Download The host from a pathogen`s point of view

Senior Freshman BY2209 Infection & Immunity
Lecture 2:
How pathogens
make you ill
Prof Jay Hinton, Microbiology Department
The host from a pathogen’s point of
view...
1
How we see the perils of the
outside world
Major barriers to infection are
skin & mucosal surfaces
2
Normal Flora can colonise...
●
●
●
●
●
●
●
●
Skin
N
Nose
Mouth
Throat
Vagina
Urethra
Gastrointestinal tract
Basically every mucosal surface…
 Except deep lungs
Bacteria live everywhere
SGM Archive
SGM Archive
● They are all over us!
Between toes
A cough
© SGM, 2005
3
Bacteria live everywhere
Ear wax
Sweaty socks
SG
GM Archive
SG
GM Archive
SG
GM Archive
● They are all over us!
Nasal secretion
© SGM, 2005
Bacterial distribution in the human GI tract
Oesophagus
Bacteria from ingested food
Duodenum 101-104 cfu/ml
Stomach
101-103 cfu/ml
The acidic stomach is
an excellent barrier that
prevents much
bacterial infection
Colon
109-1012 cfu/g faeces
109-1010 Bifidobacteria
103-105 Lactobacilli
Ileum 101-104 cfu/g faeces
.
4
How many friendly bacteria do you
have inside you?
● 1000 Trillion
 1000, 000, 000, 000, 000
● How many?
 One thousand million million
● How many?
y
 1 Kg
The Human-microbe relationships
● Microbes colonize the human host
 Either as members of the normal flora in harmony
with the host
 Or subverting host defenses and causing disease
● Few microbes able to invade tissues, produce toxic
substances, or inflict noticeable damage
● That’s lucky!
 Considering that microbial cells living on the
human body, our Normal Flora, outnumber our own
cells by 100-fold
● Pathogens...
 The minority of microorganisms
 Can cause us harm
5
The GI tract
is a harsh
environment
37OC
p 2
pH
(aerobic)
pH 7,
anaerobic,
Digestive enzymes
Normal flora
(1000 species)
The GI tract
is a harsh
environment
6
Useful Terms - Infection & Immunity
Infectious disease
Disease caused by infecting micro-organism or
virus
Disease
Noticeable impairment of body function
Colonisation
Establishment/ growth of micro-organism on body
surface
Pathogen
Any disease-causing micro-organism or virus
Opportunistic pathogen
Organisms that cause disease ONLY when
introduced into unusual location
Bacteraemia
Bacteria circulating in bloodstream
Septicaemia
Acute illness due to infectious agents OR their
toxins circulating in bloodstream
Systemic Infection
Widespread infection through blood or lymphatic
system
Useful Terms – Microbial Pathogenesis
Pathogen
Any disease-causing micro-organism or virus
Pathogenicity
Ability of a pathogen to produce an infectious
disease in an organism
Virulence determinants
Attribute of micro-organism or virus that promote
pathogenicity
Virulence
Relative level of symptoms associated with a
g
given
p
pathogen
g
7
Microbes & Virulence
Production
& delivery of
various
factors
Adhesion to
host tissues
Replication
& evasion
of immunity
Damage to
host
tissues by
toxins
Microbes and humans
● Disease can come about in several
overlapping ways
 Some
S
bacteria
b t i from
f
normall flora
fl
can cause
disease if they gain access to deep tissues
 By
trauma, surgery, catheters, or a foreign body
e.g. Streptococcus epidermidis
● Immunocompromised patients
 Many members of normal flora & free
free-living
living
bacteria can cause disease
 Especially
if introduced into deep tissues
 Clostridium botulinum in heroin!
8
How do we know that a given
pathogen causes a specific disease?
Robert Koch
1843-1910
● Founder of public health…
● Developed “Koch’s Postulates”
In late 1800’s discovered causal agents of:
● Tuberculosis,
● Mycobacterium tuberculosis
● Cholera
● Vibrio cholerae
● Anthrax.
 Bacillus anthracis
9
Koch’s Postulates
Pure
organism
causes
same
disease.
Organism
grown in pure
culture.
Together
these
indicate
infectiousdisease
causation.
Same
organism
recovered.
Process of Disease
● Microbes cause disease while stealing space,
nutrients, and/or living tissue from their
symbiotic hosts
 e.g. Us!
● To do this, microbes do most of the following:
 Gain access to the host - contamination
 Adhere to the host - adhesion
 Replicate on the host - colonization
 Invade tissues - invasion
 And produce toxins, proteins or other agents
that cause host harm - damage
10
For successful infection, bacteria:
●
●
●
●
Sense environment
Need to know where they are...
Must express proteins to survive stress
Must express proteins required for adhesion
or invasion
● May make toxins
● May enter host cells and replicate
● May spread through host cells
The GI tract
is a harsh
environment
37OC
p 2
pH
(aerobic)
pH 7,
anaerobic,
Digestive enzymes
Normal flora
(1000 species)
11
Bacterial Virulence
● Virulence as a process is
 MULTIFACTORIAL
 A bacterial army, like a human army, needs more
than just its firearms to enter and secure enemy
territory…
“An army marches on its stomach” - Napoleon
 MULTIDIMENSIONAL
 A programme of events organised in time & space
Environmental sensing
● Bacteria can sense changes in environment
 e.g. temperature, nutrient availability, pH
● In simplest cases, change in intracellular
concentration of ion linked directly to gene
expression
 e.g. fall in intra-cellular iron levels triggers de-repression of
diphtheria toxin gene
Bacterial gene regulation is a key part of Microbiology at TCD
● In more complex cases, sophisticated signal
transduction cascades allow bacteria to regulate gene
expression in response to environmental cues
 Pathogen as an information processor
12
Stress Survival
● In addition to nutrient-limitation stress, pathogens
face many other stresses
 Acid stress within stomach
 Heat shock during fever
 Oxidative stress within macrophages
● Stress response proteins, such as chaperonins
feature as immunodominant antigens
● Detoxification proteins play a role in virulence,
virulence
 e.g. periplasmic Cu/Zn-superoxide dismutases
● Infectious dose for enteric pathogens much lower in
people with achlorhydria
 No need to overcome acid stress
Adhesion
● To avoid physical & immunological removal, bacteria must adhere to
 Cell surfaces and extracellular matrix
 e.g. in respiratory, gastrointestinal
genitourinary
y tracts
&g
 Solid surfaces
 e.g. teeth, heart valves, catheters
 Other bacteria
● Direct interaction mediated by cell-surface adhesin proteins
 Often located at ends of fimbria or curli
 & other outer membrane proteins
● Viruses have surface attachment proteins
● Adherence often combined with manipulation of host cell signalling
and cytoskeleton (Salmonella)
 Adhesion followed by Invasion
13
Adhesion
Diseases caused by
intracellular bacteria that can invade &
replicate inside mammalian cells
● Salmonella
 Gastroenteritis or Typhoid
● Shigella
 Bacterial dysentery
14
Salmonella typhimurium
invades host cells and
replicates...
● Lecture
L t
9!
Shigella replicates and spreads
inside host cells
15
Actin-based motility
Actin-based motility of
Listeria monocytogenes
Wild-type
actA mutant
16
Manipulation of host cell processes by
intracellular pathogenic bacteria
Mycobacterium tuberculosis enters
host cells and replicates...
● Lecture
L t
10!
17
Damaging host tissues with toxins
● Endotoxin
Endotoxin of Gram-negative bacteria
G
Gramnegative
cell
cytopl.
mem.
peptidoglycan
outer mem.
Lipopolysaccharide
(LPS)
Lipid A
The toxic part
Core
polysaccharide
Helps solubilise Lipid A
O sidechain
Somatic antigen
18
Endotoxin = lipopolysaccharide = LPS
Impact of Endotoxin on the host
● Actions of Endotoxin
 Fever
 Hypotension

Life-threatening complication of septicaemia

Endotoxic shock seen with dirty intravenous equipment
■ e.g. in meningococcal infection, in ITU or oncology patients
● Most of the effects of endotoxin are mediated
by tumour necrosis factor
 Attempts at therapy using anti-endotoxin or
anti-TNF antibodies
19
Damaging host tissues with toxins
● Endotoxin
● Exotoxins
 Toxins acting on cell membranes
 Toxins active inside cells
Membrane-Damaging Exotoxins
● Many bacterial toxins form pores in eukaryotic cell
membranes, producing oligomeric rings
 Streptolysin O of Streptococcus pyogenes
 Listeriolysin of Listeria monocytogenes
 Alpha-toxin of Staphylococcus aureus
● Other toxins, such as phospholipases, degrade
components of the membrane
 e.g. Clostridium perfringens alpha toxin
20
Cholera Exotoxin
Production
of watery
diarrhoea
If you’d like to hear a bit more...
● TCD Open Day Lecture 2011
● Google
G
l
 Jay Hinton Dead YouTube
It's amazing you're not dead yet!
- and more reasons to study
microbiology
21
Toxins & Vaccination
● Some bacterial proteins (exotoxins) can elicit
the features of a bacterial infection when
injected as pure proteins, e.g.
 tetanus toxin, botulinum toxin
 diphtheria toxin, anthrax toxin
● Vaccination with inactivated toxins (toxoids)
led to a huge decline in the incidence of many
bacterial infections
● Led to simplistic idea that all bacteria need to
cause disease is a single toxin…
`Did you know that beansprouts
could kill you?
● Particularly if they’re Organic...
22
The German E. coli
O104 outbreak
May – June 2011
● E. coli adhering to
gut wall
Variation in types of
pathogenic E. coli
Eliza cartoon
Acquires ‘tools’ that
make it more able
to cause disease
23
Variants of E. coli have different
combinations of ‘tools’ that help them persist
in a host and cause disease
EAEC
EHEC
Strain emergence: The German
E. coli outbreak strain – a hybrid
+
EHEC
=
EAEC
Stx-EAEC
O104
Cartoons and concept – David Gally and Eliza Wolfson, Roslin Institute
24
The German O104
outbreak strain – a hybrid
Enteroaggregative E. coli
EAEC
Shiga toxin virus
(f
(from
EHEC)
=
+
German
O104
outbreak
strain
Introduces Shiga
g
toxin genes into
bacterium
Human-adapted & adheres
well to gut wall
The dangerous combination
of Adhesion &
Toxin production
The German E. coli O104 outbreak
May – June 2011
● Over 3,200 cases
● 50 deaths
 845 cases of kidney damage
due to the toxin
25
Where did the E. coli
come from?
● Was it Spanish cucumbers?
 No
● Was it German Lettuce?
 No
● Was it German beansprouts
 Yes
 But the seeds came from Egypt…
And finally...
● The example of a bacterial pathogen that does
not enter human cells, but causes
inflammation...
inflammation
26
Characteristics of H. pylori
• Microaerophilic (5% O2, 10%CO2)
• Cork-screw morphology
• Highly motile (flagella)
Helicobacter pylori
lumen
pH <4
pH 4
p
•
• Colonizes mucus layer
• Able to grow at moderate acidity
• Adheres to epithelial cells
mucus
layer
pH 6.5
cells
Figure
10-28& ulcers
H. pylori
infection
27
Peptic ulcer disease
Pre-1990’s
• caused by stress/environmental factors
• incurable disease, often requiring surgery
• ulcers often returned despite surgery
• debilitating disease, often lethal in long term
1984
• Marshall and Warren describe isolation and culture of
Campylobacter-like micro-organism from patients with peptic
ulcer disease
Lancet. 1984 Jun 16;1(8390):1311-5
Figure 10-28
H. pylori infection,
ulcers & cancer
28
Inflammatory response to colonisation
LPS,
peptides
IL-8
LPS,
peptides
neutrophil
chemotaxis
monocyte
infiltration
IL-1
TNF
O2 -
lamina
propria
PGE
Inflammatory response initiated by presence of bacteria
H. pylori and gastrointestinal disease
Environmental factors
Atrophic
gastritis
Gastric carcinoma
MALTlymphoma
Chronic gastritis
H. pylori
(Virulence
factors)
inflammation
p ulcer
Peptic
disease
Host factors
29
Nobel Prize: don't try this at home!
An attempt to fulfil Koch’s
Postulates for Helicobacter pylori
Marshall, B.J. (1985) Med J. Aust 143:319.
Barry
Marshall
drank
Helicobacter
pylori
Caused
gastric
inflammation
Cured with
antibiotic
Fulfilled
Koch's
postulates
Proof !!
30