Candida haemulonii sensu lato: Update of the Determination of Susceptibility Profile in Argentina and Literature Review

Mechanism of azole resistance in Candida vulturna, an emerging multidrug resistant pathogen related with Candida haeumulonii and Candida auris

BACKGROUND

Candida vulturna is an emerging pathogen belonging to the Metshnikowiaceae family together with Candida auris and Candida haemulonii species complex. Some strains of this species were reported to be resistant to several antifungal agents.

OBJECTIVES

This study aims to address identification difficulties, evaluate antiungal susceptibilities and explore the molecular mechanisms of azole resistance of Candida vulturna.

METHODS

We studied five C. vulturna clinical strains isolated in three Colombian cities. Identification was performed by phenotypical, proteomic and molecular methods. Antifungal susceptibility testing was performed following CLSI protocol. Its ERG11 genes were sequenced and a substitution was encountered in azole resistant isolates. To confirm the role of this substitution in the resistance phenotype, Saccharomyces cerevisiae strains with a chimeric ERG11 gene were created.

RESULTS

Discrepancies in identification methods are highlighted. Sequencing confirmed the identification as C. vulturna. Antifungal susceptibility varied among strains, with four strains exhibiting reduced susceptibility to azoles and amphotericin B. ERG11 sequencing showed a point mutation (producing a P135S substitution) that was associated with the azole-resistant phenotype.

CONCLUSIONS

This study contributes to the understanding of C. vulturna's identification challenges, its susceptibility patterns, and sheds light on its molecular mechanisms of azole resistance.

Antifungal activity of cercosporamide produced by Phaeosphaeriaceae GV-1 against pathogenic fungi

Fungal infections affect millions of people worldwide, and the several cases are related to invasive infections, which is a problem mainly for immunocompromised people, such as transplant and cancer patients with high mortality and morbidity rates. In addition, the number of emerging and multidrug-resistant fungal species has increased in the last decade. The search for new antifungal compounds is necessary, due to the increase in cases of resistance and the toxicity of drugs used in fungal infection treatment. This work aimed to study the antifungal activity of cercosporamide produced by Phaeosphaeriaceae GV-1. Cercosporamide was tested against pathogenic fungi by determining the minimum inhibitory (MIC) and minimum fungicidal (MFC) concentrations, using the broth microdilution method. Cercosporamide showed antifungal activity in vitro against 13 of 16 strains of medical importance tested, with the most susceptible species being Candida tropicalis, with MIC and MFC of 15.6 μg/mL. Thus, cercosporamide might be considered a promising therapeutic antifungal agent.

Candida haemulonii complex, an emerging threat from tropical regions?

BACKGROUND

Candida haemulonii complex-related species are pathogenic yeasts closely related to Candida auris with intrinsic antifungal resistance, but few epidemiological data are available.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed clinical and demographic characteristics of patients with fungemia due to C. haemulonii complex and related species (C. pseudohaemulonii, C. vulturna) reported in France during 2002-2021, and compared them to data of C. parapsilosis fungemia, as they all can be commensal of the skin. We also conducted a study on adult inpatients and outpatients colonized by C. haemulonii complex, managed at the University Hospital of Martinique during 2014-2020. Finally, we performed a literature review of fungemia due to C. haemulonii complex and related species reported in Medline (1962-2022). In total, we identified 28 fungemia due to C. haemulonii complex in France. These episodes were frequently associated with bacterial infection (38%) and high mortality rate (44%), and differed from C. parapsilosis fungemia by their tropical origin, mainly from Caribbean and Latin America. All isolates showed decreased in vitro susceptibility to amphotericin B and fluconazole. In Martinique, we found that skin colonization was frequent in the community population, while colonization was strongly associated with the presence of foreign devices in ICU patients. The literature review identified 274 fungemia episodes, of which 56 were individually described. As in our national series, published cases originated mainly from tropical regions and exhibited high crude mortality.

CONCLUSIONS/SIGNIFICANCE

Multidrug-resistant C. haemulonii complex-related species are responsible for fungemia and colonization in community and hospital settings, especially in tropical regions, warranting closer epidemiological surveillance to prevent a potential C. auris-like threat.

Extracellular Vesicles from Candida haemulonii var. vulnera Modulate Macrophage Oxidative Burst

Members of the Candida haemulonii species complex are multidrug-resistant emergent yeast pathogens able to cause superficial and invasive infections in risk populations. Fungal extracellular vesicles (EVs) play a critical role in the pathogenicity and virulence of several species and may perform essential functions during infections, such as carrying virulence factors that behave in two-way communications with the host, affecting survival and fungal resistance. Our study aimed to describe EV production from Candida haemulonii var. vulnera and evaluate whether murine macrophage RAW 264.7 cells respond to their stimuli by generating an oxidative response after 24 h. For this purpose, reactive oxygen species detection assays demonstrated that high concentrations of yeast and EVs (10¹⁰ particles/mL) of Candida haemulonii did not change macrophage viability. However, the macrophages recognized these EVs and triggered an oxidative response through the classical NOX-2 pathway, increasing O₂^•- and H₂O₂ levels. However, this stress did not cause lipid peroxidation in the RAW 264.7 cells and neither lead to the activation of the COX-2-PGE₂ pathway. Thus, our data suggest that low concentrations of C. haemulonii EVs are not recognized by the classical pathway of the oxidative burst generated by macrophages, which might be an advantage allowing the transport of virulence factors via EVs, not identified by the host immune system that could work as fine tube regulators during infections caused by C. haemulonii. In contrast, C. haemulonii var. vulnera and high EV concentrations activated microbicidal actions in macrophages. Therefore, we propose that EVs could participate in the virulence of the species and that these particles could be a source of antigens to be exploited as new therapeutic targets.

First two fungemia cases caused by Candida haemulonii var. vulnera in China with emerged antifungal resistance

Candida haemulonii var. vulnera is a rare variant of C. haemulonii, which has been previously reported to cause human infections. Owing to the close kinship between C. haemulonii sensu stricto and C. haemulonii var. vulnera, accurate identification of C. haemulonii var. vulnera relied on DNA sequencing assay targeting, for example, rDNA internal transcribed spacer (ITS) region. In this work, two strains of C. haemulonii var. vulnera were collected from the China Hospital Invasive Fungal Surveillance Net (CHIF-NET). The identification capacity of three matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and VITEK 2 YST ID biochemical methods were evaluated against ITS sequencing. In addition, antifungal susceptibility testing was performed using Sensititre YeastOne. Moreover, we comprehensively screened drug-resistant related genes by whole-genome sequencing. The two strains were not correctly identified to species variant level using MALDI-TOF MS and YST ID cards. Both strains were resistant to amphotericin B (minimum inhibitory concentration [MIC] > 2 μg/ml). Moreover, strain F4564 and F4584 exhibited high MIC to fluconazole (>256 μg/ml) and 5-flucytosine (>64 μg/ml), respectively, which were supposed to result from key amino acid substitutions Y132F and G307A in Erg11p and V58fs and G60K substitutions in Fur1p. The rare species C. haemulonii var. vulnera has emerged in China, and such drug-resistant fungal species that can cause invasive diseases require further close attention.

Liver abscess caused by Candida haemulonii var. vulnera. First case report in Peru

BACKGROUND

Liver abscesses caused by Candida species are mainly found in immunocompromised hosts, associated with conditions (such as neutropenia and mucositis) that facilitate the spreading of microorganisms from the gastrointestinal tract.

CASE REPORT

We present the case of a non-immunocompromised 72-year-old woman with a liver abscess caused by Candida haemulonii var. vulnera, in whom potential associated conditions could be polycystic kidney disease and renal replacement therapy. The patient experienced clinical resolution after percutaneous drainage and treatment with caspofungin.

CONCLUSIONS

To our knowledge, this is the first case reported in Peru of a liver abscess due to Candida haemulonii var. vulnera, a clinical presentation that has not been described previously. This finding should prompt us to establish active surveillance of causal agents of systemic candidiasis.

Susceptibility of the Candida haemulonii Complex to Echinocandins: Focus on Both Planktonic and Biofilm Life Styles and a Literature Review

Candida haemulonii complex (C. haemulonii, C. duobushaemulonii and C. haemulonii var. vulnera) is well-known for its resistance profile to different available antifungal drugs. Although echinocandins are the most effective class of antifungal compounds against the C. haemulonii species complex, clinical isolates resistant to caspofungin, micafungin and anidulafungin have already been reported. In this work, we present a literature review regarding the effects of echinocandins on this emergent fungal complex. Published data has revealed that micafungin and anidulafungin were more effective than caspofungin against the species forming the C. haemulonii complex. Subsequently, we investigated the susceptibilities of both planktonic and biofilm forms of 12 Brazilian clinical isolates of the C. haemulonii complex towards caspofungin and micafungin (anidulafungin was unavailable). The planktonic cells of all the fungal isolates were susceptible to both of the test echinocandins. Interestingly, echinocandins caused a significant reduction in the biofilm metabolic activity (viability) of almost all fungal isolates (11/12, 91.7%). Generally, the biofilm biomasses were also affected (reduction range 20–60%) upon exposure to caspofungin and micafungin. This is the first report of the anti-biofilm action of echinocandins against the multidrug-resistant opportunistic pathogens comprising the C. haemulonii complex, and unveils the therapeutic potential of these compounds.

Understanding the Emergence of Multidrug-Resistant Candida: Using Whole-Genome Sequencing to Describe the Population Structure of Candida haemulonii Species Complex

The recent emergence of a multidrug-resistant yeast, Candida auris, has drawn attention to the closely related species from the Candida haemulonii complex that include C. haemulonii, Candida duobushaemulonii, Candida pseudohaemulonii, and the recently identified Candida vulturna. Here, we used antifungal susceptibility testing and whole-genome sequencing (WGS) to investigate drug resistance and genetic diversity among isolates of C. haemulonii complex from different geographic areas in order to assess population structure and the extent of clonality among strains. Although most isolates of all four species were genetically distinct, we detected evidence of the in-hospital transmission of C. haemulonii and C. duobushaemulonii in one hospital in Panama, indicating that these species are also capable of causing outbreaks in healthcare settings. We also detected evidence of the rising azole resistance among isolates of C. haemulonii and C. duobushaemulonii in Colombia, Panama, and Venezuela linked to substitutions in ERG11 gene as well as amplification of this gene in C. haemulonii in isolates in Colombia suggesting the presence of evolutionary pressure for developing azole resistance in this region. Our results demonstrate that these species need to be monitored as possible causes of outbreaks of invasive infection.

On the Origins of a Species: What Might Explain the Rise of Candida auris?

Candida auris is an emerging multidrug-resistant yeast first described in 2009 that has since caused healthcare-associated outbreaks of severe human infections around the world. In some hospitals, it has become a leading cause of invasive candidiasis. C. auris is markedly different from most other pathogenic Candida species in its genetics, antifungal resistance, and ability to spread between patients. The reasons why this fungus began spreading widely in the last decade remain a mystery. We examine available data on C. auris and related species, including genomic epidemiology, phenotypic characteristics, and sites of detection, to put forth hypotheses on its possible origins. C. auris has not been detected in the natural environment; related species have been detected in in plants, insects, and aquatic environments, as well as from human body sites. It can tolerate hypersaline environments and higher temperatures than most Candida species. We explore hypotheses about the pre-emergence niche of C. auris, whether in the environmental or human microbiome, and speculate on factors that might have led to its spread, including the possible roles of healthcare, antifungal use, and environmental changes, including human activities that might have expanded its presence in the environment or caused increased human contact.