MRSA, new topics

Abstract

Staphylococcus aureus (S. aureus) has acquired antimicrobial resistance to various kinds of antibiotics, after acquired rapidly after new antibiotics become available for clinical use. To date, MRSA has been known as the most important pathogen of hospital infection. Vancomycin (VCM) has been used as the drug of choice for MRSA infection in the past 20 years, however, the first low level vancomycin-resistant S. aureus (L-VRSA) strain was isolated in 1997 in Japan. L-VRSA is defined as an S. aureus strain with a MIC of more than 8μg/ml to VCM and L-VRSA strains have been widely reported in various countries since 1997. The level of resistance of L-VRSA is high enough to survive the treatment of MRSA infection with VCM. Moreover, a VRSA strain with a higher level of VCM resistance was isolated in the United States in 2002. This strain is speculated to acquire VCM resistance genes from VCM-resistant enterococci that were simultaneously isolated from identical infected sites in patients. From the beginning of the 1990's, increased incidence of community-acquired MRSA (C-MR-SA) has been observed in the United States, Europe and Australia. Although C-MRSA strains tend to be susceptible to various kinds of antibiotics except for β-lactam types, it was found that various virulent factors such as toxins are expressed from C-MRSA strains. These toxins may be associated with the high mortality of C-MRSA infections. In 2001, whole genome sequences of several MRSA strains, including VRSA and C-MRSA, were determined. This is expected to elucidate the mechanism of VCM resistance and C-MRSA-specific pathogenicities. It is recommended that VCM monotherapy, combination therapy of VCM with rifampicin and/or co-trimoxazole, teicoplanin with β-lactam antibiotics, sulbactam/ampicillin and arbekacin be used for MRSA infections. Proper antibiotic use is also important as an effective and established preventive measure for hospital infections.