Foodborne pathogens and mechanisms Flashcards
What are the three factors that we look at regarding microorganism interactions of food?
Intrinsic factors: Physico-chemical properties of the food itself.
Extrinsic factors: Environmental such as storage environment.
Implicit factors: the properties and interactions of the micro-organisms themselves when in the food material.
What are the three modes of food-borne illness?
There is infection, which is when the ingestion of viable cells causes microbial growth in the system.
The is Intoxication, which is where the microbes produce a toxin which affects the host regardless of microbial state
Lastly there is toxicoinfection, this is where the consumption of live cells causes an infection but still allows them to produce toxins.
What does Listeria monocytogenes cause? and where does it come from?
It causes Listeriosis, this is a rare severe infection that can be fatal. There is a invasive strain and a non ivasive strain.
It is typically found due to environmental factors such as dust, water or vegetation contamination. It can also be sourced from faeces.
What foods is Listeria found in?
Typically ready to eat products such as bagged salad, cold meat and pre-packaged fruits. It is also found in unpasteurised dairy products and by extensions processed milk based foods.
What are the characteristics of Listeria monocytogenes?
It is a poor competitor It is not heat resistant but it is psychrotropic Able to contaminate post process High salt tolerance (deli meat not safe) Forms a biofilm.
What are the symptoms of Listeria?
Nonivasive - It is a mild infection that gives fever, headaches, diarrhoea. The incubation period is a few days
Invasive - High mortality, fatal in at risk population can cause miscarriage. and gives fever, septicaemia and meningitis.
What is the pathogenesis of Listeria?
Intracellular Pathogen - It enters the cell and multiplies.
It can then cross cell membranes and keep multiplying.
Pathway is cell infection, crosses intestinal barrier, gets into lymph nodes, into spleen and then finally brain and placenta.
What is staphylococcus Aureus? Where is it found?
Staphylococcus is a intoxication microbe that is found in skin cells, nasal tracts and mucous glands. It is often found in kitchens and on food that has been handled with poor hygiene.
What are the characteristics of Staphylococcus?
It is a poor competitor
Has a high salt tolerance
It is tolerant to water activity of 0.83, however does not produce the toxin under 0.93
What are the symptoms of Staphylococcus?
It is a intoxicator, that works as a neurotoxin.
that causes vomiting, nausea, cramps, diarrhoea and headaches. it is self limiting and has a very short incubation time. It needs 10^5 CFU/g to produce enough toxin.
What is Bacillus cereus? Where is it found?
It is a spore forming bacteria, this means it converts from vegetative cells to spore forming cells in accordance to multiplication.
It is found in soil, water and plants. It can also be found in milk due udders being close to plant life.
In food the emetic version can be found in high starch products, where the diarrhoeal version can be found in proteinaceous mediums.
What are the characteristics of Bacillus cereus?
It is a spore/endospore that is hydrophobic and survives high heats.
It causes either Intoxication Emetic syndrome or Toxicoinfection Diarrhoeal syndrome.
What are the symptoms of Bacillus Cereus?
Emetic syndrome - causes nausea, vomiting and discomfort
Diarrhoeal syndrome - Causes Abdominal pain and watery diarrhoea.
What is the pathogenesis of Bacillus Cereus?
Emetic - The Cereulide toxin binds to and stimultaes the vagus nerve causes vomiting
Diarrhoeal - The Enterotoxin (toxicoinfection).
What is Clostriudium Perfringes? where is it found?
It is an Anaerobic, Gram Positive Rod toxin producing endospore that is widespread in the environment. There are two types. Type A, which causes food poisoning and gas gangrene and Type C which causes enteritis necroticans.
Is is found in Soil, Plants, water, human tract, animals and raw/processed food.
It is particularly good in proteinaceous materials such as meat, gravy and hotbox food.
