Extracellular phospholipase production of oral Candida albicans isolates from smokers, diabetics, asthmatics, denture wearers and healthy individuals following brief exposure to polyene, echinocandin and azole antimycotics

Abstract Objective Candida albicans is the primary causative agent of oral candidosis, and one of its key virulent attributes is considered to be its ability to produce extracellular phospholipases that facilitate cellular invasion. Oral candidosis can be treated with polyenes, and azoles, and the more recently introduced echinocandins. However, once administered, the intraoral concentration of these drugs tend to be sub-therapeutic and rather transient due to factors such as the diluent effect of saliva and cleansing effect of the oral musculature. Hence, intra-orally, the pathogenic yeasts may undergo a brief exposure to antifungal drugs. We, therefore, evaluated the phospholipase production of oral C. albicans isolates following brief exposure to sub-therapeutic concentrations of the foregoing antifungals. Materials and methods Fifty C. albicans oral isolates obtained from smokers, diabetics, asthmatics using steroid inhalers, partial denture wearers and healthy individuals were exposed to sub-therapeutic concentrations of nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole for one hour. Thereafter the drugs were removed and the phospholipase production was determined by a plate assay using an egg yolk-agar medium. Results The phospholipase production of these isolates was significantly suppressed with a percentage reduction of 10.65, 12.14, 11.45 and 6.40% following exposure to nystatin, amphotericin B, caspofungin and ketoconazole, respectively. This suppression was not significant following exposure to fluconazole. Conclusions Despite the sub-therapeutic, intra oral, bioavailability of polyenes, echinocandins and ketoconazole, they are likely to produce a persistent antifungal effect by suppressing phospholipase production, which is a key virulent attribute of this common pathogenic yeast.

Antifungal activities of tacrolimus in combination with antifungal agents against fluconazole-susceptible and fluconazole-resistant Trichosporon asahii isolates

ABSTRACT The antifungal activity of tacrolimus in combination with antifungal agents against different fungal species has been previously reported. Here we report the in vitro interactions between tacrolimus and amphotericin B, fluconazole, itraconazole, and caspofungin against 30 clinical isolates of both fluconazole-susceptible and fluconazole-resistant Trichosporon asahii. For these analyses, we used the broth microdilution method based on the M27-A3 technique and checkerboard microdilution method. Tacrolimus showed no activity against T. asahii strains (minimal inhibitory concentrations, MICs > 64.0 µg mL−1). However, a larger synergistic interaction was observed by the combinations tacrolimus + amphotericin B (96.67%) and tacrolimus + caspofungin (73.33%) against fluconazole-susceptible isolates. Combinations with azole antifungal agents resulted in low rates of synergism for this group (fluconazole + tacrolimus = 40% and itraconazole + tacrolimus = 10%). Antagonistic interactions were not observed. For the fluconazole-resistant T. asahii group, all tested combinations showed indifferent interactions. The synergism showed against fluconazole-susceptible T. asahii isolates suggests that the potential antifungal activity of tacrolimus deserves in vivo experimental investigation, notably, the combination of tacrolimus with amphotericin B or caspofungin.

Impact of brief exposure to antifungal agents on the post-antifungal effect and hemolysin activity of oral Candida albicans

AbstractPost-antifungal effect (PAFE) of Candida and its production of hemolysin are determinants of candidal pathogenicity. Candida albicans is the foremost aetiological agent of oral candidosis, which can be treated with polyene, azole, and echinocandin antifungals. However, once administered, the intraoral concentrations of these drugs tend to be subtherapeutic and transient due to the diluent effect of saliva and cleansing effect of the oral musculature. Hence, intra-orally, Candidamay undergo a brief exposure to antifungal drugs.Objective Therefore, the PAFE and hemolysin production of oral C. albicans isolates following brief exposure to sublethal concentrations of the foregoing antifungals were evaluated.Material and Methods A total of 50 C. albicans oral isolates obtained from smokers, diabetics, asthmatics using steroid inhalers, partial denture wearers and healthy individuals were exposed to sublethal concentrations of nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole for 60 min. Thereafter, the drugs were removed and the PAFE and hemolysin production were determined by previously described turbidometric and plate assays, respectively.Results Nystatin, amphotericin B, caspofungin and ketoconazole induced mean PAFE (hours) of 2.2, 2.18, 2.2 and 0.62, respectively. Fluconazole failed to produce a PAFE. Hemolysin production of these isolates was suppressed with a percentage reduction of 12.27, 13.47, 13.33, 8.53 and 4.93 following exposure to nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole, respectively.Conclusions Brief exposure to sublethal concentrations of antifungal drugs appears to exert an antifungal effect by interfering with the growth as well as hemolysin production of C. albicans.

Chloroquine sensitizes biofilms of Candida albicans to antifungal azoles

Biofilms formed by Candida albicans, a human pathogen, are known to be resistant to different antifungal agents. Novel strategies to combat the biofilm associated Candida infections like multiple drug therapy are being explored. In this study, potential of chloroquine to be a partner drug in combination with four antifungal agents, namely fluconazole, voriconazole, amphotericin B, and caspofungin, was explored against biofilms of C. albicans. Activity of various concentrations of chloroquine in combination with a particular antifungal drug was analyzed in a checkerboard format. Growth of biofilm in presence of drugs was analyzed by XTT-assay, in terms of relative metabolic activity compared to that of drug free control. Results obtained by XTT-metabolic assay were confirmed by scanning electron microscopy. The interactions between chloroquine and four antifungal drugs were determined by calculating fractional inhibitory concentration indices. Azole resistance in biofilms was reverted significantly (p < 0.05) in presence of 250 µg/mL of chloroquine, which resulted in inhibition of biofilms at very low concentrations of antifungal drugs. No significant alteration in the sensitivity of biofilms to caspofungin and amphotericin B was evident in combination with chloroquine. This study for the first time indicates that chloroquine potentiates anti-biofilm activity of fluconazole and voriconazole.

The activity of echinocandins, amphotericin B and voriconazole against fluconazole-susceptible and fluconazole-resistant Brazilian Candida glabrata isolates

The extensive use of azole antifungal agents has promoted the resistance of Candida spp to these drugs. Candida glabrata is a problematic yeast because it presents a high degree of primary or secondary resistance to fluconazole. In Brazil, C. glabrata has been less studied than other species. In this paper, we compared the activity of three major classes of antifungal agents (azoles, echinocandins and polyenes) against fluconazole-susceptible (FS) and fluconazole-resistant (FR) C. glabrata strains. Cross-resistance between fluconazole and voriconazole was remarkable. Among the antifungal agents, the echinocandins were the most effective against FS and FR C. glabrata and micafungin showed the lowest minimal inhibitory concentrations.

Equinocandinas / Echinocandins

The echinocandins, caspofugin, micafungin, and anidulafungin, are lipopeptides that inhibit fungal growth by binding to β - (1.3) d glucan synthase. This enzyme is responsible for the formation of the peptidoglycan cell wall, and it is essential in fungi such as Candida spp, but less important in the case of Aspergillus and Fusarium species. We review the history, pharmacology and clinical trials that have showed clinical efficacy similar to amphotericin B for the management of fungal infections such as candidemia, invasive candidiasis and aspergillosis, even in cases refractory to initial treatment. These drugs have less toxicity and discontinuation is uncommonly required. Despite similar spectrum and tolerability, there are several pharmacological differences. Only a few clinical trials compare the clinical efficacy between them and their clinical application cannot be generalized. However, the echinocandins have demonstrated clinical efficacy in patients with invasive candidiasis and in others forms of systemic mycoses.

Las equinocandinas -caspofugina, micafungina y ani-dulafungina- son lipopéptidos que inhiben el crecimiento fúngico al unirse a la β-(1,3) d glucano sintetasa, enzima esencial para la síntesis en la pared celular de hongos como Candida spp, y menos importante en el caso de especies de Aspergillus y Fusarium. Se revisa la historia, farmacología y los diferentes ensayos clínicos que han evidenciado similar eficacia clínica a la de anfotericina B para el manejo de infecciones micóticas como candidemia, candidiasis invasora y aspergilosis, inclusive en casos refractarios al manejo inicial. Estos medicamentos tienen menor toxicidad y en pocos casos hay necesidad de retiro del tratamiento. Dado su espectro y tolerabilidad similar, su farmacología permite diferenciarlas. Se dispone de información limitada de estudios clínicos que las comparen entre ellas, limitando la extrapolación de la información a todo el grupo. Sin embargo, presentan eficacia clínica comprobada en pacientes con varias micosis invasoras.

Susceptibilidad in vitro a anidulafungina en 100 cepas de especies de Candida aisladas previo a la introducción de esta equinocandina en Chile / In vitro andulafungin susceptibility of 100 of Candida strains obtained previously to the introduction of this echinocandin in Chile

Fungi, particularly yeasts, have become important opportunistic pathogens that can be resistant to antifungal agents or develop resistance. To address this problem, new molecules such as echinocandins, have been developed. Susceptibility to anidulafungin was studied in yeasts isolated previous to the introduction of this drug in Chile. One hundred strains of different yeast species isolated from invasive fungal infections during 2007 and 2008 were studied. Susceptibility testing of anidulafungin was performed by broth microdilution according to CLSI. All strains were susceptible to anidulafungin. MIC50 and MIC90 were 0.125 µg/mL and 1 µg/mL, respectively. Compared to other yeasts, C. parapsilosis showed a slight increase in the MICs for anidulafungin (MIC50, 1 µg/mL, MIC90, 2 µg/mL), but remained within the susceptible range. Both, fluconazole resistant (8) and dose dependant susceptible strains (16) were susceptible to anidulafungin. In vitro, this echinocandin appears to be an effective therapeutic alternative.

Los hongos, especialmente las levaduras, se han transformado en importantes patógenos oportunistas y algunos de ellos tienen o desarrollan resistencia a los antifúngicos. Para enfrentar esta problemática se han desarrollado nuevas moléculas, como las equinocandinas. Este trabajo evaluó la susceptibilidad in vitro a anidula-fungina en levaduras obtenidas previo a la incorporación de este antifúngico en Chile. Para ello, se seleccionaron 100 cepas de diversas especies aisladas de enfermedad fúngica invasora durante los años 2007 y 2008 en Chile, a las cuales se les midió la susceptibilidad in vitro por micro-dilución en caldo para anidulafungina según CLSI. Todas las cepas fueron sensibles a anidulafungina con CIM50 y CIM90 de 0,125 µg/mL y 1 µg/mL, respectivamente. Se detectó un ligero aumento de las CIM en C. parapsilosis respecto a las otras levaduras (CIM50 de 1 µg/mL y CIM90 de 2 µg/mL) considerándose estos valores en el rango de sensibilidad. La correlación de la susceptibilidad frente a fluconazol evidenció que cepas resistentes (n: 8) y sensibles dosis dependientes (n: 16) fueron sensibles a anidulafungina. Esta equinocandina aparece, in vitro, como una alternativa terapeutica efectiva frente a las levaduras aisladas en nuestros pacientes.

Nuevos antifúngicos: Las equinocandinas / New antifungal agents: Echinocandins

La familia de lipopéptidos conocidos como equinocandinas emerge como las nuevas "penicilinas antifúngicas", capaces de destruir la pared celular micótica al inhibir la síntesis del glucano, fundamental constituyente de la estructura fúngica. Las equinocandinas han mostrado in vitro e in vivo, ser fungicidas contra la mayoría de las especies de Candida y fungistáticas contra Aspergillus sp, sin exhibir acción sobre células de mamíferos. Tres agentes emergen como los principales representantes de esta clase; caspofungina, micafungina y anidulafungina, estando las dos primeras ya licenciadas para su uso en humanos. Su óptimo perfil de seguridad, con baja incidencia y severidad de efectos adversos, cómoda posología y pocas interacciones con otros fármacos, representan notables ventajas para la terapéutica antifúngica moderna. Comparativamente han mostrado tener eficacia clínica similar a anfotericina B, sin la toxicidad que este polieno tradicionalmente muestra, lo que sumado a la ausencia de antagonismo con otros antifúngicos permite sugerir que la terapia combinada pudiera ser un nuevo estándar de manejo para la tan temida aspergilosis invasora.

The lipopeptide family known as echinocandins emerge as the new "antifungal penicillins", because their ability to destroy the fungal cell wall as they inhibit glucan synthesis, the main component of fungal structure. Echinocandins are fungicidal in vitro and in vivo against most Candida species and fungistatic against Aspergillus sp, without antifungal activity over mammal cells. Three drugs are representative of this class; caspofungin, micafungin and anidulafungin, the two first have been licensed for human use. Their optimal security profile, with low incidence and severity of adverse effects, kind posology and few interactions with other drugs, represent noticeable advantages for modern antifungal therapy. They have similar clinical efficacy as amphotericin B, without its toxicity, which besides the absence of antagonism with other antifungal drugs, allows to suggest that combined antifungal therapy could represent a new standard for the management of the feared invasive aspergillosis.