listeria Flashcards
listeria monocytogenes
- gram-positive, facultatively anaerobic, rod-shaped (can respire aerobically + anaerobically)
- ubiquitous
- increasingly recognised as a serious public health problem
- large outbreak of foodborne listeriosis in Canada in 1981 was key observation
outbreak of foodborne listeriosis in Canada in 1981
- the first conclusive evidence of foodborne transmission of L monocytogenes
- unusual number of cases of perinatal listeriosis
- coleslaw identified as likely route of transmission
- cabbage used to make coleslaw was contaminated with listeria from sheep manure
- during storage of cabbage over the winter listeria were able to multiply
listeriosis the disease
- rare but potentially life threatening disease
- in healthy adults mild infection with flu like symptoms or gastroenteritis
- susceptible individuals - long incubation period (10-70 days), influenza like symptoms due to bacteraemia
- pregnant women - possible neonatal infection and meningitis
-listeriosis is uncommon - estimated 1600 cases and 260 fatalaties in the US - mortality rate of 25-30%
2011 outbreak
US
- 147 illnesses, 33 deaths, 1 miscarriage involving 28 states consumption of cantaloupe from a single farm
1997 - italy
- 1556 cases, symptoms of fever and GI symptoms, corn and tuna salad served in a school cafeteria, 292 children hospitalised but no deaths
2019
south african
- 37 cases nationwide, processed meat sausage, 193 deaths
2000 - British Columbia
84 cases typically with febrile gastroenteritis assocated with soft cheese due to swallows defecating in a water cistern and contaminating cheese during curd washing step
listeria - food borne pathogen
- listeria grows at low temps, including refrigeration temps of below 5
- resistant to acid and high salt
- killed by cooking and pasteurisation
- foods most likely to be contaminated with listeria are:
- unpasteurised cheeses
- cold cuts of meat
- pates
- smoked fish
what happens when we ingest listeria - typical immunocompetence scenario
when food is contaminated and it’s ingested, It goes in gastrointestinal tract and colonises lower intestine.
- It’s very successful in that it’s got lots of adaptions
- it causes a febrile gastroenteritis.
- get fever. We’re getting that response by the body to a more invasive infection and we’re also getting gastroenteritis because the infection is localized to the GI tract.
- organisms can obviously be shed in the faeces and then that can return to the soil and contaminate that environment and ultimately potentially contaminate food again, so we’ve got this cycle.
what happens when we ingest listeria - condition known as pyrogranulomatous,
if we get a different scenario we can get translocation from the gut to the liver here and a Condition known as pyogranulomatous,
- inflammation in the liver and is often subclinical
- And then if we have a strong immune response, we’ll get that limited to these locations in the body and you get febrile gastroenteritis typically
But if we don’t have a strong immune response, then we can go on to get bacteraemia, so dissemination leading to septicemia and then to spread throughout the body.
listeria crossing barriers
- one of the Key properties is that the organism can cross barriers in the body
- listeria is able to cross the blood brain barrier and cause meningoencephalitis and meningitis
- It’s also able to cross the placenta leading to placentitis and abortion and neonatal septicemia.
. So once the immune system fails to control infection and limit it to the GI tract and the liver then you have these much more serious outcomes of infection and that explains why fatality rates are so high and
immunocompromised groups
virulence factors - attachment
- in this case for Listeria the advantages it wants to be taken up into a host cell.
So it produces virulence factors known as internalins and they are involved in uptake within the cell programmed by the bacterium
virelence factors - what happens when it is taken up into a vacuole
- Typically this event would lead to destruction of the bacteria as we get a lysosome forming a mature lysosome
- but that’s not what happens with listeria, we see a different approach to controlling uptake into a vacuole by a bacterial pathogen
- Listeria can lyse this vacuole, So it produces proteins that break down the vacuole and release the listeria in to the cytoplasmic niche now, which is an advantageous Niche because it’s protected from the immune system in large part.
- listeriolysin - lysis of the vacuole
virulence factors - movement
it uses host cell Machinery to propel its movements both within the cell and into adjacent cells
- and to do that It produces a protein called ActA
- this leads to is bumping up against the cell membrane
-It’s kind of random movement that’s directed by recruitment of actin
-That propels the bacterium into adjacent cells and we get uptake of the cell into a now double membrane vacuole within an adjacent cell
- So we’re getting spread through tissue.
virulence factors - breakdown of the double membrane vacuole
- Then we see Breakdown of the vacuole - this time It’s a double membrane vacuole, but that’s no problem for Listeria and then release into an adjacent cell where it can multiply again.
So we get localized multiplication typically within the gut and also in some cases dissemination elsewhere in the body,
