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J Bacteriol. 1969 February; 97(2): 481-487
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

In Vitro and In Vivo Activity of Hamycin Against Blastomyces dermatitidis¹

^a Division of Allergy and Infectious Diseases, and Departments of Medicine and Biometry, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23219

ABSTRACT

Clinical responses of patients with blastomycosis to treatment with hamycin have been variable. An explanation for this was sought in a series of studies in which in vitro and in vivo susceptibilities to hamycin of five strains of Blastomyces dermatitidis were compared. Minimal inhibitory concentrations of hamycin for the five strains indicated uniformly high levels of in vitro susceptibility (0.008 to 0.016 µg/ml). In vivo activity was measured in infected mice treated intraperitoneally for a period of 28 days with doses of the drug ranging from 0.001 to 0.030 mg per mouse. Significant differences in response to treatment among the five strains were noted (P < 0.001), and protective doses were found to vary from 0.001 to >0.030 mg per mouse per day. Further observations of infected mice after treatment revealed marked rates of relapsing infection, and several strains caused death. Persistent inapparent infections were also detected on culture of selected organs. Toxicity due to hamycin alone was not observed. These results suggest that variations in clinical responses to hamycin therapy in treatment of blastomycosis reflect differences in pathogenesis and host response in vivo to the infecting organism rather than differences in susceptibility of B. dermatitidis to hamycin.

¹ Portions of this paper were presented at the 67th Annual Meeting, American Society for Microbiology, New York, N.Y., 30 April–4 May 1967 (Bacteriol. Proc., p. 72, 1967).