Fluconazole susceptibilities of Candida species and distribution of species recovered from blood cultures over a 5-year period

Trends in species distribution and susceptibility to fluconazole among blood stream isolates of Candida species in the United States

National surveillance of blood stream infections (BSI) attributable to Candida spp. has been limited to date. Recent studies have suggested in increase in the proportion of BSI attributable to non-Candida albicans species and have also raised concerns regarding the emergence of antifungal resistance among Candida spp. The increased utilization of broad-spectrum antifungal agents and the recognition of Candida spp. as prominent pathogens with the potential for developing antifungal resistance, emphasize the need for ongoing surveillance of antifungal susceptibility patterns. In this investigation trends in species distribution and susceptibility to fluconazole among BSI isolates of Candida spp. referred to our laboratory by United States hospitals were evaluated over the 7-year period from 1992 to 1998. A total of 1579 BSI isolates from more than 50 medical centers were processed. Overall, C. albicans accounted for 52% of isolates followed by C. glabrata (18%), C. parapsilosis (15%), C. tropicalis (11%), and C. krusei (2%). The proportion of BSI isolates that were C. albicans ranged from 45% in 1992 to 60% in 1998. Among the non-C. albicans isolates, C. glabrata succeeded C. parapsilosis as the most common species beginning in 1995. Overall, the susceptibility of all Candida species (C. albicans plus all other species) to fluconazole remained stable (MIC90, 16 micrograms/mL). The fluconazole MIC90 for C. albicans was 0.5-2.0 micrograms/ml for all years studied except 1995 (8.0 micrograms/mL) and was 1.0 microgram/mL overall. The present study suggests a continued prominent role of C. albicans as a cause of BSI, and a constant level of susceptibility of Candida BSI isolates to fluconazole over 7 years. These data should serve as a baseline for future surveillance efforts for anti-fungal agents tested against yeast BSI isolates.

Comparison of three commercial systems for the identification of germ-tube negative yeast species isolated from clinical specimens

Three commercial systems were evaluated for their ability to identify 171 germ-tube negative yeasts isolated from clinical specimens. The Yeast Biochemical Card and Analytical Profile Index 20 AUX identified 97% of 171 strains tested. The Biolog system had poor clinical utility: only 48% of strains were identified. For Yeast Biochemical Card and Analytical Profile Index 20 AUX, 9% and 6%, respectively, required repeat testing and both systems required supplemental tests for 28% of the strains. These observations indicate that considerable expertise and a battery of reagents in addition to the basic systems are required for accurate identification of germ-tube negative yeasts.

Comparison of the API Candida system with the AUXACOLOR system for identification of common yeast pathogens

Two commercial systems for the identification of yeasts were evaluated by using 159 clinical isolates that had also been identified by conventional biochemical and morphological methods. The API Candida system correctly identified 146 isolates (91.8%), and the AUXACOLOR system correctly identified 145 isolates (91.2%). However, of the 146 isolates identified by the API Candida system, 23 required supplemental biochemical tests or morphological assessment to obtain the correct identification. The AUXACOLOR system gave no identification in 13 cases (8.2%), while the API Candida system gave an unreadable profile in only one case. Incorrect identifications were more common with the API Candida system (12 isolates; 7.5%) than with the AUXACOLOR system (1 isolate; 0.6%).

Trends in antifungal use and epidemiology of nosocomial yeast infections in a university hospital

This report describes both the trends in antifungal use and the epidemiology of nosocomial yeast infections at the University of Iowa Hospitals and Clinics between fiscal year (FY) 1987-1988 and FY 1993-1994. Data were gathered retrospectively from patients' medical records and from computerized databases maintained by the Pharmacy, the Program of Hospital Epidemiology, and the Medical Records Department. After fluconazole was introduced, use of ketoconazole decreased dramatically but adjusted use of amphotericin B decreased only moderately. However, the proportion of patients receiving antifungal therapy who were treated with amphotericin B declined markedly. In FY 1993-1994, 26 patients of the gastrointestinal surgery service received fluconazole. Among these patients, fluconazole use was prophylactic in 16 (61%), empiric in 3 (12%), and directed to a documented fungal infection in 7 (27%). Rates of nosocomial yeast infection in the adult bone marrow transplant unit increased from 6.77/1,000 patient days in FY 1987-1988 to 10.18 in FY 1989-1990 and then decreased to 0 in FY 1992-1993. Rates of yeast infections increased threefold in the medical and surgical intensive care units, reaching rates in FY 1993-1994 of 6.95 and 5.25/1,000 patient days, respectively. The rate of bloodstream infections increased from 0.044/1,000 patient days to 0.098, and the incidence of catheter-related urinary tract infections increased from 0.23/1,000 patient days to 0.68. Although the proportion of infections caused by yeast species other than Candida albicans did not increase consistently, C. glabrata became an important nosocomial pathogen.

Antifungal activity of voriconazole (UK-109,496), fluconazole and amphotericin B against hematogenous Candida krusei infection in neutropenic guinea pig model

Voriconazole (UK-109,496) is a new triazole with in vitro activity against a wide spectrum of fungi including yeasts intrinsically resistant to fluconazole such as Candida krusei. In this study the efficacy of voriconazole was compared to amphotericin B and fluconazole in a neutropenic guinea pig model of hematogenously disseminated C. krusei infection. In guinea pigs, neutropenia was established by using cyclophosphamide (intraperitoneally, i.p., 100 mg/kg on day 1 and 4), and dexamethasone (orally, 2 mg/kg/day, for 8 days). Neutropenic guinea pigs were infected with 0.5 ml of yeast cell suspension (1 x 10(8) CFU) intravenously. Challenged animals were treated with antifungals starting 1 h postinfection for 7 days. The animals were divided into five groups: untreated control, amphotericin B (1 mg/kg i.p. on alternate days), fluconazole (20 mg/kg orally twice daily), and voriconazole (two groups: 5 and 10 mg/kg orally twice daily) groups. Guinea pigs were sacrificed 1 day after the last treatment. Brain, liver, and kidneys were removed and weighed, tissues were homogenized and fungal burden determined by serial quantitative counts. Voriconazole at dosages of 5 or 10 mg/kg b.i.d. was shown to be significantly more efficacious than either amphotericin B or fluconazole in eradicating C. krusei from brain, liver and kidney tissue. These data indicate that voriconazole could be efficacious for the treatment of infections caused by fluconazole-resistant Candida, such as C. krusei.

Antifungal resistance in non- albicans Candida species

Non- Candida albicans species have emerged as important bloodstream pathogens. They tend to have decreased susceptibility to antifungal agents in vitro and cause infections associated with high morbidity and mortality. Fluconazole resistance can emerge in any Candida spp., but is most commonly seen with Candida krusei, for which resistance is universal, and with Candida glabrata. Amphotericin B resistance has also been increasingly reported, most notably in isolates of Candida lusitaniae and Candida guilliermondii. Efforts are underway to correlate in-vitro antifungal susceptibility of individual Candida isolates with response to therapy of patients with candidemia. Future advances in this field might allow physicians to identify Candida isolates resistant to specific antifungal agents and thereby tailor therapy of candidemia. Copyright 1999 Harcourt Publishers Ltd.

No increase in frequency of antifungal resistance among yeasts isolated from normally sterile sites in patients at Foothills Hospital from 1993 to 1996

OBJECTIVE

To determine the prevalence of resistance to antifungal drugs among yeasts isolated from sterile sites from patients in one hospital and the relationship of resistance to antifungal use, and to assess whether resistance was increasing.

METHOD

Susceptibility testing performed by National Committee for Clinical Laboratory Standards (NCCLS) (Villanova, Pennsylvania) microdilution method and by E test. Antifungal use was determined by selected chart review and from pharmacy data. SPECIMENS AND SETTING: Tertiary care adult hospital with neonatal intensive care.

POPULATION STUDIED

Distinct yeast isolates from sterile site specimens collected during the years 1993 to 1996.

RESULTS

A total of 132 yeast isolates were studied, of which 78 (59%) were Candida albicans. The proportion of C albicans remained steady over the four-year period, and there was no trend to increased resistance among C albicans. The number of isolates of all species with fluconazole microdilution minimum inhibitory concentration (MIC) greater than 8 mg/L in each of the four years were one of 32 in 1996, three of 26 in 1994, six of 33 in 1995, and one of 41 in 1996. A single isolate had an itraconazole microdilution MIC greater than 0.5 mg/L in each year. Prior use of antifungal therapy was rare in this patient population.

CONCLUSIONS

The increase in resistance to antifungal drugs reported by some centres did not occur in this institution over the course of the study. This experience may reflect differences in infection control practices and in patterns of use of antifungal agents. The NCCLS method was found to be superior to the E test as a routine method for testing susceptibility of yeasts.

Rapid identification of up to three Candida species in a single reaction tube by a 5' exonuclease assay using fluorescent DNA probes

We used fungus-specific PCR primers and species-specific DNA probes to detect up to three Candida species in a single reaction tube by exploiting the 5' to 3' exonuclease activity of Taq DNA polymerase. Probes to the internal transcribed spacer region of the rRNA gene were labeled at the 5' end with one of three fluorescent reporter dyes, 6-carboxy-fluorescein (FAM), tetrachloro-6-carboxy-fluorescein (TET), or hexachloro-6-carboxy-fluorescein (HEX), and at the 3' end with a quencher dye, 6-carboxy-tetramethyl-rhodamine. During PCR amplification, each reporter dye emits a characteristic wavelength as it is cleaved from its specific target DNA and from the quencher dye. Therefore, signals from up to three probes can be detected simultaneously during the PCR assay. Six probes were designed for use in this study: CA-FAM, CT-TET, and CP-HEX were added to one tube to simultaneously detect the typically fluconazole-sensitive species C. albicans, C. tropicalis, and C. parapsilosis, respectively. CG-FAM and CK-TET were added to a second tube to simultaneously detect the typically more innately fluconazole-resistant species C. glabrata and C. krusei, respectively. All-CAN-TET, a Candida genus probe, was added to a third tube to detect DNAs from all Candida species tested. DNAs recovered from 61 blood culture bottles, including 23 positive for C. albicans, 18 positive for C. glabrata, 6 positive for C. tropicalis, 6 positive for C. krusei, 5 positive for C. parapsilosis, and 3 positive for mixed fungemias, were tested. Control samples included those from blood culture bottles with no growth (n = 10) or from patients with confirmed bacteremia (n = 10). Probes detected and correctly identified the organisms in 58 of 61 specimens (95.1%) and gave no false-positive results. This method is simple and rapid and does not require post-PCR hybridization and incubation steps. It is sensitive and specific for the detection and identification of Candida species from blood culture bottles, including those containing mixtures of Candida species, and should facilitate an earlier specific diagnosis, leading to more appropriately targeted antifungal drug therapy.

Constant low rate of fungemia in norway, 1991 to 1996. The Norwegian Yeast Study Group

Since 1991 information on yeast isolates from blood cultures has been recorded prospectively from all microbiological laboratories (5 university and 16 county or local hospital laboratories) in Norway (population, 4.3 million). From 1991 to 1996 a total of 571 episodes of fungemia in 552 patients occurred (1991, 109 episodes; 1992, 81 episodes; 1993, 93 episodes; 1994, 89 episodes; 1995, 98 episodes; and 1996, 101 episodes). The fungemia rates per 10,000 patient days were 0.29 in 1991 and 0.27 in 1996. The average rates for the years 1991 to 1996 were 0.37 for the university laboratories and 0.20 for the other laboratories. These rates are low compared to the rate (0. 76) in five Dutch university hospitals in 1995 and the rate (2.0) in Iowa in 1991. The four most frequently isolated species were Candida albicans (66%), Candida glabrata (12.5%), Candida parapsilosis (7.6%), and Candida tropicalis (6.4%). The incidences of both C. albicans (range, 63 to 73%) and C. glabrata (range, 8.4 to 15.7%) varied somewhat throughout this period, but no significant increase or decrease was noted. MICs of amphotericin B, flucytosine, and fluconazole were determined for 89% of the isolates. All were susceptible to amphotericin B, and only 29 (5.6%) strains had decreased susceptibility to flucytosine. All C. albicans isolates were susceptible to fluconazole. The percentage of yeast isolates with decreased susceptibility to fluconazole (MICs, >/=16 microgram/ml) did increase, from 9.6% in 1991 and 1992 to 12.2% in 1994, 16.1% in 1995, and 18.6% in 1996. This was largely due to increases in the percentages of resistant C. glabrata and Candida krusei strains in the last 2 years. Compared to the incidence in other countries, it is remarkable that Norway has such a low and constant incidence of fungemia. A possible reason for this difference might be a restricted antibiotic use policy in Norway.

Therapy of Candida infections: susceptibility testing, resistance, and therapeutic options

OBJECTIVE

Review the epidemiology of fungal infections, approved susceptibility testing methods, the scope of antifungal resistance, and advances in the treatment of fungal infections.

DATA SOURCES

MEDLINE databases (from 1966 to March 1998) were searched for literature pertaining to the epidemiology and management of fungal infections.

STUDY SELECTION AND DATA EXTRACTION

Articles were selected to assist in providing the reader an understanding of the epidemiology and management of fungal infections.

DATA SYNTHESIS

Fungi have emerged as an important class of pathogens. Even though fungi rank as the fourth most commonly encountered nosocomial bloodstream pathogen, and are associated with the highest mortality of commonly encountered pathogens, only within the past year have methods for conducting and guidelines for interpreting in vitro susceptibility tests been approved. Under the guidance of these standards, we have begun to understand important issues regarding fungi such as the scope and mechanisms of antifungal resistance. Although there has not been a significant addition to our antifungal armamentarium since 1992, advances in antifungal therapy have been realized with the reformulation of available agents and the delineation of the pharmacodynamic characteristics of several antifungals. Additionally, several new agents, including a new class of antifungals, probably will enter into clinical use within the next 5 years.

CONCLUSIONS

We have entered an era in which our understanding of fungi is increasing tremendously. Clinicians need to familiarize themselves with the current concepts surrounding the management of fungal infections in order to provide optimal care for their patients.

Clinical evaluation of the ASTY colorimetric microdilution panel for antifungal susceptibility testing

A method using a commercially prepared colorimetric microdilution panel (ASTY; Kyokuto Pharmaceutical Industrial Co., Ltd.) was compared in four different laboratories with the National Committee for Clinical Laboratory Standards (NCCLS) reference microdilution method by testing 802 clinical isolates of Candida spp. (C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, C. lusitaniae, C. guilliermondii, C. lipolytica, C. rugosa, and C. zeylanoides) against amphotericin B, 5-fluorocytosine (5FC), fluconazole, and itraconazole. Reference MIC endpoints were established after 48 h of incubation, and ASTY endpoints were established after 24 and 48 h of incubation. ASTY endpoints were determined to be the time at which the color of the first well changed from red (indicating growth) to purple (indicating growth inhibition) or blue (indicating no growth). Excellent agreement (within 2 dilutions) between the reference and colorimetric MICs was observed. Overall agreement was 93% at 24 h and 96% at 48 h. Agreement ranged from 90% with itraconazole and 5FC to 96% with amphotericin B at 24 h and from 92% with itraconazole to 99% with amphotericin B and 5FC at 48 h. The ASTY colorimetric microdilution panel method appears to be comparable to the NCCLS reference method for testing the susceptibilities of Candida spp. to a variety of antifungal agents.

Hospital specificity, region specificity, and fluconazole resistance of Candida albicans bloodstream isolates

In a survey of bloodstream infection (BSI) isolates across the continental United States, 162 Candida albicans isolates were fingerprinted with the species-specific probe Ca3 and the patterns were analyzed for relatedness with a computer-assisted system. The results demonstrate that particular BSI strains are more highly concentrated in particular geographic locales and that established BSI strains are endemic in some, but not all, hospitals in the study and undergo microevolution in hospital settings. The results, however, indicate no close genetic relationship among fluconazole-resistant BSI isolates in the collection, either from the same geographic locale or the same hospital. This study represents the first of three fingerprinting studies designed to analyze the origin, genetic relatedness, and drug resistance of Candida isolates responsible for BSI.

In vitro activity of voriconazole against Candida species

The in vitro activity of voriconazole was compared with that of itraconazole and fluconazole against 181 isolates of Candida albicans, 124 isolates of Candida glabrata, and 20 isolates of Candida krusei obtained from the early 1980s through the mid-1990s. Voriconazole had greater intrinsic activity than fluconazole or itraconazole against all three Candida species. For C. glabrata, C. krusei, and C. albicans, the MIC50 values for voriconazole were 1 microgram/mL, 0.5 microgram/mL, and 0.01 microgram/mL, respectively compared with fluconazole MIC50 values of 8 micrograms/mL, 64 micrograms/mL, and 0.25 microgram/mL, respectively. If isolates from AIDS patients were excluded, MIC values for isolates from the 1990s were no higher than those noted for isolates from the 1980s. Voriconazole, a new triazole antifungal agent, appears to have enhanced activity against these three species of Candida; the clinical relevance of these findings should be studied in treatment trials.

Causative pathogens in onychomycosis and the possibility of treatment resistance: a review

Onychomycosis is caused primarily by dermatophytes, Candida species, and nondermatophytic molds. Dermatophytes, particularly Trichophyton rubrum, are by far the most common pathogens. There is some question as to whether Candida actually breaks down nail material or only invades the proximal nail bed. Similarly, the clinical significance of molds is unknown, because they may be colonizing organisms rather than destructive pathogens. It is, therefore, important to identify the pathogen in the array of organisms that may be isolated in culture. The increasing use of fluconazole in prophylaxis and treatment of systemic yeast infections and infections in patients with AIDS has been associated with the emergence of resistant Candida albicans, as well as previously minority species of Candida, such as C. glabrata and C. krusei. This may be of relevance to the treatment of onychomycosis with azole antifungals.

National surveillance of nosocomial blood stream infection due to Candida albicans: frequency of occurrence and antifungal susceptibility in the SCOPE Program

Surveillance of nosocomial blood stream infections (BSI) in the USA between April 1995 and June 1996 revealed that Candida was the fourth leading cause of nosocomial BSI, accounting for 8% of all infections. Fifty-two percent of 379 episodes of candidemia were due to Candida albicans. In vitro susceptibility studies using the 1997 National Committee for Clinical Laboratory Standards reference method demonstrated that 92% of C. albicans isolates were susceptible to 5-fluorocytosine and 90% were susceptible to fluconazole and itraconazole. Geographic variation in susceptibility of fluconazole and itraconazole was observed. Isolates from the Northwest and Southeast regions were more frequently resistant to fluconazole (13.3-15.5%) and to itraconazole (17.2-20.0%) than those from the Northeast and Southwest regions (2.9-5.5% resistant to fluconazole and itraconazole). Continued surveillance for infections caused by C. albicans and other species of Candida among hospitalized patients is recommended.

Clinical, cellular, and molecular factors that contribute to antifungal drug resistance

In the past decade, the frequency of diagnosed fungal infections has risen sharply due to several factors, including the increase in the number of immunosuppressed patients resulting from the AIDS epidemic and treatments during and after organ and bone marrow transplants. Linked with the increase in fungal infections is a recent increase in the frequency with which these infections are recalcitrant to standard antifungal therapy. This review summarizes the factors that contribute to antifungal drug resistance on three levels: (i) clinical factors that result in the inability to successfully treat refractory disease; (ii) cellular factors associated with a resistant fungal strain; and (iii) molecular factors that are ultimately responsible for the resistance phenotype in the cell. Many of the clinical factors that contribute to resistance are associated with the immune status of the patient, with the pharmacology of the drugs, or with the degree or type of fungal infection present. At a cellular level, antifungal drug resistance can be the result of replacement of a susceptible strain with a more resistant strain or species or the alteration of an endogenous strain (by mutation or gene expression) to a resistant phenotype. The molecular mechanisms of resistance that have been identified to date in Candida albicans include overexpression of two types of efflux pumps, overexpression or mutation of the target enzyme, and alteration of other enzymes in the same biosynthetic pathway as the target enzyme. Since the study of antifungal drug resistance is relatively new, other factors that may also contribute to resistance are discussed.

Fungal infection in the intensive care unit

Fungal infection in critically ill patients is an increasingly prevalent problem. Candida spp. cause the majority of these infections in ICU. They occur most commonly in patients with severe underlying illness, multiple courses of antibiotics and intravascular catheters. Clinical diagnosis is difficult due to nonspecific signs and the frequent occurrence of widespread superficial colonization with Candida spp. in ventilated patients. Most patients are diagnosed using inferential evidence of infection, such as persistent pyrexia despite antibiotics, raised serum C-reactive protein and the presence of individual risk factors. Amphotericin B and fluconazole are the most commonly used anti-fungals dependent on the identity of the fungus. Most of these infections are endogenous; however, a proportion may be caused via the hands of healthcare staff or contaminated medical equipment.

National surveillance of nosocomial blood stream infection due to species of Candida other than Candida albicans: frequency of occurrence and antifungal susceptibility in the SCOPE Program. SCOPE Participant Group. Surveillance and Control of Pathogens of Epidemiologic

A national surveillance program of nosocomial blood stream infections (BSI) in the USA between April 1995 and June 1996 revealed that Candida was the fourth leading cause of nosocomial BSI, accounting for 8% of all infections. Forty-eight percent of 379 episodes of candidemia were due to species other than Candida albicans. The rank order of non-C. albicans species was C. glabrata (20%) > C. tropicalis (11%) > C. parapsilosis (8%) > C. krusei (5%) > other Candida spp. (4%). The species distribution varied according to geographic region, with non-C. albicans species predominating in the Northeast (54%) and Southeast (53%) regions, and C. albicans predominating in the Northwest (60%) and Southwest (70%) regions. In vitro susceptibility studies demonstrated that 95% of non-C. albicans isolates were susceptible to 5-fluorocytosine, and 84% and 75% were susceptible to fluconazole and itraconazole, respectively. Geographic variation in susceptibility to itraconazole, but not other agents, was observed. Isolates from the Northwest and Southeast regions were more frequently resistant to itraconazole (29-30%) than those from the Northeast and Southwest regions (17-18%). Molecular epidemiologic studies revealed possible nosocomial transmission (five medical centers). Continued surveillance for the presence of non-C. albicans species among hospitalized patients is recommended.

[Evaluation of a breakpoint test for determination of fluconazole susceptibility of yeasts]

Using the breakpoint test at 1 g/ml and 4 g/ml fluconazole, a minimal inhibitory concentration (MIC) of < or = 4 g/ml fluconazole was determined against 78.5% of the 1254 clinical yeast isolates. When compared with the micro broth dilution test, none of a subset of 128/1254 strains had a higher MIC in the dilution test than in the breakpoint test, however, in 43.0% of the 128 strains the MIC was lower in the micro broth dilution test when compared to the MIC of the breakpoint test. In a subset of 94 strains with an MIC of > 4 g/ml fluconazole determined in the breakpoint test, the elevated MIC could be confirmed only in 45.7% of the strains when using the micro broth dilution test. The percentage of breakpoint test confirmation as well as the number of strains with decreased susceptibility towards fluconazole (> 4 g/ml) were species dependent, thus, the number of decreased-susceptible Candida albicans strains was smaller than that of C. glabrata or other Candida species such as C. krusei, C. inconspicua and some C. tropicalis strains. The breakpoint test allows to identify susceptible strains with a high accuracy. Strains with an MIC > 4 g/ml fluconazole should be tested in the micro dilution test to confirm decreased susceptibility and thus to indicate the need for higher dosage of fluconazole or a change of the antifungal therapy. The breakpoint test proved to be a rapid and reliable screening test.

Comparison of broth macrodilution, broth microdilution and E-test susceptibility tests of Cryptococcus neoformans for fluconazole

Forty Cryptococcus neoformans strains isolated from cerebral spinal fluid specimens collected from 39 patients were included in the study. The MICs for fluconacole were determined by YNB macrodilution test, microdilution tests using both RPMI1640 and YNB medium and E-tests on solidified RPMI1640 medium, Casitone and YNB agar. In comparison with the reference macrodilution method NCCLS M27-P both the microdilution as well as the E-test techniques can be used for fluconacole susceptibility testing of Cr. neoformans.

Active efflux by multidrug transporters as one of the strategies to evade chemotherapy and novel practical implications of yeast pleiotropic drug resistance

Mankind is faced by the increasing emergence of resistant pathogens, including cancer cells. An overview of the different strategies adopted by a variety of cells to evade chemotherapy is presented, with a focus on the mechanisms of multidrug transport. In particular, we analyze the yeast network for pleiotropic drug resistance and assess the potentiality of this system for further understanding of the mechanism of broad specificity and for development of novel practical applications.

Molecular typing and fluconazole susceptibility of urinary Candida glabrata isolates from hospitalized patients

At our community teaching hospital between August 1994 and August 1995, Candida glabrata accounted for 14% of all Candida isolates and for 31% of urinary Candida isolates. The culture site was urine for 68% of C. glabrata isolates compared to 30% of all Candida isolates (p < 0.001, chi 2). To study the association between C. glabrata and isolation from the urine, we analyzed all available C. glabrata urinary isolates over a 3-month period (23 isolates from 20 patients) using electrophoretic karyotyping, random amplified polymorphic DNA analysis, and fluconazole susceptibility testing. Random amplified polymorphic DNA generated eight types, although electrophoretic karyotyping generated 17 types. Combining the two methods resulted in 19 types indicating that urinary C. glabrata strains at our hospital are genetically diverse and the association between C. glabrata and urinary tract isolation does not appear to be due to horizontal transmission of a single or small number of strains. In vitro susceptibility tests showed that C. glabrata isolates from patients receiving fluconazole had significantly higher minimum inhibitory concentrations to fluconazole than those not receiving fluconazole (p < 0.05). Despite a limited number of patients and isolates, our data suggest that selection of less susceptible organisms by the presence of antifungal agents may be an important contributor to increased urinary isolation of C. glabrata from patients in our hospital.

Update on antifungal resistance

Overuse of antifungal agents has resulted in the selection of naturally resistant Candida species, as well as expression of resistance from previously susceptible species resulting from genetic mutations and/or selection of resistant subpopulations. Strategies for the appropriate use of antifungal agents need to be developed to prevent further development of resistance.

Use of CHROMagar Candida for genital specimens in the diagnostic laboratory

OBJECTIVE

To evaluate CHROMagar Candida (CA), a new yeast differential medium, for yeast isolation in a clinical laboratory for the routine examination of high vaginal swabs.

METHODS

Results of high vaginal swab cultures processed in a standard manner on plates containing equal halves of Sabouraud dextrose agar (SDA) and CA were compared. Non-Candida albicans yeast isolates were further speciated with API 20C AUX or API 32C. To assess the ease of use of CA, laboratory staff lacking in experience of the medium were asked to identify 23 unlabelled yeast cultures on CA by referring to six labelled reference plates.

RESULTS

Of the 1784 swab cultures processed, yeasts were isolated from 373 SDA and 368 CA. Of the 78 non-albicans isolates further speciated, CA identified correctly all cultures of C krusei and C tropicalis, and 82% of C glabrata. All the 38 inexperienced laboratory staff achieved 100% accuracy for C albicans and over 90% for C krusei and C tropicalis.

CONCLUSIONS

CA is a satisfactory isolation medium for genital specimens, allowing immediate and correct identification of the commonly encountered yeasts and easy recognition of mixed cultures.

Rapid identification of Candida species in blood cultures by a clinically useful PCR method

Widespread use of fluconazole for the prophylaxis and treatment of candidiasis has led to a reduction in the number of cases of candidemia caused by Candida albicans but has also resulted in the emergence of candidemias caused by innately fluconazole-resistant, non-C. albicans Candida species. Given the fulminant and rapidly fatal outcome of acute disseminated candidiasis, rapid identification of newly emerging Candida species in blood culture is critical for the implementation of appropriately targeted antifungal drug therapy. Therefore, we used a PCR-based assay to rapidly identify Candida species from positive blood culture bottles. This assay used fungus-specific, universal primers for DNA amplification and species-specific probes to identify C. albicans, C. krusei, C. parapsilosis, C. tropicalis, or C. glabrata amplicons. It also used a simpler and more rapid (1.5-h) sample preparation technique than those described previously and used detergent, heat, and mechanical breakage to recover Candida species DNA from blood cultures. A simple and rapid (3.5-h) enzyme immunosorbent assay (EIA)-based format was then used for amplicon detection. One hundred fifty blood culture bottles, including 73 positive blood culture bottle sets (aerobic and anaerobic) from 31 patients with candidemia, were tested. The combined PCR and EIA methods (PCR-EIA) correctly identified all Candida species in 73 blood culture bottle sets, including bottles containing bacteria coisolated with yeasts and 3 cultures of samples from patients with mixed candidemias originally identified as single-species infections by routine phenotypic identification methods. Species identification time was reduced from a mean of 3.5 days by routine phenotypic methods to 7 h by the PCR-EIA method. No false-positive results were obtained for patients with bacteremias (n = 18), artificially produced non-Candida fungemias (n = 3), or bottles with no growth (n = 20). Analytical sensitivity was 1 cell per 2-microl sample. This method is simpler and more rapid than previously described molecular identification methods, can identify all five of the most medically important Candida species, and has the potential to be automated for use in the clinical microbiology laboratory.

Multicenter randomized trial of fluconazole versus amphotericin B for treatment of candidemia in non-neutropenic patients. Canadian Candidemia Study Group

A randomized trial was conducted to compare the efficacy and safety of fluconazole versus that of amphotericin B in the treatment of candidemia in non-neutropenic adults. Enrollment was stratified by disease severity (APACHE II score). Patients were randomized (1:1) to receive amphotericin B 0.6 mg/kg/day (cumulative dose 8 mg/kg) or fluconazole 800 mg intravenous loading dose, then 400 mg daily for four weeks (intravenous for at least 10 days). Patients were monitored for six months. A total of 106 patients were enrolled. A protocol amendment implemented midway through the trial required patients to be removed from the study and treated with amphotericin B if species identification indicated candidemia due to Candida glabrata or Candida krusei. Baseline characteristics were similar for the two groups; 103 patients (fluconazole, 50; amphotericin B, 53) met the major enrollment criteria. The intention-to-treat analysis indicated successful therapy in 50% of fluconazole recipients compared to 58% of the amphotericin B group (p = 0.39; one-sided 95% CI, -8 to 24%). The efficacy analysis included 84 patients (fluconazole, 42; amphotericin B, 42); successful outcomes were observed in 57% and 62% of cases in the fluconazole and amphotericin B groups, respectively (p = 0.66: one-sided 95% CI, -12 to 22%). The mortality at day 14 for the fluconazole group was 26% and for the amphotericin B group 21% (p = 0.52; chi-square test) and remained similar throughout the course of follow-up, Drug-related adverse events were more frequent with amphotericin B than with fluconazole and prompted switching of therapy for two (4%) and zero cases, respectively. Fluconazole and amphotericin B were associated with similar clinical response rates and survival in the treatment of candidemia among non-neutropenic patients; however, drug-related adverse events were more frequent with amphotericin B.

Azole resistance in Candida

Resistance of Candida to azoles is an increasing problem. Susceptibility testing of Candida against fluconazole and ketoconazole is now feasible and desirable. Good correlation of resistance in vitro with clinical failure of fluconazole therapy has now been shown in mucosal candidiasis. The relationship, if any, between resistance and clinical failure in the context of invasive candidiasis is not clear at present and additional correlative work needs to be done. Monitoring of resistance trends in Candida is clearly important now.

Antifungal agents in the 1990s. Current status and future developments

Significant advances in antifungal therapy have occurred in the last decade. Most of these advances have been tied to the introduction of the triazoles, itraconazole and fluconazole. Itraconazole has proved efficacious for the treatment of subacute to chronic infections with the endemic mycoses and other opportunistic filamentous fungi, including Aspergillus spp. Fluconazole is now routinely used for mucocutaneous and systemic candidiasis, and its use for coccidioidal meningitis has obviated the need for intrathecal amphotericin B in most patients. Large, well controlled trials in AIDS patients with cryptococcal meningitis have shown the benefit of induction therapy with amphotericin B and flucytosine, followed by consolidation and life-long maintenance therapy with fluconazole. Concomitant with the increased use of these well tolerated, effective oral triazole agents has come the emergence of drug resistance in AIDS patients and shifts in the species of yeasts causing infection in hospitalised patients. Amphotericin B remains the drug of choice for many fungal infections, especially those that are life-threatening. Lipid-containing formulations of amphotericin B have recently been approved: these preparations significantly reduce the risk of amphotericin B-induced nephrotoxicity. Several new fungicidal agents are currently in early trials. With the increasing number of available antifungal drugs, future studies will help define the appropriate niche for each and the possible benefit of therapy with combinations of drugs.

Isolation and characterization of fluconazole- and amphotericin B-resistant Candida albicans from blood of two patients with leukemia

Infections with fluconazole-resistant Candida albicans isolate have rarely been described in clinical settings other than oropharyngeal candidiasis in patients with late-stage AIDS. We report on two patients with leukemia who developed fungemia caused by fluconazole-resistant C. albicans after receiving fluconazole prophylaxis (400 mg/day) and empiric amphotericin B therapy (0.5 mg/kg of body weight per day). The fluconazole MICs for the isolates were > or = 64 micrograms/ml, and the isolates were resistant to other azoles and had membrane sterol changes consistent with a mutation in the delta 5,6-sterol desaturase gene. The lack of ergosterol in the cytoplasmic membrane of the fluconazole-resistant strains also imparted resistance to amphotericin B. Both patients were successfully treated with high-dose amphotericin B (1 to 1.25 mg/kg/day) and flucytosine (150 mg/kg/day).

Multiple efflux mechanisms are involved in Candida albicans fluconazole resistance

Fluconazole-susceptible Candida albicans strains accumulated [3H]fluconazole at a rate of approximately 2 pmol/min per 10(9) cells. Fluconazole accumulation was not affected by the pretreatment of cells with sodium azide or with 2-deoxyglucose. The rate of fluconazole accumulation became saturated at high fluconazole concentrations and was not affected by the addition of ketoconazole, and there was no fluconazole accumulation in cells incubated at 4 degrees C. A fluconazole-resistant mutant of C. albicans SGY-243 was isolated following growth enrichment in fluconazole-containing medium. Cells of the mutant strain, designated FR2, showed a reduced rate of fluconazole accumulation compared with SGY-243 and were not resistant to other azole antifungal agents. The rates of fluconazole accumulation by C. albicans FR2 and the other azole-resistant strains, B59630, AD, and KB, were increased in the presence of sodium azide, suggesting that fluconazole resistance in these strains may be associated with an energy-dependent drug efflux. Fluconazole-resistant C. albicans strains all contained elevated amounts (2- to 17-fold) of mRNA encoding Cdr1, and an ATP-binding cassette-type transporter. In addition, C. albicans FR2 also contained increased amounts of mRNA encoding Benr, a major facilitator superfamily transporter. These results suggest that fluconazole enters C. albicans cells by facilitated diffusion and that fluconazole resistance may involve energy-dependent drug efflux associated with increased expression of Benr and/or Cdr1.

Microdilution antifungal susceptibility testing of Candida albicans and Cryptococcus neoformans with and without agitation: an eight-center collaborative study

The growth patterns observed in the trailing wells when fluconazole is being tested may give rise to readings that suggest resistance or increased MICs for known susceptible strains. We conducted a multicenter study to evaluate the intralaboratory and interlaboratory reproducibilities of a method that uses agitation to disperse these types of growth. Ten strains of Candida albicans and five strains of Cryptococcus neoformans were tested against fluconazole, flucytosine, and amphotericin B by using a microdilution adaptation of the proposed reference method of the National Committee for Clinical Laboratory Standards for yeasts (M27-T). The endpoint criterion used before agitation was consistent with the M27-T recommendation, while a criterion of 50% or more reduction of growth compared with the control was used after agitation. The results of this study showed that use of agitation and the modified endpoint criterion both improved intralaboratory and inter-laboratory agreement and increased the frequency of interpretable MICs. The MICs obtained by this method were comparable to those obtained by the broth macrodilution M27-T method. Like M27-T, this method was not able to definitely distinguish amphotericin B-susceptible from -resistant strains, although the MICs for the resistant strains were consistently higher than those for the susceptible ones. The findings imply that agitation should be seriously considered when antifungal agents, particularly fluconazole, are tested in a microdilution format.

In vitro activity of BMS-181184 compared with those of fluconazole and amphotericin B against various candida spp

We compared the in vitro activity of BMS-181184, the first compound of a new class of antifungal agents, the pradimicins, with those of fluconazole and amphotericin B against 64 clinical isolates of Candida species. MICs were determined by a microdilution method with high resolution medium for BMS-181184 and fluconazole and antibiotic medium no. 3 with 2% glucose for amphotericin B. MICs of BMS-181184 for all yeasts were in the range of 0.78 to 12.5 micrograms/ml. BMS-181184 was active against isolates resistant to other antifungal agents, consistent with a novel mode of action. Minimum fungicidal concentrations for 16 isolates showed that BMS-181184 was fungicidal. Clinical studies are now required to confirm its activity.

The changing face of candidemia: emergence of non-Candida albicans species and antifungal resistance

OBJECTIVES

To assess the changing epidemiology of candidemia in the 1990s, to evaluate the clinical implications for the presence of non-Candida albicans in blood, and to evaluate the presence of antifungal resistance in relation to prior antifungal administration.

DESIGN

Multicenter prospective observational study of patients with positive blood cultures for Candida species or Torulopsis glabrata.

SETTING

Four tertiary care medical centers.

RESULTS

Four hundred twenty-seven consecutive patients were enrolled. The frequency of candidemia due to non-C. albicans species significantly increased in each hospital throughout the 3.5-year study period (P = 0.01). Thirteen percent of candidemias occurred in patients who were already receiving systemic antifungal agents. Candidemias developing while receiving antifungal therapy were more likely caused by non-C. albicans species than by C. albicans species (P = 0.0005). C. parapsilosis and C. krusei were more commonly seen with prior fluconazole therapy, whereas T. glabrata was more commonly seen with prior amphotericin B therapy. Candida species isolated during episodes of breakthrough candidemia exhibited a significantly higher MIC to the antifungal agent being administered (P < 0.001).

CONCLUSION

In this large scale study, the non-C. albicans species, especially T. glabrata, emerged as important and frequent pathogens causing fungemia. This finding has major clinical implications given the higher complication and mortality rate associated with the non-C. albicans species. The change in the pattern of candidemia might be partly attributed to the increase in number of immunocompromised hosts and the widespread use of prophylactic or empiric antifungal therapy. This is an ominous sign given the in vitro resistance of the non-C. albicans species to currently available antifungal agents.

Mixed oropharyngeal candidiasis due to Candida albicans and non-albicans Candida strains in HIV-infected patients

In order to determine the clinical significance of mixed oropharyngeal candidiasis (Candida albicans plus a non-albicans strain of Candida) in patients infected with HIV-1, a retrospective chart review was done in 12 HIV-1-infected patients with a clinical episode of oropharyngeal candidiasis, in whom a mixed culture of Candida albicans (found to be fluconazole-sensitive) plus a non-albicans species of Candida was obtained from their oral cavities. This group was compared with 26 HIV-positive patients (control group) with oropharyngeal candidiasis due to Candida albicans (found to be fluconazole-sensitive). Antifungal susceptibility testing was performed by a broth microdilution test with RPMI-2% glucose. A fungal strain was considered fluconazole-sensitive if its MIC was < 0.5 micrograms/ml. Both the study and control groups had similar clinical and demographic characteristics. All the patients were severely immunocompromised, with a mean CD4+ lymphocyte count of 63/mm3 (95% CI 41-84) and 80/mm3 (95% CI 25-135) in the study and control groups, respectively. In the study group, seven patients had Candida albicans and Candida krusei in their oral cavity, four had Candida albicans and Candida glabrata, and one had Candida albicans and Candida tropicalis. Antifungal therapy consisted of ketoconazole (5 patients in the study group, 14 in the control group) or fluconazole (7 patients in the study group, 12 in the control group); no statistically significant difference in clinical outcome was observed. Fungal strain persistence after therapy was frequently observed in both groups. It is concluded that non-albicans strains of Candida, less sensitive to azole drugs than their Candida albicans counterparts, are not clinically relevant in episodes of mixed oropharyngeal candidiasis in HIV-1-infected patients.

Susceptibilities of Candida spp. to antifungal agents visualized by two-dimensional scatterplots of relative growth

The growth of 811 clinical yeast isolates in the presence of single concentrations of antifungal agents was measured spectrophotometrically and expressed as a percentage of growth in inhibitor-free control cultures. Two-dimensional scatterplots of the relative growth data allowed for the simple visual determination of some susceptibility trends, including correlations in relative growth between different agents and in relative susceptibilities between different yeast species. A positive susceptibility correlation was found for relative growth results with the azole antifungal agents fluconazole, itraconazole, and ketoconazole for 504 Candida albicans isolates. The relative growth scatterplots for fluconazole versus itraconazole showed that 50 (9.9%) of 504 C. albicans isolates were outliers with respect to the 95% confidence limits for a line of correlated relative growth established with an initial test panel of 59 isolates of this species. The outlying isolates were relatively less susceptible to fluconazole than to itraconazole under the conditions of the test. Most of the outliers were received in 1993 and 1994; only 3.9% of the isolates received in 1991 and 1992 and 1.7% of the isolates received before 1991 showed this differential susceptibility. In addition, most of the outliers came from patients with human immunodeficiency virus infections. The relative growth scatterplots confirmed the known high susceptibility of most Candida parapsilosis isolates to both fluconazole and itraconazole and the specifically low susceptibility of Candida krusei isolates to fluconazole. The scatterplots also illustrated a tendency towards lower (and correlative) relative growth among oral isolates obtained from AIDS patients who responded to azole antifungal treatment than among isolates from clinical nonresponders.

Direct identification and recognition of yeast species from clinical material by using albicans ID and CHROMagar Candida plates

Two chromogenic media, Albicans ID and CHROMagar Candida agar plates, were compared with a reference medium, Sabouraud-chloramphenicol agar, and standard methods for the identification of yeast species. This study involved 951 clinical specimens. The detection rates for the two chromogenic media for polymicrobial specimens were 20% higher than that for the Sabouraud-chloramphenicol agar plates. The rates of identification of Candida albicans for Albicans ID and CHROMagar Candida agar plates were, respectively, 37.0 and 6.0% after 24 h of incubation and 93.6 and 92.2% after 72 h of incubation, with specificities of 99.8 and 100%. Furthermore, CHROMagar Candida plates identified 13 of 14 Candida tropicalis and 9 of 12 Candida krusei strains after 48 h of incubation.

Routine use of CHROMagar Candida medium for presumptive identification of Candida yeast species and detection of mixed fungal populations

OBJECTIVE: To assess the value of the new differential culture medium CHROMagar Candida for routine investigation of clinical specimens. METHODS: During a whole year, 6150 clinical samples were plated on CHROMagar Candida medium. After incubation, the green colonies were considered to be Candida albicans. The colonies of other colors were identified using Bichrolatex-krusei, or by their assimilation pattern on ID 32C test strips and their morphology on rice cream-agar-Tween. RESULTS: Among the 6150 clinical samples, 1643 were positive for fungi. Aspergillus fumigatus and Geotrichum sp. were the predominant filamentous fungi isolated. Candida albicans was the most common species isolated (1274 of the positive samples; 77.5%), and Candida glabrata was the second most common yeast isolated (174 positive samples; 10.6%). Other yeast species were detected at lower frequencies, mainly Candida tropicalis (3.8%), Candida krusei (2.7%), Saccharomyces cerevisiae (2.7%) and Candida kefyr (2.3%), and 16 samples revealed a lipophilic species, Malassezia furfur. Mixed fungal populations accounted for 14.7% of the positive samples. Two or more yeast species were detected in 206 of the 242 specimens containing mixed fungal populations, and five yeast species were detected in one sample. Additionally, we did not observe significant differences in the isolation of yeasts or filamentous fungi from the 366 samples simultaneously plated on CHROMagar Candida and Sabouraud dextrose agar. Close agreement between the two culture media was observed for 89.9% of these samples. CONCLUSIONS: CHROMagar Candida medium was shown to be extremely helpful in a routine clinical mycology service, facilitating the detection of mixed cultures of yeasts and allowing direct identification of C. albicans, as well as rapid presumptive identification of the other yeasts: C. glabrata, C. tropicalis, C. krusei and S. cerevisiae. This chromogenic medium thus appears to be suitable as a primary culture medium, particularly for the mycologic surveillance of immunocompromised patients.

Application of CHROMagar Candida for rapid screening of clinical specimens for Candida albicans, Candida tropicalis, Candida krusei, and Candida (Torulopsis) glabrata

CHROMagar Candida is a new differential culture medium that allows selective isolation of yeasts and simultaneously identifies colonies of Candida albicans, C. tropicalis, and C. krusei. We evaluated the use of this medium with 316 yeast isolates including 247 isolated directly on CHROMagar from clinical material. Over 95% of stock and clinical isolates of C. albicans, C. tropicalis, and C. krusei were correctly identified on the basis of colony morphology and pigmentation on CHROMagar. Additionally, CHROMagar also allowed the identification of C. (Torulopsis) glabrata at a similar level of accuracy. The overall agreement between two observers in reading the CHROMagar plates was 95%. Growth of Candida sp. isolates on CHROMagar had no adverse effect on antifungal MICs or Vitek identification results. In parallel, cultures of 548 stool and rectal swab specimens set up on CHROMagar and Sabouraud glucose agar (SGA) were positive in 234 instances. CHROMagar was positive and SGA was negative for 11 specimens, and CHROMagar was negative and SGA was positive for 18 specimens. A single yeast species was isolated on both media from 162 specimens, and in 146 (90%) of these specimens the same species was detected on both CHROMagar and SGA. A total of 43 of the 234 positive cultures contained mixtures of yeast species. Twenty (47%) of these mixed cultures were detected only on CHROMagar. CHROMagar is extremely useful in making a rapid presumptive identification of common yeast species. This capability plus the ability to detect mixed cultures of Candida spp. promises to improve and streamline the work flow in the mycology and clinical microbiology laboratory.

Systemic Candida infections

Over the past two decades, Candida species have come to be regarded as important agents of nosocomial infection. In this paper, initially presented as a teaching conference at the Yale University School of Medicine, we summarize recent information pertaining to the epidemiology, diagnosis, and treatment of systemic Candida infections.

Demonstration of synergy with fluconazole and either ibuprofen, sodium salicylate, or propylparaben against Candida albicans in vitro

The combination of fluconazole with either ibuprofen, sodium salicylate, or propylparaben resulted in synergistic activity (fractional inhibitory index, < 0.5) against Candida albicans NCYC 620 in a microdilution checkerboard assay. Synergism between miconazole and ibuprofen was also demonstrated. In three or four clinical isolates of C. albicans from AIDS patients, the combination of fluconazole and ibuprofen was synergistic. Preparation of the inoculum and the growth conditions used were those recommended by the National Committee for Clinical Laboratory Standards for susceptibility testing. A visual estimation of total inhibition of growth and determination of an 80% reduction in the optical density at 492 nm compared with those for the control were taken as endpoints for the calculation of synergy, and a good correlation between both estimates was demonstrated.

Comparison of two alternative microdilution procedures with the National Committee for Clinical Laboratory Standards reference macrodilution method M27-P for in vitro testing of fluconazole-resistant and -susceptible isolates of Candida albicans

The National Committee for Clinical Laboratory Standards has proposed a reference broth macrodilution method for in vitro antifungal susceptibility testing of yeasts (the M27-P method). This method is cumbersome and time-consuming and includes MIC endpoint determination by the visual and subjective inspection of growth inhibition after 48 h of incubation. Two alternative microdilution procedures for MIC endpoint determination, a spectrophotometric MIC endpoint test that evaluates 80% growth inhibition by the drug and a colorimetric method with an oxidation-reduction indicator (Alamar Blue), were compared with the M27-P method for fluconazole susceptibility testing of 45 susceptible and resistant isolates of Candida albicans. The spectrophotometric method was performed with RPMI 1640 medium with 2% glucose, and the other two tests were performed with plain RPMI 1640 medium. All tests were incubated at 35 degrees C. Excellent agreement was demonstrated between the M27-P method and both 24-h microdilution tests (97.7%) as well as between the two microdilution tests (95.5%). Also, there was agreement in the detection in vivo of fluconazole resistance by the three methods. These preliminary data indicate that both microdilution methods may serve as less subjective alternatives to the M27-P method for the determination of fluconazole MIC endpoints.