In vitro activity of antibacterial agents on Haemophilus influenzae isolates

One hundred and eight clinical isolates of Haemophilus influenzae, consecutively occurring and epidemiologically unrelated, were examined for susceptibility against twelve antibacterial agents by disc diffusion and agar dilution. These were also serotyped and tested for beta-lactamase production. All isolates were sensitive to erythromycin, trimethoprim, chloramphenicol and cefotaxime. Six (5.5%) strains were ampicillin resistant (MIC 128 mg/1), and five of them were beta-lactamase producers. Tetracycline resistance was seen in 52.8% of the isolates. This is probably related to the high consumption of tetracyclines in our population. Cefotaxime (modal MIC 0.03 mg/1) and cefaclor (modal MIC 0.03 mg/1) were the most active parenteral and oral cephalosporins respectively.