Proceedings to avoid contaminants during isolation and storage of standard fungal strains

Abstract

The fungal strains for scientific purposes are isolated from environments, where interaction of extensive taxonomical groups is a common phenomenon, requiring development of a method that assures elimination of microbial interference and preserves original characteristic of strains. In this study, using Fusarium strains isolated from corn and animal food, the interference of antibiotic resistant bacteria and yeast contamination in the fungal strains storage was evaluated. Although frequent contamination by tetracycline, streptomycine and chloramphenicol resistant microorganisms was detected in both corn and animal food, tetracycline showed the best antibacterial effect. Following 6 months storage at 4ºC, 36 cultures of 168 single spored Fusarium strains developed atypical colonies, indicating some contamination. By plating these cultures in BDA medium added with antibiotic, 21 strains were purified, but the technique was unable to reisolate the remaining ones. The purity of these 15 strains was recuperated using dilution/plate technique proposed here, which used combination of dilution process followed by plating in BDA medium surface. The procedure is recommended as the final step for fungal strains recuperation, which allows elimination of fast growing undesirable organisms