Lecture 1- Bacterial Properties

Question 1

Define the term ‘acid fastness’

Answer 1

The ability of cells to resists decolorisation by acids during lab staining procedures

Question 2

What is the purpose of gram staining

Answer 2

to distinguish between two different kinds of bacterial cell walls

Question 3

Describe the process of gram staining

Answer 3

• bacteria stained with crystal violet
• Washed with iodine which acts as mordant
• rinsed in alcohol to remove stain
• stained with counterstain (safranin)

Question 4

What colour do gram +ve bacteria stain?

Answer 4

• stains deep violet because thick peptidoglycan retains dye

- only one layer

Question 5

What colour do gram -ve bacteria stain?

Answer 5

• stains pink from counterstain because of thin peptidoglycan layer

Question 6

Describe the structure of gram negative cell walls

Answer 6

• has two membranes
• a thin peptidoglycan layer
• thick lipopolysaccharide layer on top
• LPS layer had lipoprotein and this layer = PAMP

Question 7

What are mycobacteria? Give examples

Answer 7

Don’t fall into Gram-ve or Gram+ve category

• M. tuberculosis
• M. leprae

Question 8

Give examples of gram -ve

Answer 8

• E. coli (EPEC- diarrhoea, EHEC- toxin–> dysentary+ kidney failure)
• Salmonella (typhimurium- food poisoning, type- typhoid)
• Shigella (dysentary)
• Vibrio cholera (cholera)
  neisseria (meningitides and gonorrhoea)

Question 9

Give examples of gram positive bacteria

Answer 9

Staphylococcus aureus (skin disease, endocarditis, bacteraemia)
Strep pneumonia 
Strep pyogenies (tonsillitis, scarlet fever, bacteremia)

Question 10

What must bacterial pathogens be able to do to infect?

Answer 10

1) Colonize (using pilli and fimbriae to cling)
2) Persist (avoid the host immune system)
3) Replicate (acquire nutrients)
4) Disseminate (within cells, tissues, organs and hosts)
5) Cause disease

Question 11

Name some extracellular pathogens

Answer 11

Staph, Strep, Yersinia and Neisseria

Question 12

What are the three ways of surviving in the host cell? Give examples for each of the methods

Answer 12

1) ESCAPE from endosomes and phagosomes (Listeria, Shigella)
2) Prevent FUSION with lysosomes (Salmonella, Mycobacteria)
3) SURVIVE in Phagosome (Coxiella)

Question 13

Which two structures help salmonella with invasion?

Answer 13

1) Flagellum- rotatory filamentous structures for movement

2) Type III secretion system

Question 14

What is the function of the injectisome in salmonella?

Answer 14

1) Delivers bacterial virulence proteins
2) This causes actin polymerisation into filaments
3) —> Membrane ruffling
4) –> Bacterial internalisation

Question 15

What type of bacteria are injectisomes found on?

Answer 15

Gram Negative bacteria

Question 16

How do Listeria infect the host?

Answer 16

1) Phagocytosis by zipper mechanism into vesicle
2) Breaks out of vacuole
3) Polymerises actin at one end of cell
4) Uses this actin for propulsion
5) Forms streams of actin called COMET TAILS

Question 17

What is the core genome in bacteria?

Answer 17

Housekeeping genes expressed in all bacteria

Question 18

How do bacteria replicate?

Answer 18

By binary fission ( so daughter cells are identical to parent cells)

Question 19

What are the three different types of horizontal gene transfer?

Answer 19

Transformation
Transduction
Conjugation

Question 20

What is transformation? Which bacteria do this?

Answer 20

Incorporation of naked DNA (DNA from lysis of bacteria) from the environment

• Neisseria
• Streptococcus

Question 21

What is transduction?

Answer 21

Incorporation of host bacterial DNA into invading bacteriophage genomes which are then incorporated into the next host’s DNA

Question 22

What is conjugation?

Answer 22

Transfer of bacterial plasmid DNA to neighbouring bacteria through sex pillus

Question 23

What are pathogenicity islands?

Answer 23

Horizontally acquired DNA that contribute to virulence. They are flanked by core host genes and tRNA genes.