CylE and mig as virulence genes of streptococci isolated from mastitis in cows and buffaloes in Egypt

Document Type : Original Articles


Bacteriology, Mycology and Immunology, Veterinary Medicine, Mansoura University


Objective: A study is carried out to investigate the prevalence of mastitis caused by Streptococcus agalactiae and Streptococcus dysgalactiae in cows and buffaloes, their antibiotics susceptibility, minimum inhibitory concentrations (MIC), and molecular investigation of some virulence genes.
Samples: A total of 288 milk samples gathered from 72 mastitic animals from households and small-scale dairy farms in Egypt, were analyzed.
Procedures: Isolation and identification of S. agalactiae and S. dysgalactiae were performed using conventional techniques. The identified isolates were examined for antimicrobial resistance by disk diffusion assay, MIC by broth microdilution method as well as virulence genes by PCR.
Results: Forty-five out of 72 animals show the clinical signs of mastitis. Microbiological evaluation of 288 mastitis milk samples displayed 190 (65.72%) streptococci strains composing of 60% S. agalactiae and 40% S. dysgalactiae strains. The antibiotic susceptibility tests revealed that S. agalactiae strains were resistant to trimethoprim (100%), followed by tetracycline and minocycline (37.7%). Moreover, S. dysgalactiae strains were highly resistant to lincomycin, tetracycline (87.52 each), followed by trimethoprim (81.6) and minocycline (75%). Additionally, the highest MIC with the widest range (1 to ≥128 μg/mL) were 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 is displayed in 6 (60%) S. agalactiae strains, whereas the mig gene is found in 4 (40%) S. dysgalactiae strains.


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