Salmonella enterica Final

Characterisitcs of Salmonella enterica

- Gram-negative opportunistic pathogen

- Rod-shaped, motile

- can live inside a host and in the environment

How is Salmonella enterica broad range

can infect humans, food animals, and pets/wild animals

What type of disease does Salmonella enterica give

foodborne gastroenteritis; frequently food-poisoning related

Typhoid Fever

S. Typhi causative agent

Typhoid serovars

Typhoid, Typhi, Paratyphi, Sendai

Host specificty of typhoid serovars

Human restricted

Disease of typhoid serovars

fever, abdominal pain, transient diarrhea or constipation, salmon-colored rash on trunk

Non-typhoid serovars

Typhimurium, enterditis

Host specificty of non-typhoid serovars

broad range

Disease of non-typhoid serovars

gastroenteritis: abdominal pain, vomiting, and inflammatory diarrhea

what do some non-typhoidal Salmonella (NTS) strains cause

bloodstream infections in some parts of the world; 20-25% lethal

How does chronic carriage of S. enterica persist in the body

- Infection without obvious symptoms

- Infection with symptoms

Commone resevoir of S. enterica

gallbladder

what serovars does persistance in the body occur with

typhoidal and non-typhoidal serovars

How can chronic carriage occur

- Bacteria can be shed from host and spread to others

- Antibiotic treatment cannot clear all bacteria from the body, which can cause recurrent infections

Typhoid Mary

A cook who carried typhoid fever and passed it on to many people in and around NYC since she was infected and was asymptomatic

longer term challenges of Salmonella infection

reactive arthritis, which is an inflammatory response that occurs usually after infection is cleared

Treatment of S. enterica

quinolone, macrolide, or cephalosporin classes

What is becoming a large problem with S. enterica

multi-drug and extensive drug resistance strains are becoming problematic

two species of Salmonella

- salmonella enterica with > 2600 serotypes

- salmonella bangori

What does salmonella enterica subspecies enterica infect

majority of cases in humans and domestic animals

model pathogen to understand infection

S. Typhimurium

salmonella enterica subspecies enterica examples

- S. typhimurium (broad specificity)

- S. typhi (humans only)

S. enterica serovar Typhimurium LT2 vs. S. enterica serovar Typhi CT18

- Typhimurium: circular chromosome, ORFs, < 40 pseudogenes

- Typhi: ciruclar chromosome, genes not ORFs, 204 pseudogenes

what does the presence of many pseudogenes in serovar Typhi indicate

they were important to ancestors but current serovars no longer need it

Salmonella pathogenicity islands

- which include genes important for survival in host

- suggests frequent gene acquisition through horizontal gene transfer

type III secretion systems (T3SS) encoded on SPI-1 and SPI-2

- SPI-1 T3SS: important for early infection

- SPI-2 T3SS: important for later stages of infection

these T3SSs secrete effector proteins to mediate infection

Pathogensis of Salmonella

Intracellular pathogen that resides in compartments called salmonella-containing vacuoles

effector characteristics for salmonella infection

- > 30 effectors produced

- secreted by two type III secretion systems (T3SSs)

route of entry for S. enterica infection

- survives low pH in the stomach

- In the intestinal epithelium: enters M cells & other epithelial cells

Gastroenteritis in the intestine

induce local inflammatory response

Systemic illness serotypes

enter macrophages and spread

SPI-1 T3SS characteristics

- turned on before infection

- predominantly involved in inducing pathogen uptake into SCV

SPI-2 T3SS characteristics

- turned on after uptake into SCV

- involved in promoting bacterial survival, replication and spread

when are effectors proteins secreted

it is an intricately times process where virulence factors are made when needed

how are effectors multifunctional

- have evolved multiple domains to target different host processes

- important in some cell types and not others

- function in multiple cell types and have different consequences

Salmonella Infection in Epithelial Cells (Non-phagocytic) mechanism

1. SPI-1 T3SS effectors induce invasion ruffle → bacterial uptake into SCV

2. Endocytic pathway begins to target SCVs

3. SPI-2 T3SS effectors secreted to promote bacterial survival & replication

4. Salmonella inhibits lysosomal pathway

5. SCVs migrate to the perinuclear region and multiply near Golgi

6. Effectors induce the formation of tubules (Salmonella-induced tubules (SITs)) that extend to the cell periphery

7. SCVs migrate along microtubules to cell periphery

How do we visualize a salmonella infection

- stain for both bacteria & host (SCV)

- often use antibodies to detect

- LAMP proteins are markers for SCV membrane

types of host cells and their function

- phagocytic: sample the env and uptake pathogens

- non phagocytic: dont take up pathogens/dont sample

How do SPI-1 T3SS Effectors Control Uptake into Non-phagocytic Host Cells

1. Turns on SPI-1 T3SS to secrete these effectors into

the host before infection

2. Effectors function by mimicking host regulatory

proteins that control uptake → turn on host uptake machinery

How do effectors behave in non-phagocytic cells

control both turning on ruffling and subsequently turning it off

how is uptake from the extracellular environment occur

It is controlled by the Ras superfamily of small GTPases where the rho family contribute to phagocytosis

what do Rho GTPases act as

the plasma membrane

how do Rho GTPases act when active

host binding partner proteins bind the Rho and cause actin polymerization, which causes the PM to ruffle outward to mediate pathogen uptake

what is important for pathogen uptake

ruffling must be deactivated in order for uptake to be completed

4 Salmonella effectors that control uptake

- SopB, SopE, SopE2 turn on localized ruffling to promote uptake by mimicking GEFs

- SptP turns off ruffling to complete uptake by mimicking GAP

Why do both SPI-1 and SPI-2 T3SS Effectors suppress autophagy

it is the host cell response to infection and xenophagy would get rid of the pathogen

What does SpoF do

suppresses autophagy at the initiation (induction) stage

How does SpoF suppress autophagy

it is an enzyme that ADP ribosylates V-ATPase which disupts interaction with Atg6L1 complex

SPI-2 T3SS effectors (important for bacterial positioning)

SseF, SseG, SifA, PipB2

Why do does SCV go to the perinuclear region during intermediate infection

Thought to bring the pathogen in proximity to Golgi for nutrient acquisition

Why do does SCV go to the cell periphery region during late infection

bring the pathogen in proximity to the plasma membrane for cell-to-cell spread

What do the effectors for bacterial positions so: SseF and SseG

help tether the SCV to Golgi

Trafficking (movement) of intracellular compartments utilize

- a compartment

- a motor protein

- microtubule

motor proteins used to transport cargo in the cell

kinesin and dynein

which way does kinesin move compartments

towards the cell periphery

which way does dyenin move compartments

towards the nucleus

how does a cell get compartment specificity

use regulatory proteins to control trafficking

what do adaptor proteins do

bind to molecular motors to conjugate compartments to the microtubules

what do SifA and PipB2 do

manipulate host trafficking to control the positioning of the SCV

How does SifA act during intermediate infection

SifA binds dynein adapter complex BLOC-2 → uses it to maintain perinuclear positioning of SCVs

How does PipB2 behave in late stages of infection

PipB2 moves compartments to the cell periphery, causing LAMP2+ compartments to move there from the nucleus

How does PipB2 & SifA manipulate host microtubules

control the movement of bacteria & host organelles

what does PipB2 interact with

interacts with

light chain of kinesin

What does SifA interact with

a multifunctional effector, also contributes by

binding to the adapter

protein SKIP

Possible roles of tubule formation

- Nutrient acquisition

- Cell-to-cell spread

How to tubules (SITs) act in the host cell

induced by Salmonella; extend throughout the host cell along microtubules

Effectors important for Salmonella-induced tubule (SIT) formation

- SifA, PipB2, and SopD2: Manipulation of host microtubule function

- SseF and SseG: Tethering to Golgi (anchor point)

- SteA: unknown

What effectors from SPI-2 T3SS suppress autophagy later during infection

SseF and SseG

when do SseF and SseG target autophagy

at the induction stage

what does the ULK1 complex initiate

general autophagy

what does GTPase Rab1 regulate

ULK1 complex; its role is to recruit ULK1 to the complex and Rab1 is activated by a GEF called TRAPPIII

How do effectors PipA, GogA & GtgA behave in relation to the NF-kB pathway

- they are proteases that cleave TFs p65 & RelB which inhibit gene expression

- this causes not activation of the immune response in the cells

Adaptive Immune Response:

Dendritic cells

capture, degrade, and present antigens to T cells to activate

How do SPI-2 T3SS Effectors Suppress Antigen Presentation in Dendritic Cells

- antigens in compartments must traffic along microtubules to get to cell periphery

- disruption of normal trafficking is likely to impair loading of peptides on MHC-II

What do Salmonella SPI-2 effectors suppress

antigen presentation in dendritic cells by inhibiting loading of MHC-II

Five effectors known to manipulate microtubule-based trafficking of intracellular compartments:

SifA, PipB2, SopD2, SseF and SseG

what is present in all salmonella strains

SPI-1 T3SS with SPI-1 effectors from pathogenicity islands acquired earlier

What does S. bongori have that S. enterica does not

SPI-22 (T6SS)

What does S. enterica have that S. bongori does not

- SPI-2 T3SS

- SPI-2 effectors

How did S. Typhi become human specific?

Functional loss of almost half of effectors (pseudogenes) which could be responsible for the inability to survive in other hosts

How can other salmonella infect other mammals

use GtgE degrades Rab32 to suppress BLOC-3 Complex function

what is another effector is also involved in targeting Rab32 (non human example)

SopD2 also targets Rab32 to suppress its function; SopD2 and GtgE work together to target Rab32

How Does SopD2 Target Rab32?

SopD2 is a GAP that hydrolyzes GTP to inactivate Rab32

what is Rab32 important for

host defense against bacterial pathogens; trafficking of antimicrobial cargo

pathway important in many hosts, except humans

Most serovars of Salmonella enterica have functional effectors GtgE & SopD2, what do they do in a broad amount of hosts

inactivate Rab32

Where can S. Typhi survive

can only survive in humans, where Rab32 is not essential

Salmonella Typhi where GtgE & SopD2 are pseudogenes

- cannot inactivate Rab32

- bacteria cannot survive in non-human hosts

How has S. Typhi Has Evolved Specialized Virulence Factors to Target Humans

through Vi antigen and Typhoid toxin

What is the Vi antigen derived from

- horizontal gene transfer since it is not in S. Typhimurium or S. Paratyphi genomes

what does the Vi antigen form

polysaccharide capsule (viaB gene locus)

What does the Vi antigen do

- protection against neutrophil & phagocytic respiratory burst

What does S. Paratyphi have instead of Vi antigen

a very long O-antigen chains on LPS

What is typhoid toxin unique to

to S. Typhi and S. Paratyphi

when are typhoid toxins secreted

after the pathogen is taken into the cell

AB toxin family

What do typhoid toxins target

human cells specifically by recognizing surface glycoprotein sialoglycans with acetyl neuraminic acid termini

exotoxin of typhoid toxin

CtdB

what does CtdB do

deoxyribonuclease, causes DNA damage; arrests in G2/M phase of cell cycle