Molecular Characterization and Antimicrobial Sensitivity of Pathogens from Sub-Clinical and Clinical Mastitis in Eastern China

Prevalence of sub-clinical and clinical coliform mastitis with antimicrobial sensitivity profile of various mastitis-causing organisms was investigated. Milk samples collected from 299 cows infected with clinical mastitis to evaluate the prevalence of coliform mastitis and 1660 quarters milk samples randomly collected from 415 lactating cows for detection of subclinical mastitis (SCM) by Hangzhou Mastitis Test (HMT). SCM at quarters and cow level was recorded to be 20.2 and 52.3%, respectively. Occurrence of SCM in left rear quarter was high (26.7%). Statistical analysis of risk factors showed, cows with 6-9 years of age (P=0.046; Odds ratio (OR), +1.414; 95% confidence interval (CI)=1.006-1.988 and 60.7%), cows with 4-7 calves (P=0.028; OR, +1.502; 95% CI=1.044-2.160 and 62.2%), and cows in late stage of lactation (P=0.039; OR, +1.947; 95% CI=1.023-3.702 and 68%), were more susceptible to SCM. All the 115 organisms from SCM milk samples and 103 Escherichia coli from CM samples were confirmed by PCR techniques. Minimum inhibitory concentration (MIC) results revealed that E. coli isolates were resistant to penicillin group (93-99%), fluoroquinolones (40-74%), cephalosporins (54-66%), oxytetracycline (91%), gentamycin (82%), SUL-TRM (88%) and were sensitive to florfenicol. Staphylococcus aureus isolates were resistant to ampicillin (91%), oxytetracycline (59%) and methicillin (29%). Streptococcus agalactiae isolates were 8 to 15% resistant to used antimicrobials. In conclusion, cows with SCM were reservoir of various bacterial pathogens and high prevalence of E. coli in clinical mastitis milk could be major complications for mastitis treatment due to their multidrug resistance profile.