Molecular Detection and Sensitivity to Antibiotics and Bacteriocins of Pathogens Isolated from Bovine Mastitis in Family Dairy Herds of Central Mexico

Abstract

Thirty-two farms (n=535cows) located in the state of Guanajuato, Mexico, were sampled. Pathogens from bovine subclinical mastitis (SCM) and clinical mastitis (CLM) were identified by 16S rDNA and the sensitivity to both antibiotics and bacteriocins ofBacillus thuringiensiswas tested. Forty-six milk samples were selected for their positive California Mastitis Test (CMT) (≥3) and any abnormality in the udder or milk. The frequency of SCM and CLM was 39.1% and 9.3%, respectively. Averages for test day milk yield (MY), lactation number (LN), herd size (HS), and number of days in milk (DM) were 20.6 kg, 2.8 lactations, 16.7 animals, and 164.1 days, respectively. MY was dependent on dairy herd (DH), LN, HS, and DMP<0.01, and correlations between udder quarters from the CMT were around 0.49P<0.01. Coagulase-negative staphylococci were mainly identified, as well asStaphylococcus aureus,Streptococcus uberis,Brevibacterium stationis,B. conglomeratum, andStaphylococcus agnetis. Bacterial isolates were resistant to penicillin, clindamycin, ampicillin, and cefotaxime. Bacteriocins synthesized byBacillus thuringiensisinhibited the growth of multiantibiotic resistance bacteria such asS. agnetis,S. equorum,Streptococcus uberis,Brevibacterium stationis, andBrachybacterium conglomeratum, but they were not active againstS. sciuri, a microorganism that showed an 84% resistance to antibiotics tested in this study.