Modifications of a Candida albicans biotyping system

Association of genotypes with infection types and antifungal susceptibilities in Candida albicans as revealed by recent molecular typing strategies

Candida albicans is a commensal microorganism in the mucosa of healthy individuals, but is also the most common opportunistic fungal pathogen of humans. It causes from benign infections such as oral and vaginal candidiasis to fatal, systematic diseases in immunocompromised or critically ill patients. In addition to improved therapy, the rapid and accurate identification of the disease-causing strains is crucial for diagnosis, clinical treatment and epidemiological studies of candidiasis. A variety of methods for strain typing of C. albicans have been developed. The most commonly used methods with the focus on recently developed molecular typing or DNA-fingerprinting strategies and the recent findings in the association of specific and genetically similar genotypes with certain infection types and the correlation between azole susceptibilities and certain genotypes of C. albicans from China are reviewed.

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.

Candida albicans: a review of its history, taxonomy, epidemiology, virulence attributes, and methods of strain differentiation

The dimorphic yeast Candida albicans has been recognized as an increasingly important human pathogen particularly in immunocompromised hosts because of advanced age, infection or immunosuppressive therapy. This review outlines the history, taxonomy and epidemiology of this medically important yeast as well as discussing some of characteristics which are purported to be related to its virulence. Methods utilized for strain differentiation in the study of the epidemiologic relationship of members of this species are discussed.

Comparison of seven phenotyping methods for Candida albicans

Seven different phenotyping methods for strain differentiation of Candida albicans (auxonotyping, enzymotyping, resistotyping, Phongpaichit's morphotyping, Hunter's morphotyping and Odds and Abbott's biotyping method-1980 and 1983 versions) were compared on a single population of 94 strains. 77.6% of the strains belonged to auxonotyping 1, 59.6% to enzymotyping A, 34% to resistotyping B and 30.8% to BC, 40.4% to Phongpaichit's morphotyping 000,000 and 40.4% to Hunter's morphotyping 'No fringe/Smooth surface'. Using biotyping systems (1980 and 1983 versions), the most frequent biotypes were 145 (29.8%) and 147 (31.9%) respectively. The Discriminatory Index of Hunter and Gaston was employed to carry out comparisons among the different systems. The best discriminatory results, although far from ideal, were found using Phongpaichit's morphotyping (DI = 0.827) and Odds and Abbott's method (DI = 0.815 and 0.831--1980 and 1983 versions). A good discriminatory result was also found using Hunter's morphotyping method together with the biotyping of Odds and Abbott (1983 version). These approximated the ideal (DI = 0.950) and showed minimal difficulty in interpretation. The proposed combined method revealed high discrimination among the vulvovaginal strains, and suggested the absence of transmissible pathogenic strains.

Chromosomal alterations of Candida albicans are associated with the gain and loss of assimilating functions

We have demonstrated that a normal laboratory strain of Candida albicans spontaneously produces mutants which acquire the ability to assimilate certain carbon sources that are not utilized by the parental strain. The examination of mutants acquiring the ability to utilize either sorbose or D-arabinose revealed a few additional phenotypic changes, including the gain and loss of the capacity to assimilate other carbon sources. The change of assimilation patterns resembled the polymorphic variation of assimilation patterns found among different wild-type strains of C. albicans. Most importantly, these sorbose- and D-arabinose-positive mutants were associated with chromosomal rearrangements, with each class of positive mutants having alterations of specific chromosomes. These findings demonstrated for the first time that chromosomal alterations in C. albicans are involved in genetic variation of fundamental functions of this asexual microorganism.

Comparison of restriction enzyme analysis versus pulsed-field gradient gel electrophoresis as a typing system for Torulopsis glabrata and Candida species other than C. albicans

Candida species have recently emerged as important nosocomial pathogens. Because of the lack of a reliable system for detecting differences within the same species, little is known about the epidemiology of infection with Candida species. We describe a typing system for Torulopsis glabrata and the non-C. albicans Candida species that uses contour-clamped homogeneous electric field electrophoresis (CHEF), a version of pulsed-field gradient gel electrophoresis, and compared it with restriction enzyme analysis (REA) of genomic DNA. One hundred seventeen clinical isolates from 40 patients were evaluated. CHEF and REA were performed on each of the isolates, and the results of the two procedures were compared. The REA procedure revealed 8 different types of Candida lusitaniae, 20 of Torulopsis glabrata, 5 of Candida tropicalis, 3 of Candida parapsilosis, and 7 of Candida kefyr, whereas the CHEF method revealed 14 different types of C. lusitaniae, 16 of T. glabrata, 10 of C. tropicalis, 10 of C. parapsilosis, and 7 of C. kefyr. The CHEF technique yielded unique patterns of electrophoretic karyotypes that could be used to distinguish intraspecies variations. When compared with REA, CHEF demonstrated greater sensitivity in recognizing subtle strain-to-strain variations in most isolates and will be a useful epidemiologic tool for studying non-C. albicans Candida species and T. glabrata.

Comparison of molecular typing methods for Candida albicans

Four molecular approaches to determining the types of Candida albicans strains were compared. The strains used were those whose repeated DNA (ribosomal and mitochondrial) EcoRI restriction fragment length polymorphisms (RFLP) were determined by Stevens et al. (D. A. Stevens, F. C. Odds, and S. Scherer, Rev. Infect. Dis. 12:258-266, 1990). Scherer and Stevens (S. Scherer and D. A. Stevens, Proc. Natl. Acad. Sci. USA 85:1452-1456, 1988) used the same strains to examine the Southern blots of genomic EcoRI digests probed with the repeated sequence 27A. The results of these investigators were compared with determinations of RFLPs generated from repeated DNA by the enzyme HinfI and examination of the karyotypes of strains under two sets of conditions, one for the smaller chromosomes and one for the larger ones. Analysis of RFLPs of repeated DNA is most convenient but shows the lowest degree of resolution. Use of the repeated sequence and use of karyotype have very high resolution, but the former method is more convenient than the latter. HinfI digestion is more sensitive than EcoRI digestion but equally convenient. By using all four methods, separate types were identified for 18 of the 20 strains examined.

Identification of oral yeasts by polyacrylamide gel electrophoresis

Protein profiles of sonicated cells for 9 species of yeast isolated from oral samples were obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and visualized with a silver stain. The profiles obtained on 12% acrylamide gels were distinct, and characteristic for 6 species of Candida, and Torulopsis glabrata, Yarrowia lipolytica, and Saccharomyces cerevisiae. Using this method, 79 fresh isolates of yeasts from saliva samples were identified; 58 as Candida albicans, 9 as Candida parapsilosis, 1 as Candida tropicalis, and 11 as T. glabrata. SDS-PAGE offers a rapid, convenient alternative or adjunct to yeast identification systems based on carbohydrate assimilation tests.

Comparison of restriction enzyme analysis and pulsed-field gradient gel electrophoresis as typing systems for Candida albicans

Candida species are an important cause of infection in immunocompromised hosts and the leading cause of nosocomial fungal infections. Study of the epidemiology of Candida infection has been difficult because of lack of a reliable typing system. We describe a typing system utilizing contour-clamped homogeneous electric fields (CHEF), which is a modified version of pulsed-field gradient gel electrophoresis, and compared it with restriction enzyme analysis (REA) of genomic DNA. The study was done with 35 Candida albicans clinical isolates from separate patients. CHEF and REA were performed on each isolate, and the patterns were compared. The REA procedure revealed 17 strain types while the CHEF procedure was able to distinguish 23 strain types of C. albicans. The CHEF technique yields unique patterns of chromosomal bands that can be used to distinguish clinical isolates and demonstrates greater sensitivity than REA.

The use of biotyping and DNA fingerprinting in typing Candida albicans from hospitalized patients

The application of typing procedures for the purpose of strain differentiation among isolates of Candida albicans obtained from hospitalized patients has been limited. We have applied biotyping and DNA restriction fragment analysis (DNA fingerprinting) by using EcoRI to the study of C. albicans isolates obtained from hospitalized patients. A total of 68 isolates from 15 patients were studied. Thirteen subtypes were identified by biotyping, 8 by DNA fingerprinting, and 21 by a combination of the biotyping and DNA fingerprinting approaches (composite subtype). Both techniques were highly reproducible. In examining the strain variation among isolates obtained from multiple anatomic sites over time, we found that similar, if not identical, strains were recovered from the oropharynx, urine, stool, and blood in a given patient, and these strains persisted. Only rarely did two patients share the same composite subtype suggesting sporadic nosocomial transmission. The combination of biotyping and DNA fingerprinting improved strain discrimination compared to either method alone. Further investigation with these and other epidemiologic typing methods will be necessary to enhance the understanding of the epidemiology and pathogenesis of candidiasis in hospitalized patients.

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.

The process of microbial translocation

The process of microbial translocation was studied using Candida albicans, Escherichia coli, or endotoxin instilled into Thiry-Vella loops of thermally injured guinea pigs and rats. Translocation of C. albicans occurred by direct penetration of enterocytes by a unique process different from classical phagocytosis. Translocation between enterocytes was not observed. Internalization was associated with a disturbance of the plasma membrane and brush border, but most internalized organisms were not surrounded by a plasma membrane. Passage of the candida into the lamina propria appeared to be associated with disruption of the basal membrane with extrusion of cytoplasm of the cell and candida. Organisms in the lamina propria were commonly phagocytized by macrophages but also were found free in lymphatics and blood vessels. Translocation of E. coli and endotoxin also occurred directly through enterocytes rather than between them, but translocated endotoxin diffused through the lamina propria and muscular wall of the bowel wall by passing between rather than through the myocytes. These descriptive phenomena provide new insight into the role of the enterocyte and intestinal immune cells in the translocation process.