African ST173 Cryptococcus deuterogattii strains are commonly less susceptible to fluconazole: An unclear mechanism of resistance

Reduced Susceptibility to Azoles in Cryptococcus gattii Correlates with the Substitution R258L in a Substrate Recognition Site of the Lanosterol 14-α-Demethylase

Cryptococcus neoformans and Cryptococcus gattii cause cryptococcosis, a life-threatening fungal infection affecting mostly immunocompromised patients. In fact, cryptococcal meningitis accounts for about 19% of AIDS-related deaths in the world. Because of long-term azole therapies to treat this mycosis, resistance to fluconazole leading to treatment failure and poor prognosis has long been reported for both fungal species. Among the mechanisms implicated in resistance to azoles, mutations in the ERG11 gene, encoding the azole target enzyme lanosterol 14-α-demethylase, have been described. This study aimed to establish the amino acid composition of ERG11 of Colombian clinical isolates of C. neoformans and C. gattii and to correlate any possible substitution with the in vitro susceptibility profile of the isolates to fluconazole, voriconazole, and itraconazole. Antifungal susceptibility testing results showed that C. gattii isolates are less susceptible to azoles than C. neoformans isolates, which could correlate with differences in the amino acid composition and structure of ERG11 of each species. In addition, in a C. gattii isolate with high MICs for fluconazole (64 μg/mL) and voriconazole (1 μg/mL), a G973T mutation resulting in the substitution R258L, located in substrate recognition site 3 of ERG11, was identified. This finding suggests the association of the newly reported substitution with the azole resistance phenotype in C. gattii. Further investigations are needed to determine the exact role that R258L plays in the decreased susceptibility to fluconazole and voriconazole, as well as to determine the participation of additional mechanisms of resistance to azole drugs. IMPORTANCE The fungal species Cryptococcus neoformans and C. gattii are human pathogens for which drug resistance or other treatment and management challenges exist. Here, we report differential susceptibility to azoles among both species, with some isolates displaying resistant phenotypes. Azoles are among the most commonly used drugs to treat cryptococcal infections. Our findings underscore the necessity of testing antifungal susceptibility in the clinical setting in order to assist patient management and beneficial outcomes. In addition, we report an amino acid change in the sequence of the target protein of azoles, which suggests that this change might be implicated in resistance to these drugs. Identifying and understanding possible mechanisms that affect drug affinity will eventually aid the design of new drugs that overcome the global growing concern of antifungal resistance.

Fluconazole Resistance and Virulence in In Vitro Induced-Fluconazole Resistant Strains and in Clinical Fluconazole Resistant Strain of Cryptococcus deuterogattii

Neuromeningeal cryptococcosis is a life-threatening infection of the central nervous system, caused by encapsulated yeast belonging to the Cryptococcus neoformans and Cryptococcus gattii species complexes. Recent data showed that virulence and antifungal resistance are variable for yeasts belonging to the C. gattii species complex. There is an increase in resistance to fluconazole for yeasts of the C. gattii species complex and the virulence is variable according to the genotype. In the present study, (i) we explored and compared the mechanisms of resistance to fluconazole between C. deuterogattii clinically resistant strains and induced fluconazole-resistant strains by exposure to fluconazole in vitro, and (ii) we studied their virulence in the Galleria mellonella study model. We demonstrated that the fluconazole resistance mechanisms involved were different between clinically resistant strains and induced resistant strains. We also demonstrated that fluconazole-induced resistant strains are less virulent when compared to the original susceptible strains. On the contrary, the clinically resistant strain tested maintains its virulence compared to fluconazole-susceptible strains of the same sequence type.

Significance of differential expression profiles of ABC transporters in azole susceptibility between Cryptococcus gattii VGI and VGII strains

Azoles were used as the primary antifungal agents to treat the Cryptococcus gattii (C. gattii) infection. Evidence showed that subtypes of C. gattii respond differently to azoles, but the mechanism is largely elusive. In this study, we aimed to find the mechanisms of differences in azole drug susceptibility in different subtypes of C.gattii. Eight clinical strains of C. gattii were collected for molecular typing, multilocus sequence typing (MLST) analysis, and antifungal susceptibility testing. Based on drug susceptibility differences, the RNA sequencing data were analyzed to find candidate azole drug susceptibility genes, and qPCR validation was performed. Five VGI subtypes and three VGII subtypes were identified among the eight strains of C.gattii. The clinical isolates showed high genetic diversity, and seven sequence types (STs) were identified. The geometric mean (GM) of minimum inhibitory concentration (MIC) for fluconazole, voriconazole, and itraconazole of VGI subtype was significantly lower than that of VGII subtype, and genes related to transporter activities were differentially expressed between VGI and VGII strains. The results of the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the DEGs (differential expressed genes) were found to be enriched in multiple ABC transporters. We further performed qPCR to quantify the expression level of seven ABC transporters. We found that ABC transporters ATM1, MDR1, PDR5, PDR5-3, and PXA2 were expressed significantly higher in VGII strains than in VGI strains. Our work revealed four novel ABC transporters, ATM1, PDR5, PDR5-3, and PXA2, promising candidate targets regulating azole susceptibility in C. gattii strains.

Multilocus sequence typing of strains from the Cryptococcus gattii species complex from different continents

BACKGROUND

Cryptococcus neoformans and Cryptococcus gattii species complexes are pathogens causing cryptococcal meningitis, a fungal infection that leads to death unless treated. Worldwide, it is estimated to kill over 180,000 individuals annually.

OBJECTIVES

We aim to investigate the molecular diversity of C. gattii isolates from strains isolated from 1995 to the present day from different continents.

METHOD

In this study, we analysed the molecular diversity by MLST and antifungal susceptibility by using the broth microdilution method according to the CLSI M27-A4 protocol of a total of 26 strains from Cryptococcus gattii species complex from both clinical and environmental sources.

RESULTS

Genotyping showed that most of the strains (17/26; 65.4%) belonged to serotype B and were distributed between three genotypes: VGI (13/17; 76.5%), VGII (3/17; 17.6%) and VGVI (1/17; 5.9%). The serotype C strains (9/26; 34.6%) were distributed between the VGIII (1/9; 11.1%) and VGIV (8/9; 88.9%) genotypes. The 26 strains belonged to 17 different MLST subtypes, and we highlight four new MLST genotypes (ST553, 554, 555 and 556). The two environmental strains were identified as serotype B and genotype VGI, but were of ST 51 and 154. All isolates have wild-type MIC of fluconazole and flucytosine. Regarding amphotericin B, five VGI strains showed MICs to AMB equal to 1 µg/ml, and according to the ECV for these genotypes, they were considered non-wild-type strains.

CONCLUSIONS

The current study reveals the genetic diversity and new sequence types among strains from the C. gattii complex species.

First report of cryptococcosis due to Cryptococcus gattii sensu stricto VGI in an Ivorian HIV negative patient

INTRODUCTION

Cryptococcus gattii species complex is endemic to tropical and subtropical regions and is described as a causative agent of cryptococcosis in immunocompetent individuals.

CASE PRESENTATION

We describe the first case of cryptococcosis in a HIV-negative patient from Ivory Coast infected by Cryptococcus gattii sensu stricto VGI. Isolates were recovered from cerebrospinal fluid (CSF) prior to systemic antifungal treatment up to 42 days after detection of the presence of yeasts in the CSF. Eighteen isolates were recovered, genetic diversity and antifungal susceptibility analyses were performed. All the isolates belonged to the Cryptococcus gattii sensu stricto (B;VGI) and were identified as a new sequence type (ST) 553 by Multilocus Sequence Typing (MLST) analyses. Susceptibility testing showed that all the strains had a wild-type phenotype for fluconazole, amphotericin B and flucytosine. Treatment with fluconazole (1200mg/day) was initiated with success.

CONCLUSION

This is the first case report of the presence of C. gattii sensu stricto VGI in a HIV-negative ivorian patient and the second report of the presence of species from the C. gattii complex species in this country.