12. Various common food toxins and toxicity

I found the various common food toxins, pathogens and its toxicity.

In food, the common foodborne pathogens are Bacillus Cereus, Clostridium Botulinum, Esherichia Coli, Listeria Monocytogenes, Salmonella, Staphylococcus Aureus, and Asperigillus Flavus.

Peanut butter which is produced by the company contains foodborne pathogens such as Salmonella, Aspergillus Flavus, Staphylococcus Aureus, Rhizopus and Clostridium Botulinum. It also contains mycotoxins such as Aflatoxin which is produced by Asperigillus Flavus.

Bacillus Cereus
- cause Bacillus Cereus Food poisoning and it produces a diarrhoeal enterotoxin.
-sources: milk, dairy products.
- can be identified by the isolation and enumeration of B.cereus, preferably in both the infected food and the faeces of the victims.
- Procedures for isolation and enumeration of B.cereus involve direct agar plating techniques. However methods for detecting B.cereus enterotoxins are neither highly specific nor quantitative.
- Optimum temperature range for this emetic toxin production is 25 to 30 C. the emetic toxin is heat stable and can withstand normal cooking temperatures. So food is to be cooled rapidly to a temperature that prevents the growth of B.Cereus and food to be held in a warm state should be maintained above 60C.

Clostridium Botulinum
- can cause food borne botulism and produces C.botulinum toxin.
- Sources: may occur in almost all food, vegetable or animal origin.
- No microbiology methods are specifically designed for C.botulinum. Methods of enumerating the clostridia usually rely on reduction of sulphite to sulphide with the formation of black colonies which demonstrates the presence of C.botulinum by enrichment culture and toxin tests.

Escherichia Coli
- can cause infection and food borne illness.
- Sources: Milk, meat.
- Isolation of pathogenic E.coli involves plating sample on MacConkey or eosin-methylene blue agar.
- Enrichment and selective procedures would be carried out after black colonies are picked and identified as E.coli.
- Detection for E.coli is facilitated by enrichment and electromagnetic separation. Several biochemical tests are done to identify E.coli and some examples are Gram’s stain positive, indole positive, mannitol-positive, and Voges-Proskauer-negative. Important measures are taken to prevent food poisioning by education food workers in safe food handling techniques and proper personal hygiene.

Listeria Monocytogenes
- can cause listeriosis.
- sources: raw meat, wet sirfaces in food processing plants.
- an opportunistic pathogen that is capable of surving and multiplying in simple nutrient media and outside animal hosts.
- able to grow in simple bacteriological media. It is able to grow at low temperatures and thus multiply.
- Isolation can be done after plating onto non selective media such as blood soy agar and selective media such as modified McBride’s agar. Several enzyme-linked immunosorbent assay (ELISA) methods and nucleic acid probes are available for identification purposes.
- Listeriosis can be reduced whereby HACCP should be applied from farm to consumers to minimize the risk of food borne illnesses.

Salmonella
- can cause gastroenteritis, enteric fever and bacteraemia, focal infections and sequelae.
- sources: food of animal origin.
- Detection of salmonella involves pre-enrichment, enrichment, selective differential plating, isolation and identification.
- enumerated by the most probable number technique though it is a cumbersome procedure and too expensive for use in large number of samples.
- Identification of Salmonella can be done by primary screening on non selective differential agars such as triple sugar iron (TSI), and further identification can be done by biochemical testing of pure cultures. With the use of heat, irradiation, acidification and combinations of factors are used to destroy salmonella in food since low numbers of salmonellae can cause illness.

Staphylococcus Aureus
- can cause staphylococcal food poisoning.
- Sources: mucous membrane, and skin of all food animals.
- method of enumeration is Baird Parker’s medium.
- procedure for detecting staphylococcal enterotoxin in food is a combination of extraction, concentration and final detection of the toxin by the use of enzyme-linked immunosorbent assay (ELISA).
- Control can be achieved by preventing products from contamination and avoiding conditions where growth may occur.

Asperigillus
- produces mycotoxins and can cause mycotoxin poisoning.
- sources: peanut, corn, cottonseed.
- Enumeration of Asperigillus flavus can be done on antibacterial enumeration medium that contains inhibitors to reduce colony spreading.
- Identification of Asperigillus flavus grow rapidly on standard identification media such as malt extract agar. Asperigillus also produces mycotoxins such as aflatoxins which are found to be acute and chronically toxic in both animals and in man.
- ELISA techniques are used for toxin estimation and controlling of aflatoxin in corn can be directly detected when they fluoresce under UV light.


Reference:
Blackie Academic & Professional. Microorganisms In Foods 5. Microbiological specifications of food pathogens. 1996

p.s: book found in school library.