Bovine mastitis, distribution of pathogens and antimicrobial resistance in the Southern Dairy Basin of Uruguay

Abstract

A total of 53 farms were selected in Southern dairy region of Uruguay, in order to estimate the prevalence of subclinical mastitis, the incidence of clinical mastitis, distribution and antimicrobial susceptibility of mastitis pathogens. The prevalence of sub-clinical mastitis was determined in base on somatic cell counts in quarter’s milk samples and a threshold value of > 300,000 cells/ mL.; 9,016 milk quarters samples were collected from 2,254 dairy cows and the mean prevalence at herd level was 54.2% of affected cows. The main pathogen isolated from positive samples was Staphylococcus aureus (21.4%). During one with a mean incidence rate of clinical mastitis of 11.8 cases per 100 cow/year at risk. Milk samples were obtained from 341 clinical cases for bacteriological isolation, the most prevalent pathogen isolated was Staphylococcus aureus (27.8%). A total of 864 strains belonging to staphylococci, streptococci and enterococci isolated from clinical and subclinical mastitis cases were analyzed for their susceptibility to antimicrobial agents. The susceptibility patterns were studied by Agar disk diffusion method. The 39.1% of Staphylococcus aureus strains from subclinical cases and 36% from clinical cases were resistant to penicillin, and 29.4% and 33.3% of coagulase negative staphylococci strains, respectively. All the streptococcal isolates were susceptible to penicillin, while 12.5% of enterococci strains were resistant. In conclusion, Uruguay maintain a high level of sub clinical infection in the dairy herds, and Staphylococcus aureus is confirmed as the principal pathogen with a high percentage of penicillin resistance.