Suspected mode of antimycotic action of brevicin SG1 against Candida albicans and Penicillium citrinum

Brevicin SG1, a novel, broad spectrum bacteriocin produced by Lactobacillus brevis SG1 isolated from ‘ogi’, a traditional Nigerian fermented cereal, was studied for its effects on fungal hyphal growth and morphology. The bacteriocin caused some morphological changes and a decrease in the total mass of Candida albicans and, cellular damage and an inhibition of pre-formed germ tubes in Penicillium citrinum. The inhibitory action was concentration- dependent, confirming that antibiosis was the mode of antagonism. Transmission scanning electron microscopy (TSEM) study revealed that the bacteriocin caused hyphal destruction and lysing of the cell wall in P. citrinum and distortion of shape in C. albicans. TSEM result suggested that the fungal cell wall and the cell membrane were the main target of this antifungal compound and the suspected mode of action was fungiolytic. Disintegration of fungal hyphae was probably due to a membrane disorder causing increased membrane permeability and the consequent osmotic effect. The bacteriocin was stable over a wide range of pH (1–10) especially between pH 5–7 while its production was maximal at pH 6.5. The production and stability of the bacteriocin at a broad pH makes it a suitable agent for controlling spoilage organisms of most foods and for using it as starter cultures of fermented foods. It also has the potential for probiotic usage.