Lecture 2 - Microbial pathogenesis Flashcards
what are indigenous microflora?
all microbes (bacteria, fungi, protozoa) that reside on or within a person
does a fetus have indigenous microflora?
no, colonisation happens during and after birth
What are the main sites of indigenous microflora in humans? give some examples
- bacteria on skin
- oral streptococci
- gut flora
- vaginal flora
describe our indigenous microflora on our skin
around 1 trillion bacteria, streptococcus and staphylococcus metabolise sweat to produce body odor
describe oral streptococci
biofilms of bacteria which is ~400 cells thick of surface teeth
- dental plaque
describe gut flora
more than 500 species of bacteria in the gut, weighing 3.3 pounds.
they breakdown carbohydrates, make essential nutrients like vitamins K and B12 and crowd out harmful bacteria
describe vaginal flora
beneficial bacteria of the lactobacillus family. they secrete lactic acid to protect against invaders such as pathogenic yeast
- candida albicans (vaginal thrush)
What is HPV?
Fossil viruses
what is symbiosis?
organisms living together in close association
what is mutualism?
symbiosis that is beneficial to both symbionts
what is neutralism?
neither symbiont is effected by the relationship
what is commenalism?
beneficial to only one symbiont, but doesn’t effect the other
what is parasitism?
beneficial to one symbiont (parasite) and harmful to the other (host)
what is synergism?
two or more microorganisms team up to cause disease
- synergistic or polymicrobial infection
what is a pathogen?
microorganism that causes disease
what is an opportunistic pathogen?
has the potential to cause disease
sites of microbial infection and shedding
what are the bacterial portals of entry?
- ingestion
- inhalation
- trauma
- needlestick
- athropod bite
- sexual transmission
Describe Kochs postulates
- microorganism must be found in similarly diseased animals but not in healthy ones (same symptoms)
- microorganism must be isolated from a diseased animal and grown in pure culture
- the isolated microorganism must cause the original disease when injected in a susceptible host
- the microorganism must be re-isolated from the experimentally infected animals - get same bacteria
what is the germ theory?
theory states that microorganisms are the cause of many diseases.
what was koch’s postulates originally designed to do?
establish a causal relationship between a causative microbe and a disease
Koch’s original postulates were based on?
TB and cholera
what are the three flaws in postulates 1, 2, and 3?
1: some organisms can be carried asymptomatically
2: some organisms cannot be grown in culture, and we must use PCR
3: must is replaced by ‘should’, as as infection by certain organism does not always cause disease.
what are the periods in the course of an infectious disease?
1: incubation period
2: prodromal period
3: illness
4: convalescent period
what is the incubation period?
time between infection and onset of symptoms
what is the prodromal period?
patient feels ‘out of sorts’ but no disease symptoms
what is the illness period?
experience of symptoms associated with disease
what is the convalescent period?
time during which patient recovers
what are the steps in pathogenesis of infectious diseases?
1: entry
2: attachment
3: multiplication
4: invasion or spread (aka systemic disease)
5: evasion of host defenses
6: damage to host tissues
which step of pathogenesis does coughing attempt to counteract?
attachment
what are the four types of human carriers?
passive carrier (never had disease)
incubatory carrier (during incubation period)
convalescent carrier (recovering)
active carrier (recovered but still carries)
what is a localised infection?
pathogens are contained at site of infection
what is a systemic infection?
pathogen spreads throughout the body (dangerous is enters bloodstream)
what is an acute infection?
rapid onset and rapid recovery
what is a chronic infection?
slow onset and slow recovery
what is a latent infection?
recurring infection from when a pathogen was not completely eradicated after initial recovery.
what is a secondary infection?
a disease that follows a primary infection (pneumonia after mild respiratory infection)
what is microbial intoxication?
when the toxin the microorganism produces in vitro causes illness, and not the microorganism itself.
(e.g. strep produces toxins but wont cause infection when ingested, as its site of attachment is in the respiratory system, and they cannot pass the stomach)
what is the incubation time of a microbial toxin?
there is no incubation time, as it isn’t an infection.
what are virulence factors?
they are a measure of pathogenicity.
the majority of pathogens are o_____________
opportunistic
what is an adhesin?
promotes attachment onto the host cell. often paired with pili for distance
- also biofilm can act as an adhesin
what are the common virulence factors?
- adhesins
- invasins
- cytolysins
- spreading factors
- immunopathogenic factors
- immune evasion factors
what is a biofilm?
a sticky web of polysaccharides secreted by microorganisms, typically staph
what are cytolysins?
a virulence factor that causes cells to lyse by binding as oligomers to pores and causing them to open and the cell to lyse by osmosis. they may do this for:
- access to nutrients (Fe in RBCs)
- immune evasion (WBC)
- bacterial spreading
