Skip to main page content

• HOME
• Current Issue
• Archive
• Alerts
• About ASM
• Contact us
• Tech Support
• Journals.ASM.org

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jacobsen, M. D. Articles by Odds, F. C. Search for Related Content PubMed PubMed Citation Articles by Jacobsen, M. D. Articles by Odds, F. C.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, February 2007, p. 317-323, Vol. 45, No. 2
0095-1137/07/$08.00+0     doi:10.1128/JCM.01549-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Strain Typing and Determination of Population Structure of Candida krusei by Multilocus Sequence Typing

Mette D. Jacobsen,¹ Neil A. R. Gow,¹ Martin C. J. Maiden,² Duncan J. Shaw,¹ and Frank C. Odds^1*

Aberdeen Fungal Group, School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom,¹ The Peter Medawar Building for Pathogen Research and Department of Zoology, University of Oxford, Oxford OX1 3SY, United Kingdom²

Received 26 July 2006/ Returned for modification 11 September 2006/ Accepted 23 October 2006

Top Abstract Introduction Materials and Methods Results Discussion References

 
A multilocus sequence typing (MLST) scheme for Candida krusei was devised, based on sequencing of six gene fragments of the species. The existence of heterozygous results for each of the six fragments sequenced confirms that C. krusei is diploid for at least part of its genome. The C. krusei MLST scheme had a discriminatory index of 0.998, making this system ideal for strain typing of C. krusei clinical isolates. MLST data for 122 independent C. krusei isolates from a range of geographical sources were analyzed by eBURST, structure, and the unweighted-pair group method using average linkages to derive a population structure comprising four subtype strain clusters. There was no evidence of geographical associations with particular subtypes. Data for pairs of isolates from seven patients showed that each patient was colonized and/or infected with strain types that were indistinguishable by MLST. The C. krusei MLST database can be accessed online at http://pubmlst.org/ckrusei/.

Top Abstract Introduction Materials and Methods Results Discussion References

 
Candida krusei is one of the less common Candida species found as a cause of human infections. As an agent of opportunistic bloodstream Candida infections in susceptible hosts, it accounts for up to 6% of Candida sp. isolates in North American surveys (25) and occasionally has higher prevalence rates in surveys from Europe and other parts of the world (25). The ARTEMIS survey indicated a global prevalence for C. krusei of 2 to 3% among all bloodstream isolates (23), and a study of >3,000,000 patients in intensive care units in the United States indicated an overall prevalence of 1.2% among bloodstream isolates, with an annual incidence ranging from 0 to 0.14 cases per 10,000 central venous catheter days (32).

There is considerable institutional variation in C. krusei prevalence rates between different studies (25), with frequencies of 15% or more reported for bloodstream isolates from some Italian hospitals (10, 19). C. krusei fungemia is more likely to be associated with neutropenia in patients with hematological malignancies than among those with solid tumors or located in intensive care units (1, 12, 15, 16). It is relatively seldom associated with indwelling venous catheters but commonly generates tell-tale cutaneous exanthemata (1, 16).

C. krusei first came to attention as an "emerging" cause of bloodstream infection when it was found to be resistant at the species level to fluconazole (34). Isolates of C. krusei are treated as intrinsically resistant to fluconazole regardless of results of susceptibility tests (17), and prior exposure to fluconazole is a statistically significant risk factor in surveys of patients with C. krusei fungemia (1, 16). In fact, C. krusei shows lower in vitro susceptibility than C. albicans to most antifungal classes in vitro, including amphotericin B, caspofungin, and flucytosine (21, 22). The azole-resistant properties of C. krusei and the widespread use of fluconazole prophylaxis might have been expected to result in a rise in the overall incidence of C. krusei infection. Although several surveys of individual institutions document a rise in C. krusei candidemia through the 1990s and early 2000s, the largest surveys reveal no such trend (8, 20, 32).

Multilocus sequence typing (MLST) is a highly accurate and portable system for distinguishing between isolates of a microbial species (14, 33). It depends on sequencing a set of gene fragments that are rich in single-nucleotide polymorphisms (SNPs) between different isolates. Among pathogenic fungi, formal MLST systems have been developed for C. albicans (3), C. glabrata (6), and C. tropicalis (30). MLST facilitates determinations of population structures and epidemiological correlates of properties, such as geographical and anatomical origins of isolates and their transmission within and between patients (2, 6, 29). C. krusei isolates have previously been typed by electrophoretic karyotyping (5), restriction fragment length polymorphism analysis (5), DNA fingerprinting (4), and microsatellite polymorphism approaches (26). In this study, we present a scheme for MLST with C. krusei. We use MLST to show that patients tend to be colonized and/or infected with the same strain type and that the population structure of C. krusei consists of four clusters of closely related strain subtypes, with one comprising just two isolates that were markedly different from the other isolates tested. The results also confirm that C. krusei is diploid (7, 26).

Top Abstract Introduction Materials and Methods Results Discussion References

 
Isolates. All 129 C. krusei isolates used for this study (Table 1) were originally cultured from clinical samples. The identities of all isolates were confirmed by standard morphological and physiological criteria. Several isolates came from our collection of pathogenic fungi, and fresh isolates were recently received for routine test purposes or were kindly supplied by the Mycology Reference Laboratory in Bristol, United Kingdom, the regional Mycology Laboratory in Leeds, United Kingdom, and the University of Iowa. Fourteen of the isolates were duplicates from seven patients, either from different anatomical sites or taken at different times (Table 1). A set of 122 single-source isolates was therefore available, including one from each of the pairs of isolates. The isolates represented probable genetic diversity, based on their dates, anatomical sites, and geographical sources of isolation. The yeasts were maintained on Sabouraud agar (Oxoid, Basingstoke, United Kingdom).

View this table: [in this window] [in a new window]

TABLE 1. List of isolates typed, with their year of isolation, geographical and anatomical sources, and DST

Choice of loci for MLST. Initially, amino acid sequences of 11 proteins from C. albicans, C. tropicalis, C. glabrata, and Saccharomyces cerevisiae were aligned to identify regions of homology. Degenerate primers were designed for DNA sequences in areas with high levels of homology to permit PCR amplification of the open reading frames from an isolate of C. krusei. The selected DNA fragments from C. krusei were ligated into the pGEM-T Easy vector (Promega) and sequenced on an ABI 3730 DNA analyzer (Foster City, CA), using the M13fwd and M13rev primers (5'-GTTTTCCCAGTCACGAC and 5'-CAGGAAACAGCTATGAC, respectively). New sets of primers specific for C. krusei were designed, and sequencing was repeated for 20 C. krusei isolates selected to represent wide geographical and anatomical diversity. DNASTAR (Lasergene) software was used to identify polymorphic sites. Final primer sets were designed to amplify fragments of 500 to 750 bp containing the largest possible number of SNPs. For the MLST scheme, we reduced the set of genes to six genes (Table 2), which was the minimum combination that afforded differentiation of all 20 isolates.

View this table: [in this window] [in a new window]

TABLE 2. Genes used for MLST

DNA extraction, amplification, and sequence determination. Genomic DNAs were extracted from yeasts grown in yeast extract-peptone-dextrose broth as previously described (30, 31).

PCRs were used to amplify the gene fragments listed in Table 2. Reaction volumes of 50 µl contained 100 ng of genomic DNA, 2.5 U Taq DNA polymerase (Promega, Madison, WI), 5 µl of 10x buffer (supplied with the enzyme), 1.5 mM MgCl₂, a 100 µM concentration of each deoxynucleoside triphosphate (Promega), and 0.2 µM (each) forward and reverse primers. A Flexigene thermocycler (Techne, Cambridge, United Kingdom) was used with a first cycle of denaturation for 5 min at 94°C, followed by 30 cycles of denaturation at 94°C for 1 min, annealing at 48°C for 1 min, and elongation at 72°C for 1 min, with a final extension step of 10 min at 72°C. The amplified products were precipitated by adding 20% polyethylene glycol-2.5 M NaCl solution to the PCR products in microdilution plates (30), which were sealed, vortexed, incubated at room temperature for 30 min, and centrifuged for 1 h at 2,250 x g (4°C). The supernatant was discarded, and the plate was inverted onto a piece of 3-mm chromatography paper and centrifuged again at 500 x g for 1 min to remove any residual polyethylene glycol from the wells. Pellets were washed with 150 µl of 70% ethanol, precipitated as described above, and resuspended in 60 µl of sterile water. Both strands of purified gene fragments were sequenced on an ABI 3730 DNA analyzer (Foster City, IA), using the same primers that were used in the PCR step. The sequence data were analyzed with DNASTAR software. Heterozygosities were defined by the presence of two coincident peaks in the forward and reverse sequence chromatograms. The one-letter code for nucleotides from the International Union of Pure and Applied Chemistry (IUPAC) nomenclature was used to define results.

Statistical analysis of MLST data. Phylogenetic analyses by the unweighted-pair group method using average linkages (UPGMA) were conducted with MEGA, version 2.1 (13). The analysis was applied to concatenated polymorphic base sequence data as previously described (30). Briefly, a single concatenated sequence was generated by representing each SNP as two bases, which were identical when the sequence showed a homozygous result and represented the different bases from each allele for a heterozygous result. The majority of the sequences, which were identical for all isolates, were excluded from the analysis. The significance of the UPGMA cluster nodes was determined by bootstrapping with 1,000 randomizations. The eBURST package (9; http://eburst.mlst.net/) was used to determine putative relationships between isolates. The eBURST algorithm placed all isolates differing at only one or two of six sequenced fragments into clonal complexes and, where possible, predicted the founding or ancestral diploid sequence type (DST) of each complex. The output was a display of the most parsimonious patterns of descent of each DST from the ancestral type. Discriminatory power was calculated according to the method of Hunter (11).

To assign boundaries to clusters of closely related strain subtypes, the information from the UPGMA analysis was combined with results from eBURST and from a haplotype analysis with the structure package (24). structure assigns isolates to one of K population groups according to a probability estimate based on their genotypes, as defined by SNPs. PHASE software (27, 28) was first used to determine putative haplotypes at each gene fragment; these data formed the input for the structure package, set to a K of 7 with no admixture, the value that gave the lowest value of (a measure of the likelihood of haplotypes originating mostly from a single population [24]) in pilot runs with different values of K. The output assigned individual isolates to one of seven populations according to their dominant genotype, Q (24). For most isolates, the result was unequivocal, reproducible assignment to a single population; for some isolates, assignments differed between runs. The package was therefore run three times with the same data, and the final structure population assignment was taken as the result obtained consistently in 2/3 or 3/3 replicate runs.

Top Abstract Introduction Materials and Methods Results Discussion References

 
C. krusei strain differentiation by MLST. Heterozygous sequencing results were obtained for all six fragments sequenced, suggesting that C. krusei has a diploid, or at least partially diploid, genome. MLST distinguished 94 DSTs among a total of 129 isolates, which indicates a discriminatory power of 0.998 (Table 1). DST 30 was the most common type encountered, representing 9 of the 129 isolates (Table 1). All six gene fragments were similarly discriminatory, with ratios of genotypes to SNPs ranging from 1.75 for HIS3 to 2.33 for ADE2 (Table 2). The C. krusei MLST database is available for open public access at http://pubmlst.org/ckrusei/.

The number of new genotypes found for each fragment sequenced fell with increasing numbers of isolates sequenced, but the number of DSTs continued to increase at an average rate of 7.3 new DSTs per 10 isolates typed.

Nucleotide polymorphisms and amino acid changes. The changes resulting from the 60 SNPs in the six gene fragments were synonymous in 30 instances. Among the 30 nonsynonymous changes, 16 were nontrivial, e.g., changes of acidic side chains to basic side chains or of aliphatic to aromatic side chains.

Paired C. krusei isolates from single patients. For the seven patients from whom two separate C. krusei isolates were obtained either at different times or from different anatomical sites, DSTs were identical for both isolates but different for each of the patients (Table 1).

Population structure of 122 isolates from single sources. eBURST analysis of the C. krusei MLST genotypes revealed seven clonal clusters, but 50 isolates were singletons that did not belong to any clonal cluster. To reduce the proportion of singletons, the eBURST analysis was repeated to allow two genotype differences between isolates, which generated eight clonal clusters with 36 singleton isolates. The largest clonal cluster resulting from tests with four of six genotypes being identical comprised 19 DSTs and was based on DST 55 as the putative ancestral member. Cluster 2 was founded on DST 63 as the most probable ancestor and contained 18 DSTs. Clusters 3, 4, and 5 represented six, five, and five DSTs, respectively, while clusters 6 through 8 comprised just two or three DSTs.

The UPGMA dendrogram for 122 C. krusei isolates, based on P distances for the concatenated SNPs determined by MLST, is shown in Fig. 1. The bootstrap values for the nodes in this dendrogram were extremely low and did not help to robustly distinguish internal structure. At an arbitrarily selected cutoff P distance of 0.07, the dendrogram could be subgrouped into four clusters of isolates, which stood out clearly when the dendrogram was represented as an unrooted radial display (Fig. 1, inset).

View larger version (37K): [in this window] [in a new window]

FIG. 1. UPGMA dendrogram based on P distances for 122 C. krusei isolates, each from a separate source. Bootstrap values are indicated for the major cluster nodes. For each isolate, the subtype assignment, DST, eBURST clonal cluster assignment, and structure group assignment are shown. Subtype boundaries are indicated by solid lines, and possible clusters within subtype 1 are indicated with dotted lines. Inset, radial display of the dendrogram to demonstrate the four subtypes with clarity.

The large group of isolates designated subtype 1 (Fig. 1) contained isolates from four eBURST clonal clusters and four structure groups. Within subtype 1, there was good correlation between isolates in clonal clusters 2, 3, and 5 and those in structure groups 4, 6, and 5, respectively (Fig. 1). The isolates in UPGMA subtype 2 fell mainly into structure group 1, although 7 of the 30 isolates in this subgroup were from structure groups 4 and 7; all of these were singletons by eBURST analysis. UPGMA subtype 3 correlated perfectly with structure group 3 and with clonal cluster 1 and therefore represents the most robust subtype of the four. Subtype 4 consisted of just two isolates, AMR1015 and AM2005/0530, which were also the only isolates in structure group 2.

Geographical origins of subtypes. There was insufficient information on the anatomical sources of the isolates typed to permit statistical analysis for possible associations between subtypes and sites of C. krusei commensalism or infection. The geographical origins of all of the isolates were known (Table 1). The geographical distributions of isolates in the four subtypes were as follows: subtype 1 (56 isolates), United Kingdom (21 [37.5%]), other European countries (24 [42.9%]), North America (6 [10.7%]), and elsewhere (5 [8.9%]); subtype 2 (29 isolates), United Kingdom (13 [44.8%]), other European countries, (2 [6.9%]), North America (4 [13.8%]), and elsewhere (10 [34.5%]); and subtype 3 (35 isolates), United Kingdom (17 [48.6%]), other European countries and North America (7 each [20.0%]), and elsewhere (4 [11.4%]). The two isolates in subtype 4 came from the United Kingdom and Europe. These differences in geographical distributions within subtypes were not statistically significant (Fisher-Freeman-Halton exact test; P = 0.3).

Top Abstract Introduction Materials and Methods Results Discussion References

 
We have demonstrated that MLST can be used to distinguish strain types within the species C. krusei, thus adding C. krusei to the existing list of Candida species (C. albicans, C. glabrata, and C. tropicalis) that can be subtyped by the MLST approach (3, 6, 30). We consider the four subtypes we defined by an arbitrary similarity cutoff point for the UPGMA dendrogram in this study to be reasonably robust, despite very low bootstrap values, since they correlate reasonably with clusters defined by eBURST and with groups determined by triplicate runs of haplotypes in the structure package (Fig. 1). A larger database of isolates from more geographically disparate sources may ultimately lead to better subtype definition and reveal enrichment of MLST-based subtypes by geographical source, as shown for the other three Candida species (6, 29, 30). However, it was not easy to assemble even the panel of 129 C. krusei isolates used in this study, since the species is the least frequently isolated among species regarded as "medically associated" yeasts.

C. krusei is the anamorph of the ascomycetous yeast Issatchenkia orientalis. However, no reports exist to suggest that clinical isolates of C. krusei can be mated to generate the teleomorph. The low bootstrap values in the UPGMA dendrogram and the high proportion of singletons found in eBURST analyses may be evidence of departure from clonal reproduction in C. krusei, and deeper study of mating types in the species may be warranted.

Carlotti et al. used a DNA fingerprinting probe and differentiated 12 clusters of related types among 58 C. krusei isolates (4). Shemer et al. found 17 haplotypes of C. krusei, based on microsatellite typing of a highly polymorphic locus, among 50 isolates (26). Both studies therefore indicated a high inherent level of diversity among isolates of C. krusei. By using MLST, we found 94 distinct DSTs in a panel of 122 separate-source isolates, also suggesting a high level of interisolate diversity. The level of strain diversity indicated by the UPGMA dendrogram for C. krusei isolates (Fig. 1) is at least as big as that for the equivalent C. albicans dendrogram (29), which means that MLST, with its high discriminatory index, its portability, its ability to detect new SNPs (unlike microsatellite typing), and the availability of a public database of results (http://pubmlst.org/ckrusei/), is the current tool of choice for typing new isolates of the species.

Because the reported incidences of C. krusei bloodstream infections vary considerably between institutions (25), MLST could be used to investigate possible single-institution outbreaks of C. krusei infection. Although we found no evidence for geographical enrichment of isolates within C. krusei subtypes, it is perhaps worth noting that a set of five isolates from different patients in a single hospital in Leeds, United Kingdom, in the year 2002 (AMR49-04, AMR49-03, AMR1316, AMR1491, and AMR1317) coclustered with a high similarity within subtype 3 (Fig. 1) and that four isolates (AM2005/0531, AM2005/0493, AM2005/0533, and AM2006/0128) originating from Slovakia, possibly from a single institution, were indistinguishable by MLST, suggesting that the patients from whom the isolates were obtained were infected by a single C. krusei strain type located in the institutions concerned.

Results for the seven pairs of isolates from different patients show that, as with C. albicans (2, 18), patients tend most often to be colonized or infected at different sites with the same strain, thus indicating endogenous infection with a clonal strain type. The appearance of heterozygosities for some isolates in each of the six gene fragments sequenced confirms previously published suggestions that the genome of C. krusei is diploid (7, 26).

Studies with C. krusei have been relatively limited compared with those for more commonly encountered Candida species, and they typically focus on the innate resistance of C. krusei to fluconazole and other antifungal agents. The introduction of a portable and discriminatory MLST system for C. krusei will greatly facilitate future studies with the species by allowing different laboratories to compare results and will contribute to the growth of the central web database for strain types.

 
This study was funded by the Wellcome Trust (grants 069615 and 074898).

We are grateful to Elizabeth Johnson, Richard Barton, Michael Pfaller, and Richard Hollis for kindly supplying several isolates of C. krusei.

 
* Corresponding author. Mailing address: Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, United Kingdom. Phone and fax: 44 1224 555828. E-mail: f.odds{at}abdn.ac.uk.

Published ahead of print on 22 November 2006.

Top Abstract Introduction Materials and Methods Results Discussion References

 

1
1. Abbas, J. 2000. Candida krusei fungemia—an escalating serious infection in immunocompromised patients. Arch. Intern. Med. 160:2659-2664.[Abstract/Free Full Text]
2
2. Bougnoux, M. E., D. Diogo, N. Francois, B. Sendid, S. Veirmeire, J. F. Colombel, C. Bouchier, H. Van Kruiningen, C. d'Enfert, and D. Poulain. 2006. Multilocus sequence typing reveals intrafamilial transmission and microevolutions of Candida albicans isolates from the human digestive tract. J. Clin. Microbiol. 44:1810-1820.[Abstract/Free Full Text]
3
3. Bougnoux, M. E., A. Tavanti, C. Bouchier, N. A. R. Gow, A. Magnier, A. D. Davidson, M. C. J. Maiden, C. d'Enfert, and F. C. Odds. 2003. Collaborative consensus for optimized multilocus sequence typing of Candida albicans. J. Clin. Microbiol. 41:5265-5266.[Abstract/Free Full Text]
4
4. Carlotti, A., R. Grillot, A. Couble, and J. Villard. 1994. Typing of Candida krusei clinical isolates by restriction endonuclease analysis and hybridization with CkF1,2 DNA probe. J. Clin. Microbiol. 32:1691-1699.[Abstract/Free Full Text]
5
5. Dassanayake, R. S., Y. H. Samaranayake, and L. P. Samaranayake. 2000. Genomic diversity of oral Candida krusei isolates as revealed by DNA fingerprinting and electrophoretic karyotyping. APMIS 108:697-704.[CrossRef][Medline]
6
6. Dodgson, A. R., C. Pujol, D. W. Denning, D. R. Soll, and A. J. Fox. 2003. Multilocus sequence typing of Candida glabrata reveals geographically enriched clades. J. Clin. Microbiol. 41:5709-5717.[Abstract/Free Full Text]
7
7. Doi, M., M. Homma, A. Chindamporn, and K. Tanaka. 1992. Estimation of chromosome number and size by pulsed-field gel electrophoresis in medically important Candida species. J. Gen. Microbiol. 138:2243-2251.[Abstract/Free Full Text]
8
8. Edmond, M. B., S. E. Wallace, D. K. McClish, M. A. Pfaller, R. N. Jones, and R. P. Wenzel. 1999. Nosocomial bloodstream infections in United States hospitals: a three-year analysis. Clin. Infect. Dis. 29:239-244.[Medline]
9
9. Feil, E. J., B. C. Li, D. M. Aanensen, W. P. Hanage, and B. G. Spratt. 2004. eBURST: inferring patterns of evolutionary descent among clusters of related bacterial genotypes from multilocus sequence typing data. J. Bacteriol. 186:1518-1530.[Abstract/Free Full Text]
10
10. Girmenia, C., P. Martino, F. DeBernardis, G. Gentile, M. Boccanera, M. Monaco, G. Antonucci, and A. Cassone. 1996. Rising incidence of Candida parapsilosis fungemia in patients with hematologic malignancies—clinical aspects, predisposing factors, and differential pathogenicity of the causative strains. Clin. Infect. Dis. 23:506-514.[Medline]
11
11. Hunter, P. R. 1990. Reproducibility and indices of discriminatory power of microbial typing methods. J. Clin. Microbiol. 28:1903-1905.[Abstract/Free Full Text]
12
12. Kibbler, C. C., S. Seaton, R. A. Barnes, W. R. Gransden, R. E. Holliman, E. M. Johnson, J. D. Perry, D. J. Sullivan, and J. A. Wilson. 2003. Management and outcome of bloodstream infections due to Candida species in England and Wales. J. Hosp. Infect. 54:18-24.[CrossRef][Medline]
13
13. Kumar, S., K. Tamura, I. B. Jakobsen, and M. Nei. 2001. MEGA2: Molecular Evolutionary Genetics Analysis software. Bioinformatics 17:1244-1245.[Abstract/Free Full Text]
14
14. Maiden, M. C. J., J. A. Bygraves, E. Feil, G. Morelli, J. E. Russell, R. Urwin, Q. Zhang, J. J. Zhou, K. Zurth, D. A. Caugant, I. M. Feavers, M. Achtman, and B. G. Spratt. 1998. Multilocus sequence typing: a portable approach to the identification of clones within populations of pathogenic microorganisms. Proc. Natl. Acad. Sci. USA 95:3140-3145.[Abstract/Free Full Text]
15
15. Meunier, F., M. Aoun, and N. Bitar. 1992. Candidemia in immunocompromised patients. Clin. Infect. Dis. 14:S120-S125.
16
16. Munoz, P., M. Sanchez-Somolinos, L. Alcala, M. Rodriguez-Creixems, T. Pelaez, and E. Bouza. 2005. Candida krusei fungaemia: antifungal susceptibility and clinical presentation of an uncommon entity during 15 years in a single general hospital. J. Antimicrob. Chemother. 55:188-193.[Abstract/Free Full Text]
17
17. NCCLS. 2002. Reference method for broth dilution antifungal susceptibility testing of yeasts; approved standard—second edition, vol. 17, no. 9. NCCLS, Wayne, PA.
18
18. Odds, F. C., A. D. Davidson, M. D. Jacobsen, A. Tavanti, J. A. Whyte, C. C. Kibbler, D. H. Ellis, M. C. J. Maiden, D. J. Shaw, and N. A. R. Gow. 2006. Candida albicans strain maintenance, replacement, and microvariation demonstrated by multilocus sequence typing. J. Clin. Microbiol. 44:3647-3658.[Abstract/Free Full Text]
19
19. Pagano, L., A. Antinori, A. Ammassari, L. Mele, A. Nosari, L. Melillo, B. Martino, M. Sanguinetti, F. Equitani, F. Nobile, M. Carotenuto, E. Morra, G. Morace, and G. Leone. 1999. Retrospective study of candidemia in patients with hematological malignancies. Clinical features, risk factors and outcome of 76 episodes. Eur. J. Haematol. 63:77-85.[Medline]
20
20. Pfaller, M. A., and D. J. Diekema. 2002. Role of sentinel surveillance of candidemia: trends in species distribution and antifungal susceptibility. J. Clin. Microbiol. 40:3551-3557.[Free Full Text]
21
21. Pfaller, M. A., D. J. Diekema, S. A. Messer, L. Boyken, R. J. Hollis, and R. N. Jones. 2003. In vitro activities of voriconazole, posaconazole, and four licensed systemic antifungal agents against Candida species infrequently isolated from blood. J. Clin. Microbiol. 41:78-83.[Abstract/Free Full Text]
22
22. Pfaller, M. A., D. J. Diekema, S. A. Messer, R. J. Hollis, and R. N. Jones. 2003. In vitro activities of caspofungin compared with those of fluconazole and itraconazole against 3,959 clinical isolates of Candida spp., including 157 fluconazole-resistant isolates. Antimicrob. Agents Chemother. 47:1068-1071.[Abstract/Free Full Text]
23
23. Pfaller, M. A., D. J. Diekema, M. G. Rinaldi, R. Barnes, B. Hu, A. V. Veselov, N. Tiraboschi, E. Nagy, and D. L. Gibbs. 2005. Results from the ARTEMIS DISK global antifungal surveillance study: a 6.5-year analysis of susceptibilities of Candida and other yeast species to fluconazole and voriconazole by standardized disk diffusion testing. J. Clin. Microbiol. 43:5848-5859.[Abstract/Free Full Text]
24
24. Pritchard, J. K., M. Stephens, and P. Donnelly. 2000. Inference of population structure from multilocus genotype data. Genetics 155:945-959.[Abstract/Free Full Text]
25
25. Sandven, P. 2000. Epidemiology of candidemia. Rev. Iberoam. Micol. 17:73-81.[Medline]
26
26. Shemer, R., Z. Weissman, N. Hashman, and D. Kornitzer. 2001. A highly polymorphic degenerate microsatellite for molecular strain typing of Candida krusei. Microbiology 147:2021-2028.[Abstract/Free Full Text]
27
27. Stephens, M., and P. Donnelly. 2003. A comparison of Bayesian methods for haplotype reconstruction. Am. J. Hum. Genet. 73:1162-1169.[CrossRef][Medline]
28
28. Stephens, M., N. J. Smith, and P. Donnelly. 2001. A new statistical method for haplotype reconstruction from population data. Am. J. Hum. Genet. 68:979-989.
29
29. Tavanti, A., A. D. Davidson, M. J. Fordyce, N. A. R. Gow, M. C. J. Maiden, and F. C. Odds. 2005. Population structure and properties of Candida albicans, as determined by multilocus sequence typing. J. Clin. Microbiol. 43:5601-5613.[Abstract/Free Full Text]
30
30. Tavanti, A., A. D. Davidson, E. M. Johnson, M. C. J. Maiden, D. J. Shaw, N. A. R. Gow, and F. C. Odds. 2005. Multilocus sequence typing for differentiation of strains of Candida tropicalis. J. Clin. Microbiol. 43:5593-5600.[Abstract/Free Full Text]
31
31. Tavanti, A., N. A. R. Gow, S. Senesi, M. C. J. Maiden, and F. C. Odds. 2003. Optimization and validation of multilocus sequence typing for Candida albicans. J. Clin. Microbiol. 41:3765-3776.[Abstract/Free Full Text]
32
32. Trick, W. E., S. K. Fridkin, J. R. Edwards, R. A. Hajjeh, and R. P. Gaynes. 2002. Secular trend of hospital-acquired candidemia among intensive care unit patients in the United States during 1989-1999. Clin. Infect. Dis. 35:627-630.[CrossRef][Medline]
33
33. Urwin, R., and M. C. J. Maiden. 2003. Multi-locus sequence typing: a tool for global epidemiology. Trends Microbiol. 11:479-487.[CrossRef][Medline]
34
34. Wingard, J. R., W. G. Merz, M. C. Rinaldi, T. R. Johnson, J. E. Karp, and R. Saral. 1991. Increase in Candida krusei infection among patients with bone marrow transplantation and neutropenia treated prophylactically with fluconazole. N. Engl. J. Med. 325:1274-1277.[Abstract]

---

Journal of Clinical Microbiology, February 2007, p. 317-323, Vol. 45, No. 2
0095-1137/07/$08.00+0     doi:10.1128/JCM.01549-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Cannon, R. D., Lamping, E., Holmes, A. R., Niimi, K., Baret, P. V., Keniya, M. V., Tanabe, K., Niimi, M., Goffeau, A., Monk, B. C. (2009). Efflux-Mediated Antifungal Drug Resistance. Clin. Microbiol. Rev. 22: 291-321 [Abstract] [Full Text]  
• Lamping, E., Ranchod, A., Nakamura, K., Tyndall, J. D. A., Niimi, K., Holmes, A. R., Niimi, M., Cannon, R. D. (2009). Abc1p Is a Multidrug Efflux Transporter That Tips the Balance in Favor of Innate Azole Resistance in Candida krusei. Antimicrob. Agents Chemother. 53: 354-369 [Abstract] [Full Text]  
• Desnos-Ollivier, M., Bretagne, S., Raoux, D., Hoinard, D., Dromer, F., Dannaoui, E. (2008). Mutations in the fks1 Gene in Candida albicans, C. tropicalis, and C. krusei Correlate with Elevated Caspofungin MICs Uncovered in AM3 Medium Using the Method of the European Committee on Antibiotic Susceptibility Testing. Antimicrob. Agents Chemother. 52: 3092-3098 [Abstract] [Full Text]  
• O'Donnell, K., Sutton, D. A., Fothergill, A., McCarthy, D., Rinaldi, M. G., Brandt, M. E., Zhang, N., Geiser, D. M. (2008). Molecular Phylogenetic Diversity, Multilocus Haplotype Nomenclature, and In Vitro Antifungal Resistance within the Fusarium solani Species Complex. J. Clin. Microbiol. 46: 2477-2490 [Abstract] [Full Text]  
• Odds, F. C., Jacobsen, M. D. (2008). Multilocus Sequence Typing of Pathogenic Candida Species. Eukaryot Cell 7: 1075-1084 [Full Text]  
• McManus, B. A., Coleman, D. C., Moran, G., Pinjon, E., Diogo, D., Bougnoux, M.-E., Borecka-Melkusova, S., Bujdakova, H., Murphy, P., d'Enfert, C., Sullivan, D. J. (2008). Multilocus Sequence Typing Reveals that the Population Structure of Candida dubliniensis Is Significantly Less Divergent than That of Candida albicans. J. Clin. Microbiol. 46: 652-664 [Abstract] [Full Text]  
• Lin, C.-Y., Chen, Y.-C., Lo, H.-J., Chen, K.-W., Li, S.-Y. (2007). Assessment of Candida glabrata Strain Relatedness by Pulsed-Field Gel Electrophoresis and Multilocus Sequence Typing. J. Clin. Microbiol. 45: 2452-2459 [Abstract] [Full Text]  
• Balajee, S. A., Tay, S. T., Lasker, B. A., Hurst, S. F., Rooney, A. P. (2007). Characterization of a Novel Gene for Strain Typing Reveals Substructuring of Aspergillus fumigatus across North America. Eukaryot Cell 6: 1392-1399 [Abstract] [Full Text]  
• Odds, F. C., Bougnoux, M.-E., Shaw, D. J., Bain, J. M., Davidson, A. D., Diogo, D., Jacobsen, M. D., Lecomte, M., Li, S.-Y., Tavanti, A., Maiden, M. C. J., Gow, N. A. R., d'Enfert, C. (2007). Molecular Phylogenetics of Candida albicans. Eukaryot Cell 6: 1041-1052 [Abstract] [Full Text]  
• Kahn, J. N., Garcia-Effron, G., Hsu, M.-J., Park, S., Marr, K. A., Perlin, D. S. (2007). Acquired Echinocandin Resistance in a Candida krusei Isolate Due to Modification of Glucan Synthase. Antimicrob. Agents Chemother. 51: 1876-1878 [Abstract] [Full Text]  
• Bain, J. M., Tavanti, A., Davidson, A. D., Jacobsen, M. D., Shaw, D., Gow, N. A. R., Odds, F. C. (2007). Multilocus Sequence Typing of the Pathogenic Fungus Aspergillus fumigatus. J. Clin. Microbiol. 45: 1469-1477 [Abstract] [Full Text]  

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jacobsen, M. D. Articles by Odds, F. C. Search for Related Content PubMed PubMed Citation Articles by Jacobsen, M. D. Articles by Odds, F. C.