An introduction to microbes

Question 1

what is meant by the microbial world?

Answer 1

bacteria
fungi
viruses
parasites

Question 2

which microbes are prokaryotic?

Answer 2

without a nucleus:
* all bacteria of medical importance
* archea - a collection of evolutionarily distinct organisms

Question 3

what shapes are bacteria?

Answer 3

• most bacteria are rod, sphere or corkscrew
• most bacteria (except mycoplasams) have rigid cell wall sorrounding cell membrane

Question 4

do viruses have a cell wall?

Answer 4

no

Question 5

how does a virus compare in size to a bacteria?

Answer 5

viruses are about 100x smaller than bacteria

Question 6

where do viruses multiply?

Answer 6

• viruses contain DNA or RNA sorrounded by a protein coat
• may have an envelope derived from the membrane of host cell from which virus is released
• virsuses require host cell structure and enzymatic machinery to replicate
• rate at which virals replicate ranges from rapid lysis and release to gradual and prolonged release

Question 7

what is the cell envelope of a bacteria?

Answer 7

all material external to and enclosing the cytoplasm, contains:
1. cell membrane
2. cell wall
3. capsule if present

Question 8

what is the cell membrane of a bacteria?

Answer 8

phospholipid membrane which controls permeability

Question 9

what is the cell wall of a bacteria?

Answer 9

all bacterial cell wall contain a peptidoglycan layer - this layer determines the shape of cell + composed of a cross-linked polymeric mesh

Question 10

what is the capsule of a bacteria?

Answer 10

many bacteria secrete a sticky polysaccharide coating around the cell - the capsule
* allows bacteria to adhere to surfaces
* protects bacteria from antibodies + phagocytosis

Question 11

which bacteria contain a capsule?

Answer 11

encapsulated bacterias:
* strep pneumoniae
* nisseria meningitidis
* haemophilius influenza type B

Question 12

what are the differences between gram positive and negative bacteria?

Answer 12

positive:
* thick, multi-layered, peptidoglycan cell wall that are exterior to cytoplasmic membrane
* stain blue/purple

negative:
* thin peptidoglycan layer + outer membrane has embedded lipopolysaccharides (LPS)
* the LPS is antigenic and can be used to identify strain and species of bacteria

Question 13

what is gram stain?

Answer 13

helps us to visualise the different bacteria in light microscope better

Question 14

what components of the bacteria is the gram stain linked to?

Answer 14

cell wall components