In-vitro activity of imipenem against 100 strains of serotype b and nontypable Haemophilus influenzae, including strains resistant to ampicillin, chloramphenicol or both

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Abstract
Imipenem, along with ampicillin, chloramphenicol, ceftazidime, aztreonam and ceftriaxone were tested against 100 clinical isolates of Haemophilus influenzae. Eighty-eight of the isolates were serotype b, 35 isolates were β-lactamase producers, and five isolates were chloramphenicol resistant. Inoculum densities of 1 × 103, 1 × 105 and 1 × 108 cfu/ml were tested for all isolates. MIC90s and MBC90s at the two lower inoculum densities for imipenem, ceftazidime, aztreonam and ceftriaxone were in the susceptible range for all categories of isolates tested. Imipenem, ceftazidime and aztreonam displayed elevated MBC90s at the high inoculum density. The effect of the high inoculum density upon the ceftriaxone MBC90 was below the level of detection afforded by the study design.