What is a microbe?
It is a bacteria, virus, helminth, parasite or fungi
What are the 4 relationships for microbes interacting with hosts?
- Commesnalism: 1 benefits, no effect on the other
- Mutualism: both benefit
- Parasitism: 1 benefits, other is adversely affected
- Opportunism: a change in the living relationship, which causes parasitism: Staphylococcus aureus, clostridioides dificile and escherichia Coli
Define Kochs Postulates
- Suspected pathogen must be in all unhealthy and none in healthy population
- Pathogen must be grown in a pure culture
- Pathogen must be able to infect a healthy animal
- Pathogen must be reisolated and shown to be the same pathogen
What are the exceptions of Kochs postulates?
- Can’t be grown in a pure culture
- Asymptomatic patients
- Not present in animal models
What are the 6 steps of infection?
- Attachment and entry, evades innate immune response and causes infection
- Local/general spread to the body, containing to evade immune response
- Multiplication and strengthening
- Evasion of host defenses: full life cycle and microbial battle
- Shedding/transmission to spread to new hosts
- Damage to host
What are the 6 stages of disease?
- Incubation: sick but no or little symptoms
- Prodromal: exponential replication, worsening of sickness
- Invasive: extreme exponential replication, extreme sickness, pathogen out competing immune system
- Acme: peak
- Decline: immune response winning
- Convalescence: Recovery
What are the 2 ways of visualizing bacteria?
- Macroscopy: naked eye. 16 streak, shame, size, pigmentation, elevation, margin, opacity, texture
- Microscopy: using a microscope, staining
What is the gram stain technique?
The staining of bacteria to distinguish between gram negative and positive
What is the difference between gram -ve and +ve
- +ve has thick cell wall
- -ve creates AB resistance
Describe the structure of the gram positive bacteria
- Thick cell wall: peptidoglycan layer
- Within the wall traverses the lipoteicoic acids and are anchored to the membrane
- Lipid bilayer plasma membrane with integral proteins
- Evolved with humans
Describe the structure of gram negative bacteria
- Outer membrane with porins and Lipid A
- Lipid A has lipid polysaccharides attached with an O-antigen at the end.
- Below this membrane is a thin peptidoglycan layer within the periplasmic space
- Below this is the cytoplasmic membrane
- Evolved with dirt, becomes AB resistant
Why is gram -ve ba trial more resistant to AB than +ve?
Because the lipid A, lipopolysaccarides, O-antigen and porins can adapt to AB, making it harder to kill or invade the bacteria.
What are the staining techniques to distinguish gram +/-ve bacteria?
- Crystal Violet: peptidoglycan purple in +ve
- Iodine sets the staining
- Alcohol: washes away not set stains (-ve)
- Safranin: red stain of -ve
What are the 3 energy sources of bacteria?
- Oxygen (aerobic/anaerobic)
- Carbon/nitrogen (sugars/proteins)
- Enzymes (cytochrome oxidase)
What are the 3 tests to determine a bacteria energy source?
- Fermentation: sugars present, red:none, yellow: lots, anaerobic, yellow with bubble: lots aerobic
- Catalase: bubbles of hydrogen peroxide
- Oxidase test: purple enzymes are present
Describe bacterial fission
- DNA makes 2 identical copies
- Each copy moves to polar ends of the cell
- Cell splits to make 2 genetically identical copies
Describe the phases of growth
- Lag phase: initial adaptation to conditions
- Logarithmic phase: exponential increase
- Stationary: division=deaths
- Death: decrease in cell numbers
How is bacterial quantity measured?
- Turbidity
- Density
Measured within a spectrometer and optical density taken
Describe the characteristics of a virus
- Not living
- Needs a host cell to reproduce
- No machinery of its own
- No cell membrane
What is the lifecycle of a virus?
- Attachment to host
- Penetration of cell
- Uncoating to release viral genome
- Replication
- Assembly
- Maturation and release of progeny through membrane of cell
What is tropism?
Where the virus has a specific target, eg. Humans only, organ only, specific cell
Describe the early stages of viral lifecycle
- Nucleocapsid releases genome
- Genome both transcribes to make new capsid proteins and replicates to make new genomes
- New proteins and genomes form together to make lots of new nucleocapsids
- Now ready for release! Late lifecye
Describe the late lifecycle of virus
- Nucleocapsid either lyses the host cell to release nucleocapsids (naked)
- Nucleocapsid pinches cell wall of host cell to create a viron coat for protection (enveloped)
