[Comparison of the activity of different macrolides on strains of Haemophilus 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.