JAC Advance Access originally published online on June 9, 2004
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Journal of Antimicrobial Chemotherapy 2004 54(1):117-121; doi:10.1093/jac/dkh317
JAC vol.54 no.1 © The British Society for Antimicrobial Chemotherapy 2004; all rights reserved.
Phenotypic and molecular characterization of macrolide and streptogramin resistance in Streptococcus mitis from neutropenic patients
1 Laboratoire du Centre National de Greffe de Moelle Osseuse, 1006 Tunis, Tunisia; 2 Service de Microbiologie, CHU Côte de Nacre, 14033 Caen Cedex, France
* Corresponding author. Tel: +33-2-31-06-45-72; Fax: +33-2-31-06-45-73; Email: leclercq-r{at}chu-caen.fr
Objectives: To determine the prevalence of macrolide and streptogramin resistance in Streptococcus mitis isolates from neutropenic patients and to identify mechanisms of macrolide and streptogramin resistance in resistant isolates.
Methods: MICs of erythromycin, spiramycin, lincomycin and pristinamycin were determined for S. mitis isolates. Macrolide-resistance genes were characterized by PCR and ribosomal mutations by sequencing.
Results: A total of 169 S. mitis isolates were recovered from 66 patients at the Tunisian Bone Marrow Transplant Centre. Of these, 120 (70%) were non-susceptible to erythromycin and one was resistant to pristinamycin; 48.5% of isolates had an MLSB phenotype with cross-resistance between erythromycin, spiramycin and lincomycin, 4% had a dissociated MLSB phenotype with resistance to erythromycin and spiramycin but apparent susceptibility to lincomycin and 47.5% displayed the M phenotype. Resistance determinants were characterized in 33 isolates. Ten of 14 isolates with the cross MLSB resistance contained an erm(B)-like gene and four a combination of erm(B)- and mef(A)-like genes. Four of the five isolates with a dissociated MLSB phenotype contained erm(B)-like and one a combination of erm(B)- and mef(A)-like genes. All the 14 isolates with an M phenotype contained mef(A)-like genes. The pristinamycin-resistant strain had G105 and A108 substitutions in the conserved C terminus of the L22 ribosomal protein.
Conclusions: The prevalence of macrolide resistance is high in S. mitis from neutropenic patients and is due to the spread of erm(B)- or mef(A)-like genes alone or combined. Resistance to streptogramins is rare and in this case associated with ribosomal mutation.
Keywords: oral streptococci , ribosome , mutation , drug resistance
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