The formula for a modified Vogel and Johnson Agar is presented. In addition to the ingredients found in Vogel and Johnson Agar, the new medium contains, per liter: 5 g of beef extract, 2 g of deoxyribonucleic acid, 2 g of phosphatidyl choline and 780 units of catalase spread on the plates before inoculation. This new medium is as effective as Baird-Parker Agar in enumeration of stressed Staphylococcus aureus, and in enumeration of staphylococci from naturally contaminated processed food samples.
Microdilution and broth dilution techniques were compared for the susceptibility testing of 50 clinical yeast isolates to 5-fluorocytosine and amphotericin B. Good correlation between methods was obtained with all isolates except Cryptococcus neoformans.Several broth dilution techniques for the susceptibility testing of yeasts to 5-fluorocytosine (5-FC) and amphotericin B (AmB) have been described elsewhere (5,9, 11-13). These methods are cumbersome to perform, and the development of more rapid and simple procedures is desirable.This report describes the comparison of a microdilution and broth dilution technique for the susceptibility testing of yeasts to both 5-FC and AmB. Comparisons were made between tests incubated for 24 and 48 h at 25 and 35°C. Stability of the drugs at -70°C is also discussed.Organisms. Fifty yeast isolates were obtained from clinical specimens in the mycology laboratory at Hartford Hospital and identified by standard methods (2-4). These included 14 strains of Cryptococcus neoformans, 22 strains of Candida albicans, 15 Candida species not albicans, 4 strains of Torulopsis glabrata, and 1 strain each of Geotrichum candidum and Trichosporon species. The yeasts were maintained at room temperature on Sabouraud dextrose agar slants.Drugs. 5-FC was supplied as a pure powder by Hoffman-LaRoche, Inc., Nutley, N.J. The drug was dissolved in sterile distilled water with the aid of gentle heat from a bunsen burner, sterilized through a 0.45-,um filter, and frozen at -70°C in 1.5-ml portions of 1,000 jig/ml. AmB (Fungizone) was obtained from E.R. Squibb and Sons, Inc., Princeton, N.J., rehydrated with 100% dimethyl sulfoxide, and frozen at -70°C in 1.5-ml portions of 1,000 ,ug/ml.Methods. The broth dilution technique for 5-FC was performed in yeast nitrogen broth as described by Shadomy (11,12). AmB was tested in Sabouraud dextrose broth (5, 7, 9). Duplicate twofold dilutions of each drug were prepared in 1-ml volumes on the day of testing and inoculated with 50 pl of a 105-cells-per-ml yeast suspension in the appropriate liquid medium. The final density was 5 x 103 cells per ml. One set of tubes was incubated at 35°C, and another was incubated at 25°C. The microdilution technique was performed in microtiter U-bottom trays (Flow Laboratories, Rockville, Md.) with a semiautomatic pipetter and diluter (Cooke Laboratory Products, Alexandria, Va.) to prepare the twofold serial dilutions. The trays were individually wrapped in plastic and stored at -70°C. Trays were removed from the freezer 0.5 h before use and thawed at room temperature. The same suspension as used for broth dilution was used for microdilution, yielding a final inoculum density of 104 cells per ml. Duplicate trays were sealed with tape; one tray was incubated at 25°C and another was incubated at 35°C. The minimum inhibitory concentration (MIC) was read at 24 and 48 h as the least amount of drug which inhibited visual growth. A C. albicans no. 6631 control was provided by Hoffman-LaRoche and run each day of testing with both 5-FC and A...
Evidence is presented suggesting that the decreased enumeration of heat-stressed Staphylococcus aureus cells on selective media is the result of accumulation of metabolic H2O2. It accumulates due to the decreased activity of catalase caused by the synergistic effects of heat and NaCl. Heated cells enumerated anaerobically on tryptic soy agar (TSA) containing 6.5% NaCl (TSAS 6.5) exhibited a 200-fold increase compared to cells enumerated aerobically on the same medium. The anaerobic counts on TSAS 6.5 were similar to the aerobic counts on TSA. Increases in both death and injury occurred when S. aureus was propagated in tryptic soy broth (TSB) plus 10% NaCl (TSBS) instead of TSB before thermal injury. Addition of catalase to TSA and TSA containing 7.5% NaCl (TSAS) increased the count to approximately the same levels on TSA and TSAS as that found following thermal injury after propagation in TSB. Catalase activity was 12-fold higher in stationary phase cells propagated in TSB than in TSBS. Indirect evidence indicates that toxic levels of H2O2 accumulated rapidly, causing one to two log decreases in enumeration after 30 to 60 min incubation on TSAS.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.