Production of ochratoxin A by Aspergillus ochraceus NRRL-3174 before and after exposures to 60Co irradiation

Ochratoxin production and taxonomy of the yellow aspergilli (Aspergillus section Circumdati)

Aspergillus section Circumdati or the Aspergillus ochraceus group, includes species with rough walled stipes, biseriate conidial heads, yellow to ochre conidia and sclerotia that do not turn black. Several species are able to produce mycotoxins including ochratoxins, penicillic acids, and xanthomegnins. Some species also produce drug lead candidates such as the notoamides. A polyphasic approach was applied using morphological characters, extrolite data and partial calmodulin, β-tubulin and ITS sequences to examine the evolutionary relationships within this section. Based on this approach the section Circumdati is revised and 27 species are accepted, introducing seven new species: A. occultus, A. pallidofulvus, A. pulvericola, A. salwaensis, A. sesamicola, A. subramanianii and A. westlandensis. In addition we correctly apply the name A. fresenii (≡ A. sulphureus (nom. illeg.)). A guide for the identification of these 27 species is provided. These new species can be distinguished from others based on morphological characters, sequence data and extrolite profiles. The previously described A. onikii and A. petrakii were found to be conspecific with A. ochraceus, whilst A. flocculosus is tentatively synonymised with A. ochraceopetaliformis, despite extrolite differences between the two species. Based on the extrolite data, 13 species of section Circumdati produce large amounts of ochratoxin A: A. affinis, A. cretensis, A. fresenii, A. muricatus, A. occultus, A. ochraceopetaliformis (A. flocculosus), A. ochraceus, A. pseudoelegans, A. pulvericola, A. roseoglobulosus, A. sclerotiorum, A. steynii and A. westerdijkiae. Seven additional species produce ochratoxin A inconsistently and/or in trace amounts: A. melleus, A. ostianus, A. persii, A. salwaensis, A. sesamicola, A. subramanianii and A. westlandensis. The most important species regarding potential ochratoxin A contamination in agricultural products are A. ochraceus, A. steynii and A. westerdijkiae.

Relationship of mould count, ergosterol and ochratoxin A production

The relationship between viable mould count, ergosterol content and ochratoxin A (OA) formation was studied at different inoculum concentrations of Aspergillus ochraceus NRRL 3174 and Penicillium verrucosum NRRL 3260 grown on sterile long-grain enriched white rice as the substrate. Ergosterol was determined by extraction, saponification and quantification using high performance thin layer chromatography (HPTLC) with UV detection. Ergosterol and ochratoxin A were detected after 3 days of incubation and reached their maximum at 7-10 days of incubation. After that, a decline in the concentrations in both ergosterol and ochratoxin was observed. Ergosterol measurement by HPTLC appeared to be a useful method to detect fungal activity, which corresponded to ochratoxin production. Thus, the ergosterol assay may have a use as an early indicator of potential mycotoxin production.

Molecular analysis of variability within the toxigenic Aspergillus ochraceus species

Genetic variability of Aspergillus ochraceus was examined at the DNA level. Based on the HaeIII-Bg/II generated mitochondrial DNA restriction profiles, most isolates could be classified into two distinct groups. These two groups could also be distinguished by the random amplified polymorphic DNA technique, and with telomeric PCR amplifications. Phylogenetic analysis of sequences of the intergenic transcribed spacer region of some of the strains resulted in a dendrogram with the same topology as that based on mitochondrial DNA and amplified DNA data. None of the isolates with type 2 mtDNA profiles produce ochratoxins. Some strains (e.g., A. ochraceus ICMP 939) displayed strain-specific mitochondrial DNA patterns, and their amplified DNA profiles were also different from all other A. ochraceus strains examined.

Role of the competitive microbial flora in the radiation-induced enhancement of ochratoxin production by Aspergillus alutaceus var. alutaceus NRRL 3174

The radiation sensitivity and the toxigenic potential of conidiospores of the fungus Aspergillus alutaceus var. alutaceus were determined after irradiation with 60Co gamma rays and high-energy electrons. Over the pH range of 3.6 to 8.8, the doses required for a 1 log10 reduction in viability based on the exponential portion of the survival curve ranged from 0.21 to 0.22 kGy, with extrapolation numbers (extrapolation of the exponential portion of the survival curve to zero dose) of 1.01 to 1.33, for electron irradiation, and from 0.24 to 0.27 kGy, with extrapolation numbers of 2.26 to 5.13, for gamma irradiation. Nonsterile barley that was inoculated with conidia of the fungus and then irradiated with either electrons or gamma rays and incubated for prolonged periods at 28 degrees C and at a moisture content of 25% produced less ochratoxin A with increasing doses of radiation. Inoculation of barley following irradiation resulted in enhanced ochratoxin levels compared with unirradiated controls. In these experiments, inoculation with 10(2) spores per g produced greater radiation-induced enhancement than inoculation with 10(5) spores per g. There was no radiation-induced enhancement when the barley was surface sterilized by chemical means prior to irradiation. These results are consistent with the hypothesis that a reduction in the competing microbial flora by irradiation is responsible for the enhanced mycotoxin production observed when nonsterile barley is inoculated with the toxigenic fungus A. alutaceus var. alutaceus after irradiation.

Occurrence of some mycotoxins (aflatoxin, ochratoxin A, citrinin, zearalenone and vomitoxin) in various Egyptian feeds

Ninety five samples of various Egyptian feedstuffs were investigated for the aflatoxin B1, B2, G1, and G2 means thin layer chromatography (TLC). Out of these samples 44.2% were positive (maize, rice crack, rice germ, rice germ cake, rice bran, wheat bran, cotton seed, cotton seed cake, peanut, and mixed feed for broilers, egg production, calf fattening and milk production). High percentage (90.5%) of the positive samples were contaminated with less than 100 ppb total aflatoxins. Peanut from "Ismailia" showed the highest contamination-mean of 400 ppb aflatoxin B1. The contamination relationship between kernels and shell of the same pods of the peanut was 1:7. The lowest contamination-mean was 5 ppb B1 in soya bean samples. All samples of horse bean and fish meal were negative. Aflatoxin B1 was present alone so frequently (in 76.2% of the positive samples). The relationship between the concentrations of aflatoxins B2:G1:B1 was 1:2.3:22.4. 51 different samples of foods and feeds from various Egyptian regions were collected and investigated for the nephrotoxic mycotoxin ochratoxin A means TLC. Twelve samples (23.5%) from them were designated as positive samples. The positive samples belonged to white maize, wheat, wheat bran, beans, rice germ, rice germ cake, broilers feed, egg production feed, and milk production feed; whereas the yellow maize (hybrid), soya beans, wheat soya meal, rice crack, cotton seed, cotton seed cake, and fish meal samples were negative. The contamination range was from 4 ppb to 577 ppb with an average of 58.2 +/- 22.9 ppb. Half of the positive samples was contaminated with 10-100 ppb whereas 41.7% from the positive samples had less than 10 ppb and 8.3% only had more than 100 ppb. Citrinin is existing in Egyptian food and feedstuffs. Out of 52 different samples--from various Egyptian regions-15.4% were positive. These were rice bran, rice germ, maize (white), wheat bran, cotton seed cake and fish meal. The highest contamination was in fish meal (40-70 ppb) whereas the lowest was in wheat bran (3 ppb). Mean of the contamination level was 25.9 +/- 3.4 ppb with a range of 3-70 ppb. For the first time in the Egyptian foods and feeds will be informed about the presence of the mycotoxin zearalenone with a high concentration. From several Egyptian places, 64 samples were collected (4 samples for each food or feed stuff).(ABSTRACT TRUNCATED AT 400 WORDS)

Microbiological safety of irradiated foods

This paper attempts to summarize relevant information on microbiological safety of irradiated foods in the light of previous reports of expert committees and current literature references. After a brief survey of the relative radiation resistance of food-borne microorganisms, the importance of microbial load for dose requirement, and the role of post-irradiation conditions, it addresses the following questions: Could selective changes in the microflora, caused by non-sterilizing radiation doses, make known pathogens more likely to occur, or bring into prominence unfamiliar pathogens? Is it probable that 'mutational' (including adaptive) changes might make pathogens more virulent, more harmful, or more difficult to recognize, and could new pathogens arise in this way? Is it possible that development of radiation-resistant strains might render the antimicrobial irradiation processes ineffective? The present survey of relevant scientific evidence related to these questions reaffirms the basic conclusion of earlier reviews, that microbiological safety of irradiated food is fully comparable with that of foods preserved by other acceptable preservation methods. Similar to other preservation processes, gains in microbiological or keeping quality attained by food irradiation can be and must be safeguarded by proper control in the food irradiation facilities and by proper care of the product before and after processing.

Effect of gamma-irradiation on F-2 and T-2 toxin production in corn and rice

Fusarium graminearum and F. tricinctum were grown on moistened corn and rice. After inoculation the substrates were exposed to gamma-irradiation and growth rate together with mycotoxin production were measured. A delay in mycelium growth and an increase in F-2 and T-2 toxin production occurred after irradiation with 1 and 3 kGy. The maximum F-2 production was 10.7 mg/kg on rice at 3 kGy, whereas T-2 was 735 micrograms/kg on rice at 3 kGy. At 9 kGy neither growth nor toxin production could be detected in any inoculated corn and rice substrate.

Mould spoilage and mycotoxin formation in grains as controlled by physical means

Low oxygen concentrations (less than 1%) and/or increased concentrations of CO2 or N2 have been found to be highly effective in preventing the development of mould on grain and in inhibiting selected mycotoxins, e.g. aflatoxins, ochratoxin, patulin, penicillic acid and T-2. However, the levels of CO2 needed to inhibit mould growth are much higher than those required for the inhibition of mycotoxin production. The degree of inhibition achieved by elevated CO2 concentrations is dependent on other environmental factors, such as relative humidity (RH) and temperature. Nevertheless, the biosynthetic pathways for mycotoxin production are merely blocked, but not damaged by high CO2 levels. Irradiation has been shown to destroy the conidia of moulds but the information concerning the effect of irradiation on mycotoxin formation seems to be contradictory. Aflatoxin production was increased in irradiated wheat grain, but decreased in barley and maize when the grain was irradiated prior to inoculation. The number of spores in the inoculum, grain condition, relative humidity and other environmental factors could all affect the results obtained. However, ochratoxin formation by Aspergillus ochraceus was consistently enhanced by irradiation of spores or mycelium.