Antifungal activity of some Sternbergia taxa: effects on germ tube and biofilm formation

Natural products are rapidly becoming the primary sources of novel antimicrobial agents, as resistance to existing antimicrobial agents is increasing. Apart from determining the antimicrobial activity of natural products, it is also important to understand their effects on the virulence factors of microorganisms. This study aimed to determine the antimicrobial activity of Sternbergia species prevalent in Turkey and investigate their role in the inhibition of germination tube and biofilm formation, both of which are known to be important virulence factors of Candida albicans. The antimicrobial activities of the plant extracts were evaluated using bore-plate and broth microdilution method. The extracts' capacity to inhibit the formation of the germ-tube was also evaluated. The findings of our study revealed that Sternbergia lutea, Sternbergia vernalis possessed antimicrobial activities, with MIC values ranging between 0.048 mg/mL and 0.39 mg/mL. The highest antimicrobial activity was observed against Candida dubliniensis (0.048 mg/mL). While evaluating the inhibition of fungal germination activities, S. vernalis extract (at a concentration of 0.09 mg/mL) was found to be the most effective against C. albicans ATCC 90028 strain. The results also indicated that S. vernalis extracts at sub-MIC levels inhibited germ tube formation and modulated the tail-length of germinated cells, both of which are important virulence factors of C. albicans. Furthermore, the inhibition of biofilm-formation was also investigated, and it was found that two Sternbergia spp. extracts at or below MIC levels inhibited biofilm formation.

Search for Genes Potentially Related to Germ Tube Formation in Candida albicans by Differential-Display Reverse Transcription Polymerase Chain Reaction

Candida albicans exhibits the ability to grow in either a yeast or a mycelia form in response to different environmental factors. The mycelia form, found in infected tissues, is important as a virulence factor in the adherence of the organism to the host epithelium. In vitro, the morphological transition can be induced by environmental shifts in the growing conditions, or by a variety of exogenous factors, including ambient pH, nutritional status and temperature. The differential-display reverse transcription polymerase chain reaction (DDRT-PCR) is a powerful technique for comparing gene expression between cell types, stages of development or differentiation. Hyphae related genes were identified and characterized using a PCR-based differential display. Candida albicans formed a germ tube when cultured in rabbit serum, RPMI 1640 medium or 39degrees C-YPD medium. We gained 21 cDNA bands showing a different expression pattern from that of the uninduced culture. DNA was extracted from the same location of the isolated bands, and PCR was performed under the same conditions, which reamplified the PCR product, showing the specific expression patterns according to the culture conditions. We cloned 18 germ tube-related cDNA clones (inserts average size is 80 - 700 bp) and sequenced them. The nucleotide sequences of the 18 clones were identified through in the present study from GenBank, and were found to have the accession number (AF405213-AF405230). We could not find any nucleotide sequence having a high homology with these clones. This study could form a part of the projects in the search for genes related to the germ tube formation of C. albicans.