[Investigation of macrolide-lincosamide-streptogramin B (MLS(B)) and telithromycin resistance in clinical strains of staphylococci]

Abstract

The aim of this study was to determine the prevalence of macrolide-lincosamide-streptogramin B (MLS(B)) resistance and also to search for telithromycin resistance in staphylococcus strains isolated at Hacettepe University Hospital, Ankara, Turkey. A total of 381 Staphylococcus aureus isolates and 94 coagulase-negative staphylococci (CNS) were tested by disc approximation method. Methicillin resistance of these isolates was searched by disc diffusion test using 30 microg cefoxitin discs. Distribution of erm genes was detected by PCR method. Of 381 isolates 112 (29.4%) S. aureus and 58 (61.7%) CNS were found to be resistant to erythromycin. Among these, the inducible MLS(B) (iMLS(B)) resistance was the most prevalent pattern, being 56.2% and 41.4% among S. aureus and CNS isolates, respectively. The frequency of constitutive MLS(B) resistance (cMLS(B)) was 40.2% for S. aureus and 34.5% for CNS. Macrolide-streptogramin B (MS(B)) resistance pattern was detected only in CNS isolates (24.1%). In 4 (3.6%) of S. aureus isolates mixed pattern demonstrating both inducible and constitutive patterns was detected. None of the isolates susceptible to erythromycin showed resistance to telithromycin. As a remarkable finding of this study D-shaped inhibition zones around the telithromycin discs was observed in all of the isolates with iMLS(B) and macrolide-streptogramin B (MS(B)) resistance phenotypes. The isolates showing cMLS(B) pattern were also resistant to telithromycin (no zone of inhibition around the telithromycin discs). A total of 170 erythromycin resistant staphylococcal isolates were tested for the presence of erm and msrA genes. Among the S. aureus isolates with iMLS(B) and cMLS(B) phenoypes, the most common findings were the detection of ermA (44/63) and ermA + ermC (35/45) genes, respectively. All of the four isolates with mixed phenotype harboured ermA gene. With respect to CNS isolates, the most frequently detected gene was ermC (37/58); whereas iMLS(B) and cMLS(B) resistant CNS isolates had ermC (11/24) and ermA + ermC (10/20) as the most prevalent resistance genes, respectively. msrA gene was detected in 11 of 14 CNS isolates with MS(B) resistance. Two of these were also carrying ermA while 3 isolates harboured ermCalong with msrA gene. The results of this study showed that inducible MLS(B) resistance was the most prevalent phenotype among the clinical staphylococcal isolates in our hospital. All of these isolates also demonstrated inducible resistance pattern against telithromycin, a new antibiotic suggested particularly for the treatment of infections with iMLS(B) resistant bacteria. The telithromycin resistance patterns need to be tested in other centers and the impact of this issue on the clinical use of telithromycin should be investigated.