Antibiotic resistance of Staphylococcus aureus isolated from fresh cow milk in settled Fulani herds in Kaduna State, Nigeria
Three Hundred and Sixty fresh cow milk samples were collected from settled Fulani herds in Kaduna State and examined for S. aureus and their antibiotic resistance. Fifty five samples (15.3%) were positive for S. aureus. The occurrence of S. aureus was statistically significant (P<0.005) based on locations. Statistical analysis showed that all the S. aureus (n=55) were coagulase and DNase positive while 40.0% (n=22) produced alpha haemolysin, 45.5% (n=25) produced beta haemolysin and 14.5% (n=8) produced gamma haemolysin. The resistance pattern of the 55 S. aureus isolates showed that all the isolates were resistant to two or more antibiotics. Multidrug resistance was detected in 96.4% of the isolates. All the S. aureus were resistant to penicillin 55 (100.0%) rates of resistance to ampicillin (90.9%; n=50), tetracycline (81.8%; n=45) and erythromycin (75.5%; n=41). High frequencies of resistance were recorded against vancomycin (61.8%; n=34), nalidixic acid (40.0%; n=22), streptomycin (32.7%; n=18), oxacillin and cefoxitin (29.1%; n=16), trimethoprim (27.3%; 15) and gentamicin (23.7%; n=13). Chi square test showed that significant (P<0.05) number were susceptible to ciprofloxacin (92.7%; n=51), gentamicin (70.9%; n=39), oxacillin (70.9%; n=39), chloramphenicol (65.5%; n=36) and streptomycin (67.7%; n=37). The MIC results for oxacillin and vancomycin showed values > 256 μg for all resistant strains showed no zone of inhibition along the entire length and MIC was read as greater than the highest value on the strip (256). The multiple drug resistance indices revealed that 96.4% of the S. aureus strains were resistant to 3 or more antibiotics tested. The study demonstrated that cow milk in the study areas are contaminated with resistant strains of S. aureus of animal and human biotypes and can serve as means of spread to humans through the consumption of raw milk and milk products. This can be eliminated through improving the general herd hygiene, proper management practices and proper milking hygiene.
Keywords: antibiotic resistance, Staphylococcus aureus, cow milk, settled Fulani herds, MIC, Haemolysin, Kaduna State