Prevalence and antimicrobial susceptibilities of coagulase-negative Staphylococci isolated from mammary secretions in pregnant Holstein heifers

Mammary secretions of 913 quarters from 229 pregnant Holstein heifers were obtained aseptically to determine the prevalence of coagulase-negative Staphylococci isolated during periparturient period. Quarter samples were collected 14 to 10 days before expected parturition. Analysis of culture data indicated that 78.5% (717/913) of samples were negative, 20.5% (187/913) contained coagulase-negative Staphylococci, 0.33% coagulase-positive Staphylococci, 0.33% E. coli, 0.22% Arcanobacterium pyogenes and 0.11% environmental Streptococci spp. A total of 187 isolates of coagulase-negative Staphylococci were tested in vitro for susceptibility to 8 antimicrobial agents. Susceptibility was detected in 180 (96.3%), 187 (100%), 163 (87.2%), 168 (89.8%), 183 (97.9%), 187 (100%), 174 (93%) and 164 (87.7%) isolates for oxytetracycline, gentamicin, streptomycin, tylosin, cloxacillin, enrofluxacin, trimethoprim+ sulphamethoxazole and penicillin G, respectively. More than 93.8% of the isolates were susceptible to all antimicrobial agents tested. In conclusion, results of this study suggest that coagulase-negative Staphylococci spp. is the most prevalent microorganism isolated from intramammary secretions in pregnant heifers which is susceptible to common antibiotics in vitro.