Characterzation of erythromycin resistance phenotypes and genotypes among vancomycin sensitive and vancomycin resistant Staphylococcus aureus isolated from bovine raw milk

Staphylococcus aureus is the causing agent of endocarditis, sepsis and Staphylococcal food poisoning. The purpose of this study was to assess erythromycin sensitivity in 50 Vancomycin Resistant S. aureus (VRSA) and Vancomycin Sensitive S. aureus (VSSA) isolates from bovine raw milk and also to determine the distribution of erythromycin resistance genes among the isolates. Broth microdilution method was used to determine vancomycin resistance and minimum inhibitory concentration of erythromycin. The presence of the ermA, ermB, ermC and msrA genes encoding erythromycin resistance was examined by PCR. 84% of the isolates were susceptible while 16% were resistant to vancomycin. A single isolate of S. aureus was sensitive to erythromycin which did not possess any of the erythromycin resistance genes. 90% of the isolates were resistant to erythromycin, of which, no resistance gene were found in 24.4% and 51.1% were ermB positive. ErmA was not found in any of the isolates. Simultaneous presence of resistance genes was detected in eight isolates. There was not any significant relationship between erythromycin resistance genes and MICE. 37.5% of VRSA isolates contained none of the erythromycin resistance genes while 25% contained two resistance genes. Mean MICE of VRSA was higher than VSSA isolates. All the VRSA isolates were also erythromycin resistant. There was no significant relationship between erythromycin resistance genes and vancomycin sensitivity.