Agriculture Reference
In-Depth Information
Infection in humans
The incubation period is
12-24 hours, after which profuse diarrhoea and
abdominal pain develop. Less commonly, fever and
vomiting may be present. The symptoms may persist
for 7 days.
Part 2: Meat microbiology
Bacteriological examination of carcases
In the healthy and physiologically normal animal, those
organs which have no direct contact with the exterior
may be regarded as virtually sterile, though the actual
operation of slaughter and dressing has a significant
potential to introduce bacteria to the blood, tissues and
organs. These micro-organisms are usually a mixed flora
of non-specific micro-organisms of environmental as
well as faecal origin but can include pathogens such
as
Salmonella
,
Campylobacter
,
E. coli
and other food-
poisoning organisms. In addition, specific pathogens
may be present in organs or tissues such as the spleen,
muscular tissue or lymph nodes, and their presence can
only be attributed to a generalised septic or bacteraemic
infection in the animal at the time of slaughter. Where
such organisms are of intestinal origin, their entry into
the systemic circulation may be explained by a breakdown
in the natural resistance of the animal with migration of
the organisms from the intestinal tract. Haematogenous
invasion may, however, occur from other naturally
infected cavities of the body for the same reason. Such
systemic invasion is most likely to occur in animals that
are ill or exhausted, which should be identified during
the ante-mortem inspection. Subsequent bacteriological
examination of the flesh and organs post-mortem would
provide definitive material assistance to an inspector
charged with assessing the fitness or otherwise of a
carcase for human food.
Source of human infection
The organism is
found in seawaters, especially if the temperature is
greater than 10°C. Fish and shellfish from affected
waters may cause illness if inadequately cooked or if
subsequently re-contaminated. It is rarely acquired in
the United Kingdom, although one incident involving
locally caught crab was reported on the south coast of
England.
Bacillus cereus
Bacillus cereus
has been recognised as an uncommon
cause of food poisoning since the 1970s. It is a Gram-
positive, spore-forming, motile bacillus producing two
different toxins. A heat-sensitive enterotoxin causes a
diarrhoeal illness, while the heat-stable 'emetic' toxin
causes vomiting. The spores are heat resistant and can
survive normal cooking temperatures. The bacteria are
widespread in the environment, including soil and
water, and consequently contaminate many foods, par-
ticularly dry foods such as cereals. Any food such as
meat, dairy products and vegetables can be vehicles of
infection.
Infection in humans
The two toxins produce different
disease syndromes. The more common illness is vomiting
caused by the 'emetic' toxin after an incubation period of
1-5 hours. This is particularly associated with rice and
pasta. The diarrhoeal illness caused by the enterotoxin
has an incubation period of 8-16 hours. Both forms of
infection usually last no longer than 24 hours and com-
plications are rare.
Indications for examination
The examination of food of animal origin for fitness
requires the three stages of ante-mortem, gross post-
mortem and, where necessary, further laboratory tests.
There is no justification for conducting a bacteriological
examination on a carcase or its organs when they exhibit
marked pathological changes of a non-infectious nature.
Such conditions or evidences of severe systemic disturbance
are themselves sufficient to justify condemnation of the
carcase. A bacteriological examination can never substitute
for a careful organoleptic examination; its value is as a
supplementary test to assist judgement when septicaemic
or bacteraemic infection is suspected. The only thing to be
gained from a bacteriological examination of such overtly
unfit material is the identification of the infecting organism
- this in itself may be sufficient reason.
A bacteriological examination may be considered
obligatory in the case of animals which:
Source of human infection
Many foods are con-
taminated with a few spores and these can survive the
initial cooking. If food is subsequently kept at ambient
temperature, the spores germinate and the vegetative
cells multiply rapidly, producing toxin in the food. The
'emetic' toxin is not destroyed by further heating, but the
enterotoxin can be inactivated by thorough reheating.
This latter toxin can, however, also be produced in the
intestine of the patient following consumption of the
vegetative cells. The disease is controlled by keeping
cooked foods either hot or at refrigeration temperatures.
About 30 outbreaks a year are described in the United
Kingdom.
1
Have been slaughtered in emergency
2
Have been slaughtered on account of a disease
associated with systemic disturbances
