remains one of the most prevalent and economically damaging diseases of dairy herds, and Streptococcus uberis is a leading environmental pathogen implicated in both clinical and subclinical infections. In this study, we characterized S. uberis isolates from mastitis-suspected dairy cows in the Aegean Region of Türkiye using phenotypic and molecular identification, virulence and antimicrobial resistance (AMR) gene profiling, antimicrobial susceptibility testing, and ERIC-PCR genotyping. Overall, 167 milk samples were cultured and S. uberis was isolated from 11 samples (6.6%). Identification was performed with VITEK® 2 and confirmed by 16S rRNA PCR (1.400bp). Virulence genes were widely distributed, including capsule genes (hasB 91%, hasC 82%, hasA 73%) and adhesion/invasion-related loci (gapC and oppF 82% each, skc 91%, sua 64%, cfu 73%), whereas lbp showed lower prevalence (27%). AMR gene screening revealed high carriage of penicillin-binding protein genes (pbp1A, pbp2A, pbp2B 100%; pbp1B 90.9%), blaTEM (72.7%), blaZ (9.1%), ermA/ermB (100%), tetM (54.5%), and gyrA/parC (27.3% each). Phenotypically, resistance was frequent, notably to tetracycline (100%) and penicillin G (63.6%), with heterogeneous patterns to other agents, indicating multidrug resistance. ERIC-PCR demonstrated marked genetic heterogeneity, identifying two small clusters (2 and 3 isolates) and six unique profiles at a 70% similarity cut-off, consistent with multiple environmental sources rather than a single dominant clone. These findings underscore the need for improved environmental hygiene and susceptibility-guided therapy, and support further molecular surveillance of circulating strains and resistance mechanisms. Keywords : Antimicrobial resistance, Bovine mastitis, ERIC-PCR, Streptococcus uberis, Virulence genes