Emerging Antimicrobial Resistance in Coagulase-Positive Staphylococci and E. coli Isolated from Bovine Clinical Mastitis in Sri Lanka

Background and Aim: Mastitis is an economically important disease in dairy cattle, and one of the most common diseases both in developed and developing countries. The disease prevalence is quite high in Sri Lanka; both clinical and subclinical mastitis were reported, Staphylococcus aureus and E. coli are important bacterial organisms which cause clinical mastitis in dairy cattle. The antimicrobial resistance of these two bacterial species are increasing all around the world, only limited literature is found locally. The objectives of the study were to determine phenotypic antimicrobial-resistant profile in commonly reported two organisms from the clinical mastitis in the country.

Materials and Methods: Samples (n=197) were collected from regional veterinary investigation centers (n = 6) as a routine clinical submission for diagnosis of mastitis, one government dairy farm in 2018-2019. Coagulase positive Staphylococcus (n=41) and E. coli (n=17) were isolated and identified by conventional tests and standard biochemical tests. Antimicrobial susceptibility testing was done and interpreted as described by EUCAST.The coagulase-positive Staphylococcus isolates were screened for mecA and E. coli were screened for CTX-M and NDM by conventional PCR tests as described.

Results and Discussion: Methicillin resistance was not shown in coagulase-positive Staphylococcus aureus in the study and a high frequency of resistance was reported against ampicillin (98.0%), amoxicillin (64.7%), amikacin (68.6%), cloxacillin (64.7%) and oxytetracycline (56.9%). E.coli were shown 100% resistance to ampicillin, amoxicillin, sulfamethoxazole, and trimethoprim alone. High resistance frequencies were shown for oxytetracycline (80%), chloramphenicol (80%), sulfa trimethoprim combination (66.7%) and doxycycline (60%). Only 26.7% of E. coli was shown resistance for cefotaxime and only 4 were shown CTX-M by conventional PCR.

Conclusions: Antimicrobial resistance is emerging in these two species of bacteria, national resistant surveillance and evidence-based antimicrobial usages are recommended to combat against emerging resistance in livestock.