[Haemophilus influenzae: phenotype characteristics of strains isolated in 12 Catalan hospitals over one year]

Influence of the beta-lactam resistance phenotype on the cefuroxime versus cefditoren susceptibility of Streptococcus pneumoniae and Haemophilus influenzae recovered from children with acute otitis media

OBJECTIVES

To study the influence of resistance phenotypes (based on sentinel antibiotics: penicillin and amoxicillin with/without clavulanate) on the cefuroxime versus cefditoren susceptibility of Streptococcus pneumoniae and Haemophilus influenzae recovered from children with acute otitis media.

METHODS

Middle ear isolates (193 S. pneumoniae and 114 H. influenzae) received in the Spanish Reference Laboratory (Instituto de Salud Carlos III) were tested. Antimicrobial susceptibility to penicillin, amoxicillin with/without clavulanate, cefuroxime and cefditoren was determined by agar dilution using Mueller-Hinton agar supplemented with 5% sheep blood for S. pneumoniae and Haemophilus Test Medium for H. influenzae. Strains were classified according to penicillin susceptibility (S. pneumoniae) or beta-lactamase production (H. influenzae).

RESULTS

The decrease in penicillin susceptibility of S. pneumoniae (from the susceptible to the resistant category) decreased amoxicillin and cefuroxime susceptibility rates from 100% to 34% and 0%, respectively. All pneumococcal strains were inhibited by 0.5 mg/L cefditoren, including those from penicillin-resistant serotypes 14, 23F, 6B and 9V with higher amoxicillin versus penicillin MICs. Susceptibility rates of beta-lactamase-positive H. influenzae strains were 93.8% and 85.4% to amoxicillin/clavulanate and cefuroxime, respectively. Resistance to amoxicillin/clavulanate (MIC>or=8/4 mg/L) was 12.1% (8 out of 66) and 6.3% (3 out of 48) in beta-lactamase-negative and -positive strains, respectively. All H. influenzae strains were inhibited by <or=0.06 mg/L cefditoren.

CONCLUSIONS

Susceptibility to sentinel beta-lactams cannot predict activity of other members of the group. The addition of clavulanic acid to amoxicillin does not guarantee 100% coverage of H. influenzae, regardless of beta-lactamase production.

[Activity of telithromycin and other oral antibiotics against respiratory tract pathogens with acquired mechanisms of resistance]

INTRODUCTION

Antimicrobial resistance among strains of Streptococcus pneumoniae, Haemophilus influenza, and Streptococcus pyogenes has limited the usefulness of conventional agents for the treatment of some infectious diseases related with these microorganisms. There is thus a clear need for new antimicrobial agents active against these resistant strains.

OBJECTIVES

To assess the in vitro susceptibility to telithromycin and other oral antimicrobial agents of 307 strains of S. pneumoniae, H. influenzae, and S. pyogenes with acquired mechanisms of resistance to macrolides and/or beta-lactams.

METHODS

Antimicrobial susceptibility testing was performed by the agar dilution method, and results were preferentially evaluated according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines.

RESULTS

The activity of telithromycin against erythromycin-resistant S. pneumoniae was excellent. All the strains were inhibited with 2 mg/l, regardless of the mechanism of macrolide resistance exhibited. Telithromycin was slightly more active than the tested macrolides in beta-lactamase-producing H. influenzae strains, with a MIC90 of 2 mg/l. Telithromycin also demonstrated potent activity against macrolide-resistant S. pyogenes. The MIC of telithromycin was > 4 mg/l for only one out of the 202 tested strains.

CONCLUSIONS

Telithromycin is a very promising therapeutic option against bacterial pathogens of the respiratory tract, including strains that have developed mechanisms of resistance to macrolides and/or beta-lactams.