Pathogenic bacteria

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Pathogenic bacteria virulence factors
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What is a pathogen?
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Types of microbes causing infectious
disease Type Branch Cellular?
Genome Nuclear Example (Kingdom)
membrane?
Metazoan Eucarya yes DNA
yes Ascaris parasites (Animalia)

lumbricoides Protozoan Eucarya yes
DNA yes Plasmodium parasites
(Protista)
falciparum Fungi /
Eucarya yes DNA yes
Candida yeasts (Fungi)

albicans Bacteria Eubacteria yes
DNA no Streptococcus
(not Archaea)
pyogenes Viruses
no DNA/RNA no Herpes
simplex Prions
no no genes no
BSE (Mad Cow Disease)
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How do you identify a pathogen?
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Robert A. Koch 1843-1910
Kochs Postulates - 1882 Confirming Germ theory
of disease

• Bacteria must be associated with the lesion
• Bacteria must be isolated in pure culture
• Isolated bacterium must produce disease when
  inoculated into human or animal
• Bacteria must be re-isolated from intentionally
  infected animal or human

not all bacteria can be cultivated on artificial
medium
no animal models for some diseases
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Molecular Kochs Postulates
Nucleic acid sequence of pathogen should be
found in association with disease or diseased
organ Nucleic acid sequence should be absent
from healthy individual Resolution of disease
should result in decrease in pathogen associated
nucleic acid sequences Presence of pathogenic
nucleic acid in a healthy individual should
predict development of disease Nature of the
microorganism inferred from nucleotide sequence
should be consistent with biological
characteristics of organism Sequence based
findings should be reproducible
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How to distinguish infection from colonization
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Asymptomatic colonization by pathogenic bacteria
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Disease
immune competent/compromised immunizations age tra
uma genetics antimicrobial therapy
I. secretion of factors (toxins) II. direct host
cell manipulation
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Host bacterial defenses
Natural barriers normal flora - affected by diet
/ antibiotics (competitive exclusion) pH -
acidic / alkaline (inhibits growth) mucin -
viscous glycoproteins (barrier / bacterial
trapping) defensins - antibacterial peptides
(damage bacterial membranes) collectins -
lectins (bacterial aggregation) (PRR) epithelial
shedding - (removes attached bacteria)
Innate immune response PRR - (pattern recognition
receptor) macrophages / PMNs / dendritic cells /
NK cells / mast cells / basophils / eosinophils
Acquired immune response B-cells / antibody
production - extracellular bacteria T- cells /
cytotoxity response - intracellular bacteria
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Emergence of infectious disease
habitat change adapt by regulation mutation gene
transfer
most successful bacteria achieve balance with
environment (host)
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Two basic types of pathogens
overt (exogenous) pathogen - aggressive
pathogen, requires acquired immunity for host
defense opportunistic (endogenous) pathogen -
becomes a pathogen when host is compromised

• damage to epithelium
• introduction of bacteria to sites where they are
  not
• normal flora - linked to presence of foreign
  body,
• catheters, prosthesis, biofilms
• disruption of normal flora by antibiotics
• suppression of immune system by drugs
• impairment of host defenses due to infection

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Types of diseases caused by bacteria
Localized infection
e.g. Clostridium tetani - spores enter /
germinate in deep wound - toxin produced -
toxin disseminates
Disseminated infection
e.g. Staphylococcus aureus - wound infection /
abcess - organism invades bloodstream -
organism invades heart, kidney, lungs, brain bones
Intoxication
e.g. Clostridium botulinum - spores in
contaminated food germinate, multiply,
produce toxin - toxin ingested - botulism
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What is the difference between virulence and
pathogenicity?
virulence pathogenicity (ability to cause
disease)
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Measurement of virulence
LD50 vs. ID50
LD50 - number of bacteria needed to kill 50 of
animals ID50 - number of bacteria necessary to
infect 50 of the animals exposed to the bacterium
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What is a virulence factor?
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Virulence factors of bacteria
I. adherence / colonization pili motility /
chemotaxis (flagella) outer membrane
proteins II. infectious process exotoxins /
endotoxins type III / type IV secretion
processes intracellular growth (invasion) III.
protection against host defense capsule / cell
wall / outer membrane antigenic
variation biofilm formation
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I. Adherence / colonization
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pilus-pili-fimbraie
- immunodominant protein neutralized by host
antibodies vaccine candidate
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flagellum / flagella
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flagella movement
Macnab, Ornston, 1977 Kahn 1978)
Smooth swimming Tumble
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chemotaxis (movement in response to an
environmental stimuli)
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outer membrane proteins (OMPs)
Function - adhesin - invasion
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II. Infectious process
exotoxins / endotoxins type III / type IV
secretion system intracellular growth
Model infectious agents will be used to examine
mechanisms of bacterial pathogenesis
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Bacterial model systems
Bacterial toxins

• mechanism of toxicity
• protein design (structure vs. function)
• vaccine production
• tool to manipulate host cell function
• toxin re-design for therapeutics
• biological warfare

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Bacterial model systems

• Intracellular survival (invasion)

Mycobacterium tuberculosis Yersinia spp. Listeria
monocytogenes
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Bacterial model systems

• Bacterial secretion

• type III secretory process
• direct manipulation of host
• cell signaling proteins
• Pseudomonas aeruginosa
• Salmonella spp.

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Bacterial model systems

• Emerging diseases

• Comparison of pathogens
• EPEC
• ETEC
• EAggEC
• EHEC - (OH157H7)
• EIEC
• Salmonella
• Shigella

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III. Bacterial protection against host defense
antigenic variation capsule / cell wall / outer
membrane biofilm formation
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Antigenic variation
Neisseria gonorrhoeae adaptation - antigenic
variation of pili
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capsule /cell wall /outer membrane
The surface of Bacillus anthracis. The bacterial
membrane is evident as the innermost layer
surrounding the cytoplasm. P denotes the
peptidoglycan cell wall. S refers to the S-layer
which consists of two proteins including the
major antigen. C denotes the poly-D-glutamic acid
capsule that is exterior to and completely covers
the S-layer proteins. (From Mesnage, et al.
Journal of Bacteriology, 18052-58, 1998)
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capsule (highly hydrated gelatinous matrix -
composed of carbohydrates and proteins)
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biofilm (living capsule - 3D-bacterial community
growing on a surface)
Examples of biofilms dental plaque growth on
catheters growth in heart tissue chronic cystic
fibrosis lung infection natural biofilm - slimy
(green) mass attached to rocks in mountain streams
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Concepts

• terms pathogenesis /virulence, colonization,
  infection, disease
• understanding of a pathogen origin of emerging
  infectious
• disease
• types of diseases caused by bacteria
• definition of virulence factor types of
  virulence factors
• those that affect
• I. adherence / colonization
• II. infectious process
• III. protection against host defense