Lack of Association between Fluconazole Susceptibility and ERG11 Nucleotide Polymorphisms in Cryptococcus neoformans Clinical Isolates from Uganda

A case of hypophysis with HIV negative cryptococcal meningitis

The clinical mortality of cryptococcal meningitis (CM) is high. There is no report of hypopituitarism associated with HIV negative CM so far. The patients with hypopituitarism complicated with CM are easy to be misdiagnosed and mistreated. A patient with hypopituitarism and HIV negative CM was admitted to Weihai Municipal Hospital on August 27, 2021. The patient was treated for 18 years after craniopharyngioma with headache for more than 2 months, nausea and vomiting for 4 days. MRI showed abnormal enhancement of the right basal ganglia, edema of surrounding tissue, and multiple striated enhancement of the bilateral cerebellar hemisphere. The smear of cerebrospinal fluid showed a large number of fungi and Cryptococcus. Culture of cerebrospinal fluid showed positive in Cryptococcus. The patient's HIV and syphilis antibodies were negative. The condition of the patient was improved after active antifungal therapy. The clinician should make a definite diagnosis and give early treatment as soon as possible.

Correlation of antifungal susceptibility and sequence types within Cryptococcus neoformans VNI from HIV patients, and ERG11 gene polymorphism

INTRODUCTION

Here we tested the correlation between minimum inhibitory concentrations (MICs) of major antifungal agents and sequence types (STs) within Cryptococcus neoformans VNI isolates, and explored the ERG11 gene of included strains.

MATERIALS AND METHODS

We analysed 23 C. neoformans strains categorised into two groups according to the distribution of the ST profile in Kinshasa clinics (Democratic Republic of Congo): major ST [ST93 (n = 15)], and less common STs [ST659 (n = 2), ST5 (n = 2), ST4 (n = 1), ST 53 (n = 1), ST31 (n = 1), and ST69 (n = 1)]. The MICs of the major antifungal agents [amphotericin B (AMB), 5-fluorocytosine (5FC) and fluconazole (FCZ)] were determined following EUCAST guidelines. ERG11 gene sequences were extracted from whole genome sequence of the isolates and compared with the wild-type gene sequence of the C. neoformans VNI.

RESULTS

Although major ST isolates appeared to have lower median MICs for AMB and 5FU than less common ST isolates (0.50 vs. 0.75 mg/L for AMB, 2 vs. 4 mg/L for 5FU, respectively), FCZ susceptibility was similar in both groups (4 mg/L) (p-value >0.05). The susceptibility profile of C. neoformans strains separately considered did not significantly affect the patients' clinical outcomes (p-value >0.05). Furthermore, two structural modalities of the ERG11 gene were observed: (1) that of the reference gene, and (2) that containing two exonic silent point substitutions, and one intronic point substitution located in a sequence potentially involved in pre-mRNA splicing (c.337-22C > T); with no association with the MICs of the isolates (p-value >0.05).

CONCLUSIONS

The lack of association/correlation found in this study calls for further investigations to better understand the mechanisms of C. neoformans resistance to antifungal agents.

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.

ERG11 Analysis among Clinical Isolates of Trichosporon asahii with Different Azole Susceptibility Profiles

We analyzed a cohort of Trichosporon asahii strains with different MICs of fluconazole and voriconazole and evaluated the presence of ERG11 mutations. ERG11 mutation conferring an amino acid change was found and its resistance potential was evaluated by cloning into Saccharomyces cerevisiae susceptible host strain. Transformants were not resistant to either fluconazole nor voriconazole. Our results suggest that ERG11 variants exist among T. asahii isolates, but are not responsible for resistance phenotypes.

An Atypical ABC Transporter Is Involved in Antifungal Resistance and Host Interactions in the Pathogenic Fungus Cryptococcus neoformans

ATP-binding cassette (ABC) transporters represent one of the largest protein superfamilies. Functionally diverse, ABC transporters have been implicated in many aspects of microbial physiology. The genome of the human fungal pathogen Cryptococcus neoformans encodes 54 putative ABC transporters and most of them remain uncharacterized. In a previous genetic screen for fungal regulators of phagocytosis, we identified an uncharacterized gene, CNAG_06909, that modulates host interactions. This gene encoded a half-size ABC transporter of the PDR-type, and phenotypic studies of a strain with this gene deleted revealed an altered antifungal susceptibility profile, including hypersensitivity to fluconazole (FLC). This gene, which we named PDR6, localized to the endoplasmic reticulum (ER) and plasma membrane (PM), and when absent, less ergosterol was observed in the PM. Additionally, we observed that the pdr6Δ strain displayed a reduction in secreted polysaccharide capsular material. These changes to the cellular surface may explain the observed increased uptake by macrophages and the reduced intracellular survival. Finally, studies in mice demonstrated that Pdr6 function was required for the normal progression of cryptococcal infection. Taken together, this study demonstrates a novel dual role for PDR transporters in C. neoformans, which could represent a potential target for antifungal therapeutics. Furthermore, the atypical half-size transporter encoded by PDR6 is conserved in many fungal pathogens, but absent in model nonpathogenic fungi. Hence, this study provided a function for this unique group of fungal half-size PDR transporters that, although conserved, remain largely understudied.