Improved culture method for the isolation of Histoplasma capsulatum and Blastomyces dermatitidis form contaminated specimens.

Studies were performed to evaluate a method for selective isolation of Histoplasma capsulatum and Blastomyces dermatitidis from contaminated specimens. Ammonium hydroxide placed on an agar medium surface was found to inhibit the growth of many bacteria, yeasts, and saphrophytic fungi normally found in specimens such as animal tissues and sputum. In one study involving the culture of B. dermatitidis from canine tissues, 24% more isolations were obtained on a medium using NH4OH compared with a similar medium. Increases in the isolation of H. capusulatum from sputum specimens were also obtained, ranging from 20 to 32% compared with four other media without NH4OH.