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Differences in potential for selection of clindamycin-resistant mutants between inducible erm(A) and erm(C)

Claire Daurel1, Corinne Huet, Anne Dhalluin

  • 1Service de Microbiologie, CHU Côte de Nacre, 14033 Caen cedex, France.

Journal of Clinical Microbiology
|December 14, 2007
PubMed

Insights

The erm(C) gene in Staphylococcus aureus leads to a significantly higher mutation rate for clindamycin resistance compared to the erm(A) gene. This finding is crucial for understanding antibiotic resistance development in staphylococci.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Inducible macrolide-lincosamide-streptogramin B (MLS(B)) resistance in staphylococci is often mediated by erm(C) or erm(A) genes.
  • The D-zone test is used to identify this inducible resistance phenotype.
  • Clindamycin resistance can emerge in Staphylococcus aureus with inducible MLS(B) resistance, even when clindamycin appears effective in vitro.

Purpose of the Study:

  • To compare the frequencies of mutation to clindamycin resistance in Staphylococcus aureus isolates carrying erm(C) versus erm(A) genes.
  • To investigate the genetic potential of erm(C) and erm(A) in selecting for clindamycin-resistant mutants.

Main Methods:

  • Mutation frequency analysis for clindamycin resistance in 28 S. aureus isolates with inducible MLS(B) resistance (18 erm(C), 10 erm(A)).
  • Inclusion of control isolates with erythromycin susceptibility or msr(A) gene (efflux).
  • Cloning of erm(C) and erm(A) genes into S. aureus RN4220 to assess gene-specific effects.

Main Results:

  • Isolates with the erm(C) gene showed a 14-fold higher mean mutation frequency to clindamycin resistance (4.7 x 10(-7)) compared to isolates with the erm(A) gene (3.4 x 10(-8)).
  • Mutation frequencies for erm(A) isolates were only slightly higher than for control isolates (1.1 x 10(-8)).
  • The difference in mutation frequency between erm(C) and erm(A) was also observed when genes were cloned into S. aureus RN4220.

Conclusions:

  • The erm(C) and erm(A) genes possess distinct genetic potentials for selecting clindamycin-resistant mutants in S. aureus.
  • Distinguishing between erm(C) and erm(A) may be possible using the disk diffusion test based on high- versus low-level resistance to oleandomycin.

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