MGY277H1 Study Guide - Final Guide: Rheumatic Fever, Streptococcus, Complement System
8 Jun 2018
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LECTURE 11 – PRINCIPLES OF PATHOGENENSIS
LEARNING OBJECTIVES (Bold, underlined and italics):
Define the terms primary pathogen, opportunist, and virulence
Primary Pathogen is microbes or virus that cause disease in otherwise healthy
individual
- Eg. plague, malaria, measles, influenza
Opportunistic Pathogen (opportunistic) causes disease only when body’s innate or
adaptive defenses are compromised or when introduced into unusual location
- Can be members of normal microbiota or common in environment
- E.g. Pseudomonas – come in contact routinely with healthy individuals with out
harmful effects but can cause fatal infections in individuals with cystic fibrosis
and in burn patients
Virulence refers to degree of pathogenicity
- highly virulent – more likely to cause disease
Virulence factors are traits that allow microorganism to cause disease (e.g. toxins a
microbe produces and sometimes be transferred horizontally)
Describe genomic islands and pathogenicity islands
Genomic Islands – Large blocks of newly acquired genes are called “genomic islands”
Pathogenicity Islands – if newly acquired genes are involved in disease, they are called
“Pathogenicity islands”
Describe conjugation, competence/transformation, and transduction
Conjugation (jumping plasmids)
- Some plasmids encode genes that help them jump from cell to cell, which allows
the plasmid to find new hosts
- Often packed with genes to promote survival of their hosts including drug
resistance genes, phage resistance genes, and immune evasion genes
- Plasmid DNA that is forcing itself into a new host
Competence/transformation
- Some bacteria have energy driven protein complexes in their membrane that
actively pump naked DNA form environment into cytoplasm
- Usually the bacteria want the DNA as food but sometimes it is incorporated into
genome
Transduction – Phage
- Phage (bacteriophage) are viruses that infect bacteria
- Before they kill a bacterial cell they pack their virions with copies of their own
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phage DNA
- However sometimes, by accident, a few virions will package a fragment of DNA
from their bacterial host
- When those virions go and infect the next cell they don’t kill the new cell because
they aren’t delivering viral DNA – they’re delivering a segment of DNA from the
previously infected cell
- DNA can get incorporated into the genome.
Describe how prophages can contribute to disease and evolution
Phage encoded genes (lysogeny - intergration)
- Some phage don’t kill their hosts right away but instead choose to integrate their
own DNA into the host DNA this is called ‘lysogeny’
- Replicate along with host chromosomes
- Some strains of Ecoli carry DNA from several different phages scattered around
their genomes
- The DNA of these latent viruses (“prophages”) stay in the bacterial cell as long as
conditions are good
- When the host cell gets stressed or damaged the viral DNA is activated and the
virus makes more copies of itself and it then kills its host
- Releasing dozens of new viral particles that go and infect more cells.
- Prophage benefit by keeping the host cell alive – in fact they often encode extra
genes to kill off other phages. Sometimes prophages encode toxins or other
factors critical for virulence (pg 312 in book)
Compare and contrast acute, chronic, and latent infections
Acute infections: symptoms develop quickly, last a short time (e.g., strep throat)
Chronic infections: develop slowly, last for months or years (e.g., tuberculosis, HIV)
Latent infections: never completely eliminated; microbe exists in host tissues without
causing symptoms – not contagious when latent
- Decrease in immunity may allow reactivation
- Symptomatic phase can be either acute or chronic
- Chicken pox (acute illness) results from varicella-zoster virus; immune response
stops, but virus takes refuge in sensory nerves, can later produce viral particles
resulting in shingles
- Tuberculosis, cold sores, genital herpes also examples
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Describe the requirements for adherence and colonization
Adherence
- First-line defenses weep microbes away
- Adhesion does not always lead to disease eg normal microbial binds but does not
cause disease
- Adhesins attach to host cell receptor
o Often located at tips of pili (also called fimbriae)
o Can be component of capsules or various cell wall proteins
o Binding highly specific; exploits host cell receptor eg normal role of the
receptor used by Gonorrhoeae is to help protect host cells from damage by
complement system
▪ Are typically glycoproteins or glycolipids
o Dictates type of cell/tissue infected
▪ Eg – Ecoli adhesion allows them to bind to only small intestine
cells
Colonization
- Microbe must multiply to colonize
o Growth in biofilms
- Must deal with host immunity
o Eg Host has lactoferrin or transferrin that binds to the iron that limit the
cell growth
o Siderophores – iron binding molecules by the pathogens
o Avoidance of secretory IgA (protects mucosal cells)
▪ Rapid pili turnover (to shed any bound antibody), antigenic
variations, IgA proteases 9cleave IgA antibodies)
o Compete with normal microbiota, tolerate antimicrobial molecules made
by other microbes
Explain the role of type III secretion systems in infection
Delivering Toxins (“effector proteins”) directly into Host Cells
via secretion systems in Gram- negatives
- Several types discovered; some can inject molecules
other than proteins
- Type III secretion system (injectisome) - syringe like
Incubation period Convalescence Illness
ACUTE. Illness is short term. Symptoms develop quickly but last short time. The pathogen is eliminated by
the host defenses. Person is usually immune to reinfection.
Incubation period
CHRONIC. Symptoms develop slowly and Illness persists over a long time period.
Incubation period
LATENT. Infectious agent never completely eliminated, may exist in host tissue without causing symptoms.
Illness may recur if immunity weakens.
Illness Convalescence Latency Recurrence
Illness (long lasting)
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Document Summary
Define the terms primary pathogen, opportunist, and virulence. Primary pathogen is microbes or virus that cause disease in otherwise healthy individual. Opportunistic pathogen (opportunistic) causes disease only when body"s innate or adaptive defenses are compromised or when introduced into unusual location. Can be members of normal microbiota or common in environment. Pseudomonas come in contact routinely with healthy individuals with out harmful effects but can cause fatal infections in individuals with cystic fibrosis and in burn patients. Highly virulent more likely to cause disease. Virulence factors are traits that allow microorganism to cause disease (e. g. toxins a microbe produces and sometimes be transferred horizontally) Genomic islands large blocks of newly acquired genes are called genomic islands . Pathogenicity islands if newly acquired genes are involved in disease, they are called. Some plasmids encode genes that help them jump from cell to cell, which allows the plasmid to find new hosts.
