Drug resistance in isolated bacteria from milk of sheep and goats with subclinical mastitis in Shahrekord district

Four-hundred milk samples from half udders of 20 flocks of native breed goats were aseptically collected. The samples were examined by California mastitis test (CMT). Twenty-one (5.25%) of 400 were CMT-positive. The CMT-positive samples were then cultured and the following bacteria were isolated: Staphylococcus aureus in 3 (14.28%), CNS (coagulase-negative staphylococci) in 14 (66.66%), streptococci in 4 (19.04%) and Mycoplasma spp. in 11 (52.38%) samples. The isolated staphylococci were examined to evaluate their resistance to different antibiotics by disc diffusion method. CNS resistance to amikacin was 78.5%, to penicillin was 50%, to tetracycline 50%, to ampicillin 42.8%, and to doxycycline was 28.5%. Four-hundred native breed sheep milk samples were taken from 19 flocks in the same conditions. The samples were examined by CMT test. 19 (4.75%) of 400 were CMT-positive. The CMT-positive samples were cultured and the following bacteria were isolated: S. aureus in 2 (10.5%), CNS in 7 (36.8%), streptococci in 2 (10.5%), Pasteurella in 1 (5.26%) and Mycoplasma in 9 (47.37%) samples. The isolated staphylococci were examined for antibiotic susceptibility. CNS resistance to amikacin was 42.8%, and to tetracycline, ampicillin, oxycycline and penicillin was 14.3%. Both isolates of S. aureus were resistance to penicillin.