1 - Bacterial properties

Question 1

Which type of bacteria have a thick peptidoglycan layer?

Answer 1

Gram positive

Question 2

Does peptidoglycan retain or lose the gram stain?

Answer 2

retains it

i.e. thicker peptidoglycan= more purple (stained)

Question 3

What colour do gram positive and negative bacteria appear when they are gram stained?

Answer 3

gram positive - deep violet

gram negative - pink

Question 4

Following the gram stain, what can be done to identify the bacteria?

Answer 4

• culture and microscopy
• biochemical and serological tests
• DNA techniques such as PCR
• sensitivities to antibiotics is determined

Question 5

How does salmonella invade a cell?

Answer 5

• polymerise the actin into filaments
• this ruffles the plasma membrane and bacteria get stuck in the ruffle
• as the process dies down and returns to normal, the trapped bacteria is internalised

Question 6

What is the structure of the flagella and how they propel bacteria through fluids?

Answer 6

filamentous structures that are organised as a series of rods and filaments that rotate to allow propulsion

Question 7

How do bacteria replicate?

Answer 7

binary fission (vertical gene transmission)

Question 8

EXAM QUESTION:

Compare the structures of gram positive and gram negative and give examples

Answer 8

GRAM POSITIVE:
- one membrane
- thick layer of peptidoglycan
- retains gram stain - dark violet
- surface proteins
- e.g. Staph. aureus and pneumonia
GRAM NEGATIVE:
- 2 membranes (inner + outer)
- thin layer of peptidoglycan
- doesn't retain gram stain swell - pink
- LPS on surface (a PAMP)
- e.g. E.coli, salmonella, shigella

Question 9

What are acid-fast bacteria?

give some examples

Answer 9

• have lipid-rich cell walls (due to containing mycolic acid).
• they are resistant to penetration by chemical dyes such as those used in the Gram stain.
• other tests such as the Ziehl-Neelsen are performed instead to identify the bacteria in these cases.
• e.g. Mycobacterium tuberculosis, which causes TB.

Question 10

What are the 3 shapes of bacteria?

Answer 10

BACILLI - rods
COCCI - spheres
SPIRILLI - spirals