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

Aromatic Diboronic Acids as Effective KPC/AmpC Inhibitors

Over 30 compounds, including para-, meta-, and ortho-phenylenediboronic acids, ortho-substituted phenylboronic acids, benzenetriboronic acids, di- and triboronated thiophenes, and pyridine derivatives were investigated as potential β-lactamase inhibitors. The highest activity against KPC-type carbapenemases was found for ortho-phenylenediboronic acid 3a, which at the concentration of 8/4 mg/L reduced carbapenems' MICs up to 16/8-fold, respectively. Checkerboard assays revealed strong synergy between carbapenems and 3a with the fractional inhibitory concentrations indices of 0.1-0.32. The nitrocefin hydrolysis test and the whole cell assay with E. coli DH5α transformant carrying blaKPC-3 proved KPC enzyme being its molecular target. para-Phenylenediboronic acids efficiently potentiated carbapenems against KPC-producers and ceftazidime against AmpC-producers, whereas meta-phenylenediboronic acids enhanced only ceftazidime activity against the latter ones. Finally, the statistical analysis confirmed that ortho-phenylenediboronic acids act synergistically with carbapenems significantly stronger than other groups. Since the obtained phenylenediboronic compounds are not toxic to MRC-5 human fibroblasts at the tested concentrations, they can be considered promising scaffolds for the future development of novel KPC/AmpC inhibitors. The complexation of KPC-2 with the most representative isomeric phenylenediboronic acids 1a, 2a, and 3a was modeled by quantum mechanics/molecular mechanics calculations. Compound 3a reached the most effective configuration enabling covalent binding to the catalytic Ser70 residue.

Calcineurin Inhibitors Synergize with Manogepix to Kill Diverse Human Fungal Pathogens

Invasive fungal infections have mortality rates of 30–90%, depending on patient co-morbidities and the causative pathogen. The frequent emergence of drug resistance reduces the efficacy of currently approved treatment options, highlighting an urgent need for antifungals with new modes of action. Addressing this need, fosmanogepix (N-phosphonooxymethylene prodrug of manogepix; MGX) is the first in a new class of gepix drugs, and acts as a broad-spectrum, orally bioavailable inhibitor of the essential fungal glycosylphosphatidylinositol (GPI) acyltransferase Gwt1. MGX inhibits the growth of diverse fungal pathogens and causes accumulation of immature GPI-anchored proteins in the fungal endoplasmic reticulum. Relevant to the ongoing clinical development of fosmanogepix, we report a synergistic, fungicidal interaction between MGX and inhibitors of the protein phosphatase calcineurin against important human fungal pathogens. To investigate this synergy further, we evaluated a library of 124 conditional expression mutants covering 95% of the genes encoding proteins involved in GPI-anchor biosynthesis or proteins predicted to be GPI-anchored. Strong negative chemical-genetic interactions between the calcineurin inhibitor FK506 and eleven GPI-anchor biosynthesis genes were identified, indicating that calcineurin signalling is required for fungal tolerance to not only MGX, but to inhibition of the GPI-anchor biosynthesis pathway more broadly. Depletion of these GPI-anchor biosynthesis genes, like MGX treatment, also exposed fungal cell wall (1→3)-β-D-glucans. Taken together, these findings suggest the increased risk of invasive fungal infections associated with use of calcineurin inhibitors as immunosuppressants may be mitigated by their synergistic fungicidal interaction with (fos)manogepix and its ability to enhance exposure of immunostimulatory glucans.

Natural alkaloid tryptanthrin exhibits novel anticryptococcal activity

Cryptococcal meningitis is a prevalent invasive fungal infection that causes around 180 000 deaths annually. Currently, treatment for cryptococcal meningitis is limited and new therapeutic options are needed. Historically, medicinal plants are used to treat infectious and inflammatory skin infections. Tryptanthrin is a natural product commonly found in these plants. In this study, we demonstrated that tryptanthrin had antifungal activity with minimum inhibitory concentration (MIC) of 2 μg/ml against Cryptococcus species and of 8 μg/ml against Trichophyton rubrum. Further analysis demonstrated that tryptanthrin exerted fungistatic and potent antifungal activity at elevated temperature. In addition, tryptanthrin exhibited a synergistic effect with the calcineurin inhibitors FK506 and cyclosporine A against Cryptococcus neoformans. Furthermore, our data showed that tryptanthrin induced cell cycle arrest at the G1/S phase by regulating the expression of genes encoding cyclins and the SBF/MBF complex (CLN1, MBS1, PCL1, and WHI5) in C. neoformans. Screening of a C. neoformans mutant library further revealed that tryptanthrin was associated with various transporters and signaling pathways such as the calcium transporter (Pmc1) and protein kinase A signaling pathway. In conclusion, tryptanthrin exerted novel antifungal activity against Cryptococcus species through a mechanism that interferes with the cell cycle and signaling pathways.

LAY SUMMARY

The natural product tryptanthrin had antifungal activity against Cryptococcus species by interfering cell cycle and exerted synergistic effects with immunosuppressants FK506 and cyclosporine A. Our findings suggest that tryptanthrin may be a potential drug or adjuvant for the treatment of cryptococcosis.

Antifungal Susceptibility Testing: Current Approaches

Although not as ubiquitous as antibacterial susceptibility testing, antifungal susceptibility testing (AFST) is a tool of increasing importance in clinical microbiology laboratories. The goal of AFST is to reliably produce MIC values that may be used to guide patient therapy, inform epidemiological studies, and track rates of antifungal drug resistance. There are three methods that have been standardized by standards development organizations: broth dilution, disk diffusion, and azole agar screening for Aspergillus Other commonly used methods include gradient diffusion and the use of rapid automated instruments. Novel methodologies for susceptibility testing are in development. It is important for laboratories to consider not only the method of testing but also the interpretation (or lack thereof) of in vitro data.

Role of Virulence Determinants in Candida albicans' Resistance to Novel 2-bromo-2-chloro-2-(4-chlorophenylsulfonyl)-1-phenylethanone

We investigated the role of KEX2, SAP4-6, EFG1, and CPH1 in the virulence of Candida under a novel compound 2-bromo-2-chloro-2-(4-chlorophenylsulfonyl)-1-phenylethanone (Compound 4). We examined whether the exposure of C. albicans cells to Compound 4, non-cytotoxic to mammalian cells, reduces their adhesion to the human epithelium. We next assessed whether the exposure of C. albicans cells to Compound 4 modulates the anti-inflammatory response (IL-10) and induces human macrophages to respond to the Candida cells. There was a marked reduction in the growth of the sap4Δsap5Δsap6Δ mutant cells when incubated with Compound 4. Under Compound 4 (minimal fungicidal concentration MFC = 0.5–16 µg/mL): (1) wild type strain SC5314 showed a resistant phenotype with down-regulation of the KEX2 expression; (2) the following mutants of C.albicans: sap4Δ, sap5Δ, sap6Δ, and cph1Δ displayed decreased susceptibility with the paradoxical effect and up-regulation of the KEX2 expression compared to SC5314; (3) the immune recognition of C. albicans by macrophages and (4) the stimulation of IL-10 were not blocked ex vivo. The effect of deleting KEX2 in C. albicans had a minor impact on the direct activation of Compound 4’s antifungal activity. The adhesion of kex2Δ is lower than that of the wild parental strain SC5314, and tends to decrease if grown in the presence of a sub-endpoint concentration of Compound 4. Our results provide evidence that SAP4–6 play a role as regulators of the anti-Candida resistance to Compound 4. Compound 4 constitutes a suitable core to be further exploited for lead optimization to develop potent antimycotics.

Design and studies of multiple mechanism of anti-Candida activity of a new potent Trp-rich peptide dendrimers

PURPOSE

Eight peptide dendrimers were designed as structural mimics of natural cationic amphiphilic peptides with antifungal activity and evaluated for their anti-Candida potential against the wild type strains and mutants.

METHODS

Dendrimer 14 containing four Trp residues and dodecyl tail and a slightly smaller dendrimer 9 decorated with four N-methylated Trp that displayed 100 and 99.7% of growth inhibition at 16 μg/mL respectively, were selected for evaluation against the Candida albicans mutants with disabled biosynthesis of aspartic proteases responsible for host tissue colonization and morphogenesis during biofilm formation (sessile model). Flow cytometry method was employed to detect apoptotic cells with membrane alterations (phosphatidylserine translocation), and differentiation of apoptotic from necrotic cells was also performed. Simultaneous staining of cell surface phosphatidylserine with Annexin-V-Fluorescein and necrotic cells with propidium iodide was conducted.

RESULTS

14 at 16 μg/mL caused C. albicans cells to undergo cellular apoptosis but its increasing concentrations induced necrosis. 14 influenced C. albicans biofilm viability as well as hyphal and cell wall morphology. Confocal microscopy and cell wall staining with calcofluor white revealed that in epithelial model the cell surface structure was perturbed at MIC of peptide dendrimer. It appears that tryptophan or 1-methyltryptophan groups displayed at the surface and positive charges hidden in the dendrimer tree along with hydrocarbon tail located at C-terminus are important for the anti-Candida activity since dendrimers containing tryptamine at C-terminus showed only a moderate activity.

CONCLUSIONS

Our results suggest that membranolytic dendrimer 14, targeting cellular apoptotic pathway and impairing the cell wall formation in mature biofilm, may be a potential multifunctional antifungal lead compound for the control of C. albicans infections.

Recent Developments and Biological Activities of N-Substituted Carbazole Derivatives: A Review

Carbazoles represent an important class of heterocycles. These have been reported to exhibit diverse biological activities such as antimicrobial, antitumor, antiepileptic, antihistaminic, antioxidative, anti-inflammatory, antidiarrhoeal, analgesic, neuroprotective and pancreatic lipase inhibition properties. A series of carbazole derivatives such as N-substituted carbazoles, benzocarbazoles, furocarbazoles, pyrrolocarbazoles, indolocarbazoles, imidazocarbazoles, etc. have been synthesized. The N-substituted derivatives have gained the attention of researchers due to their therapeutic potential against neurological disorders and cell proliferation. Herein an attempt is made to review the medicinal importance of recently synthesized N-substituted carbazoles.

The expression of the Candida albicans gene SAP4 during hyphal formation in human serum and in adhesion to monolayer cell culture of colorectal carcinoma Caco-2 (ATCC)

Candida albicans SAP4 gene encodes secretory aspartyl protease Sap4 which is involved in hyphae formation and virulence. Transcriptional factors Cph1 and Efg1 govern the expression of several C. albicans genes and contribute to morphogenesis. We investigated the expression of SAP4 in C. albicans clinical isolate and mutants lacking Efg1 or/ and Cph1 grown in human serum and during contact with Caco-2 cell line. mRNA was analyzed with the use of RT-PCR; relative quantification was normalized against an ACT1 in cells after 18-h growth either in serum or on monolayer as well as in their counterparts in YEPD medium. We assessed the role of Sap4, Efg1 and Cph1 in adhesion of C. albicans to epithelial cells. Additionally, adherence assay was performed with sap4/sap4. Adhesion was expressed as a percent of adherent cells to monolayer at 90 min vs. total cells added (100%). No differences were observed in adhesion of efg1/efg1 and sap4/sap4 compared with SC5314 (P≥0.05 statisitically insignificant). SAP4 expression indicated that it is not involved in adapting to the tested conditions. SAP4 expression can be strainspecific and is not solely controlled by the Efg1 pathway but also by the Cph1 pathway. Neither Efg1 nor Sap4 can influence adhesion.

Synthesis, Antibacterial, and Antifungal Activities of Novel Pyridazino Carbazoles

Strategy to synthesize novel carbazole, that is, 2,3-dihydro-2-phenyl-6H-pyridazino[4, 5-b]carbazole-1,4-dione (2), is developed as key reaction. This novel compound showed ideal reactivity toward different functional groups like methyl, carboxylic, nitro, piperazine, and amine; thus series of its derivatives are synthesized sequentially with the aim to fuel up the carbazole compounds with new versatile derivatives. All compounds were investigated for their activity against bacteria (MRSA andS. typhi) and fungi (Candida albicans). Among tested compounds3,6, and8exhibited pronounced antibacterial activities while2,5, and9also showed moderate activities.2,3,5,7, and9showed stronger antifungal activity againstCandida albicanscomparable to positive control.

High incidence of antifungal drug resistance in Candida tropicalis

Drug resistance among yeasts is an increasing problem. Isolates of Candida krusei and Candida glabrata are recognized as having reduced susceptibility to fluconazole and resistance to this drug has also arisen in Candida albicans isolated from AIDS patients on long term azole therapy. Candida tropicalis (CT) is being increasingly isolated from human disease and is associated with invasive infection, however, data regarding this organism's drug susceptibility is limited. We report our findings on 60 isolates of CT isolated from patients with serious infection in the North West of England. Over 60% of isolates were from adult Intensive Care Unit (ICU) patients, and almost half were from the respiratory tract. Susceptibility to fluconazole, flucytosine, itraconazole and ketoconazole were tested by standardised methods - 48% of the isolates were resistant to fluconazole (MIC > 12.5 mg/l), and 10% had intermediate susceptibility (MIC 6.25-12.5 mg/l). For flucytosine 17% of isolates were resistant (MIC > 8 mg/l) and 22% had intermediate susceptibility (MIC 2-8 mg/l). Three isolates were resistant to both drugs. For itraconazole 17% of isolates were resistant (MIC > 1 mg/l), and 12% showed intermediate susceptibility (MIC 0.5-1 mg/l). Resistance to ketoconazole was seen in 33% of isolates (MIC > 1 mg/l) and 10% showed intermediate susceptibility (MIC 0.5-1 mg/l). Differences in the degree of cross resistance between the azole drugs was observed. Candida tropicalis should be added to the list of yeasts in which drug resistance is commonly found. Given the high invasiveness of Candida tropicalis, its affinity for patients on ICU and the high incidence of drug resistance in this species, identification and susceptibility tests should be performed on all yeast isolates from patients on ICU.

Infectious keratitis caused by Aspergillus tubingensis

PURPOSE

To report 2 cases of keratomycosis caused by Aspergillus tubingensis.

METHODS

The therapeutic courses were recorded for 2 male patients, 52 and 78 years old, with fungal keratitis caused by black Aspergillus strains. Morphological examination of the isolates was carried out on malt extract agar plates. A segment of the beta-tubulin gene was used for molecular identification. Antifungal susceptibilities were determined by the E test method for molds and the broth microdilution technique National Committee for Clinical Laboratory Standards M38-A.

RESULTS

A 52-year-old man presented with complaints of pain and redness in the right eye. The patient was successfully treated with natamycin and econazole eyedrops, itraconazole eye ointment, and oral ketoconazole. A 78-year-old man presented with total corneal necrosis in the right eye. A therapeutic keratoplasty was performed, and topical natamycin and econazole were applied. At the postoperative visit after 3 weeks, almost the full corneal graft was clear with formed anterior chamber. Black Aspergillus strains were isolated from the corneal scrapings of both cases and initially identified as Aspergillus niger based on culture characteristics. Sequence analysis of a segment of the beta-tubulin gene revealed that the isolates are representatives of A. tubingensis.

CONCLUSIONS

Aspergillus tubingensis is closely related with A. niger, the differentiation of these 2 species is difficult by classical morphological criteria. To our knowledge, the presented cases of fungal keratitis are the first reports on ocular infection caused by A. tubingensis.

Mycotic keratitis due to Aspergillus nomius

We report the first known case of fungal keratitis caused by Aspergillus nomius. Ocular injury was known as a predisposing factor. The patient was treated with natamycin and econazole eye drops, itraconazole eye ointment, and oral ketoconazole. A therapeutic penetrating keratoplasty was performed 16 days after presentation. A sequence-based approach was used to assign the isolate to a species.

Corneal ulcer due toNeocosmospora vasinfectain an immunocompetent patient

We report a case of Neocosmospora vasinfecta keratitis in a 55-year-old man. While the patient did not recall any specific trauma or eye injury, he might have sustained a trivial wound during the course of his duties as a farmer. Direct examination of corneal scrapings revealed fungus filaments. As topical treatment with natamycin and econazole and subsequent systemic ketoconazole therapy failed, a full thickness therapeutic keratoplasty was performed. Post-operative treatment with amphotericin B and clotrimazole combined with cyclosporine resulted in a complete cure. The residual corneal infiltration in the recipient cornea became clear in a week. The fungal isolate was initially identified as a Fusarium species, but later reidentified through the use of morphological characteristics and sequence analysis of the internal transcribed spacer region as N. vasinfecta. The latters is a Hypocrealean fungus not hitherto reported as a causative agent of keratomycosis.

Susceptibility of Candida species to photodynamic effects of photofrin

The in vitro susceptibility of pathogenic Candida species to the photodynamic effects of the clinically approved photosensitizing agent Photofrin was examined. Internalization of Photofrin by Candida was confirmed by confocal fluorescence microscopy, and the degree of uptake was dependent on incubation concentration. Uptake of Photofrin by Candida and subsequent sensitivity to irradiation was influenced by culture conditions. Photofrin uptake was poor in C. albicans blastoconidia grown in nutrient broth. However, conversion of blastoconidia to filamentous forms by incubation in defined tissue culture medium resulted in substantial Photofrin uptake. Under conditions where Photofrin was effectively taken up by Candida, irradiated organisms were damaged in a drug dose- and light-dependent manner. Uptake of Photofrin was not inhibited by azide, indicating that the mechanism of uptake was not dependent on energy provided via electron transport. Fungal damage induced by Photofrin-mediated photodynamic therapy (PDT) was determined by evaluation of metabolic activity after irradiation. A strain of C. glabrata took up Photofrin poorly and was resistant to killing after irradiation. In contrast, two different strains of C. albicans displayed comparable levels of sensitivity to PDT. Furthermore, a reference strain of C. krusei that is relatively resistant to fluconazole compared to C. albicans was equally sensitive to C. albicans at Photofrin concentrations of >/=3 microg/ml. The results indicate that photodynamic therapy may be a useful adjunct or alternative to current anti-Candida therapeutic modalities, particularly for superficial infections on surfaces amenable to illumination.

Proficiency testing program for clinical laboratories performing antifungal susceptibility testing of pathogenic yeast species

Antifungal susceptibility testing is expected to facilitate the selection of adequate therapy for fungal infections. The general availability of antifungal susceptibility testing in clinical laboratories is low, even though a number of standard methods are now available. The objective of the present study was to develop and evaluate a proficiency testing program (PTP) for the antifungal susceptibility testing of pathogenic yeasts in laboratories licensed by the New York State Department of Health. A number of quality control standards, and methods for documenting laboratory performance, were developed in consultation with the laboratory directors. The participating laboratories were provided with five American Type Culture Collection strains of pathogenic yeasts for which the minimum inhibitory concentrations (MICs) of amphotericin B and fluconazole were well defined. A majority of laboratories (14 of 17) used broth microdilution, and these were evenly split between the NCCLS M-27A protocol and the Sensititre YeastOne method. The other three laboratories performed susceptibility testing with Etest. Overall, the levels of agreement between MIC reference ranges and the reported MICs were 85 and 74% for amphotericin B and for fluconazole, respectively. All laboratories except one successfully detected fluconazole resistance in a Candida krusei strain. However, amphotericin B resistance in a Candida lusitaniae strain was not detected by any of the participating labs. It is concluded that a suitably designed PTP could adequately monitor the competence of clinical laboratories performing antifungal susceptibility testing.

Effect of the echinocandin caspofungin on expression of Candida albicans secretory aspartyl proteinases and phospholipase in vitro

Although the echinocandin caspofungin primarily inhibits the synthesis of cell wall 1,3-beta-D-glucan, its fungicidal activity could also potentially perturb the expression of virulence factors involved in the ability of Candida albicans to cause infection. Expression of the C. albicans secretory aspartyl proteinase (SAP) and phospholipase B (PLB) virulence genes was determined by reverse transcription-PCR after the addition of caspofungin to cells grown for 15 h in Sabouraud dextrose broth. In cells that remained viable, expression of SAP1 to SAP3, SAP7 to SAP9, and PLB1 was unaltered after exposure to fungicidal concentrations (4 to 16 micro g/ml) of caspofungin over a period of 7 h. However, expression of SAP5 increased steadily beginning 1 h after exposure to caspofungin. These results indicate that caspofungin is rapidly fungicidal against C. albicans, before any suppression of SAP or PLB1 gene expression can occur.

In vitro activity of nystatin compared with those of liposomal nystatin, amphotericin B, and fluconazole against clinical Candida isolates

We investigated the in vitro activity of nystatin and liposomal nystatin against 103 Candida isolates to determine the effect of both time and medium on MICs. We also compared the nystatin MICs with those of amphotericin B and fluconazole. Testing was performed in accordance with the National Committee for Clinical Laboratory Standards M27-A microdilution methodology with RPMI 1640, RPMI 1640 supplemented with glucose to 2% (RPMI-2), and antibiotic medium 3 supplemented with glucose to 2% (AM3). While nystatin MICs were similar to or slightly lower than liposomal nystatin MICs in RPMI 1640 and RPMI-2, they were markedly higher than liposomal nystatin MICs in AM3. Use of AM3 and determination of the MIC after 24 h of incubation provided a slightly wider range of liposomal nystatin MICs (0.06 to >16 microg/ml). Under these conditions, the MICs at which 90% of isolates were inhibited of nystatin and liposomal nystatin were 2 and 1 microg/ml, respectively. Nystatin and liposomal nystatin in general showed good activity against all Candida spp. tested. Although the MICs of nystatin and liposomal nystatin tended to rise in parallel with the amphotericin B MICs, nystatin and liposomal nystatin MICs of 1 to 2 and 0.5 to 1 microg/ml, respectively, were obtained for seven and six, respectively, of nine isolates for which amphotericin B MICs were >or=0.25 microg/ml. No correlation between fluconazole and nystatin or liposomal nystatin MICs was observed. As amphotericin B MICs of >or=0.25 microg/ml correlate with in vitro resistance, these results suggest that liposomal nystatin might have activity against some amphotericin B-resistant isolates. In vivo testing in animal models is required for clarification of this issue.

In vitro antifungal susceptibility testing

With the rising frequency of fungal infections, as well as increasing reports of resistance to antifungal agents, it is imperative that clinically applicable antifungal susceptibility testing be available. In 1997 the National Committee for Clinical Laboratory Standards published standard guidelines for antifungal susceptibility testing of Candida sp and Cryptococcus neoformans with amphotericin B, flucytosine, fluconazole, itraconazole, and ketoconazole. Although the methods are standard, they are time consuming, can be difficult to interpret, and are approved only for testing limited organisms and drugs. Modifications to the methods and alternative approaches have been proposed to make these tests more convenient and efficient, applicable to a greater number of species, and appropriate for performing in the clinical laboratory.

Quality control limits for broth microdilution susceptibility tests of ten antifungal agents

Broth microdilution susceptibility tests of Candida species have now been standardized by the National Committee for Clinical Laboratory Standards (NCCLS). An eight-laboratory collaborative study was carried out in order to document reproducibility of tests of Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 by the NCCLS method. Replicate broth microdilution tests were used to define control limits for 24- and 48-h MICs of amphotericin B, flucytosine, fluconazole, voriconazole, ketoconazole, itraconazole, caspofungin (MK 0991), ravuconazole (BMS 207147), posaconazole (SCH 56592), and LY 303366.

Fatal disseminated Trichoderma longibrachiatum infection in an adult bone marrow transplant patient: species identification and review of the literature

Trichoderma longibrachiatum was recovered from stool surveillance cultures and a perirectal ulcer biopsy specimen from a 29-year-old male who had received an allogeneic bone marrow transplant for acute lymphoblastic leukemia. The amphotericin B (2.0 microgram/ml) and itraconazole (1.0 microgram/ml) MICs for the organism were elevated. Therapy with these agents was unsuccessful, and the patient died on day 58 posttransplantation. At autopsy, histologic sections from the lungs, liver, brain, and intestinal wall showed infiltration by branching septate hyphae. Cultures were positive for Trichoderma longibrachiatum. While Trichoderma species have been recognized to be pathogenic in profoundly immunosuppressed hosts with increasing frequency, this is the first report of probable acquisition through the gastrointestinal tract. Salient features regarding the identification of molds in the Trichoderma longibrachiatum species aggregate are presented.

Current and emerging azole antifungal agents

Major developments in research into the azole class of antifungal agents during the 1990s have provided expanded options for the treatment of many opportunistic and endemic fungal infections. Fluconazole and itraconazole have proved to be safer than both amphotericin B and ketoconazole. Despite these advances, serious fungal infections remain difficult to treat, and resistance to the available drugs is emerging. This review describes present and future uses of the currently available azole antifungal agents in the treatment of systemic and superficial fungal infections and provides a brief overview of the current status of in vitro susceptibility testing and the growing problem of clinical resistance to the azoles. Use of the currently available azoles in combination with other antifungal agents with different mechanisms of action is likely to provide enhanced efficacy. Detailed information on some of the second-generation triazoles being developed to provide extended coverage of opportunistic, endemic, and emerging fungal pathogens, as well as those in which resistance to older agents is becoming problematic, is provided.

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

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

Detection of resistance to amphotericin B among Cryptococcus neoformans clinical isolates: performances of three different media assessed by using E-test and National Committee for Clinical Laboratory Standards M27-A methodologies

Although reliable detection of resistance in vitro is critical to the overall performance of any susceptibility testing method, the recently released National Committee for Clinical Laboratory Standards M27-A methodology for susceptibility testing of yeasts discriminates poorly between resistant and susceptible isolates of Candida spp. We have previously shown that both substitution of antibiotic medium 3 for RPMI 1640 medium in the microdilution variant of the M27-A method and use of the E-test agar diffusion methodology permit detection of amphotericin B-resistant Candida isolates. To determine the relevance of these observations to Cryptococcus neoformans, we have evaluated the performances of both the M27-A and the E-test methodologies with this yeast using three different media (RPMI 1640 medium, antibiotic medium 3, and yeast nitrogen base). As with Candida, we found that only antibiotic medium 3 permitted consistent detection of resistant isolates when testing was performed in broth by the M27-A method. When testing was performed by the E-test agar diffusion method, both RPMI 1640 medium and antibiotic medium 3 agar permitted ready detection of the resistant isolates. Reading of the results after 48 h of incubation was required for testing in broth by the M27-A method, while the MIC could be determined after either 48 or 72 h when the agar diffusion method was used.

Amphotericin-B colloidal dispersion. A review of its use against systemic fungal infections and visceral leishmaniasis

Formulation of amphotericin B with sodium cholesteryl sulphate alters the pharmacokinetic properties of the drug, particularly reducing its distribution to the kidneys. The antifungal activity in vitro of amphotericin B colloidal dispersion (ABCD) is similar to that of conventional amphotericin B (C-AmB) against true pathogenic organisms including Blastomyces, Coccidioides, Histoplasma and Paracoccidioides species and the opportunistic organisms such as Candida and Cryptococcus species. In animal models, ABCD was generally less effective than an identical dose of C-AmB, but overall was more effective because of its improved therapeutic index. Although ABCD appeared to be more effective than C-AmB in resolving infection and improving survival in patients with proven or probable invasive aspergillosis, the retrospective design of the study and the greater prevalence of neutropenia in patients treated with the conventional formulation necessitate cautious interpretation of the results. ABCD has been effective and seldom caused nephrotoxicity in patients with fungal infection who had previously failed to adequately respond or had developed renal toxicity with C-AmB. Similarly, ABCD was effective in patients with proven or suspected fungal infection after bone marrow transplantation. Preliminary results from a pilot study comparing ABCD and C-AmB in patients with neutropenia and persistent fever reported similar response rates with both formulations. ABCD is an effective treatment for visceral leishmaniasis in immunocompetent patients. In 1 study, about 12% of ABCD recipients discontinued the drug because of adverse events; infusion-related events were the most common cause of discontinuation. The renal tolerability of ABCD is better than that of C-AmB. ABCD appears to be an effective alternative to conventional amphotericin B in patients with invasive aspergillosis or visceral leishmaniasis and in those with proven or suspected systemic fungal infection who are intolerant of the conventional formulation or have pre-existing renal impairment. Preliminary data also suggest that ABCD is an alternative to C-AmB when used empirically in patients with neutropenia and fever. Nevertheless, the efficacy of ABCD compared with that of the conventional formulation has yet to be adequately demonstrated and the role of ABCD relative to that of liposomal and other lipid-based formulations has not been determined.

CONCLUSIONS

ABCD, like other lipid-based and liposomal formulations of amphotericin B, has been designed to deliver the active drug to the target site, while reducing renal toxicity. The aim of increasing the therapeutic index compared with C-AmB has been achieved.

Evaluation of a colorimetric method for detecting amphotericin B-resistant Candida isolates

Substitution of Antibiotic Medium 3 for RPMI 1640 in the microdilution variant of M27-A has been proven to permit detection of amphotericin B-resistant Candida isolates. For this purpose, we have studied the utility of the colorimetric indicator alamarBlue to simplify the former process because it is a readily available commercial system. When used in combination with the NCCLS-recommended RPMI 1640, alamarBlue did not improve the ability of RPMI 1640 to detect resistant isolates. When used in combination with Antibiotic Medium 3, alamarBlue reduced discrimination between susceptible and resistant isolates by increasing the MIC of susceptible isolates. Thus, alamarBlue does not improve detection of amphotericin B resistance among Candida isolates.

In vitro activities of terbinafine in combination with fluconazole and itraconazole against isolates of Candida albicans with reduced susceptibility to azoles

A checkerboard microdilution method was applied to study the in vitro interaction of terbinafine with either fluconazole and itraconazole against 30 strains of Candida albicans. Synergy was observed in 40% of the terbinafine-fluconazole interactions and in 43% of the terbinafine-itraconazole interactions, while antagonism was not observed. Even when only additivity was achieved, the combinations still showed beneficial effects since at least twofold reductions in the MICs of both drugs were found in 100% of the terbinafine-fluconazole interactions and in 76% of the terbinafine-itraconazole interactions.

Variations in fluconazole susceptibility and DNA subtyping of multiple Candida albicans colonies from patients with AIDS and oral candidiasis suffering one or more episodes of infection

Five Candida albicans colonies from each infection in AIDS patients receiving fluconazole therapy for oropharyngeal candidiasis over a 2-year period were evaluated by antifungal susceptibility testing and DNA subtyping, and the results were correlated with clinical response to determine the occurrence of clinically significant selection of more-resistant C. albicans over multiple infections. A total of 534 C. albicans isolates were obtained from 38 patients who exhibited 84 episodes of infection. Antifungal susceptibility testing revealed that the MICs for 93% of the isolates were < or = 8.0 microg/ml and the MICs for 7% of the isolates were > or = 64 microg/ml. DNA subtyping revealed 70 different subtypes, with 78% of patients with one infection exhibiting one DNA subtype and 80% of patients with more than one infection exhibiting multiple DNA subtypes. Also, patients who had multiple infections had lower CD4 counts than those with single infections. Differences between the single-infection group and the multiple-infection group regarding the number of DNA subtypes and CD4 counts were both statistically significant. Of the 74 evaluable infections all were successfully treated with regular-dose (100-mg/day) fluconazole, except for three patients who ultimately responded to higher-dose fluconazole. Only one patient may have shown clinically significant selection of a more-resistant C. albicans strain over multiple courses of treatment. Interestingly, MICs reached only 8.0 microg/ml, even though doses of 400 mg of fluconazole were necessary for clinical cure.

Lot-to-lot variability of antibiotic medium 3 used for testing susceptibility of Candida isolates to amphotericin B

We have previously shown that use of antibiotic medium 3 in the microdilution variant of the M27-T test method permits detection of amphotericin B-resistant Candida isolates. As this medium is not standardized and our initial work used only a single lot of antibiotic medium 3, we studied the lot-to-lot variability of three commercial lots of antibiotic medium 3 obtained from two sources. The MICs obtained with the new lots were lower than those of with the original lot, but the new lots still consistently separated putatively resistant and putatively susceptible isolates and this permits proposal of possible breakpoints for this assay system.

Carrier effects on biological activity of amphotericin B

Amphotericin B (AmB), the drug of choice for the treatment of most systemic fungal infections, is marketed under the trademark Fungizone, as an AmB-deoxycholate complex suitable for intravenous administration. The association between AmB and deoxycholate is relatively weak; therefore, dissociation occurs in the blood. The drug itself interacts with both mammalian and fungal cell membranes to damage cells, but the greater susceptibility of fungal cells to its effects forms the basis for its clinical usefulness. The ability of the drug to form stable complexes with lipids has allowed the development of new formulations of AmB based on this property. Several lipid-based formulations of the drug which are more selective in damaging fungal or parasitic cells than mammalian cells and some of which also have a better therapeutic index than Fungizone have been developed. In vitro investigations have led to the conclusion that the increase in selectivity observed is due to the selective transfer of AmB from lipid complexes to fungal cells or to the higher thermodynamic stability of lipid formulations. Association with lipids modulates AmB binding to lipoproteins in vivo, thus influencing tissue distribution and toxicity. For example, lipid complexes of AmB can be internalized by macrophages, and the macrophages then serve as a reservoir for the drug. Furthermore, stable AmB-lipid complexes are much less toxic to the host than Fungizone and can therefore be administered in higher doses. Experimentally, the efficacy of AmB-lipid formulations compared with Fungizone depends on the animal model used. Improved therapeutic indices for AmB-lipid formations have been demonstrated in clinical trials, but the definitive trials leading to the selection of an optimal formulation and therapeutic regimen have not been done.

Effect of media on growth rate and susceptibility testing of Cryptococcus neoformans

The effect of four media or media combinations on the growth and the in vitro susceptibility to amphotericin B, 5-fluorocytosine, fluconazole and itraconazole of 51 isolates of Cr. neoformans was studied. The drug concentration producing a 50% decrease in OD405 (IC50) was determined in microtiter format. The following MOPS buffered media or media combinations (antifungal drug diluent/inoculum diluent) were used: RPMI 1640 (RPMI)/RPMI, Yeast nitrogen base (YNB)/YNB, RPMI/YNB and RPMI/High resolution broth. Amphotericin B was further tested in M3 broth in the microdilution format and on RPMI agar with the E-test. Growth rates (OD405) were higher in YNB, RPMI/YNB, RPMI/HR and M3 as compared to RPMI alone. After 48 h of incubation, IC50 values obtained with RPMI alone and with RPMI/YNB correlated within two dilutions for 98, 95, 95 and 100% of test strains with amphotericin B, 5-fluorocytosine,fluconazole and itraconazole respectively. The E-test provided the widest range of IC values with amphotericin B. Growth of Cr. neoformans can be enhanced in susceptibility tests using microtiter plates with drugs diluted in RPMI by preparing the inoculum in YNB. However, when using spectrophotometric endpoint determinations, sufficient growth is obtainable with most isolates for test interpretation at 48 h in RPMI alone.

Quality control guidelines for National Committee for Clinical Laboratory Standards--recommended broth macrodilution testing of ketoconazole and itraconazole

Ketoconazole and itraconazole were tested in a multilaboratory study to establish quality control (QC) guidelines for yeast antifungal susceptibility testing. Two isolates that had been previously identified as QC isolates for amphotericin B, fluconazole, and flucytosine (Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258) were tested in accordance with the National Committee for Clinical Laboratory Standards M27-P guidelines. Each isolate was tested 20 times with the two antifungal agents in the five laboratories by using a lot of RPMI 1640 unique to each laboratory as well as a lot common to all five laboratories, thus generating 200 MICs per drug per organism. Overall, 96 to 99% of the MICs for each drug fell within the desired 3-log2 dilution range (mode +/- 1 log2 dilution). By using these data, 3-log2 dilution QC ranges encompassing 98% of the observed MICs for three of the organism-drug combinations and 94% of the observed MICs for the fourth combination were established. These QC ranges are 0.064 to 0.25 micrograms/ml for both ketoconazole and itraconazole against C. parapsilosis ATCC 22019 and 0.125 to 0.5 micrograms/ml for both ketoconazole and itraconazole against C. krusei ATCC 6258.

Factors affecting the results of a broth microdilution antifungal susceptibility testing in vitro

In experiments involving 10 antifungal drugs and 46 strains of potentially pathogenic fungi, the factors affecting the results of in vitro susceptibility testing were studied. The composition of the test medium, inoculum size, temperature and length of incubation were the most pronounced effects influencing the results of testing in vitro. Minimal inhibitory concentrations (MIC) of the antimycotics tested were lowest in complex media (Brain Heart Infusion, Antibiotic Medium 3, Sabouraud broth) except for 5-fluorocytosine which was most effective in Yeast Nitrogen Base medium. Inoculum sizes of 10(3) to 10(4) cfu* mL(-1) had no marked effect on MIC but starting from a final concentration of 10(5) cfu*mL(-1), an abrupt increase in MIC in azole derivatives and 5-fluorocytosine was observed. There was a direct relationship between the duration of incubation and MIC of fungistatic antimycotics. The influence of the incubation temperature became generally manifest primarily in fungi with retarded growth at elevated temperature (>35 degrees C). In these fungal species, a tendency towards a decrease in MIC with increasing temperature was apparent. The other factors studied (medium pH, buffer, solvent) had no substantial influence on the antifungal activity of the drugs tested.

Fatal outcome of disseminated candidosis after allogeneic bone marrow transplantation under treatment with liposomal and conventional amphotericin-B. A report of 4 cases with determination of the Mic values

Four patients undergoing allogeneic bone marrow transplantation were treated with liposomal (3 patients) and conventional (one patient) amphotericin-B for disseminated candidosis. Candida krusei was isolated from 3, and C. glabrata from 1 patient. The patients were treated with liposomal amphotericin-B in doses from 3 to 5 mg/kg. The fourth patient received conventional amphotericin-B in a reduced dose due to renal impairment. The patients died from multiorgan failure due to disseminated fungal infection. In 1 case, the switch to the conventional drug resulted in clearance before death. The 3 fungus isolates, together with the fourth strain obtained from patient no. 4 without any exposition to liposomal amphotericin-B were tested for their susceptibility to conventional, liposomal and discoidal amphotericin-B. All strains showed good sensitivity to the conventional and discoidal drug. The minimal inhibitory concentrations (MIC) of liposomal amphotericin-B were 1 to 3 titre steps higher indicating a reduced sensitivity of the tested strains to this preparation. We conclude that the use of liposomal amphotericin-B is recommended mainly on the base of the low incidence of side-effects. Intensive microbial resistance tests, pharmacokinetic investigations and randomized studies are necessary before the conventional drug is replaced as the gold standard for systemic antimycotic therapy.

Comparison of Etest and National Committee for Clinical Laboratory Standards broth macrodilution method for antifungal susceptibility testing: enhanced ability to detect amphotericin B-resistant Candida isolates

The National Committee for Clinical Laboratory Standards (NCCLS) proposed macrobroth reference method (M27P) for susceptibility testing of yeasts is technically difficult. We evaluated Etest, a simple agar-based MIC methodology, as a possible alternative. In studies of six yeast quality control strains, Etest yielded results identical to those obtained by the NCCLS reference method for both amphotericin B and fluconazole. In studies of 91 clinical Candida isolates, agreement +/- 2 dilutions between the two methods was 95% for fluconazole with phosphate-buffered RPMI 1640 agar and 96 to 97% for amphotericin B with either MOPS (morpholinepropanesulfonic acid)-buffered RPMI 1640 agar or antibiotic medium 3 agar. While the two methods had excellent general agreement, testing of a collection of amphotericin B-resistant isolates demonstrated that, unlike the NCCLS reference method, Etest readily identified the resistant isolates and could do so with a defined medium. Etest is equivalent to the NCCLS proposed method for susceptibility testing of yeasts and superior in its ability to detect amphotericin B resistance.

Fluconazole. An update of its pharmacodynamic and pharmacokinetic properties and therapeutic use in major superficial and systemic mycoses in immunocompromised patients

Fluconazole is a triazole antifungal agent which is now an established part of therapy in patients with immune deficiencies. It is effective against oropharyngeal/oesophageal candidiasis (candidosis) when used orally once daily either as treatment or secondary prophylaxis in patients with AIDS or as treatment or primary prophylaxis in neutropenia associated with cancer therapy. Fluconazole also resolves symptoms in up to 60% of patients with cryptococcal meningitis and AIDS. However, in this infection its efficacy as treatment relative to that of amphotericin B is equivocal, and its major role is as the drug of choice for maintenance therapy following amphotericin B induction. In this regard, fluconazole has been proven superior to amphotericin B and to itraconazole 200 mg/day. Comparisons with other drugs used for the treatment of mucosal candidiasis in patients with AIDS show fluconazole to be superior to nystatin, similar to itraconazole and at least as effective as clotrimazole and ketoconazole; it was more so than the latter azole in 1 study. In patients undergoing chemotherapy or bone marrow transplantation, fluconazole as primary prophylaxis has produced greater clinical benefit than a clotrimazole regimen. The incidence of adverse events appears to be somewhat higher in patients with AIDS compared with HIV-negative cohorts, but the qualitative pattern of events is similar. The most frequent events are gastrointestinal complaints, headache and skin rash: rare exfoliative skin reactions and isolated instances of clinically overt hepatic dysfunction have occurred in patients with AIDS. Issues yet to be clarified include: the use of fluconazole in children with AIDS, in whom results have been promising; its efficacy against other fungal infections encountered in immunocompromised patients; whether the drug influences mortality, as has been suggested by one placebo-controlled trial in patients undergoing bone marrow transplant; and the appropriateness of its potential for use as primary prophylaxis against cryptococcal meningitis in patients with AIDS, where it shows efficacy but there is concern over increasing risk of development of secondary resistance. Notwithstanding these undefined aspects of its clinical profile, fluconazole is now confirmed as an important antifungal drug in the management of fungal infections in patients with immune deficiencies. In patients with AIDS it is the present drug of choice as maintenance therapy against cryptococcal meningitis and is a preferred agent for secondary prophylaxis against candidal infections; it is also a favoured agent for primary prophylaxis in patients at risk because of neutropenia associated with chemotherapy or bone marrow transplantation .

Antifungal susceptibility testing of yeasts: evaluation of technical variables for test automation

The technical parameters for antifungal susceptibility testing with Candida species were reexamined to determine the optimal conditions for testing with semiautomated preparations of broth microdilution cultures, automated spectrophotometric readings of the cultures, and dose-response and endpoint determinations by means of a computer spreadsheet. Tests were based on proposed standard method M27P of the National Committee for Clinical Laboratory Standards for antifungal agents. RPMI 1640 broth with extra glucose to a final concentration of 2% gave higher and more reproducible drug-free control readings without affecting susceptibility endpoint readings. An inoculum of 8 x 10(4) yeasts per ml prepared from a carbon-limiting broth culture without further standardization was found to give optimal control readings after 48 h of incubation at 37 degrees C. For flucytosine, fluconazole, itraconazole, and ketoconazole, endpoints based on 50% growth inhibition (50% inhibitory concentration) gave the minimum variation with inoculum size and the fewest endpoint differences with RPMI 1640 medium obtained from two different suppliers. The 50% inhibitory concentration was also the optimal endpoint for fluconazole and ketoconazole susceptibilities in comparison with broth macrodilution MICs determined by the method of the National Committee for Clinical Laboratory Standards. Intralaboratory reproducibility was determined by retrospective analysis of replicate results for isolates retested at random over a 2-year period. This approach showed less favorable reproducibility than has been reported from purpose-designed, prospective antifungal susceptibility studies, but it may better reflect real-life test reproducibility. Susceptibility data for 616 clinical isolates of yeasts, representing 16 Candida and Saccharomyces spp., confirmed the tendency of Candida lusitaniae isolates to show relatively low susceptibilities to amphotericin B, the tendency of Candida krusei isolates to show low flucytosine and fluconazole susceptibilities, and the presence of some isolates in the species Candida albicans, Candida glabrata, and Candida tropicalis with low susceptibilities to azole derivative antifungal agents. The study demonstrates the value of automation and standardization in all stages of yeast susceptibility testing, from plate preparation to data analysis.

Comparison of visual and spectrophotometric methods of MIC endpoint determinations by using broth microdilution methods to test five antifungal agents, including the new triazole D0870

A study to compare three different methods for reading MIC endpoints tested by the broth microdilution modification of the National Committee for Clinical Laboratory Standards (Villanova, Pa.) reference method was conducted. MICs of amphotericin B, flucytosine, fluconazole, itraconazole, and a new triazole, D0870, were determined for five reference yeast strains and 100 clinical isolates of Candida spp. MICs were read visually according to National Committee for Clinical Laboratory Standards guidelines from microdilution trays that had been (VS) and had not been (V) shaken. MICs were also determined spectrophotometrically (SP) at 492 nm. SP endpoints were determined as the concentrations resulting in a > or = 50% inhibition of growth (flucytosine and azoles) and a > or = 90% inhibition of growth (amphotericin B) relative to control growth. The five reference strains were tested nine times each against all five antifungal agents, and the MIC results for each reading method were compared with a 3-log2 dilution reference range determined by the macrodilution (M27-P) method. Overall, 84 to 100% of the MICs determined by V, 93 to 100% of those determined by VS, and 89 to 100% of those determined by SP fell within the 3-log2 dilution reference range for each reference strain and antifungal agent. Reproducibility was 99% for V and SP and 98% for VS. Agreement among the three methods of reading ranged from 97 to 99%. Excellent agreement among reading methods was also observed for all antifungal agents when tested against 100 clinical isolates. Agreement between the standard V method (no agitation) and VS ranged from 99 to 100%, and that between V and SP ranged from 89 to 99%. The VS and SP reading methods provided more definitive endpoints than the V method, which does not involve shaking.

Quality control guidelines for National Committee for Clinical Laboratory Standards recommended broth macrodilution testing of amphotericin B, fluconazole, and flucytosine

Amphotericin B, fluconazole, and flucytosine (5FC) were tested in a multilaboratory study to establish quality control (QC) guidelines for yeast antifungal susceptibility testing. Ten candidate QC strains were tested in accordance with National Committee for Clinical Laboratory Standards M27-P guidelines against the three antifungal agents in each of six laboratories. Each laboratory was assigned a unique lot of RPMI 1640 broth medium as well as a lot of RPMI 1640 common to all of the laboratories. The candidate QC strains were tested 20 times each against the three antifungal agents in both unique and common lots of RPMI 1640. A minimum of 220 MICs per drug per organism were generated during the study. Overall, 95% of the MICs of amphotericin B, fluconazole, and 5FC fell within the desired 3 log2-dilution range (mode +/- 1 log2 dilution). Excellent performance with all three drugs was observed for Candida parapsilosis ATCC 22019 and C. krusei ATCC 6258. With these strains, on-scale 3 log2-dilution ranges encompassing 96 to 99% of the MICs of all three drugs were established. These two strains are recommended for QC testing of amphotericin B, fluconazole, and 5FC. Reference ranges were also established for an additional four strains for use in method development and for training. Four strains failed to perform adequately for recommendation as either QC or reference strains.

In vitro activity of D0870 compared with those of other azoles against fluconazole-resistant Candida spp

We compared the in vitro activity of a new triazole, D0870, with those of fluconazole, itraconazole, and ketoconazole against 41 clinical isolates of fluconazole-resistant Candida belonging to nine different species. The 50% inhibitory concentrations (IC50s) were determined by a microdilution method with morpholinopropanesulfonic acid (MOPS)-buffered RPMI medium and an inoculum of approximately 10(4) yeasts per ml. After incubation for 48 h at 37 degrees C the optical density at 550 nm was measured. The IC50 was the lowest drug concentration which reduced the optical density at 550 nm by > or = 50% compared with that for a drug-free control. D0870 had significant activity against many of the isolates. Its activity was comparable to that of ketoconazole, slightly superior to that of itraconazole, and markedly superior to that of fluconazole against Candida albicans. Against Candida glabrata, Candida krusei, and Candida inconspicua, it had activity similar to those of itraconazole and ketoconazole but had activity superior to that of fluconazole. D0870 IC50s for some isolates were increased. This may be due to cross-resistance mechanisms because the IC50s of both itraconazole and ketoconazole for these isolates were often high. When IC50s and IC80s were compared there was a marked organism and drug variation. With C. glabrata much higher endpoints for itraconazole were observed when an IC80 endpoint was used. For C. albicans there was also a significant shift upward in endpoints for itraconazole and ketoconazole. Values were changed little when IC50 and IC80 endpoints of D0870 were compared. For 35 of 41 isolates tested the D0870 IC50 was less than the 2.5-mg/liter breakpoint threshold proposed previously. Therefore, D0870 may be a useful agent for the therapy of infections caused by fluconazole-resistant Candida spp.

Variations in DNA subtype, antifungal susceptibility, and slime production among clinical isolates of Candida parapsilosis

Candida parapsilosis is an important nosocomial pathogen that can proliferate in high concentrations of glucose and form biofilms on prosthetic materials. We investigated the genotypic diversity, slime production, and antifungal susceptibility among 60 isolates of C. parapsilosis from 44 patients and 10 patient care providers from five different medical centers. Molecular typing was performed using macrorestriction digest profiles with BssHII followed by pulsed-field gel electrophoresis (REAG) and by electrophoretic karyotyping (EK). Slime production was evaluated by growing the organisms in Sabouraud broth with 8% glucose and examining the walls of the tubes for the presence of an adherent slime layer. Antifungal susceptibility to amphotericin B, 5-fluorocytosine, fluconazole, and itraconazole was determined using National Committee for Clinical Laboratory Standards proposed standard methods. Overall 28 different DNA types were identified by REAG and EK methods. MIC90 values ranged from 0.12 microgram/ml for itraconazole to 1.0 microgram/ml for fluconazole and amphotericin B. Sixty-five percent of the isolates produced slime: 37% were moderately to strongly positive, 28% were weakly positive, and 35% were negative. Overall, 83% of blood and catheter isolates were slime positive versus 53% of isolates from all other sites (P < 0.05). These data underscore the genetic diversity and susceptibility of C. parapsilosis to antifungal agents. Slime production may be important in enabling C. parapsilosis to cause catheter-related bloodstream infections.

Strain delineation and antifungal susceptibilities of epidemiologically related and unrelated isolates of Candida lusitaniae

Candida lusitaniae is an important nosocomial pathogen that may express resistance to one or more antifungal agents including amphotericin B. We investigated the genotypic diversity and antifungal susceptibility among 47 clinical isolates from 33 patients hospitalized in 12 different medical centers. Strain delineation was performed by restriction endonuclease analysis of genomic DNA (REAG) with the restriction enzyme Sfi I followed by pulsed-field gel electrophoresis and by electrophoretic karyotyping (EK). Antifungal susceptibility of the isolates to amphotericin B, 5-fluorocytosine (5FC), fluconazole, and itraconazole was determined using National Committee for Clinical Laboratory Standards standard methods. Minimum inhibitory concentration (MIC)90 values ranged from 0.5 micrograms/ml for itraconazole to 512 micrograms/ml for 5FC. In general, isolates from a given patient or epidemiologically related isolates from a nosocomial cluster were identical by molecular typing methods. Epidemiologically unrelated isolates were all distinctly different by both EK and REAG typing methods. Although elevated amphotericin B MICs ( > or = 2 micrograms/ml) were observed in only three isolates, extended incubation (72 h) revealed amphotericin B MICs of 2-16 micrograms/ml in a subset of isolates suggesting potential amphotericin B resistance. These data document the genetic diversity, nosocomial transmission, and antifungal susceptibility of clinical isolates of C. lusitaniae.