Bacterial Intoxications Flashcards
Foodborne intoxication
Caused by consumption of food containing toxins produced by micro-‐organisms
• Toxins cause disease/illness
• Live micro-‐organisms do not need to be present in
the food at the time of consumption
• High numbers of bacteria required to produce illness
• Includes:
– Clostridium botulinum
– Staphylococcus aureus
– Bacillus cereus
Foodborne infections
Caused by consump2on of food containing live disease
causing micro-organisms: pathogenic bacteria or viruses
• Food serves as a carrier for infec2on
• Growth of micro-‐organism in food may not be necessary but increases chances of illness
• Infec2ous dose varies – may be quite small
• Examples:
Salmonella, Campylobacter, Escherichia coli,
Vibrio, viruses
Food toxicoinfec2on
Combina2on of food intoxica2on and food infec2on
• Micro-‐organism grows to very high numbers in the
food and con2nues to grow in gut where it produces
a toxin
– Clostridium perfringens
Bacterial Toxigenesis
Ability to produce toxins
• Endotoxins – Cell-associated lipopolysaccharide (LPS) toxins
[Gram nega2ve bacteria]
• Exotoxins – Extracellular protein diffusible toxins
Endotoxins vs Exotoxins
8
Clostridium botulinum
Gram-‐posi2ve rod
• Strict anaerobe
• Spore forming, motile
• Found in range of habitats including soil and marine
environments
• Common in some raw foods such as fish and has been
isolated from fruit and vegetables
Diseases caused by C. botulinum
- Wound botulism – rare, wounds infected with C. botulinum which then produce toxin.
• Infant botulism – Ingested C. botulinum spores (syrup
and honey) – germinate and grow in infant gut (early
stages of weaning) producing toxin
– Constipation followed by progressive flaccid paralyis
– Common in US
• Foodborne botulism – Inges2on of food contaminated
with botulinum toxin
Botulinum neurotoxin
it’s a protein
One of the most potent biological toxins known
Mechanism of Botulinum neurotoxin
Binds to nerve ending at nerve-‐ muscle junc2on
– Blocks the release of acetylcholine responsible for
transmission of s2muli
– Produces flaccid paralysis
• 7 immunologically dis2nct toxin serotypes
A, B, C, D, E, F and G
Foodborne botulism
when it occurs?
Incubation period
- Occurs after inges2on of food containing the neurotoxin
* Incuba2on period 12-‐72hours
Symptoms of Foodborne botulism
– Nausea, vomi2ng, fa2gue, dizziness and headaches;
dryness of skin, mouth and throat, cons2pa2on, paralysis
of muscles, double-‐vision
– Finally respiratory failure due to respiratory paralysis which may lead to death by asphyxiation
Fatality rates of Foodborne botulism
60% - before 1949
now- ~10%
Treatment of Foodborne botulism
alkaline stomach washing to remove any toxin in stomach (neurotoxin inactivated by alkali)
• Intravenous toxin specific or polyvalent anti‐toxin to
neutralise circula2ng toxin
Disease causing strains of C. botulinum
Strains of C. botulinum can be divided into four func2onal groups based on shared metabolic or phenotypic characteris2cs
• Group I: Proteoly2c. Produce toxins A, B or F
(A and B most important)
– most commonly associated with canned foods
• Group II: Non-‐proteoly2c. Produce toxins B, E, or F
(type E most important in botulism caused by fish products)
• Group III: Non-‐proteoly2c and produce toxins C or D
• Group IV: Produce toxin G
Group I and II – most common foodborne causes of botulism
C. Botulinum Group I
Charateristics, growth temp, toxic dose, resistant to pH, spore forming?
• Proteoly2c – breakdown protein in food producing
rancid and cheesy odour
• Highly potent neurotoxin (10 ng toxic to adults)
• Mesophilic
• Do not grow at refrigera2on temperatures
• Spores are more resistant to heat than other groups
- problems where heat treatment is relied upon for microbiological safety of foods
• Not par2cularly resistant to pH with no growth below
pH 4.7 or 4.0 in protec2ve, high protein foods
C. Botulinum Group I - Associated foods in US & EU
• United States
– Home-‐canned foods with low-‐acid contents most
frequent source of infec2on
– Spores survive inadequate cooking and canning process, germinate, reproduce and produce neurotoxin
in the anaerobic environment of food
• Europe
– Inadequate home curing of meats
Environmental factors that promote the growth of C. Botulinum Group I in foods
- Absence of oxygen
- pH greater than 4.6
- Warm storage conditions e.g. cans kept at room temp
- High moisture content
- Lack of competing bacterial microflora in food
C. Botulinum Group II
Charateristics, growth temp, toxic dose, resistant to pH, spore forming?
• Non-‐proteoly2c
• Psychrotrophic
• Can grow and produce toxin at ~ 3 °C
• Spores of Group II are less heat resistant – D value for
Group II is 0.6 to 3.3 mins at 80°C
• Group II are more sensi2ve to salt – No growth in presence of 5% salt compared to no growth at 10% for
Group I strains
• Most common Group II strain is C. botulinum type E
C. Botulinum Group II - Associated foods
• Fish and uncooked fish products (especially psychrotrophic Type E strain)
• Smoked, cured or vacuum packed fish, home fermented fish or marine mammal meat products
• Increased consumer demand for ready-to- eat foods
but with reduced preserva2ves– Such foods often vacuum packed and rely on refrigera2on
• Safety issues arise upon temperature abuse
C. Botulinum Type E strain pose serious risk in
foods, such as?
minimally processed, vacuum packed fish as it can grow
slowly and produce toxin at 3°C
Control of C. Botulinum Group i & II
No means of preventing or controlling contamination
of foods by C. botulinum
• Food processing assumes spores are present and
applies process condi2ons and preserva2ves
to kill spores and/or prevent their growth and toxin
produc2on
• Thermal inac2va2on – most effec2ve
• Group I strains – poten2al safety problem in canned foods – inac2vated by hea2ng to 116-‐121°C at 0.68 to
0.97 atm for 20-‐100 minutes
• Excessive hea2ng not always op2on–may have undesirable effects on food taste and texture
factors that control C. botulinum growth and toxin produc2on
• pH – less than 4 ensures no growth of Group I in canned foods. pH 5 will prevent growth of Group II
• Water ac2vity of 0.94 inhibits growth of Group I.
0.975 inhibits growth of Group II
• Salt concentra2on of 10% inhibits Group I.
Group II inhibited by 5% salt concentra2on
• Nitrite (at levels greater than 100 mg per kg of food)
inhibits C. botulinum strains. Inhibi2on increases with
acidity
• Temperature of storage
