Lancefield classification and antimicrobial resistance of hemolytic streptococci isolated from bovine mastitis

Streptococcal species are known to be responsible for bovine mastitis. The aim of the present study was to determine antimicrobial drug resistance patterns of hemolytic streptococci distributed according to Lancefield serogrouping. Streptococcus sp. strains were isolated from 124 bovine milk samples from 31 cows with subclinical or clinical mastitis submitted to Mehmet Akif Ersoy University Faculty of Veterinary Medicine, Department of Microbiology Laboratory in Burdur province, Turkey from January 2015 to January 2017. A total of 63 Streptococcus sp. were isolated and the most frequently obtained isolates were classified as Lancefield’s serogroup B (84.13%), the remaining isolates as serogroup F (15.87%). Out of 63 isolates, 53 (84.13%) showed beta‑hemolytic activity whereas 10 (15.87%) alpha‑hemolytic activity. Antimicrobial resistance was assessed by disk diffusion test against the most common antibiotics used in the field. Among the 63 Streptococcus sp. tested, the highest antimicrobial resistance patterns were observed for neomycin (95.24%), trimethoprim sulphamethoxazole (87.30%) and gentamicin (69.84%). None of the isolates showed resistance to amoxicillin‑clavulanic acid, except for one serogroup F isolate. The resistance rates for the other antimicrobials ranged from 1.59% to 38.04%. A total of 50 isolates exibited multi‑drug resistance to ≥ 3 antimicrobial agents tested. Overall, our results suggested that there is an urgent need to enhance awareness among the dairy farmers in choosing the appropriate drug for treating mastitis.