Lecture 2: Microbial Pathogenesis Flashcards
Define symbiosis
organisms that live together in close association
What are the 4 types of symbiosis and define them
mutualism (beneficial to both symbionts)
neutralism (neither symbiont is affected by relationship)
commensalism (beneficial to only one symbiont)
parasitism (harmful to one symbiont, host, beneficial to the other, parasite)
define synergism
two or more microorganisms “team up” to cause disease. AKA polymicribial infection
Define a pathogen
microorganism that cases disease
less thazt 3% of microorganisms
What is an opportunistic pathogen
microorganism that has the potential to cause disease
carry disease, it can become pathogenic in the right environment
What are the main sites of indigenous microflora in humans? give some examples
- bacteria on skin (1 trillion, staph and strep feed of sweat and produce BO)
- oral streptococci (biofilm, strep)
- gut flora (>500 species, make nutrients lie vitamins K and B12, crowd out harmful bacteria)
- vaginal flora (beneficial bacteria, lactic acid against yeast)
What is the difference between microbial intoxication and infection disease?
Infectious disease - a pathogen colonises the body and causes the diseases
microbial intoxication - a pathogen produces a toxin in vitro, toxin causes the disease, dont need the bactria itself to cause disease
Describe Kochs postulates
- microoganism must always be found in similariy diseases animmals but not in healthy ones (same symptoms)
- microorganism must be isolated from a diseases animal and grown in pure culture
- the isolated microogranism must cause the original disease when inoculated in a susceptibel host
- the microorganism must be re-isolated from the experimentally infected animals - get same bacteria
explain the steps by which microogranisms cause disease
- entry: “portal of entry”
- attachment: binding to host tissue (colonisation) –> if they cannot colonise they cannot cause an infection
- multiplication: at infection site (localised infection) –> proliferation, harder for immune system to get rid of the bacteria
- invasion or spread (system disease)
- evasion of host defenses (immune evasion) –> overcome immune responses, become symptomatic
- damage to host tissue: symptoms, disability, death
the the types of virulence mechanisms of microorganisms
- promote attachment to host cells (adhesins, biofilms)
- help bacterium enter host cell (invasins)
- damage host cell or tisse (cytolysins)
- help bacteria to spread from local infection (spreading factors)
- over-stimulate immune response (immunopathogenic factors)
- mediate immune evasion
Describe how adhesins work
allow for the attachment to host tissue and thus colonisation
Describe how Biofilms work
thick layer of secreted polysaccharides, immune systen has trouble reaching the bacteria in thick biofilm, same thing for antibiotics –> hard to get to bacteria trapped in biofilm
Describe how invasins work
bacteria binds to invasin and allows it to enter the cell resulting in intracellular growth, resistance to antibiotics because it cant get to the bacteria and protection from the immune system
Describe how cell and tissue destruction works (cytolysins)
destroy cells, results in access to nutrients, immune evasion (destroy WBC) and bacterial spreading
Define immune evasion factors
mechanism by which a pathogens can evade the immunoge response of a host’s cells and continue proliferating and causing disease
