Comparison of Toxicity of Different Mycotoxins to Several Species of Bacteria and Yeasts: Use of Bacillus brevis in a Disc Diffusion Assay

Abstract

Twelve species of bacteria and two species of yeast were tested for sensitivity against 11 different mycotoxins using a disc diffusion assay. Among the bacterial species, Bacillus brevis appeared to be the most sensitive microorganism, being sensitive to eight mycotoxins (AFB1, ochratoxin A [OA], citrinin [CT], patulin [PAT], penicillic acid [PA], cyclopiazonic acid [CPA], penitrem A [PT-A], and zearalenone [ZEE]). This microorganism was not affected by a high concentration (500 μg per disc) of any of the trichothecenes (T-2 toxin, HT-2 toxin, diacetoxyscirpenol, and deoxynivalenol). Kluyveromyces marxianus, a species of yeast, was the only microorganism that was inhibited by all four of the trichothecenes but was not inhibited by the other mycotoxins. The area of the inhibition zone produced by some of the mycotoxins such as OA with the B. brevis assay was dramatically influenced by the pH of the medium, while the toxicity of other mycotoxins such as AFB1 was relatively pH independent. The sensitivity of the B. brevis assay also tended to decrease at agar volumes above 6 ml and as the number of microbes per plate increased. The lowest amounts of the different ochratoxins; OA, OB and OC (OA ethyl ester) that could be detected under optimal conditions were 0.5, 20, and 2 μg per disc, respectively. The lowest amounts of CPA, AFB1 CT, PAT, PA, PT-A, and ZEE that were detectable were 0.5, 1, 1, 1, 1, 1, and 10 μg per disc, respectively. These results demonstrate that B. brevis can be used as a positive indicator organism to detect the presence of several common non-trichothecene mycotoxins. The results demonstrate that, used together, B. brevis and K. marxianus can be used as indicator organisms in a bioassay approach to the detection of several of the most common mycotoxins.