Alexin - Pathogens in Food (original) (raw)

When food goes off or it's contaminated, it is called food spoilage. However, absense of food spoilage doesn't mean that food is safe. Food can make you sick even if it looks good.

There are two ways microbes can make food unsafe to eat.

  1. Poison - They can produce poison in food, so when we eat it we get poisoned.
  2. Infection - We can eat enough of the microbes themselves that they can live inside us and cause trouble by, for instance, creating poisons.

In both cases the microbes that make you ill are called pathogens.

[21]Here are the common dangerous pathogens that can make food unsafe:-

[21]It is virtually impossible for scientists to detect food borne virus. The viruses consist of small section of nucleic acid wrapped in a protein shell. They are inanimate in the environment. They reproduce inside the cells of other living things. Ultimately we catch virsuses from sick animals - usually humans. Human viruses can accumulate in shell fish from waters which are contaminated by sewage. [11]Crops can also be irrigated with sewage contaminated water. Only a few virus particles are needed to cause infection. There are two virus types which are important to food safety. They can be identified by the illnesses they give you:-

  1. Noroviruses - give you gastroenteritis. They only reproduce in the intestine. To spread infection they cause virus loaded projectile vomiting and diarrhoea. They can also cause fever and chills. Areas where sick people have been should be cleaned.[11]They're destroyed by chlorine bleach. After eating them there is an incubation period of a day then illness for 24 hours and the virus is then in the stools for a week.
  2. Hepatitis A Viruses - causes infectious hepatitis. The symptoms are - lack of appetite, vomiting then jaundice(blockage in bile, skin becomes yellow, constipation, weakness). This disease is worse for older people. After eating the virus there can be an incubation period of 4 weeks and illness for a few weeks.

To prevent illness from viruses in shell fish, they are cooked at 90 Centigrade for 1.5 minutes. Infection can come from food handlers while the virus incubates inside them.(Hepatitis A virus can incubate for 4 weeks)[11]Most types of food viruses are killed by heating to 70 Centigrade for 2 minutes.

[21] Protozoa are single celled little animals that can be distinguished from bacteria because their insides are separated into little bags called organelle whereas in bacteria their insides including their DNA float about the inside them. Pathogenic protazoa may not reproduce in the environment. They grow in other hosts. It's difficult for scientists to investigate them.
Cryptosporidium causes gastroenteritis. It is typically spread via water contaminated with human or animal faeces. Infective dose is less than 10 and possibly only 1 oocyst(the hardy spore form of the microbe). It doesn't grow on food and is killed by heating at 45 Centigrade for 20 minutes. It is resistant to chlorine bleach.
Giardia Lamblia causes gastroenteritis and 15% of the US population is infected with it. It is spread in water and food.

I've also had a look at mycotoxins which are poisons produced by moulds. It seems to be uncertain how dangerous these are in low doses. Large doses of these poisons cause sickness and can cause death but its also suspected that in low doses they may be an unreported cause of other illness, particularly liver cancer.
For more information sees - Mycotoxins

THE MOST COMMON PATHOGENS

The most common illness caused by microbes in food is gastroenteritis which is an inflammation of the stomach and/or intestine and generally makes you vomit or gives you diarrhoea.
The microbes most commonly responsible for food borne illness worldwide are varieties of Escherichia Coli which are spread in areas of lower hygiene. This pathogen is the cause of 'travellers tum'. Its historical occurrence in less hygienic areas is shown in the names 'Tokyo trots', 'Delhi belly' and 'Rangoon runs'.
In the west Escherichia Coli is less common. The most common problems in Great Britain are Campylobacterand Salmonella Gastroenteritis from poultry and meat and in the EU Campylobacter illnesses have recently taken over from Salmonella as the chief cause of illness. Incidents of Salmonella Enteriditis are currently increasing.

COMMERCIAL STERILIZATION

The effectiveness of sterilization by heat treatment is measured by subjecting a food to a specific temperature and then timing how long it takes for all but a tenth of the microbes to be killed. This time is the D value for the specified temperature. For example, for Clostridium Botulinum spores the D value at 121 Centigrade is 0.2 minutes. It takes 0.2 minutes to kill all but a tenth of the spores(its a lot longer at lower temperatures). To achieve the commercial sterilization standard for Clostridium Botulinum spores the food is cooked for 12 times as long as the D value. After this time, in theory, only 1 out of every 1,000,000,000,000 clostridium spores will survive(which is to say practically none). In a real situation the food will be cooked for longer than this period, which allows for uniformity of heating and for a safety margin.

[20]HUMAN CARRIERS

It's suspected that the greatest causes for Clostridium Perfringens, E. coli, Listeria, Salmonella and Staphylococcus Aureus diseases are meat products.
But, here are some figures that give a rough idea of how human-harboured concentrations of pathogens relate to infective dose.
"One in fifty employees is shedding 109 pathogens per gram of faeces without showing any clinical symptoms"[20]. Failing to wash hands leaves up to 107 pathogens under the finger nails.

Concentrations of Microbes in the gut(- intestinal fauna measured in number of microbes per gram of faeces):-

Clostridium Botulinum is common and is found in it's dormant form(also called endospore or spore form) in soil - particularly in river bed soil. It can survive in its spore form for many years and can survive freezing. It only grows in the absence of oxygen but if it grows on food it can produce a powerful poison - which is a neurotoxin called Botulin or Botulinus toxin. This is possibly the most deadly toxin known to science. Nanograms of the poison can cause illness. Botulin poisoning is called botulism.
The toxin can be destroyed by cooking at 80 Centigrade for 10 minutes(or 5 minutes at 85 Centigrade)
[5]The toxin stops nerves working properly. It causes nausea 6 hours after eating then tiredness, blurred vision, muscle weakness then the breathing muscles stop working - causing death. You need to take an anti-toxin to limit permenant damage. The death rate for botulism is about 10% with hospital treatment.
There are 7 strains of Clostridium Botulinum which are defined by their different neurotoxins, labelled A-G.
Botulinum toxin A is marketed as Botox and is used to relax muscles. This can be used to reduce wrinkles but more seriously in treating medical conditions that cause spasms in facial muscles(Blephorospasm and Strabismus) and can cause blindness and speech loss.
To prevent botulism you can either destroy all the spores in the food, prevent the bacteria from growing in the food or heat the food before eating to destroy the poison.
Spores are killed by heat treatment using a standard called commercial sterilization. Clostridium Botulinum spores are the most heat resistant among the food pathogens. Food can be sterilized by heating to 100 Centigrade for 6 hours or to 120 for 4 minutes.
Clostridium Botulinum growth in food is prevented by acidic conditions. There is no growth beneath a pH of 4.5. Growth is inhibited by salt and low temperatures (but some strains of the bacteria can grow at temperatures as low as 3.3 centigrade). In some foods chemicals called Nitrites or the presence of nisin may be used to control the growth of Botulinum. (Nisin is a collection of polypeptides - which are chains of 10 or more amino-acids - that are produced by the bacteria Streptococcus Lactis.)
The most common cause of botulism in the west is home preserved foods. Botulism used to be associated with sausage production in Europe and it gets its name from the Latin for sausage - botulus.
There have been isolated incidences of botulism caused by commercial canned foods. The cans were heat treated to sterilize the food but were then cooled with unsterile water. The rapid cooling caused the cans to contract and this briefly broke their seals. This allowed contaminated water to be sucked in.

Babies can get a separate condition called infant botulism by eating honey. In this case the spores grow inside the baby and produce poison. The symptoms include unusual floppiness(It is a potential cause of floppy baby syndrome).

[11][21]Clostridium Perfringens starts producing toxins while its growing in your intestines. The toxins are generally not life threatening. They cause gastroenteritis which is usually gone within 24 hours. You need to eat about a million cells per gram to get infected. But under certain circumstances it is exceptionally fast growing. At 44 Centigrade one bacterium can multiply to 17 million in 4 hours. Foods should be kept at a temperature less than 5 Centigrade or kept warm at greater than 60 Centigrade to prevent growth. It is an intestinal germ in healthy humans and animals. Its dormant form(spore) is in soil and it exist harmlessly in food. There may be a curious link between repeated cooking and the production of poison.
In a typical case of infection, raw meat will have some dormant bacteria spores on it. The meat is cooked but the spores survive cooking and the bacteria multiply if the food is allowed to cool to room temperature. Typical infective dose can occur within 4 hours. When the germs are eaten they start producing poison. You become sick about 12 hours later and recover within 24 hours.

[10]Escherichia Coli is the most common cause of gastroeneritis in the world. Gastroenteritis is the inflammation of the stomach or intestine and causes vomiting or diarrhoea. disease from Escherichia Coli is less common in areas of higher sanitation and is not so common in the West. The bacterium is present in the intestines of humans and animals. In the intestine, it, along with other bacteria, perform various useful functions. It produces B vitamins(including B12) and vitamin K which can be absorbed and used by the host animal.
The illness Escherichia Coli is spread by the faecal-oral route. The existence of Escherichia Coli in the environment, for instance in water, is a standard indicator used to check for contamination by faeces.
Meat, particularly beef, may be contaminated by animal faeces during slaughter and evisceration(disembowelling). Due to the most dangerous form of Escherichia Coli(Escherichia Coli O157) millions of pounds of beef may be recalled from shops in the US each year. In Feb 2008 Westland/Hallmark Meats company recalled 143 million lbs of beef.
Escherichia Coli O157:H7 is a potentially deadly form of this bacteria.
[11]Illness prevention relies on sterilising the food rather than modifying food storage as only 10 bacterial cells may be required to cause infection. The bacteria causes gastroenteritis which may cause bloody diarrhoea. (The pathogen is then called Enterohaemorrhagic Escherichia Coli - EHEC) Of those who have bloody diarrhoea(Haemorrhagic Colitis) 30% go on to develope Haemolytic Uraemic Syndrome(HUS), which occurs when the bacteria toxins enter the bloodsteam and cause kidney and blood cell damage. 8-10% of these cases die.
The bacterium is killed by cooking at 70�C and only grows between 7�C and 45�C. It survives acid conditions(pH 3.6) but stops growing in the range pH 4-4.4 It is resistant to salt, drying and freezing.
The common pathogen Escherichia Coli is combated by a general improvement in sanitation in food preparation.
Escherichia Coli O157 is combated by regulations to farming practices, and combated in food preparation by adequately cooking meat.

[21]Yersinia Enterocolitica causes diarrhoea and abdominal pains several days after infection. Sickness can last 1-3 weeks. Infection is probably from uncultured milk or raw pork. (Raw pork is eaten in Belgium). It's killed by temperatures above 60 Centigrade and grows well at low temperatures.
Yersinia lives in animals mouths and intestines. People can be carriers. Untreated water can cause contamination.
Yersinia Enterobacter is related to Yersinia Pestis which causes bubonic and pneumonic plague.

[11][21] Listeria Monocytogenes is rare but dangerous. It can cause gastroenteritis about 24 hours after eating but the more serious illnesses up to 70 daysafter eating. The more dangerous form can cause meningitis(swelling of brain and spine sacks), septicaemia(blood poisoning), meningoencephalitis(swelling of brain and connecting tissue). In this case the symptoms are severe headache, vomiting, stiff neck. Puss forms around the brain and spine. It can cause death within 24 hours. Listeria lives and grows on grass. 5-10% of people are carriers. Its in the guts of animals like sheep and cattle. Their milk can be contaminated and food can be contaminated by their faeces. Listeria can grow on food at fridge temperatures. Infective dose can be less than 1000 cells. It grows at temperatures greater than -0.4 Centigrade but is generally killed by cooking(70 centigrade for 2 minutes - UK standard).

Staphylococcus Aureus is usually harboured by human food handlers(maybe in skin lesions). The bacteria are typically transferred by touch and this illness is countered by a no touch policy in food preparation. It is killed by heating to 70 Centigrade but if left to breed in food, it produces a heat tolerant poison(proteinaceous enterotoxins). The poison causes nausea, vomiting and abdominal pain. The bacteria are usually found in fatty foods that have little or no cooking(e.g. cream cakes or ham sandwiches). It is not inhibited by salt.
[11]Staphylococcus Aureus is naturally present up 50% of peoples noses. It may be found on the skin and may cause wound infections. It requires a high level of growth to create enough toxin to cause illness(which is gastroenteritis(inflammation of the stomach and intestines) and generally lasts less than 24hours). It is more tolerant to dry, salty sugary environments than other pathogens.
It is recommended to rapidly cool food after cooking to less than 5 Centigrade or to keep food heated at over 60 Centigrade so the bacteria don't get a chance to grow in the food.

Salmonella - Mechanized mass processing of poultry carcasses has meant that cross-contamination with Salmonella can be expected. Salmonella is destroyed in meat by boiling for 30 minutes. Bacteria multiply in inadequately cooked foods which are left at room temperature. An infective dose may develope, usually 100,000 to 1000,000 but in the very young or old doses 10 to 100 cells may be infective. Salmonella is in raw eggs in the UK. Because of animal feed contamination and contamination during butchery "all retail meat may be regarded as potentially contaminated"[1]. Fat may protect the bacteria during cooking. Milk and eggs can be pasteurised by heating to 71 Centigrade for 15 seconds. Diarrhoea and vomiting occurs 14-36 hours after infection. Carriers can harbour Salmonella in their guts for a period(a few weeks but rarely for over a year). So they could infect others if they're involved in food preparation.
Spices from areas of unhygenic standards should be cooked.
[11]Salmonella Typhi is the cause of typhoid fever which occurs in developing countries. It is tranfered in food by contact with people who have typhoid or by contaminated water.
[11]Salmonella may have an infective dose as low as 100 cells in some high fat low moisture foods(like chocolate and peanut butter). So bad storage methods and growth is not needed to cause infection. It is combated by heating food to 70 Centigrade for 2 minutes and preventing recontammination. Salmonella can't grow in temperatures less than 7 Centigrade. The constituents of high fat and low water foods may need to be heat processed(for instance in roasting cocoa beans and peanuts.)
[Scientific American magazine 5/5/09]
US Salmonella outbreaks due to peanut butter. Almonds must be pasteurized(US) and peanuts may be heat treated.

[21]Vibro Parahaemolyticus(Kanagawa-positive) needs salt to grow. You get ill by eating raw sea food in which the bacteria have had time to grow. There is an infective dose of about a million bacteria. Once in your intestine it produces a poison which gives you gastroenteritis for 3-5 days. It is more common in sea food from warm areas. It doesn't grow below 4 Centigrade so raw seafood should be refridgerated.

[21]Vibro Cholerae causes cholera which is a big problem in areas of poor sanitation like parts of India. Cholera can cause severe bodily water loss by diarrhoea and sometimes vomiting. The infective dose is about a million. So you can get it by eating food from unsanitary areas. It doesn't occur often in the West.
It can grow on some food(seafood, cooked foods where there's not many competing microbes) and survives freezing. Its killed by heating to 70 Centigrade.

Bacillus Cereus.The dormant form(spore form) is generally found in the environment and particularly on cereals. It requires oxygen to grow. In the case of rice, if the spores survive cooking and the rice is left at room temperature to dry then the bacteria will multiply and produce enterotoxins which are heat stable and are not destroyed by the short frying period in making fried rice. The toxin causes vomiting or diarrhoea.

[11] Campylobacter in some instances may cause severve bloody diarrhoea.[21]Campylobacter doesnt normally grow on food.
Campylobacteriosis is the most common cause for infective diarrhoea in developed countries. It comes from the guts of animals and is tranfered to meat during slaughter or evisceration(disembowelling). It may infect poultry and milk. Infection can also occur by drinking water infected with faeces - there is a low infective dose. Only a few hundred bacteria are needed for infection. After about 3 days incubation, it causes ill feeling, malaise, dysentery and abdominal pain.
[22]In the EU in 2005 there were 197000 reported cases of Campylobacteriosis and 176000 cases of Salmonella. The most common form was Campylobacter Jejuni.
[22]Campylobacter is easily killed by cooking. It is sensitive to salt, drying, pH, oxygen, freezing. It can be carried by most animals and can be in raw milk and untreated water. It occurs worldwide. In europe, it is the suspected cause of most illness is poultry. Chickens can become carriers by chicken-to-chicken and chicken-to-animal interaction. So most free-range chickens in Europe are infected because of contact with wild animals. Chicken corpses may be infected after death in the meat works. Human infection probably comes from cross contamination with meat products during food preparation particularly with summer foods.
The pathogen can be controlled by adequately cooking meats, pasteurising milk and chlorinating water.

Some moulds can produce poisons called mycotoxins(from myco which is Greek for mushroom). [21]These moulds produce toxins when they're stressed by sudden environmental changes, like drying.
The Food and Agricultural Organisation of The United Nations estimated that 25% of the worlds food crops are affected with mycotoxins. But its apparently not certain how dangerous the toxins are. [16]Some toxins(like aflatoxin) survive cooking and food processing. [16]Mycotoxins are particularly a problem for tropical and subtropical regions, especially China, where they may be produced by moulds growing on grains. The main toxin of concern is Aflatoxin which gets its name from the mould _A_spergillus _Fla_vus. It can also be produced by Aspergillus Parasiticus, Aspergillus Nominus and Aspergillus Niger. Only some Aspergillus species and strains can produce the toxin.
[10]Aspergillus is very common in the environment and it floats about in the air. (This may be the cause of some peoples allergies.) It grows easily on any food and typically after 48 hours at 25 Centigrade a fluffy white fungal growth will develope. It will then become powdery and change colour depending on the color of its spores.
In 1960 100,000 English turkeys died from eating peanuts contaminated with alfatoxins. This gave everyone the willies and now in the US aflatoxin content in food is regulated by the Food and Drug Administration.
SO IS IT DANGEROUS OR NOT?
You might expect that because we're descended from a long line of omnivores(animals which eat anything) who's diet no doubt included a lot of mould, that we might have built up some natural resistence to mould toxins.
[14]In support of this, pigs, our fellow omnivores can eat and then contain alflatoxins without showing signs of illness.(So the concern is that pig meat may contain it if their food is contaminated). [19]Also primates have mechanisms for detoxifying aflatoxins that lower animals don't.
However in case studies of poisoning in poorly fed villages(their crops became mouldy) the poison caused death in smaller doses(per unit body weight) than those that kill healthly animals.
There is, however, a single case of a US lab worker who took aflatoxin - unbeknown to the employing organisation and so the results aren't properly varified. Doses a little lower than that which is lethal for animals were taken over a two day period. The participant became sick, but not critically sick, and then recovered. The same thing was repeated over a longer period 6 months later and the same dose was taken per day but the result was only mild illness. There were apparently no long term health effects.
[14]Aflatoxins definitely do cause cancer in animals. [19]Also, population studies show a higher rate of liver cancer in humans in areas where there are contaminated crops (but the data is confused by a higher occurrence of Hepatitus B which could cause the cancer) [16]A recent work relates cancer risk and genetic ability to metabolise the toxin - so the association may be causal.
As regards 'domestic' food moulds, oriental domestic moulds seam to combat mycotoxins. Rhizopus Oligosporus(a mould used in tempe production) can inhibit Apsergillus Flavus and Aspergillus Parasiticus which produce aflatoxin.[18]Rhizopus strains and Neurospora(which is used to make ontjom) strains can breakdown aflatoxin B1.
[19]In the west the domestically used moulds(Penicillium species) can produce mild poisons but not under the conditions found in traditional food fermentation.

Sources

[1] - { "The Cambridge World History of Food" ed by Kenneth F. Kiple & Kriemhild Conee\ Ornelas, }
[2] - { "The Oxford Companion to Food" Alan Davidson(2008) }
[3] - { "The New Soy Cookbook" Lorna Sass(1998) }
[4] - { "What you must know about Vitamins, Minerals, Herbs and More", Pamela Wartian Smith MD MPH (2008) }
[5] - { 5-Britannica(Nutrition) }
[6] - { "Fermented Foods" ed by AH Rose(1982)}
[7] - { Nutraceuticals by Arthur J Roberts MD, Mary E O'Brien MD, Genell Subak-Sharpe(2001) ; The official American Nutraceutical Guide}
[8] - { The Encyclopedia of Mens Health, Glen S Rothfield MD MAC and Deborah S Romaine(2005)}
[9] - { "The Complete Guide to Nutritional Health", Pierre Jean Cousin & Kirsten Hartvig(2004)}
[10] - { "Microbes and People - An A-Z of Micro-organisms in Our Lives", Neeraja Sankaran(2000)}
[11] - { "Make it Safe - A Guide to food safety" Katherin Scurrah(2010), Project leader of CFNS : CSIRO publishing, Autralia}
[12] - { "Fermented Foods of The World: A Dictionary and Guide" by Geoffrey Campbell-Platt(1987)}
[13] - { "Cultured Foods" by Wendy Zeffert(1999)}
[14] - { "Toxins A-Z" by John Harte and Co.(1991)}
[15] - { "Understanding Nutrition" by Ellie Whitney(2005) the eleventh edition}
[16] - { "Essentials of Human Nutrition" Third Edition, Edited by Jim Munro and A Steward Truswell(2007, profs in Aus and NZ)}
[17] - { "Principles of Food Sanitation" 3rd Edition, Dr Norman G Marriott (1994)}
[18] - { "Exploitation of Micro-Organisms", ed by D. Gareth Jones(1993)}
[19] - { "Fungi and Food Spoilage" 2nd Edition, J I Pitt and A D Hocking(1997)}
[20] - { "The Microbiology of Safe Food" by Stephen J Forsyth(2000)}
[21] - { "Micro-Facts:The Working Companion for Food Micro-Biologists" 6th Edition(2007) by Dr Peter Wareing and Rhea Fernandes}
[22] - { "Food:Engineering & Ingredients" v32 no1 (2008)}