Epidemiology of invasive candidiasis: a persistent public health problem

Invasive candidiasis (IC) is a leading cause of mycosis-associated mortality in the United States. We examined data from the National Center for Health Statistics and reviewed recent literature in order to update the epidemiology of IC. IC-associated mortality has remained stable, at approximately 0.4 deaths per 100,000 population, since 1997, while mortality associated with invasive aspergillosis has continued to decline. Candida albicans remains the predominant cause of IC, accounting for over half of all cases, but Candida glabrata has emerged as the second most common cause of IC in the United States, and several less common Candida species may be emerging, some of which can exhibit resistance to triazoles and/or amphotericin B. Crude and attributable rates of mortality due to IC remain unacceptably high and unchanged for the past 2 decades. Nonpharmacologic preventive strategies should be emphasized, including hand hygiene; appropriate use, placement, and care of central venous catheters; and prudent use of antimicrobial therapy. Given that delays in appropriate antifungal therapy are associated with increased mortality, improved use of early empirical, preemptive, and prophylactic therapies should also help reduce IC-associated mortality. Several studies have now identified important variables that can be used to predict risk of IC and to help guide preventive strategies such as antifungal prophylaxis and early empirical therapy. However, improved non-culture-based diagnostics are needed to expand the potential for preemptive (or early directed) therapy. Further research to improve diagnostic, preventive, and therapeutic strategies is necessary to reduce the considerable morbidity and mortality associated with IC.

Oral health in Florida nursing homes

OBJECTIVES

The purpose of this study was to measure the oral health and hygiene status among 265 South Florida nursing home residents aged between 45 and 98 years.

METHODS

The oral health and hygiene status of the residents were assessed by noting the presence of calculus, caries, gingivitis, cheilitis, apthous ulcer, dry mouth and red or white lesions.

RESULTS

The incidence of nursing home residents with calculus was 79.6% and the remaining 20.4% were edentulous. More than half of residents had oral problems (50.6%) the commonest was gingivitis (36.6%), followed by caries (26%) and tooth fracture (15.9%). Almost half the residents wore dentures (47.2%). Statistical analysis was conducted using analysis of variance (P-values). Ageing of the residents was statistically correlated to a worsening of oral hygiene status (P<0.0066), absence and presence of one or two dentures (P<0.0034) and a loss of teeth (P<0.0001).

CONCLUSIONS

The ageing of residents is correlated to increasing oral health problems and the loss of teeth. Oral health neglect affects almost all of the nursing home residents. Care providers should receive education and training from dental hygienists to improve the standard of oral hygiene and health of the elderly.

Candida pseudorugosa sp. nov., a novel yeast species from sputum

Two yeast strains, strains XH 1026 and XH 1164, isolated from the sputum of an intensive care unit patient with acute pneumonia, were originally identified as Candida albicans and C. tropicalis, respectively. Sequence analysis of the 26S rRNA gene D1/D2 domain and the internal transcribed spacer (ITS) region indicated that the two strains represent a novel yeast species closely related to C. rogusa. The name Candida pseudorugosa sp. nov. is therefore proposed (type strain, AS 2.3107 [CBS 10433]). The new species is able to grow at 42 degrees C and is resistant or insusceptible to amphotericin B (MIC, 2 microg/ml), caspofungin (MIC, 64 microg/ml), itraconazole (MIC, 1 microg/ml), and nystatin (MIC, 16 microg/ml); dose-dependent susceptible to fluconazole (MIC, 16 microg/ml); and susceptible to flucytosine (MIC, 0.125 microg/ml) and voriconazole (MIC, 0.125 to 0.25 microg/ml). The code for C. pseudorugosa sp. nov. provided by the API 20C AUX system is identical to that for C. rugosa. The colonies of the new species on CHROMagar Candida appear blue-green, similar to those of C. albicans. In addition to the molecular method based on D1/D2 domain or ITS region sequencing, use of the combination of the API system and CHROMagar Candida is helpful for the correct identification of C. pseudorugosa sp. nov.

Inflammatory response and clinical course of adult patients with nosocomial bloodstream infections caused by Candida spp

Candida spp. are an important cause of nosocomial bloodstream infection (nBSI) and are associated with significant morbidity and mortality. An historical cohort study was performed to evaluate the clinical course of 60 randomly selected adult patients with nBSIs caused by Candida spp. Patients with BSI caused by Candida albicans (n = 38) and non-albicans spp. (n = 22) were compared with 80 patients with Staphylococcus aureus BSI by serial systemic inflammatory response syndrome (SIRS) and APACHE II scores. The patients had a mean age of 52 years, the length of hospital stay before BSI averaged 21 days, and 57% of patients required care in an intensive care unit before BSI. The mean APACHE II score was 17 on the day of BSI, and 63% of BSIs were caused by C. albicans. Antifungal therapy within the first 24 h of onset of BSI was appropriate in 52% of patients. Septic shock occurred in 27% of patients, and severe sepsis in an additional 8%. Overall mortality was 42%, and the 7-day mortality rate was 27%. The inflammatory response and clinical course were similar for patients with BSI caused by C. albicans and non-albicans spp. In univariate analysis, progression to septic shock was correlated with high overall mortality, as was an APACHE II score >25 at the onset of BSI. In multivariate analysis, the APACHE II score at the onset of BSI and a systemic inflammatory response independently predicted overall mortality, but the 7-day mortality rate was only predicted independently by the APACHE II score. Clinical course and mortality in patients with Candida BSI were predicted by systemic inflammatory response and APACHE II score, but not by the infecting species.

Pharmacodynamics of caspofungin in a murine model of systemic candidiasis: importance of persistence of caspofungin in tissues to understanding drug activity

Pharmacokinetic and pharmacodynamic studies were conducted in a murine model of systemic candidiasis to determine the pharmacodynamic parameter linked with caspofungin efficacy. Additional studies defined the importance of persistent tissue drug concentrations to treatment outcome. The pharmacokinetics of caspofungin were determined in the serum and kidneys of infected mice over 96 h. Population pharmacokinetic analysis demonstrated a serum terminal half-life (t(1/2)) for caspofungin of 20.2 h when only serum concentrations were considered, but the terminal t(1/2) increased to 59.2 h when serum and kidney concentration-time data were co-modeled. In dose-range studies, the dose-response effect was well described by an inhibitory sigmoid curve for the exposure-effect killing caused by the drug (r2 > 0.96; P << 0.001). In dose-fractionation studies, fungal counts in kidneys were not statistically different for total doses given as one, two, or four equally divided doses over 96 h, indicating that the area under the concentration-time curve/MIC is the pharmacodynamic parameter that predicts caspofungin efficacy in our infection model. In a separate study, mice infected with Candida albicans 24 h after serum concentrations of caspofungin fell below the MIC for the fungal isolate had significant reductions in fungal densities in their kidneys compared with the growth of fungi in the kidneys of untreated controls (P = 0.005). This in vivo biological assay demonstrates that therapeutic concentrations of caspofungin persist at the site of infection in kidney tissue well after serum concentrations fall below the MIC, underscoring the primacy of caspofungin levels in tissues on determining treatment outcome.

EAP1, a Candida albicans gene involved in binding human epithelial cells

Candida albicans adhesion to host tissues contributes to its virulence and adhesion to medical devices permits biofilm formation, but we know relatively little about the molecular mechanisms governing C. albicans adhesion to materials or mammalian cells. Saccharomyces cerevisiae provides an attractive model system for studying adhesion in yeast because of its well-characterized genetics and gene expression systems and the conservation of signal transduction pathways among the yeasts. In this study, we used a parallel plate flow chamber to screen and characterize attachment of a flo8Delta S. cerevisiae strain expressing a C. albicans genomic library to a polystyrene surface. The gene EAP1 was isolated as a putative cell wall adhesin. Sequence analysis of EAP1 shows that it contains a signal peptide, a glycosylphosphatidylinositol anchor site, and possesses homology to many other yeast genes encoding cell wall proteins. In addition to increasing adhesion to polystyrene, heterologous expression of EAP1 in S. cerevisiae and autonomous expression of EAP1 in a C. albicans efg1 homozygous null mutant significantly enhanced attachment to HEK293 kidney epithelial cells. EAP1 expression also restored invasive growth to haploid flo8Delta and flo11Delta strains as well as filamentous growth to diploid flo8/flo8 and flo11/flo11 strains. Transcription of EAP1 in C. albicans is regulated by the transcription factor Efg1p, suggesting that EAP1 expression is activated by the cyclic AMP-dependent protein kinase pathway.

Lessons from the genome sequence of Neurospora crassa: tracing the path from genomic blueprint to multicellular organism

We present an analysis of over 1,100 of the approximately 10,000 predicted proteins encoded by the genome sequence of the filamentous fungus Neurospora crassa. Seven major areas of Neurospora genomics and biology are covered. First, the basic features of the genome, including the automated assembly, gene calls, and global gene analyses are summarized. The second section covers components of the centromere and kinetochore complexes, chromatin assembly and modification, and transcription and translation initiation factors. The third area discusses genome defense mechanisms, including repeat induced point mutation, quelling and meiotic silencing, and DNA repair and recombination. In the fourth section, topics relevant to metabolism and transport include extracellular digestion; membrane transporters; aspects of carbon, sulfur, nitrogen, and lipid metabolism; the mitochondrion and energy metabolism; the proteasome; and protein glycosylation, secretion, and endocytosis. Environmental sensing is the focus of the fifth section with a treatment of two-component systems; GTP-binding proteins; mitogen-activated protein, p21-activated, and germinal center kinases; calcium signaling; protein phosphatases; photobiology; circadian rhythms; and heat shock and stress responses. The sixth area of analysis is growth and development; it encompasses cell wall synthesis, proteins important for hyphal polarity, cytoskeletal components, the cyclin/cyclin-dependent kinase machinery, macroconidiation, meiosis, and the sexual cycle. The seventh section covers topics relevant to animal and plant pathogenesis and human disease. The results demonstrate that a large proportion of Neurospora genes do not have homologues in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. The group of unshared genes includes potential new targets for antifungals as well as loci implicated in human and plant physiology and disease.

Normal host defense during systemic candidiasis in mannose receptor-deficient mice

Pathogen pattern recognition receptors (PRRs) recognize common structural and molecular motifs present on microbial surfaces and contribute to induction of innate immune responses. The mannose receptor (MR), a carbohydrate-binding receptor expressed on subsets of macrophages, is considered one such PRR. In vitro experiments have implicated the MR in phagocytosis of mannose-bearing microbes, including Candida albicans, and enhancement of antifungal response by macrophages. However, the significance of the MR's contribution to immune response during systemic C. albicans infection has never been directly demonstrated. Using MR-deficient mice in an in vivo infection experiment, we examined the role of the MR in immune response during disseminated candidiasis. MR(-/-) and wild-type control mice were challenged intraperitoneally with C. albicans, and the survival rates, tissue fungal burden, inflammatory cell recruitment, and specific antibody production after infection were evaluated. We found no significant difference in survival between the two mouse strains. MR(-/-) mice had higher average fungal burdens in some of the organs on days 7 and 21 but exhibited competence in inflammatory cell recruitment and antibody production. We also observed in vitro that MR(-/-) peritoneal cavity macrophages were equally capable of C. albicans uptake and that phagocytosis could be blocked with beta-glucan. We conclude that the MR is not required for the normal host defense during disseminated candidiasis or for the phagocytosis of C. albicans and that a beta-glucan receptor may be required for C. albicans phagocytosis.

European Confederation of Medical Mycology (ECMM) prospective survey of candidaemia: report from one Italian region

An ECMM epidemiological prospective survey of candidaemia was performed in one Italian region (Lombardy; population: 8 924 870) by the National Society of Medical Mycology (FIMUA) from September 1997 to December 1999. In total, 569 episodes were reported with an overall rate of 0.38/1000 admissions, 4.4/100000 patient days. Predisposing factors included presence of an intravascular catheter (89%), antibiotic treatment (88%), surgery (56%), intensive care (45%), solid tumour (28%), steroid treatment (15%), haematological malignancy (7%), HIV infection (6%), fetal immaturity (4%). Mucous membrane colonization preceded candidaemia in 83% of patients. Candida albicans was identified in 58% of cases, followed by Candida parapsilosis (15%), Candida glabrata (13%), Candida tropicalis (6%). Septic shock occurred in 95 patients. Crude mortality was 35%, the highest in C. tropicalis fungaemia (44%), the elderly (64%) and solid tumour cancer patients (43%). Intravascular catheter removal was associated with higher survival rate (71 vs. 47%). This survey underscores the importance of candidaemia in hospital settings.

Candida albicans is phagocytosed, killed, and processed for antigen presentation by human dendritic cells

Candida albicans is a component of the normal flora of the alimentary tract and also is found on the mucocutaneous membranes of the healthy host. Candida is the leading cause of invasive fungal disease in premature infants, diabetics, and surgical patients, and of oropharyngeal disease in AIDS patients. As the induction of cell-mediated immunity to Candida is of critical importance in host defense, we sought to determine whether human dendritic cells (DC) could phagocytose and degrade Candida and subsequently present Candida antigens to T cells. Immature DC obtained by culture of human monocytes in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 phagocytosed unopsonized Candida in a time-dependent manner, and phagocytosis was not enhanced by opsonization of Candida in serum. Like macrophages (Mphi), DC recognized Candida by the mannose-fucose receptor. Upon ingestion, DC killed Candida as efficiently as human Mphi, and fungicidal activity was not enhanced by the presence of fresh serum. Although phagocytosis of Candida by DC stimulated the production of superoxide anion, inhibitors of the respiratory burst (or NO production) did not inhibit killing of Candida, even when phagocytosis was blocked by preincubation of DC with cytochalasin D. Further, although apparently only modest phagolysosomal fusion occurred upon DC phagocytosis of Candida, killing of Candida under anaerobic conditions was almost equivalent to killing under aerobic conditions. Finally, DC stimulated Candida-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of both viable and heat-killed Candida cells. These data suggest that, in vivo, such interactions between DC and C. albicans may facilitate the induction of cell-mediated immunity.

Candidemia in pediatric surgery patients

Candida spp. are the fourth leading cause of bloodstream infection. While the literature on neonatal candidemia is abundant, its prevalence in pediatric surgery cases is hardly mentioned. This study was carried out over a 5-year period to evaluate the prevalence of candidemia in pediatric surgery intensive care unit patients (ICU), and to examine both the neonatal and hospital risk factors for developing candidemia in comparison to control groups of patients with either no infection or with bacteremia, type and outcome of therapy. A total of 1,359 pediatric surgery patients admitted to the ICU and high dependency unit (HDU) were included in the study. Using relevant specimens from them, a microbiological survey was carried out on admission and weekly thereafter. Twenty-five patients developed candidemia during the study period. Twenty-one of them were admitted to ICU. Nine were low birth weight and immature neonates. All 25 patients had underlying disease, most involving the gastroentestinal tract and requiring surgical intervention. All patients had been given broad-spectrum beta-lactam antibiotics with or without aminoglycosides and an anti-anaerobic drug prior to candidemia. The data show that patients who were not infected had very few risk factors that could predispose to candidemia. The bacteremic group of patients had more risk factors: mainly ICU stay, prior antibiotic therapy or GI surgery. The candidemia patients outnumbered these two groups in both neonatal and hospital risk factors. Twenty-three candidemia patients had received amphotericin B and 2 had fluconazole. Seventeen of them improved and the rest expired during therapy. Fourteen of the Candida isolated were C. albicans while the rest belonged to other Candida spp. dominated by C. parapsilosis. In conclusion, candidemia was infrequent in pediatric surgery patients. ICU stay, GI surgery and prior broad-spectrum antibiotic therapy were important risk factors.

Systemic infection following intravenous inoculation of mice with Candida albicans int1 mutant strains

The Candida albicans gene INT1 is associated with epithelial adhesion, hyphal formation, and virulence. C. albicans strains carrying two, one, or no functional INT1 alleles were used to assess the association between mortality and C. albicans persistence in the liver and kidney of intravenously inoculated mice. Mice were injected with 10(5) C. albicans CAF2 (parent strain, INT1/INT1), C. albicans CAG3 (homozygous disruptant, Int1/int1), or C. albicans CAG5 (heterozygous reintegrant, int1/int1 + INT1). Mortality was monitored and mice were sacrificed on Days 1, 7, 14, and 21 for quantitative analysis of kidney and liver microbes, with histologic analysis of these tissues as well. Mortality was highest for mice injected with the wild-type strain CAF2 (INT1/INT1) and lowest for mice injected with the homozygous disruptant CAG3 (int/int1). Yeast were readily cleared from the liver of all mice injected with any of the three C. albicans strains. Although the mutant strains CAG3 and CAG5 are defective for hyphal formation in vitro, there was histological evidence of abundant hyphal formation in the renal pelvis of mice injected with these strains. Compared to the wild-type strain, mutant strains were associated with reduced mortality but increased C. albicans persistence in the kidney. Thus, the absolute ability to form hyphae in the kidney did not appear to modulate either C. albicans-induced mortality or the course of progressive infection in the kidney. In addition, reduced virulence was paradoxically associated with increased, not decreased, persistence of C. albicans in the kidney.

In vitro activity of a new polyene, SPA-S-843, against yeasts

The in vitro activity of a new water-soluble polyene, SPA-S-843, was evaluated against 116 strains of Candida, Cryptococcus, and Saccharomyces spp. and compared with that of amphotericin B. SPA-S-843 demonstrated better inhibitory activity against all of the yeasts examined and better fungicidal activity against Candida albicans, Candida glabrata, Candida krusei, and Candida tropicalis than did amphotericin B.

Cloning and disruption of caPLB1, a phospholipase B gene involved in the pathogenicity of Candida albicans

The Candida albicans PLB1 gene was cloned using a polymerase chain reaction-based approach relying on degenerate oligonucleotide primers designed according to the amino acid sequences of two peptide fragments obtained from a purified candidal enzyme displaying phospholipase activity (Mirbod, F., Banno, Y., Ghannoum, M. A., Ibrahim, A. S., Nakashima, S., Yasuo, K., Cole, G. T., and Nozawa, Y. (1995) Biochim. Biophys. Acta 1257, 181-188). Sequence analysis of a 6.7-kilobase pair EcoRI-ClaI genomic clone revealed a single open reading frame of 1818 base pairs that predicts for a pre-protein of 605 residues. Comparison of the putative candidal phospholipase with those of other proteins in data base revealed significant homology to known fungal phospholipase Bs from Saccharomyces cerevisiae (45%), Penicillium notatum (42%), Torulaspora delbrueckii (48%), and Schizosaccharomyces pombe (38%). Thus, we have cloned the gene encoding a C. albicans phospholipase B homolog. This gene, designated caPLB1, was mapped to chromosome 6. Disruption experiments revealed that the caplb1 null mutant is viable and displays no obvious phenotype. However, the virulence of strains deleted for caPLB1, as assessed in a murine model for hematogenously disseminated candidiasis, was significantly attenuated compared with the isogenic wild-type parental strain. Although deletion of caPLB1 did not produce any detectable effects on candidal adherence to human endothelial or epithelial cells, the ability of the caplb1 null mutant to penetrate host cells was dramatically reduced. Thus, phospholipase B may well contribute to the pathogenicity of C. albicans by abetting the fungus in damaging and traversing host cell membranes, processes which likely increase the rapidity of disseminated infection.

Linkage of adhesion, filamentous growth, and virulence in Candida albicans to a single gene, INT1

Adhesion and the ability to form filaments are thought to contribute to the pathogenicity of Candida albicans, the leading cause of fungal disease in immunocompromised patients. Int1p is a C. albicans surface protein with limited similarity to vertebrate integrins. INT1 expression in Saccharomyces cerevisiae was sufficient to direct the adhesion of this normally nonadherent yeast to human epithelial cells. Furthermore, disruption of INT1 in C. albicans suppressed hyphal growth, adhesion to epithelial cells, and virulence in mice. Thus, INT1 links adhesion, filamentous growth, and pathogenicity in C. albicans and Int1p may be an attractive target for the development of antifungal therapies.

Systemic candidiasis in cardiac surgery patients

OBJECTIVE

To examine the frequency, predisposing factors and consequences of systemic candidiasis in cardiac surgery patients. We also examined fluconazole efficacy in the treatment of disseminated fungal disease.

METHODS

A total of 2615 adult patients of mean +/- S.D. age 60.8 +/- 8.7 years who underwent open heart surgery between July 1993 and April 1995, were enrolled in the initial protocol. Patients were divided in two groups according to length of stay in the intensive care unit (ICU). The cut-off was a length of stay of 9 days.

RESULTS

In the group of patients with prolonged stay (n = 54), 11 patients (20.3%) developed systemic candidiasis, usually after the twentieth postoperative day. Predisposing factors were patient age, history of diabetes mellitus, presence of central venous catheters, prolonged mechanical ventilatory support, prolonged ICU stay, and administration of antibiotics and of total parenteral nutrition for a prolonged period. The patients who developed systemic candidiasis had a median ICU and hospital stay of 58 and 60 days respectively. The mortality rate was 27.2%. Patients receiving fluconazole, improved and eventually negative cultures were obtained.

CONCLUSIONS

We concluded that a significant percentage of patients who remained in the cardiothoracic ICU for more than 9 days developed systemic candidiasis. Systemic candidiasis resulted in a significant prolongation of ICU and hospital length of stay, thus increasing extensively total hospitalization costs. Fluconazole seems to be an effective and well-tolerated agent in the treatment of severe life-threatening systemic candidiasis, and a very good alternative to amphotericin B, in cardiac surgery patients.

Epidemiology of nosocomial fungal infections

This paper briefly reviews the current knowledge of the epidemiology and modes of transmission of nosocomial fungal infections and some of the therapeutic options for treating these diseases. In the mid-1980s, many institutions reported that fungi were common pathogens in nosocomial infections. Most, if not all, hospitals care for patients at risk for nosocomial fungal infections. The proportion in all nosocomial infections reportedly caused by Candida spp. increased from 2% in 1980 to 5% in 1986 to 1989. Numerous studies have identified common risk factors for acquiring these infections, most of which are very common among hospitalized patients; some factors act primarily by inducing immunosuppression (e.g., corticosteroids, chemotherapy, malnutrition, malignancy, and neutropenia), while others primarily provide a route of infection (e.g., extensive burns, indwelling catheter), and some act in combination. Non-albicans Candida spp., including fluconazole-resistant C. krusei and Torulopsis (C.) glabrata, have become more common pathogens. Newer molecular typing techniques can assist in the determination of a common source of infection caused by several fungal pathogens. Continued epidemiologic and laboratory research is needed to better characterize these pathogens and allow for improved diagnostic and therapeutic strategies.

Evaluation of pulsed-field gel electrophoresis as a typing system for Candida rugosa: comparison of karyotype and restriction fragment length polymorphisms

Nosocomial infections with Candida species have emerged as an increasingly important cause of morbidity and mortality in intensive care units. Ten Candida rugosa isolates from a previously documented cluster of C. rugosa infections in one hospital (nine burn unit isolates and one isolate from another hospital ward) and eight C. rugosa isolates recovered in a referral fungus testing laboratory (comparison isolates) from distinct geographic areas were investigated by molecular techniques. Isolates were from multiple anatomic sites. Pulsed-field gel electrophoresis (PFGE) of whole-cell DNA was performed with the 18 C. rugosa isolates as a marker of strain identity. The PFGE karyotypes of the C. rugosa isolates were demonstrated from four to seven chromosome bands. Karyotyping revealed the same PFGE pattern for the nine outbreak isolates from the burn unit, confirming clonal strain transmission. The isolate from the other hospital ward had a distinct karyotype. Distinct PFGE karyotype patterns were demonstrated for the eight comparison isolates. Restriction fragment length polymorphisms (RFLP) generated from whole-cell DNA digested with SfiI demonstrated the same RFLP pattern among outbreak isolates. Among comparison isolates, karyotyping distinguished some isolates that were indistinguishable by RFLP patterns. Karyotyping by PFGE appears to be the most useful molecular typing tool for discrimination among strains of C. rugosa and will be a useful marker for evaluating the epidemiology of future C. rugosa infections.

Molecular typing of Candida albicans strains isolated from nosocomial candidemia

Yeasts of the genus Candida have been recognized as important microorganisms responsible for nosocomial fungemia. Six blood-stream and two intravenous central catheter C. albicans strains were isolated from eight patients and studied by electrophoretic karyotyping of chromosomal DNA by pulsed-field gel electrophoresis. Seven chromosomal DNA profiles were identified. Two patients showed isolates with the same profile, suggesting nosocomial transmission. Karyotyping of C. albicans revealed an excellent discriminatory power among the isolates and may therefore be useful in the study of nosocomial candidemia.

Selection of candidate quality control isolates and tentative quality control ranges for in vitro susceptibility testing of yeast isolates by National Committee for Clinical Laboratory Standards proposed standard methods

The National Committee for Clinical Laboratory Standards has developed a proposed standard method for in vitro antifungal susceptibility testing of yeast isolates (National Committee for Clinical Laboratory Standards, document M27-P, 1992). In order for antifungal testing by the M27-P method to be accepted, reliable quality control (QC) performance criteria must be developed. In the present study, five laboratories tested 10 candidate QC strains 20 times each against three antifungal agents: amphotericin B, fluconazole, and 5-fluorocytosine. All sites conformed to the M27-P standards and used a common lot of tube dilution reagents and RPMI 1640 broth medium. Overall, 98% of MIC results with amphotericin B, 95% with fluconazole, and 92% with 5-fluorocytosine fell within the desired 3-log2 dilution range (mode +/- 1 log2 dilution). Excellent performance with all three antifungal agents was observed for six strains: Candida albicans ATCC 90028, Candida parapsilosis ATCC 90018, C. parapsilosis ATCC 22019, Candida krusei ATCC 6258, Candida tropicalis ATCC 750, and Saccharomyces cerevisiae ATCC 9763. With these strains, 3-log2 dilution ranges encompassing 94 to 100% of MICs for all three drugs were established. Additional studies with multiple lots of RPMI 1640 test medium will be required to establish definitive QC ranges.

An experimental model for study of Candida survival and transmission in human volunteers

In order to determine the potential for cross-transmission of Candida spp. between health-care workers and patients, the survival of clinical isolates of five species of Candida on the palms of human volunteers was tested. One hundred microliters of a McFarland 1.0 density suspension (5 x 10(5) cfu) from an overnight culture of Candida albicans, Candida krusei, Candida parapsilosis, Candida tropicalis and Candida glabrata was used as inoculum. The degree of hydrophobicity of the different Candida species was also tested and did not influence the survival. The half-lives were brief, being 9.5, 12.4, 7.4, 12.8, 9.6 min for Candida albicans, Candida krusei, Candida glabrata, Candida parapsilosis, and Candida tropicalis, respectively, but at 45 min 2.6 x 10(3) to 3 x 10(4) organisms remained on the hands. Survival of Candida albicans for as long as 24 h on inanimate surfaces was observed. Transmission from one hand to a second hand occurred in 69% of the experiments and from the first to a third hand in 38%. Transmission to and from inanimate surfaces was successful in most of the experiments (90%). This experimental model aids in the biological study of Candida spp. and suggests some of the potential mechanisms of transmission.

Multisite reproducibility of colorimetric broth microdilution method for antifungal susceptibility testing of yeast isolates

MICs of fluconazole and amphotericin B were determined independently for 100 coded yeast isolates by each of six laboratories to determine reproducibility of results by using a colorimetric oxidation-reduction-based broth microdilution test. In addition, each site tested five quality control isolates on at least four different occasions during the study. Results agreed within a three-dilution range (mode +/- 1 log2 dilution) for 96.2% of fluconazole tests and 92.7% of amphotericin B tests. Agreement among tests with the quality control isolates was 99.4% with fluconazole and 98.6% with amphotericin B. These results indicate that the colorimetric microdilution method is reproducible among laboratories.

Candidemia: current epidemiologic characteristics and a long-term follow-up of the survivors

All consecutive patients with positive blood culture for Candida species over a 6-year period were evaluated to define recent epidemiologic characteristics of candidemia, and to assess the prevalence of late complications. We encountered 106 cases; medical records were available for 99 of them. The rate of candidemia was increasing until 1990, after which it declined. C. albicans was the most common species, but in the last 2 years, C. tropicalis and C. parapsilosis were emerging. Overall mortality rate was 54.5% without significant variation during the study period. Antifungal therapy was withheld in 24/99 cases (24.2%). Decision to withhold treatment was taken in 19/59 cases (32.2%) before the availability of fluconazole in 1990, compared with 5/40 cases (12.5%) afterward (p < 0.05). Follow-up was possible in 35 instances for an average period of 17.1 months (range: 1-48 months); 7 of these individuals, all with transient candidemia, were untreated. None of the survivors developed late complications. These findings demonstrate that candidemia appears to be declining since 1990, with a noticeable decrease in the prevalence of C. albicans but an increase in that of C. tropicalis and C. parapsilosis, that fewer patients are left untreated since fluconazole became available, and that the risk of late complications among the survivors is low.

Evaluation of four commercial systems for identification of medically important yeasts

Four commercially available systems for identification of yeasts were evaluated using 178 clinical isolates and seven reference strains previously identified by a conventional method. After 72 h of incubation, the rate of correct identification was 86.5% with API20C Aux, 86% with Auxacolor, 68% with Mycotube and 51.1% with Candifast. When considering only the reference strains included in the manufacturers' databases, the identification rate was 90%, 91%, 87% and 61.2% respectively. Although the results at 72 h obtained with API20C Aux and Auxacolor were similar, Auxacolor led to more rapid identification of the strains, 67.9% versus 14.6% being identified at 24 h and 80.9% versus 64% being identified at 48 h.

Laboratory aids in the diagnosis of invasive candidiasis

The laboratory diagnosis of candidiasis continues to be problematic; however, there have been several advances in the past decade which promise to enhance our ability to identify patients at high risk for infection and/or to document invasive candidiasis in critically ill and immunocompromised patients. The introduction of commercially available biphasic blood culture medium and subsequently the lysis-centrifugation procedure has markedly improved the ability of laboratories to detect fungemia. Although serologic methods have not been very successful in diagnosing candidiasis in immunocompromised patients, several antigen detection methods are now under investigation. In addition, detection of fungal metabolites such as D-arabinitol remains promising. Finally, application of the techniques of molecular biology for typing and detection of fungal pathogens has expanded our understanding of candidal infections and may offer the most sensitive and specific means of diagnosing invasive candidiasis.

Critical assessment of blood culture techniques: analysis of recovery of obligate and facultative anaerobes, strict aerobic bacteria, and fungi in aerobic and anaerobic blood culture bottles

Recent reports have documented a decrease in anaerobic bacteremias and have questioned the need for routine anaerobic blood cultures. At the same time, we and others have noted an increase in fungal bloodstream infections. In this two-part study, we first compared recoveries of obligate anaerobic bacteria with those of fungi over a 13-year period and then examined the recoveries of all bacteria and fungi in aerobic and anaerobic blood culture bottles during a 12-month period. During the 13-year period, the number of patients with anaerobic bacteremia remained relatively constant (average, 39 patients per year), while the incidence of fungemia steadily increased, from 12 patients in 1978 to 117 patients in 1990. Of the 1,090 anaerobic isolates, 55.1 and 90.2% were recovered in aerobic and anaerobic bottles, respectively, compared with 98.6 and 37.0% of the 2,582 fungi. During the 12-month period of evaluation, 2,980 bacteria and fungi were recovered in cultures collected from 1,555 patients. Overall, 21.1% more organisms were recovered in aerobic bottles than in anaerobic bottles, including significantly more Staphylococcus species; gram-positive aerobic bacilli; Escherichia, Enterobacter, Pseudomonas, Xanthomonas, and Acinetobacter species; miscellaneous gram-negative bacilli; and yeasts. Only anaerobic gram-negative bacilli and non-spore-forming gram-positive bacilli were isolated more commonly in anaerobic bottles. These data support the concepts that bacteremia caused by obligate anaerobic bacteria is decreasing relative to sepsis caused by other bacteria and fungi and that the routine use of unvented anaerobic blood culture bottles reduces the recovery of common aerobic bloodstream pathogens.

Impact of the changing epidemiology of fungal infections in the 1990s

The increase in fungal infections over the past decade is striking. This is particularly true for hospitalized patients where the rate of candidal bloodstream infection has increased by as much as 487% over the decade of the 1980s. This increase in fungal infections is accompanied by a significant excess mortality and excess length of stay in hospital. The emergence of "new" fungal pathogens such as Candida krusei, Torulopsis glabrata, Fusarium and Trichosporon beigelii is now recognized as a significant problem in many patient populations. The documentation of nosocomial transmission of fungal pathogens and the recognition of resistance to both new and established anti-fungal agents poses a significant problem entering the 1990s. Continued effort is needed to develop new and better therapeutic agents and more effective strategies for prophylaxis of endogenous infections and prevention of transmission within the hospital setting.