Effects of Fildes Enrichment on Antibiotic Susceptibility Testing of Haemophilus influenzae in the Autobac

The results of this investigation showed that the Autobac could be used to determine the susceptibility of Haemophilus influenzae to ampicillin, chloramphenicol, and tetracycline when eugonic broth was supplemented with 1.5% Fildes enrichment. An excellent correlation was obtained between the susceptibilities as determined by the agar dilution minimal inhibitory concentration method and the Autobac. For ampicillin all H. influenzae isolates with minimal inhibitory concentrations of </=1 mug/ml had light scattering indexes of >/=0.60. Those isolates with minimal inhibitory concentrations of >/=4 mug/ml had light scattering indexes of </=0.49. For chloramphenicol and tetracycline all isolates had minimal inhibitory concentrations of </=1 mug/ml and light scattering indexes of >/=0.71.