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Volume 30, Number 11—November 2024
Research

Detection in Orchards of Predominant Azole-Resistant Candida tropicalis Genotype Causing Human Candidemia, Taiwan

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Author affiliation: National Tsing Hua University, Hsinchu, Taiwan (K.-Y. Tseng); National Health Research Institutes, Miaoli, Taiwan (K.-Y. Tseng, Y.-Z. Chen, Z.-L. Zhou, C.-J. Wu, Y.-C. Liao, C.-C. Lin, D.-J. Tsai, F.-J. Chen, L.-Y. Hsieh, K.-C. Huang, C.-H. Huang, K.-T. Chen, W.-L. Chu, C.-M. Lin, S.-M. Shih, C.A. Hsiung, Y.-C. Chen, H.-K. Sytwu, H.-J. Lo); National Yang Ming Chiao Tung University, Hsinchu (Z.-L. Zhou, Y.-L. Yang, H.-J. Lo); Taiwan Agricultural Research Institute, Taichung, Taiwan (J.-N. Tsai); Kaohsiung District Agricultural Research and Extension Station, Pingtung, Taiwan (M.-N. Tseng); Taichung District Agricultural Research and Extension Station, CHangHua, Taiwan (H.-L. Liu); National Cheng Kung University Hospital and Medical College, Tainan, Taiwan (C.-J. Wu); National Taiwan University Hospital College of Medicine, Taipei, Taiwan (Y.-C. Chen); China Medical University, Taichung (H.-J. Lo)

Cite This Article

Abstract

Fluconazole-resistant clade 4 Candida tropicalis causing candidemia in humans has been detected in tropical/subtropical areas, including those in China, Singapore, and Australia. We analyzed 704 individual yeasts isolated from fruits, soil, water, and farmers at 80 orchards in Taiwan. The most common pathogenic yeast species among 251 isolates recovered from farmers were Candida albicans (14.7%) and C. parapsilosis (11.6%). In contrast, C. tropicalis (13.0%), C. palmioleophila (6.6%), and Pichia kudriavzevii (6.0%) were prevalent among 453 environmental isolates. Approximately 18.6% (11/59) of C. tropicalis from the environment were resistant to fluconazole, and 81.8% (9/11) of those belonged to the clade 4 genotype. C. tropicalis susceptibility to fluconazole correlated with susceptibilities to the agricultural azole fungicides, difenoconazole, tebuconazole, and triadimenol. Tandem gene duplications of mutated ERG11 contributed to azole resistance. Agriculture environments are a reservoir for azole-resistant C. tropicalis; discontinuing agricultural use of azoles might reduce emergence of azole-resistant Candida spp. strains in humans.

Candida spp. account for ≈8%–15% of invasive infections leading to hospitalization; the emergence of drug-resistant non–C. albicans Candida spp. is particularly troublesome for optimal health recovery of immunocompromised patients, especially those in hospital intensive care units (1,2). C. tropicalis is one of the leading non–C. albicans species causing candidemia in humans residing in tropical Asia and Latin America (3–5) and is also the leading cause of invasive candidiasis in patients with hematologic malignancies (4,6). Because of major differences in geographic distribution of human-invasive Candida spp., each country or region must conduct its own surveillance program to assess the dominant species and emergence of drug-resistant strains (1,2,7). The recent sporadic outbreaks of multidrug-resistant C. auris infections in >14 countries located in 5 continents demonstrate the still unmet need for this surveillance (8,9).

The National Health Research Institutes (NHRI) of Taiwan established the Taiwan Surveillance of Antimicrobial Resistance of Yeasts (TSARY) program in 1999 to periodically monitor national trends in species distribution and antifungal drug susceptibility of pathogenic yeasts isolated from patients (10). Subsequent surveillance was conducted in 2002, 2006, 2010, 2014, and 2018 (11–15). Resistance to fluconazole was found in 25 of 294 C. tropicalis isolates from TSARY 2014 and in 31 of 314 C. tropicalis isolates from TSARY 2018; moreover, 91.1% (51/56) of fluconazole-resistant C. tropicalis belonged to the clade 4 genotype (15). Since 2014, other studies have also reported the isolation of azole-resistant C. tropicalis, particularly in the Asia-Pacific region (16–18). Tandem gene duplications of the ERG11 gene encoding a Y132F amino acid mutation have reportedly contributed to azole-resistant phenotypes in clade 4 C. tropicalis isolates from China, Singapore, and Australia (19). However, little data have been generated regarding the genetics of Candida spp. collected from environmental sources.

C. tropicalis has been recovered from soil and aquatic environments (20,21). Furthermore, the azole-resistant C. tropicalis clade 4 genotype has been isolated from fruits purchased at a supermarket in northern Taiwan (22). Thus, identifying potential sources of the fluconazole-resistant C. tropicalis clade 4 genotype became critical. Aspergillus fumigatus fungi recovered from soil and compost have been reported to be genetically related to clinically resistant isolates, raising the possibility that an environmental source of azole-resistant C. tropicalis might account for resistant strains in humans (23). Through collaborations with healthcare and agriculture sectors, we determined whether the azole-resistant C. tropicalis clade 4 genotype existed in orchard environments by investigating the distribution of yeasts in 3 different types of orchards. We also analyzed potential mechanisms contributing to azole resistance in C. tropicalis.

Materials and Methods

Study Design

We designed this study to evaluate yeast species distribution by using an orchard survey and to investigate the genetic relatedness among fluconazole-resistant C. tropicalis isolates. NHRI designed an orchard survey that was used by agricultural research institutes and stations located in representative regions of Taiwan. NHRI’s Human Experiment and Ethics Committee approved the orchard survey (study no. EC1070117).

Most orchards in Taiwan are located in central and southern areas; therefore, we surveyed a total of 80 orchards—31 papaya, 28 wax apple, and 21 grape orchards—located in those 2 areas during July 2012–January 2013. We designated this survey as orchard survey 2012. We collected 1 fruit and 1 soil sample from east, west, south, north, and center collection points within each orchard. Thus, we collected 5 fruit and 5 soil samples from each orchard. From the orchard farmers, we collected swab samples from armpits and hands, as well as oral mouth rinse samples. We analyzed a total of 400 fruit and 400 soil samples, 80 samples of water, and 80 samples each of armpit swab, hand swab, and mouth rinse samples.

Microbiologic Processing

We isolated yeasts from samples as previously described (21,24). In brief, we maintained all swab samples at room temperature and transported them to the laboratory within 24 hours after collection. We streaked the samples onto BBL CHROMagar Candida plates (BD Biosciences, https://www.bdbiosciences.com). We identified the isolates by rDNA sequencing of the internal transcribed spacer or the D1/D2 domain regions (25) and submitted all novel rDNA sequences to GenBank (Appendix Table 1, 2). We further analyzed 1 isolate per species per type of sample. We labeled the strains from orchard survey 2012 with YFA12 and strains from TSARY 2014 with YM14 followed by 4 numbers.

Drug Susceptibility Testing

Because Pichia kudriavzevii (formerly C. krusei) is intrinsically resistant to fluconazole, we determined susceptibilities of C. albicans, C. parapsilosis, C. tropicalis, and Nakaseomyces glabratus (formerly C. glabrata), all common yeasts causing human infections, to 2–64 mg/L fluconazole. We analyzed susceptibilities of all 66 C. tropicalis isolates to difenoconazole (1–32 mg/L), tebuconazole (1–32 mg/L), and triadimenol (2–64 mg/L), 3 commonly used fungicides in agriculture in Taiwan. We incubated cultures at 35°C for 24 hours in RPMI medium 1640 (Thermo Fisher Scientific, https://www.thermofisher.com) and measured the growth of each isolate by using a Multiskan FC microplate photometer (Thermo Fisher Scientific). We defined MICs as the concentration of drug capable of reducing the turbidity of cells by >50%. We used procedures and clinical breakpoints for yeast strains as previously described (26). For fluconazole, the clinical breakpoints for C. albicans, C. parapsilosis, and C. tropicalis were MICs of <2 mg/L for susceptible, >8 mg/L for resistant, and 4 mg/L for susceptible-dose dependent. For N. glabratus, we considered a fluconazole MIC of <32 mg/L to be susceptible-dose dependent and >64 mg/L resistant. The breakpoints for fungicides in agriculture have not been defined. We used Spearman correlation coefficient analysis to evaluate the correlations between susceptibilities to fluconazole and to agricultural fungicides. We used the following guide to evaluate the strength of the correlation: very weak, 0.00–0.19; weak, 0.20–0.39; moderate, 0.40–0.59; strong, 0.60–0.79; and very strong, 0.80–1.0.

Multilocus Sequence Typing

We conducted multilocus sequence typing (MLST) as described previously (27,28). In brief, we sequenced DNA fragments of 6 C. tropicalis genes, ICL1, MDR1, SAPT2, SAPT4, XYR1, and ZWF1a, by using specific primers (Appendix Table 2) and included those sequences in the analyses. We aligned the sequences by using BioNumerics 3.0 (Applied Maths, https://www.applied-maths.com) and compared them with C. tropicalis sequences in the public MLST database (http://pubmlst.org) to determine the level of sequence identities and diploid sequence type (DST). We performed phylogenetic analysis by using the unweighted pair group method with arithmetic means algorithm and MEGA 11 software (https://www.megasoftware.net) as previously described (29). We determined the genome types of 66 C. tropicalis isolates recovered from the orchards and chose a cutoff p-distance value of 0.01 because it separated clades that contained known isolates. We generated a global phylogenetic tree of C. tropicalis composed of 1,368 DSTs listed in the C. tropicalis MLST database, as previously described (22).

Qualitative Analysis of CDR1, ERG11, and MDR1 Transcripts by Real-Time PCR

We determined the expression levels of genes involved in azole resistance in 17 C. tropicalis isolates collected from orchards and patients, including 14 fluconazole-resistant (11 clade 4 and 1 each of clades 2, 3, and 8) and 3 fluconazole-susceptible isolates. We harvested the cells after growing them to an optical density of 0.7–0.9 in YPD liquid medium (BD Biosciences) at 30°C for 6 hours. After sequencing CDR1, ERG11, and MDR1 gene fragments (Appendix Table 2), we normalized expression levels against ACT1 in each isolate. Then, we used the mRNA levels in a fluconazole-susceptible isolate, YFA120877 (control strain), recovered from orchard survey 2012, as the denominator for normalization.

Whole-Genome Sequencing and ERG11 Copy Number Variant Detection

We conducted whole-genome sequencing (WGS) of 14 orchard-derived C. tropicalis isolates that had different genotypes, including 8 isolates resistant and 6 susceptible to fluconazole. We also sequenced 16 isolates from patients in TSARY 2014, including 7 resistant and 9 susceptible to fluconazole, and the C. tropicalis strain ATCC750 (American Type Culture Collecton, https://www.atcc.org). We constructed a multiplexing nanopore sequencing library with high molecular weight DNAs by using the Ligation Sequencing Kit and Native Barcoding Expansion Kit (both Oxford Nanopore Technologies, https://www.nanoporetech.com) according to the manufacturer’s instructions. We analyzed a standard 72-hour sequencing script by using MinKNOW software (Oxford Nanopore Technologies), collected raw reads, and then basecalled and demultiplexed by using the standalone application guppy (30). After inputting an estimated genome size of 15 Mbp, we obtained long-length and high-quality (coverage ×80; i.e., 1.2 Gbp) sequencing reads by using a customized script, GetFastq.py (31). We then filtered and aligned the reads against the ERG11 gene (GenBank accession no. XM_002550939) by using minimap2 (https://github.com/lh3/minimap2) and a customized script to test for copy number variants. This script separated reads containing ERG11 sequences into 3 groups: single copy ERG11 reads, multiple-copy ERG11 reads, and unsure ERG11 reads that included partial ERG11 sequences. For the single and multiple copy groups, we selected a reference read and polished with Medaka version 1.4.3 (https://github.com/nanoporetech/medaka).

Use of Azole Compounds in Taiwan

Fluconazole (1992), itraconazole (1992), ketoconazole (1981), and voriconazole (2004) have been available in Taiwan for >2 decades. Posaconazole was introduced in 2010. We retrospectively analyzed systemic antifungal drugs administered in healthcare settings in Taiwan by using data obtained from the Taiwan National Health Insurance Research database; the details of the database and methods have been described previously (32). We determined the defined daily dose (DDD) of total azole, fluconazole, itraconazole, ketoconazole, and voriconazole in 2005 (1 year after voriconazole was introduced) and 2013 (1 year before TSARY 2014). We did not include the DDD for posaconazole because it was introduced after 2005. We estimated the amounts of azole-type compounds used in agriculture in Taiwan according to Domestic Manufacturers Production & Sale of Pesticides, an annual publication by the Taiwan Crop Protection Industry Association (33).

Results

Distribution of Yeasts Isolated from Orchard Environment and Farmers

We isolated 704 individual yeasts from 310 samples, including 74 from fruit, 63 from soil, 59 from hand, 58 from oral rinse, 31 from water, and 25 from armpit samples. The isolated yeasts comprised 34 genera and 83 species; 41 of those species have been reported to cause disease in humans. Of the 704 yeasts, 453 (64.3%) were isolated from the environment and 251 (35.7%) from farmers (Table 1; Appendix Table 3). Most (251/453 [55.4%]) environmental isolates were from fruits, and most (126/251 [50.2%]) isolates from farmers were from hand swab samples.

Figure 1

Detection in orchards of predominant azole-resistant Candida tropicalis genotype causing human candidemia, Taiwan. Samples from fruit, soil, and water at different orchards were collected. Swab samples from the hands and armpits and oral rinse samples were collected from orchard farmers. Colors indicate source of different yeast species. Numbers of Candida spp., Nakaseomyces glabratus (formerly C. glabrata), and Pichia kudriavzevii (formerly C. krusei) yeast isolates were determined for each sample type.

Figure 1. Detection in orchards of predominant azole-resistant Candida tropicalisgenotype causing human candidemia, Taiwan. Samples from fruit, soil, and water at different orchards were collected. Swab samples from the hands...

The most common human pathogenic yeasts recovered from the environment were C. tropicalis (59/453 [13.0%]), Candida palmioleophila (30/453 [6.6%]), and P. kudriavzevii (27/453 [6.0%]), whereas the leading 2 human pathogenic yeasts recovered from the farmers were C. albicans (37/251 [14.7%]) and C. parapsilosis (29/251 [11.6%]) (Figure 1). Furthermore, yeast species had different prevalences according to the collection site (Table 1). C. tropicalis (32/153 [20.9%]) and C. palmioleophila (26/153 [17%]) were 2 major species found in soil, and P. kudriavzevii was prevalent in water (7/49 [14.3%]). Most (35/37) C. albicans and all 3 N. glabratus isolated from farmers were found in oral rinse samples. Of the 35 armpit swab samples, 12 (34.3%) contained C. parapsilosis and 5 (14.3%) Rhodotorula mucilaginosa.

Susceptibility of 4 Major Candida spp. to Fluconazole

All 39 C. albicans, 29 C. parapsilosis, and 3 N. glabratus isolates were susceptible to fluconazole (<2 mg/L), whereas 11 (16.7%) C. tropicalis isolates were resistant (>8 mg/L), 14 susceptible-dose dependent (4 mg/L), and 41 susceptible (<2 mg/L) to fluconazole (Table 2). In addition, we found that yeast susceptibilities to fluconazole were positively correlated with susceptibilities to 3 azole fungicides used in agriculture (Table 2). All 11 fluconazole-resistant C. tropicalis isolates were collected from the environment in 3 different orchards: grape (n = 4 isolates), papaya (n = 4), and wax apple (n = 3) (Appendix Table 4).

Genetic Relatedness of C. tropicalis Isolates

We analyzed the DSTs of all 66 C. tropicalis isolates (Appendix Table 4). The genotype distribution among the 42 fluconazole-susceptible isolates was more diverse, and they were classified into 12 different genotypes: clade 8 (n = 12 isolates); clades 3 and 6 (n = 6 each); clade 4 (n = 5); clade 1 (n = 4); clade 5 (n = 3); clades 2, 10, and 17 (n = 1 each); and DST1394, DST1402, and DST564 (n = 1 each). The 13 fluconazole–susceptible-dose dependent isolates were classified into 5 genotypes: clade 4 (n = 9), clades 8 and 10 (n = 1 each), and DST1394 and DST598 (n = 1 each). Most (≈69%) fluconazole–susceptible-dose dependent isolates belonged to clade 4, of which 88.9% (8/9) belonged to DST225. Furthermore, 9 (81.8%) of 11 fluconazole-resistant isolates belonged to clade 4, consistent with the finding among fluconazole-resistant C. tropicalis causing infections in patients.

Molecular Characteristics of C. tropicalis Isolates

We analyzed the expression of genes involved in fluconazole resistance in C. tropicalis isolated from orchards and patients (Table 3). ERG11 mRNA levels increased 3.8–13-fold in all 11 clade 4 isolates compared with that of the azole-susceptible control strain, YFA120877. In contrast, the levels of ERG11 mRNA in 3 non–clade 4 fluconazole-resistant isolates, including clades 2, 3, and 8, were not increased. In addition to ERG11, the expression of MDR1 in 3 clade 4 fluconazole-resistant and 1 clade 5 fluconazole-susceptible isolates was increased compared with the control. CDR1 expression in the clade 8 fluconazole-resistant isolate was also increased.

Figure 2

Phylogenetic analysis of Candida tropicalis in study of detection in orchards of predominant azole-resistant genotype causing human candidemia, Taiwan. Red numbers indicate fluconazole resistance at MICs of >8 mg/L. We conducted whole-genome sequencing of 31 isolates. Sequence comparisons indicated that all but 1 clade 4 isolate was fluconazole resistant and that isolates from orchards and patients were genetically related. Scale bar indicates nucleotide substitutions per site. ATCC, American Type Tissue Collection; DST, diploid sequence type, ND, not determined.

Figure 2. Phylogenetic analysis of Candida tropicalis in study of detection in orchards of predominant azole-resistant genotype causing human candidemia, Taiwan. Red numbers indicate fluconazole resistance at MICs of ...

To further investigate mutations of the azole drug target, ERG11, that contributes to fluconazole-resistance we completed WGS of 31 isolates (Table 3). Sequence comparisons indicated that all but 1 clade 4 isolates clustered together (Figure 2), confirming genetic relatedness among fluconazole-resistant isolates from orchards and patients. All 12 clade 4, but not the 3 non–clade 4 (clades 2, 3, and 8), fluconazole-resistant isolates contained Y132F or S154F mutations in the Erg11 protein. In contrast, all but 1 fluconazole-susceptible isolates had wild-type Erg11 protein. The difference between the clade 4 fluconazole-resistant and fluconazole-susceptible isolates was the 4–9 tandem gene duplications of ERG11 found in resistant isolates, whereas the susceptible isolate, YFA121078, had only 1 copy of the ERG11 gene.

Discussion

We found that fluconazole-resistant C. tropicalis isolated from fruits, soils, and water in orchards in Taiwan were genetically similar to those causing prolonged colonization and tissues damage in humans. This finding might be associated with both increasingly frequent clinical use of azoles in humans and intense use of azole fungicides in agriculture in Taiwan. We provide epidemiologic evidence indicating that orchards are a reservoir for clade 4 fluconazole-resistant C. tropicalis. First, infections in humans were sporadic and unrelated to each other (15,34), and no identifiable hospital outbreaks occurred. Second, most patients had major underlying conditions and had not been treated with azole drugs within 6 months before hospital admission (15). Last, we identified a specific causative clade 4 that shared the same DST genotypes common to both orchards and patients.

Sequential accumulation of adaptive chromosomal mutations has been reported to be associated with drug resistance in fungi (35,36). Selection of azole-resistant A. fumigatus has been associated with agricultural use of azoles (37); isolates carrying tandem repeat 34/L98H mutations in the Cyp51A (Erg11) protein were recovered from 2 azole-naive patients with pulmonary aspergillosis (38). C. albicans and other yeast species isolated from patients with HIV infections and from vine grapes in Bavaria, Germany, were also cross-resistant to medical and agricultural azole drugs (39); however, the genetic relatedness among those resistant isolates was not determined.

The YFA121078 isolate was susceptible to fluconazole even though it had both Y132F and S154F mutation in the Erg11 protein, suggesting that >1 mutations in Erg11 might not be sufficient to contribute to treatment failure, but might allow C. tropicalis to survive when low levels of azole are present in the environment. The expression of MDR1 mRNA in YM140896, a fluconazole-susceptible isolate, was 2.5-fold higher than that of the control strain. Furthermore, the expression of MDR1 mRNA in 3 clade 4 fluconazole-resistant isolates was also higher than that of the control strain. Those findings suggest that overexpression of MDR1 alone might not cause treatment failure. Our findings are consistent with a concept that fluconazole resistance might be caused by accumulation of molecular changes in different genes, including mutations and overexpression.

An outbreak of C. auris in a neuroscience intensive care unit in the United Kingdom was linked to reusable axillary temperature probes (40). Among 21 fluconazole-susceptible C. tropicalis isolates collected from patients in Italy who had neurologic disorders, 9 belonged to DST747 and 6 to DST333. Isolates from door handles, bedside tables, bed handles, and the hands of healthcare workers also belonged to 1 of those DSTs (41). Hence, a specific Candida spp. clone can persist in the environment and be horizontally transmitted within a healthcare setting.

The detection of the same clade 4 genotype of fluconazole-resistant C. tropicalis from agricultural sites and infected humans suggests that fluconazole-resistant C. tropicalis in environments can be a threat to healthcare. A 7-year (2011–2017) observational study of adult patients with C. tropicalis bloodstream infections at National Taiwan University Hospital showed that 9 of 58 fluconazole-resistant C. tropicalis isolates were DST225 and 6 were DST506, all belonging to clade 4 (34). Furthermore, 23 of 30 fluconazole-resistant C. tropicalis isolates from Shanghai, China, belonged to clade 4 DST505–7 (42). Therefore, active surveillance to detect emergence and dissemination of azole-resistant C. tropicalis in clinical settings should be considered and should not be limited to tropical Asia and Latin America.

Because 29 of 31 fluconazole-resistant C. tropicalis isolated during TSARY 2018 belonged to the clade 4 genotype, we conducted a follow-up survey of orchards in 2018. Preliminary data showed that >90% of fluconazole-resistant C. tropicalis isolates from orchard environments in that survey belonged to clade 4 (H.J. Lo, unpub. data). Our findings demonstrate that the clade 4 fluconazole-resistant C. tropicalis genotype is persistent in Taiwan in both clinical settings and the environment.

MLST is a convenient and cost-effective tool to study genetic relatedness and diversity of microbes. We showed that clade assignment from MLST aligned well with the tree topology according to WGS results, which is consistent with our previous report of genetic relatedness among 2 clades detected by MLST and confirmed by mitochondrial genome sequencing (43). Nevertheless, when we compared the WGS results among clade 4 strains, we ruled out the possibility that YM141031, which fell outside of the clade 4 cluster (Figure 2), had large insertions or deletions within its genome. Therefore, it is possible that the clade 4 C. tropicalis ancestor was divided into 2 different progenies because of drug selection pressure. The fluconazole-susceptible ancestor of YM141031 has wild-type ERG11 and survives in an azole drug-free environment, whereas the ancestor of YFA121078, found in the clade 4 cluster, has mutations in ERG11 and survives in the presence of low levels of azole drugs. YFA121078 developed into a fully fluconazole-resistant strain by ERG11 copy number variation or other potential mechanisms contributing to drug resistance. Thus, the combination of clade 4 genotype and ERG11 mutations might help to rapidly identify drug-resistant clade 4 C. tropicalis.

Twenty-nine different types of azole fungicides have been used in Taiwan. The annual azole fungicide use in agriculture in Taiwan increased from 82.1 tons in 2005 to 145.7 tons in 2013 (33). Difenoconazole use increased from 9.2 tons in 2005 to 32 tons in 2013 and tebuconazole increased from 2.1 tons in 2005 to 12.7 tons in 2013; ≈0.5 tons of triadimenol were used during both periods. Correlations between increased agricultural azole use and the appearance of azole resistance in human fungal pathogens have been found. We found that C. tropicalis could be traced to a few farmers. However, no farmers harbored clade 4 azole-resistant isolates. Nevertheless, we have established a foundation for more in-depth and systematic studies to evaluate the horizontal transmission of the C. tropicalis genotype in the agricultural setting and its implications in the clinical setting.

In conclusion, our findings reemphasize the importance of the One Health concept. In Taiwan, total clinical azole use increased from 14,691 DDD in 2005 to 21,991 DDD in 2013; fluconazole increased from 12,707 DDD in 2005 to 19,053 DDD in 2013, itraconazole increased from 362 DDD in 2005 to 760 DDD in 2013, and voriconazole increased from 332 DDD in 2005 to 1,396 DDD in 2013, whereas ketoconazole decreased from 1,291 DDD in 2005 to 677 DDD in 2013, according to data derived from the Taiwan National Health Insurance Research database (32). Antimicrobial drug stewardship efforts in hospitals can reduce the selection of drug-resistant organisms. However, if no efforts are made in agriculture to discontinue use of antimicrobial drug classes used in human medicine, vulnerable patients will continue to become infected with highly resistant organisms and have fewer treatment options. Our findings indicate that agriculture environments are one reservoir for azole-resistant C. tropicalis; discontinuing agricultural use of azoles might reduce emergence of azole-resistant Candida spp. strains in humans.

Mr. Tseng is an epidemiologist at the Taiwan National Health Research Institutes. His research interests focus on molecular epidemiology, mechanisms of antimicrobial drugs, and bioinformatics.

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Acknowledgments

We thank Calvin Kunin, Shau-Ku Huang, Clifford McDonald, Geneviève Milon, and Mark Swofford for their assistance with the manuscript; Pfizer for supplying fluconazole; and Mission Biotech for assistance with techniques for sequencing and real-time PCR.

This work was supported in part by grants from the Ministry of Science and Technology, Taiwan (grant nos. 112-2314-B-400-007 and 112-0324-01-30-06), National Health Research Institutes (grant nos. IV-112-PP-02, IV-112-PP-11, IV-113-PP-01, and IV-113-PP-05), Taiwan Centers for Disease Control (grant no. MOHW111-CDCC-114-124301).

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DOI: 10.3201/eid3011.240545

Original Publication Date: October 19, 2024

1These authors contributed equally to this article.

Table of Contents – Volume 30, Number 11—November 2024

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Hsiu-Jung Lo, Taiwan Mycology Reference Center, National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, 35 Keyan Rd, Zhunan, Miaoli County 350, Taiwan

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