W. F. O. Marasas

Fumonisins: History, World-Wide Occurrence and Impact

The history, toxicological effects, world-wide natural occurrence and impact of the fumonisins, food-borne carcinogenic mycotoxins produced by Fusarium moniliforme, are reviewed from the original description of the fungus in 1881 to the present. Following the isolation and characterization of fumonisin B1 and B2 and the publication of the first 3 papers on fumonisins by South African researchers in 1988, the interest in these compounds increased dramatically during 1989 and 1990 because of numerous outbreaks of mycotoxicoses in animals associated with the 1989 corn crop in the USA. Major advances made during this period were published in approximately 49 papers from 1988 to 1991. During the period 1992 to 1994, there was an explosion in the literature on fumonisins and at least 212 papers were published. The information contained in the more than 260 papers on fumonisins published to date is reviewed with respect to toxicological effects, association with animal and human diseases, and world-wide natural occurrence in corn and corn-based feeds and foods. Impact of the fumonisins is addressed with respect to their implications for human and animal health, risk assessment and establishment of tolerance levels.

Fumonisins: Isolation, chemical characterization and biological effects

The fumonisin B mycotoxins (FB1 and FB2) have been purified and characterized from corn cultures of Fusarium moniliforme strain MRC 826. Fumonisin B1 (FB1, the major fumonisin produced in culture, has been shown to be responsible for the major toxicological effects of the fungus in rats, horses and pigs. Recent investigations on the purification of compounds with chromatographic characteristics similar to FB1 have led to the identification of two new fumonisins, FB3 and FB4. Fumonisins A1 and A2, the N-acetyl derivatives of FB1 and FB2 respectively, were also purified and shown to be secondary metabolites of the fungus. Short-term carcinogenesis studies in a rat liver bioassay indicated that over a period of 15 to 20 days, at dietary levels of 0.05–0.1%, FB2 and FB3 closely mimic the toxicological and cancer initiating activity of FB1 and thus could contribute to the toxicological effects of the fungus in animals. In contrast, no biological activity could be detected for FA1 under identical experimental conditions. These studies and others have indicated that the fumonisin B mycotoxins, although lacking mutagenicity in the Salmonella test or genotoxicity in the DNA repair assays in primary hepatocytes, appear to induce resistant hepatocytes similar to many known hepatocarcinogens.

Infection of maize by Fusarium species and contamination with fumonisin in africa

Fusarium is one of the major fungal genera associated with maize in Africa. This genus comprises several toxigenic species including F. verticillioides and F. proliferatum, which are the most prolific producers of fumonisins. The fumonisins are a group of economically important mycotoxins and very common contaminants of maize-based foods and feeds throughout the world. They have been found to be associated with several animal diseases such as leukoencephalomalacia in horses and pulmonary oedema in pigs. Effects of fumonisins on humans are not yet well understood. However, their occurrence in maize has been associated with high incidences of oesophageal and liver cancer. Infection of maize by Fusarium species and contamination with fumonisins are generally influenced by many factors including environmental conditions (climate, temperature, humidity), insect infestation and pre- and postharvest handling. Attempts to control F. verticillioides and to detoxify or reduce fumonisin levels in maize have been undertaken. However, more research studies are urgently needed in order to understand more about this toxin. Fumonisins are less documented because they are recently discovered mycotoxins compared to aflatoxins. To date in Africa, apart from South Africa, very little information is available on Fusarium infection and fumonisin contamination in maize. It is a matter of great concern that on this continent, millions of people are consuming contaminated maize and maize-based foods daily without being aware of the danger. Key words : Fusarium, fumonisins, maize, Africa. nAfrican Journal of Biotechnology Vol. 2 (12), pp. 570-579, December 2003

Toxicity of a moniliformin-producing strain of fusarium moniliforme var. subglutinans isolated from maize

Pure cultures of a very toxic strain of Fusarium moniliforme Sheldon var. subglutinans Wr. & Reink., isolated from maize (Zea mays L.) and cultured on autoclaved maize, were fed to ducklings and rats. Ducklings consuming 0·5–2·0 g of mouldy meal died within 2 hr and those given doses of material derived from a methanol extraction of chloroform-extracted meal died in less than 60 min. The culture material was also acutely toxic to rats, males being more sensitive than females to the toxic effects of low dietary levels of mouldy meal. Semi-quantitative analysis based on UV spectrophotometry of methanol extracts of this mouldy meal revealed very high levels of moniliformin (up to 11·3 g/kg) in the toxic mouldy meal, and bioassay in ducklings demonstrated a dose-effect relationship for batches of culture material containing different levels of the toxin. The oral LD50 of chemically pure moniliformin was 3·68 mg/kg in 7-day-old ducklings and 50·0 and 41·57 mg/kg, respectively, in male and female inbred BD IX black rats (c.100 g), with both species showing progressive muscular weakness, respiratory distress, cyanosis, coma and death. Autopsy of the rats showed acute congestive heart failure and the histological lesions, although non-specific, were characterized particularly by acute focal myocardial degeneration and necrosis, while severe cloudy swelling and scattered single-cell necrosis occurred in the liver, kidney, pancreas, adrenal glands, gastric mucosal glands and crypts of the small intestine. The myocardium was also the site of the major lesions in rats fed. F. moniliforme var. subglutinans culture material. Acute hydropic degeneration, focal Zenkers necrosis, myolysis and fibrosis occurred in all the experimental groups to an extent varying with the duration of intake and the dietary level of the mouldy feed. Rats on a diet containing 8% culture material showed the most extensive lesions. Less severe myocardial lesions occurred in rats fed a diet containing 2% culture material.

Mycoflora of Argentinian corn harvested in the main production area in 1990

Corn (Zea mays) is the main cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the corn kernels. This paper reports on the identification of internal and external mycoflora of corn kernels harvested in the main production area in Argentina in 1990. A mycological survey was carried out on 178 corn samples, from five locations in that area and the isolation frequency and relative density of the prevalent fungal genera compared. GenusFusarium was the most prevalent component of the internal seedborne mycoflora in the five locations.Penicillium was prevalent in all locations, taking into account the frequency. However, this genus was predominant only in two locations, when the relative density was considered. The predominantFusarium wasF. moniliforme and the most frequently isolated species ofAlternaria, Aspergillus andPenicillium wereA. alternata, A. flavus andP. decumbens, respectively.Diplodia species were not isolated from any of the samples.

FUSARIUM THAPSINUM (GIBBERELLA THAPSINA) : A NEW SPECIES IN SECTION LISEOLA FROM SORGHUM

A group of Fusarium strains first distin- guished by the production of a diffusing yellow pig- ment is now described as a separate species, Fusarium thapsinum. The teleomorph, Gibberella thapsina, can be formed under laboratory conditions by crossing strains of opposite mating type on carrot agar. Fusar- ium thapsinum was recovered from banana, maize, peanut and sorghum in Egypt, South Africa, the Phil- ippines, Thailand, and nine states in the United States. Members of this species are morphologically similar to Fusarium moniliforme (Gibberella fujikuroi mating population A), but the two groups are repro- ductively isolated and can be distinguished by other characters such as mycotoxins produced, isozyme polymorphism, electrophoretic karyotype, benomyl sensitivity, and differences in the sequence of the in- ternally transcribed spacer (ITS) region of the ribo-

Exposure assessment for fumonisins in the former Transkei region of South Africa

The fumonisins are mycotoxins produced mainly by Fusarium verticillioides and F. proliferatum in maize, the predominant cereal staple for subsistence farming communities in southern Africa. In order to assess exposure to these mycotoxins in the Bizana (now known as Mbizana) and Centane magisterial areas of the former Transkei region of the Eastern Cape Province of South Africa, the actual maize consumption by different age groups in these communities was measured. In the groups 1–9 years (nu2009=u2009215) and 10–17 (nu2009=u2009240) years, mean consumption (±standard error) was 246u2009±u200910.8 and 368u2009±u200910.3u2009gu2009peru2009personu2009day−1, respectively, with no significant difference (pu2009>u20090.05) between the magisterial areas. For adults (18–65 years) mean maize consumption in Bizana (nu2009=u2009229) and Centane (nu2009=u2009178) were significantly different (pu2009<u20090.05) at 379u2009±u200910.5 and 456u2009±u200911.9u2009g per personu2009day−1, respectively. An exposure assessment was performed by combining the maize consumption distribution with previously determined levels of total fumonisin (fumonisins B1 and B2 combined) contamination in home-grown maize in these two areas. Assuming an individual adult body weight of 60u2009kg, fumonisin exposure in Bizana, an area of relatively low oesophageal cancer incidence, was 3.43u2009±u20090.15u2009µgu2009kg−1 bodyu2009weightu2009day−1, which was significantly lower (pu2009<u20090.05) than that in Centane (8.67u2009±u20090.18u2009µgu2009kg−1u2009bodyu2009weightu2009day−1), an area of high oesophageal cancer incidence. Mean fumonisin exposures in all age groups in both Bizana and Centane were above the provisional maximum tolerable daily intake (PMTDI) of 2u2009µgu2009kg−1 bodyu2009weightu2009day−1 set by the Joint FAO/WHO Expert Committee on Food Additives.

Hepato- and cardiotoxicity of Fusarium verticillioides (F. moniliforme) isolates from Southern African maize

Abstract From crops of South African and Transkeian maize were isolated 21 Fusarium verticillioides ( F. moniliforme ) strains that do not produce moniliformin, and their toxicity to ducklings and rats was determined. The pathological effects of one strain (MRC 602) were fully characterized and used as a basis for comparison with the other isolates. Acute mortality was common in ducklings fed the isolates, while in rats the mean time to death was at least 24 days even with the most toxic isolate. All the rats fed the MRC 602 isolate died, the mean times to death being 49 and 78 days, respectively, for continual intake of 32 and 16% levels of the fungal-culture material in the diet. Cirrhosis and nodular hyperplasia of the liver, and the occurrence of acute and proliferative endocardial lesions and concurrent intraventricular thrombosis were frequently encountered and were considered to be the most important lesions. Toxic nephrosis, endothelial proliferation in the pulmonary vessels, and thrombosis of the larger vessels in the heart, liver, pancreas, small intestine and lungs were considered to be less important or occurred less often. Lesions considered to be secondary to the above changes were also encountered.

A mutagen produced by Fusarium moniliforme

A mutagenic compound produced by Fusarium moniliforme on maize was isolated by CHCl3--iso-PrOH extraction, solvent partitioning and liquid chromatography on silica gel and Sephadex LH-20. HPLC studies showed that different mutagenic and non-mutagenic forms can be derived from the mutagen (P3) and that prolonged exposure to longwave u.v. light and to high temperatures causes a total loss of its u.v. absorption and mutagenic characteristics. Spectral data presented for P3 include u.v., i.r., mass spectra as well as 1H NMR and 13C NMR. Mass spectral data indicated a molecular formula of C23H29NO7.

Reduction of patulin in apple juice samples — influence of initial processing

Abstract Patulin is a secondary metabolite produced by a wide range of fungi including Penicillium expansum, a common contaminant of apples. Patulin is reputed to be a mutagen and recommendations have been made that levels should not exceed 50 ng g in apple juice intended for human consumption. The production of apple juice requires the use of ripe fruit, which may be pre-disposed to fungal contamination with P. expansum and concurrent contamination with patulin. During a study using selected over-ripe fruit, triplicate samples of apples were withdrawn at several points prior to maceration. The mean patulin level in the non-processed fruit was found to be 920 ng g , but this level dropped to 190 ng g following an initial water treatment step. Analyses of the wash water showed that appreciable levels had been transferred from the solid to the aqueous phase. Additional removal, by hand, of rotten and damaged fruit prior to further processing, significantly reduced the mean patulin level in the juice to 55 ng g . High patulin levels were recorded in the rotten fractions ( mean = 2335 ng g ). Mycological analyses tended to support the chemical data, in that removal of the rotten fruit significantly reduced the total fungal counts in the juice samples.