Chapter 1: Bacterial Taxonomy

Question 1

Common stain to quickly determine bacterial morphology

Answer 1

Gram stain

Question 2

Gram stain steps

Answer 2

(1) Crystal violet (blue) for 60s
(2) Wash with water and flood with iodine for 60s
(3) Wash with water and decolourise with 95% alcohol
(4) Counterstain with safranin (red) and wash with water

Question 3

Colour of gram positive organisms? Why this colour?

Answer 3

Blue; absorb crystal violet)

Question 4

Colour of gram negative organisms? Why this colour?

Answer 4

Red; cannot hold crystal violet as washed off by alcohol but absorb safranin

Question 5

Do both gram positive and negative bacteria have more than one layer to protect cytoplasm and nucleus?

Answer 5

Yes

Question 6

Do both gram positive and gram negative bacteria have peptidoglycan layers?

Answer 6

Yes: gram negatives just have a thinner layer

Question 7

Composition of a single peptidoglycan chain

Answer 7

Repeating disaccharide with 4 amino acids in a side chain extending from each disaccharide.

Question 8

Composition of the entire peptidoglycan chain

Answer 8

Each components AAs covalently bind AAs of other chains to form a cross-linked structure

Question 9

Enzyme that catalyses cross-linkages in peptidoglycan

Answer 9

Transpeptidase

Question 10

Location of transpeptidase?

Answer 10

Inner cytoplasmic membrane

Question 11

Common inhibitor of transpeptidase

Answer 11

Penicillin binds to and inhibits transpeptidase. Hence transpeptidase is known as penicillin binding protein

Question 12

Features of the gram positive cell wall with respect to peptidoglycan. What about gram negatives?

Answer 12

Extensive cross linking of amino-acid side chains in gram +ve; gram -ves = thin with simple cross linking

Question 13

Outer cell wall of gram +ve bacteria composition?

Answer 13

Thick layer of peptidoglycan, teichoic acid, polysaccharides and proteins

Question 14

Inner cell wall composition of gram +ves?

Answer 14

Phospholipid bilayer with embedded proteins (membrane spanning). Touches the cytoplasm

Question 15

Do bacterial inner cell membranes contain cholesterol and other sterols?

Answer 15

NO. Only animals

Question 16

What is the structure of gram negative bacterial cell walls?

Answer 16

(1) Cytoplasmic membrane = phospholipid bilayer + protein then periplasmic space (protein and enzymes)
(2) Thin peptidoglycan layer
(3) Outer cell membrane

Question 17

Do peptidoglycan layers in Gram negative organisms contain teichoic acid? What do they contain instead?

Answer 17

NO! They have murein lipoprotein (small + helical)

Question 18

Relationship between murein lipoprotein and outer membrane

Answer 18

Murein lipoprotein extends from peptidoglycan layer and binds to the outer membrane

Question 19

Composition of the outer membrane of gram negative bacteria

Answer 19

Phospholipid bilayer but the outward facing lipid is lipopolysaccharide (LPS). Hydrophobic tails pointing to the centre still

Question 20

What is the composition of lipopolysaccharide (LPS)

Answer 20

3 covalently linked components

(1) O-specific side chain/O-specific antigen [OUTER carbohydrate chains composed of 1-50 oligosaccharide units]
(2) Central core polysaccaride (water soluble)
(3) Lipid A (endotoxin)

Question 21

With respect to LPS, do O-specific side chains/O-specific antigens vary between organisms?

Answer 21

Yes. Differ between organisms and are antigenic determinants

Question 22

Composition of Lipid A (endotoxin)

Answer 22

Disaccharide with multiple fatty acid chains reaching into membrane

Question 23

Do Gram-positive organisms have endotoxin

Answer 23

No except Listeria monocytogenes

Question 24

What are the clinical implications of Gram positive bacteria

Answer 24

Thick peptidoglycan layer allows diffusion of low molecular weight compounds e.g. antibiotics, detergents and dyes)

Question 25

What are the clinical implications of Gram negative bacteria

Answer 25

Outer LPS containing membrane acts as a diffusion barrier to acting on inner membrane

Question 26

4 types of bacterial morphology?

Answer 26

1. Cocci (spherical)
2. Bacilli (rods)
3. Spiral (comma shapes, S-shape, spirals)
4. Pleomorphic (lacks distinct shape)

Question 27

Name for short bacilli

Answer 27

Coccobacilli

Question 28

2 clinically important gram positive cocci

Answer 28

Streptococcus and Staphyloccocus

Question 29

2 clinically important gram positive cocci arrangement

Answer 29

Streptococcus - strips of cocci

Staphyloccus - clusters of cocci

Question 30

What is the purpose of spores in bacteria

Answer 30

Protect dormant bacteria from harsh environment

Question 31

Names of 2 spore-forming gram positive bacteria

Answer 31

Clostridium and Bacillus

Question 32

Names of 2 non spore-forming gram positive bacteria

Answer 32

Corynebacterium and Listeria