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Burkholderia cocovenenans
In many countries,
fermented vegetable matter, as an alternative to fresh meat, forms an important source of
protein. One such product is the many varieties of tempe, produced in Indonesia. Tempe is
prepared principally from soybeans or other legumes. Soybean tempe (tempe kedele) is a
high-protein food with significant nutritional properties and a good public health record.
In the Regency of Banyumas and surrounding areas of Central Java, Indonesia, tempe
bongkrek and other-coconut based products are prepared from partly defatted coconut. The
raw material for tempe bongkrek sometimes is mixed with the residue from the manufacture
of tofu (soybean curd) and allowed to ferment with the mould Rhizopus oligosporus. The
final product is a compact cake in which the white mould covers and penetrates the
substrate and binds the particles together. Tempe is consumed as cubes or slices,
especially after deep frying. Under certain conditions, the contaminating bacterium,
Burkholderia cocovenenans may grow in tempe bongkrek, producing two toxins: colourless
bongkrek acid and yellow-coloured toxoflavin. Bongkrek food poisoning usually has a
latency period of 4 to 6 hours. Typical symptoms are malaise, abdominal pains, dizziness,
extensive sweating, marked tiredness and sleepiness after which the patient passes into a
coma. Death occurs from 1 to 20 hours after the onset of the initial symptoms. Laboratory
techniques for the detection of Burkholderia cocovenenans in foods have been established,
but as yet have not been standardised. An efficient and specific enrichment procedure is
required to examine food and environmental samples for the presence of the bacteria.
Mycotoxigenic Fungi
Toxic fungal metabolites, mycotoxins,
have been responsible for a number of major epidemics in man and animals. The natural
fungal flora of foods is dominated by three genera, Aspergillus, Fusarium and Penicillium,
and it is not coincidental that these three genera produce the most important mycotoxins.
Fusarium species are destructive pathogens on cereal crops and other commodities, and
produce mycotoxins before, or immediately after, harvest. Certain species of Aspergillus
and Penicillium are also plant pathogens or commensals, but these genera are more commonly
associated with commodities and foods during drying and storage. It is important to
realise that not all species of these three genera are capable of producing human disease.
Mycotoxins are metabolites which are usually produced as the fungus matures. There
are four basic types of toxicity: acute, chronic, mutagenic and teratogenic. The most
commonly described effect of acute mycotoxin poisoning is deterioration of liver or kidney
function, which in severe cases may lead to death. However, some mycotoxins act by
primarily by interfering with protein synthesis, and produce effects ranging from skin
sensitivity or necrosis to extreme immunodeficiency. Others are neurotoxins, which
in low doses may cause sustained trembling in animals, but at only slightly higher doses
cause permanent brain damage or death.
Long term affects of low levels of mycotoxin ingestion are also varied. The prime chronic
effect of many mycotoxins is the induction of cancer, especially of the liver. Some toxins
affect DNA replication, and hence can produce mutagenic or teratogenic effects--although
these have only been demonstrated in laboratory or domestic animals, not in man.
Generally, specialised tests are necessary to identify the species of the three genera
discussed here. This will often require use of "Reference Laboratories" which
have the capability of fully identifying a fungus and also analysing the capability of the
fungus to produce mycotoxins. The major toxigenic species of significance in foods of
Aspergillus are A. flavus, A. parasiticus, A. ochraceus and A. versicolor. Similarly
Fusarium sporotrichioides, F. poae, F. equiseti, F. graminearum, F. moniliforme, F.
proloferatum and Penicillium crustosum, P. roqueforti and P. verrucosum.
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