Post Antifungal Effect (PAFE)

Post-drug exposure effects are important to understand and optimize drug efficacy. Creative Biolabs has developed in vitro models to help you study of post antifungal effects (PAFEs).

The post antifungal effect (PAFE) refers to growth suppression of surviving fungi following the removal of antifungals in the absence of host defense mechanisms. It is a phenomenon which is observed both in vitro and in vivo. Antifungals are capable of exerting many different effects on surviving fungi even though they are just transitorily exposed to the drug. The mechanisms of post antifungal effect include delayed recovery of enzyme and non-enzyme protein activities; changes in cell morphology, metabolism, growth and generation time; changes in cell receptors; susceptibility to phagocytosis; and altered susceptibility to an antifungal following re-exposure. PAFE is more enduring comparing the effect of changes in growth rate.

The ability of an antifungal to induce a PAFE is an attractive property since its ability to suppress fungal growth even through concentrations fall below the MIC. The knowledge of PAFE would be clinically useful in determining dosage regimens of a new drug. For oral fungal diseases, like oral candidosis, the diluent effect of saliva and the cleansing effect of the oral musculature tend to reduce the effective therapeutic concentrations and thus influence the bioavailability of antifungal agents. Evaluating PAFE for the oral fungal disease is more important than evaluating antifungal susceptibility only.

Figure 1. Effect of drug exposure over time (h) on the viability of A. corymbifera (A) and R. oryzae (R) spores at 4 × and 1 × MIC. (a) Amphotericin B (RPMI-1640); (b) nystatin (RPMI-1640); (c) nystatin (AM3); (d) amphotericin B (AM3). (Vitale et al. 2003)

Creative Biolabs offers customized PAFE assay for both yeast and filamentous fungi (spores). The steps of PAFE assay are:

1. The first step is determining MIC (minimum inhibitory concentration) for an antifungal. We offer several methods for testing MIC.
2. After MIC evaluation, we prepare the cell suspension. The concentration of yeast cells or filamentous fungi spores is adjusted to (1-5) × 10⁵ cells/mL and the cell suspension is added to tubes containing antifungal agents (test group) or no-drug broth (control group). The concentration of antifungal agents can be fixed (like MIC or twice the MIC) or gradient of the corresponding MIC (e.g. 0.5, 1, 2, and 4 times) according to your need. After incubation for a period, the cells are washed and centrifuged for several times and re-suspended to the same concentration.
3. PAFE assay. PAFE was determined by comparing the growth time of the exposed spores with that of the controls. We measure the time required for reaching the optical density of 0.05 in value at 520 nm. The growth time required for drug-exposed cell suspension and the drug-free control cell suspension are compared. All the groups can be placed in a microtitration plates, and the optical density of the suspension can be measured in a computerized spectrophotometric reader automatically. This automatically reading system can largely save your time and total expenditure.

Creative Biolabs can make a tailored optimum PAFE system according to your needs. For more detailed information, please feel free to contact us or directly sent us an inquiry.

Reference

1. Vitale RG, Meis JFGM, Mouton JW, et al. (2003). “Evaluation of the post-antifungal effect (PAFE) of amphotericin B and nystatin against 30 zygomycetes using two different media”. Journal of Antimicrobial Chemotherapy 52: 65–70. DOI: 10.1093/jac/dkg285
2. Ellepola AN, Khajah R, Jayatilake S, et al. (2015). “Impact of brief exposure to antifungal agents on the post-antifungal effect and hemolysin activity of oral Candida albicans”. J Appl Oral Sci 23(4):412-418.

For Research Use Only.