19th European Congress of Clinical Microbiology and Infectious Diseases, Helsinki, Finland, 16 - 19 May 2009, vol.15, no.4, pp.613-677
P. Sagiroglu*, B. Aksu, U. Over-Hasdemir (Istanbul, TR)
Objective: Macrolide resistance due to antibiotic efflux in Streptococcus pneumoniae is getting increased in many parts of the world. Macrolide efflux pump encoded by either mefA or mefE genes confers low-level resistance to 14- and 15-membered macrolides but not to 16-membered macrolides, lincosamids, or streptogramin B.
We aimed to determine the prevalence of erythromycin resistance and the role of mef directed efflux pump in S. pneumoniae strains isolated in our university hospital during 2008.
Methods: The prevalence of erythromycine resistance have been determined by disk diffusion method in 91 S. pneumoniae isolates. Broth microdilution method was applied in detection of erythromycin and clindamycin MICs of the pneumococcal strains which were found to be resistant to erythromycin in disk diffusion test. Two major macrolide resistance mechanisms regarding efflux and target modification were investigated in erythromycin resistant S. pneumoniae isolates, phenotypically and genotypically. Double disc method was used to determine the macrolide resistance phenotypes (cMLSB, iMLSB and M phenotype). The presence of mef genes and ermB genes were analysed by PCR using primers that distinguish mefA and mefE genes.
Results: Resistance to erythromycin was detected in 28.6% (n:26) of the isolates. Erythromycin MICs ranged from 2 µg/ml to ≥512 mg/mL and MIC50 of the resistant strains was ≥512 µg/mL. Twenty-four of erythromycin resistant isolates were in cMLSB phenotype and 2 were in M phenotype (Table 1).
Table 1. Phenotypic and genotypic test results in erythromycin resistant S. pneumoniae isolates
|Resistance phenotype||No. of isolates (%)||MIC range (μg/mL)*||Resistance genotype no. of isolates (%)|
|Erythromycin||Clindamycin||erm (B)||mef (E)||erm (B)+ mef (E)|
|cMLSB||24 (92.3)||128-≥512||≥512||10 (38)||0||14 (53.8)|
|M||2 (7.7)||2–4||0.125–0.25||0||2 (8)||0|
Determined by broth microdilution recommended by the CLSI.
In the isolates representing M phenotype, erytromycin MICs remained in low level (2–4 µg/mL) and their clindamycin MICs were in susceptibile range. Of the 26 erytromycin resistant strains, 14 (53.8%) were found to harbour mefE and ermB genes together; whereas 2 (7.7%) of them harboured mefE alone.
Conclusion: This is the first report indicating the high prevalence of mefE gene together with ermB gene in macrolide resistant S. pneumoniae isolates in Turkey. Although target modification (ErmB) was determined as the mechanism responsible of high level erythromycin resistance in our strains; the presence of mefE gene either alone or together with ermB in these isolates signifies a new threat in macrolide resistance of S. pneumoniae in our region.