Comparative in vitro activity of imipenem against Haemophilus influenzae and Haemophilus parainfluenzae.

A microdilution broth method was used to test 77 clinical isolates of Haemophilus influenzae and Haemophilus parainfluenzae, including beta-lactamase-positive and -negative strains, for susceptibility to ampicillin, chloramphenicol, and imipenem. Except for ampicillin against beta-lactamase-producing strains (MIC for 90% of strains [MIC90], greater than or equal to 128 micrograms/ml), all three antimicrobial agents had comparable in vitro activity (MIC90, less than or equal to 1 microgram/ml) against these bacterial strains.