Multidrug-Resistant Candida haemulonii and C. auris, Tel Aviv, Israel

Abstract

Candida auris and C. haemulonii are closely related, multidrug-resistant emerging fungal pathogens that are not readily distinguishable with phenotypic assays. We studied C. auris and C. haemulonii clinical isolates from 2 hospitals in central Israel. C. auris was isolated in 5 patients with nosocomial bloodstream infection, and C. haemulonii was found as a colonizer of leg wounds at a peripheral vascular disease clinic. Liberal use of topical miconazole and close contact among patients were implicated in C. haemulonii transmission. C. auris exhibited higher thermotolerance, virulence in a mouse infection model, and ATP-dependent drug efflux activity than C. haemulonii. Comparison of ribosomal DNA sequences found that C. auris strains from Israel were phylogenetically distinct from isolates from East Asia, South Africa and Kuwait, whereas C. haemulonii strains from different countries were closely interrelated. Our findings highlight the pathogenicity of C. auris and underscore the need to limit its spread.

Keywords: Candida auris; Candida haemulonii; Israel; antimicrobial resistance; bloodstream infection; fungi; virulence.

Figure 1

Phylogenetic relationships of Candida auris and C. haemulonii strains isolated in Tel Aviv, Israel, compared with reference strains. Phylogenetic trees were generated from internal transcribed spacer (A) and D1/D2 domain of the ribosomal DNA large subunit sequences (B). The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) is shown next to each branch. Bold indicates strains from Tel Aviv. GenBank accession numbers are provided in parentheses. Scale bar indicates nucleotide substitutions per site.

Figure 2

Comparison of rhodamine 6G efflux over time among Candida isolates from Tel Aviv, Israel. Rhodamine 6G efflux is expressed as relative fluorescence units measured in culture supernatants after the addition of 8 mM glucose. Statistical significance was measured with 1-way analysis of variance and Dunnett’s post-test comparing each C. haemulonii and C. auris strain with the averaged value of C. glabrata strains at the corresponding time point. White bars, 5 min; gray bars, 15 min; black bars, 25 min. *p<0.0001.

Figure 3

Differing thermotolerance of Candida auris and C. haemulonii. A) Sabouraud dextrose agar plates showing growth of representative Candida strains after 24 h incubation at 35°C–42°C; B) Thermal growth range of Candida isolates from Tel Aviv, Israel.

Figure 4

Differing virulence of Candida auris and C. haemulonii assessed in a mouse model of hematogenous disseminated candidiasis. Virulence was assessed in immunosuppressed BALB/c mice after intravenous injection of yeast cell suspension. A) Survival curves showing significantly shorter survival of mice infected with C. albicans than C. auris and no death among mice infected with C. haemulonii. B) Kidney fungal load (CFU per gram of tissue) shown to be significantly higher in mice infected with C. albicans than in those infected with C. auris, whereas no viable yeast was cultured from kidneys of mice infected with C. haemulonii. C) In mouse kidneys, C. auris cells formed aggregates and no hyphae (top) whereas C. albicans formed extensive tissue-invasive hyphae (bottom); C. haemulonii was not detected in tissue sections (middle). Grocott methenamine silver staining, original magnification ×100 for panels, ×400 for insets.