Journal Article

Antimicrobial susceptibility patterns and macrolide resistance genes of viridans group streptococci from normal flora

Helena Seppälä, Marjo Haanperä, Mohammad Al-Juhaish, Helinä Järvinen, Jari Jalava and Pentti Huovinen

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 52, issue 4, pages 636-644
Published in print October 2003 | ISSN: 0305-7453
Published online October 2003 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dkg423
Antimicrobial susceptibility patterns and macrolide resistance genes of viridans group streptococci from normal flora

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Objectives: Our aim was to study the antimicrobial susceptibilities and macrolide resistance mechanisms of viridans group streptococci isolated from the normal flora.

Methods: In vitro susceptibilities of 16 antimicrobials were studied for 161 viridans streptococci (on average 5.8 isolates per person) from the normal flora of 28 elderly persons. Resistance mechanisms of erythromycin-resistant isolates were studied by the double disc test and PCR.

Results: In all, 16.8% of the isolates were non-susceptible (MIC ≥ 0.25 mg/L) to penicillin, but none showed high-level resistance (MIC ≥ 4 mg/L). Resistance to erythromycin, tetracycline, quinupristin/dalfopristin, levofloxacin and moxifloxacin was found in 22.4, 27.3, 13.0, 1.9 and 1.9% of the isolates, respectively. Combined resistance to erythromycin and tetracycline was found in 13.0% of the isolates. Erythromycin-resistant isolates were isolated from 57% of the study persons. Of the erythromycin-resistant isolates 80.6% were of the M phenotype and 19.4% were of the macrolide–lincosamide–streptogramin B (MLSB) phenotype (one isolate with constitutive and six with inducible expression). Isolates with the M phenotype were the least susceptible to telithromycin, a new ketolide. The mef(A) gene was found in the isolates with the M phenotype and the erm(B) gene in the isolates with the MLSB phenotype.

Conclusions: The distribution of phenotypes among the viridans streptococci resembles that found in Streptococcus pyogenes, with predominance of the M phenotype. However, the coding gene for the MLSB phenotype, erm(B), is the same in viridans streptococci as in Streptococcus pneumoniae. Viridans group streptococci carrying different resistance traits provide a pool of resistant bacteria that may transfer resistance determinants to more pathogenic organisms.

Keywords: Keywords: α-haemolytic streptococci, erythromycin resistance, commensal flora, elderly persons

Journal Article.  6213 words. 

Subjects: Medical Oncology ; Critical Care

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