Microbiology Lecture 6 Flashcards
Define commenalism.
Host has no benefit, microbe benefits.
Define muutalism.
Both benefit.
Define neutralism.
Neither are benefited nor harmed.
What type of interaction do our normal flora have with us?
Commensalism.
Are all our floral bacteria commenals?
Not entirely, E. coli provides benefits by providing B vitamins, competition, and taking up attachment sites.
Describe the morphology of staphylcoccus epidermidis, where it grows, what it feeds on, and its effect on us.
Gram positive, round in clusters.
Grows on the skin surface, feeding on sebum.
No harm to humans.
Describe the morphology of staphylcoccus aureus, where it grows, what it feeds on, and its effect on us.
Like epidermidis, but lives in moist skin.
It can invade through broken skin, and is an opportunistic commensal.
What does golden staph typically refer to?
Staphylococcus aureus, but usually the antibiotic resistant form.
What effect does contact with broken skin have on staphylococcus aureus?
Activates genes encouraging tissue spread and toxin production.
Which gram type bacteria does better on dry surfaces like skin? Why is this so?
Gram positive, as they have a thicker cell wall, and more adapted to desiccation.
Gram negative can still grow in dry conditions, just better when moist.
Name 4 bacteria that grow at the conjunctiva of the eye.
Staphylococcus epidermidis
Staphylococcus aureus
Propionibacterium
Diphtheroids
Name 2 bacteria that grow within the nose and throat.
Staphylococcus epidermidis
Staphylococcus aureus
Name 2 bacteria that grow within the mouth. How do these populations grow?
Streptococcus
Anaerobes
Streptococcus grows in a layer at night when there is no salivary movement, and dries out. Underneath the layer becomes anoxic, encouraging anaerobe growth.
Name 4 bacteria that grow within the large intestines.
E. coli
Bacteroides (anaerobes)
Lactobacillus
Enterococcus
What is the bacterial population of the urogenital tract like?
Lower urethra has a resident bacterial population.
The bladder is sterile. Infection caused when resident population reaches it.
Name 3 instances of mutualism.
Rumen and cellulose digesting bacteria
Legumes and rhizobacteria
Lichen
Define the effect of competition.
Harmful to both parties.
Define amensalism
No effect on host, negative on bacteria.
Define parasitism.
Negativ effect on host, positive to bacteria.
What is the harm of staphylcoccus epidermidis? What about another bacteria similar to it?
When it grows on plastics to form a biofilm. Aureus also does this.
Does pseudomonas aeruginosa do well in low moisture? Does it grow on plastic?
No, does very well in high moisture. Grows on plastic.
How is pathogenicity measured?
By virulence
Define infection.
Define disease.
Infection - microbe is growing in a host, with or without host damage.
Disease - damage that impairs host function.
What are two ways microbes cause disease?
Invasion
Toxin production
Define the incubation period.
The beginning of infection - no signs or symptoms
Define the prodromal period.
Mild signs and symptoms.
Define the illness period.
Most severe signs and symptoms - microbe numbers peak.
Define the decline period.
Signs and symptoms begin to disappear. This period begins as the peak number of microbes begins to decrease.
Define the convalescence period.
Period of recovery. May continue to be a source of infection however.
Define direct contact transmission.
Direct contact with the microbial population.
Define indirect contact transmission.
The microbial population is spread to a secondary surface first.
Define droplet transmission.
Aerosolisation - sneezing
Define vehicle transmission.
Foodborne, airborne, waterborne etc.
Name an airborne bacteria.
Legionella - causing legionnaires disease.
Name 3 disease vectors.
Fleas, mosquitoes, ticks.
Define koch’s postulates (3).
- Microorganism must be isolated from the host, grown in pure culture, and identified.
- Isolated organism is injected into a healthy host to cause the same disease.
- Same bacteria must be isolated from the new host, cultured, and identified as the same organism.
What are kochs postulates used for? Can they always be used?
To define the causative organism of a disease. No, when the organism cannot be cultured in the lab or when they grow as a co-culture.
When cant kochs postulates be used (3)?
When the organism cannot be cultured, or if it requires a co-culture (viruses in a host cell), or when the disease requires more than one organism to be present.
Define kochs molecular postulates (6).
- Causative organism is identified by analysing genes.
- Trait should be more associated with pathogens than non-pathogens.
- Gene inactivation should reduce virulence.
- Replacement with a wild-type gene should restore virulence.
- Gene should be expressed at some point in the disease.
- Antibodies directed against the gene products should confer host protection.
