title: Rapid method for determining antimicrobial susceptibility of Haemophilus influenzae.
abstract: A method was developed to determine the susceptibility of Haemophilus influenzae to ampicillin, cefamandole, and chloramphenicol by using the MS-2 system (Abbott Laboratories) for determining minimum inhibitory concentrations (MIC). The MS-2 results for 132 strains of H. influenzae were compared with the results of agar disk diffusion, agar dilution, and beta-lactamase tests. Twenty-four strains (18.2%) of H. influenzae were resistant to ampicillin by the agar dilution method, as opposed to 25 strains by the MS-2 method. For a beta-lactamase-negative strain, the agar dilution MIC was 4 micrograms/ml, and the MS-2 MIC was 16 micrograms/ml. Twenty-one strains produced beta-lactamase; two beta-lactamase-negative strains were resistant by MS-2, agar dilution, and agar disk diffusion. In addition, one beta-lactamase-negative strain, for which the agar dilution MIC was 32 micrograms/ml and the MS-2 MIC was 16 micrograms/ml, was sensitive by agar disk diffusion. Overall, the MS-2 method compared favorably with the agar dilution method for determining the MIC of ampicillin, cefamandole, and chloramphenicol for H. influenzae.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002435:Cefamandole / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D003470:Culture Media; D006193:Haemophilus influenzae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D001618:beta-Lactamases / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D002435:Cefamandole; D002701:Chloramphenicol; D000667:Ampicillin; D001618:beta-Lactamases