Influence of Streptomycin on Type b Haemophilus influenzae

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Abstract
The sensitivity of a strain of H. influenzae can be assayed reliably by inoculating Levinthal agar plates containing varying concs, of streptomycin with a 2-mm. loop of a culture grown for 6 hrs. on Levinthal agar or broth. The lowest conc, of drug which prevents visible growth after 48 hrs.'' incubation is the minimal effective conc. (MEC). Expts. with 22 cultures isolated prior to treatment from patients with severe Type b H. influenzae suggested that this organism is highly sensitive to streptomycin. The development of resistance in vitro was studied in 16 sensitive strains. In 1-3 wks., 7 strains acquired the ability to grow in the presence of 525 units/ml. Six required 4 wks. to reach this point. Three strains after 4 wks. failed to grow in concs, above 157 units/ml. The resistant strains were used for determining the correlation between MEC in vitro and the MED needed to protect mice against 15 to 20 million organisms. The in vitro test recommended apparently suffices to assay sensitivity of strains from patients to be treated with streptomycin. The protective capacity of streptomycin alone was found to equal that obtained by combining its action with sulfadiazine. Streptomycin alone was more effective against massive H. influenzae infections in mice than serum used in conjunction with sulfadiazine, and 10 human patients with in-fluenzal meningitis were successfully treated on this basis.