Bacterial Structure, Function and Growth

Question 1

About how big are bacteria? (in microns)

Answer 1

0.2 μm – 10 μm

RBC’s are like 7 um

Question 2

What are the two sugars in the rigid mesh peptidoglycan layer?

Answer 2

N-acetylglucosamine (GlcNAc) aka NAG
N-acetylmuramic acid (MurNAc) NAM

momma NAGs you when you eat’NAM proteo-sugaz

Question 3

What are the major differences between gram + and - bacteria?

Answer 3

Positive:
Has Puffier Peptidoglycan wall + teichoic acid + lipoteichoic acid

Negative:
Two membranes. Not as much peptidoglycan layer in between (periplasmic space). Lipopolysaccharide chains. Porins. LIPOPROTEIN (anchors OM to peptidoglycan)

Question 4

Why is the peptidoglycan layer important?

Answer 4

Usually required for strength and rigidity against osmotic forces
□ Targeted by antibiotics
□ Recognized by host innate resistant mechanisms
-Phagocytosis, complement, inflammation, direct killing by lysozyme

Question 5

How is the peptidoglycan layer assembled?

Answer 5

MurNAc is linked to 5 glycine chain which is cross-linked from one chain (via DAP in gram-negative bacteria or L-lys in gram-positive bacteria) to D-ala on another chain

-Targeted by vancomycin (D-alanine residues)

Question 6

What do you call the firmly attached, gelatinous, and usually complex polysaccharides that coat the surface of individual bacteria?

Answer 6

Capsule

Question 7

How do capsules increase virulence?

Answer 7

Resist phagocytosis

**Protein-capsular polysccharide conjugate vaccine used in kids

Question 8

(Back to LPS because it is in 4 slides)

What are the components of the most common lipid of the outer membrane: Lipopolysaccharide, aka Endotoxin?

Answer 8

1. Lipid A
2. Core polysaccharide, and
3. O side-chain oligosaccharides that function as somatic antigens (O antigen)

Question 9

What is the toxic component of LPS (endotoxin)?

Answer 9

Lipid A

It induces TNF and IL-1

Question 10

What are the functions of the teichoic acids on Gram (+)?

Answer 10

Covalently linked to PG layer

Functions:

1. Ion homeostasis
2. Adherence an colonization
3. Interacts with innate immune system through TLR
4. Lipoteichoic acids help to anchor the cell wall to the membrane

Question 11

What does the extracellular glycocalyx do?

Answer 11

Formation of biofilm “slime layer”

Question 12

How does the biofilm help bacteria? (can you give 3 reasons)

Answer 12

1. Allows the bacteria to adhere to surfaces like rocks, teeth, catheters, host cells, other bacteria
2. Protects cells from phagocytosis, host defensive proteins (complement, antibody, defensins)
3. Serves to limit access of many antimicrobial agents to the embedded cells

Question 13

What do flagella do?

Answer 13

• motility
• role in pathogenesis (phase variation)
• H-antigen of flagella are used to classify enteric bacteria

Question 14

Which rotations, clockwise or counterclockwise, are used for the following:

1) Swimming (running)
2) tumbling

Answer 14

1) running = counterclockwise

2) tumbling = clockwise (clock hands make tumbling motion)

Question 15

What are pili used for?

Answer 15

• adherence to cells/ tissue

- conjugation (sex pillus)

Question 16

Bacteria Use Multiple Secretion Systems to:

Answer 16

• Deliver Proteins to the Cell Surface,
• Assemble Organelles on the Cell Surface,
• Export Proteins to the Extracellular Milieu,
• Inject Proteins or DNA Into host Cells!
  >Type III, IV, VI

Question 17

What is the purpose of the cytoplasmic membrane

Answer 17

anatomical and physiological barrier between the inside and outside of the bacterial cell

Question 18

Correctly name the four phases of bacterial growth in order

Answer 18

1. Lag phase
2. exponential phase
3. stationary phase
4. death phase

Question 19

In what phase are bacteria most resistant to antibiotics?

Answer 19

Stationary phase:

• because penicillin or other β-lactam antibiotics act on growing cells.
• In nature, bacteria probably spend most of their time in stationary phase.

Question 20

How many bacteria do you need to have to see turbidity? (cloudiness)

Answer 20

greater than 10^7/mL

Question 21

What are the two forms of energy currency?

Answer 21

ATP (biosynthetic interconversions)
PMF ( Proton Motor Force: flagellar rotation, membrane transport)

Bacteria also require “reducing power” in the form of NAD(P)H

Question 22

How do bacteria generate ATP and NADH? How are these processes different?

Answer 22

1. Fermentation: organic compounds serve as both electron donor and electron acceptor
2. Respiration: terminal electron acceptor is (typically) molecular oxygen

Question 23

What enzyme interconverts ATP and PMF?

Answer 23

membrane ATPase

Question 24

How do antimicrobials work on the principle of selective toxicity?

Answer 24

Select for components unique to bacteria, or concentrations that will affect bacteria and not host

Question 25

What’s the difference between the following:

• indifferent anaerobes
• facultative anaerobes
• microaerophilic bacteria

Answer 25

• indifferent anaerobes: ferment with or w/o oxygen present
• facultative anaerobes: respires with O2, ferments w/o O2
• microaerophilic bacteria: grows best at low O2 concentrations and can’t grow without it

Question 26

List some of the principal targets for the major groups of antibiotics used in human medicine.

Answer 26

• Cell wall antimicrobials
• Outer and cytoplasmic membrane antimicrobials
• Inhibitors of protein synthesis at the ribosomal level
• Inhibitors of nucleic acid synthesis
• Metabolic inhibitory antimicrobials