Antimicrobial and Antibacterial Agents

Fluconazole resistance of Candida tropicalis, the leading non-albicans Candida spp. causing candidemia in humans residing in tropical Asia and Latin America, is troublesome for healthcare. This study was designed to determine the potential role of agricultural azole-fungicides on the emergence of fluconazole-resistant C. tropicalis in environments and in humans with systemic infections. Yeasts sampled from fruits, soils, water, and farmers in 82 farms were identified by ribosomal DNA sequencing. Multilocus sequence typing was further used to determine the genetic relationships of C. tropicalis isolates from the agricultural sites to those isolated from patients. Of 698 individual yeasts from 478 samples, 449 (64.3%) were from the environment and 249 (35.7%) from farmers. The most common Candida spp. causing diseases in humans recovered from the farmers was Candida albicans (14.9%), followed by Candida parapsilosis (11.6%). In contrast, C. tropicalis (13.1%) and Candida krusei (6.0%) were prevalent in the environment. Nine of 10 (90%) and 22 of 25 (88%) fluconazole-resistant C. tropicalis from environments and patients, respectively, were genetically related. Overexpression of ERG11, the azole target, contributed to fluconazole resistance. Most patients (18/25) were azole-naïve. Furthermore, there was no evidence of human-to-human transmission. The identification of fluconazole-resistant C. tropicalis from agricultural sites where azole-fungicides are commonly applied allowed documenting close genetic relationship to isolates from patients with invasive infections supports the concept that the microorganisms were transmitted from the farms to humans. Further studies are needed to determine the possible route of fluconazole-resistant C. tropicalis transmission in clinical settings.