Abstract:
Bovine mastitis is the most prevalent infectious disease in dairy herds worldwide.
Staphylococcus aureus is the major microorganism causing infectious mastitis. A crosssectional study was conducted from December 2018 to September 2019 in Shinshicho town,
Kembata Tembaro Zone, Southern Ethiopia, to determine the prevalence, associated risk
factors and antimicrobial susceptibility patternsof S.aureus isolates from mastitic
lactatingcow‟s milk indairy farm. A total of 384 lactating dairy cows were screened for
mastitis based on clinical examinations and California mastitis test (CMT) result, out of which
160 were positive. The occurrence of mastitis was 41.7 %in cows and 21.1% in quarters. Out
of the occurrences of mastitis, 5% and 36.7% were clinical and subclinical respectively.
Staphylococcus aureus was isolated from 1.8% (n=7) and 14.3% (n=55) of the clinical and
subclinical mastitis respectively with the total isolation frequency of 16.1% (n=62).
Multivariable logistic regression analysis of the effect of different risk factors on the
prevalence of S.aureus showed that; adult cows were more likely positive than their younger
counterparts (OR=3.64, 95%CI: 1.64-8.11), cows in late lactation stage were more likely to
be positive than cows in early lactation stage (OR=4.21, 95%CI: 1.52-11.66), the dairy farms
having a large herd size greater than 5 cattle were more likelypositivefor S.aureus than farms
having a small herd size(OR=3.05, 95%CI: 1.65-5.61), and dairy farms with muddy floor
were more likely positive than cemented floor husbandry systems (OR=2.26, 95%CL:1.23-
4.17). All the S.aureus isolates were subjected to antimicrobial susceptibility tests. The
highest rate of susceptibility was to Chloramphenicol (95.2%) followed by Gentamicin
(91.9%), Cephalothin (90.3%), Kanamycin (88.7%) and Streptomycin (80.6%). The current
study revealed that; S.aureus has absolute resistance to Ampicillin, Amoxicillin, Penicillin-G,
and Polymyxin. Also, 53.2% of the isolates were found to be multiple drug resistance
phenotypes. Staphylococcus aureus is one of the pathogens causing mastitis in dairy farms in
the study area and might be imposing public health impacts if raw milk is consumed. Larger
herd size, aged cow, late lactation stage and muddy or soil floor are risk factors associated
with the occurrence of S.aureus mastitis. Hence, more attention should be given in large herd,
culling old cow, treating in late lactation stage and wise use of antimicrobial.
