Sterility testing: detection of fungi and yeasts in the presence of preservatives

Abstract

Thirty-four strains of fungi and yeasts were studied for growth in six media in the presence of Merthiolate. All strains were killed in a 1:500,000 dilution; 1:5,000,000 was the maximum concentration that permitted recovery of all strains in Fluid Thioglycollate Medium (FTM). Fluid Sabouraud Medium (FSM) containing either sodium thioglycollate or sodium hydrosulphite was almost as effective. FTM with sodium hydrosulphite substituted for sodium thioglycollate and Bonnel-Raby medium were inferior to FTM, also to FSM. Rate of initiation of growth was reduced in the low concentration of 1:7,000,000 with maximum recovery at 21 days, whereas maximum recovery occurred in 7–10 days in the six control media which were similar in promoting growth. Phenylmercuric borate, phenol, benzethonium chloride and parabens were also fungicidal. Results are discussed relative to the discontinued use of FSM in the United States in official sterility testing and for the use of FTM in the test of mercurial-preserved biologies incubated at 20–25 °C.