Influence of temperature and concentration on the postantifungal effect and the effects of sub-MIC concentrations of four antifungal agents on previously treated Candida species

Postantifungal Effect of Antifungal Drugs against Candida: What Do We Know and How Can We Apply This Knowledge in the Clinical Setting?

The study of the pharmacological properties of an antifungal agent integrates the drug pharmacokinetics, the fungal growth inhibition, the fungicidal effect and the postantifungal activity, laying the basis to guide optimal dosing regimen selection. The current manuscript reviews concepts regarding the postantifungal effect (PAFE) of the main classes of drugs used to treat Candida infections or candidiasis. The existence of PAFE and its magnitude are highly dependent on both the fungal species and the class of the antifungal agent. Therefore, the aim of this article was to compile the information described in the literature concerning the PAFE of polyenes, azoles and echinocandins against the Candida species of medical interest. In addition, the mechanisms involved in these phenomena, methods of study, and finally, the clinical applicability of these studies relating to the design of dosing regimens were reviewed and discussed. Additionally, different factors that could determine the variability in the PAFE were described. Most PAFE studies were conducted in vitro, and a scarcity of PAFE studies in animal models was observed. It can be stated that the echinocandins cause the most prolonged PAFE, followed by polyenes and azoles. In the case of the triazoles, it is worth noting the inconsistency found between in vitro and in vivo studies.

The post-antifungal effect (PAFE) of amphotericin B, nystatin, ketoconazole and 5-fluorocytosine and its impact on the colonization traits of Candida glabrata

The post-antifungal effect (PAFE) has been shown to affect Candida pathogenicity, but there is little information on either PAFE or its association with the colonization traits of Candida glabrata. The objective of this study was to determine, in vitro, the PAFE on 14 C. glabrata isolates following exposure to amphotericin B (AMB), nystatin (NYS), ketoconazole (KETO) and 5-fluorocytosine (5FC). In addition, we evaluated the impact of PAFE on yeast adherence to buccal epithelial cells (BEC), cell-surface-hydrophobicity (CSH) and biofilm growth (BG) on denture acrylic surfaces. PAFE was induced following a 1-h exposure of yeasts to (x1-x4MIC) of AMB, NYS, KETO and 5FC in RPMI medium and, measured using automated turbidometry. The BEC adhesion, CSH and BG assays were performed by the methods of Kimura & Pearsall, Sweet et al., and Jin et al., respectively. Significant differences in PAFE (P < 0.001) were observed after exposure to AMB and NYS, but not KETO and 5FC. Following exposure to AMB, NYS, KETO and 5FC, significant inter-strain differences (P < 0.001) were observed in percentage terms in adhesion (39.0%, 43.48%, 38.28%, 35.07%) and biofilm growth (42.86%, 39.86%, 42.81%, 36.38%), respectively. Short exposure of C. glabrata to sub-cidal concentrations of antifungals modulates yeast growth and also affects some of their colonization traits.

Dormancy of Candida albicans cells in the presence of the polyene antibiotic amphotericin B: simple demonstration by flow cytometry

Flow cytometry light scattering was used to monitor size increase of Candida albicans (isolate ATCC 10231) cells in the presence or absence of the antifungal drug amphotericin B (AmB). This non-invasive and descriptive method allowed for the differentiation of dead and dormant sub-populations of cells. When inoculated into a growth medium without AmB, a progressive increase in light scattering was observed over a period of approximately 4 h, but without proliferation of the yeast. After this period, the light scattering distribution regressed to baseline level, whereas cell proliferation started. In the presence of AmB, all the cells shrank in size within approximately 4 h and proliferation was temporarily halted. However, in the presence of 0.4 microM AmB, a progressive increase of light scattering occurred after 21 h which was similar to that observed within the first 4 h in the absence of the antifungal. After approximately 24 h of incubation at this concentration of AmB, proliferation resumed. These observations indicate that this renewed cell proliferation was due to the reawakening of dormant cells in the presence of AmB (45% in the presence of 0.4 microM AmB) rather than the result of the development of viable cells that had escaped detection. This simple descriptive approach could be extended to other fungal strains or species, to other antifungal drugs and possibly to bacteria.

Amphotericin B dose optimization in children with malignant diseases

In this study, rational dosing guidelines for amphotericin B-deoxycholate (AmB) are proposed for children. AmB steady-state trough concentrations (C(ss,trough)) and plasma creatinine concentrations (C(creat)) were measured in 83 children (age: 10 months to 18 years) receiving prophylactic AmB therapy (1 mg/kg/day). Maximum tolerable AmB C(ss,trough) were identified by determining the probability of large (>24%, 75th percentile) increases in C(creat) after 6 days of AmB for a series of C(ss,trough) ranges. Dose requirements were determined using a concentration-targeting approach. The 0.76-1.05 mg/l C(ss,trough) range provided the maximum concentrations that still had a low probability (p < 0.29) of adverse renal effects. 1 mg/kg/day AmB produces C(ss,trough) within this range for children weighing 25-45 kg. Lighter children (10-25 kg) require higher AmB doses (1.25-1.5 mg/kg/day) to achieve target C(ss,trough), while heavier children (45-55 kg) require lower doses (0.75 mg/kg/day). These starting dose guidelines may require individualization and prospective evaluation.

Isolation of fluconazole-tolerant micromycetes onto different cultivation media

On studying the dependence of quality and/or quantity of environmental fluconazole-tolerant micromycetes on culture medium in vitro, the highest number of isolates was obtained in Sabouraud agar (SA) without fluconazole (59 CFU/mg of soil sample at 25 degrees C and 31 CFU/mg at 37 degrees C). In the case of SA, fluconazole inhibited the growth of micromycetes to 83%. Significant differences were found between the average concentration of CFU/mg for six cultivation media without and with fluconazole (70 mg/L) at 25 and 37 degrees C. The genus Aspergillus (A. flavus, A. fumigatus, aspergilli from A. glaucus and A. niger group, A. nidulans, A. versicolor, A. ustus), Scopulariopsis brevicaulis and Penicillium sp. were the most common isolates. Sabouraud agar combined with malt extract agar, dichloran-18% glycerol agar and potato-dextrose agar were the most suitable for isolation of fluconazole-tolerant fungi.

Sublethal injury and resuscitation of Candida albicans after amphotericin B treatment

Amphotericin B treatment was previously shown to inhibit Candida albicans reproduction and reduce the fluorescence of vitality-specific dyes without causing a corresponding increase in the fluorescence of the mortality-specific dyes bis-(1,3-dibutylbarbituric acid)trimethine oxonol and SYBR Green I. In the present study, we have confirmed these results and have shown that the numbers of CFU are reduced by 99.9% by treatment with 0.5 micro g of amphotericin B per ml for 10 h at 35 degrees C. This reduction was not due to fungal cell death. First, the level of reduction of the tetrazolium salt 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide increased in the presence of concentrations of amphotericin B that caused greater than 90% reductions in the numbers of CFU. Second, fungal cells treated with amphotericin B at a concentration of 0.5 micro g/ml were resuscitated by further incubation at 22 degrees C for 15 h in the continued presence of amphotericin B. Third, recovery of the ability to replicate was prevented by sequential treatment with 20 micro g of miconazole per ml, which also increased the fluorescence of mortality-specific dyes to near the maximal levels achieved with 0.9 micro g of amphotericin B per ml. Sequential treatment with fluconazole and flucytosine did not increase the levels of staining with the mortality-specific dyes. Itraconazole was less effective than ketoconazole, which was less effective than miconazole. The practice of equating the loss of the capacity of C. albicans to form colonies with fungal cell death may give incorrect results in assays with amphotericin B, and the results of assays with caution with other antifungal agents that are lipophilic or that possess significant postantifungal effects may need to be interpreted.