Retrospective Study of Bacteriological Patterns and Antimicrobial Resistance Profiles of Mastitis in the Banat Region of Romania

Background: Bovine mastitis is a leading cause of economic loss in dairy farming and is increasingly complicated by antimicrobial resistance (AMR), posing challenges to treatment and public health. Objectives: This study aimed to investigate the prevalence, bacterial etiology, and AMR patterns of mastitis pathogens in dairy herds from the Banat region of Romania. Materials and Methods: A retrospective analysis was conducted on 420 dairy cows from five localities. Mastitis diagnosis involved clinical examination, indirect tests (California Mastitis Test (CMT), R-Mastitest), and bacteriological culture. Antimicrobial susceptibility was assessed using the VITEK® 2 system. Results: Out of 420 cows, 120 (28.6%) were diagnosed with mastitis. The predominant pathogens were Staphylococcus aureus (33.3%) and Streptococcus agalactiae (22.5%). Most infections were monomicrobial (70%) and affected a single under quarter (77.5%). Beta-lactam resistance was widespread among both Gram-positive and Gram-negative isolates, particularly against penicillin and ampicillin. Multidrug-resistant (MDR) strains were identified in 33.3% of all isolates, with 100% of Gram-negative isolates exhibiting MDR profiles. Conclusions: The high prevalence of S. aureus and S. agalactiae, along with widespread beta-lactam resistance and frequent MDR phenotypes, highlights the urgent need for routine AMR surveillance and targeted antimicrobial therapy in bovine mastitis control programs.