[Comparison of the activity of different macrolides on strains of Haemophilus influenzae]. / Actividad comparada de diversos macrólidossobre cepas de Haemophilus influenzae. Grupo Español de Estudio de la Actividad de Macrólidos sobre H. influenzae.

In this study we evaluated the activity of macrolides and b-lactam antimicrobials on Haemophilus influenzae isolated in 1998 in eight Spanish cities. A total of 174 clinical isolates were examined. Overall, 29% of the isolates were found to produce b-lactamase. Azithromycin was the most active of the macrolides tested in this study (MIC90 of 4 mg/l); no azithromycin-resistant strains were found. Ampicillin resistance was 29%. We found one strain intrinsically resistant to beta-lactam agents (0.65% overall); and two beta-lactamase-positive strains that were resistant to amoxicillin-clavulanic acid (1.2%). The presence of these strains, while uncommon at present, makes it necessary to test the activity of antimicrobial drugs on H. influenzae.