Method of detecting beta-lactam antibiotic induced vancomycin resistant MRSA (BIVR)

Despite the fact that the combination of vancomycin and a beta-lactam antibiotic are known to act synergistically on vancomycin-susceptible Staphylococcus aureus (VSSA), some MRSA have emerged showing antagonism to the combination of vancomycin and a beta-lactam antibiotic. These MRSA are called beta-lactam antibiotic-induced vancomycin resistant MRSA (BIVR). A method based on this antagonistic phenomenon has been devised to detect BIVR strains. The method inhibits the VSSA strain but allows the BIVR strain to grow. Forty-six commercially available beta-lactam antibiotics induced the vancomycin-resistance. Using this detection method, 717 MRSA clinical isolates obtained from eight institutes throughout Japan were thus screened and 6.3% of these were detected as BIVR when judged at 48 h.