VL3: Bacterial pathogenicity and surface structures Flashcards
How can commensal B become pathogenic (3)?
- Proliferation (higher nb than normal)
- Entry into normally sterile sites (e.g. blood, lungs, bladder)
- host immunity reduced
How does an organism cause disease? (briefly explain 2 ways)
- toxins or lytic enzymes (e.g. v.cholerae: cholera toxin)
- colonization (usually gastrointestinal or respiratory tract) and/or invasion of tissues
- > often is the actual disease caused by the immune response (e.g. salmonella endotoxin (LPS))
Describe the general courses a disease can take with examples
- active (incubation, illness, convalesence) (e.g. influenza)
- chronic (incubation, illness…) illness persists Malaria HIV
- Latent (incubation, illness, convalescence // latent period // illness may recur) tuberculosis
3 Ways of spreading disese
- Direct (human to human (air, sexually)
- vector (arthropodes) e.g. malaria, borrelia
- food, water e.g. v. cholerae
Summary of Kochs postulate
shows that an organism is pathogenic
- path in all diseased individuals (and not healthy people)
- isolate pathogen -> grow in culture
- reinfection causes disease (problem: immunity, dose)
- reisolate pathogen from reinfected person
What is the difference between primary and opportunistic pathogens ? (+ examples)
Primary pathogens are always pathogenic (rabies virus, malaria plasmodium, tuberculosis mycobacterium)
opportunistic pathogens are only pathogenic in susceptible people (candida, pseudomonas aeruginosa) present everywhere not usually pathogenic, only at some places in body, skin infections after burn injuries or lungs in CF
2 differences in host range in diffrent bacteria
ex. only in humans (helicobacter pylori, typically vertical transfer, mom child)
broad host range, e.coli salmonella
What is virulence and how is it defined?
The relative ability of a pathogen to cause disease
defined as mortality rate (LD50) of ability to invade host tissue (no experiments)
defined as ability to invade host tissue
Does the infectious dose correlate with virulence?
No
B with pathogenic mechanisms that depend on secreted molecules (distant action) need a higher dose for infection than b with local action
5 examples for major virulence factors
capsules endotoxins exotoxins immunoglobulin proteases enzymes that damage host tissue
Name some strategies for infection prevention and treatment
vaccines
antimicrobial drugs
hygiene
nutrition
sanitation
isolation
How do B establish infections? (6 steps)
Entry into the body Colonization Avoiding immune respose Adhesion Invasion Surviving within host cells
How do microbes invade the body?
Skin- through lesions or vectors (bites)
many B have ways to get through epithelia (cells specialized for engulfment or transport in various body openings)
3 methods to promote colonization
(requires ability to obtain food and evade immune mechanisms)
- sIgA proteases (prevents trapping of B in mucin)
- Iron acquisition (sideophores, direct uptake of host iron-carrying prot,Low level toxin production ( host cell lysis releases iron) , iron abistinece
- Synthesis of nutrient scavenging systems
3 methods to avoid the immune system
- antigenic variation of surface structurs (e.g. pilins Neisseria gonorrhoeae)
- using a coat of host proteins
- avoiding phagocytosis and complement activation (capusles and lps alterations)
