<p><em>Cryptococcus neoformans/gattii</em> Species Complexes from Pre-HIV Pandemic Era Contain Unusually High Rate of Non-Wild-Type Isolates for Amphotericin B</p>

Abstract

Introduction: The Cryptococcus neoformans/gattii species complexes are a leading cause of fatality among HIV-infected patients. Despite the unavailability of clinical breakpoints (CBPs) for antifungal agents, epidemiological cutoff values (ECVs) were recently proposed, and non-wild-type isolates for polyenes and azoles are being increasingly reported. However, the distributions of the susceptibility patterns for pre-HIV-era isolates have not been studied. Methods: We determined the in vitro antifungal susceptibility patterns of 233 Cryptococcus isolates, collected at the National Institutes of Health, USA, in pre-HIV pandemic era, to study minimum inhibitory concentrations (MICs) to the important drugs for cryptococcosis and to compare the results with strain genotypes. Amphotericin B susceptibility was compared to published ECV of C. neoformans. Results: The 233 Cryptococcus strains consisted of 89.7% C. neoformans species complex and 10.3% C. gattii species complex. Most were from clinical sources (189, 81.1%), and the major molecular type was VNI (146, 62.7%). The highest geometric mean (GM) was observed for fluconazole (GM = 0.96 µg/mL) while the lowest was for itraconazole (GM = 0.10 µg/mL). MICs to fluconazole in C. gattii species complex were significantly higher than C. neoformans species complex (p < 0.001). Moreover, C. neoformans/VNI strains showed significantly higher MICs than others such as C. neoformans/VNII to fluconazole (p < 0.0001) and C. deneoformans/VNIV to amphotericin B (p = 0.022) and fluconazole (p = 0.008). In our collection of 167 clinical C. neoformans species complex strains, 85 (50.9%), 24 (14.4%), and 3 (1.8%) strains had an amphotericin B (AMB)-MIC of 1, 2, and 4 µg/mL, respectively. The high percentage (66.9%, 79/118 strains) of non-wild-type clinical C. neoformans VNI strains, using an AMB-ECV of 0.5 µg/mL, was found. Moreover, 25 of 28 (89.3%) C. neoformans VNI strains from environmental and veterinary sources also had AMB-MICs above 0.5 µg/mL. In general, there was no significant difference in GM AMB-MIC of the clinical strains isolated from patients with (35 patients) and without (78 patients) prior AMB treatment (0.85 vs 0.76; p = 0.624). GM MIC of the environmental strains was not significantly different from that of the prior AMB-treatment strains (0.98 vs 0.76, p = 0.159) and the post-AMB-treatment strains (0.98 vs 0.85, p = 0.488). Conclusion: The high rate of non-wild-type among these otherwise naive isolates to amphotericin B is unexpected. Confirmation with more strains from a later era is needed.

Molecular typing, in vitro susceptibility and virulence of Cryptococcus neoformans/Cryptococcus gattii species complex clinical isolates from south‐eastern Brazil

“…Thus, the epidemiological cut‐off values (ECVs) can aid the detection of non‐wild‐type strains for antifungals in a given fungal population 25,28,29 . A high percentage of non‐wild‐type C. neoformans VNI clinical isolates by using the AMB‐ECV of 0.5 μg/mL was found in a study of clinical and environmental isolates from the pre‐HIV pandemic era 35 . In our study, only 8.2% (5/61) of C. neoformans VNI clinical isolates are a non‐wild‐type strain.…”

“…In general, differences among them are noted for in vitro antifungal susceptibility. From the pre‐HIV era until the present, C. gattii has shown higher MICs to antifungals compared to C. neoformans 5,33,35,36,41 . C. deuterogattii clinical isolates follow this trend exhibiting higher MIC for fluconazole ( P = .0101) and itraconazole ( P = .0018) than C. neoformans clinical isolates.…”

ATI-2307 Exhibits Equivalent Antifungal Activity in Cryptococcus neoformans Clinical Isolates With High and Low Fluconazole IC50

“…To date, clinical breakpoints (CBPs) are not clearly established within the field. Studies to identify epidemiologic cut-off values show IC 50 of 4 or 8 µg/mL, but there is significant variability depending upon geographic region and across time ( Mdodo et al., 2011 ; Pfaller et al., 2011 ; Smith et al., 2015 ; Pharkjaksu et al., 2020 ). Thus, clinical drug susceptibility and resistance are challenging to define in C. neoformans and instead strains are often classified based on high or low IC 50 /IC 90 values upon in vitro MIC assay.…”

Temporal trends in antifungal susceptibility of Cryptococcus neoformans isolates from a reference laboratory in the United States, 2011–2021

“…The increasing number of CNSC isolates with high AMB MICs during the last decade is concerning, given the importance of AMB as a critical component of the treatment for severe forms of cryptococcosis and new data showing its potential use in shorter courses 7 . Our reported AMB MIC trend has been described in other studies outside the United States 35–37 . In one study that evaluated the MIC distribution of different antifungal agents against Cryptococcus isolates collected from clinical and environmental samples from different countries before 1980 (prior to the HIV epidemic), 71.2% of C. neoformans isolates were AMB non‐WT.…”

“…7 Our reported AMB MIC trend has been described in other studies outside the United States. [35][36][37] In one study that evaluated the MIC distribution of different antifungal agents against Cryptococcus isolates collected from clinical and environmental samples from different countries before 1980 (prior to the HIV epidemic), 71.2% of C.…”