A method was developed for monitoring the growth of a range of bacteria and fungi in the Bactometer 32 impedimeter. 195 yeast strains, 74 strains of mould and 20 strains of bacteria were screened for sensitivity to 1 mug ml[-1] of T-2 toxin. Growth inhibition was assessed impedimetrically. Twelve bacteria, 20 moulds and 38 yeast strains were tested against roridin A, verrucarin A, deoxynivalenol, and diacetoxyscirpenol each at 1 mum ml[-1] . Deoxynivalenol was found to be only slightly toxic. Roridin A and verrucarin A were markedly more toxic than the others to the fungi, but not to the bacteria. Four microorganisms (Bacillus subtilis, Candida albicans. Hansenula fabianii and Pichia burtonii)were selected for further study. No obvious pattern of response could be discerned for the effects of different carbohydrates on microbial sensitivity to T-2 toxin. The effects of T-2 toxin on B. subtilis and C. albicans were greater if chloroform rather than dichloromethane and methanol (95:5, v/v) was used as the toxin carrying solvent, the reverse was true for H. fabianii and P. burtonii. Dose-response curves were constructed, based on impedimetric responses, and no-effect levels were determined for each species. For B. subtilis the no-effect level was 0.35 mum ml[-1], for C. albicans it was 0.40 mum ml[-1], for H. fabianii it was 0.012 mum ml[-1] and for P. burtonii it was 0.018 mum ml[-1]. H. fabianii was selected for further studies. This strain was found to be auxotrophic for proline. The effect of T-2 toxin and verrucarin A on the uptake of radiolabelled proline in H. fabianii cultures was studied. Dose-response curves were constructed for each toxin. It was found that both toxins reduced proline uptake in a dose dependent manner, the no-effect levels were 0.025 mum ml[-1] for T-2 toxin and 0.0125 mum ml[-1] for verrucarin A.

<div>Ochratoxin A (OTA) is a ubiquitous mycotoxin produced by some species of <i>Aspergillus</i> and <i>Penicillium</i>. It has been detected in a variety of foods such as cereals, coffee, grapes, cocoa, wine, and spices. Consumption of OTA has been linked to kidney and liver diseases. The aims of this study were to determine the effects of (1) water activity and temperature (2) oil content and grinding and (3) probiotic bacteria on fungal growth and OTA production by <i>Aspergillus</i> <i>fresenii</i> and <i>A. sulphureus</i>. In the first study, the two fungi were grown on ground Niger seeds with 0.82, 0.86, 0.90, 0.94 or 0.98 a_w and incubated at 20, 30 or 37°C individually. The two species showed similar growth patterns on Niger seeds under all of the testing conditions. There was no fungal growth on ground Niger seeds with 0.82 a_w and the optimal growth condition for the two species on ground Niger seeds was 0.94 a_w at 30°C. However, the optimal conditions for OTA production by <i>A. fresenii</i> and <i>A. sulphureus</i> were different. The optimal conditions for <i>A. fresenii</i> to produce OTA on ground Niger seeds was 0.90-0.94 a_wat 37°C; whereas, <i>A. sulphureus</i> produced OTA optimally with 0.90-0.94 a_w at 30°C as well as 0.94-0.98 a_w at 20°C. Overall, <i>A. sulphureus</i> produced higher levels of OTA than did <i>A. fresenii</i>. The highest concentration of OTA (643 μg/kg) produced by <i>A. fresenii</i> was detected on seed samples with 0.90 a_w incubated at 37°C for 15 days, while the highest concentration of OTA (724 μg/kg) produced by <i>A. sulphureus</i> was detected on samples with 0.98 a_w incubated at 20°C for 10 days.</div><div>In the second study, growth and OTA production by the two fungi on ground Niger seeds with different oil content (10, 25 and 35%) and on whole Niger seeds at 30°C were compared. All seed samples were adjusted to 0.94 a_w in this study. The two fungi grew most rapidly on ground seeds with 35% oil content, producing high concentrations of OTA (229-453 μg/kg). On whole seeds, <i>A. sulphureus</i> and <i>A. fresenii </i>displayed slow growth until day 5 or 10, respectively, growing rapidly after that. The two species produced either non-detectable or below the limit of quantitation (<4 μg/kg) of OTA in ground seeds with 10 or 25% oil or in whole seeds during the 30-day incubation at 30°C.</div><div>In the third study, growth inhibition of <i>A. fresenii</i> and <i>A. sulphureus</i> by probiotic bacteria <i>Bacillus coagulans</i>, <i>B. coagulans</i> (strains unique IS2TM and GBI-306086), <i>Lactobacillus acidophilus</i> (strains LA-5 and LA-14), <i>L. plantarum</i> (strains 299V and LP115), and <i>L. rhamnosus </i></div><div>was evaluated. Results of co-cultured method revealed that <i>L. plantarum</i> 299V had the highest levels of inhibition against the two fungal species; whereas, <i>L. plantarum</i> LP115, and <i>L. rhamnosus</i> showed only some inhibition effect against <i>A. sulphureus</i> and very little inhibition against <i>A. fresenii</i>. The two fungal species were not inhibited by <i>L. acidophilus</i> or <i>B. coagulans</i>.</div><div>Results from double-layer testing showed that the two <i>L. plantarum</i> strains and<i> L. rhamnosus</i> inhibited fungal growth completely when there were as few as 40-70 CFU probiotic bacterial colonies in the bottom layer of MRS agar; whereas, <i>L. acidophilus</i> inhibited fungal growth completely when the probiotic colonies were >125 CFU/plate. The three <i>B. coagulans</i> strains showed only partial growth inhibition against<i> A. fresenii</i> with 103 CFU/plate. <i>Bacillus coagulans</i> (unique IS2TM and GBI-306086) completely inhibited growth of <i>A. sulphureus</i> when there were as few as 40-70 CFU/plate; while <i>B. coagulans</i> completely inhibited the growth of <i>A. sulphureus</i> but only when there were >103 CFU plate. Even though the two fungal species were inhibited by some probiotic bacteria on MRS plates, the OTA production was not influenced.</div>