Biology of Salmonella Flashcards
What are the 2 main types of salmonella causing human disease?
typhoidal and non-typhoidal
What are the forms of typhoidal salmonella?
S.enterica typhi and S.paratyphi
Give an example of non-typhoidal salmonella?
S.eneterica typhimurium
How is salmonella typhi transmitted?
faecal-oral route
What is the difference between S.typhi and S.typhimurium in terms of human disease?
S.typhi is invasive whereas S.typhimurium is limited to the Gi tract
What is the pathway of disease in S.typhi?
orally igested, then travels to the stomach where most bacteria die but some survive to the gut where they are able to invade the invade the eptihlium of the small intensine and macropahges, undergo intracellular replication and spread through the blood to spleen and liver
How long does S.typhi stayin the gut?
10 days
When does S.typhi reach the small intestine after ingestion?
48 hours
What disease does S.typhimurium give in mice?
typhoid fever
What is the pathway of typhoid fever in mice?
invades macrophages; colonises peyers patches and mesenteric lymph nodes- intracellular replication in spleen and liver macropahges and restuls in fatal bacteraemia
How much of S.typhimurium genome is required for virulence?
3.5%
What are the areas of the genome that contains most of hte virulence genes called?
pathogenicity islands/islets
What virulence factors are required in the stomach for typimurium?
need acid tolerance as low pH
What virulence genes are used in stomach with typhimurium ?
fur, atr
What are the environmental stresses are present for typhimurium in the small intestine?
osmotic stress and anaeobiosis
What is the resposne to environmental pressure in the small intestine by typhimurium?
motility and adhesion (essentialyl escpe as fast as possible)
What virulence does typhimurium use in the small intestine for motility and adhesion?
flg; lpf; pef
What are the environmental pressures present for penetrating the eptihlium by typhimurium?
anaerobiosis and cell contact
Give examples of virulence genes used for epithelium penetration by typhimurium?
inv; spa
What are the environmental pressures present in the blood stream for typhimurium?
complement and antimicrobial peptides
What virulence genes does typhimurium use in the bloodstream?
rfb; rfc; rck; sap; htr
What are the environmental pressures present in the macrophage for typhimurium?
low pH and low magnesium
Give examples of virulence genes that typhimurium uses in the macropahges?
pag; SPI-2; spv
How does salmonella survive in the phagosome?
prevents fusion with lysosomes (similar to mycobacteria)
How is replication measured by fluorescence dilution?
cells are given constitutive green fluorescence protein and arabinose-inducible red fluorescent protein. bacteria are grown in arabinose then put into macrophages without arabinose, will turn progressively green with each replication
Why will non-replicating bacteria be able to avoid antibiotics?
generally they target actively replicating bacteria
What do the non-replicating bacteria form a reservoir for?
relapse of infection
What must non-replicating bacteria be able to do to be considered persisters?
be able to re-grow
What are the 2 types of T3SS that salmonella has?
SPI-1 and SPI-2
What is the function of SPI-1?
mediates invasion of host cells and intestinal secretory and inflammatory repsonses
What is the function of SPI-2?
bacterial replication and immune modulation
When SPI-1 expressed in salmonella?
when it is extracellular
When is SPI-2 expressed in salmonella?
when it is intracellular
How does SPI-1 work?
injects proteins into the cell which causes cell to engulf the bacteria by inducing actin polymerisation and membrane ruffling
What triggers expression of SPI-2?
acidic pH
What are the membrane targets of SPI-1 and SPI-2?
SPI-1: plasma membrane vs vaculoar
What happens to a bacteria that SPI-2 is mutated?
are unable to replicate
What are examples of some of the functions of some of the molecules released by SPI-2?
form microtubules; rearrange actin; cause cytotoxicity; prevents NFkB transcription
Who gets invasive disease by nontyphoidal salmonella?
HIV patients; malnourished; malaria patients
What is the commonest cause of bacterial bloodstream infection in africa?
salmonellae
What does host resistance to salmonella rely upon?
cell-mediated immunity: macrophages; PMNs; NK cells and complement killlin (induced by antibodies)
Why are HIV patients so susceptible to nontyphoidal salmonella?
have lots of LPS IgG which means antibodies are diverting complement from the OM- perhaps have higher as exposed to increased no. of bacteria so have higher LPS antibodies
What is the intracellular phagosomal compartment containing salmonella called?
salmonella-containing vacuole
What characterises the stage where SCV-enclosed bacteria replicate within the perinucelar area?
formation of ubulovesicular SCV strucutres- salmonella-induced filaments and the accumulation of F-actin around the bacterial phagosome-actin nest
Where is the cell does intracellular bacterial replication of salmonella take place?
next to the golgi apparatus in the perinuclear area
What is the function of SipC?
directly nucleates actin assembly leading to rapid filament growth and bundles actin filaments
Waht is the function of SipA?
not necessary for Salmonella entry but increases invasion efficiency by promoting actin poymerisation and mechanically stabilisies filaments by binding to F-actin
What is the function of SopE and SopE2?
do not directly bind actin but mimick cellular guanine exchange factors to activate Rho GTPases (Cdc42) that activate actin cytokseletal assmbly via Arp2/3
What are markers o late-endosome/lysosome?
Rab7; vacuolar ATPase and lysosomal membrnae gylcoproteins e.g LAMP1; mannose 6-phosphate receptor
What is the function of SipC?
prevents fusion of lysosome with SCV
What is the role of SopB?
diverts SCV trafficking from the endosomal maturation pathway by causing hte disappearance of late endosomal/lysosomal markers from the maturing SCV
What is thought to be the function of SCV being close to the golgi?
facilitate interception of endocytic and exocytic transport vesicles to obtain nutrients and/or membrane
What is thought to be the function of SseG and SseF?
form a function copmlex that tethers the SCV t othe golgi
What virulence factor is essential for Sif formation and maintenance of SCV integrity?
SifA
Aise from actin polymerisation, what else does stimulation og cdc42 by SopE/SopE2 and SopB cause?
Raf-1 dependent upregulation of Erk, Jnk and MAPK pathways resulting in AP-1 and NFkB upregulation–acute intestinal inflammation
What challenges the conventional view that SPI-1 effectors solely mediate salmonella invasion and SCV biogenesis and SPI-2 promote intracellular replication and systmic spread?
SipA; SopB all persistnet for hours after bacterial invasion and have key roles in SCV positioning and/or intracellular replication
How are salmonellae typically acquired?
oral ingestion of contaminated food or water; but also exposure to pet reptiles and amphibians
How do salmonella adhere to the apical surfaces of enterocytes?
using differnet fimbrial adhesins
What type of intesitinal apithelial cell do salmonellae preferentially enter?
microfold cells
What are microfold cells?
specialised epithelial cells that sample intestinal antigens through pinocytosis and transport them to lymphoid cells in the underlying peyers patches
What, in addition to the intestinal inflammatory repsonse to salmonella causes the induction of diarrhoea?
able to disrupt tight junctions which seal and the piethlial clel layer and resitrct the paracellular passage of ions, water nad immune cells
How does salmonella enter macrophages?
inducing macropinocytosis
What chemokine produced by the epithelial intestinal cells is thought to be important for the influx of PMNs?
IL-8
What is the function of the translocon?
involved in the translocation of effectors by formating a translocation pore into the host cellular membrnae
What suggests that SPI2 is also important in invasion of salmonella?
mutations can cause a significant reduction i nthe expression of several SPI-1 T3SS genes adn impair the abiility of hte bacterium to invade epithelial cells
What is interesting about the interdependence of SPI1 and SPI2?
the sequence information and genetic organisation of the 2 salmonella T3SSs as well as their phylogenetic distribtuion among saalmonella species indicate they were acquired indepently at differnet periods frmo different sources- therefore likley that selection pressure has led to cooperation
What happens when Rho GTPases are activated?
activation of WASP family members and recruitmnet of Actin-related protein-2/3 compelxes–stimulation of actin polymerisation and rearrangement into membrane ruffles
Which effector molecules are required for activating Rho GTPases?
SopE; SopE2 and SopB
What are the 2 effector proteins that further modulate the actin cytoskeleton after membrane ruffling for efficient bacterial uptake?
SipA and SipC
What are the 2 functions of SipC?
translocon and can nucleate and bundle actin
What is the overall function of SipA and SipC?
facilitate efficient bacterial uptake by directing spatial locatization of actin foci beneath the invading bacteria nd preventing disassembly of the S.typhimurium-induced actin structures
Aside from stimulating actin polymerisation and membrane ruffling, what other effect does stimulation of cdc42 by SopE, SopE2 and SopB have?
triggers several MAPK pathways resulting in AP-1 and NFkB activation; and the disruption of tight junction structure and function may occur by Rho family GTPase activation as well
Hoow does SopB stimulate cellular chloride secretion and fluid flux?
increases the intracellular conc. of D-myo-inositol tetrakisphosphate thourgh its inositol phosphatase activity
What is hte function of SptP?
GTP-ase activating protein activity on cdc42 which causes the actin cytoskeleton to regain its normal architecture; reversal of pro-inflammatory signalling cascade through its tyrosine phosphatase activity
What is the function of SspH1?
inhibits NFkB gene expression
What is the name for the vaculoar compartment that salmonellae intially inhabit in a cell?
spacious phagosome- formed by membrane ruffles
How does spacious phagosome form the SCV?
shrinks to form an adherent membrane around one or more bacteria, fuses with lysosomes and acidifies which is then SCV- contains LAMP-1
What does the presence or absence of different markers on the persistent SCV mean?
may indicate that they are variably detected rather than refelct whether or not he SCV has matured through a normal endocytic pathway
Give an example of salmonella responding to the acidic environment of the SCV?
surface remodelling of the protein, carbohydrate and membrane components of hte bacterial envelope which confer resistance to antimicrobial peptides and oxidative stress
Does salomella avoid phagolysosomal fusion?
controversial- several reports have shown they can survive once lysosome has fused with SCV- so unlikely, and studies have shown the vacuole acidifes, however this acdification may be delyaed
What is the best characterised saslmonella sensor of phagosome environment?
PhoQ sensor which responds to pH and binds to antimicrobial peptides, and promotes resistance to antimicrobial peptides
Why do salmonella undergo extensive bacterial surface remodelling after phagocytosis?
repress indicators of infection e.g SPI1 and flagellin and LPS structure
What are specific surface modifications that salmonella undergo after phagocytosis?
decrease the legnth of the O antigen; alteractions to the number of acyl chains in lipid A; changes in protein content of OM, IM and peptidoglycan
What is the O antigen?
the repeating carbohydrate polymer of LPS
What is thought to be the general role of SPI2 effectors?
promotes intracellular replication by altering host vesicular trafficking so that useful metabolic molecules are routed to the SCV
In which cells does SPI2 induce the formation of long filamentous structures- Sifs?
epithelial cells and IFNy primed macrophages
What marker is present on Sifs?
LAMP-1
What is the function of Sifs?
increase the size of SCV to accomodate bacterial replication during systemic infection and/or redirect nutrient rich organelles to the SCV
Waht effector is Sif formation reliant upon?
SifA
What is thought to be the role of SPI-2 effectors involved with actin polymerisation?
seem to decrease or remodel vaculoe assocaited actin polymerisation (VAP)- may be a period where actin removal is important, e.g to decrease inflam reponses or allow effectors to interact with memrbane surface
