Molecular probe for identification of medically important Candida species and Torulopsis glabrata

Rapid identification of Candida species in oral rinse solutions by PCR

AIMS

To determine the sensitivity and specificity of a multiplex PCR assay for the contemporary identification of major species involved in oral candidiasis, without extraction and purification of DNA from the samples under investigation; and evaluation of this method in comparison with routine phenotypic culture identification.

METHODS

78 oral rinse solutions were collected. The concentrated oral rinse technique was used for a quantitative and qualitative study. Research and identification of Candida spp, with routine phenotypic culture identification (germ-tube test in serum at 37 degrees C for 3 hours and sugar assimilation strip analysis), were performed. Each sample was analysed with multiplex PCR directly on oral rinse solution. Samples giving discrepant results between routine phenotypic and PCR identification methods were resubcultured on CHROMagar Candida plates. The fungus-specific primers ITS1, ITS2, CA3, and CA4 were used. For the identification of other species (C kefyr, C famata and C dubliniensis), ITS1F, ITS1K, and ITS2D primers were designed.

RESULTS

Multiplex PCR correctly identified all samples, including those with single species, or with mixed species, negative samples and positive samples which appeared to be negative from routine phenotypic methods.

CONCLUSION

This multiplex PCR assay provides a rapid alternative to the conventional culture based technique for the identification and speciation of the most frequently isolated Candida species. The absence of an extraction method made identification of 10 species possible in a few hours.

Flanking direct repeats of hisG alter URA3 marker expression at the HWP1 locus of Candida albicans

HWP1 encodes an adhesin of Candida albicans and has been implicated in filamentation and virulence. URA3, an often-used transformation selection marker, is apparently incorrectly expressed when integrated at the HWP1 locus, which results in an attenuated virulence phenotype. Expression of URA3 is compromised by ectopic integration at other loci as well. In contrast, prior studies from the authors' laboratory had demonstrated that the filamentation deficiency and attenuated virulence of hwp1Delta mutants were fully restored in rescued strains in which URA3 was integrated at the HWP1 locus. This discrepancy prompted a reinvestigation of these mutants. A series of congenic strains were constructed which demonstrated that the filamentation and virulence defects of a homozygous hwp1Delta mutant could be rescued without introduction of a functional HWP1 allele. Despite the absence of detectable differences in URA3 expression, analysis of suppressor mutations suggested that reduced URA3 expression gave rise to the mutant phenotypes. Several independent spontaneous suppressor mutations that restored filamentation to strains of genotype hwp1Delta : : hisG-URA3-hisG/hwp1Delta : : hisG had acquired a tandem duplication of the hisG-URA3-hisG marker cassette. The hwp1 null mutant and rescued strains differed by the presence or absence of flanking hisG sequence. Substitution of the hisG-URA3-hisG insert of the hwp1 null mutant with URA3 alone largely rescued the filamentation and virulence phenotypes. The presence of a single copy of hisG adjacent to URA3 had no effect. It is concluded that flanking direct repeats of hisG, present as part of a recyclable disruption cassette, negatively influenced URA3 expression and are responsible for the previously reported phenotypes of the hwp1 mutants.

Variation in random amplified polymorphic DNA (RAPD) profiles specific to fluconazole-resistant and -sensitive strains of Candida albicans

Random amplified polymorphic DNA analysis was used to detect genotype relatedness among clinical fluconazole-resistant and -sensitive strains of Candida albicans recovered from twenty HIV-infected patients having oropharyngeal candidiasis. Sensitive strains were obtained from a local hospital and were from patients that had not been treated with azole drugs while resistant strains were recovered from patients in different parts of Europe and their resistance was a consequence of drug-treatment given to the patients. On amplification with different arbitrary sequence decamer primers, the results demonstrated a homogeneous banding pattern for all sensitive strains that was distinct from that obtained in case of the resistant strains. The DNA profiles of strains were thus broadly clustered into two major groups of resistant and sensitive strains. The RAPD technique may be useful in differentiating fluconazole-resistant strains from the -sensitive ones for early identification of resistant isolates from AIDS patients.

The ins and outs of DNA fingerprinting the infectious fungi

DNA fingerprinting methods have evolved as major tools in fungal epidemiology. However, no single method has emerged as the method of choice, and some methods perform better than others at different levels of resolution. In this review, requirements for an effective DNA fingerprinting method are proposed and procedures are described for testing the efficacy of a method. In light of the proposed requirements, the most common methods now being used to DNA fingerprint the infectious fungi are described and assessed. These methods include restriction fragment length polymorphisms (RFLP), RFLP with hybridization probes, randomly amplified polymorphic DNA and other PCR-based methods, electrophoretic karyotyping, and sequencing-based methods. Procedures for computing similarity coefficients, generating phylogenetic trees, and testing the stability of clusters are then described. To facilitate the analysis of DNA fingerprinting data, computer-assisted methods are described. Finally, the problems inherent in the collection of test and control isolates are considered, and DNA fingerprinting studies of strain maintenance during persistent or recurrent infections, microevolution in infecting strains, and the origin of nosocomial infections are assessed in light of the preceding discussion of the ins and outs of DNA fingerprinting. The intent of this review is to generate an awareness of the need to verify the efficacy of each DNA fingerprinting method for the level of genetic relatedness necessary to answer the epidemiological question posed, to use quantitative methods to analyze DNA fingerprint data, to use computer-assisted DNA fingerprint analysis systems to analyze data, and to file data in a form that can be used in the future for retrospective and comparative studies.

The ins and outs of DNA fingerprinting the infectious fungi

DNA fingerprinting methods have evolved as major tools in fungal epidemiology. However, no single method has emerged as the method of choice, and some methods perform better than others at different levels of resolution. In this review, requirements for an effective DNA fingerprinting method are proposed and procedures are described for testing the efficacy of a method. In light of the proposed requirements, the most common methods now being used to DNA fingerprint the infectious fungi are described and assessed. These methods include restriction fragment length polymorphisms (RFLP), RFLP with hybridization probes, randomly amplified polymorphic DNA and other PCR-based methods, electrophoretic karyotyping, and sequencing-based methods. Procedures for computing similarity coefficients, generating phylogenetic trees, and testing the stability of clusters are then described. To facilitate the analysis of DNA fingerprinting data, computer-assisted methods are described. Finally, the problems inherent in the collection of test and control isolates are considered, and DNA fingerprinting studies of strain maintenance during persistent or recurrent infections, microevolution in infecting strains, and the origin of nosocomial infections are assessed in light of the preceding discussion of the ins and outs of DNA fingerprinting. The intent of this review is to generate an awareness of the need to verify the efficacy of each DNA fingerprinting method for the level of genetic relatedness necessary to answer the epidemiological question posed, to use quantitative methods to analyze DNA fingerprint data, to use computer-assisted DNA fingerprint analysis systems to analyze data, and to file data in a form that can be used in the future for retrospective and comparative studies.

Reverse transcription - 3' rapid amplification of cDNA ends-nested PCR of ACT1 and SAP2 mRNA as a means of detecting viable Candida albicans in an in vitro cutaneous candidiasis model

The presence of viable cells of Candida albicans, in broth or in a reconstructed living skin equivalent, was determined by the detection of amplicons of partial mRNA sequences of the genes encoding fungal actin (ACT1) and secreted aspartyl proteinase 2 (SAP2). The mRNA of both genes were amplified by reverse transcription-3' rapid amplification of cDNA ends-nested polymerase chain reaction. Single bands of ACT1 (315 bp) and SAP2 (162 bp) mRNA were amplified from total RNA extracts of C. albicans grown in yeast carbon base-albumin broth or in living skin equivalent tissue; only the former was amplified from Sabouraud broth-grown organisms. Primer pairs targeted for ACT1 and SAP2 were Candida genus-specific and C. albicans-specific, respectively. The sensitivity limits of the assay were 100 fg of total RNA or 10 cells of C. albicans, by ethidium bromide staining. When C. albicans-infected living skin equivalent was exposed to amorolfine, amplicons of ACT1 and SAP2 mRNA were not detected in total RNA extracts. Non-amplification of the mRNA correlated with the absence of C. albicans growth in Sabouraud agar cultures of living skin equivalent samples. Reverse transcription-3' rapid amplification of cDNA ends-nested polymerase chain reaction of the mRNA encoding specific proteins of an organism has potential application in determining the viability of the organism in tissue, thus monitoring the efficacy of an antimicrobial therapy, and in detecting mRNA expressed in very little amounts in tissue.

Postsurgical Candida albicans infections associated with an extrinsically contaminated intravenous anesthetic agent

From 16 to 30 April 1990, four of 364 (1%) postsurgical patients at one hospital developed Candida albicans fungemia or endophthalmitis. The case patients' surgeries were clustered on two days. To identify risk factors for C. albicans infections, we conducted a cohort study comparing these 4 patients with 67 control patients who had surgeries on the same days but did not acquire C. albicans infections. The participation of anesthesiologist 9 (relative risk [RR], undefined; P < 0.001) and receipt of intravenous propofol, an anesthetic agent without preservative, which was administered by an infusion pump (RR, 8.8; P = 0.048) were identified as risk factors for C. albicans infections. The anesthetic had been recently introduced in the hospital. Hand cultures of 8 of 14 (57%) anesthesiologists were positive for Candida species; one yielded C. albicans. Anesthesiologist 9 was the only one to use stored syringes of propofol in the infusion pump and to reuse propofol syringes. DNA fingerprinting with a digoxigenin-labeled C. albicans repetitive element 2 probe and electrophoretic karyotyping showed two distinct banding patterns among patient isolates. We hypothesize that extrinsic contamination of propofol by anesthesiologist 9 likely resulted in C. albicans infections. These data suggest that strict aseptic techniques must be used when preparing and administering propofol.

Nonperinatal nosocomial transmission of Candida albicans in a neonatal intensive care unit: prospective study

Nosocomial Candida albicans infections have become a major cause of morbidity and mortality in neonates in neonatal intensive care units (NICUs). To determine the possible modes of acquisition of C. albicans in hospitalized neonates, we conducted a prospective study at Grady Memorial Hospital, Atlanta, Ga. Clinical samples for fungal surveillance cultures were obtained at birth from infants (mouth, umbilicus, and groin) and their mothers (mouth and vagina) and were obtained from infants weekly until they were discharged. All infants were culture negative for C. albicans at birth. Six infants acquired C. albicans during their NICU stay. Thirty-four (53%) of 64 mothers were C. albicans positive (positive at the mouth, n = 26; positive at the vagina, n = 18; positive at both sites, n = 10) at the time of the infant's delivery. A total of 49 C. albicans isolates were analyzed by restriction endonuclease analysis and restriction fragment length polymorphism analysis by using genomic blots hybridized with the CARE-2 probe. Of the mothers positive for C. albicans, 3 of 10 were colonized with identical strains at two different body sites, whereas 7 of 10 harbored nonidentical strains at the two different body sites. Four of six infants who acquired C. albicans colonization in the NICU had C. albicans-positive mothers; specimens from all mother-infant pairs had different restriction endonuclease and CARE-2 hybridization profiles. One C. albicans-colonized infant developed candidemia; the colonizing and infecting strains had identical banding patterns. Our study indicates that nonperinatal nosocomial transmission of C. albicans is the predominant mode of acquisition by neonates in NICUs at this hospital; mothers may be colonized with multiple strains of C. albicans simultaneously; colonizing C. albicans strains can cause invasive disease in neonates; and molecular biology-based techniques are necessary to determine the epidemiologic relatedness of maternal and infant C. albicans isolates and to facilitate determination of the mode of transmission.

Evaluation of the discriminatory power of pulsed-field gel electrophoresis and PCR fingerprinting for epidemiologic typing of Candida species

OBJECTIVE: To evaluate the discriminatory power of genotyping methods (PCR fingerprinting and pulsed-field gel electrophoresis) validated for Candida albicans in other Candida species. METHODS: Molecular typing methods are increasingly being applied for studies where the interpretation of data essentially relies on the typing results rather than epidemiologic data. In this situation, the discriminatory power (ability to identify differences among epidemiologically unrelated strains) of the typing method is important in allowing one to draw valid conclusions. By applying PCR fingerprinting, electrophoretic karyotyping, and restriction fragment endonuclease analysis using standard restriction enzymes and primers proven to be useful in previous studies, we evaluated whether the use of multiple genotyping methods is sufficient to delineate known unrelated strains among seven Candida species. RESULTS: All three methods identified individual genotypes for each of the seven Candida species studied. However, optimal strain delineation required the combined use of all three typing methods and was observed only within the small number of C. albicans and C. tropicalis isolates tested in this study. CONCLUSION: Typing assays that are able to delineate a certain Candida species may not be used blindly for other species of that genus. Regarding the limited number of strains tested, further validation of the discriminative power of genotyping methods (including in C. tropicalis) should be done.

Genetic characterization of a phospholipase C gene from Candida albicans: presence of homologous sequences in Candida species other than Candida albicans

Phospholipase C (PLC) enzymes are essential in regulating several important cellular functions in eukaryotes, including yeasts. In this study, PCR was used to identify a gene encoding PLC activity in Candida albicans, using oligonucleotide primers complementary to sequences encoding highly conserved amino acid regions within the X domains of previously characterized eukaryotic phospholipase C genes. The nucleotide sequence of the C. albicans gene, CAPLC1 (2997 bp), was determined from a recombinant clone containing C. albicans 132A genomic DNA; it encoded a polypeptide of 1099 amino acids with a predicted molecular mass of 124.6 kDa. The deduced amino acid sequence of this polypeptide (CAPLC1) exhibited many of the features common to previously characterized PLCs, including specific X and Y catalytic domains. The CAPLC1 protein also exhibited several unique features, including a novel stretch of 18-19 amino acid residues within the X domain and an unusually long N-terminus which did not contain a recognizable EF-hand Ca(2+)-binding domain. An overall amino acid homology of more than 27% with PLCs previously characterized from Saccharomyces cerevisiae and Schizosaccharomyces pombe suggested that the CAPLC1 protein is a delta-form of phosphoinositide-specific PLC (PI-PLC). PLC activity was detected in cell-free extracts of both yeast and hyphal forms of C. albicans 132A following 7 h and 24 h growth using the PLC-specific substrate p-nitrophenylphosphorylcholine (p-NPPC). In addition, CAPLC1 mRNA was detected by reverse transcriptase PCR in both yeast and hyphal forms of C. albicans 132A at the same time intervals. Expression of CAPLC1 activity was also detected in extracts of Escherichia coli DH5 alpha harbouring plasmids which contained portions of the CAPLC1 gene lacking sequences encoding part of the N-terminus. Southern hybridization and PCR analyses revealed that all C. albicans and Candida dubliniensis isolates examined possessed sequences homologous to CAPLC1. Sequences related to CAPLC1 were detected in some but not all isolates of Candida tropicalis, Candida glabrata and Candida parapsilosis tested, but not in the isolates of Candida krusei, Candida kefyr, Candida guillermondii and Candida lusitaniae examined. This paper reports the first description of the cloning and sequencing of a PLC gene from a pathogenic yeast species.

Development and verification of fingerprinting probes for Candida glabrata

Since Candida glabrata has emerged as one of the most common Candida pathogens, DNA probes have been developed which fulfil the requirements for effective fingerprinting. Using a screen for complex genomic fragments containing moderately repetitive sequences, seven DNA probes were cloned which generate complex Southern blot hybridization patterns with EcoRI-digested C. glabrata DNA. All of the probes are species-specific and the majority cross-hybridize to varying degrees. The capacity of two of the probes, Cg6 and Cg12, to measure genetic distance between independent isolates is verified by comparing clustering in dendrograms based on similarity coefficients computed between all pairs of 39 independent isolates fingerprinted with Cg6, Cg12 and randomly amplified polymorphic DNA. The capacity of the probes Cg6 and Cg12 to assess microevolution in clonal populations of infecting C. glabrata over time is also demonstrated. These probes can now be used in large computer-assisted epidemiological studies.

Identification of pathogenic yeasts of the imperfect genus Candida by polymerase chain reaction fingerprinting

With the increase in the number of immunocompromised hosts, the number of fungal pathogens has increased markedly. Identification and classification, especially of yeast species and strains, is often difficult when based solely on phenotypic characteristics. Since it became clear that different fungal pathogens require specific treatment strategies, there is a need for simple, rapid and reliable methods to identify fungal isolates. Polymerase chain reaction (PCR) fingerprinting was successfully applied here to identify yeast isolates. Microsatellite [(GTG)5; (GACA)4] and minisatellite [(5'GAGGGTGGCGGTTCT 3'), derived from the core-sequence of the phage M13] specific primers were used as single primers in the PCR to amplify hypervariable interrepeat DNA sequences from over 200 European, American and Australian clinical isolates within the genus Candida. Each species, represented by its type strain, could be identified by a specific multilocus pattern, allowing for the assignment of all the isolates to the appropriate species. Intra-species variation in the multilocus profiles was about 20% compared to inter-species variation, which was up to 80%. Anamorph-teleomorph pairs could be identified by highly homologous PCR fingerprint patterns. PCR fingerprinting was more discriminatory when compared with routinely used biochemical tests (Vitek YBC and API ID 32C). PCR fingerprinting has proven to be a powerful tool for the identification of medically important yeasts. It is rapid, sensitive, reliable, highly reproducible, stable in vitro and in vivo, and applicable to large scale experiments. Potential applications include: yeast taxonomy, epidemiology, environmental surveys, and improvement of the diagnosis of mycotic diseases.

[Application of molecular biological methods for diagnosis and epidemiology of human fungal infections]

For mycological diagnosis molecular methods can be applied to detect the pathogen directly without prior cultivation and to identify species and subspecies. For the detection of infecting agents specific DNA probes and/or the polymerase chain reaction (PCR) are widely used, whereas normally only PCR can provide sufficient sensitivity for the direct detection of pathogens in clinical material. Prospects and limitations of PCR approaches for the detection of pathogenic fungi reported in the literature will be discussed. DNA polymorphisms which are useful for species identification and epidemiological strain typing of medically relevant fungi can be detected by such methods as the analysis of restriction fragment length polymorphisms (RFLP), and Southern hybridization with appropriate DNA probes, and as karyotyping by pulsed field gel electrophoresis (PFGE). These techniques which could be applied successfully to different epidemiological studies are, however, laborious and time consuming. By using a PCR-fingerprinting method which can be performed much simpler polymorphic DNA regions are amplified with different non-specific primers. Distinctive and reproducible sets of amplification products were observed for 26 different Candida and 8 other fungal species. The number and size of the amplification products obtained were characteristic for each species. By comparing species-specific PCR-fingerprints of clinical isolates with those of reference strains, clinical isolates could be identified to the species level even if they could not be identified by conventional typing methods. With all primers, PCR-fingerprints also displayed intraspecies variability. Therefore, PCR-fingerprinting can also be applied for epidemiological strain characterization among medically relevant fungi.

Rapid identification of Candida species by DNA fingerprinting with PCR

DNA polymorphisms in different species and strains of the genus Candida were assessed by amplifying genomic DNA with single nonspecific primers. This PCR method employed an arbitrary primer (the 10-mer AP3), a primer derived from the intergenic spacer regions (T3B), and the microsatellite primers (GTG)5 and (AC)10. Distinctive and reproducible sets of amplification products were observed for 26 different Candida and 8 other fungal species. The numbers and sizes of the amplification products were characteristic for each species. All yeast species tested could be clearly distinguished by their amplification patterns. With all primers, PCR fingerprints also displayed intraspecies variability. However, PCR profiles obtained from different strains of the same species were far more similar than those derived from different Candida species. By comparing species-specific PCR fingerprints of clinical isolates with those of reference strains, clinical isolates could be identified to the species level even if they could not be identified by routine biochemical methods.

Molecular probe for typing strains of Candida albicans

A method for separating strains of Candida albicans into nine possible groups was devised by using a cDNA probe for enolase and Southern blot analysis. Twenty-three isolates of C. albicans were found to be distributed among eight of the groups. Fifteen isolates from a single hospital segregated into four of the groups.

Postoperative infections traced to contamination of an intravenous anesthetic, propofol

BACKGROUND

Between June 1990 and February 1993, the Centers for Disease Control and Prevention conducted investigations at seven hospitals because of unusual outbreaks of bloodstream infections, surgical-site infections, and acute febrile episodes after surgical procedures.

METHODS

We conducted case-control or cohort studies, or both, to identify risk factors. A case patient was defined as any patient who had an organism-specific infection or acute febrile episode after a surgical procedure during the study period in that hospital. The investigations also included reviews of procedures, cultures, and microbiologic studies of infecting, contaminating, and colonizing strains.

RESULTS

Sixty-two case patients were identified, 49 (79 percent) of whom underwent surgery during an epidemic period. Postoperative complications were more frequent during the epidemic period than before it. Only exposure to propofol, a lipid-based anesthetic agent, was significantly associated with the postoperative complications at all seven hospitals. In six of the outbreaks, an etiologic agent (Staphylococcus aureus, Candida albicans, Moraxella osloensis, Enterobacter agglomerans, or Serratia marcescens) was identified, and the same strains were isolated from the case patients. Although cultures of unopened containers of propofol were negative, at two hospitals cultures of propofol from syringes currently in use were positive. At one hospital, the recovered organism was identical to the organism isolated from the case patients. Interviews with and observation of anesthesiology personnel documented a wide variety of lapses in aseptic techniques.

CONCLUSIONS

With the increasing use of lipid-based medications, which support rapid bacterial growth at room temperature, strict aseptic techniques are essential during the handling of these agents to prevent extrinsic contamination and dangerous infectious complications.

PHR1, a pH-regulated gene of Candida albicans, is required for morphogenesis

Candida albicans, like many fungi, exhibits morphological plasticity, a property which may be related to its biological capacity as an opportunistic pathogen of humans. Morphogenesis and alterations in cell shape require integration of many cellular functions and occur in response to environmental signals, most notably pH and temperature in the case of C. albicans. In the course of our studies of differential gene expression associated with dimorphism of C. albicans, we have isolated a gene, designated PHR1, which is regulated in response to the pH of the culture medium. PHR1 expression was repressed at pH values below 5.5 and induced at more alkaline pH. The predicted amino acid sequence of the PHR1 protein was 56% identical to that of the Saccharomyces cerevisiae Ggp1/Gas1 protein, a highly glycosylated cell surface protein attached to the membrane via glycosylphosphatidylinositol. A homozygous null mutant of PHR1 was constructed and found to exhibit a pH-conditional morphological defect. At alkaline pH, the mutant, unlike the parental type, was unable to conduct apical growth of either yeast or hyphal growth forms. This morphological aberration was not associated with defective cytoskeletal polarization or secretion. The results suggest that PHR1 defines a novel function required for apical cell growth and morphogenesis.

Nucleotide sequence analysis of the 5.8S rDNA and adjacent ITS2 region of Candida albicans and related species

We have determined the nucleotide sequence for the DNA encoding the 5.8S RNAs and downstream internal transcribed spacer (ITS2) regions for Candida albicans and the taxonomically related species C. parapsilosis, C. tropicalis, C. glabrata and C. krusei. Phylogenetic analysis of all known fungal 5.8S RNA sequences revealed a close relationship between C. tropicalis and C. parapsilosis, and to a lesser extent C. albicans within the yeast-like fungi. This group can itself be delineated from predominantly filamentous species. The more distal relationships between Candida (Torulopsis) glabrata and C. krusei support previous findings based on small (18S) ribosomal RNA sequence analysis, suggesting a greater degree of evolutionary divergence of these species from the C. albicans group. Among strains of C. albicans we observed conservation of the ITS2 region at the nucleotide level. Conservation was also observed for a more limited number of C. parapsilosis strains. Although the 3' region of the ITS spacer was species specific, sequence homology was observed in the 5' end within the albicans/parapsilosis/tropicalis group. Our findings suggest a rapid approach to species identification through the use of non-conserved regions flanked by highly conserved, functional domains.

Construction of an SfiI macrorestriction map of the Candida albicans genome

The opportunistic fungal pathogen, Candida albicans, is diploid as usually isolated and has no apparent sexual cycle. Genetic analysis has therefore been very difficult. Molecular genetics has yielded important information in the past few years, but it too is hampered by the lack of a good genetic map. Using the well-characterized strain 1006 and strain WO-1, which undergoes the white-opaque phenotypic transition, we have developed a genomic restriction map of C. albicans with the enzyme SfiI. There are approximately 34 SfiI restriction sites in the C. albicans genome. Restriction fragments were separated by pulsed-field electrophoresis and were assigned to chromosomes by hybridization of complete and partial digests with known chromosome-specific probes as well as by digestion of isolated chromosomes. Telomeric fragments were identified by hybridization with a telomere-specific probe (C. Sadhu, M.J. McEachern, E.P. Rustchenko-Bulgac, J. Schmid, D.R. Soll, and J.B. Hicks, J. Bacteriol. 173:842-850, 1991). WO-1 differs from 1006 in that it has undergone three reciprocal chromosomal translocations. Analysis of the translocation products indicates that each translocation has occurred at or near an SfiI site; thus, the SfiI fragments from the two strains are similar or identical. The tendency for translocation to occur at or near SfiI sites may be related to the repeated sequence RPS 1, which contains four such sites and could provide homology for ectopic pairing and crossing over. The genome size of both strains is about 16 to 17 megabases, in good agreement with previous determinations.

Rapid transcriptional autoregulation of a yeast metalloregulatory transcription factor is essential for high-level copper detoxification

Copper detoxification in the yeast Candida glabrata is carried out in large part by a family of metallothionein (MT) genes: a unique MT-I gene, a tandemly amplified MT-IIa gene, and a single unlinked MT-IIb gene. In response to elevated environmental copper levels, members of this MT gene family are transcriptionally activated by a copper-dependent, sequence-specific DNA-binding transcription factor, AMT1. AMT1 shares several structural and functional features with the Saccharomyces cerevisiae copper metalloregulatory transcription factor ACE1, which is constitutively expressed and poised for rapid transcriptional responses to the toxic metal copper. In this paper, we demonstrate that AMT1 is subject to positive transcriptional autoregulation, which is exerted through binding of copper-activated AMT1 to a single copper responsive element in the AMT1 promoter. A nonautoregulatory amt1 mutant displayed a marked decrease in both copper tolerance and expression of the MT-II genes, which are critical for high-level copper detoxification in Candida glabrata. Kinetic analysis demonstrated the remarkably rapid AMT1 mRNA accumulation in the presence of copper, which is followed by increased expression of the metallothionein gene products. These results demonstrate that AMT1-positive autoregulation plays a critical role in metal detoxification and suggest that the rapid autoactivation of the AMT1 metalloregulatory transcription factor biosynthesis is essential for C. glabrata to quickly build up a cellular defense line to protect cells upon exposure to high environmental copper levels.

Identification of clinical strains of Candida albicans by DNA fingerprinting with the polymerase chain reaction

DNA polymorphisms generated by the polymerase chain reaction (PCR) were used to differentiate clinical isolates of Candida. This PCR method employed single primers that were originally designed as hybridization probes for DNA fingerprinting experiments to probe minisatellite and microsatellite DNA sequences. To evaluate this procedure, 35 isolates from 20 patients in several intensive care units and 12 isolates obtained from the oral cavities of healthy dental patients were fingerprinted. The PCR-fingerprint patterns of isolates of Candida albicans from the immunocompromised patients revealed fewer differences than isolates from the dental service. Multiple isolates from different body sites of the same patients revealed that patients may harbour isolates of Candida with the same or different PCR-fingerprints. Since this method is generally simpler and faster than established methods of biotyping medically important yeasts, PCR-fingerprinting may prove useful for the surveying of large numbers of pathogens for epidemiological studies.

Genomic heterogeneity in the yeast Candida parapsilosis

Candida parapsilosis shows a wide intraspecies variation in chromosome/homolog size distribution. As a prerequisite for delineating modes of transmission, we have undertaken an analysis of genetic variation at different levels. In the present study we have observed that a majority of isolates display similar electrophoretic karyotype patterns consistent for the species, with variations in the smaller group of chromosomes. In two strains we observed phenotypic "switching"; one of these also exhibited a mixed karyotypic subpopulation. In contrast, a few isolates displayed a greater degree of chromosome/homolog size variation. We also observed, through randomly amplified polymorphic DNA (RAPD) analysis, results consistent with those of pulsed-field electrophoresis. Isolates displaying a high degree of chromosome/homolog variation also displayed a high degree of variation in genomic "fingerprints". Polymorphisms, although present, were much reduced in the majority of isolates. These parallel observations suggest a common underlying mechanism. Our results are consistent with the hypothesis that chromosome-sized variations in C. parapsilosis are due to random genetic events. A similar mechanism has been hypothesized for the taxonomically related yeast Candida albicans.

Rapid, polymerase chain reaction-based identification assays for Candida species

Polymerase chain reaction (PCR) amplification of specific regions in the genomes of a variety of lower eukaryotes permits rapid identification of these microorganisms. First, on the basis of the presence of both constant and variable regions in the small subunit (ssu) rRNA, a nested PCR for direct identification of various Candida species can be designed. Amplification of the entire ssu rRNA gene and subsequent reamplification of variable sequences within the V4 domains of these PCR products were combined with direct sequencing. Restriction enzyme maps were made, and species-specific oligonucleotides for hybridization analysis were selected. Unequivocal discrimination of four of the major human pathogenic yeasts (Candida albicans, Candida glabrata, Candida tropicalis, and Candida krusei) is possible if a combination of these techniques is used. Second, by using oligonucleotides aimed at repeated sequences which occur at dispersed positions in the genomes of all eukaryotes, species-specific DNA fingerprints could be generated. This interrepeat PCR using genomic DNA as template proved to be an effective tool in Candida species typing. Both techniques described here can be extrapolated to the high-speed diagnostics of numerous other prokaryotic and eukaryotic pathogens.

Detection and differentiation of fungi in clinical specimens using polymerase chain reaction (PCR) amplification and restriction enzyme analysis

We have developed a method for processing and detecting fungi in clinical specimens using the polymerase chain reaction (PCR) methodology. This PCR amplification of a segment of a ribosomal DNA gene results in a 310 bp product. The gene sequences used as amplimers have been highly conserved throughout the fungal kingdom and positive PCR results have been obtained for all genera and species of fungi tested (n = 42). Neither human nor a variety of pathogenic bacteria (n = 24) gave an amplified product. This PCR method can detect as few as 15 cells of Candida albicans in clinical specimens following a simple processing procedure. The sensitivity of the PCR for detecting other fungi remains to be determined. Analysis of the 310 bp amplified product, following digestion with the restriction enzyme HaeIII, can be used to further characterize the identity of the fungus involved into the following five groups: (i) Candida species and closely related yeasts; (ii) Cryptococci and Trichosporon species; (iii) Aspergilli and clinically related septate molds; (iv) the Zygomycetes; and (v) the dimorphic fungi.

A method for taxonomic determination of Candida albicans with DNA probes

Determination of Candida species represents an important problem derived from the clinical implications of the species belonging to this genus. DNA probes have already been used for the epidemiology of Candida albicans, as well as for taxonomic analysis of Candida and other genera, although these probes are based on non-species-specific DNA sequences. In this work we carried out a 48-h assay, allowing the identification of C. albicans from clinical isolates, using DNA probes based on C. albicans LEU2 and URA3 genes. Another probe related to C. albicans SEC18 gene was shown not to be C. albicans specific.

Genotypic identification and characterization of species and strains within the genus Candida by using random amplified polymorphic DNA

Random amplified polymorphic DNA (RAPD) was used to better characterize the genotypic relatedness among medically important Candida species. By using short oligomer primers (10-mers) with arbitrarily chosen sequences in the polymerase chain reaction, distinctive and reproducible sets of polymerase chain reaction products were observed for isolates of C. albicans, C. lusitaniae, C. tropicalis, and Torulopsis (Candida) glabrata. The RAPD analysis differentiated a physiologically homogeneous panel of C. parapsilosis into three distinct groups and showed genetic diversity within C. haemulonii. Intraspecies DNA-length polymorphisms were seen for RAPD profiles derived from different isolates of each species. Analysis of RAPDs from a panel of C. albicans, which included 16 laboratory derivatives of two reference strains, showed that the profiles of unrelated strains differed and that the derivatives of each reference strain were identifiable. Minor differences in the RAPD profiles, suggestive of mutations that had occurred during the long-term maintenance of the strains, were detected. Because of its ease and reliability, RAPD analysis should be useful in providing genotypic characters for taxonomic descriptions, for confirming the identities of stock isolates, for typing Candida species in epidemiologic investigations, and for use in the rapid identification of pathogenic fungi.

A temperature-regulated, retrotransposon-like element from Candida albicans

A repetitive element was isolated from the genome of Candida albicans. This repetitive element, which we designated alpha, was localized to a 500-bp fragment of genomic DNA. The alpha element was dispersed in the genome and varied in copy number and genomic location in the strains examined. Analyses of various loci containing the alpha element identified a locus containing a composite element. This composite element consisted of two direct repeats of the alpha element separated by approximately 5.5 kb of DNA, a structural arrangement similar to that of retrovirus-like transposable elements. The flanking alpha elements of the composite structure were 388 bp in length and were identical in sequence. They were bounded by the nucleotides 5'-TG. ... CA-3', which were part of a delimiting inverted repeat, a feature conserved in the long terminal repeats of retroviruses and retrovirus-like elements. As in retrovirus-like elements, the entire composite element, including the alpha elements, was transcribed into an approximately unit-length mRNA. The expression of this transcript was greatly increased when cells were grown at 25 versus 37 degrees C. As has been found in many retrotransposons, the composite element was flanked by a 5-bp duplication and varied in both copy number and genomic location in various strains. We conclude that the composite element is a retrotransposon-like element, and we have designated this element Tca1. We suggest that Tca1 may be relevant to the genomic evolution of C. albicans and the pathogenic potential of the organism.

Isolation, characterization, and sequencing of Candida albicans repetitive element 2

A 1059-bp Sau3A fragment, designated Candida albicans repetitive element 2 (CARE-2), was isolated from the genome of the pathogenic yeast, C. albicans. CARE-2 DNA was detected on several C. albicans chromosomes separated by transverse alternating-field electrophoresis. A high degree of interstrain variation in the pattern of hybridizing bands were observed by Southern blot analysis, with a minimum of 10-14 copies of CARE-2 per strain. A low frequency of new CARE-2 polymorphisms was observed over time for three strains grown at 25 degrees C or 37 degrees C. No new CARE-2 polymorphisms were observed from two naturally occurring switch phenotypes. To localize repeated DNA, oligodeoxyribonucleotide probes, each representing a different region of CARE-2, were hybridized to genomic blots. A lower number of copies were observed 5' and 3' to a 600-bp region of CARE-2. Nucleotide (nt) sequence analysis of CARE-2 DNA shows the element is characterized by six perfect direct repeats 6 bp in length and shows no significant DNA similarity with any known nt sequence.

Isolation and characterization of a species-specific DNA fragment for detection of Candida albicans by polymerase chain reaction

A 2-kbp DNA fragment, EO3, that was present in multiple copies in the Candida albicans genome was isolated for use in developing a detection method for C. albicans by polymerase chain reaction (PCR). Dot blot hybridization revealed that EO3 was specific for the 40 isolates of C. albicans serotypes A and B used. Using a set of primers (20-mer each) derived from the nucleotide sequence of EO3, we performed specific amplification of a 1.8-kbp DNA fragment within EO3 by PCR. All 40 isolates belonging to C. albicans serotypes A and B contained amplifiable 1.8-bkp fragments, although the DNA of the amplified products exhibited small variations in size, yielding three different fragment groups. Southern blot hybridization probed with EO3 showed that these 1.8-kbp fragments were derived from the EO3 region. Conversely, the 1.8-kbp fragment was not amplified from 38 isolates belonging to seven other medically important Candida species or from isolates of Cryptococcus neoformans, Saccharomyces cerevisiae, various bacteria, and a human cell line. The detection limit of the PCR assay for C. albicans with the EO3 fragment was shown to be approximately 2 to 10 cells and 100 cells in saline and human urine, respectively, by ethidium bromide staining and 2 and 10 cells, respectively, by Southern blot analysis. In addition, EO3 was assumed to originate from mitochondrial DNA on the basis of the results of its characterizations. These results indicate that the PCR system using the 1.8-kbp fragment as a target is a reliable method for identifying C. albicans isolates, thereby suggesting its potentials for specific and sensitive detection of C. albicans in samples from patients with candidiasis.

Gene isolation by complementation in Candida albicans and applications to physical and genetic mapping

We have isolated three genes, ARG57, SER57, and LYS1, on the basis of their function in Candida albicans. A C. albicans transformation vector containing the C. albicans URA3 gene, a Candida ARS sequence, and a portion of the Saccharomyces cerevisiae 2 microns circle containing the replication origin was constructed. Clones from genomic libraries in this vector were isolated by direct complementation of the auxotrophies in strain 1006 (arg57 ser57 lys1 ura3 MPA1). Transformants typically contain two to four plasmids in a mixed tandem multimer. A scheme to resolve mixed multimers into monomers in vivo by transformation of S. cerevisiae with Candida transformant DNA selecting Ura+ transformants was devised. Monomeric plasmids were then isolated by transformation of Escherichia coli with the S. cerevisiae transformant DNA. These were retested by transformation of strain 1006 to identify the specific plasmid that complemented the auxotrophy. The chromosomal locations of the genes were determined by hybridization to C. albicans chromosomes separated on contour-clamped homogenous electric field gels. We used these locations to assess the stability of individual C. albicans chromosomes in parasexual genetic analysis. The Lys(+)-complementing clone was shown to be LYS1 by complementation of S. cerevisiae lys1 mutants. These cloned genes help to align the Candida physical and genetic maps and provide additional markers for the transformation system.

The use of molecular techniques for epidemiologic typing of Candida species

The availability of an epidemiologic typing system for Candida species that is sensitive, rapid, inexpensive, and easy to perform would clearly be an advantage to the mycologist, microbiologist, and epidemiologist in the ongoing struggle to understand the epidemiology and pathogenesis of candidiasis. This is particularly true given the increasing prominence of organisms such as C. albicans and C. tropicalis which are ubiquitous members of the normal flora yet are also important causes of nosocomial bloodstream infection. Unfortunately, the ideal epidemiologic typing system does not yet exist. Current data suggest that the molecular typing methods of restriction endonuclease digestion of genomic DNA with ethidium bromide staining (DEtBr typing) and electrophoretic karyotyping using pulsed-field electrophoresis offer rapid, simple, and sensitive means of discriminating strains of Candida species. These methods appear at present to be the most practical typing methods for both large- and small-scale epidemiologic studies. Other typing methods using specific DNA probes provide a powerful means of identifying strains and will undoubtedly be applied more broadly in the future. Thus far, studies employing molecular typing methods have documented that (1) most patients are colonized by one strain of Candida species, (2) isolates of Candida species recovered from blood or deep tissue sites are generally identical to those obtained from colonization sites before infection developed, and (3) nosocomial transmission of a single strain of C. albicans may occur, particularly in an intensive care unit setting. Given the limitations of the available typing methods and the complex nature of the patients at risk for candidiasis, both the epidemiologist and laboratory scientist must use these methods with clear epidemiologic objectives in mind. Whenever possible, all organisms to be typed should be typed by the same person on the same day, and typing should always include unrelated as well as epidemiologically related isolates. Additional studies, based upon sound epidemiologic principles, will be necessary to clarify the role of the various molecular typing methods as epidemiologic markers of Candida species and to further our understanding of the epidemiology and pathogenesis of candidiasis.

Use of rDNA restriction fragment length polymorphisms to differentiate strains of Candida albicans in women with vulvovaginal candidiasis

Epidemiologic studies in women with recurrent Candida vaginitis have been hampered in the past by the lack of a reproducible typing system. Several molecular probes have now been developed that have the ability to differentiate strains of Candida albicans and give reproducible results. In this investigation, 24 women with Candida vaginitis were studied in a longitudinal fashion for 30 days following short-course antifungal therapy. Seven women with either recurrent vaginitis or with multiple culture-positive sites with C. albicans were included in an epidemiological study. A total of 18 isolates of C. albicans (12 vaginal and six rectal) were typed utilizing restriction fragment length polymorphisms of rDNA. This technique was able to differentiate five different strains of C. albicans. Our epidemiologic study revealed that vaginal and rectal strains recovered from the same women were usually different. None of our patients had a similar vaginal and rectal strain prior to treatment, and only one patient had the same strain isolated from both the rectum and the vagina at the time of recurrence. On the other hand, we found that the same strain of C. albicans was initially and later recovered from the vagina in four of five women who failed treatment or developed recurrent vaginitis. These results suggest that recurrent episodes of C. albicans vaginitis, following short-course antifungal therapy, are often due to relapse of the original infecting strain and not due to autoinoculation from the rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of CARE-1: Candida albicans repetitive element-1

A middle repetitive DNA element, Candida albicans repetitive element-1 (CARE-1) has been isolated from the pathogenic yeast C. albicans. CARE-1 appears to be species-specific and constitutes approx. 0.045% of total C. albicans DNA, or a reiteration frequency of about two to twelve copies per haploid genome. The CARE-1 element has been detected on several C. albicans chromosomes separated by field-inversion gel electrophoresis, suggesting that the element is dispersed. Interstrain variation was observed in the number and distribution of hybridizing bands. The element is well conserved, since no nucleotide (nt) heterogeneity was observed when the sequences of two CARE-1 family members isolated from two different chromosomes (A and B) of C. albicans were compared. CARE-1 possesses 467 bp and is characterized by several stretches of A's and T's, short direct repeats and shows no significant homology to any known nt sequence.

Chromosomal rearrangement in Candida stellatoidea results in a positive effect on phenotype

When type I Candida stellatoidea is plated onto sucrose agar at levels in excess of 10(8) cells, some isolates spontaneously form sucrose-positive colonies. These isolates do not display typical type I phenotypes but instead exhibit phenotypes intermediate between type I C. stellatoidea and C. albicans. Also, this phenotypic change only occurs in conjunction with a chromosomal rearrangement. These rearrangements have been studied in a strain naturally marked for methionine auxotrophy. Chromosome-size DNA bands separated by pulsed-field gel electrophoresis were probed with genes cloned from C. albicans. The hybridization pattern indicated that the genes on several chromosomes underwent extensive rearrangement.

Molecular probe for identification of Trichomonas vaginalis DNA

Trichomoniasis is one of the most widespread sexually transmitted diseases in the world. Diagnosis can be achieved by several methods, such as direct microscopic observation of vaginal discharge, cell culture, and immunological techniques. A 2.3-kb Trichomonas vaginalis DNA fragment present in strains from diverse geographic areas was cloned and used as a probe to detect T. vaginalis DNA in vaginal discharge by a dot blot hybridization technique. This probe was specific for T. vaginalis DNA. It recognized strains from two regions in Italy (Sardinia, Piemonte) and from Mozambique (Africa). In addition, our probe did not cross-react with bacterial (Escherichia coli, Enterococcus spp., group B streptococci, Gardnerella vaginalis, Neisseria gonorrhoeae, Chlamydia trachomatis, and Lactobacillus spp.), viral (herpes simplex virus type 2), fungal (Candida albicans), protozoan (Entamoeba histolytica, Giardia lamblia, Plasmodium falciparum, Leishmania major, and Leishmania infantum), or human nucleic acids. The probe reacted with Pentatrichomonas hominis and Trichomonas foetus. The limit signal recognized by our probe corresponded to the DNA of 200 T. vaginalis isolates. The 2.3-kb probe was used in a clinical analysis of 98 samples. Of these, 20 samples were found to be positive both with the probe and by cell culture, and only 14 of these were positive by a standard wet mount method.

A critical review of typing methods for Candida albicans and their applications

During the 1980s, a large number of typing methods for the strain differentiation of Candida albicans were described in the literature. Although these methods have been based on a variety of physiological and genetic markers, none is ideal. This review discusses the characteristics of an ideal typing method in terms of its typability, reproducibility, and discriminatory power. Ways of determining these characteristics are presented so that the available typing methods for Candida albicans can be objectively compared. Available typing methods for C. albicans include serotyping, morphotyping, resistotyping, biotyping, and killer yeast typing. Electrophoretic methods include immunoblotting, isoenzyme analysis, analysis of DNA restriction fragment length polymorphism, karyotyping, and the use of DNA probes. The application of these methods to epidemiological research, the investigation of outbreaks of disease, and the study of virulence is described. The potential impact of the phenomenon of phenotypic switching on the reproducibility of these typing methods is discussed. It is concluded that many of the available typing methods have not been adequately assessed by their developers and that several have only poor discriminatory power or reproducibility.

Characterization of the sequence of colonization and nosocomial candidemia using DNA fingerprinting and a DNA probe

The objective of this hospital-based study was to determine the relationship between colonizing and infecting strains of Candida species and Torulopsis glabrata. Surveillance cultures from high-risk patients were paired with subsequent bloodstream isolates. Organisms were typed by using restriction endonuclease digestion of chromosomal DNA with BstNI and EcoRI, followed by Southern hybridization with a DNA probe (pBD4) derived from Saccharomyces cerevisiae. Sixteen patients for whom documented colonization preceded documented bloodstream infection were identified. The mean time between obtainment of surveillance isolates and obtainment of bloodstream isolates was 8 days, with a range of 1 to 423 days. For 15 (94%) of 16 patients, the DNA fingerprint pattern (using BstNI) of the surveillance isolate was identical to that of the bloodstream isolate. Isolates from 13 (81%) of 16 patients were unique to those patients. Typing by Southern hybridization with the pBD4 probe was less discriminating. We conclude that for a well-defined subset of hospitalized patients who were colonized by Candida species before developing nosocomial candidemia, the colonizing and infecting strains were identical, suggesting endogenous acquisition of infection. Restriction endonuclease digestion of chromosomal DNA was shown to be a discriminating and reproducible typing method for Candida species and T. glabrata.

Candida albicans strain delineation

Candida albicans is a major opportunistic pathogen causing a wide spectrum of disease in human beings. Methods for strain delineation of this species to assess or predict virulence or to conduct epidemiologic or pathogenetic investigations have been developed. Although factors associated with virulence have been identified, there is no rapid system to quantitate them in a clinical laboratory. Therefore, many typing methods are based on variable phenotypic characteristics within this species including morphotyping, serotyping, antibiogram, resistogram typing, biotyping, biotyping based on commercial carbon assimilation patterns, enzyme profiles, sensitivity to yeast killer toxins, and typing based on protein variability. Phenotypically defined strains generally do not correlate with the pathogenic potential of a strain with the exception of morphotyping. However, these methods can be useful in epidemiologic investigations; for example, they have revealed that most individuals harbor one strain and that infections are frequently due to an endogenous strain. Problems with these methods usually relate to their discriminatory power. When this is maximized, reproducibility (especially between laboratories) suffers. Recently, methods based on differences in DNA structure (genotyping) for strain delineation have been developed, including electrophoretic karyotyping and restriction enzyme fragment length polymorphisms. The development of a computer-assisted data bank and analysis for these genotypic strain delineators will open investigations into the pathogenesis of this infection and permit epidemiologic studies previously not possible with this important human pathogen.

Genetics of Candida albicans

Candida albicans is among the most common fungal pathogens. Infections caused by C. albicans and other Candida species can be life threatening in individuals with impaired immune function. Genetic analysis of C. albicans pathogenesis is complicated by the diploid nature of the species and the absence of a known sexual cycle. Through a combination of parasexual techniques and molecular approaches, an effective genetic system has been developed. The close relationship of C. albicans to the more extensively studied Saccharomyces cerevisiae has been of great utility in the isolation of Candida genes and development of the C. albicans DNA transformation system. Molecular methods have been used for clarification of taxonomic relationships and more precise epidemiologic investigations. Analysis of the physical and genetic maps of C. albicans and the closely related Candida stellatoidea has provided much information on the highly fluid nature of the Candida genome. The genetic system is seeing increased application to biological questions such as drug resistance, virulence determinants, and the phenomenon of phenotypic variation. Although most molecular analysis to data has been with C. albicans, the same methodologies are proving highly effective with other Candida species.

Molecular genetics of pathogenic fungi: some recent developments and perspectives

The diagnosis and the treatment of fungal diseases remains problematic in many cases. Difficulties in diagnosis are due (1) to the ubiquitous presence of fungal pathogens that may lead to false positive test results and (2) to difficulties in the evaluation of the aetiological significance of these pathogens. The relatively small number of effective antifungal agents reflects to a large extent on the fact that many aspects of fungal physiology and virulence are not well understood. The methods of molecular genetics provide effective tools for the diagnosis of mycoses and may also contribute to the identification of new targets for antifungals by genetic analyses of fungal virulence. During the last 3 years molecular genetic methods have been developed for the asexual pathogen Candida albicans that may be used for strain identification. This success indicates a general use of molecular genetics for the analysis of fungal pathogenesis.

Genomic structure of Candida stellatoidea: extra chromosomes and gene duplication

Candida albicans and Candida stellatoidea are two closely related imperfect yeasts. Some isolates characterized as C. stellatoidea are in fact C. albicans, while others differ with respect to virulence and to karyotype, containing extra small chromosomes. Experiments in this study allowed us to infer that a typical C. stellatoidea isolate, Y2360, has 12 chromosomes rather than the 7 previously shown for C. albicans. The majority of cloned sequences tested hybridized to analogous chromosomes in C. albicans and in C. stellatoidea, although there were exceptions, and a repeated element isolated as specific for C. albicans hybridized to most of the chromosomes of C. stellatoidea. Several genes tested hybridized to one of the smaller, C. stellatoidea-specific chromosomes as well as to a larger one. The arrangement of restriction enzyme sites around the gene was the same in both the large and small chromosomes. For ADE2 and LYS2, the arrangements were identical to those of a typical C. albicans strain, FC18, suggesting a high degree of sequence conservation between the two species. Spheroplast fusion and segregation experiments showed that the ADE2 genes on both the large and small chromosomes of C. stellatoidea are active, implying that the organism is functionally at least triploid for this gene and probably for any others duplicated on the smaller chromosomes.

Current trends in Candida albicans research

Candida albicans is an opportunistic pathogen of human beings and other mammals. Two other features, besides its pathogenicity, have made it a popular organism of study. It exists in different cellular forms and can change from one form to another, depending on growth conditions. Thus, it is being used as a model system to study cellular differentiation. It can also heritably and reversibly switch its cellular and colony morphologies. The yeast is diploid and lacks a sexual cycle. Thus, it has not been possible to apply the powerful methods of genetic analysis to understand morphogenesis or pathogenesis. Few clinical isolates are haploid, but they do not form hyphae and are not yet well characterized. Recombinant DNA techniques are increasingly being applied to C. albicans to solve many of the unanswered questions of morphogenesis and pathogenesis. Genetic transformation and gene-disruption techniques were recently developed for the yeast. Thus it is possible to study the role of any cloned gene through directed mutagenesis. However, the difficulty is to clone the putative genes involved in morphogenesis or pathogenesis. Candida albicans exists in four different cellular forms, namely blastospores, pseudohyphae, hyphae and chlamydospores. Blastospore-to-hypha conversion is well studied. A variety of conditions can induce this transition. It is not clear how cells sense such varied conditions and respond appropriately. In other systems where differentiation is well understood, regulatory genes which control differentiation have been uncovered. These genes cause differential expression of other genes, and ultimately differentiated phenotypes. Thus, it is likely that differential gene expression is involved in the bud-to-hypha transition in C. albicans. Certain proteins are expressed exclusively on the cell surface of hyphae. It should be possible to clone genes coding for these proteins. A study of the expression of these genes might allow us to identify the regulatory gene which determines differentiation. Another approach to understanding morphogenesis is to study how the difference in the shape of buds and hyphae is generated. This difference appears to be due to the differential activity of apical and general growth zones, which determine growth of the cell wall. Activity of these growth zones is apparently determined by actin localization. It remains a possibility that conditions which induce hyphae formation may directly affect actin localization or cell-wall growth zones and cause differences in cell shape. Candida albicans can also heritably switch its cellular phenotype. This has come to light from a study of colony-morphology switching. Some strains can switch their colony morphology, both heritably and reversibly.(ABSTRACT TRUNCATED AT 400 WORDS)

Isoenzyme biotypes of Candida species

Isoenzyme profiles were obtained following polyacrylamide gel electrophoresis of crude extracts of Candida albicans and C. tropicalis. The two species were separated by distinct isoenzyme patterns. Within each species, variations were found for several isoenzymes. This allowed the development of a method for biotyping these fungi. Isoenzyme patterns of the sucrose-negative variants "C. stellatoidea" and "C. paratropicalis Baker, Salkin, Pincus, and D'Amato" were obtained and subjected to cluster analysis. This procedure failed to place the variants into clusters that were clearly distinct from the conventional sucrose-positive strains. All sucrose-negative strains were found to have alpha-glucosidase activity. There was an almost complete lack of heterogeneity in the isoenzyme patterns of 11 C. stellatoidea type I strains.

Electrophoretic karyotypes of Torulopsis glabrata

Chromosome-sized DNA molecules of clinical isolates of Torulopsis glabrata were resolved by a pulsed-field electrophoretic method, contour-clamped homogeneous electric fields. With the conditions established in this study, 8 to 12 bands (ranging from 445 to 3,000 kilobases) were observed. There were differences in the intensities and migrations of bands, consistent with T. glabrata being either haploid or diploid. A total of 22 distinctive electrophoretic patterns were noted among single isolates of T. glabrata recovered from 33 patients. When strains were delineated by an electrophoretic pattern, individuals usually harbored only one strain.