STREPTOCOCCUS SPP. AS ETIOLOGICAL AGENT OF SUBCLINICAL AND CLINICAL MASTITIS OF DAIRY COWS IN REPUBLIC OF BULGARIA

The aim of this study was to determine the species composition of streptococci causing subclinical, and clinical mastitis in dairy cows, their prevalence and antimicrobial drug sensitivity with respect to appropriate therapy. The study subject was the involvement and prevalence of bacteria from the genus Streptococcus in the etiology of subclinical, and clinical mastitis in dairy cows. The survey was conducted in eight cattle farms from different regions in Bulgaria in 2020 and 2021. After clinical examination and rapid mastitis test, a total of 239 cows were diagnosed with udder inflammation - 34 (14.2%) with clinical signs and 205 (85.8%) with subclinical mastitis. Laboratory analyses were performed on 346 samples. Two hundred and seventy two bacterial strains were isolated, and 151 (55.5%) were determined to belong to Streptococcus spp. Lancefield grouping and species identification of haemolytic variants was done. It was found out that in subclinical forms of mastitis, 54.5% of isolates belonged to Streptococcus spp., respectively 63.3 % of isolates in clinical forms of mastitis also belonged to Streptococcus spp. Out of them, 38.6% were S. uberis, 35.6% were identified as S. agalactiae and 25.8% − as S. dysgalactiae. In vitro tests of the sensitivity to antimicrobial drugs from various groups and classes were conducted with all field isolates. The tests demonstrated a relatively well-preserved sensitivity to antimicrobial agents with the exception of tetracycline