JAC Advance Access originally published online on November 16, 2005
Journal of Antimicrobial Chemotherapy 2006 57(1):139-141; doi:10.1093/jac/dki404
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Macrolide resistance mechanisms and in vitro susceptibility patterns of viridans group streptococci isolated from blood cultures
en Hasçelik21 School of Health Services, Hacettepe University, 06100, Ankara, Turkey; 2 Department of Microbiology and Clinical Microbiology, School of Medicine, Hacettepe University, 06100, Ankara, Turkey
Received 26 May 2005; returned 26 July 2005; revised 6 October 2005; accepted 7 October 2005
* Corresponding author. Tel: +90-312-3051587; Fax: +90-312-3102730; E-mail: aergin{at}hacettepe.edu.tr
Objectives: Our aim was to study the macrolide resistance mechanisms and antimicrobial susceptibilities of viridans group streptococci (VGS) isolated from blood cultures.
Methods: In vitro susceptibilities to nine antimicrobials were studied for 85 VGS isolated from blood cultures by agar dilution. Pheno- and genotyping of erythromycin-resistant isolates were studied by the double disc test and PCR.
Results: Resistance to erythromycin was found in 27% (n = 23) of the isolates. Erythromycin-resistant Streptococcus oralis (n = 13) predominated among the other erythromycin-resistant species isolated. The phenotypes among 23 erythromycin-resistant isolates were as follows: 12 constitutive macrolide–lincosamide–streptogramin (cMLSB) resistance phenotype and 11 macrolide (M) resistance phenotype. Of the cMLSB isolates 11 had erm(B) genes and 11 of the M phenotype isolates had mef(A) genes. Four of the cMLSB isolates had both erm(B) and mef(A) genes. None of the isolates had erm(TR) genes. Combined resistance to erythromycin with penicillin, clindamycin, chloramphenicol, tetracycline and quinupristin/dalfopristin was found in 100, 61, 74, 100 and 100% of the isolates, respectively. No resistance was found for vancomycin, linezolid and levofloxacin.
Conclusions: The macrolide resistance mechanisms of our VGS isolates revealed that the cMLSB phenotype associated with erm(B) and the M phenotype associated with mef(A) genes are found with similar frequencies.
Keywords: erythromycin resistance , MLSB , M phenotype , erm(B) , mef(A) , S. oralis
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