Lysoamidase, a drug derived from enzymes and polysaccharide of the bacterium Lysobacter sp., is used in the treatment of external bacterial infections caused by pathogenic Gram-positive microflora. The treatment of yeast cells with lysoamidase results in the lysis of young cells of all yeast species under study (Saccharomyces cerevisiae, Cryptococcus terreus, Pseudozyma fuziformiata, Torulaspora delbrueckii, Candida guilliermondii, Candida azyma, Candida catenulata, Candida boidinii, Candida lambica). The highest percentage of cell lysis by lysoamidase was observed with Candida spp., S. cerevisiae and the phytopathogen P. fuziformiata (90-95%). The action of yeast cells of S. cerevisiae with lysoamidase is accompanied by the release of intracellular enzyme alpha-glucosidase into the incubation medium. Fungal hyphae (A. heteromorphus) incubated in the presence of lysoamidase looked swollen as compared with the control; they also had lateral swellings. Treatment with lysoamidase resulted in deformation and lysis of fungal hyphae. The apical zones of hyphae were particularly sensitive to lysoamidase. In liquid medium, lysoamidase caused lysis of fungal spores. Spores of Aspergillus heteromorphus and Aspergillus japonicus were the most liable to lysoamidase action (only 24-26% germinated). Spores of Aspergillus heteromorphus did not germinate on Petri dishes (solid media) in zones treated by lysoamidase. The observed effect seems to be associated with the action of proteinase, glucanase, and chitinase constituents of lysoamidase. Lysoamidase minimizes the risk of mycosis in the treatment of bacterial infections. (C) 2003 Elsevier Ltd. All rights reserved.