A fraction from Escherichia coli with anti-Aspergillus properties.

The products of various strains of Escherichia coli (BL21, DH5alpha, HB101 and XL Blue) were investigated for antimycotic properties using pathogenic isolates of Aspergillus. Co-culture experiments revealed that E. coli strains exhibited variable activity against Aspergillus fumigatus. The lysates prepared from DH5alpha, HB101 and XL Blue strains of E. coli showed inhibitory activity against A. fumigatus in the protein concentration range of 62.50 to 250.00 microg ml(-1). The highest activity was seen in the lysate of BL21, which inhibited the growth of A. fumigatus and Aspergillus flavus completely at a concentration of 31.25 microg protein ml(-1). The MIC of BL21 lysate against Aspergillus niger was found to be 62.50 microg ml(-1). The in vitro toxicity of BL21 lysate was evaluated using a haemolytic assay. A BL21 lysate protein concentration of 1250.00 microg ml(-1) was found to be nontoxic to human erythrocytes. The standard drug amphotericin B lysed 100 % of erythrocytes at a concentration of 37.50 microg ml(-1). SDS-PAGE showed the presence of at least 15 major proteins in the lysate of BL21. Ion-exchange chromatography resolved the BL21 lysate into five fractions and fraction III was found to be endowed with anti-Aspergillus properties. The MIC of this fraction was found to be 3.90 microg ml(-1). Further work on the purification of the active molecule and its characterization is in progress.