Transcript Pathogens

Pathogens
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Infection is the invasion and growth of an organism within a host organism
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Pathogens are infectious organisms that harm their host
- Frank pathogens can cause disease in otherwise healthy individuals
- Opportunistic pathogens can only cause disease in compromised individuals
(burn victims, AIDS patients, the young or
elderly, pregnant women,
transplant patients)
- Human pathogens include bacteria, viruses, and protozoa (amoebas,
flagellates, and apicomplexans)
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Virulence is the degree of pathogenicity of a parasite determined in part by
minimal infective dose, the number of organisms needed to cause an
infection bacteria > viruses > parasites
Food borne transmission
 Ingestion of infectious agents in food
 Main
causes are poor sanitation,
hygiene
(faecal-oral
route),
Insufficiently cooked food
 Examples of food borne disease are,
 Botulism, E.coli diarrhoea
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Humans become infected by ingesting
pathogenic
bacteria,
viruses
or
parasites in water polluted by human
or animal faeces or urine.
 Examples of water borne diseases
-Cholera
-Bacillus dysentery (shigellosis)
-Tyhoid, Salmonellosis, E.coli diarrhoea
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Human become infected by being
bitten by an insect vector
 Examples of diseases are;
-malaria
-sleeping sickness
-yellow fever
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Transmission is through inhalation of
pathogens in aerosols
 Aerosols
created at waste water
treatment plants, land application of
sludge, showers
 Examples
-fungal infections
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Requires direct physical contact
between host
 Sexually transmitted diseases
 Examples are
-Gonorrhoea
-HIV/AIDS
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Food borne disease is simply disease
that results from the ingestion
infectious agents of food
 Microorganism are by far the most
important agents of food borne
disease, with bacteria causing the bulk
of food outbreak.
 Also viruses, protozoa and to a lesser
extent fungi
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Bacillus cereus, Clostridium botulinum, C.
Perfringens.
E.coli,
Salmonella
spp,
Staphylococcus spp
These microorganism once ingested with the
food, when conditions are favourable, -they
reproduce and produce toxins which cause
diseases.
Conditions,
ideal temperature
pH
water activity and growth factors
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The organism: B. cereus is Gram positive
rod, spore forming, non motile, non
capsulate and produces haemolytic
colonies on blood agar.
The organism is non lactose fermenting
and produces pale colonies on Mac
Conkey agar.
B. cereus produces beta lactamase and is
resistant
to
penicillin
and
cephalosporin's
antibiotics
The disease, Bacillus cereus produces
two distinct types of gastroenteritis
 (a) Diarrhoeal type caused by strains
of B. cereus that produces a heat
sensitive enterotoxin. The toxin is
formed during growth in the food and
also in the intestines after ingestion of
vegetative cells.
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(b) Emetic (nausea and vomiting) type
caused by strains of Bacillus cereus
that
produces
a
heat
stable
enterotoxin formed in the food during
stationary phase of growth.
 Incubation period: diarrhoeal type 816 hrs, emetic type 1-5hrs
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Symptoms, diarrhoeal type- profuse
watery diarrhoea, abdominal pain,
occasional nausea and vomiting;
emetic type, nausea and vomiting,
occasionally followed by diarrhoea
 Infective dose: very large numbers of
cells are required, diarrhoeal type
>5E5/g , emetic type>1E3/g
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Bacillus cereus is widely distributed in
the environment, soil, dust, milk, rice
vegetables and other cereals that have
been cooked and then stored in warm
temperatures
 Bacillus cereus is causes opportunistic
infections in immunocompromised
persons e.g pneumonia, bacteraemia
wound infections
 Diarrhoeal
type- meat and meat
products, soups, vegetable
dishes, dishes to which spices
have been added late in cooking
and then allowed to stand before
eating.
 Emetic type- cooked rice and
pasta
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C. botulinum is a gram positive, motile,
rod with oval sub terminal spores.
 Basically the following type of strain
exist A, B, E and F
 Two types of C. botulinum exist:
-proteolytic which include all of type of
strain A and some of type B and F
-non proteolytic all strains of type E and
some strains of type B and F
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The disease, Botulism is caused by
ingestion of a neurotoxin secreted into
food during growth of the organism.
Infant botulism is caused by ingestion of
spores of the organism leading to
subsequent growth and toxin production
of the toxin in the gut.
This happens before the establishment
of natural flora.
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Incubation period: Normally 12-36 hours
but can be between 2-hrs to 8 days.
Symptoms:
although
nausea
and
vomiting may occur, symptoms are
mainly neurological- blurred or double
vision, difficulty in swallowing, mouth
dryness, speech difficulties and limbs
and respiration becomes progressively
paralysed
The botulinal toxins are among the
most toxic substances known.
 Minimum lethal dose for mice 0.42.5ng/kg of mouse tissue
 Estimated 50% lethal dose for human
is 1ng/kg of body
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Under anaerobic conditions, e.g in low
acid canned foods such as tinned
meat or fish (not acid fruits), the
spores germinate and the bacilli
multiply, producing the toxin.
 C. botulinum can be found in soil,
water and sewage.
 C. botulinum can be isolated with
Robert’s cooked meat medium
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Botulism has also been associated with
food that has been inadequately heat
treated or heat treated so that the spores
survive and competition is low.
High water activity>0.93
Preservative present e.g. nitrite, salt are
insufficient to prevent spore germination
Food that has been held at room temp
within the growth range of the organism.
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E.coli is a gram negative usually motile
rod.
E.coli belong to large group of gram
negative
rods
referred
to
as
enterobacteria
They are naturally found the intestinal
tract, in soil, water.
Those
that
cause
primary
and
opportunistic infections in humans
belong mainly to the following genera
The disease: Although E. coli is
generally harmless part of the normal
micro flora of the gut of humans and
number of the groups of E.coli are
pathogenic and have been associated
with food borne disease.
 These are;
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Strains of E. coli are recognised as
causing diarrhoeal disease include;
 Enterotoxigenic E. coli (ETEC)
 Enteropathogenic E. coli (EPEC)
 Enteroinvasive E.coli (EIEC)
 Veterotoxigenic E.coli (VTEC)
 Enterohaemorrhagic E.coli (EHEC)
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Incubation period: 3-4 days
 Inflammation of the colon giving rise
to diarrhoea and abdominal pain with
bleeding –blood appear in stools.
 Renal failure due to blood clots in the
kidney tubules
 Infective dose: the infective dose is
thought to be low, possibly 10100organism.
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The natural habitat of E.coli 0157:H7
appears to be the intestines of dairy
cattle.
 Undercooked minced beef and raw
milk have been implicated in food
poisoning outbreaks.
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E.coli can be isolated with blood agar,
MacConkey agar, XLD and DCA agar.
 In XLD and DCA agar, yellow colonies
are produced on XLD.
 Growth of E. coli is usually inhibited
by DCA agar
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Salmonellae are gram negative rods. With
the exception of S. Pullorum-gallinum,
all salmonellae are actively motile.
They are non sporing and with the
exception of S.typhi
Salmonellae are aerobes and facultative
anaerobes.
Their optimum temperature is 37 Deg C
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Salmonella enterocolitis
Infection is by ingesting salmonellae in
food that has become contaminated
from animal and human intestinal
sources, directly or indirectly.
Common sources of infections are
poultry, meat products, eggs and egg
products
Food poisoning salmonella spp can
cause bacteraemia, inflammation of the
gall bladder, children sickle cell anaemia
Salmonella can be isolated on blood
agar (subcultures), XLD agar or DCA
and MacConkey agar
 Salmonellosis occurs within 12-24 hrs
 The symptoms may include nausea,
dairrhea, abdominal pain, fever,
headache
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The gram negative genus Vibrio
contains more than one member that
is pathogenic to human.
 Cholera is transmitted through the
ingestion of faecal contaminated food
or water
 The organism produces an exotoxincholera toxin.
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Symptoms of the disease is accompanied
by severe dehydration, vomiting,
abdominal pains and acidosis associated
with cholerae due to the action of the
exotoxin.
This causes water and electrolytes to
flow into the bowel lumen
In severe infections, typical rice water
stools containing many vibrios are
passed continuously. TREATMENT;
Explain how
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Slender rods, 2,5-3,5um appearing
mostly in pairs.
They are difficult to stain because of
waxy constuents but once stained resist
decolourisation with acid.
They are non motile, non capsulated,
non sporing, grow very slowly and are
aerobic
The microorganism is inhaled in small
particles into the bronchioles
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In Miliary TB, the TB bacilli can be transmitted
by inoculation, , inhalation and through food
such as milk and milk products
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The pathogen is transmitted by direct
contact with an infected person or a
carrier.
The bacterium, C. diptheriae is
transformed from a commensal to a
pathogen by a virus called a bacterial
phage.
The bacteria then starts to produce a
powerful exotoxin which is absorbed
into the blood stream.
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This toxin poisons heart muscle,
kidneys and nerve tissue resulting in
malfunctioning of these organs and
death may follow.
The organism, Gram positive spore
forming rod
 Five
types designated A-E are
recognised according to enterotoxin
produced
 C. perfringens type A causes the vast
majority of food poisoning out break.
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The disease, The disease is caused by
an enterotoxin that is released into
the gut when mother cells release
their spores.
 The sporulating cells are produced
from live vegetative ingested with
food
 Because live organisms are normally
required to be ingested to cause the
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 The
disease, some authors
consider this to be an infection.
 Incubation period: 6-24 hrs after
the ingestion of food.
 Infective dose: large numbers of
vegetative cells in a food are
required to produce food
poisoning, appro 8E/g>
Clostridium perfringens is found in
most soils and is consequently
present in dust.
 Many foods contain spores of the
organism, particularly animal carcases
that become contaminated during
slaughter.
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Most outbreaks have been associated
with meat or poultry that has been
boiled, stewed and then held at room
temperature or under warm conditions
or in bulk refrigerators in which
cooling is slow.