Lecture 7- Salmonella Enterica Flashcards
Salmonella enterica
- Gram-negative, non-sporulating, facultative anaerobic motile rods
- mesophilic, optimum growth temperature between 35 C and 37 C, generally have growth rate of 5-54C
- easily killed by pasteurization, sensitive to low pH, do not multiply below Aw 0.94
- heat resistance increases as the water activity decreases
- type of solutes present in the food influence heat resistance
- cells can survive under frozen or dried states for a long time
The genus of Salmonella
- the genus has 2 species
- grouped into 6 subspecies
Which salmonella is most commonly associated with foodborne illness
Serovars Typhimurium and Enteritidis
Which species causes illness in humans?
Salmonella enterica
Which food had the most outbreaks in salmonella?
Beef
Symptoms of Salmonella
- occur 8-72 hours after ingestion
- illness is self-limiting, non-bloody diarrhea, and abdominal pain
- symptoms generally resolve within 5 days
Treatment of Salmonella
Supportive treatment such as fluid and electrolyte replacement
Would you recommend antibiotic treatment for salmonella?
- Antibiotics prolong carrier state and increase AMR so they are generally not used
- Antibiotic Resistance is common
How does infection of salmonella in human occur?
- Salmonella exploits phagocytic intestinal cells, (like antigen-sampling M cell and dendritic cells), but also forces its own uptake into non-phagocytic epithelial cells Salmonella adheres to intestinal cells via fimbriae.
- once across the epithelium, salmonella can efficiently invade further epithelial cells from the basolateral side
- Salmonella remains localized to intestinal tissues, where the host’s inflammatory response to the invading pathogen is responsible for the symptoms of gastroenteritis
- during gastroenteritis, only a small proportion of the ingested bacteria invade the epithelium in this manner
- most remain in the lumen of the intestine, where they gain a selective advantage over the resident microbiota d/t host’s inflammatory response to the small invading sub-population
- in the immunocompromised, immune system may not be able to fight back, leads to systemic spread and bacteraemia can occur
Salmonella Pathogenicity Islands (SPIs)
Contain the virulence factors that Salmonella require during infection
- not all strains have the same SPIs
Virulence Factors (Ingestion) of Salmonella
- after ingestion Salmonella activates its acid tolerance response (ATR) to maintain intracellular pH in the acidic stomach
- Motility increases the chance of encountering the epithelium, Salmonella strains express functional flagella
Virulence Factors (Adhesion) of Salmonella
- Salmonella adheres to intestinal cells Salmonella cells attach to the intestinal epithelium by means of adhesins, such as those encoded within SPI-3 and SPI-4
- SPI-3 encodes MisL which binds to the fibronectin on epithelial cells, it also encodes MgtCB which is involved in intramacrophage survival
- SPI-4 contains only 6 ORFs arranged in a single operon It encodes SiiE which mediates attachment to epithelial cells, although its receptor is unknowns
Virulence Factors (Invasion) of Salmonella
- SPI-1 encodes a type 3 secretion system (T3SS) that delivers a cohort of virulence effector PRO into host cells
- effectors both drive the forced uptake of the pathogen by non-phagocytic cells, and also manipulate host cell signaling pathways, especially those involved in the inflammatory response
- while the biochemical activities of the entry effectors are well-characterized, their contributions to the invasion process are multi-faceted and only beginning to be fully understood
- SPI1-delivered effectors induce rearrangements of the host cell actin cytoskeleton, leading to the production of large surface protrusions termed membrane ruffles
- Ruffles eventually engulf the pathogen into large vesicles called Salmonella containing vacuoles (SCV)
- SCV hangs out near the golgi apparatus to intercept vesicles and obtain nutrients
What happens if you get salmonella and you are an immuno -compromised individual?
the Salmonella containing vacuoles can migrate to the basolateral side of the intestine and have direct blood access leading to a systemic infection
What is the pathology behind getting diarrhea from salmonella?
- Host responses and inflammation d/t bacterial invasion of the intestinal cells, caused by the immune system leads to diarrhea
- tight junction disruption
- Salmonella regulates actin filament dynamics to induce membrane ruffling
- four effectors used to disrupt tight junction: SipA, SopB, SopE, SopE2
