Further standardization of broth microdilution methodology for in vitro susceptibility testing of caspofungin against Candida species by use of an international collection of more than 3,000 clinical isolates

Overexpression of Candida albicans CDR1, CDR2, or MDR1 does not produce significant changes in echinocandin susceptibility

The micafungin and caspofungin susceptibilities of Candida albicans laboratory and clinical isolates and of Saccharomyces cerevisiae strains stably hyperexpressing fungal ATP-binding cassette (ABC) or major facilitator superfamily (MFS) transporters involved in azole resistance were determined using three separate methods. Yeast strains hyperexpressing individual alleles of ABC transporters or an MFS transporter from C. albicans gave the expected resistance profiles for the azoles fluconazole, itraconazole, and voriconazole. The strains hyperexpressing CDR2 showed slightly decreased susceptibility to caspofungin in agar plate drug resistance assays, as previously reported, but increased susceptibility to micafungin compared with either the strains hyperexpressing CDR1 or the null parent deleted of seven ABC transporters. The strains hyperexpressing CDR1 showed slightly decreased susceptibility to micafungin in these assays. A C. albicans clinical isolate overexpressing both Cdr1p and Cdr2p relative to its azole-sensitive isogenic progenitor acquired resistance to azole drugs and showed reduced susceptibility to caspofungin and slightly increased susceptibility to micafungin in agar plate drug resistance assays. None of the strains showed significant resistance to micafungin or caspofungin in liquid microdilution susceptibility assays. The antifungal activities of micafungin and caspofungin were similar in agarose diffusion assays, although the shape and size of the caspofungin inhibitory zones were affected by medium composition. The assessment of micafungin and caspofungin potency is therefore assay dependent; the differences seen with agar plate drug resistance assays occur over narrow ranges of echinocandin concentrations and are not of clinical significance.

Assessment of the paradoxical effect of caspofungin in therapy of candidiasis

Paradoxical growth of some Candida albicans isolates in the presence of caspofungin (CAS) in vitro has been demonstrated previously. We sought to determine whether a similar phenomenon occurred in vivo. A systemic model of candidiasis was studied in CD-1 mice by intravenous inoculation of different isolates of C. albicans. Infected animals were treated with CAS at various dosages (0.01 to 20 mg/kg) and CFU remaining in the kidneys determined. Four clinical isolates that showed paradoxical growth in vitro and one that did not were tested. Recovery of CFU from the kidneys showed that dosages of CAS at 0.1 mg/kg and above were efficacious in the reduction of C. albicans, but were not curative. Against isolates that show paradoxical growth in vitro, CAS was efficacious, but lacked dose responsiveness above 0.5 mg/kg against three of the four. One isolate, 95-68, showed paradoxical growth in vivo with significantly higher CFU recovered from mice given CAS at 20 mg/kg than those given CAS at 5 mg/kg, but the effect was not reproducible in a subsequent experiment. When CAS was given prophylactically and therapeutically, improved efficacy and cure rate were observed. Overall, these data indicate that CAS is highly efficacious against systemic murine candidiasis and a paradoxical effect was not reproducibly demonstrated in vivo.

In vitro susceptibilities of Candida spp. to caspofungin: four years of global surveillance

Caspofungin is being used increasingly as therapy for invasive candidiasis. Prospective sentinel surveillance for emergence of in vitro resistance to caspofungin among invasive Candida spp. isolates is indicated. We determined the in vitro activity of caspofungin against 8,197 invasive (bloodstream or sterile-site) unique patient isolates of Candida collected from 91 medical centers worldwide from 1 January 2001 to 31 December 2004. We performed antifungal susceptibility testing according to the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) M27-A2 method and used a 24-h prominent inhibition endpoint for determination of the MIC. Of 8,197 invasive Candida spp. isolates, species distribution was as follows: 54% Candida albicans, 14% C. glabrata, 14% C. parapsilosis, 11% C. tropicalis, 3% C. krusei, and 4% other Candida spp. Overall, caspofungin was very active against Candida (MIC50/MIC90, 0.03/0.25 microg/ml; 98.2% were inhibited at a MIC of < or = 0.5 microg/ml and 99.7% were inhibited at a MIC of < or = 1 microg/ml). Results by species (expressed as MIC50/MIC90 and the percentage inhibited at < or = 1 microg/ml) were as follows: C. albicans, 0.03/0.06, 99.9; C. glabrata, 0.03/0.06, 99.9; C. parapsilosis, 0.5/0.5, 99.0; C. tropicalis, 0.03/0.06, 99.7; C. krusei, 0.12/0.5, 99.0; and C. guilliermondii, 0.5/1, 94.4. Of the 25 isolates with caspofungin MICs of >1 microg/ml, 12 isolates were C. parapsilosis, 6 isolates were C. guilliermondii, 2 isolates were C. rugosa, and 1 isolate each was C. albicans, C. glabrata, C. krusei, C. lusitaniae, and C. tropicalis. There was no significant change in caspofungin activity over the 4-year study period. Likewise, there was no difference in activity by geographic region. Caspofungin has excellent in vitro activity against invasive clinical isolates of Candida from centers worldwide. Our prospective sentinel surveillance reveals no evidence of emerging caspofungin resistance among invasive clinical isolates of Candida.

Activities of micafungin against 315 invasive clinical isolates of fluconazole-resistant Candida spp

Micafungin is a new echinocandin exhibiting broad-spectrum activity against Candida spp. The activity of the echinocandins against Candida species known to express intrinsic or acquired resistance to fluconazole is of interest. We determined the MICs of micafungin and caspofungin against 315 invasive clinical (bloodstream and other sterile-site) isolates of fluconazole-resistant Candida species obtained from geographically diverse medical centers between 2001 and 2004. MICs were determined using broth microdilution according to the CLSI reference method M27-A2. RPMI 1640 was used as the test medium, and we used the MIC endpoint of prominent growth reduction at 24 h. Among the 315 fluconazole-resistant Candida isolates, 146 (46%) were C. krusei, 110 (35%) were C. glabrata, 41 (13%) were C. albicans, and 18 (6%) were less frequently isolated species. Micafungin had good in vitro activity against all fluconazole-resistant Candida spp. tested; the MICs at which 50% (MIC(50)) and 90% (MIC(90)) of isolates were inhibited were 0.03 microg/ml and 0.06 microg/ml, respectively. All the fluconazole-resistant Candida spp. were inhibited at a micafungin MIC that was </=1 microg/ml. Among the most common fluconazole-resistant Candida spp. tested in the collection, C. glabrata exhibited the lowest micafungin MICs (MIC(90), </=0.015 microg/ml), followed by C. albicans (MIC(90), 0.03 microg/ml) and C. krusei (MIC(90), 0.06 microg/ml). The new echinocandin micafungin has excellent in vitro activity against 315 invasive clinical isolates of fluconazole-resistant Candida, which represents the largest collection to date of fluconazole-resistant Candida isolates tested against micafungin. Micafungin may prove useful in the treatment of infections due to azole-resistant Candida.

Progressive loss of echinocandin activity following prolonged use for treatment of Candida albicans oesophagitis

OBJECTIVES

To illustrate the progressive loss of cross-echinocandin activity on Candida albicans isolates with strong clonal homology from a patient with advanced HIV infection and chronic oesophagitis progressively resistant to uninterrupted micafungin treatment.

METHODS

Antifungal susceptibility profiles for different antifungal agents were determined against serial C. albicans isolates retrieved before and during therapy. Multilocus sequencing typing (MLST) was performed on each of the isolates. FKS1 mutations conferring reduced susceptibility to echinocandin drugs were determined by DNA sequence analysis.

RESULTS

Four C. albicans isolates showing identical allelic homology were retrieved from the patient at the initiation and during therapy with micafungin. The progressive lack of clinical response to micafungin therapy was associated with increased MICs of all three echinocandin drugs (caspofungin, micafungin and anidulafungin) in association with the acquisition of mutations in the FKS1 gene.

CONCLUSIONS

This report documents for the first time a progressive loss of activity of all three echinocandin drugs against clonally related C. albicans isolates following long-term clinical exposure to this new class of antifungal agents.

Caspofungin: a review of its use in the treatment of fungal infections

Caspofungin (Cancidas) is the first of a new class of antifungal agents, the echinocandins, that inhibit the synthesis of the fungal cell wall component beta-(1,3)-D-glucan. Caspofungin is administered once daily by slow intravenous infusion and is used to treat infections caused by Candida spp. and Aspergillus spp. Caspofungin is a valuable new antifungal agent with a novel mechanism of action. In comparative clinical trials, caspofungin was no less effective than liposomal amphotericin B in the empirical treatment of neutropenic patients with persistent fever, amphotericin B deoxycholate in the treatment of invasive candidiasis or fluconazole in the treatment of oesophageal candidiasis. Caspofungin also displayed broadly similar efficacy to amphotericin B deoxycholate in oesophageal or oropharyngeal candidiasis and was effective as salvage therapy in patients with invasive aspergillosis who were refractory to or intolerant of standard therapy. The tolerability profile of caspofungin was similar to that of fluconazole and superior to that of amphotericin B deoxycholate and liposomal amphotericin B. Therefore, in the appropriate indications, caspofungin is a viable alternative to amphotericin B deoxycholate, liposomal amphotericin B or fluconazole.

Effectiveness of anidulafungin in eradicating Candida species in invasive candidiasis

In a phase 2 open-label, dose-ranging study in patients with candidemia, anidulafungin was effective in eradicating Candida albicans and other species of Candida. The anidulafungin MIC distribution showed that Candida albicans and C. glabrata were the most susceptible species and C. parapsilosis was the least susceptible species.

Emergence of disseminated candidiasis caused by Candida krusei during treatment with caspofungin: case report and review of literature

Current data indicate that caspofungin has in vitro activity against virtually all Candida species. However, we report herein a case of disseminated candidiasis due to Candida krusei which emerged during caspofungin treatment. Lung and brain secondary sites were then successfully treated using a combination of amphotericin B plus flucytosine, amphotericin B lipid complex, and voriconazole, sequentially. Among the total of four well documented cases of refractory invasive candidiasis during caspofungin therapy, the common risk factors appear to involve prior abdominal surgery, persistent foreign body, and anatomical sites where drug concentrations may be sub-optimal for Candida species with increased MICs. Caspofungin failure should be suspected in patients with persistent or emergent signs and symptoms of deep-seated invasive candidiasis.

In vitro activities of anidulafungin against more than 2,500 clinical isolates of Candida spp., including 315 isolates resistant to fluconazole

Anidulafungin is an echinocandin antifungal agent with potent activity against Candida spp. We assessed the in vitro activity of anidulafungin against 2,235 clinical isolates of Candida spp. using the CLSI broth microdilution method. Anidulafungin was very active against Candida spp. (the MIC at which 90% of strains are inhibited [MIC(90)] was 2 microg/ml when MIC endpoint criteria of partial inhibition [MIC-2] were used). Candida albicans, C. glabrata, C. tropicalis, C. krusei, and C. kefyr were the most susceptible species of Candida (MIC(90), 0.06 to 0.12 microg/ml), and C. parapsilosis, C. lusitaniae, and C. guilliermondii were the least susceptible (MIC(90), 0.5 to 2 microg/ml). In addition, 315 fluconazole-resistant isolates were tested, and 99% were inhibited by < or =1 microg/ml of anidulafungin. These results provide further evidence for the spectrum and potency of anidulafungin activity against a large and geographically diverse collection of clinically important isolates of Candida spp.

Caspofungin susceptibility testing of isolates from patients with esophageal candidiasis or invasive candidiasis: relationship of MIC to treatment outcome

The caspofungin clinical trial database offers an opportunity to assess susceptibility results for Candida pathogens obtained from patients with candidiasis and allows for correlations between efficacy outcomes and MICs. Candida isolates have been identified from patients enrolled in four studies of esophageal candidiasis and two studies of invasive candidiasis. The MICs of caspofungin for all baseline isolates were measured at a central laboratory using NCCLS criteria (document M-27A); MICs for caspofungin were defined as the lowest concentration inhibiting prominent growth at 24 h. MICs were then compared to clinical and microbiological outcomes across the two diseases. Susceptibility testing for caspofungin was performed on 515 unique baseline isolates of Candida spp. obtained from patients with esophageal candidiasis. MICs for caspofungin ranged from 0.008 to 4 microg/ml; the MIC50 and MIC90 were 0.5 and 1.0 microg/ml, respectively. Susceptibility testing was also performed on 231 unique baseline isolates of Candida spp. from patients with invasive candidiasis. The majority (approximately 96%) of MICs were between 0.125 and 2 microg/ml, with MIC50 and MIC90 for caspofungin being 0.5 and 2.0 microg/ml, respectively. Overall, caspofungin demonstrated potent in vitro activity against clinical isolates of Candida species. A relationship between MIC for caspofungin and treatment outcome was not seen for patients with either esophageal candidiasis or invasive candidiasis. Patients with isolates for which the MICs were highest (>2 microg/ml) had better outcomes than patients with isolates for which the MICs were lower (<1 microg/ml). Additionally, no correlation between MIC and outcome was identified for specific Candida species.

An Overview of Antifungal Drugs and Their Use for Treatment of Deep and Superficial Mycoses in Animals

Fungal infections are often challenging to manage, given the limited numbers of therapeutics and a general lack of applicable clinical literature for their use in a given animal species. This article reviews some of the underlying principles that can affect the therapeutic outcome for a given antifungal, and provides specific information from the literature that is intended to highlight the distinctive properties of the most commonly used antifungals in veterinary medicine to better facilitate their successful application in clinical practice.

Comparison of results of voriconazole disk diffusion testing for Candida species with results from a central reference laboratory in the ARTEMIS global antifungal surveillance program

The accuracy of antifungal susceptibility testing is important for reliable resistance surveillance and for the clinical management of patients with serious infections. Our primary objective was to compare the results of voriconazole disk diffusion testing of Candida spp. performed by centers participating in the ARTEMIS program with disk diffusion and MIC results obtained by the central reference laboratory. A total of 2,934 isolates of Candida spp. were tested by CLSI disk diffusion and reference broth microdilution methods in the central reference laboratory. These results were compared to the results of disk diffusion testing performed in the 54 participating centers. All tests were performed and interpreted following CLSI recommendations, as follows: susceptible (S), MIC of or=17 mm); susceptible dose dependent (SDD), MIC of 2 microg/ml (14 to 16 mm); and resistant (R), MIC of >or=4 microg/ml (or=4 microg/ml) by MIC testing. External quality assurance data obtained by surveillance programs such as the ARTEMIS Global Antifungal Surveillance Program ensure the generation of useful surveillance data and result in the continued improvement of antifungal susceptibility testing practices.

Caspofungin susceptibility testing of Candida inconspicua: correlation of different methods with the minimal fungicidal concentration

Minimal inhibitory and minimal fungicidal concentrations of caspofungin were determined for 48 Candida inconspicua isolates. By using CLSI (formerly NCCLS) methodology with the partial inhibition endpoint criterion, caspofungin exhibited a good fungicidal effect against C. inconspicua (the MIC(90) was 0.25 microg/ml and the minimum fungicidal concentration [MFC] was 0.5 microg/ml after 24 h). Total inhibition yielded falsely elevated MICs, exceeding even the respective MFCs.

Flow cytometry susceptibility testing for the antifungal caspofungin

Rapid antifungal susceptibility testing for the antifungal agent caspofungin can be performed using flow cytometry (FC). An FC procedure using acridine orange provided minimum inhibitory concentration (MIC) results within 7 to 9 h which were compared with results obtained using the NCCLS M27-A2 protocol. To evaluate the consistency of this method, susceptibility testing using caspofungin was performed using 73 isolates of eight different species of Candida from various clinical samples in Central California. Macrotiter or microdilution tests were performed according to the NCCLS M27-A2 protocol, and the MICs were compared to those provided by our flow cytometry method. All isolates tested had results within the sensitive interpretive category, and 90% of the results compared within 1 dilution, showing excellent agreement between the methods. The MIC at which 50% of the isolates tested were inhibited (MIC50) and the MIC90 of caspofungin for all eight Candida species were within 1 dilution. This flow cytometer 7-h protocol for testing the antifungal susceptibility of Candida species to caspofungin provided results equivalent to those obtained with the M27-A2 protocol.

Sensititre YeastOne caspofungin susceptibility testing of Candida clinical isolates: correlation with results of NCCLS M27-A2 multicenter study

The ability of Sensititre YeastOne to discriminate isolates with reduced caspofungin susceptibility was determined against 36 Candida spp. (6 with a known FKS1 mutation). Results were compared with those of M27-A2. The MIC endpoint was 100% growth inhibition. Overall agreement (+/-2 log2) was 87.16%. Sensititre YeastOne detected strains with reduced caspofungin susceptibility.

Fatal Blastoschizomyces capitatus sepsis in a neutropenic patient with acute myeloid leukemia: first documented case from Greece

Blastoschizomyces capitatus (formerly known as Geotrichum capitatum and Trichosporon capitatum) is a rare, yet an emerging, cause of invasive infections in immunosuppressed patients. Profound and prolonged neutropenia is the crucial predisposing factor for this yeast infection. Blastoschizomyces capitatus was isolated from peripheral blood cultures of a profoundly neutropenic patient with acute myeloid leukemia (M2 FAB). Despite administration of antifungal chemotherapy with liposomal amphotericin B at 4.5 mg kg(-1) daily, the patient succumbed 4 days after initiation of treatment. Infections attributed to B. capitatus have generally a poor prognosis, although the yeast shows in vitro susceptibility to antifungal agents. Low flucytosine, caspofungin acetate, voriconazole and amphotericin B minimum inhibitory concentration values were also recorded with our isolate. The clinical relevance of the in vitro susceptibility testing against the isolate and the current antifungal chemotherapy regimens against B. capitatus systemic infections are discussed.

Impact of real-time fungal susceptibility on clinical practices

PURPOSE OF REVIEW

In the past two decades standardized in-vitro antifungal susceptibility tests have been developed in response to increasing invasive fungal infections. Our purpose is to review the utility of real-time Candida antifungal susceptibility testing and its effects on clinical outcomes in the context of the new antifungal agents, existing antifungal susceptibility testing methods, and the changing epidemiology and susceptibilities of Candida spp.

RECENT FINDINGS

New antifungal agents active against Candida spp. are now available. Caspofungin is approved for the treatment of invasive candidiasis but standardized antifungal susceptibility testing has not been developed. The newer triazoles, such as voriconazole, posaconazole and ravuconazole, are not yet approved for invasive candidiasis. As infections caused by non-albicans Candida spp. with growing resistance to fluconazole increase, antifungal susceptibility testing may be important to guide therapy. Unfortunately, few studies exist describing the impact of real-time antifungal susceptibility testing on the treatment of invasive fungal infections.

SUMMARY

Newer antifungal agents with broader anti-Candida activity, fewer adverse events and minimal resistance are currently available. The challenge clinicians face is choosing when to use these agents appropriately, while considering the changing Candida epidemiology and susceptibility trends without over-treating fluconazole-sensitive pathogens. Unfortunately, the correlation of antifungal susceptibility testing results by any method and clinical outcome is mostly lacking. We suggest that a concerted examination of the utility of real-time antifungal susceptibility testing and its effect on clinical outcomes by guiding appropriate antifungal therapy for high-risk patients with invasive candidiasis is warranted.

Geographic variation in the susceptibilities of invasive isolates of Candida glabrata to seven systemically active antifungal agents: a global assessment from the ARTEMIS Antifungal Surveillance Program conducted in 2001 and 2002

We examined the susceptibilities to amphotericin B, flucytosine, fluconazole, posaconazole, ravuconazole, voriconazole, and caspofungin of 601 invasive isolates of Candida glabrata and grouped the isolates by geographic location: North America (331 isolates), Latin America (58 isolates), Europe (135 isolates), and Asia-Pacific (77 isolates). Caspofungin (MIC at which 90% of isolates tested are susceptible [MIC(90)], 0.12 microg/ml; 100% of strains are susceptible [S] at a MIC of Collapse

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MESH Headings

• Antifungal Agents/pharmacology
• Candida glabrata/drug effects
• Drug Resistance, Fungal
• Microbial Sensitivity Tests
• Time Factors

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Affiliation(s)

M A Pfaller Department of Pathology, Roy J and Lucille A Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
S A Messer
L Boyken
S Tendolkar
R J Hollis
D J Diekema

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