Occurrence of Antibiotic Resistance in Bacteria Isolated from Milk of Dairy Cows in Small-Holder Farms in Juja Sub-County, Kenya

Sub-clinical mastitis (SCM) remains a serious hindrance to small-holder dairy farms in Kenya. A cross-sectional study was conducted to determine the risk factors associated with occurrence of SCM and antibiotic resistance in smallholder dairy farms in a peri-urban set-up area of Juja Sub-county, Kenya. Milk samples was obtained from 120 lactating dairy cows in 60 farms and screened for SCM using California mastitis test (CMT). Positive CMT samples were cultured and bacteria identification was done using standard methods. A questionnaire survey was administered at the household level to assess the risk factors associated with SCM. Sensitivity of the Staphylococcus aureus and Escherichia coli isolated from milk against commonly used antibiotics was determined using disc diffusion method. The prevalence of SCM at cow and udder level was found to be 66.7% and 61.3%, respectively. The highest prevalence of SCM was in Kalimoni (88.8%), Murera (82.7%) and Witeithe (71.4%) wards. The least affected area being Juja (60%) and Theta (44.4%) wards. Sub-clinical mastitis was significantly higher (p=0.007) in Friesian (74.1%) and Guernsey (66.7%) breeds as compared to the indigenous breed (53.8%). Cows with parity of four and above had higher (p=0.001) prevalence of SCM (73.7%) as compared to those of lower parity stage. Additionally, the prevalence (81%) of SCM in cows at late lactation was higher (P=0.002) compared to early (61.5%) and mid-lactation (56.4%), respectively. Higher prevalence (59%) of SCM was found in cows kept in less frequently cleaned housing compared to those more frequently cleaned (10%). The bacterial organisms isolated from the milk were Staphylococcus spp. (41.7%), Klebsiella spp. (24.5%), Pseudomonas spp. (22.1%), Escherichia coli (6.8%), Shigella spp. (1.8%) and Salmonella spp. (3.1%). The isolated Staphylococcus spp. and E. coli were most resistant to Oxytetracycline (79%, 100%, respectively) and Streptomycin (44%, 90%, respectively). Multidrug resistance (MDR) involving a combination of oxytetracycline, tetracycline, streptomycin and chloramphenicol and gentamycin was observed amongst Staphylococcus spp. (29.4%) and E. coli (45.5%) isolates. In conclusion, the study showed that large proportion of dairy cows was affected by SCM and the antibiotic resistance (AR) was high. This calls for animal health extension experts and other relevant stakeholders in the industry to train farmers on efficient control of SCM and emerging cases of AR.