Evolution of enteric pathogens - PowerPoint PPT Presentation

Loading...

PPT – Evolution of enteric pathogens PowerPoint presentation | free to view - id: 4d061-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Evolution of enteric pathogens

Description:

SPI-5 contains 6 genes, 4 of which are required for enteritis in a calf model ... Unlike 'typical' E.coli, Shigella can't utilize lactose, mannitol are non-motile. ... – PowerPoint PPT presentation

Number of Views:43
Avg rating:3.0/5.0
Slides: 15
Provided by: maxtep
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Evolution of enteric pathogens


1
Evolution of enteric pathogens
2
family Enterobacteriacea
  • Genera
  • Human, animal pathogens
  • Salmonella, Yersinia, Aeromonas, E.coli/Shigella
  • Commensals/symbionts of animals
  • E.coli, Citrobacter
  • Plant pathogens
  • Erwinia
  • Environmental bacteria
  • Aeromonas, Klebsiella
  • Why so different?
  • Links to plant-related past?
  • Most grow on plant-derived sugars
  • Salmonella, E.coli cannot break down pectin.
    Yersinia, Klebsiella can

3
Evolution of Salmonella
  • Serovars are differentiated based on antigens
  • O polysaccharide antigen
  • H1, H2 flagella
  • 2,501 serovars are recognized
  • Some (sv Typhimurium, Newport) have a broad host
    range
  • Gallinarum and Pullorum --gt chickens (fowl
    typhoid)
  • Typhi, Parathyphi --gt primates (typhoid fever)
  • Cholerasuis --gt pigs (pig paratyphoid)
  • Dublin --gt cattle (bacteremia)
  • Other svs are host-adapted
  • Not all serovars are virulent
  • Sv Bongori
  • Sv Sophia
  • Common in chickens in Australia, not known to
    have caused disease in humans
  • All Salmonella have pathogenicity islands (SPIs)

4
SPIs
  • SPIs Salmonella pathogenicity islands. Absent
    in E.coli
  • SPI-1 carries genes involved in epithelial cell
    invasion. 40-kb, chromosomal
  • mutants are virulent only if delivered by direct
    injection
  • SPI-2 required for intracellular survival during
    infection
  • even when injected, mutants are not fully
    virulent
  • SPI-3 consists of 10 genes required for Mg2
    acquisition and growth in macrophages.
  • Present in some serovars, lost from others
  • SPI-4 carries 18 genes involved in survival
    within macrophages
  • SPI-5 contains 6 genes, 4 of which are required
    for enteritis in a calf model

5
Evolution of Salmonella relatedness of subspecies
Relatedness tree is based on the relatedness of
DNA sequences of multiple genes (loci)
I
major pathogens
enterocolitis, enteric fever
VI
II
IIIb
SPI-2
Gain of SPI-1
IV
VII
IIIa
S. bongori
V
Typically non-pathogenic
6
Evolution of Salmonella relatedness of subspecies
I differs from V by 8, E.coli from S. enterica
by 15 I and V diverged 65-75 mln yrs
ago Salmonella and E.coli diverged 120 mln yrs ago
I
major pathogens
enterocolitis, enteric fever
VI
II
IIIb
SPI-2
Gain of SPI-1
IV
VII
IIIa
S. bongori
V
Typically non-pathogenic
7
Evolution of virulence in E.coli
  • Normally a commensal in human gut
  • occupies large intestine and lower small
    intestine
  • the only gut inhabitant using oxygen and thus
    maintains anaerobiosis
  • virulent and commensal strains do not cluster
    separately (i.e. many commensal strains have
    closely related pathogens)
  • some E.coli sv are closely related to different
    Shigella sp

8
Virulent E.coli strains
  • Enterotoxigenic
  • plasmid-borne genes for enterotoxins
  • adhesin pili
  • a non-invasive pathogenic E.coli
  • Enteropathogenic.
  • carry LEE island encoding proteins involved in
    attachment, a protein injection system (Type 3)
  • EAF plasmid with genes for adherence
  • Enterohemorrhagic
  • LEE island carries a phage-encoded Shiga toxin
  • virulence EHEC plasmid
  • Enteroaggregative
  • Enteroinvasive (include Shigella)
  • carry pINV
  • Unlike typical E.coli, Shigella cant utilize
    lactose, mannitol are non-motile.
  • Most enteroinvasive E.coli have the same
    deficiencies
  • Uropathogenic

9
EHEC O157H7
  • Discovered in the 1980s
  • Common in cattle.
  • commensal in cattle
  • pathogen in humans
  • Virulence factors
  • LEE
  • stx (Shiga toxin) and EHEC plasmid are possibly
    recent acquisitions
  • Evolution
  • gained O157 by recombination,
  • then split into two lineages sorbital-negative
    and b-glucuronidase negative
  • both major lineages carry phage-encoded stx genes

10
How related are E. coli?
UPEC
Commensal
3
21
7.6
includes 247 islands gt1kB
39
3
7
17
includes 108 islands gt1kB
EHEC
Loosely based on Lan and Reeves, 2006
11
Evolution of Yersinia
  • 11 species, only 3 are significant pathogens
  • Y. pseudotuberculosis, Y. enterocolitica
  • food-, waterborne pathogens that cause
    gastroenterocolitis
  • share virulence factors not found in
    non-pathogenic isolates
  • escape human immune system thanks to an outer
    membrane protein encoded by a 70-kB virulence
    plasmid
  • carry virulence determinants (production of
    siderophore) on a High Pathogenicity Island (HPI)
  • HPI is highly mobile and was found in other
    enterics
  • chromosomally encoded virulence factors also
    present

12
Evolution of Yersinia
  • Y. pestis
  • causes plague
  • transmitted by fleas
  • a clone of Y. pseudotuberculosis.
    Indistinguishable by common methods
  • distinct from Y. pseudotuberculosis in its
    virulence strategy
  • colonizes flea gut.
  • genes on pFra plasmid are involved
  • is transmitted to a host through a bite
  • reverse blood flow during biting due to partial
    blockage of the fleas proventriculus. Blood
    meal is regurgitated. hemin storage genes are
    found in both Y. pestis and Y.
    pseudotuberculosis
  • disseminates in blood from the infection site

13
Population genetics of enterics
  • All bacterial populations are clonal to some
    extent
  • Recombination
  • important source of variation
  • for enterics, recombination appears more
    important then mutation
  • frequency differs for different species
  • Neisseria -- frequent, Salmonella -- rare
  • Through recombination clones adapt to specific
    niches

14
Conclusions
  • Many virulence determinants are carried on mobile
    genetic elements
  • Pathogenicity islands, virulence plasmids are
    shared between clones and species
  • Surface antigen polymorphism
  • O antigen is the main target for immune system
    and phages (high selective pressure)
  • Gene decay
  • Genes mutate, and loss of function is OK
  • e.g. Shigella is non-motile, cant utilize
    lactose or decarboxylate lysine.
  • Occupies a different niche (inside a eukaryotic
    cell) than commensal E.coli (in the gut of
    mammals where lactose is found). Making flagella
    is expensive, flagella is also an antigen
About PowerShow.com