Use of impedimetry to detect trichothecene mycotoxins. 1. Screen for susceptible microorganisms

Effect of polymyxin B nonapeptide and polymyxin B sulphate on trichothecene mycotoxin sensitivity of yeasts using a conductimetric instrument

The addition of polymyxin B sulphate (PBS), or an inactive by-product, polymyxin B nonapeptide (PBN) to a yeast bioassay system, increased its sensitivity to various toxic agents. The nil effect level (NEL) of T-2 toxin was reduced from 0.1 to 0.01 microgram/ml for Kluyveromyces fragilis GK 1005 in the presence of these agents when using a Malthus AT 192 conductimetric instrument. Other synergistic agents (DMSO, ethanol, cetyl trimethyl ammonium bromide and Triton X-100) gave poor results in the conductimetric system. PBN also increased sensitivity of K. fragilis GK 1005 towards cycloheximide in the Malthus system, and PBS reduced the NEL of T-2 toxin for K. fragilis GK 1005 in a disc diffusion assay from 0.2 to 0.04 microgram per disc. No yeasts were found sensitive to the trichothecene deoxynivalenol (DON) even at a DON concentration of 10 micrograms/ml, except in the presence of PBN and PBS. The minimal inhibitory concentration (mic) of DON in the presence of PBS was 2 micrograms/ml for K. fragilis GK 1005.

A medium for the detection of yeasts using a conductimetric method

A new medium is described for the detection of yeasts using a Malthus microbial growth analyser which measures conductivity. This medium is superior to previous media devised for use in the Malthus, and allows the detection of a wide range of yeasts including those important in food spoilage. The new medium was inferior to existing media used to detect yeasts in the Bactometer 32 instrument which measures impedance.