Table of Food-borne Bacteria Showing the Associated Features Relevant to Food Safety.
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|Food-borne Bacteria||Onset||Symptoms/ Infectious Dose||Temperature (0C) |
|B. cereus||8 -16 h||Abdominal pain and diarrhoea/ > 105cells||10 30-35||4.9-9.3||Gram-positive bacilli||B. cereus sources vary depending on the syndrome. Contaminated starchy food that contains pre-formed toxins, including leftover boiled/fried rice and pasta, is implicated in the emetic form of B. cereusinfection (Morris & Potter 2013). In contrast, beef, dairy products, salads or desserts and vanilla sauces are the common causes of the diarrhoeal syndrome that develop due to the toxin produced in the gastrointestinal tract (Morris & Potter 2013).|
|C. perfringens||6-24 h (incubation period). Average onset time is 8-24 h.||Watery diarrhoea, nausea and stomach cramps/ >108 cells. The symptoms can last for 1-2 weeks. Dehydration is a common complication associated with C. perfringens infection. The ingestion of a large number of cells (>108) causes disease||15 43-47||5.0-7.0||Gram-positive bacteria||Common environmental sources of C. perfringens include soil, sewage and spore-contaminated food. It also occurs in the gut of animals, including humans. Associated food sources include raw or dried meat and poultry and roast beef (Talukdar et al. 2016)|
|E. coli||1-10 days. The onset time of Shiga toxin-producing E. coli (STEC) is <8 days. The duration of illness is 5-10 days, but in severe cases, haemolytic uremic syndrome (kidney complications) may occur after a week (Morris & Potter 2013).||Bloody diarrhoea, stomach pain and vomiting. The patient may also experience occasional fever, fatigue and irritability. The symptoms associated with haemolytic uremic syndrome are reduced 24-hour voiding, dark-coloured urine, facial paleness, kidney injury caused by STEC-damaged red blood cells and sometimes death (Morris & Potter 2013)||7 35-40||4.4-7.0. However, STEC can survive in acidic conditions (pH = 2.5-3)||Gram-negative bacteria||Food sources include contaminated or undercooked meats, raw milk, fruits and vegetables, especially sprouts (Morris & Potter 2013). Additionally, dairy products such as cheeses produced from unpasteurised milk are other vehicles of transmission. Other sources include contaminated drinking water and swimming pools. Poor hand hygiene practices, especially after cleaning animal sheds also increases the risk of infection. Faecal material of infected persons is another source of E. coli.|
|2-70 days after ingestion||Fever, muscle aches, stiff neck, severe migraines and GI complications such as nausea, vomiting and severe diarrhoea (Morris & Potter 2013). Influenza-like symptoms and miscarriages or still births may occur during pregnancy. Immunocompromised persons often develop bacteraemia. The infectious dose is 10-1006colony-forming units in healthy subjects (Morris & Potter 2013)||-1.530-37||4.3-9.6||Gram-positive coccobacilli||– Raw (unprocessed) milk and its products such as soft cheeses (Morris & Potter 2013) |
– Ready-to-eat beef products and hot dogs
– Refrigerated meat-based sandwich spreads
– Smoked/dried seafood and raw sprouts
Conventional methods for the inactivation of B. cereus and its spores in food involve heat treatment. According to Soni et al. (2016), moderate to high temperatures (75-1210C) can eliminate all Bacillus and Clostridium vegetative cells and spores, improving the safety of meat and dairy products.
Dry or wet thermal processing methods such as pasteurisation and sterilisation are effective in inactivating B. cereus. The amount of heat treatment applied depends on the properties or components of food; thus, some techniques are associated with a consequential loss of flavour or aroma (Soni et al. 2016). Another technology used to achieve B. cereus inactivation and reduce spore numbers is UV treatment. A UV dose of 350 J/m2 at 248 nm can inactivate B. cereus cells and sterilise packaging materials (Soni et al. 2016).
The inactivation of B. cereus spores (often resistant to UV irradiation), thermal treatment is added after a UV dose to increase spore sensitivity to higher temperatures. Hydrogen peroxide can be applied to disinfect packaging materials and kill the spores. High-pressure processing technology – heating and compression – is also used to inactivate B. cereus vegetative cells through membrane and protein denaturation. This method retains the fresh-like attributes of food products like milk, beef, and cheese. Pulsed electric field (PFF) is another option for inactivating B. cereus cells but not spores. PFF entails prolonged short electric pulses to damage bacterial membranes, killing the bacterial cells and endospores.
Inactivation strategies for C. perfringens include physical and chemical approaches. Heat treatment through half-hour incubation of food in water (90-1000C) has been shown to eliminate up to 90% of C. perfringens spores (Talukdar et al. 2016). Another physical technique that has been shown to be effective against vegetative cells and most spores of this bacterial species is high hydrostatic pressure treatment. Chemical agents such as nitrates and nitrites can inhibit the germination of C. perfringens spores in beef products (Talukdar et al. 2016).
However, its use in curing meat is restricted because it forms cancer-causing compounds, which makes it a health risk to consumers. Other safe and effective inhibitory agents include organic acids such as sorbate and benzoate and their derivatives. Natural antimicrobials, including plant-derived essential oils like cinnamaldehyde, are used in the food industry to inactivate C. perfringens cells (Talukdar et al. 2016).
Other compounds that are effective against this bacterial species are tannins, gallic acid, green tea extracts, and bacteriocins such as lacticin. The inactivation of E. coli in food items involves heat treatment (>680C). Pasteurisation of milk and juice products can effectively eliminate this pathogen (Soni et al. 2016). Low-dose UV irradiation is also used to eliminate STEC from poultry and spices. UV disinfection and bacteriophages have been used to eliminate E. coli in all the stages of food processing and packaging to protect consumers from STEC toxins.
A variety of chemical disinfectants have shown significant antibacterial efficacy against Listeria monocytogenes. They include paracetic acid, oleuropein and iodofores (Morris & Potter 2013). Bacteriophages are also used to inactivate L. monocytogenes cells during food processing. Their bactericidal effect results from the removal of bacterial biofilms. A thermal inactivation method that has been shown to be effective against this bacterial species include steam blanching at 960C for 1-2 minutes (Morris & Potter 2013). The technique can be used to eliminate L. monocytogenes in ready-to-eat food such as vegetables and carrots. Optimised High hydrostatic pressure conditions and ohmic heat treatment kill bacterial cells without altering the nutritional content or flavour of food items (Morris & Potter 2013).
Another technology that is effective against L. monocytogenes is cold atmospheric-pressure plasma (CAP). It utilises reactive ion species and ambient gases with antibacterial activity, such as nitrogen monoxide (NO) to kill vegetative cells. Since the method does not involve high temperatures or pressure, the quality of food products processed this way is preserved. Thus, CAP is often applied to dairy products and ready-to-eat food items such as fruits and salads.
Morris, JG & Potter, ME (eds) 2013, Foodborne infections and intoxications, 4th edn, Academic Press, Cambridge, MA.
Soni, A, Oey, I, Silcock, P & Bremer, P 2016, ‘Bacillus spores in the food industry: a review on resistance and response to novel inactivation technologies’, Comprehensive Reviews in Food Science and Food Safety, vol. 15, no. 6, pp. 1139-1148.
Talukdar, PK, Udompijitkul, P, Hossain, A & Sarker, MR 2016, ‘Inactivation strategies for Clostridium perfringens spores and vegetative cells’, Applied and Environmental Microbiology, vol. 83, no. 1, pp. 1-12.