Mastitogenic Bacteria Isolated from Clinical Mastitis Cases Associated with Teat Lesions and their Antimicrobial Sensitivity

Mastitis is the most common and most expensive disease that impacts dairy farms in Egypt. In this study, we investigated bacterial mastitis cases that did not respond to antimicrobial treatment from buffaloes and cows. Milk samples (11) were collected from diseased animals (5 buffaloes and 6 cows). The samples were tested microbiologically to isolate and identify the causative bacteria and antimicrobial susceptibility. The antimicrobial sensitivity of the isolated bacteria was tested by using minimum inhibitory concentration technique according to the clinical national laboratory standards.  The total number of bacterial isolates from the cases was 15 isolates. Staphylococcus aureus (S. aureus) was isolated alone in two cases (13.33% of the isolates), and S. aureus isolated in combination with Arcanobacterium pyogenes (A. pyogenes) in one case (6.67%), and S. aureus isolated in combination with both A. pyogenes and Streptococcus agalactiae (S. agalactiae) in two cases (13.33%), and Coagulase negative staphylococci (CNS) isolated alone in one case (6.67%), and CNS isolated in combination with Klebsiella pneumoniae in one case (6.67%), and A. pyogenes isolated alone in two cases (13.33%). In two cases were not able to isolate any bacterial pathogen. In terms of susceptibility to antibiotics, the isolated strains were sensitive to clindamycin with MICs ranging from 0.125 to <0.03125 µM. The same isolates exhibited medium sensitivity to gentamicin and ciprofloxacin with MICs ranging from 0.5 to 8 µM. Most S. aureus isolates were resistant to oxytetracycline with a MIC of 128 µM. Most of the isolated bacteria were resistant to polymyxin B with a MIC > 128 µM. With the exception of the A. pyogenes isolates, all the isolated bacteria were sensitive to enrofloxacin with a MIC <1 µM.