Cloxacillin

Disk diffusion antimicrobial susceptibility tests were performed on the confirmed S. aureus isolates. The common used antibiotics for treating respiratory disease in farm animals were chosen for the antimicrobial susceptibility tests, including ampicillin (10 μg), cloxacillin (5 μg), cefoxitin (30 μg), cefazolin (30 μg), gentamicin (10 μg), vancomycin (30 μg), and tetracycline (30 μg) (Oxoid Ltd., Hampshire, UK). Briefly, S. aureus colonies were picked and subcultured by streaking on nutrient agar (Himedia Laboratories, Mumbai, India) and incubating the plate at 37°C for 18–24 hr. Then, a sterilized loop was used to pick four or five colonies from the nutrient agar and they were suspended in 2 ml of Mueller-Hinton broth (Difco Laboratories, Inc., NJ, USA). After adjusting to a turbidity of 0.5 McFarland standards, a sterile swab was dipped into the tube and streaked on Mueller-Hinton agar (Difco Laboratories, Inc., NJ, USA). Then, the appropriate antimicrobial-impregnated disks were placed on the surface of the agar, and the plate was incubated at 37°C for 18–24 hr. Thereafter, we measured the zones of inhibition and determined the antimicrobial susceptibility of the isolates using interpretative standards for Staphylococcus species. The results were reported as susceptible, intermediate, or resistant [8 , 9 ].