From 2000 to 2005, the data of all clinical isolates of Staphylococcus aureus including methicillinsusceptible
S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) from 28 hospitals in the National
Antimicrobial Resistance Surveillance, Thailand (NARST) program were reviewed and analyzed for the
prevalence and pattern of antimicrobial susceptibility by WHONET software program. Among all isolates,
around 26% of MRSA have been noted in each year. The rates of erythromycin-resistant MRSA were relatively
high, ranging from 94.5% to 96.8%, followed by clindamycin resistant (37.4% to 68.9%), fosfomycin-resistant
(7.7% to 17%), vancomycin-resistant (0.1% to 0.8%), and teicoplanin resistant (0.2% to 1.3%). The rates of
antimicrobial resistance MSSA were constantly low, with erythromycin resistance ranging from 3.7% to 4.6%,
clindamycin resistance ranging from 1.4% to 2.3%, fosfomycin resistance ranging from 0.7% to 1.4%,
vancomycin resistance ranging from 0.1% to 1.2%, and teicoplanin resistance ranging from 0.1% to 1.1%. An
increasing trend of vancomycin resistance in S. aureus determined by the disk diffusion method should be
further confirmed by appropriate susceptibility methods. Molecular typing methods are needed to determine
the epidemiological association between these resistant isolates.

Keywords: Anti-bacterial agents, Drug resistance, multiple, bacterial, Methicillin resistance, Microbial
sensitivity tests, Staphylococcus aureus, Thailand