PPrevalence of Staphylococcus aureus Isolates with Decreased Susceptibility to Teicoplanin and Evaluation of Methods for Detection

Jeong, Seok Hoon; Hwang, Hyun Yong; Choi, Byeong Gil; Kim, Mi Hyang; Lee, Chang Youn; Rim, Hark; Moon, Jae Gon

Abstract

BACKGROUND
The purpose of this study was to investigate the prevalence of Stap hylococcus aureus with decreased susceptibility to glycopeptides in Korea and to evaluate the methods for detection.
METHODS
From March to May 1998, 106 clinical isolates of S. aureus were collected from patients of the Kosin Medical Center . Antimicrobial susceptibilities for vancomycin and teicoplanin were determined by NCCLS disc diffusion method and the MICs were determined by agar dilution method. Correlation between both results was evaluated.
RESULTS
MICs of vancomycin and teicoplanin against S. aureus isolates were 0.5 ~2 microgram/mL and 0.25 ~8 microgram/mL. Some S. aureus isolates showed decreased susceptibility to teicoplanin (MIC 4 microgram/mL, 33 strains; MIC 8 microgram/mL, 1 strain), but none showed decreased susceptibility to vancomycin. A positive correlation was observed between the inhibitory zone diameters of teicoplanin disc and the MICs of teicoplanin(P< 0.0 1). Inhibitory zone diameter differences between vancomycin and teicoplanin discs also showed a positive correlation with the MICs of teicoplanin (P< 0.01). Strains whose inhibitory zone diameters of teicoplanin disc were less than 16 mm, the sensitivity and positive predictive value for the detection of strains with MICs more than 4 microgram/mL were 100 % (34/ 34) and 43% (34/ 79), respectively. In strains with inhibitory zone diameter difference of more than 4 mm, the sensitivity and positive predictive value of detection in MICs of more than 4 microgram/mL were 94 % (32/ 34) and 70 % (32/46), respectively.
CONCLUSION
Although S. aureus with intermediate or full resistance to glycopeptides was not isolated in this study, few strains had decreased susceptibility to teicoplanin. We conclude that when the inhibitory zone diameters of teicoplanin disc are less than 16 mm or inhibitory zone diameter difference between vancomycin and teicoplanin discs is more than 4 mm, the presence of S. aureus isolates with decreased susceptibility to teicoplanin should be suspected.