Serotypes, biotypes, and antimicrobial susceptibility of clinical isolates of Haemophilus influenzae.

Serotypes, biotypes, and antimicrobial susceptibility of Haemophilus influenzae isolated from clinical specimens were investigated. Of 100 strains. only five were encapsulated. Three were type b (two from blood and one from spinal fluid), one was type c (from pus), and one was type e (from sputum). All strains were biotypable. Of these, 33% were biotype II, 26% biotype I, 26% biotype III, 2% biotype IV, 8% biotype V, and 5% biotype VI. The minimal inhibitory concentration (MIC) of 10 antibiotics was measured by agar dilution method. Among them, cefotaxime was the most effective (the geometric mean of MIC was 0.013 microgram/ml), followed by cefoperazone, cefamandol, doxycycline, chloramphenicol, ampicillin, oxytetracycline, cefaclor, and cefazoline. Erythromycin had the highest geometric mean of MIC (4.86 micrograms/ml). Twenty-seven isolates (27%) were resistant to ampicillin, and all the ampicillin-resistant isolates were beta-lactamase producer. Biotype III were the most resistant isolates to ampicillin among different biotypes.