First Characterization of Class 1 Integron in Corynebacterium bovis Isolated from Subclinical Bovine Mastitis

Integrons play major roles in spreading and expression of antibiotic resistance genes among bacteria especially Gram-negative bacteria. However, the incidences of class 1 integrons in Gram-positive bacteria remained elusive. The present study was conducted to monitor the prevalence of class 1 integrons in Corynebacterium bovis (C. bovis) isolated from cases of bovine mastitis in Egypt. A total of 35 Corynebacteria spp., isolated from milk samples of subclinical mastitis, were examined using PCR analysis with 16S rRNA specific primers. The results revealed a prevalence of 8 (22.8%) C. bovis strains in the examined samples. All isolates of C. bovis showed an elevated level of resistance, mostly against spectinomycin, streptomycin followed by tetracycline, ampicillin, kanamycin, chloramphenicol and sulfamethoxazole-trimethoprim. Using PCR and DNA sequencing, two isolates of C. bovis were identified containing class 1 integrons that encoded aminoglycoside adenyltransferase type A (aadA1) as a gene cassette. The aadA1 confers resistance to spectinomycin/streptomycin. Additionally, class 1 integron resistance genes in C. bovis isolates were described utilizing PCR and DNA sequencing. These resistance genes conferred resistance to several antimicrobial agents frequently used in dairy farming. This study reports, for the first time, the detection and identification of class 1 integron containing aadA1 gene in C. bovis of animal origin