Haemophilus influenzae in otitis media and sinusitis: serotypes and susceptibilty to ampicillin and amoxycillin in vitro.

In order to obtain Haemophilus influenzae, other than Type b, with highly probable human pathogeniticy strains were collected that had been isolated in abundant numbers from middle ear or maxillary sinus secretions of 157 patients with otitis media or sinusitis. The distribution of serotypes was as follows: nontypable 33.8%, Type b 26.1% Type a 19.1%, Type c 7.6%, Type e 5.7%, Type f 5.1%, and Type d 2.5%. The type distribution did not depend on the source of the strains. All strains were susceptible to ampicillin and amoxycillin in vitro; the broth dilution minimum inhibitory concentrations (MIC) of both antibiotics varied only fourfold; typical MIC values were 0.125 microgram/ml and 0.25 microngram/ml, respectively. Susceptibility did not vary with the source or type of the strains nor with the presence or absence of concomitant penicillin therapy.