The effect of cryptolepine on the morphology and survival of Escherichia coli, Candida albicans and Saccharomyces cerevisiae

The antimicrobial activity of the indoloquinoline alkaloid, cryptolepine, isolated from Cryptolepis sanguinolenta (Fam. Periplocaceae) was determined against selected micro-organisms. The minimum inhibitory concentration (MIC) ranges obtained, expressed as μg ml⁻¹, were: 5–10 for Saccharomyces cerevisiae NCPF 3139; 10–20 for S. cerevisiae NCPF 3178; 20–40 for Escherichia coli NCTC 10418; 40–80 for E. coli NCTC 11560, Candida albicans ATCC 10231 and C. tropicalis NCPF; and 80–160 for C. albicans NCPF 3242 and NCPF 3262.
Biocidal effects were noted at concentrations 2–4 times those of the MIC of the alkaloid following challenge with 10⁶ cfu ml⁻¹ of micro-organisms. Time-kill studies showed a reduction in viable count from 10⁶ to < 10 cfu ml⁻¹ in 4 h in C. albicans ATCC 10231 exposed to 320 μg ml⁻¹ of the agent; 3 log cycle reductions were recorded for the 6 h counts of E. coli NCTC 10418 and S. cerevisiae NCPF 3139 exposed to 40μg ml⁻¹ and 160 μg ml⁻¹ of the alkaloid respectively.
These results were consistent with findings using scanning electron microscopy. Exposure of cells to biocidal concentrations of cryptolepine produced filamentation prior to lysis in E. coli NCTC 10418 and extreme disturbance of surface structure, including partial and total collapse, followed by lysis in C. albicans ATCC 10231 and S. cerevisiae NCPF 3139.