Abstract
Candidemia, a bloodstream infection caused by genus Candida, has a high mortality rate. Candida albicans was previously reported to be the most common causative species among candidemia patients. However, during the past 10 years in Thailand, Candida tropicalis has been recovered from blood more frequently than C. albicans. The cause of this shift in the prevalence of Candida spp. remains unexplored. We conducted in vitro virulence studies and antifungal susceptibility profiles of 48 C. tropicalis blood isolates collected during 2015–2017. To compare to global isolates of C. tropicalis, multilocus sequence typing (MLST), a minimum spanning tree, and an eBURST analysis were also conducted. C. tropicalis and C. albicans were the most (47–48.7%) and second-most (21.5–33.9%) common species to be isolated from candidemia patients, respectively. Of the C. tropicalis blood isolates, 29.2, 0, 100, and 93.8% exhibited proteinase activity, phospholipase activity, hemolytic activity, and biofilm formation, respectively. Moreover, 20.8% (10/48) of the isolates were resistant to voriconazole and fluconazole, and also showed high minimum inhibitory concentrations (MICs) to posaconazole and itraconazole. In contrast, most of the isolates were susceptible to anidulafungin (97.9%), micafungin (97.9%), and caspofungin (97.9%), and showed low MICs to amphotericin B (100%) and 5-flucytosine (100%). The MLST identified 22 diploid sequence types. Based on the eBURST analysis and minimum spanning tree, 9 out of 13 members (69.2%) of an eBURST group 3 were resistant to voriconazole and fluconazole, and also showed high MICs to posaconazole and itraconazole. Association analysis revealed the eBURST group 3 was significantly associated with the four triazole resistance (p < 0.001). In conclusion, the eBURST group 3 was associated with the triazole resistance and resistance to many antifungal drugs might be collectively responsible for the prevalence shift.
Highlights
Candida species is a cause of mild superficial to serious invasive infections in humans worldwide
A large surveillance study in 1997–2016 reported that 46.3–57.4% of all candidemia cases were caused by C. albicans whereas only 8.3–10.7% were caused by Candida tropicalis (Pfaller et al, 2019)
As a mechanism of the increased prevalence of C. tropicalis in Thailand remains controversial, we investigated the molecular epidemiology of C. tropicalis recovered from blood cultures at a tertiary care hospital in Thailand
Summary
Candida species is a cause of mild superficial to serious invasive infections in humans worldwide. Candida spp. was ranked as the fourth most frequent cause of bloodstream infections with a high mortality rate (Wisplinghoff et al, 2004). Candida albicans was globally reported to be the most common causative species isolated from the blood of candidemia patients (Guinea, 2014). Considered to be a less prevalent candidemia-causing species, bloodstream infections due to C. tropicalis are continuing to rise globally (Guinea, 2014). One report revealed that C. tropicalis has a higher rate of fluconazole resistance than C. albicans (Khairat et al, 2019). An investigation in Southern India, C. tropicalis a predominant species (54.3%), demonstrated that the ability to develop rapid resistance to fluconazole involves the increasing prevalence (YeSudhaSon and MohanraM, 2015)
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