Anne E. Jennings

5-Fluorocytosine Resistance in Cryptococcus neoformans

Isolates of Cryptococcus neoformans from six patients were obtained before and after unsuccessful therapy with 5-fluorocytosine (5-FC). Post-therapy isolates exhibited massive and stable 5-FC resistance. The frequency of drug-resistant mutants in susceptible isolates of C. neoformans was <0.001% (70.4 ± 17.9 per 107 cryptococci), whereas mutant frequencies in resistant isolates approached 100%. Non-drug-induced, spontaneously appearing 5-FC resistant mutants were documented in four susceptible isolates of C. neoformans by use of the statistical method of fluctuation analysis. Mutation rates on these same four isolates ranged from 1.2 × 10−7 to 4.8 × 10−7. Total intracellular uptake and incorporation of cytosine-5-3H (CyH3) and 5-fluorocytosine-2-14C (5-FC14) into a trichloroacetic acid-insoluble fraction were markedly reduced in six isolates with in vivo-acquired resistance when compared with susceptible pretreatment strains from the same patients. Five of these six isolates also had acquired massive resistance to 5-fluorouracil (5-FU), suggesting that a mutation in the uridine-5′-monophosphate pyrophosphorylase was responsible for drug resistance. The sixth isolate, which remained susceptible to 5-FU, appeared to have a defect in a cytosine-specific permease accounting for 5-FC resistance. A single isolate with in vitro-acquired 5-FC and 5-FU resistance had no reduction in uptake or incorporation of CyH3 or 5-FC14. The mechanism of resistance in this isolate is discussed.

Variant Forms of Pulmonary Cryptococcosis

Abstract Cryptococcus neoformanswas cultured from the sputum bronchial washings, or lung of 32 patients, 25 of whom were white men. Eight patients had invasive pulmonary disease; this was demonstra...

Variables Influencing Susceptibility Testing of Cryptococcus neoformans to 5-Fluorocytosine

The minimum inhibitory concentration (MIC) of 5-fluorocytosine (5-FC) was determined for 65 isolates of Cryptococcus neoformans by using a twofold serial tube dilution method. The MIC was profoundly influenced by incubation temperature, inoculum size, and duration of incubation. By using a standard set of test conditions, 100% of 49 pretreatment isolates of C. neoformans were susceptible to 10 μg of 5-FC per ml or less, and 9 (56%) of 16 isolates recovered during or after 5-FC therapy were massively drug resistant (MIC > 320 μg/ml). With the standard test conditions recommended here, the tube dilution method was found to be both accurate and reproducible, and the results correlated with the treatment status of patients.

Factors Influencing Susceptibility of Nocardia Species to Trimethoprim-Sulfamethoxazole

Demonstration of synergism between trimethoprim and sulfamethoxazole against 10 Nocardia isolates was found to be critically dependent upon the isolate, the duration of incubation, and the trimethoprim-sulfamethoxazole ratio. Inoculum effect was not significant. The trimethoprim-sulfamethoxazole ratio in the commercial, fixed-dose combination was found to contain too little trimethoprim to be optimal for Nocardia.

Experimental Therapy of Cladosporiosis and Sporotrichosis with 5-Fluorocytosine

Cladosporium trichoides and Sporothrix schenckii are fungi known to be pathogenic for man. No effective chemotherapy is available for cladosporiosis, and systemic sporotrichosis can be very resistant to antifungal chemotherapy. Experimental infections of mice with these fungi resembled their respective infections in man and provided a model for evaluating a new antifungal agent, 5-fluorocytosine (5-FC). Our results with four isolates of C. trichoides demonstrated a statistically significant dose-related therapeutic effect with 5-FC. Mortality was significantly reduced in all treatment groups, and survivors showed no clinical sign of disease despite positive brain cultures. Results with a single isolate of S. schenckii were less encouraging. Fatality rate was significantly decreased in all treatment groups, but no trend was noted with increasing 5-FC dosage. Survivors manifested the signs of active disease, and all liver and spleen cultures were positive for S. schenckii. These results indicated that (i) 5-FC may be the first drug useful in the treatment of cladosporiosis, and (ii) 5-FC may have only limited therapeutic benefit in systemic sporotrichosis. Images

Identification of Cryptococcus neoformans in a routine clinical laboratory

Eight taxonomic tests were compared for their ability to distinguishCryptococcus neoformans from the non-pathogenic species ofCryptococcus. Eight isolates ofCryptococcus were obtained from the American Type Culture Collection and 43 isolates were obtained directly from human and natural sources. The tests which appeared to be most valuable to the routine diagnostic laboratory were growth at 37° C, characteristic growth on Guizotia seed agar and virulence for mice.