Comparison of agar dilution, broth dilution, and disk diffusion testing of ampicillin against Haemophilus species by using in-house and commercially prepared media

An evaluation to determine the optimal method for the in vitro susceptibility testing of Haemophilus strains to ampicillin was undertaken. In our hands, in-house-prepared Haemophilus Test Medium used by either the broth macrodilution or agar dilution method produced the most consistent results, especially for beta-lactamase-negative, ampicillin-resistant H. influenzae strains.