Induction of telithromycin resistance by several macrolide antibiotics in Enterococcus spp. and Streptococcus spp.

Abstract number: P2046

Perez J., Culebras E., Gomez M., Picazo J.

Objectives: Macrolide resistance in Enterococcus spp. and Streptococcus spp. is an increasing problem worldwide. Telithromycin (TL) was developed as an alternative for the treatment of respiratory diseases caused by microorganisms resistant to macrolides. We evaluated the resistance to this antibiotic in 10 strains belonging to both genera, all of them resistant to macrolides and with differences in their genotypic and phenotypic characteristics.

Methods: We selected 10 clinical isolates resistant to erythromycin (ER) collected at our Hospital. All isolates showed flattening of the inhibition halo of TL induced by several macrolides by the disk diffusion method. The isolates selected for this study were: 4 Enterococcus spp. (1 E. casseliflavus, 1 E. avium, 1 E. faecalis and 1 E. faecium) and 6 Streptococcus spp. (2 S. agalactiae, 2 S. pyogenes, 1 group G Streptococcus and 1 group F). We determined their phenotypic patterns by disk diffusion test and their genotypes by PCR amplification with specific primers. Susceptibility to different macrolides was determined by the agar dilution method. MICs of TL were also analysed after induction with several MLS antibiotics.

Results: All strains were resistant to ER and azithromycin with MIC90 > 256 mg/L and 128 mg/L respectively. Only three isolates were resistant to TL. Four strains harboured erm(B) gene, one strain erm(A) gene, and one strain mef(A) gene. We observed reduction of the inhibition halo of TL after induction with macrolides in 4 of the microorganisms analysed (1 E. avium, 1 E. faecalis, 1 group F and 1 group G Streptococcus). However, only in the group F Streptococcus, an increase in MICs of TL values was observed.

Conclusions: 1) Resistance induction to TL by macrolides is common in all species of these genera, and it is independent of genotypic and phenotypic characteristics. 2) ER is the higher inductor of TL resistance of all the macrolides studied. 3) Absence of correlation between increased MICs values and reduction of the inhibition halo of TL is probably due to differences in sensitivity of the methods.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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