Evaluation of the etest method using Mueller-Hinton agar with glucose and methylene blue for determining amphotericin B MICs for 4,936 clinical isolates of Candida species

Mixed oral candidiasis in type 2 diabetic patients: Identification and spectrum of sensitivity

Introduction

Patients with type 2 diabetes mellitus are susceptible to acquire Candida spp. infections, sometimes involving more than one species. The resistance of some species to antimycotic agents can cause treatment failure.

Objectives

To determine the frequency and clinical varieties of mixed oral candidiasis in patients with type 2 diabetes mellitus, the involved species, and its sensitivity spectra when exposed to antifungals used as candidiasis treatment.

Material and methods

We developed an analytical cross-sectional study with 72 patients with type 2 diabetes mellitus with hyperglycemia (HbA1C ≥ 7%) and an oral candidiasis diagnosis. The causal species of oral candidiasis were identified through microbiological techniques, and sensitivity tests were carried out using the diffusion method in a plate with strips (E-test ®).

Results

We included 72 patients in the study, 32 (44%) males and 40 (56%) females. Patients were divided into three age groups: young adults (17%), adults (74%), and older adults (9%). The mean age of the patients was 51 years. No significant differences were found between mixed oral candidiasis and groups (sex and age), or between mixed oral candidiasis and gender, glycosylated hemoglobin level (HbA1C), antihyperglycemic treatment, or type 2 diabetes mellitus time of diagnosis. We found a correlation between the adult group and development of mixed or simple oral candidiasis. The results showed eight (13%) cases of mixed oral candidiasis: seven with a coinfection of two species and one with a coinfection of three species. The identified species were Candida albicans, C. glabrata, C. dubliniensis, C. kefyr, C. tropicalis, and C. krusei. Most of these species presented sensitivity against ketoconazole and fluconazole, and higher resistance to itraconazole.

Conclusions

Mixed oral candidiasis occurs in approximately 10% of the patients with type 2 diabetes mellitus and its treatment can be ineffective when the etiological agent is not identified.

Antifungal susceptibility testing in Candida species: current methods and promising new tools for shortening the turnaround time

INTRODUCTION

Invasive fungal diseases (IFDs) have received attention as an emerging public health threat, are difficult to diagnose and to treat, and are associated with substantial morbidity and mortality. The standard of care in IFD management requires an early and targeted antifungal treatment, hence covers - amongst others - species identification and antifungal susceptibility testing (AFST).

AREAS COVERED

This review gives an overview of methods currently applied in AFST and highlights promising new tools for shortening the turnaround time focusing on Candida species.

EXPERT OPINION

The performance of the broth microdilution reference methods for AFST is not suitable for daily laboratory practice as they are too labor-intensive and time-consuming. Other conventional approaches such as disk diffusion assays, epsilometer tests, colorimetric or automated approaches are easier in handling, and in part, show good correlations with the reference methods. Promising results for shortening the turnaround time in providing MIC data or resistance detection include matrix-assisted laser desorption/ionization-time of flight mass spectrometer (MALDI-TOF MS) assisted AFST, molecular-based techniques and modified conventional approaches applying direct inoculation methods. These underlying AFST concepts are promising but in part completely different, have their own advantages and disadvantages, and need further clinical validation.

Relative Abundances of Candida albicans and Candida glabrata in In Vitro Coculture Biofilms Impact Biofilm Structure and Formation

Candida is a member of the normal human microbiota and often resides on mucosal surfaces such as the oral cavity or the gastrointestinal tract. In addition to their commensality, Candida species can opportunistically become pathogenic if the host microbiota is disrupted or if the host immune system becomes compromised. An important factor for Candida pathogenesis is its ability to form biofilm communities. The two most medically important species-Candida albicans and Candida glabrata-are often coisolated from infection sites, suggesting the importance of Candida coculture biofilms. In this work, we report that biofilm formation of the coculture population depends on the relative ratio of starting cell concentrations of C. albicans and C. glabrata When using a starting ratio of C. albicans to C. glabrata of 1:3, ∼6.5- and ∼2.5-fold increases in biofilm biomass were observed relative to those of a C. albicans monoculture and a C. albicans/C. glabrata ratio of 1:1, respectively. Confocal microscopy analysis revealed the heterogeneity and complex structures composed of long C. albicans hyphae and C. glabrata cell clusters in the coculture biofilms, and reverse transcription-quantitative PCR (qRT-PCR) studies showed increases in the relative expression of the HWP1 and ALS3 adhesion genes in the C. albicans/C. glabrata 1:3 biofilm compared to that in the C. albicans monoculture biofilm. Additionally, only the 1:3 C. albicans/C. glabrata biofilm demonstrated an increased resistance to the antifungal drug caspofungin. Overall, the results suggest that interspecific interactions between these two fungal pathogens increase biofilm formation and virulence-related gene expression in a coculture composition-dependent manner.IMPORTANCECandida albicans and Candida glabrata are often coisolated during infection, and the occurrence of coisolation increases with increasing inflammation, suggesting possible synergistic interactions between the two Candida species in pathogenesis. During the course of an infection, the prevalence of each Candida species may change over time due to differences in metabolism and in the resistance of each species to antifungal therapies. Therefore, it is necessary to understand the dynamics between C. albicans and C. glabrata in coculture to develop better therapeutic strategies against Candida infections. Existing in vitro work has focused on understanding how an equal-part culture of C. albicans and C. glabrata impacts biofilm formation and pathogenesis. What is not understood, and what is investigated in this work, is how the composition of Candida species in coculture impacts overall biofilm formation, virulence gene expression, and the therapeutic treatment of biofilms.

Use of Mueller-Hinton broth and agar in the germ tube test

Candida albicans is often isolated from clinical samples, thus its presumptive differentiation from other species of the same genus can be based on its ability to form the germ tube in human serum. Nevertheless, there are two other species that share this characteristic: C. dubliniensis and C. africana. The aim of this study was to compare four different substrates to perform the germ tube (GT) test. The Candida spp. isolates were identified using a manual system (135 C. albicans, 24 C. tropicalis and one C. dubliniensis). The germ tube test was performed with fresh, previously frozen serum and Mueller-Hinton (MH) broth and agar. GT was observed in 96% (130/136) of the isolates through the fresh serum technique, 94% (128/136) through previously frozen serum, 92% (125/136) in MH agar, and 90% (122/136) in MH broth. The sensitivity of each test was higher than 90%, with 100% specificity. Both the MH agar and broth were able to identify the true positives, and false positives were not found. However, some C. albicans isolates were not identified. MH agar and broth may be used in laboratory for the rapid presumptive identification of C. albicans, as an alternative method for germ tube test.

Canadian clinical practice guidelines for invasive candidiasis in adults

Candidemia and invasive candidiasis (C/IC) are life-threatening opportunistic infections that add excess morbidity, mortality and cost to the management of patients with a range of potentially curable underlying conditions. The Association of Medical Microbiology and Infectious Disease Canada developed evidence-based guidelines for the approach to the diagnosis and management of these infections in the ever-increasing population of at-risk adult patients in the health care system. Over the past few years, a new and broader understanding of the epidemiology and pathogenesis of C/IC has emerged and has been coupled with the availability of new antifungal agents and defined strategies for targeting groups at risk including, but not limited to, acute leukemia patients, hematopoietic stem cell transplants and solid organ transplants, and critical care unit patients. Accordingly, these guidelines have focused on patients at risk for C/IC, and on approaches of prevention, early therapy for suspected but unproven infection, and targeted therapy for probable and proven infection.

Detection of amphotericin B resistance in Candida haemulonii and closely related species by use of the Etest, Vitek-2 yeast susceptibility system, and CLSI and EUCAST broth microdilution methods

The emerging fungal pathogens Candida haemulonii and Candida pseudohaemulonii often show high-level resistance to amphotericin B (AMB). We compared the utilities of five antifungal susceptibility testing methods, i.e., the Etest using Mueller-Hinton agar supplemented with glucose and methylene blue (Etest-MH), the Etest using RPMI agar supplemented with glucose (Etest-RPG), the Vitek-2 yeast susceptibility system, and the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) broth microdilution methods, for the detection of AMB-resistant isolates of C. haemulonii and closely related species. Thirty-eight clinical isolates (8 C. haemulonii, 10 C. pseudohaemulonii, and 20 Candida auris isolates) were analyzed. Of the 18 C. haemulonii and C. pseudohaemulonii isolates, 18, 15, 18, 10, and 9 exhibited AMB MICs of >1 μg/ml by the Etest-MH, Etest-RPG, Vitek-2, CLSI, and EUCAST methods, respectively. All 20 C. auris isolates showed AMB MICs of ≤1 μg/ml by all five methods. Of the methods, the Etest-MH generated the broadest distribution of AMB MICs for all 38 isolates and showed the best discrimination between the C. haemulonii and C. pseudohaemulonii isolates (4 to 32 μg/ml) and those of C. auris (0.125 to 0.5 μg/ml). Taking the Etest-MH as the reference method, the essential agreements (within two dilutions) for the Etest-RPG, Vitek-2, CLSI, and EUCAST methods were 84, 92, 55, and 55%, respectively; the categorical agreements were 92, 92, 79, and 76%, respectively. This study provides the first data on the efficacy of the Etest-MH and its excellent agreement with Vitek-2 for discriminating AMB-resistant from AMB-susceptible isolates of these Candida species.

Correlation of Etest and Neo-Sensitabs diffusion assays on Mueller-Hinton-methylene blue agar with broth microdilution reference method (CLSI-M27-A2) for testing susceptibilities of Cryptococcus neoformans to amphotericin B and fluconazole

Cryptococcus neoformans causes disseminated infection in 7-8% of HIV positive patients admitted to Hospital F. J. Muñiz in Buenos Aires. Meningoencephalitis is the most frequent clinical manifestation and is one of the main causes of death in those patients with AIDS. The standard treatment for this mycosis consists of amphotericin B followed by fluconazole until two successive cultures of CFS are negative. Although resistance to these drugs is infrequent, minimal inhibitory concentrations (MIC) of some antifungals can be high. Since it is important to know the susceptibility levels of this fungus to the antifungal drugs usually employed in our institution, we analyzed the susceptibility test results of C. neoformans with two diffusion methods (Etest and NeoSensitabs tablets) employing Mueller-Hinton agar with 2% glucose and 0.5 microg/ml methylene blue. These results were compared with MICs obtained through the use of the broth microdilution reference method (CLSI). Results showed good agreement with the reference method, with no very major errors and only two major errors for fluconazole using NeoSensitabs tablets. For all the above mentioned, we confirm the usefulness of Mueller-Hinton agar to evaluate C. neoformans susceptibility to amphotericin B and fluconazole with these two agar diffusion methods.

Evaluation of the VITEK 2 system to test the susceptibility of Candida spp., Trichosporon asahii and Cryptococcus neoformans to amphotericin B, flucytosine, fluconazole and voriconazole: a comparison with the M27-A3 reference method

We compared the susceptibilities of 302 isolates (209 Candida spp., 89 Cryptococcus neoformans and four Trichosporon asahii) against amphotericin B (AMB), flucytosine (5FC), fluconazole (FLC) and voriconazole (VRC) obtained with an automated commercial system (VITEK 2, bioMérieux, Spain) and the Clinical and Laboratory Standards Institute (CLSI M27-A3) reference broth microdilution method (BMD). Reference BMD MIC endpoints were determined visually after 24-72 h of incubation, depending on the species, and VITEK 2 system MIC endpoints were determined spectrophotometrically by automated components of this equipment. For Candida spp. and T. asahii, the overall MIC agreement between of the results of the VITEK 2 system and the 24/48-h BMD was: 34/62% for AMB; 96.3% at 24/48-h for 5FC; 87.8/87.3% for FLC and 95.3/92% for VRC, respectively. The overall categorical agreement between both methods was: 98.5/97.6% for AMB at 24/48-h; 95.3% for 5FC at 24/48-h; 85.4/84.4% at 24/48-h for FLC; and 97.6/92.95% at 24/48-h for VRC. For C. neoformans, essential agreement was good for FLC (91%) and 5FC (84.2%) but not so good for AMB (69%). Excellent categorical agreement was obtained for all antifungal agents tested except for 5FC (69.7%). This new system could play an important role in the clinical laboratory, but more studies are necessary to verify its ability to identify resistant isolates.

Epidemiology of invasive mycoses in North America

The incidence of invasive mycoses is increasing, especially among patients who are immunocompromised or hospitalized with serious underlying diseases. Such infections may be broken into two broad categories: opportunistic and endemic. The most important agents of the opportunistic mycoses are Candida spp., Cryptococcus neoformans, Pneumocystis jirovecii, and Aspergillus spp. (although the list of potential pathogens is ever expanding); while the most commonly encountered endemic mycoses are due to Histoplasma capsulatum, Coccidioides immitis/posadasii, and Blastomyces dermatitidis. This review discusses the epidemiologic profiles of these invasive mycoses in North America, as well as risk factors for infection, and the pathogens' antifungal susceptibility.

Müeller-Hinton methylene blue media as an alternative to RPMI 1640 for determining the susceptibility of Cryptococcus neoformans and Cryptococcus gattii to posaconazole with Etest

Mueller-Hinton modified agar (MH-GMB) was compared with RPMI + 2% glucose-agar to determine the MICs of 80 isolates of Cryptococcus neoformans and C. gattii to posaconazole with Etest. MH-GMB minimised trailing and agreement between both media was 94%. Agreement of M27-A2 microbroth reference method was 98% with RPMI and 94% with MB-GMB.

In vitro susceptibility testing in fungi: a global perspective on a variety of methods

Candida and Aspergillus species are the most common causes of invasive fungal infections in immunocompromised patients. The introduction of new antifungal agents and recent reports of resistance emerging during treatment have highlighted the need for in vitro susceptibility testing. For some drugs, there is a supporting in vitro-in vivo correlation available from studies of clinical efficacy. Both intrinsic and emergent antifungal drug resistance are encountered. Various testing procedures have been proposed, including macrodilution and microdilution, agar diffusion, disk diffusion and Etest. Early recognition of infections caused by pathogens that are resistant to one or more antifungals is highly warranted to optimise treatment and patient outcome.

Caspofungin Etest endpoint for Aspergillus isolates shows poor agreement with the reference minimum effective concentration

The Clinical and Laboratory Standards Institute (CLSI) M38-A2 reference broth microdilution (BMD) method for the antifungal susceptibility testing of filamentous fungi now includes guidelines for testing echinocandin activity using the minimum effective concentration (MEC) as the endpoint measurement. In this study, we compared the caspofungin Etest MIC on RPMI agar and Mueller-Hinton agar (supplemented with glucose and methylene blue [MGM]) to the BMD MEC for 345 clinical Aspergillus isolates, including A. flavus, A. fumigatus, A. nidulans, A. niger, and A. terreus. The essential agreement (+/-1 log(2) dilution) of the Etest on MGM and RPMI agar with the reference BMD MEC was 18 and 26%, respectively. The geometric mean values for BMD MEC and MGM Etest were 0.137 and 0.024 microg/ml, respectively, and the geometric mean values for BMD and RPMI agar were 0.128 and 0.031 microg/ml, respectively. Comparatively, 91% of paired MGM and RPMI Etest results were within 2 log(2) dilutions of each other and consistently produced clearly defined endpoints. In conclusion, the caspofungin Etest MIC, like the BMD MEC, is a reproducible endpoint but is markedly lower than the reference BMD. In anticipation of susceptibility breakpoint assignments, optimization studies will be required to improve the concordance of these two assays so that the potential for underreporting echinocandin resistance in Aspergillus is mitigated.

Mutants with heteroresistance to amphotericin B and fluconazole in Candida

Several studies have reported the occurrence of infections caused by Candida yeasts as well as the increasing prevalence of non albicans species. The aim of the present work is focused on the obtaining of heteroresistance to amphotericin B and fluconazole in Candida species using two distinct methodologies: selection and induction. Resistant samples were obtained by selective pressure using a medium with fluconazole for growth, followed by growth in a medium with amphotericin B. The selective pressure was also created beginning with growth in amphotericin B medium followed by growth in fluconazole medium. Concomitantly, samples were submitted to the induction of resistance through cultivation in increasing concentrations of fluconazole, followed by cultivation in increasing concentrations of amphotericin B. Subsequently, the induction began with amphotericin B followed by fluconazole. Three samples resistant to fluconazole and amphotericin B were obtained, two by induction (C. glabrata and C. tropicalis) and one by selection (C. tropicalis). Both C. tropicalis originated from the same wild sample. After successive transfers for drug free medium, only the sample obtained by selection was able to maintain the resistance phenotype. These results suggest that the phenotype of heteroresitance to fluconazole and amphotericin B can be produced by two methodologies: selection and induction.

Current status of antifungal susceptibility testing methods

Antifungal susceptibility testing is a very dynamic field of medical mycology. Standardization of in vitro susceptibility tests by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST), and current availability of reference methods constituted the major remarkable steps in the field. Based on the established minimum inhibitory concentration (MIC) breakpoints, it is now possible to determine the susceptibilities of Candida strains to fluconazole, itraconazole, voriconazole, and flucytosine. Moreover, utility of fluconazole antifungal susceptibility tests as an adjunct in optimizing treatment of candidiasis has now been validated. While the MIC breakpoints and clinical significance of susceptibility testing for the remaining fungi and antifungal drugs remain yet unclear, modifications of the available methods as well as other methodologies are being intensively studied to overcome the present drawbacks and limitations. Among the other methods under investigation are Etest, colorimetric microdilution, agar dilution, determination of fungicidal activity, flow cytometry, and ergosterol quantitation. Etest offers the advantage of practical application and favorable agreement rates with the reference methods that are frequently above acceptable limits. However, MIC breakpoints for Etest remain to be evaluated and established. Development of commercially available, standardized colorimetric panels that are based on CLSI method parameters has added more to the antifungal susceptibility testing armamentarium. Flow cytometry, on the other hand, appears to offer rapid susceptibility testing but requires specified equipment and further evaluation for reproducibility and standardization. Ergosterol quantitation is another novel approach, which appears potentially beneficial particularly in discrimination of azole-resistant isolates from heavy trailers. The method is yet investigational and requires to be further studied. Developments in methodology and applications of antifungal susceptibility testing will hopefully provide enhanced utility in clinical guidance of antifungal therapy. However, and particularly in immunosuppressed host, in vitro susceptibility is and will remain only one of several factors that influence clinical outcome.

Candida krusei, a multidrug-resistant opportunistic fungal pathogen: geographic and temporal trends from the ARTEMIS DISK Antifungal Surveillance Program, 2001 to 2005

Candida krusei is well known as a fungal pathogen for patients with hematologic malignancies and for transplant recipients. Using the ARTEMIS Antifungal Surveillance Program database, we describe geographic and temporal trends in the isolation of C. krusei from clinical specimens and the in vitro susceptibilities of 3,448 isolates to voriconazole as determined by CLSI (formerly NCCLS) disk diffusion testing. In addition, we report the in vitro susceptibilities of bloodstream infection isolates of C. krusei to amphotericin B (304 isolates), flucytosine (254 isolates), anidulafungin (121 isolates), caspofungin (300 isolates), and micafungin (102 isolates) as determined by CLSI broth microdilution methods. Geographic differences in isolation were apparent; the highest frequency of isolation was seen for the Czech Republic (7.6%) and the lowest for Indonesia, South Korea, and Thailand (0 to 0.3%). Overall, 83% of isolates were susceptible to voriconazole, ranging from 74.8% in Latin America to 92.3% in North America. C. krusei was most commonly isolated from hematology-oncology services, where only 76.7% of isolates were susceptible to voriconazole. There was no evidence of increasing resistance of C. krusei to voriconazole from 2001 to 2005. Decreased susceptibilities to amphotericin B (MIC at which 90% of isolates were inhibited [MIC(90)], 4 microg/ml) and flucytosine (MIC(90), 16 microg/ml) were noted, whereas 100% of isolates were inhibited by < or =2 microg/ml of anidulafungin (MIC(90), 0.06 microg/ml), micafungin (MIC(90), 0.12 microg/ml) or caspofungin (MIC(90), 0.25 microg/ml). C. krusei is an uncommon but multidrug-resistant fungal pathogen. Among the systemically active antifungal agents, the echinocandins appear to be the most active against this important pathogen.

Multicenter comparison of the VITEK 2 antifungal susceptibility test with the CLSI broth microdilution reference method for testing amphotericin B, flucytosine, and voriconazole against Candida spp

A fully automated commercial antifungal susceptibility test system (VITEK 2; bioMérieux, Inc., Hazelwood, MO) was compared in three different laboratories with the Clinical and Laboratory Standards Institute (formerly the NCCLS) reference broth microdilution method (BMD) by testing 2 quality control strains, 10 reproducibility strains, and 426 isolates of Candida spp. against amphotericin B, flucytosine, and voriconazole. Reference BMD MIC endpoints were established after 24 and 48 h of incubation. VITEK 2 system MIC endpoints were determined spectrophotometrically after 9.1 to 27.1 h of incubation (mean, 12 to 14 h). Excellent essential agreement (within 2 dilutions) between the VITEK 2 system and the 24- and 48-h BMD MICs was observed for all three antifungal agents: amphotericin B, 99.1% and 97%, respectively; flucytosine, 99.1% and 98.8%, respectively; and voriconazole, 96.7% and 96%, respectively. Both intra- and interlaboratory agreements were >98% for all three drugs. The overall categorical agreements between the VITEK 2 system and BMD for flucytosine and voriconazole were 98.1 to 98.6% at the 24-h BMD time point and 96.9 to 97.4% at the 48-h BMD time point. The VITEK 2 system reliably detected flucytosine and voriconazole resistance among Candida spp. and demonstrated excellent quantitative and qualitative agreement with the reference BMD method.

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.

Invasive Candidiasis

Invasive candidiasis remains an important nosocomial infection that continues to present major diagnostic and therapeutic challenges to the clinician. Changes in the epidemiology of this disorder have occurred for many reasons, and included especially the extensive use of prophylactic antifungal agents, broad-spectrum antibacterial agents, and medical devices (eg, chronic indwelling intravascular catheters). The diagnosis of IC remains elusive in many patients, and there is a critical need for improved diagnostics that will provide clinicians the opportunity to intervene earlier in the course of disease. Newer antifungal agents offer promise in the treatment of candidemia and other forms of IC, but the optimal use of these agents, particularly in the approach to non-albicans Candida infections, needs to be explored in more detail. Furthermore, despite an overwhelming amount of data concerning risk factors and excess mortality associated with the development of IC, there is no consistent approach to treatment and primary prevention among individuals who are deemed to be at highest risk for this complication. Research that focuses on these important clinical areas could provide valuable insights into the diagnosis and management of this common and evolving infection.

Amphotericin B and Caspofungin Resistance in Candida glabrata Isolates Recovered from a Critically Ill Patient

BACKGROUND

Consecutive Candida glabrata isolates recovered from a patient in an intensive care unit were resistant to amphotericin B (minimum inhibitory concentration, up to 32 mu g/mL; determined by Etest [AB Biodisk]). Analyses at the national reference laboratory showed that some isolates were also resistant to azoles and caspofungin. In this study, 4 isolates were studied thoroughly using susceptibility assays and a mouse model and to determine clonality.

METHODS

Different broth microdilution tests, Etests, and time-kill studies for antifungals were performed in different media. Three of the 4 isolates were examined in an in vivo experiment, in which mice were challenged intravenously with 1 of 3 isolates and treated daily with amphotericin B, caspofungin, or saline. For the clonality studies, arbitrarily primed polymerase chain reaction (PCR) was performed with the 4 isolates, 8 isolates obtained from nonrelated patients, and a reference strain.

RESULTS

The murine model indicated that 1 isolate was resistant to amphotericin B, 1 had intermediate susceptibility, and 1 was fully susceptible. Two of the 3 isolates were resistant to caspofungin. Microdilution methods did not reliably differentiate between amphotericin B-susceptible and -resistant isolates. All assays identified caspofungin-susceptible and -resistant isolates. Arbitrarily primed PCR showed that the 4 isolates probably were of clonal origin.

CONCLUSIONS

We have documented the emergence of amphotericin B-resistant and caspofungin-resistant C. glabrata isolates during treatment of a critically ill liver transplant recipient. Only the Etest predicted amphotericin B resistance in the isolates. We recommend that important fungal strains recovered from patients who are receiving antifungal therapy should be tested for susceptibility to the antifungal drug used, because resistance can be present initially or may occur during treatment.