Salmonella spp. Flashcards
How many species are currently recognized in the genus Salmonella?
Two species:
* Salmonella enterica
* Salmonella bongori
How many subspecies does Salmonella enterica have?
Six subspecies:
* I
* II
* IIIa
* IIIb
* IV
* VI
What was Salmonella bongori previously classified as?
Subespecies V of Salmonella enterica
What are the general characteristics of Salmonella?
- Gram-negative bacilli
- Non-spore-forming
- Facultative anaerobe
What type of flagella do motile Salmonella possess?
Peritrichous flagella
T/F. Salmonella species ferment lactose.
False, most don´t
Which Salmonella serotype does not produce gas on sugar fermentation?
Salmonella typhi
What type of sample is preferred for Salmonella isolation?
Freshly passed stool
What are examples of low-selective media used for Salmonella isolation?
MacConkey agar and deoxycholate agar
What are examples of intermediate-selective media for Salmonella?
- Salmonella-shigella agar
- Xylose-lysine-deoxycholate agar
- Hektoen enteric agar
What selective chromogenic medium is used for Salmonella?
CHROMagar Salmonella
What are examples of highly selective media for Salmonella?
- Selenite with brilliant green
- Bismuth sulfite agar
What special medium is preferred for Salmonella Typhi?
Bismuth sulfite agar
What is the purpose of DNA-based syndrome panels in Salmonella detection?
Rapid identification of gastroenteritis causes
What methods can be used after primary isolation to confirm Salmonella?
- Commercial identification systems
- Screening media like TSI agar and lysine-iron agar
How do S. Typhi and S. Paratyphi differ from NTS (Non-Typhoidal Salmonella) in terms of reservoirs?
- S. Typhi and Paratyphi have human-only reservoirs
- NTS can be acquired from multiple animal reservoirs
What are the main transmission routes of NTS?
- Food: Eggs, poultry, undercooked ground meat, dairy
- Direct contact: with animals or their environment
- Contaminated water
Where does Salmonella commonly reside in food animals?
In the intestines
What are common sources of cross-contamination leading to sporadic salmonellosis?
- Raw poultry during food handling
- Poor hand hygiene
What fresh produce has been linked to recent Salmonella outbreaks?
- Papayas
- Cantaloupe
- Pistachios
- Cucumbers
- Alfalfa sprouts
- Bean sprouts
- Tomatoes
What manufactured food products have been linked to Salmonella infections?
- Milk and milk products
- Icea cream
- Powdered infant formula
How does Salmonella infection begin?
Through ingestion of contaminated food or water
What is the initial barrier to Salmonella colonization?
Gastric acidity
How do conditions that increase gastric pH affect Salmonella susceptibility?
They increase susceptibility
What adaptive response allows Salmonella to survive gastric acidity?
Acid tolerance response
What host antimicrobial factors does Salmonella need to evade in the intestinal lumen?
- Antimicrobial peptides
- Bile salts
- IgA
What physical barrier must Salmonella cross before reaching intestinal epithelial cells?
The protective mucous barrier
How does Salmonella adhere to intestinal epithelial cells?
By expressing distinct fimbriae that enable tight adherence
How does Salmonella invade intestinal epithelial cells?
Bacteria-mediated endocytosis
After salmonella adheres to the apical epithelial surface there’s a cytoskeletal rearrangement that leads to:
- Disrtuption of the epithelial brush border
- Induction of membrane ruffles that encoles bacteria in vesicles
What happens to Salmonella-containing vesicles after internalization?
Some vesicles transcytose to the basolateral membrane
What happens to the apical epithelial brush border after Salmonella invasion?
It is reconstitued
Whats the function of T3SS in salmonella?
- Bacteria-mediated endocytosis
- Intestinal epithelial invasion
This proteins promote membrane ruffling and Salmonella invasion by interacting with the actin cytoskeleton.
SipC and Sip A
This protein:
* Inserts into the host cell plasma membrane to facilitate translocation of additional virulence proteins.
* Nucleates actin polymerization.
* Stimulates actin filament bundling.
SipC
This protein:
* Enhances actin polymerization.
* Stabilizes actin filaments.
* Lowers the critical concentration required for polymerization.
SipA
What SPI-1 translocated proteins activate Rac1 and Cdc42 during Salmonella invasion?
SopE and SopE2
Proteins activated by SopE and SopE2.
Rac1 and Cdc42
What cellular effects result from SopE and SopE2 activation of Rho GTPases?
- Membrane ruffling
- Macropynocitosis
This protein:
* Acts as an inositol polyphosphatase.
* Stimulates Rho GTPases.
* Promotes membrane ruffling.
By inducing a secretory response in the intestinal epithelium salmonella triggers…
Neutrophil recruitment
This induces synthesis and polarized secretion of inflammatory mediators and neutrophil chemokines (e.g., IL-8).
Translocation of SPI-1 proteins
What effect does SopB accumulation have on the intestine?
Causes basal chloride secretion and increases fluid flux (diarrhea)
Which SPI-1 translocated proteins contribute to intestinal secretory and inflammatory responses?
SopA and SopD
Intestinal inflammation may also be induced by activation of which innate immune receptors?
- TLR4 by LPS
- TLR5 by flagellin
How does inflammation contribute to diarrhea in Salmonella infection?
Disrupts the epithelial barrier, leading to fluid secretion
This protein inactivates Rho GTPase signaling, reducing membrane ruffling and proinflammatory signaling.
SptP
This proteins help mantain host cell integrity and evade the immune response. They inhibit NF-κB activation.
SspH1 and AvrA
How does Salmonella generate energy in a microaerobic environment?
By using tetrathionate reductase complex
What converts thiosulfate into tetrathionate?
Neutrophil-derived reactive oxygen radicals
Why does tetrathionate respiration give Salmonella an advantage?
Allows Salmonella to outcompete commensal bacteria in the gut
Why are typhoidal salmonellae poor intestinal colonizers?
They lack tetrathionate respiration
How does Salmonella enter macrophages?
Through bacteria-mediated macropinocytosis or phagocytosis.
Why is Salmonella survival in macrophages important?
Enables dissemination and systemic disease
T/F. Salmonella can survive inside the phagolysosome.
True
Two-component regulatory system that helps Salmonella adapt to the intracellular environment (acidity).
PhoP/PhoQ
What bacterial modifications occur after PhoP/PhoQ activation?
- Changes in LPS structure
- Membrane modifications
- Repression of flagellin synthesis
What structure does S. Typhi synthesize for immune evasion?
Vi capsule
How does the Vi capsule protect S. Typhi?
Resists phagocytosis, complement killin, and LPS recognition
What advantage does the Vi capsule provide inside macrophages?
Promotes survivial within macrophages
What is the role of SPI-2 translocated proteins in Salmonella?
They alter phagosome trafficking to promote bacterial growth
Common manifestations of salmonella infection.
- Gastroenteritis
- Enteric fever
- Bacteremia and vascular infection
- Localized infections
- Chronic carrier state
What type of Salmonella causes acute gastroenteritis?
Nontyphoidal salmonella
What are the common symptoms of NTS gastroenteritis?
- Nausea
- Vomiting
- Diarrhea
What systemic symptoms can occur with NTS gastroenteritis?
- Fever
- Abdominal cramping
- Chills
- Headache
- Myalgias
What conditions can NTS gastroenteritis mimic?
- Pseudoapendicitis
- Inflammatory bowerl disease
- Toxic megacolon
Who is at high risk for severe NTS disease?
- Elderly
- Immunocompromised individuals
What long-term condition is linked to NTS gastroenteritis?
Irritable bowel syndrome
What bacteria cause enteric fever?
S.Typhi and S. Paratyphi
What is required for a definitive diagnosis of enteric fever?
Isolation of the bacteria from:
* Blood, bone marrow, or a sterile site
* Intestinal secretions
* Punch bipsy of rose spots
Faint salmon-colored lesions on the trunk, seen in week 1 of enteric fever.
Rose spots
What are the hallmark symptoms of enteric fever?
Fever and abdominal pain
T/F. Gastroenteritis caused by salmonella just needs fluid and electrolyte treatment. Antimicrobial treatment is not recommended.
True
Which organ is colonized by salmonella in the chronic carrier state?
Gallbladder
