Lecture 13: Shigella and Salmonella

T/F: E. coli, Shigella, and Salmonella are all closely related

True

T/F: Shigella is zoonotic

True

Shigellosis in humans is also known as….

Bacillary Dysentary

_______ are the most natural reservoir of Shigella

Humans

Shigella and E. coli are very similar bacterium, what two key features separate the two?

• Shigella can’t ferment lactose (E. coli can )

• Shigella is Non-motile (E. coli is motile)

What are the 2 Virulence factors of Shigella?

1. Invasion plasmid

2. Shiga Toxin (Stx)

Shigella possesses a Shiga Toxin (Stx) as a virulence factor. Another bacterium possesses a similar type of virulence factor, name that bacterium

• STEC (Shiga-Toxin producing E.coli) 

  • Stx1/Stx2

Shigella is spread ____-____, and has a very _____ infectivity

• Fecal-Oral

• High Infectivity (<10 bacteria can cause disease)

Where does Shigella replicate (Intracellular, Extracellular, Both)?

Intracellular

Shigella bacteria are limited to one part of the G.I tract, what part is it?

Colon

T/F: Salmonella shares the shame general features of Enterobacteriaceae

True

Does Salmonella replicate inside/outside/both the cell?

Both, it’s a facultative intracellular bacterium

You isolate a bacterium that could either be Shigella, E. coli, or Salmonella. After further testing you discover this bacterium produces Hydrogen Sulfide Gas (H2S), which type of bacteria is this most likely to be?

Salmonella it’s the only one that normally produces Hydrogen sulfide gas

In regards to Salmonella, what is the Vi antigen? Which strains of Salmonella is it found in?

• Vi Antigen

  • Virulence antigen, it is a virulence-associated capsular polysaccharide

• Typhi, Paratyphic C, and Dublin

All Salmonella are motile except for which 2 strands?

1. S. Pillorum

2. S. Gallinarum

What are the two species of Salmonella? How many subspecies of each?

1. S. enterica

   1. 6 Subspecies

2. S. bongori

Which type of Salmonella has the most serovars?

S. enterica subspecies enterica

The serovars of Salmonella denote the _______ and _______ that is associated with that particular type of Salmonella

Syndrome (Typhi for typhoid fever) and host specificity (S. Abortusovis or S. Abortusequi)

What are all the subcategories of Salmonella?

Genus → ______ → ________ → ________

Genus → species → subspecies → Serotype

T/F: When writing the Serotype of Salmonella, the first letter is Capitalized and the whole word is not italicized

True

Which 2 of these Salmonella serovars are Host Adapted (not host-restricted)?

• Typhi

• Dublin

• Paratyphyi

• Gallinarum

• Enteritidis

• Cholerasuis

• Abortusovis

1. Dublin

2. Cholerasuis

Host-adapted is when they are associated with one specific host species and cause severe disease in that species but are capable of infecting humans and other species accidentally

Most Salmonella serovars are _________ (Host-adapted/Non-host-adapted)

Nonhost-adapted (Generalists)

The Salmonella Dublin serotype infects _______

Cattle

What are the clinical signs of Salmonella Dublin?

• Acute/chronic diarrhea

• Septicemia

• Abortion

What are the 2 main Salmonella-specific virulence factors? What do they do?

1. SPI-1

   1. Invasion

2. SPI-2

   1. Intracellular surivial

SPI= Salmonella Pathogenicity Islands

What are the 5 steps of Salmonella Pathogeneicity?

1. Transmission

2. Attachment 

   1. Distal ileum and Colon

3. Invasion (SPI-1)

4. Inflammatory Signals (This step causes cell death and sloughing)

5. Phagocytosed by macrophages

6. Activation of SPI-2 allows for survival and multiplication within macrophages within the SCV (Salmonella containing vacuole)

7. Macrophages disseminate Salmonella systemically

When an animal is a carrier for Salmonella, where does this bacterium reside?

• Salmonella can remain dormant in the Liver or gall bladder

• It can reactivate and shed into the gut

Without ________ Salmonella cannot spread systemically through the body

Macrophages

Which virulence factor of Salmonella allows it to evade phagocytosis by Macrophages?

SPI-2

Other than avoiding phagocytosis by macrophages, how else does Salmonella evade the immune system?

1. Alteration in LPS chain lengths

2. Antigenic switching of flagella

   1. Changing between two flagellar antigens, making it harder for the immune system to detect it

   2. Flagella antigens H1 and H2

S. Gallinarum is host adapted to _______

Poultry

T/F: Salmonella Gallinarum is a reportable disease

True

Salmonella Enteritidis is a very important disease in chicken eggs as it can infect the outside and inside of the eggs (penetration of the bacteria through the egg shell) and spread diseases to humans. However, there is another way that it can infect the inside of the egg without penetrating the shell, what is it?

• Ser. Enteriditis phage type (PT) 4

  • Infection of the ovary and oviduct

  • Ser. Enteritidis PT 4 are already internally infected when laid

T/F: The gut microbiome of the animal plays no role in Salmonella infections

False, having a good microbiome can help prevent Salmonella infection by competitive exclusion

What is the name of the broth that is selective for Salmonella?

Rappaport Vassiliadis (RV) Broth

T/F: Salmonella infected macrophages are harder to treat with antibiotics and allow for the Salmonella to surivive in a “dormant“ state

True

T/F: Shigella is transmitted by fecal contamination of food and water

True

T/F: Dublin is a host adapted serovar of Salmonella

True

T/F: Salmonella Typhimurium is an example of a host-adapted Salmonella serovar

False

T/F: Salmonella carriers look healthy but can shed large numbers of Salmonella bacteria in their feces

True

T/F: Reptiles are not a risk for Salmonella infections in humans

False

T/F: Poultry eggs can be contaminated internally and externally with Salmonella Bacteria

True

T/F: Salmonella replicates inside macrophages

True

List the surface antigens that determine a serotype

• LPS (O antigens)

• Flagella (H-antigens)

• Capsular Antigens (Vi Antigens)

Summarize the pathogenesis of Salmonella in a few lines

Salmonella becomes latent in which organs?

Gall bladder and Liver

T/F: Salmonella is a facultative intracellular pathogen

True