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Ellepola, Arjuna Nishanatha Bandara (2000)
PhD Thesis: The post-antifungal effect (PAFE) and its impact on the pathogenic attributes of
Candida albicans
Abstract:
The opportunistic fungal pathogen Candida albicans is the main aetiological agent of oral
candidosis. The common antimycotics used in the treatment of candidoses comprise the
polyenes (nystatin and amphotericin B), the azoles (ketoconazole and fluconazole), and the
DNA analogue, 5-fluorocytosine. In the oral cavity the diluent and flushing action of saliva
tend to reduce the availability of these agents with resultant limited exposure of pathogens to
the drugs. However, the behaviour of fungi under the latter conditions is ill-understood. The
post-antifungal effect (PAFE) is a novel concept which refers to the suppression of fungal
growth following limited exposure to antimycotics and subsequent removal of the drug. This
thesis relates to an enquiry into the P AFE of five different antimycotics on ten oral isolates
of C. albicans and its impact on the pathogenic attributes of these isolates, including the
adherence to denture acrylic surfaces and buccal epithelial \cells (BEC), the relative cell
surface hydrophobicity (CSH) and germ tube formation.
The mean PAFE of nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole
on C. albicans isolates were 2.89, 2.83, 3.18, 0.65 and 0.16 hours, respectively. On
evaluating the adherence to denture acrylic surfaces during the PAFE period, the foregoing
antimycotics elicited a mean percentage reduction of 86.48%, 90.85% (p < 0.01 for all
isolates), 66.72%, 65.88% and 47.42% (p < 0.01 for 70% to 85% of the isolates), respectively.
A similar analysis of the adherence to BEC revealed a mean percentage reduction of 72.88%
(p < 0.01), 16.52% (p < 0.01 for 30% of the isolates), 40.16% (p < 0.01) and 24.36% (p <
0.01 for 70% of the isolates), following exposure to nystatin, 5-fluorocytosine, ketoconazole
and fluconazole, respectively. Ultrastructural analysis revealed a minority of internally
collapsed cells with an intact cell wall leaving "cell ghosts" and deflated cells following
exposure to nystatin though other drugs did not elicit perceptible changes.
When the effect of drug exposure on the CSH of Candida was examined, a significant
reduction was observed for nystatin (27.14%; p = 0.01) and ketoconazole (19.47%; p = 0.04)
but not for the rest. Further, when the relationship between adhesion to BEC and CSH of the
isolates was evaluated a positive correlation emerged in the yeasts pre- exposed to 5-
fluorocytosine, ketoconazole and fluconazole (γ= 0.48 - 0.55; p<0.001 for all), but not
nystatin.
Evaluation of the ability to form germ tubes by these isolates following brief exposure to the
two polyenes, the DNA analogue and the two azoles elicited a mean percentage reduction of
97.68%, 97.52% (p < 0.01 for all isolates), 12.63%,30.84%, and 15.93% (p< 0.01 for 10% to
50% of the isolates), respectively. On ultrastructural studies, abrogated attempts at germ tube
formation was seen only with polyene-exposed cells.
To conclude, the preceding investigations have comprehensively defmed the PAFE of
common antimycotics and its possible impact on the pathogenic attributes of C. albicans. In
clinical terms these novel fmdings imply that antimycotics help eliminate the pathogen at
high concentrations while suppressing their virulence on minimal exposure to sub-
therapeutic concentrations.

Source: http://facdent.hku.hk/learning/abstract/2000%20Ellepola%20ANB.pdf