Antimicrobial susceptibility profile of Enterococcus species isolated from cows with clinical mastitis and from bulk milk tanks in Brazil

Vancomycin-resistant enterococci (VRE) have been reported as a major hazard to human and animal health, causing problems like clinical mastitis in dairy cattle and nosocomial infections in humans. The aim of this study was to determine the in vitro microbial susceptibility profile of enterococci isolated from dairy farms in São Paulo and Minas Gerais states, Brazil. A total of 310 samples of Enterococcus species from bovine mastitis (52) and bulk tanks (258) were analyzed. The sensibility profile was studied by the disk diffusion method, and the isolates intermediately resistant to vancomycin were submitted to the minimum inhibitory concentration (MIC) test. The enterococci also were classified according to their multiresistance profile. All isolates were sensitive to vancomycin. Most of the isolates from the bulk tanks were resistant to cephalexin (93.8%), novobiocin (98.8%), cefoxitin (91.9%) and oxacillin (91.9%), while those isolated from mastitis presented a high resistance to trimethoprim/sulfamethoxazole (84.7%), novobiocin (100%), cefoxitin (88.5%) and oxacillin (80.8%). All isolates were sensitive to vancomycin (VSE). The high prevalence of isolates resistant to multiple antimicrobials emphasizes the risks existing in the use of ineffective antibiotics.