Evaluation of direct microscopic examination versus culture in the diagnosis of superficial fungal infections

Actin gene-targeted RT-PCR could be a useful method for evaluating in vitro fungicidal activity against dermatophytes

This study examined the effects of the antifungal agents amorolfine hydrochloride (AMF) and bifonazole (BFZ) on actin mRNA expression determined by reverse transcription-polymerase chain reaction (RT-PCR) amplification, and the morphology of Trichophyton mentagrophytes. In AMF-treated cultures, the hyphal cells of T. mentagrophytes exhibited concentration- and/or time-dependent progressively degenerative morphological damage. Those cultures exhibiting severe and necrotic morphological changes (such as crushed, bent and flattened hyphal cells) did not express actin mRNA. In BFZ-treated cultures, similar morphological changes were seen in the hyphae of T. mentagrophytes, but these changes were milder than observed in the AMF-treated samples, and actin gene fragments were amplified in all of these samples. These results indicate that actin gene-targeted RT-PCR could be a useful tool for testing the susceptibility of dermatophytes to antifungal agents in vitro.

Reverse transcription - 3' rapid amplification of cDNA ends-nested PCR of ACT1 and SAP2 mRNA as a means of detecting viable Candida albicans in an in vitro cutaneous candidiasis model

The presence of viable cells of Candida albicans, in broth or in a reconstructed living skin equivalent, was determined by the detection of amplicons of partial mRNA sequences of the genes encoding fungal actin (ACT1) and secreted aspartyl proteinase 2 (SAP2). The mRNA of both genes were amplified by reverse transcription-3' rapid amplification of cDNA ends-nested polymerase chain reaction. Single bands of ACT1 (315 bp) and SAP2 (162 bp) mRNA were amplified from total RNA extracts of C. albicans grown in yeast carbon base-albumin broth or in living skin equivalent tissue; only the former was amplified from Sabouraud broth-grown organisms. Primer pairs targeted for ACT1 and SAP2 were Candida genus-specific and C. albicans-specific, respectively. The sensitivity limits of the assay were 100 fg of total RNA or 10 cells of C. albicans, by ethidium bromide staining. When C. albicans-infected living skin equivalent was exposed to amorolfine, amplicons of ACT1 and SAP2 mRNA were not detected in total RNA extracts. Non-amplification of the mRNA correlated with the absence of C. albicans growth in Sabouraud agar cultures of living skin equivalent samples. Reverse transcription-3' rapid amplification of cDNA ends-nested polymerase chain reaction of the mRNA encoding specific proteins of an organism has potential application in determining the viability of the organism in tissue, thus monitoring the efficacy of an antimicrobial therapy, and in detecting mRNA expressed in very little amounts in tissue.

Evaluation of antifungal effects of terbinafine and itraconazole using neutral red staining

Neutral red staining is a newly described method for evaluating the viability of fungal cells. Using this method, the antifungal effects of terbinafine and itraconazole were evaluated in vitro. When the number of neutral red-positive Trichophyton mentagrophytes conidia treated with these two oral antifungals was compared with the number of culture-proved viable T. mentagrophytes conidia, a strong positive correlation was found. This result confirms that neutral red staining is a useful method for evaluating the viability of T. mentagrophytes in vitro, and that it can be used for the evaluation of antifungal activity. We conclude that the effectiveness of an antifungal drug should not be evaluated by direct microscopic examination alone, but with the additional aid of mycological culture or neutral red staining.

Application of neutral red staining for evaluation of the viability of dermatophytes and Candida in human skin scales

The fungal elements observed by direct microscopic examination sometimes fail to grow on subsequent culture. To elucidate the cause of this discrepancy, the viability of dermatophytes and Candida in skin scales was evaluated by neutral red staining. Autoradiographic study using 3H-thymidine confirmed that grain-positive cells (viable cells) were stained with neutral red, whereas negative cells (non-viable cells) were not stained. Taking this as a baseline, the correlation between neutral red-positive fungal elements in scales taken from 211 patients with tinea and 27 patients with cutaneous candidosis and cultures on Sabouraud glucose agar was studied. Strong positive correlations were found in both mycoses. These findings suggest that neutral red staining provides a useful method for evaluating the viability of dermatophytes and Candida in human skin scales.