Estimation of fungi in the presence of bacteria

A quantitative assay of mixed cultures of bacteria and the fungus Aspergillus flavus was carried out. The assay was based on the estimation of glucosamine formed by the hydrolysis of chitin. The bacteria used were typical Gram-positive and Gram-negative bacteria commonly found in spoiled food. They included, Escherichia coli, Bacillus cereus, Staphylo coccus aureus and Pseudomonas aeruginosa. The experiments carried out involved mixing cultures of bacteria and fungi immediately prior to estimation or alternatively fungal and bacterial cultures were mixed, grown for 40 hours and then estimated for glucosamine. Results obtained show, that when cultures are mixed immediately prior to estimation, there is no significant effect on glucosamine levels. When Gram-negative bacteria are grown with A.flavus prior to estimation there is no significant effect on glucosamine levels compared with pure cultures of A.flavus. However, when Gram-positive bacteria are mixed with fungi grown for 40 hours and glucosamine is estimated, there is a significant reduction in the level of glucosamine formed. It was shown that this is due to bacterial growth competing with the fungi and causing a considerable reduction in the amount of fungal mycelium formed.