Salmonella Enterica: Infections and Virulence Factors

Salmonella enterica

Bacterial species causing various infections.

Serovars

Different strains of Salmonella enterica.

Typhimurium

Serovar associated with common Salmonella infections.

Typhi

Serovar causing typhoid fever.

Enteriditis

Serovar linked to egg-related infections.

Paratyphi

Serovar causing paratyphoid fever.

Salmonella infection

Requires high doses for successful infection.

Infection dose

1 million to 100 million bacteria needed.

Growth rate

Salmonella grows rapidly in suitable conditions.

Global cases

1.3 billion cases of Salmonella annually.

US infections

1.4 million Salmonella infections yearly.

Food-borne deaths

30% of food-borne disease deaths from Salmonella

Salmonellosis

• Diarrhea, stomach cramps, abdominal pain

• Starts 12-72 hours after ingestion

• Lasts 4-7 days

• Complications:  severe diarrhea, spread to blood stream (septic shock)

Symptoms onset

Symptoms start 12-72 hours post-ingestion.

Duration of illness

Lasts 4-7 days typically.

Typhoid fever

Caused by Salmonella enterica Typhi.

• Fever 

• Abdominal pain

• Transient diarrhea

• Rash

• 10-15% death rate

• Complications:  high fever, convulsions, delirium, ulceration of the intestinal mucosa

Typhoid symptoms

Includes fever, abdominal pain, and rash.

Death rate

10-15% death rate in untreated typhoid cases.

Virulence factors

• Multiple fimbriae (fim– for adherence)

• Type III secretion system:  injects proteins that increase membrane ruffling

• SipA– cause membrane ruffling; activate proteins that inhibit actin depolymerization

Sop and Sip

Proteins that rearrange host cytoskeleton.

Neutrophil chemotaxis

IL-8 attracts neutrophils to infection site.

Inflammation effects

Prostaglandins increase cAMP, causing diarrhea.

Mary Mallon

Famous asymptomatic carrier of typhoid fever.

• Mary Mallon

• Asymptomatic carrier of typhoid

• S. typhi in gall bladder

• Shed in feces

• Contaminated watr and food

Carrier status

Asymptomatic individuals can spread Salmonella.

Early Events

• Sop and Sip– rearrange cytoskeleton

• Turn on NF-κB

• Disruption of tight junctions

• IL-1 and IL-8 secreted

• Inflammation

Survival inside epithelial cells

• Phagosome fuses with lysosome

• Forms microtubule bundle around it

• Replicates inside

Inflammation and Gut Metabolism

• Inflammation converts thiosulfate to tetrathionate

• Salmonella uses tetrathionate as a final electron acceptor

• Outcompetes other gut bacteria

Neutrophil chemotaxis

• IL-8– cytokine that brings in
neutrophils
• PEEC– pathogen-elicited
epithelial chemoattractant
(secreted into lumen)

Inflammation and Diarrhea

• Prostaglandins increase cAMP levels

• Decreased absorption of Na+

• Increased Cl- secretion

• Water loss and diarrhea

Survival in macrophages

• Spv genes– necessary for survival in macrophages

• PagC— membrane protein that protects against toxic products of lysosomes