Abstract
Bovine mastitis caused by multidrug resistant Staphylococcus aureus is a huge problem reported worldwide, resulting in prolonged antibiotic treatment and death of livestock. The current study is focused on surveillance of antibiotic susceptibility along with genotypic and phenotypic characterization of the pathogenic S. aureus strains causing mastitis in India. One hundred and sixty seven milk samples were collected from mastitis-affected cows from different farms in India resulting in thirty nine isolated S. aureus strains. Antibiotic sensitivity profiling revealed the majority of the strains (n = 24) to be multidrug resistant and eleven strains showed reduced susceptibility to vancomycin (MICs = 2μg/ml). All strains were oxacillin sensitive, but 19 strains were positive for the mecA gene, which revealed the occurrence of oxacillin susceptible mecA positive strains (OS-MRSA) for the first time from India. Additionally, 32 strains were positive for the pvl gene, a virulence determinant; of these 17 were also OS-MRSA strains. Molecular characterization based on multilocus sequence typing (MLST), spa typing, agr typing and SCCmec classification revealed strains belonging to different groups. Moreover, strains showed spa types (t2526, t9602) and MLST sequence types, ST-72, ST-88 and ST-239 which have been earlier reported in human infections. The prevalence of OS-MRSA strains indicates the importance of including both the genetic and phenotypic tests in characterizing S. aureus strains. Increased genotypic variability with strain related to human infections and pvl positive isolates indicates a worrisome situation with the possibility of bilateral transfer.
Highlights
Staphylococcus aureus causes numerous infections in humans including sepsis, toxic shock syndrome, bacteremia, endocarditis, and surgical wound infections while in livestock animals bovine mastitis is the mainly reported disease [1]
No resistance was found towards oxacillin, cefoxitin, vancomycin, teicoplanin and linezolid
Using only phenotypic tests could result in misidentification of OS-MRSA as methicillin susceptible S. aureus strains (MSSA), this will misrepresent of the prevalence of OS-MRSA and further complicate treatment
Summary
Staphylococcus aureus causes numerous infections in humans including sepsis, toxic shock syndrome, bacteremia, endocarditis, and surgical wound infections while in livestock animals bovine mastitis is the mainly reported disease [1]. S. aureus is a major pathogen causing mastitis, and different states of India report a high prevalence rate of 57% and 41.6% [5]-[6]. A report on bovine mastitis by Kumar et al, 2011 indicated MRSA prevalence rate of 13.1% in cattle, as did another current report which showed a prevalence rate of 9.6% [6]-[7]. A lower prevalence of MRSA infections in cattle have been reported in the USA (4%) and Korea (4.2%), a report from China showed a high prevalence of MRSA strains (47.6%) [8]—[10]
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