Effect of medium composition, agitation and the presence of EDTA on the antimicrobial activity of cryptolepine.

The antimicrobial activity of cryptolepine is influenced by the type of medium employed, agitation and the presence of non-inhibitory concentrations of EDTA. The use of Mueller-Hinton broth (MHB), iso-sensitest broth and tryptone soya broth (TSB) produced lower minimum inhibitory concentrations (MICs) for some of the test organisms compared with nutrient broth or yeast dextrose broth (YDB). For example, a fourfold drop in MIC was recorded for Saccharomyces cerevisiae in MHB compared with the same organism tested in YDB. Agitation of the broths during incubation nearly always produced lower MICs for the bacteria, an eightfold decrease in MIC being recorded for Escherichia coli cultured in nutrient broth with agitation compared with a statically maintained culture. A non-inhibitory concentration (10(-3) mol l-1) of disodium EDTA enhanced the antimicrobial activity of cryptolepine. Against E. coli NCTC 11,560, an eightfold decrease in MIC and minimum bactericidal concentration (MBC) was recorded when tested in the presence of EDTA.