Bacterial Properties

Question 1

What is the difference between Gram-negative and Gram-positive bacteria?

Answer 1

Gram-negative bacteria have a thin peptidoglycan layer with two membranes (cytoplasmic and outer membranes)
stains pink

Gram-positive bacteria have a thick peptidoglycan layer, which retains the dye well. It only has one membrane
stains purple

Question 2

Give examples of some Gram-negative pathogenic bacteria and the diseases they cause.

Answer 2

E. coli – diarrhoea, dysentery, kidney failure

Salmonella - food poisoning, typhoid

Shigella – dysentery

Neisseria – meningitis + gonorrhoea

Vibrio cholerae - cholera

Question 3

What feature is found only on Gram-negative cell walls?

Answer 3

Lipopolysaccharide

Question 4

Give examples of some Gram-positive pathogenic bacteria and the diseases they cause.

Answer 4

Staphylococcus aureus – skin infections, endocarditis, bacteraemia, pneumonia

Streptococcus pneumoniae – pneumonia, meningitis, otitis media

Streptococcus pyogenes – tonsillitis, necrotising fasciitis, scarlet fever

Question 5

Give examples of some Mycobaceria and the diseases they cause

Answer 5

Mycobacterium tuberculosis – TB

Mycobacterius leprae - leprosy

Question 6

What is another way of classifying bacteria?

Answer 6

Intracellular and Extracellular pathogens

Question 7

Give examples of some extracellular pathogens.

Answer 7

Staphylococcus
Streptococcus
Neisseria
Yersinia

Question 8

What are the three methods by which bacteria survive in the host cell?

(intracellular)

Answer 8

• Escape
• Preventing fusion with lysosome
• Surviving in the phagolysosome

Question 9

Give examples of bacteria that survive using each of the above methods.

Answer 9

Escape – Listeria, Shigella
Prevent fusion of lysosome – Salmonella, Mycobacteria, Chlamydia
Survive in phagolysosome - Coxiella

Question 10

Motility and Invasion require which two multi-protein machines?

Answer 10

Flagella

Type III Secretion system

Question 11

Describe the role of the type III secretion system.

Answer 11

• A protein machine assembles which provides a channel (translocon) through which virulence proteins (effectors) can be injected into the host cell
• The virulence proteins then stimulate actin polymerisation and membrane ruffling which allows bacterial internalisation
• Gram-positive bacteria don’t have the type III secretion system

Question 12

Describe another way in which actin is manipulated by bacteria.

Answer 12

Bacteria (such as listeria and shigella)

• breaks out of the vacuole
• assembles actin at one pole of the bacterial cell
• This polymerisation of actin generates force
  which propels the bacterium
• This leads to the spread of the bacterium from one cell to another
• These streams of actin are known as COMET TAILS

Question 13

What are the three mechanisms of horizontal gene transmission?

Answer 13

• Transformation
• Transduction
• Conjugation

Bacteria can take up DNA from the environment

Question 14

Explain each of the three mechanisms of horizontal gene transmission.

briefly

Answer 14

Transformation – the uptake of naked DNA from the environment
Transduction – bacteriophages infect a bacterium and take up some of the bacterial DNA. The bacteriophage then carries the bacterial DNA to another bacterium.
Conjugation – transfer of genetic material in the form of a plasmid via a conjugation tube

Question 15

What is a Pathogenicity Island?

Answer 15

Horizontally acquired genes that contribute to the virulence

• contributes to evolution of bacterial pathogens
• bacteria occupy a huge component of the biodiversity in the world.
• he high reproductive rate and ability to mix DNA means that there is huge selection pressure among bacteria making them very sophisticated.

Question 16

show diagram of gram positive bacteria

Answer 16

*

Question 17

show diagram of gram negative bacteria

Answer 17

*

Question 18

what features do both types of bacterial have?

what protein does only g neg have?

Answer 18

• Both membranes have embedded channel proteins
• the outer membrane consists of mainly LPS
• therefore LPS is only present in gram negative bacterial cells

Question 19

what do bacterial pathogens need to be able to do?

Answer 19

• colonise - clings onto surfaces
• persist - ability to avoid the host defences
• replicate - acquires nutrients needed for replication
• disseminate within cells
• causes disease - produces toxins that kill cells

Question 20

how does samonella motility and invasion work?

Answer 20

• they polymerise actin into filaments
• this ruffles the plasma membrane and means the bacteria get stuck
• as the process ends l the trapped bacteria is internalised

Question 21

the function and structure of flagella?

Answer 21

• allows the propulsion of the bacteria through the fluids

- they are filamentous structures and they rotate

Question 22

genome of bacteria?

Answer 22

• 500 -4500

much bigger than viruses

Question 23

what is the core genome and non core genome?

Answer 23

• core genome = all the bacteria of a species have these genes - these are
  housekeeping genes
• 60% non-core genes,

Question 24

explain transformation

Answer 24

• this is the uptake of naked DNA
• They can recognise naked DNA
• They have transport mechanisms which
  allow uptake of this DNA and incorporation
  into the bacterial chromosome
• Neisseria and Streptococcus

Question 25

explain transduction

Answer 25

• transfer of DNA by bacteriophage
• When phages invade bacteria, it replicates its DNA in the bacterium and cuts the bacterial DNA into small pieces
• some bacterial DNA is packaged into phage heads
• New phage particles are released
• The phage particles injects the bacterial
  DNA from the previous bacterium it
  infected into the next bacterium.
• Injected DNA may be incorporated into the
  bacterial chromosome

lots of DNA can do this

Question 26

explain conjugation

Answer 26

You get a physical bridge between bacteria, which allows the transfer of a plasmid between the bacteria.