Molecular Characterization, Virulence, and Antimicrobial Susceptibility of Mycoplasma bovis Associated With Chronic Mastitis in Dairy Cows

Mycoplasma bovis (M. bovis) is the most common Mycoplasma species, which has a growing impact on the dairy industry. The purpose of this study was to investigate the molecular characterization, virulence, and antibiotic susceptibility of M. bovis isolates from dairy cows with chronic mastitis in Egypt. Eighty-four composite milk samples from mastitic cows were aseptically collected from dairy farms in Egypt. Based on microbiological examination and the polymerase chain reaction (PCR) technique targeting the 16S rRNA, 14 (16.7%) of all milk samples were positive for Mycoplasma spp. PCR targeting M. bovis-specific gene identified six (7.14%) of the 14 mycoplasma isolates as M. bovis. PCR assays for different virulence genes showed that all M. bovis isolates exhibited the presence of vspA gene, while other virulence genes (uvrC, gap, and p40 pseudogenes) were determined in only two M. bovis isolates (2/6). The 16S rRNA gene phylogenetic analysis demonstrated 100% homology with reference strains of M. bovis isolated from different species and locations. When compared to other isolates in the GenBank, the amino acid sequence alignment of our isolate VspA-like protein indicated a distinct mutation. The in vitro antimicrobial susceptibility testing of the six M. bovis isolates in this study to seven antimicrobial drugs revealed that tilmycosin and tylosin had the lowest minimum inhibitory concentrations (MIC) values (<= 1 mu g/mL), while danofloxacin, streptomycin and florfenicol had the highest MIC values (<4 mu g/ mL). Nonetheless, this study showed the virulence of M. bovis in dairy cows in Egypt, and macrolides were found to be the most potent compounds in vitro against all tested isolates, but further studies in nationwide surveys are needed.