In vitro susceptibility patterns of nonserotypable Haemophilus influenzae from patients with chronic bronchitis

The antimicrobial susceptibility patterns of 76 nonserotypable Haemophilus influenzae (biotypes I-IV) from patients with chronic bronchitis were compared against ten orally administered antimicrobial agents. In addition the sputum ampicillin concentrations one hour after standard therapy were determined in five patients with chronic bronchitis. Ampicillin resistance was demonstrated in one strain (biotype IV) which produced beta-lactamase and two strains (biotype II) with innate resistance (MIC = 4 mg/l). Resistance to trimethoprim, chloramphenicol, ciprofloxacin and cefaclor was not detected. The incidence of resistance to tetracycline was 0.5% and cephalexin 13.2%. A high incidence of resistance to erythromycin (95%) was noted. There was no association between resistance and biotype of nonserotypable H. influenzae. The sputum ampicillin concentrations from four out of five patients given standard antibiotic doses were shown to be sufficient to inhibit the growth of the majority of nonserotypable H. influenzae strains one hour after treatment. This study shows that the incidence of nonserotypable H. influenzae resistant to ampicillin is low in this community but that resistance levels to erythromycin, commonly prescribed for the management of acute bronchitis, are high. Regular sensitivity screens are important in monitoring the value of various antibiotic regimens in the management of acute bronchitis.