GI 2 - salmonella Flashcards
(10 cards)
General features of Salmonella species
Gram-negative bacterium.
Most strains are motile via peritrichous flagella.
Rod shaped.
Facultative intracellular pathogen
(can survive inside + outside host cells).
Facultative anaerobes (can grow aerobically or anaerobically).
Two species of salmonella
Salmonella enterica
Salmonella bongori (found in reptiles)
Typhoidal salmonella
Causes Typhoid Fever.
Limited to humans only.
Sources: human-to-human only transmission. (limited to humans).
Incubation period: 7 – 21 days.
Vaccine: 3: 1) whole cell 2) oral attenuated 3) capsule-derived.
Includes S. Typhi and S. Paratyphi.
Non typhoidal salmonella
Self-limiting gastroenteritis in immunocompetent individuals. Food poisoning!
Sources: farm animals, pets, produce.
Incubation period: 6 – 72 h.
Usually non-invasive (except immunocompromised hosts), symptoms are inflammation driven (diarrhea, vomiting, cramps).
Vaccine: none.
Salmonella enterica - Transmission
Fecal-oral route (person-to-person) or contaminated/improperly cooked food/water.
Food: vegetables, chicken, pork, fruits, nuts, eggs, beef and sprouts.
Animals and their environments: Particularly reptiles (snakes, turtles, lizards), amphibians (frogs), birds (baby chicks) and pet food and
Mechanism of infection – Salmonella
Salmonella can achieve persistent infection in intestinal epithelial cells and phagocytic (e.g., macrophage) cells.
Can survive inside macrophage and replicate (limited immune response)!
Zipper: Salmonella uses a cellular receptor for invasion.
Trigger: Salmonella injects bacterial effectors (toxins) into the host cell.
Infection in humans: Salmonellosis
Salmonella enterica serovars cause >99.5% of human disease.
Incubation period of ca. 6 - 72 h after ingestion (infectious dose may be 100,000 organisms).
Small intestines colonised.
Inflammatory diarrhoea, sometimes haemorrhagic (bloody).
Fever, nausea, abdominal cramps & vomiting are common.
Usually self-limiting & symptoms typically last 2 - 7 days.
Enrichment & detection of Salmonella
Typically relies on collection of a faecal sample.
Enrichment media (Rappaport-Vassiliadis Soya (RVS) broth)
RVS Selects for Salmonella by:
A) Produces high osmotic pressure at a relatively low pH and is incubated at a high temp 40.5 – 42.5 ℃
B) Malachite green kills other bacteria but Salmonella can survive as it produces magnesium chloride.
Identification – API, PCR analysis from isolated DNA.
Serotyping based on (O: LPS; H: flagella) antigens.
Treatment of Salmonellosis
Generally self-limiting (the host eventually mounts an appropriate immune response).
Antibiotics can shorten the duration of symptoms if given early (or if infection is invasive).
e.g., ciprofloxacin, azithromycin, and third generation cephalosporins.
Dehydrated patients may require intravenous fluid & electrolyte therapy (infants and elderly).
prevention of salmonella
Carriers can shed Salmonella in their stool for months to years after the initial infection:
Good hygiene is vital to break the chain of transmission.
Salmonella can survive for hours – days on surfaces
