Abstract
Objective: This study investigated the trend of antibiotic susceptibility of Japanese MRSA clinical isolates, especially that of heterogeneous vancomycin-intermediate MRSA (heteroVISA) in the years 2005-2006 and 1999.
Materials: In Japanese hospitals, 138 MRSA strains and 477 MRSA strains isolated in 1999 and 2005-2006, respectively.
Methods: Antimicrobial susceptibility testing was done according to guideline recommendations of the Clinical and Laboratory Standards Institute (CLSI).
All strains were screened for hetero-VISA using Brain Heart Infusion agar containing 4mg/L vancomycin. The presence of strains that were hetero-VISA was confirmed by population analysis.
Results: The susceptibility pattern of MRSA clinical isolates to 10 antimicrobial agents did not change markedly between the two time periods. However, the rate of arbekacin resistance in 2005 2006 was significantly lower than that in 1999 (p=0.003). Curiously, the detection rate of hetero-VISA decreased to 0.6 % in 2005-2006 from 5.1 % in 1999.
Conclusions: The reason for the decrease in hetero-VISA is unknown but it may have been due to a modern practice of therapeutic drug monitoring (TDM) for vancomycin treatment and the reduction of the use of beta-lactam antibiotics after the clinical introduction of vancomycin in 1991.
