Risk Factors of Mastitis and Antibiotic Susceptibility of Staphylococcus aureus and Escherichia coli isolated from Cows Kept by Farmers in Githunguri Sub-County, Kenya

Mastitis poses a major challenge in dairy cattle farming as it leads to production and economic losses. Some mastitis causing bacteria have shown resistance to some antibiotic and the risk factors associated with the antimicrobial resistance (AMR) are not well understood. The current study assessed the prevalence and risk factors associated with occurrence of mastitis in dairy cows kept by small-holder farmers in Githunguri Sub-County, Kenya. Further, susceptibility of the isolated Staphylococcus aureus and Escherichia coli to commonly used antibiotics was evaluated. The study design was cross sectional where 91 milk samples from 40 farms were sampled from two wards in the study area. Structured questionnaires were used to assess risk factors of mastitis. The milk obtained from lactating cows was first subjected to California mastitis test (CMT) and then taken to microbiology laboratory for isolation and identification of Staphylococcus aureus and Escherichia coli using standard bacteriological tests. Antibiotics sensitivity of the isolated bacteria was examined using disc diffusion method. Based on CMT, the overall prevalence of mastitis was 50.5%. The prevalence of mastitis was associated (p<0.05) with hygiene levels, being highest (69.2%) in the dairy cattle whose udder and leg hygiene were dirty. Highest prevalence of mastitis (p<0.05) was found in cows who were not milked regularly (52.4%) compared to those who were milked regularly (47.6%) (p<0.05). Cows which were cleaned using bore hole water had higher prevalence (53.3%) of mastitis compared to those cleaned using tap water (46.7%) (p<0.05). Cows that produced between 21-30 liters of milk per day had the highest prevalence (66.7%) of mastitis, while those producing between over 30 liters milk per day had lower prevalence (25%) (p<0.05). The prevalence of S. aureus and E. coli were 30.8% and 12.1%, respectively. Staphylococcus aureus isolates showed varied resistance to all the tested antibiotics with the highest resistance being against Oxytetracycline (57.7%) and Tetracycline (38.5%) but were sensitive to Vancomycin (100%), Ampicillin (100%), Chloramphenicol (96.2%), Penicillin (92.3%) and Gentamycin (92.3%). All the Escherichia coli isolates were sensitive to Chloramphenicol, Kanamycin, Gentamycin and Oxytetracycline but were resistant to Ampicillin (88.9%) and Vancomycin (88.9%) amongst other antibiotics. In conclusion, half of the sampled cows had mastitis whose risk factors was associated with poor hygiene and irregular milking of the cows. The isolated bacteria showed varied resistance to commonly used antibiotics. To reduce the prevalence of the mastitis and AMR, there is need for extension service workers to train farmers on improved management of the mastitis.