Topic 2 Microbiology - Bacteria

Question 1

What are characteristics of bacteria?

Answer 1

Microscopic organisms,
Prokaryotes,
Lack a true nucleus,
Mostly have one chromosomes - examples with more than one exist but are the exceptions e.g. Borrelia Burgdorferi,
DO NOT all look the same

Question 2

What do many dyes rely on?

Answer 2

many rely on cationic organic compounds combining with the negatively charged cell envelope

Question 3

What are the steps of gram-staining?

Answer 3

1. smear preparation by addition of inoculum and a drop of distilled water
2. heat fixing of bacterial smear.
3. primary staining by crystal violet
4. treatment with iodine
5. treatment with alcohol
6. counter staining with safranin
7. observation

Question 4

Why are there differences in staining patterns in gram-staining?

Answer 4

due to differences in the structure of the bacterial cell wall

Question 5

Describe Gram-positive bacteria?

Answer 5

Gram-positive bacteria retain the Gram dye complex (crystal violet-iodine) when washed with ethanol and appear blue/purple

Question 6

Describe Gram-negative bacteria?

Answer 6

Gram-negative cells do not retain the dye when washed with ethanol and appear pink (the colour of the counter stain)

Question 7

What are Gram-variable organisms?

Answer 7

organism where there cell wall structure changes under different growth conditions - leading to a difference in Gram-staining

Question 8

Describe bacteria’s structure?

Answer 8

Bacteria are unicellular and have clearly identifiable sub-cellular features

Question 9

Describe a gram-positive cell wall

Answer 9

approximately 20-80 nm thick

approximately 90% peptidoglycan, this includes teichoic acids

Question 10

Describe a gram-negative cell wall

Answer 10

approximately 7-8 nm thick

approximately 5-20% peptidoglycan

they lack teichoic acids

there is an additional membrane layer present

Question 11

What is the outer layer in a gram-negative bacteria known as?

Answer 11

LPS = Lipopolysaccharide Layer

it exists as a lipid bilayer

surrounds the peptidoglycan and cytoplasmic membrane

Question 12

What are examples of endospores?

Answer 12

species from the genera Clostridium and Bacillus

Question 13

What are endospores highly resistant to?

Answer 13

heat and many antimicrobials. also resistant to UV radiation, gamma radiation
therefore they can persist in an environment for long periods of time.

Question 14

Describe bacterial genetics

Answer 14

Bacteria have relatively small genomes.

very little redundant DNA

Around a couple of thousand genes

Seldom (if at all) use introns

Able to respond quickly to environmental changes

Gene expression levels change rapidly (both upregulated and downregulated)

Question 15

Where are bacterial genetic components found?

Answer 15

Most of the essential genes are located on the bacterial chromosome (single copy)

There are some other genetic components (plasmids) which generally contain non-essential (luxury) genes - can be multiple copies

Question 16

Describe genes in a single chromosome in bacteria?

Answer 16

genes - structural components and metabolism

‘housekeeping genes’

only single copies of genes on chromosomes

Question 17

describe genes in plasmids in bacteria

Answer 17

genes - antibiotic resistance, virulence, conjugation

‘luxury genes’

often several copies of plasmids

Question 18

Through what process can free DNA infect bacteria?

Answer 18

Transformation

Question 19

In transformation how does a recipient cell acquire DNA?

Answer 19

normally from lysed cells

Question 20

What species can transformation naturally occur?

Answer 20

Bacillus, streptococcus, Haemophilus, Neisseria

Question 21

What is a competent cell?

Answer 21

a cell which can be transformed

Question 22

Through what process can plasmids be passed from one bacterium to another?

Answer 22

conjugation

Question 23

What does conjugation require?

Answer 23

cell to cell contact (normally same species)

Question 24

how is cell to cell contact initiated in conjugation?

Answer 24

initiated by a pilus on the donor

Question 25

What happens when the pilus attached during conjugation?

Answer 25

pilus of donor attaches to recipient

pilus disassembles drawing recipient closer

cell wall/cytoplasmic membrane fuse forming a conjugation bridge

DNA can be moved through the bridge from the donor to the recipient

only one strand of DNA is transferred - the donor keeps the other one

Recipient can now replicate the DNA to become double stranded

Donated DNA is the same in both cells now - both potential donors

Question 26

What is the transfer of DNA facilitated by in conjugation?

Answer 26

plasmids

e.g. F+ strain passing plasmid to F- strain, which becomes a new F+ strain
Plasmid carries all genes needed for its own transmission

Question 27

What is the transfer of DNA said to be in conjugation?

Answer 27

undirectional

Question 28

Through what process do bacterial viruses or phages infect bacteria?

Answer 28

transduction

Question 29

What are Bacteriophages?

Answer 29

viruses which infect bacteria

Question 30

What are bacteriophages potential therapeutic uses?

Answer 30

used against dysentery (shigellosis) and staphylococcal skin infections

Question 31

For lab tests etc what conditions should you be aware of for the experiment?

Answer 31

Aerobic versus anaerobic

optimal temps or temp range

optimal pH

length of time required for growth

salt tolerance

haemolysis

degradation of certain compounds

Question 32

In phenotypic identification what phenotypic features are used in screening?

Answer 32

colony morphology

gram staining

microscopic morphology

cell association/aggregation

grow on selective/differential media

biochemical/metabolic profile

Question 33

What happens during biochemical phenotype?

Answer 33

pure culture are grown

then perform biochemical analyses

Question 34

How many cell membranes does a gram-negative cell wall have?

Answer 34

2 cell membranes

Question 35

How can and how cant bacterial spores be killed?

Answer 35

Cannot be killed with alcohols and hydrogen peroxide

Can usually be killed by autoclavation at 121^0C

Question 36

What are bacterial spores resistant to?

Answer 36

Radiation

Question 37

What are the 3 ways bacteria an acquire new genetic material?

Answer 37

Transduction, transformation and conjugation