A study was carried out to investigate the prevalence of mastitis caused by Streptococcus agalactiae and Streptococcus dysgalactiae in cows and buffalo reared in households and smallholder dairy farms, and to detect their antibiotics susceptibility, and molecular investigation of some virulence genes (cylE and mig genes).
Design: Observational study.Samples: A total of 288 milk samples were gathered from 72 mastitic animals (48 cows and 24 buffalo) from households and smallholder dairy farms in Dakahlia and Domiatte Governorates, Egypt.Procedures: Isolation and identification of S. agalactiae and S. dysgalactiae was performed using conventional techniques. The identified isolates were examined for antimicrobial resistance by disk diffusion assay, Minimum inhibitory concentration MIC by broth microdilution method as well as virulence genes (cylE and mig genes) by polymerase chain reaction (PCR).Results: Forty-five (62.5%) out of 72 animals showed the clinical signs of mastitis. Microbiological evaluation of 288 mastitis milk samples was displayed 190 (65.72%) streptococci strains composing of 114 (60%) S. agalactiae and 76 (40%) S. dysgalactiae strains. The antibiotic susceptibility tests revealed that S. agalactiae strains was resistant to trimethoprim (100%), followed by tetracycline and minocycline (37.7%), whereas intermediate resistant was observed to other tested antibiotics. Moreover, S. dysgalactiae strains were highly resistant to lincomycin, tetracycline (87.52 each), followed by trimethoprim (81.6) and minocycline (75%), while all strainswere susceptible to penicillin, amoxicillin, cephapirin, and cefquinome. Additionally, the highest MIC with the widest range (1 to ≥128 μg/mL) was observed to trimethoprim for S. agalactiae and to erythromycin and lincomycin for S. dysgalactiae. In contrast, the lowest MIC was detected to penicillin, amoxicillin, cefquinome, and erythromycin for S. agalactiae and to penicillin, amoxicillin, cephapirin, cefquinome, and rifaximin for S. dysgalactiae. The cylE gene was displayed in 6 (60%) S. agalactiae strains, whereas the mig gene was found in 4 (40%) S. dysgalactiae strains.
Conclusion and clinical relevance:Our data highlights the importance of awareness of antibiotic resistant strains of S. agalactiae and S. dysgalactiae in various mastitic animals (cows and buffalo) in Egypt.