Escherichia coli
The mutated form of E. coli can cause problems with meat, vegetables and fruit.
Raw meat is infected with E. coli from insanitary conditions in abattoirs. Once raw
meat is handled care must be taken to wash one’s hands before touching any other
surface. Vegetables grown in soil, especially organic vegetables, where manure is
used as a fertiliser, will have E. coli contamination. E. coli is classed as a low dose
pathogen, which means only a few bacteria are required to cause illness.
Fruit pickers in the UK and other countries work on farms that are vast in size. There are
very few toilet facilities on the farms and when a worker needs to go to the toilet they
will go in the field and not wash their hands afterwards. The faecal contamination on
their hands is transferred to the fruit. The food is not washed or disinfected before it
reaches the shops. Another problem in shops is the amount of people that handle
your fruit and salad vegetables before you eat them. Therefore, always wash your
fruit well before use.
E coli 0157:H7 first emerged as a serious pathogen in 1982 in the USA in an
undercooked beef burger.
When the bacteria are shed with faeces, it can mutate into one of several pathogenic
variants including Enterohaemorrhagic E coli (EHEC).
Ruminants have also been found to be the main reservoir for EHEC. EHEC has
caused diarrhoea and deaths in outbreaks in Europe, the USA, Japan and Africa.
In 1996, in the world’s worst case of E coli 0157:H7 food poisoning in Wishaw,
Lanarkshire, 22 people died.
Between 1997 and 2000 the reported cases of EHEC in Northern Ireland increased
from 30 to 54 per annum.
In 2005 there were 156 cases of EHEC poisoning in South Wales, with 1 fatality. In
2010 there were 93 cases of EHEC in Godstone Community Farm, Surrey.
EHEC has been found in ground beef and chicken drumsticks in Turkey. Globally,
there are approximately 600 million cases of EHEC every year and 700,000 deaths
in children younger than 5 years of age. Presently there are 25,000 cases of EHEC
every year in the UK.
E coli commensal bacteria mutate into pathogens usually by plasmids (circular DNA
in bacteria) which can transfer virulence factors into non-pathogenic bacteria to
produce pathogenicity islands which turn the good, commensal bacteria into
pathogens.
E coli produce a Shiga-type toxin. So named because the effects
resemble the dysentery causing bacteria, Shigella dysenteriae. The toxin is a
verotoxin, which is an enterotoxin, affecting the GI tract, mainly the small intestine. A
severe influx of water occurs causing vomiting and diarrhoea. The bacteria grow in
the small intestine and release further verotoxin which kills epithelial cells and
produces blood in the diarrhoea. It also results in HUS and kidney failure. The
disease is particularly serious in vulnerable groups such as the elderly, very young,
ill people, immuno-deficient/suppressed, pregnant, people on certain drug therapies.
E coli 0157:H7 is acid tolerant, therefore stomach acid does not kill it if ingested. It
can grow at a low pH of 4.4 (a potential problem, therefore, with untreated apple
juice). It is a gram negative rod shaped bacterium and a major cause of acute renal
failure in children. Only a small infective dose of 10-100 bacterial cells are required
to cause a disease and is known as a low dose pathogen.
Although there are 700,000 child deaths directly attributable to EHEC, 2.2 million
children die, globally, from diarrhoeal diseases, many of which may be due to EHEC.
This cannot be substantiated, however, due to lack of data, inaccurate reporting,
reliable diagnosis, etc.
Although the main source of EHEC is ruminants, other more indirect sources have
been identified:
- Faecally contaminated water
- Undercooked minced meat/burgers
- Raw milk
- Cheese from unpasteurised milk
- Apple juice
- Salads and vegetables, especially organic produce using manure as a fertilizer
- Swimming pools
- Bean sprouts and alfalfa beans.
Most of the above can be attributed to cross contamination from faeces.
During a recent holiday in the UK, I witnessed quite a few local seagulls were using
the camp site swimming pool as a bathing area, with obvious contamination
implications.
After the Lanarkshire outbreak in 1996, Professor Hugh Pennington of Aberdeen
University was asked by the government to undertake an enquiry and to publish his
recommendations. The recommendations included:
- An education awareness programme for farm workers
- Stronger enforcement of hygiene standards at abattoirs
- Quicker implementation of HACCP***
- Physical segregation of raw and high risk foods
- More improved food hygiene training for food handlers and an awareness scheme in schools
- More substantial research into E coli
- More resources available for education and awareness
- More improved outbreak control and reporting procedures
(HACCP*** is an acronym for Hazard analysis critical control points. It is a risk
assessment of a food business to identify any stages where contamination may
occur and to introduce control measures to ensure contamination does not occur.)
In the UK and other developed countries, many of the Pennington recommendations
can be implemented, providing finance is available. For example education and
awareness can be spread through training, especially with regards personal hygiene.
However, even in the UK, after training, many catering staff do not regularly enforce
this most basic of hygiene controls. In 2002, 1016 catering staff were questioned
regarding hand washing in the workplace. They were given several scenarios and
asked if they washed their hands after the particular example.
Do you wash your hands after: Percentage of staff who answered “no”
Going to the toilet? 39%
Before starting work? 50%
After handling raw meat? 52%
After handling fruit and vegetables? 85%
These are quite disturbing results, considering the staff have been trained in food
safety (a legal requirement under Food Safety legislation).
Apart from the controls stated under the Pennington recommendations, thorough
cooking food to at least 70°C (USA) or 75°C (UK) core temperature will kill the
pathogen. Why there are temperature differences between the USA and UK is
unknown. Temperatures above 60°C will kill E coli, as with most food safety
pathogens. (Most pathogens start to die at 52°C)
The majority of illnesses and deaths attributable to EHEC relate to developing
countries. In the UK there are adequate potable water and toilet facilities. In
developing countries 1.1 billion people are without clean drinking water and 2.4
billion people without adequate sanitation.
These countries do not have enough money to finance any education or awareness
programmes to control EHEC. Many people live in poverty and, because of poor
diets, cannot fight EHEC infection. Diagnosis of infection can be quite difficult and
time consuming in developed countries. In developing countries diagnosis is quite
often too late, due to lack of equipment, expertise and logistical problems of location.
Quite often people suffering from EHEC are living in the deserts, forests, mountain
ranges, where there are no direct communication routes.
Spread of EHEC has been quite extensive in the last 30 years from its roots in the
USA to spreading to a global audience. This is due to more travel, import/export of
contaminated foodstuffs and poor hygiene control when the pathogen emerges.
Where countries have identified EHEC, doctors have prescribed antibiotics, resulting
in antibiotic resistant strains.
The ideal situation regarding control of EHEC would be localised elimination followed
by global eradication. However, as E coli is a natural commensal of humans and
EHEC a symbiont of ruminants, elimination and eradication is going to be impossible
due to its ubiquitous nature.
The only way forward is by more vigorous controls. In the UK, for example, the
regulations should be tighter with stiffer penalties for the food industry. Food safety
training should be given a priority in schools and industry, especially in abattoirs and
fruit and salad farms. It has been suggested that all raw meat in the UK is
contaminated with pathogens including EHEC. Although the infection can be killed
by thorough cooking, cross contamination caused by touching the infected raw meat,
not washing hands, and touching other surfaces causes many problems. If high risk
food such as sandwiches, cooked meats and buffet items are placed on the
contaminated surface, the EHEC are transferred to the food. It has been shown that EHEC can survive for up to 60 days on a stainless steel surface, which has not been
adequately cleaned. Raw food must be kept separate from ready to eat, high risk
food.
Apart from C perfringens and C botulinum there is also one serotype called C
difficile, which causes major diarrhoeal problems in hospitals. Clostridia are a major
source of infection with large joints of meat, large pots of gravy or soup which are
allowed to simmer slowly for several hours without being stirred. The bacteria grow
in the cool spots within liquids. The bacteria release a toxin which is heat-stable. So
even if the liquid is brought to the boil it will not deactivate the toxin and poisoning
will ensue.
Bacillus cereus is a major cause of poisoning with rice and rice products. This will be
covered in more detail when the best way to handle rice to prevent food poisoning is
discussed under spores.
Listeria are bacteria that will grow in a fridge in cold conditions. These bacteria can
be found in unpasteurised food products such as milk, cheese and pates. Listeria is
a major problem with pregnant women. It affects the unborn child by preventing
oxygen and nutrients from reaching the foetus. Abortion, miscarriage or stillbirth
could arise.
Campylobacter is the major cause of infection with poultry. Campylobacteriosis has
flulike symptoms. Campylobacter are also present in live birds. This includes wild
and domestic birds.