Detection of resistance to amphotericin B among Cryptococcus neoformans clinical isolates: performances of three different media assessed by using E-test and National Committee for Clinical Laboratory Standards M27-A methodologies.
Although reliable detection of resistance in vitro is critical to the overall performance of any susceptibility testing method, the recently released National Committee for Clinical Laboratory Standards M27-A methodology for susceptibility testing of yeasts discriminates poorly between resistant and susceptible isolates of Candida spp. We have previously shown that both substitution of antibiotic medium 3 for RPMI 1640 medium in the microdilution variant of the M27-A method and use of the E-test agar diffusion methodology permit detection of amphotericin B-resistant Candida isolates. To determine the relevance of these observations to Cryptococcus neoformans, we have evaluated the performances of both the M27-A and the E-test methodologies with this yeast using three different media (RPMI 1640 medium, antibiotic medium 3, and yeast nitrogen base). As with Candida, we found that only antibiotic medium 3 permitted consistent detection of resistant isolates when testing was performed in broth by the M27-A method. When testing was performed by the E-test agar diffusion method, both RPMI 1640 medium and antibiotic medium 3 agar permitted ready detection of the resistant isolates. Reading of the results after 48 h of incubation was required for testing in broth by the M27-A method, while the MIC could be determined after either 48 or 72 h when the agar diffusion method was used.
Lozano-Chiu
M
M
Division of Infectious Diseases, Department of Internal Medicine, Center for the Study of Emerging and Reemerging Pathogens, University of Texas Medical School, Houston, Texas, USA. mchiu@heart.med.uth.tmc.edu
Paetznick
V L
VL
Ghannoum
M A
MA
Rex
J H
JH
D000666:Amphotericin B / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003453:Cryptococcosis / Q000188:drug therapy / Q000382:microbiology*; D003455:Cryptococcus neoformans / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D003470:Culture Media; D004352:Drug Resistance, Microbial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*
D000900:Anti-Bacterial Agents; D003470:Culture Media; D000666:Amphotericin B