Biomedical subjects

M A Ghannoum

Publications and source records attributed to M A Ghannoum.

At least 37 records · Page 2Linked to original sources

PubMed2001

Biofilm formation by the fungal pathogen Candida albicans: development, architecture, and drug resistance.

Biofilms are a protected niche for microorganisms, where they are safe from antibiotic treatment and can create a source of persistent infection. Using two clinically relevant Candida albicans biofilm models formed on bioprosthetic materials, we demonstrated that biofilm formation proceeds through three distinct developmental phases. These growth phases transform adherent blastospores to well-defined cellular communities encased in a polysaccharide matrix. Fluorescence and confocal scanning laser microscopy revealed that C. albicans biofilms have a highly heterogeneous architecture composed of cellular and noncellular elements. In both models, antifungal resistance of biofilm-grown cells increased in conjunction with biofilm formation. The expression of agglutinin-like (ALS) genes, which encode a family of proteins implicated in adhesion to host surfaces, was differentially regulated between planktonic and biofilm-grown cells. The ability of C. albicans to form biofilms contrasts sharply with that of Saccharomyces cerevisiae, which adhered to bioprosthetic surfaces but failed to form a mature biofilm. The studies described here form the basis for investigations into the molecular mechanisms of Candida biofilm biology and antifungal resistance and provide the means to design novel therapies for biofilm-based infections.

Antifungal Agents↗

PubMed2001

Utility of 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenyl-amino)carbonyl]-2H-tetrazolium hydroxide (XTT) and minimum effective concentration assays in the determination of antifungal susceptibility of Aspergillus fumigatus to the lipopeptide class compounds.

The susceptibility of Aspergillus fumigatus to mulundocandin, an echinocandin-like compound, and other antifungal agents was assessed by the National Committee for Clinical Laboratory Standards (NCCLS) M38-P method, a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenyl-amino)carbonyl]-2H-tetrazolium hydroxide (XTT)-based colorimetric assay, and determination of morphologic alterations by microscopy. In contrast to the NCCLS M38-P method, which does not predict the activity in vivo, the XTT-based assay showed that A. fumigatus is susceptible to mulundocandin. Thus, the XTT-based assay might be useful for determination of the susceptibilities of molds to echinocandins. Further evaluation is warranted.

Antifungal Agents↗

PubMed2001

Antifungal resistance of candidal biofilms formed on denture acrylic in vitro.

Denture biofilms represent a protective reservoir for oral microbes. The study of the biology of Candida in these biofilms requires a reliable model. A reproducible model of C. albicans denture biofilm was developed and used to determine the susceptibility of two clinically relevant C. albicans isolates against 4 antifungals. C. albicans, growing as a biofilm, exhibited resistance to amphotericin B, nystatin, chlorhexidine, and fluconazole, with 50% reduction in metabolic activity (50% RMA) at concentrations of 8, 16, 128, and > 64 microg/mL, respectively. In contrast, planktonically cultured C. albicans were susceptible (50% RMA for the same antifungals was obtained at 0.25, 1.0, 4.0, and 0.5 microg/mL, respectively). In conclusion, results obtained by means of our biofilm model show that biofilm-associated C. albicans cells, compared with cells grown in planktonic form, are resistant to antifungals used to treat denture stomatitis.

Acrylic Resins↗

PubMed2001

New developments in chemotherapy for non-invasive fungal infections.

Dermatomycosis and subcutaneous mycosis comprise the non-invasive fungal infections commonly encountered in clinical practice around the world. The limited activity of early topical antifungal agents prompted the development of more effective systemic agents. While griseofulvin has been used for more than four decades, the use of early azoles, such as ketoconazole have resulted in better patient compliance and thus greater success. However, poor response and recurrence in dermatomycosis, as well as toxicity associated with ketoconazole therapy, has led to the search for newer antifungal agents and more effective treatment strategies. Terbinafine, itraconazole and fluconazole have the advantage of non-toxicity and a broad spectrum of activity. An overview of non-invasive fungal infections, antifungal agents in clinical use and recent developments in antifungal therapy is reviewed in this article.

Animals↗

PubMed2000

The exciting future of antifungal therapy.

Invasive fungal infections are becoming more common. Current therapy is generally limited to amphotericin B in its parent and lipid formulations, 5-fluctyosine, fluconazole, and itraconazole. Toxicity, drug-drug interactions, and increasing fungal resistance reduce the usefulness of these drugs, and the need for new therapies is pressing. This article briefly discusses the limitations of antifungal minimum inhibitory testing, and then summarizes new antifungal drugs in development that have been tested in humans. It also addresses novel treatment strategies such as drug combination therapy, pharmacological reformulations to improve the efficacy or reduce the toxicity of current antifungal drugs, immune function augmentation, and vaccine development. All of these strategies, although in their infancy, will enhance the clinician's ability to care for patients with invasive fungal infections.

Antifungal Agents↗

PubMed2000

A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns.

BACKGROUND: Onychomycosis, a fungal infection of the nail bed, is responsible for up to 50% of nail disorders. Although several surveys have been conducted in different parts of the world, there have been no multicenter epidemiologic surveys of onychomycosis in North America. OBJECTIVE: A 12-center study was undertaken to (1) determine the frequency of onychomycosis, (2) identify organisms recovered from the nails, and (3) determine the antifungal susceptibility of isolates. METHODS: A total of 1832 subjects participated in this study and completed a comprehensive questionnaire, and nail clippings were collected for potassium hydroxide examination and culturing. RESULTS: The frequency of onychomycosis, as defined by the presence of septate hyphae on direct microscopy and/or the recovery of a dermatophyte, was found to be 13.8%. In general, the dermatophyte isolates were susceptible to the antifungals tested. CONCLUSION: Because of the limited number of large-scale studies, the baseline incidence is not firmly established. However, the higher frequency of onychomycosis in this study may confirm the suspected increase in incidence of disease in North America.

Adolescent↗

PubMed2000

An evaluation of the in vitro activity of terbinafine.

Terbinafine has previously been shown to be highly active against dermatophytes and many other filamentous fungi. However, its activity against yeasts is controversial, with earlier reports suggesting that it has low activity, while more recent studies demonstrated that terbinafine is effective against yeasts. In this study, the in vitro activity of terbinafine was evaluated against a broad range of fungal isolates. We examined the susceptibility of 100 yeast strains (10 species including Candida albicans, non-C. albicans, fluconazole-susceptible and -resistant candidal strains), and 184 strains of filamentous fungi and dermatophytes (29 species including Aspergillus, Fusarium, Sporothrix, Trichophyton rubrum, T. mentagrophytes, T. tonsurans, Microsporum canis and Epidermophyton floccosum), using the NCCLS M27-A microdilution methodology for yeasts and a modified M38-P methodology for moulds. The endpoint for terbinafine was defined as 80% inhibition compared with the growth control well. The mean yeast and filamentous fungi minimum inhibitory concentration values +/- SEM (in microg ml(-1)) for terbinafine were: 6.60 +/- 0.73 and 1.04 +/- 0.28, respectively. In conclusion, our data suggest that terbinafine, in addition to its potent activity against dermatophytes, is considerably effective against a broad range of yeasts and filamentous fungi in vitro. Therefore, investigations concerning its antifungal activity in vivo against such organisms should be pursued.

Antifungal Agents↗

PubMed2000

Potential role of phospholipases in virulence and fungal pathogenesis.

Microbial pathogens use a number of genetic strategies to invade the host and cause infection. These common themes are found throughout microbial systems. Secretion of enzymes, such as phospholipase, has been proposed as one of these themes that are used by bacteria, parasites, and pathogenic fungi. The role of extracellular phospholipase as a potential virulence factor in pathogenic fungi, including Candida albicans, Cryptococcus neoformans, and Aspergillus, has gained credence recently. In this review, data implicating phospholipase as a virulence factor in C. albicans, Candida glabrata, C. neoformans, and A. fumigatus are presented. A detailed description of the molecular and biochemical approaches used to more definitively delineate the role of phospholipase in the virulence of C. albicans is also covered. These approaches resulted in cloning of three genes encoding candidal phospholipases (caPLP1, caPLB2, and PLD). By using targeted gene disruption, C. albicans null mutants that failed to secrete phospholipase B, encoded by caPLB1, were constructed. When these isogenic strain pairs were tested in two clinically relevant murine models of candidiasis, deletion of caPLB1 was shown to lead to attenuation of candidal virulence. Importantly, immunogold electron microscopy studies showed that C. albicans secretes this enzyme during the infectious process. These data indicate that phospholipase B is essential for candidal virulence. Although the mechanism(s) through which phospholipase modulates fungal virulence is still under investigations, early data suggest that direct host cell damage and lysis are the main mechanisms contributing to fungal virulence. Since the importance of phospholipases in fungal virulence is already known, the next challenge will be to utilize these lytic enzymes as therapeutic and diagnostic targets.

Amino Acid Sequence↗

PubMed2000

Candida albicans and Candida krusei differentially induce human blood mononuclear cell interleukin-12 and gamma interferon production.

Protection against Candida infection involves both innate and acquired immune responses, and cytokines produced by monocytes during the innate response may modify the acquired immune response by T cells. We hypothesized that Candida species which differ in pathogenicity can differentially induce production of immunoregulatory cytokines by human monocytes, which in turn modify T cells for immune responses to Candida. To test this hypothesis, we examined the effects of Candida albicans and Candida krusei on immunoregulatory cytokine production by human monocytes and gamma interferon (IFN-gamma) production by peripheral blood mononuclear cells (PBMC). Purified monocytes were incubated with live or heat-killed strains of C. albicans and C. krusei at the optimal Candida/monocyte ratio of 0.5. Cytokines in the supernatants were measured by enzyme-linked immunosorbent assay. Our data demonstrated that live C. albicans and C. krusei significantly induced interleukin-10 (IL-10), monocyte chemotactic factor 1, IL-1beta, and tumor necrosis factor alpha production by monocytes relative to unstimulated monocytes. In contrast, unlike C. krusei, pathogenic live strains of C. albicans induced no or only a minimal level of IL-12. The expression of IL-12 p40 mRNA levels by reverse transcription-PCR corroborated the IL-12 protein (p70) findings. In human PBMC, human blood monocytes were the major source of both IL-10 and IL-12 production in response to C. albicans and C. krusei. Upon activation of T cells in the presence of Candida-modified monocytes and antigen-presenting cells, IL-12 production by PBMC treated with Candida organisms correlated strongly with the level of IFN-gamma production by T cells. These results indicate that the virulence of C. albicans may be related to its ability to induce the monocytic type II cytokine IL-10, with a selective inhibition of IL-12 production, which may be responsible for the observed lack of T-cell IFN-gamma and may restrain an effective type I immune response to Candida.

Candida↗

PubMed2000

Antifungal susceptibility testing of dermatophytes: establishing a medium for inducing conidial growth and evaluation of susceptibility of clinical isolates.

A standardized reference method for dermatophyte in vitro susceptibility testing is lacking. In a previous study, Norris et al. (H. A. Norris, B. E. Elewski, and M. A. Ghannoum, J. Am. Acad. Dermatol. 40(6, part 2):S9-S13) established the optimal medium and other growth variables. However, the earlier study did not address two issues: (i) selection of an optimal medium for conidial formation by dermatophytes and (ii) validation of the method with a large number of dermatophytes. The present study addresses these two points. To select which agar medium best supported conidial growth, representative isolates of dermatophytes were grown on different agars. Preliminary experiments showed that only oatmeal cereal agar supported the production of conidia by Trichophyton rubrum. We tested the abilities of 251 T. rubrum isolates to form conidia using three different cereal agars and potato dextrose agar. Overall, oatmeal cereal and rice agar media were comparable in their abilities to support T. rubrum conidial growth. Next, we used the oatmeal cereal agar for conidial formation along with the optimal conditions for dermatophyte susceptibility testing proposed by Norris et al. and determined the antifungal susceptibilities of 217 dermatophytes to fluconazole, griseofulvin, itraconazole, and terbinafine. Relative to the other agents tested, terbinafine possessed the highest antifungal activity against all of the dermatophytes. The mean +/- standard error of the mean MICs of fluconazole, itraconazole, terbinafine, and griseofulvin were 2.07 +/- 0.29, 0.13 +/- 0.01, 0.002 +/- 0.0003, and 0.71 +/- 0.05 microgram/ml, respectively. This study is the first step in the identification of optimal conditions that could be used for the standardization of the antifungal susceptibility testing method for dermatophytes. Inter- and intralaboratory agreement as well as clinical correlations need to be established.

Antifungal Agents↗

PubMed2000

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.

Antifungal Agents↗

PubMed2000

New investigational antifungal agents for treating invasive fungal infections.

Systemic fungal infections have been recognised as a major cause of morbidity and mortality during the last two decades. There are only a few therapeutic options for these infections. Severe toxicity, such as impairment of renal function, limits the use of amphotericin B. Flucytosine is associated with side effects and drug resistance. Fluconazole and itraconazole are safer, though emergence of resistance and innate resistance in some fungal pathogens is a concern in their use. Therefore, there is a need for developing novel drugs and/or treatment strategies to combat these infections. In recent years, increased efforts by the pharmaceutical industry and academia have led to the discovery of new re-engineered or reconsidered antifungal agents that are more efficacious, safer and have a broad spectrum of activity. Lipid formulations of polyene antifungal agents, amphotericin B and nystatin, have the advantage of improved therapeutic index. Activity against resistant fungi, high bioavailability, safety and longer half-life are the properties that encourage development of the newer triazoles (e.g., voriconazole, ravuconazole and posaconazole). Echinocandin-like lipopeptide antibiotics are among the antifungal agents with a novel mode of action. In addition to these lead investigational compounds, development of newer antifungal agents is underway.

Animals↗

PubMed1999

Oropharyngeal candidiasis in patients with HIV: suggested guidelines for therapy.

The high frequency of oropharyngeal candidiasis in immunocompromised patients has led many institutions to develop protocols to guide the use of antifungal agents in the treatment of this opportunistic infection. However, few specific recommendations have been made for directing the management of oropharyngeal candidiasis in patients infected with HIV. To meet this need, a panel of experts representing a variety of disciplines met to formulate a consensus and devise a treatment strategy for clinical application. Among other recommendations, the algorithm calls for use of a topical agent for the treatment of initial and recurring oropharyngeal candidiasis in HIV-infected patients, provided there is no esophageal involvement, patients' CD4+ lymphocyte cell count is >50 cells/mm3, and they are currently receiving or expected to receive effective antiretroviral treatment. For episodes of oropharyngeal candidiasis with concurrent esophageal involvement or where patients have a CD4+ cell count of <50 cells/mm3, are not receiving or anticipating highly active antiretroviral therapy (HAART), and have a high viral load, the algorithm suggests a systemic oral azole as the more appropriate treatment choice. Acute treatment of all oropharyngeal candidiasis episodes is preferred. Chronic suppressive antifungal treatment is to be avoided in recognition of the potential for the development of drug-resistant infection.

AIDS-Related Opportunistic Infections↗

PubMed1999

Optimal growth conditions for the determination of the antifungal susceptibility of three species of dermatophytes with the use of a microdilution method.

As a prerequisite to standardization of dermatophyte susceptibility testing, conditions that support optimal growth of different dermatophyte species must be established. Eighteen isolates of Trichophyton spp. (T rubrum, T mentagrophytes, T tonsurans) were grown in 4 different media: RPMI 1640 with L-glutamine, without sodium bicarbonate and buffered at pH = 7.0; antibiotic medium #3 (Penassay); yeast nitrogen base with 0.5% dextrose buffered at pH = 7.0; and Sabouraud dextrose broth. Incubation for 6 days at 35 degrees C produced the following results: RPMI and Sabouraud dextrose supported equally sufficient growth for all strains tested; Penassay supported growth of only 33% of the isolates tested, and buffered yeast nitrogen base did not support growth of any isolates. RPMI was selected as the optimal medium, and organisms were tested at both 30 degrees C and 35 degrees C with a standardized inoculum density of 10(3) conidia/mL. No temperature differences were noted in the amount of growth of the dermatophytes tested. With RPMI at an incubation temperature of 35 degrees C, 3 inoculum sizes (10(3), 10(4), and 10(5) conidia/mL) were tested against 4 antifungal agents: griseofulvin, itraconazole, terbinafine, and fluconazole. Inoculum size did not affect minimum inhibitory concentration (MIC) results for itraconazole or terbinafine, but a larger inoculum produced a slightly higher MIC for griseofulvin and a noticeably higher MIC for fluconazole. Our data support the use of RPMI 1640, 35 degrees C, and 4 days as an incubation temperature and time, respectively, and an inoculum of 10(3) conidia/mL as optimal conditions for the determination of the antifungal susceptibility of dermatophytes.

Antifungal Agents↗

PubMed1999

In vitro activities of voriconazole, fluconazole, and itraconazole against 566 clinical isolates of Cryptococcus neoformans from the United States and Africa.

We investigated the in vitro activity of voriconazole compared to those of fluconazole and itraconazole against 566 clinical isolates of Cryptococcus neoformans from Africa (164) and the United States (402). Isolates were obtained from cerebrospinal fluid (362), blood (139), and miscellaneous sites (65). Voriconazole (MIC at which 90% of the isolates are inhibited [MIC90], 0.12 to 0.25 microg/ml) was more active than either itraconazole (MIC90, 0.5 microg/ml) or fluconazole (MIC90, 8.0 to 16 microg/ml) against both African and U. S. isolates. Isolates inhibited by >/=16 microg of fluconazole per ml were almost all (99%) inhibited by </=1 microg of voriconazole per ml. These results suggest that voriconazole may be useful in the treatment of cryptococcosis.

Africa↗

PubMed1999

Successful treatment of fluconazole-resistant oropharyngeal candidiasis by a combination of fluconazole and terbinafine.

Increasing incidence of resistance to conventional antifungal therapy has demanded that novel therapies be introduced. Recent in vitro studies have shown that combinations involving azoles and allylamines may be effective in inhibiting fluconazole-resistant fungi. In this report, we describe the case of a 39-year-old woman who presented with white patches on her buccal mucosa, tongue, and palate with a bright erythematous erosive base. A fungal culture revealed Candida albicans. The patient failed to respond to the initially prescribed fluconazole therapy. Failure of therapy can be attributed to a developed resistance to fluconazole from the patient's intermittent use of this antifungal agent at varying dosages for the preceding 2 years due to a diagnosis of onychomycosis. In vitro testing of the culture from the patient showed elevated MICs of fluconazole, itraconzole, and terbinafine (MICs were 32, 0.5, and 64 microg/ml, respectively). Our goal was to combine therapies of fluconazole and terbinafine in an attempt to clear the fungal infection. Impressively, this combination resulted in the clearing of the clinical symptoms and the patient has successfully been asymptomatic for more than 12 months posttreatment.

Adult↗

PubMed1999

Antifungal agents: mode of action, mechanisms of resistance, and correlation of these mechanisms with bacterial resistance.

The increased use of antibacterial and antifungal agents in recent years has resulted in the development of resistance to these drugs. The significant clinical implication of resistance has led to heightened interest in the study of antimicrobial resistance from different angles. Areas addressed include mechanisms underlying this resistance, improved methods to detect resistance when it occurs, alternate options for the treatment of infections caused by resistant organisms, and strategies to prevent and control the emergence and spread of resistance. In this review, the mode of action of antifungals and their mechanisms of resistance are discussed. Additionally, an attempt is made to discuss the correlation between fungal and bacterial resistance. Antifungals can be grouped into three classes based on their site of action: azoles, which inhibit the synthesis of ergosterol (the main fungal sterol); polyenes, which interact with fungal membrane sterols physicochemically; and 5-fluorocytosine, which inhibits macromolecular synthesis. Many different types of mechanisms contribute to the development of resistance to antifungals. These mechanisms include alteration in drug target, alteration in sterol biosynthesis, reduction in the intercellular concentration of target enzyme, and overexpression of the antifungal drug target. Although the comparison between the mechanisms of resistance to antifungals and antibacterials is necessarily limited by several factors defined in the review, a correlation between the two exists. For example, modification of enzymes which serve as targets for antimicrobial action and the involvement of membrane pumps in the extrusion of drugs are well characterized in both the eukaryotic and prokaryotic cells.

Amphotericin B↗

PubMed1999

Multicenter comparison of the sensititre YeastOne Colorimetric Antifungal Panel with the National Committee for Clinical Laboratory standards M27-A reference method for testing clinical isolates of common and emerging Candida spp., Cryptococcus spp., and other yeasts and yeast-like organisms.

National Committee for Clinical Laboratory Standards (NCCLS) standard guidelines are available for the antifungal susceptibility testing of common Candida spp. and Cryptococcus neoformans, but NCCLS methods may not be the most efficient and convenient procedures for use in the clinical laboratory. MICs of amphotericin B, fluconazole, flucytosine, itraconazole, and ketoconazole were determined by the commercially prepared Sensititre YeastOne Colorimetric Antifungal Panel and by the NCCLS M27-A broth microdilution method for 1,176 clinical isolates of yeasts and yeast-like organisms, including Blastoschizomyces capitatus, Cryptococcus spp., 14 common and emerging species of Candida, Hansenula anomala, Rhodotorula spp., Saccharomyces cerevisiae, Sporobolomyces salmonicolor, and Trichosporon beigelii. Colorimetric MICs of amphotericin B corresponded to the first blue well (no growth), and MICs of the other agents corresponded to the first purple or blue well. Three comparisons of MIC pairs by the two methods were evaluated to obtain percentages of agreement: 24- and 48-h MICs and 24-h colorimetric versus 48-h reference MICs. The best performance of the YeastOne panel was with 24-h MICs (92 to 100%) with the azoles and flucytosine for all the species tested, with the exception of C. albicans (87 to 90%). For amphotericin B, the best agreement between the methods was with 48-h MIC pairs (92 to 99%) for most of the species tested. The exception was for isolates of C. neoformans (76%). These data suggest the potential value of the YeastOne panel for use in the clinical laboratory.

Amphotericin B↗