ID Flashcards
General features of E.Coli
A Gram-negative bacterium from the family
Enterobacteriaceae
• Most strains are motile via peritrichous
flagella
• Rod shaped (c. 2 µm long & 0.5 µm in
diameter)
• Facultative anaerobe
• Obtains energy by oxidation & reduction of
organic sources and ferments sugars
• Common inhabitant of the intestines of
warm-blooded animals and humans – almost
every sample grows it!
• Frequently a commensal but some variants
are adapted to cause disease
What is commensals, pathogens and opportunistic and which one is E.Coli
Commensals are microorganisms that coexist with their hosts -’true’
commensals have a mutually beneficial symbiotic relationship.
• Pathogens are equipped with genes and gene products they use to cause disease
• Opportunists are commensals enabled
to cause disease given an opportunity (ex. immune suppression, disruption of microbiome, previous antibiotics)
E.Coli can be all three
What does ubiquitous mean
Found everywhere
E.Coli is ubiquitous in microbiomes of mammals and birds
Role of E.Coli
Biosynthesis of Vitamin K and colonization resistance
Bioindicator of faecal contamination
How is E.Coli versatile?
-commensale and carried by most vertebrate
-infections can be opportunistic or caused by specific phatotypes
Infections can be: intestinal or extra-intestinal
Three types of E.Coli enteric diseases
EPEC Enteropathogenic E. coli
STEP Shiga-toxin producing E. coli
EHEC Enterohaemorrhagic E. coli
Serotyping of
pathogenic
E. coli
> 170 O antigens (LPS)
50 H antigens (Flagella)
100 K antigens (Capsule)
Some well-known E. coli serotypes associated with human foodborne illnesses:
• E. coli O157:H7
• The “big six”: E. coli O26, O45, O103, O111, O121, and O145
E.Coli virulence factors
Adherence factors: enable bacteria to attach to host cells and colonize specific
niches.
• Motility factors: Such as flagella, which enable bacterial movement and can
contribute to adhesion.
• Toxins: divided in endotoxins (e.g. lipopolysaccharide or LPS) and exotoxins (e.g.
STEC/ETEC)
• Secretion systems: used by bacteria to deliver virulence factors into host cells
E.Coli Flagella, Pili and Fimbriae
All may act as adhesins -factors
that allow adhesion to host cells
& tissues in infection
• Flagella are also important for
motility
• Some fimbrial types are strongly
associated with increased
virulence e.g. F4 (K88) and F5
(K99) and F41 in neonatal
diarrhoea and F18 in oedema
disease.
Evolution of virulence &
the role of horizontal
gene transfer
Horizontal gene transfer is a major driver of
pathogenic diversity in E. coli
• Pathogenicity Islands (or smaller Islets)
are regions of DNA acquired into the
genome encoding for virulence factors
such as T3SS
• Bacteriophage transfer of toxin genes- Stx
or Shiga-like toxins
Other mechanism allowing bacteria to
exchange their genetic material:
transposition (integration of Mobile
Genetic Elements [MGE] into different parts
of the chromosome and plasmids).
ETEC
Neonatal diarrhoea in
many animal species,
post-weaning
diarrhoea in pigs,
septicaemia etc.
Enterotoxins important in ETEC: Secretory
diarrhoea e.g traveller’s diarrhoea in
humans or post weaning diarrhoea in pigs
• Important also the Shiga-like toxins (or
verotoxins, STEC/VTEC) Stx1 and Stx2 act on
blood vessels and endothelial cells
(encoded by bacteriophage) in oedema
disease of pigs
STEC/VTEC:
Stx-toxins in pigs -
oedema disease
Pigs are affected by O138, O139 & O141
serotypes- distinct from human/cattle STEC/
EHEC
• Usually hemolytic strains, producing Stx2e and
expressing F18 adhesins.
• Toxin targets endothelial cells and inhibits protein
synthesis > cell apoptosis & vascular damage.
• Clinical signs from oedema of face and eyelids
(sleepy appearance) to severe neurological
problems (usually no diarrhea)
• Fluid accumulation or lesions in a range of tissues
including intestinal, cardio-pulmonary system &
brain (angiopathy with vessels fibrinoid necrosis).
E. coli that carry Stx are referred to as
STEC
• EHEC are a class of STEC
• EHEC (e.g. O157:H7) are carried
asymptomatically in the intestine of
healthy ruminants
• Main source from undercooked beef or
faecal contamination of veg/fruit
• Toxin during human infection may cause
haemorrhagic diarrheoa and hemolytic
uremic syndrome (HUS).
E.Coli Secretion systems
Bacteria evolved to develop various protein
nanomachines, which allow bacterial effector
proteins to be exported through the Gram-
negative membranes.
What is the LEE
The LEE T3SS is a key virulence factor in EPEC and EHEC: Attaching and effacing E.Coli
LEE=Locus of enterocyte effacement is a pathogenicity island
Characteristics attaching and effacing lesions in which the bacteria are intimately adherent to the host enterocytes with marked rearrangement of the cytoskeleton
Pedestal formation, effacement of brush border microvilli, premature enterocyte exfoliation and villous distortion
LEE encodes for T3SS, intimin, translocated intimin receptor and effector proteins mediating actin rearrangement to form the pedestal
• Unlike Salmonella SPI1 T3SS which mediates cell invasion, E. coli LEE translocate its own receptor to enterocytes
• This allows tight adherence to intestinal surface (bacteria sitting on the pedestals)
• Significant enterocyte rearrangement with brush border destruction leading to reduction of intestinal absorption surface and malabsorptive diarrhea
• Typical histopathologic findings
Disease is usually the result of what
Disease is usually the result of
virulence factors working in
concert
• Most disease is a consequence of several
factors
Host and environmental risk
factors are crucial to disease
establishment
• Insufficient passive immunity in neonates
• Husbandry practices (diet, overcrowding etc)
• Transportation
• Concurrent disease, immunosuppression,
previous antimicrobial treatments
What is the 2011 German Beansprout E Coli outbreak
O104 is an EAEC that usually causes
persistent diarrhoea
• The ‘German’ isolate acquired Stx
toxin genes-so became
persistent and ‘nasty’
• As the infection was common in
women 15-50 -unusual as EHEC
(which is what it was initially
considered to be) is usually an
infection of children & elderly
• Cucumbers were wrongly identified as
the source-though did have EHEC
contamination
Extra-intestinal pathogenic E.
coli (ExPEC) –
intestinal escape artists
• ExPEC include neonatal meningitis (NMEC), sepsis
(SepEC), urinary tract (UPEC) and avian pathogenic
(APEC) pathotypes
• Have distinct but variable virulence factors involved
in invasion and systemic survival
• No distinct genotype or virulence factor associated
with pathotypes
• Genomic plasticity, global emergence of hyper-
virulent and antibiotic-resistant strains
• Pathogenic and opportunistic infections
APEC
• Important endemic disease associated with significant
economic losses (reduced meat and egg production,
with mortality up to 20% in young broiler outbreaks).
• Disease (‘avian colibacillosis’) by APEC pathotypes and
opportunistic commensals from microbiota
• APEC can affect all species of poultry in all types of
production systems
Most common infections:
o Broiler chickens: septicaemia, perihepatitis,
airsacculitis, pericarditis, coligranuloma, swollen head
syndrome
o Laying hens: egg peritonitis and salpingitis (salpingo-
peritonitis syndrome, SPS)
o Chicks: omphalitis, septicaemia, high mortality
o Turkeys: respiratory disease and osteomyelitis/arthritis
• Can act either as a primary
pathogen or secondary to viral (ex.
infectious bronchitis and avian
influenza) and Mycoplasma spp.
infections, immunosuppressive
disease (infectious bursal disease),
or environmental stresses
(overcrowding, poor hygiene etc)
• APEC utilizes different virulence
factors to cause disease in chickens,
primarily adhesins, invasins, iron
acquisition systems, and toxins.
• Recent studies suggest APEC as
potential foodborne disease in
humans with extra-intestinal
disease.
E.Coli in small animals
infections in dogs.
• UPEC (uropathogenic): most common cause of
urinary tract infection (35-69% of canine UTIs
caused by UPEC).
o Virulence factors include specialised fimbriae to
colonise and persist on urothelial cells, iron uptake systems, cytotoxins, uropathogenic-
specific proteins and others
o Global emergence of successful clones carrying high virulence and antimicrobial resistance (ex.
ST131)
o Identical genotypes identified in people and their pets (mutually transmitted)
• UPEC but also other strains also associated with:
o Pyometra – common uterine disease in bitches
o Prostatitis in male dogs
o Other opportunistic infections
E Coli and cattle mastitis
E. coli mastitis a particular problem in housed dairy cattle over winter
• Primary agents of environmental clinical
mastitis (‘coliform mastitis’)
• E. coli colonise the udder during calving and early lactation and during the dry period
• Intramammary infection elicits a strong inflammatory response (swelling of the udder, pain, pyrexia)
• Excessive response to LPS can lead to systemic
effects and endotoxic shock (toxic mastitis
General features of Salmonella
Another Gram negative rod from the
family Enterobacteriaceae
• Facultative anaerobe, most serovars are motile,
do not ferment lactose and produce H2S
• Discovered in 1885 in pigs - wrongly described
as the cause of “Hog Cholera”
• Complex taxonomy, based on the Kaufmann &
White scheme (somatic ‘O’, flagellar ‘H’ &
capsular ‘Vi’ antigens)
• Reservoir for salmonellae is the intestinal tract
of warm & cold-blooded animals (transient,
persistent or latent carriage in mammals, birds
and reptiles)
• Broad range of serovars, host and tissue
tropism and clinical manifestations
• Facultative intracellular pathogen
Salmonella Phage Typing
for example. S. typhimurium DT104, multidrug-resistant food-
borne infection or acquired through animal and environmental
direct/indirect contact.
Genus: Salmonella
Species: S.enterica or S.bongori
Subspecies: S.enterica-> enterica I, salamaeII, arizonaIIIa diarizona IIIb houtneae IV indica Vi
S.bongori-> subsp V
Why is Salmonella important
01
02
Major foodborne
zoonoses (covered
in Veterinary Public
Health in 2nd and
3rd year)
Major cause of
enteritis in humans
and animals
03
Major cause of
systemic disease in
humans (Typhoid
fever) and animals
Veterinary significance of Salmonella
Subclinical carriage
and shedding in the
environment by many
domestic and wild
host species
In food-producing
animals, crucial
hazard of meat
contamination - pork,
poultry, beef
Vertical transmission
to eggs, foetus and
milk
Disease in food producing
animals (esp. cattle, pigs
and poultry) includes
enteritis and enterocolitis,
septicaemia, abortion and
other systemic disease
Enteric disease in
companion animals (horses
and dogs)
