Abstract
Bovine mastitis is one of the most common diseases among dairy cows and causes high economic losses in dairy industries worldwide. Streptococcus uberis is one of the most frequently identified pathogens causing the disease. In this study, 153 S. uberis strains isolated from mastitis milk samples were analyzed for their genetic diversity using multi locus sequence typing (MLST). Moreover, antibiotic susceptibility testing was performed using a microdilution assay and 11 antimicrobial agents including penicillin, which is the first line agent for treatment of bovine mastitis in Switzerland. MLST was successful for 152 (99.3%) of the strains. Overall, 103 different sequence types (STs) were determined, including 91 novel STs. S. uberis belonging to clonal complex (CC) 5 represented 47 (30.7%) of the mastitis cases. Two (1.3%) of the strains belonged to CC86 and one (0.7%) to CC143. The population structure identified in this work suggests that environmental transmission is the predominant route of infection in herds in Switzerland. Antimicrobial susceptibility testing determined a resistance rate of 11.8% for pirlimycin and elevated MIC90-values for marbofloxacin as well as for erythromycin. This study highlights the importance of genetic characterization of S. uberis and the need for veterinary breakpoints for surveillance of antimicrobial resistance in S. uberis.
Highlights
Bovine mastitis is considered to be one of the most common diseases causing high economic losses in dairy industries worldwide [1]
153 S. uberis strains were isolated from milk samples originating from 54 herds, with the majority (87%) of the farms located in the canton of Zurich
Farm type, breed of dairy cows and herd size were typical for the Swiss Midlands
Summary
Bovine mastitis is considered to be one of the most common diseases causing high economic losses in dairy industries worldwide [1]. The economic losses include costs for treatment but deficits due to decreased quantity and quality of milk, higher number of culling and death of affected animals [2]. Following the implementation of preventive control measures, the prevalence of clinical mastitis has declined in many countries during the last decades [7]. Enhanced milking hygiene (correctly maintained equipment, teat disinfection, and personnel hygiene), antibiotic treatment and culling of persistently infected animals reduced the microbial load with contagious pathogens and the risk for new infections. The control of environmental pathogens like S. uberis presents an ongoing challenge for the management of dairy herds [8, 9]. Despite the evidence supporting the essential role of S. uberis in the prevalence of bovine mastitis, only a limited
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