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 Citation Map Services E-mail this article to a friend 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 Google Scholar Google Scholar Articles by Borman, A. M. Articles by Johnson, E. M. Search for Related Content PubMed PubMed Citation Articles by Borman, A. M. Articles by Johnson, E. M.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, July 2009, p. 2307-2310, Vol. 47, No. 7
0095-1137/09/$08.00+0     doi:10.1128/JCM.00240-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Pyrosequencing Analysis of 20 Nucleotides of Internal Transcribed Spacer 2 Discriminates Candida parapsilosis, Candida metapsilosis, and Candida orthopsilosis

Andrew M. Borman,^1* Christopher J. Linton,¹ Debra Oliver,¹ Michael D. Palmer,¹ Adrien Szekely,¹ Frank C. Odds,² and Elizabeth M. Johnson¹

Mycology Reference Laboratory, Health Protection Agency, Bristol, United Kingdom,¹ Aberdeen Fungal Group, School of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom²

Received 4 February 2009/ Returned for modification 9 April 2009/ Accepted 21 April 2009

Top ABSTRACT TEXT REFERENCES

 
Two new cryptic sister species, Candida orthopsilosis and Candida metapsilosis, were recently identified by consistent DNA sequence differences among several genes within the genetically heterogeneous Candida parapsilosis complex. Here, we present data demonstrating that Pyrosequencing analysis of 20 nucleotides of internal transcribed spacer region 2 rapidly and robustly distinguishes between these three closely related Candida species.

Top ABSTRACT TEXT REFERENCES

 
Invasive fungal infections, especially those caused by Candida spp., remain a significant cause of mortality in immunocompromised patients and those undergoing invasive procedures (reviewed in references 14 and 20). Although Candida albicans remains the most common Candida species encountered in human infections, Candida parapsilosis is frequently isolated from both mucosal and systemic infections worldwide (5, 13, 15). Previous studies have demonstrated that C. parapsilosis isolates were genetically heterogeneous, and could be separated into three groups (C. parapsilosis groups I to III) by a variety of approaches, including randomly amplified polymorphic DNA analyses (9), mitochondrial DNA (12), DNA topoisomerase II (8), or internal transcribed spacer (ITS) (10) gene sequencing and isoenzyme profiles (10). On the basis of sequence differences in multiple genes, two new sister species, Candida metapsilosis and Candida orthopsilosis, were proposed in 2005 to replace C. parapsilosis groups II and III (16).

Following their initial description, it was assumed that accurate discrimination between C. parapsilosis, C. metapsilosis, and C. orthopsilosis was important principally for epidemiological surveys, since few data existed concerning the antifungal susceptibility profiles of these new species. However, recent studies suggest significant differences between the antifungal susceptibility profiles of C. orthopsilosis/C.metapsilosis and C. parapsilosis, particularly with respect to the echinocandin antifungal agents (7, 11), indicating that correct identification may also eventually have therapeutic implications.

Here, we have investigated whether Pyrosequencing technology, which is a rapid and potentially robust method of yeast identification (2-4, 6, 18), could be used to discriminate between clinical isolates of C. parapsilosis, C. orthopsilosis, and C. metapsilosis. Seventy clinical isolates presumed to be C. parapsilosis from a variety of biological specimens were included in the current study. These isolates had been referred to the United Kingdom Mycology Reference Laboratory (MRL) for identification and had been identified by us as C. parapsilosis by AUXACOLOR2 (Bio-Rad, Marnes-La-Coquette, France) testing. Six of these 70 isolates had also been previously confirmed as C. parapsilosis sensu stricto by rRNA gene sequencing (Table 1; data not shown). Reference isolates included the type strain of C. parapsilosis, the holotype strains of C. metapsilosis and C. orthopsilosis, and 10 isolates of C. orthopsilosis and 1 additional isolate of C. metapsilosis that had previously been characterized by multilocus sequence typing (MLST) (Table 1). Two clinical isolates of Lodderomyces elongisporus, which we had previously identified by rRNA gene sequencing, were also included since this yeast species had been proposed historically as a potential teleomorph for organisms that resemble C. parapsilosis physiologically (19). Twenty-one clinical isolates of C. albicans (including 8 which had undergone rRNA gene sequencing) were also included for comparison (Table 1).

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

TABLE 1. Key isolates and reference strains used in this study

Genomic DNA was prepared from all isolates using Whatman FTA filter paper technology exactly as described previously (1). PCR amplification of a fragment of the ITS2 region was performed using the primers supplied with the PyroMark fungus test (Biotage, Sweden). In all cases, PCR amplification (100-µl reaction volumes) was performed in the presence of 200 µM of each deoxynucleoside triphosphate (dNTP), 250 nM of the appropriate primers, 2 U of HotStar Taq polymerase (Qiagen, Valencia, CA), and a single FTA filter punch. Following enzyme activation at 94°C for 15 min, reactions were subjected to 40 thermal cycles with the following parameters: 94°C for 15 s, 55°C for 15 s, and 72°C for 90 s on a GeneAmp PCR Systems 9700 thermocycler (Applied Biosystems, Foster City, CA). Amplification success was evaluated by electrophoresis of a fraction of total amplification products in 1.2% (wt/vol) agarose gels run for 45 min at 120 V in Tris-borate buffer. ITS2 amplification products were subjected to Pyrosequencing analysis with the reagents supplied with the PYROGOLD SQA kit using a PyroMark ID Pyrosequencing instrument (Biotage). Analysis of the resulting sequences was performed using the IdentiFire software (Biotage) with an extended sequence database generated at the MRL using reference and type species.

Table 2 shows the Pyrosequencing profiles generated for the various yeast species. Unique Pyrosequencing profiles were obtained for each of the species tested. Importantly, sequences from the isolates of C. orthopsilosis, C. metapsilosis, L. elongisporus, and C. albicans differed from the 33-nucleotide C. parapsilosis sequence at 1, 2, 11, and 15 positions, respectively. Indeed, isolates from the four species examined could be reliably distinguished using only the first 20 nucleotides of ITS2 sequence generated by Pyrosequencing analysis. It should be noted that the Pyrosequencing profiles reported here are unique to the yeast species examined. To date, none of the approximately 50 different species of yeast we have examined by Pyrosequencing analysis share identical profiles with C. parapsilosis, C. metapsilosis, or C. orthopsilosis (unpublished date), and BLAST searches using the sequences generated by Pyrosequencing analysis fail to produce any other significant, reliable matches in the public synchronized databases (data not shown). Additionally, no intraspecific sequence variations were detected in the relatively short region of ITS2 examined by Pyrosequencing analysis for all four species studied. This may seem to contrast with previous reports suggesting that both C. orthopsilosis and C. metapsilosis exhibit more genetic variability than C. parapsilosis (7, 16, 17) and describing a subset of sequences purportedly from C. albicans in the public databases that lack the adenosine at nucleotide position 4 in the Pyrosequencing profile (data not shown). However, variability in highly conserved genes such as those encoding ribosomal DNA is more limited than that in many other genes, which is why such genes are used as the basis for discrimination of organisms at the species rather than the strain level. Future studies will be designed to test the possibility that some variability might be observed if a larger panel of isolates was studied or if a longer portion of ITS2 was analyzed by Pyrosequencing analysis.

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

TABLE 2. Pyrosequencing signature sequences for C. parapsilosis and related speciesa

Two of the 70 presumed isolates of C. parapsilosis included in the current study on the basis of physiological profiles were in fact identified as C. metapsilosis (1 isolate) and C. orthopsilosis (1 isolate) on the basis of Pyrosequencing analysis, as shown in Table 1 (MRL3144905 and MRL1136522) and Table 2 (prevalence of C. metapsilosis and C. orthopsilosis among "phenotypic C. parapsilosis" isolates of 1.4% for each species). The identities of these two isolates were formally confirmed by rRNA gene sequencing (data not shown). Previous studies have demonstrated important geographical variations in the prevalences of C. metapsilosis and C. orthopsilosis among "phenotypic C. parapsilosis" isolates (7, 11). However, it is not possible from the present data to draw firm conclusions regarding the relative prevalence of these species in the United Kingdom, since the 70 isolates of presumed C. parapsilosis studied here had been referred to our laboratory for identification, rather than collected through active surveillance. Nevertheless, the high-throughput nature of Pyrosequencing technology makes it ideally suited to evaluate the prevalence of cryptic minority species.

In conclusion, Pyrosequencing analysis of a small portion of ITS2 is sufficient to reliably discriminate between C. parapsilosis, C. metapsilosis, and C. orthopsilosis. The Pyrosequencing profiles produced for each of these species were reproducible and conserved across multiple isolates and are to date unique to each of these three species of pathogenic yeast. Given the relative rapidity and facility of Pyrosequencing analysis, we believe that this approach is ideally suited to the accurate identification of presumed isolates of C. parapsilosis, which in the light of recently reported antifungal susceptibility profiles (7, 11) may become increasingly important for informed therapeutic decisions.

 
We are grateful to the other members of the Mycology Reference Laboratory for their interest and advice and to Whatman International and Biotage AB, Sweden, for the gift of reagents.

A.M.B. was funded in part by travel grants from Whatman International and Biotage AB, Sweden.

 
* Corresponding author. Mailing address: Mycology Reference Laboratory, Health Protection Agency South-West Regional Laboratory, Myrtle Road, Kingsdown, Bristol BS2 8EL, United Kingdom. Phone: 0117 926 8683. Fax: 0117 922 6611. E-mail: Andy.Borman{at}uhBristol.nhs.uk

Published ahead of print on 29 April 2009.

Top ABSTRACT TEXT REFERENCES

 

1
1. Borman, A. M., C. J. Linton, S.-J. Miles, C. K. Campbell, and E. M. Johnson. 2006. Ultra-rapid preparation of total genomic DNA from isolates of yeast and mould using Whatman FTA filter paper technology—a re-usable DNA archiving system. Med. Mycol. 44:389-398.[CrossRef][Medline]
2
2. Borman, A. M., C. J. Linton, S.-J. Miles, and E. M. Johnson. 2008. Molecular identification of pathogenic fungi. J. Antimicrob. Chemother. 61:i7-12.[Abstract/Free Full Text]
3
3. Borman, A. M., R. Petch, C. J. Linton, M. D. Palmer, P. D. Bridge, and E. M. Johnson. 2008. Candida nivariensis, an emerging pathogenic fungus with multidrug resistance to antifungal agents. J. Clin. Microbiol. 46:933-938.[Abstract/Free Full Text]
4
4. Boyanton, B. L., R. A. Luna, L. R. Fasciano, K. G. Menne, and J. Versalovic. 2008. DNA pyrosequencing-based identification of pathogenic Candida species by using the internal transcribed spacer 2 region. Arch. Pathol. Lab. Med. 132:667-674.[Medline]
5
5. de Bernardis, F., R. Lorenzini, R. Verticchio, L. Agatensi, and A. Cassone. 1989. Isolation, acid proteinase secretion, and experimental pathogenicity of Candida parapsilosis from outpatients with vaginitis. J. Clin. Microbiol. 27:2598-2603.[Abstract/Free Full Text]
6
6. Gharizadeh, B., E. Norberg, J. Loffler, S. Jalal, J. Tollemar, H. Einsele, L. Klingspor, and P. Nyren. 2004. Identification of medically important fungi by the Pyrosequencing technology. Mycoses 47:29-33.[CrossRef][Medline]
7
7. Gomez-Lopez, A., A. Alatruey-Izquierdo, D. Rodriguez, B. Almirante, A. Pahissa, J. L. Rodriguez-Tudela, M. Cuenca-Estrella, and the Barcelona Candidemia Project Study Group. 2008. Prevalence and susceptibility profile of Candida metapsilosis and Candida orthopsilosis: results from population-based surveillance of candidemia in Spain. Antimicrob. Agents Chemother. 52:1506-1509.[Abstract/Free Full Text]
8
8. Kato, M., M. Ozeki, A. Kikuchi, and T. Kanbe. 2001. Phylogenetic relationship and mode of evolution of yeast DNA topisomerase II gene in the pathogenic Candida species. Gene 272:275-281.[CrossRef][Medline]
9
9. Lehmann, P. F., D. Lin, and B. A. Lasker. 1992. Genotypic identification and characterization of species and strains within the genus Candida by using random amplified polymorphic DNA. J. Clin. Microbiol. 30:3249-3254.[Abstract/Free Full Text]
10
10. Lin, D., L.-C. Wu, M. G. Rinaldi, and P. F. Lehmann. 1995. Three distinct genotypes within Candida parapsilosis from clinical sources. J. Clin. Microbiol. 33:1815-1821.[Abstract/Free Full Text]
11
11. Lockhart, S. R., S. A. Messer, M. A. Pfaller, and D. J. Diekema. 2008. Geographic distribution and antifungal susceptibility of the newly described species Candida orthopsilosis and Candida metapsilosis in comparison to the closely related species Candida parapsilosis. J. Clin. Microbiol. 46:2659-2664.[Abstract/Free Full Text]
12
12. Nosek, J., L. Tomáka, A. Ryovská, and H. Fukuhara. 2002. Mitochondrial telomeres as molecular markers for identification of the opportunistic yeast pathogen Candida parapsilosis. J. Clin. Microbiol. 40:1283-1289.[Abstract/Free Full Text]
13
13. Pfaller, M. A., R. N. Jones, G. V. Doern, A. C. Fluit, J. Verhoef, H. S. Sadler, S. A. Messer, A. Houston, S. Coffman, R. J. Hollis, et al. 1999. International surveillance of blood stream infections due to Candida species in the European SENTRY program: species distribution and antifungal susceptibility including the investigational triazole and echinocandin agents. Diagn. Microbiol. Infect. Dis. 35:19-25.[CrossRef][Medline]
14
14. Ruhnke, M. 2006. Epidemiology of Candida albicans infections and role of non-Candida albicans yeasts. Curr. Drug Targets 7:495-504.[CrossRef][Medline]
15
15. Sandven, P. 2000. Epidemiology of candidemia. Rev. Iberoam. Micol. 17:73-81.[Medline]
16
16. Tavanti, A., A. D. Davidson, N. A. R Gow, M. C. J. Maiden, and F. C. Odds. 2005. Candida orthopsilosis and Candida metapsilosis spp. nov. to replace Candida parapsilosis groups II and III. J. Clin. Microbiol. 43:284-292.[Abstract/Free Full Text]
17
17. Tavanti, A., L. A. M. Hensgens, E. Ghelardi, M. Campa, and S. Senesi. 2007. Genotyping of Candida orthopsilosis clinical isolates by amplification fragment length polymorphism reveals genetic diversity among independent isolates and strain maintenance within patients. J. Clin. Microbiol. 45:1455-1462.[Abstract/Free Full Text]
18
18. Trama, J. P., E. Mordechai, and M. E. Adelson. 2005. Detection and identification of Candida species associated with Candida vaginitis by real-time PCR and pyrosequencing. Mol. Cell. Probes 19:145-152.[CrossRef][Medline]
19
19. Van der Walt, J. P. 1966. Lodderomyces, a new genus of Saccharomycetaceae. Antonie van Leeuwenhoek 32:1-5.[CrossRef][Medline]
20
20. Wright, W. L., and R. P. Wenzel. 1997. Nosocomial Candida. Epidemiology, transmission and prevention. Infect. Dis. Clin. N. Am. 11:411-425.[CrossRef][Medline]

---

Journal of Clinical Microbiology, July 2009, p. 2307-2310, Vol. 47, No. 7
0095-1137/09/$08.00+0     doi:10.1128/JCM.00240-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services E-mail this article to a friend 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 Google Scholar Google Scholar Articles by Borman, A. M. Articles by Johnson, E. M. Search for Related Content PubMed PubMed Citation Articles by Borman, A. M. Articles by Johnson, E. M.