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Flashcards in Jackson: Bacterial Structure and Metabolism Deck (36)
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1

BACTERIAL MORPHOLOGY:

What is the Classification Scheme based on?

G+/-

Shapes

BACTERIAL MORPHOLOGY:
• Classification Scheme: based on cell envelope and shape
- Gram positive or Gram negative
- Rods, Cocci, Spirilla
- Pairs, tetrads, clusters, chains (not a reliable classification scheme)

2

Gram stain procedure

• Gram Stain: most commonly used diagnostic technique; color distinction based on bacterial cell wall constituents

- Procedure: ~1 minute each step
o Air dry and heat fix bacteria on slide
o Add crystal violet, rinse
o Add iodine (mordant), rinse
o Add acetone/isopropyl alcohol solution (10 drops), rinse
o Add safranin, rinse and dry
o Examine using oil immersion (1000x) objective

3

G+/- colors

Color Distinction: Gram positive are purple, Gram negative are pink

4

Gram staining mechanism

Mechanism:

o Crystal violet penetrates peptidoglycan layer to stain cytoplasm blue
o Iodine + crystal violet complexes, and it is too large to be washed out of Gram positive bacteria (thick cell wall), but is washed out of Gram negative bacteria
o Gram negative then counterstained with safranin (pink); done in order to visualize

5

Acid-Fast Bacteria: genus?

Cell walls contain:

Gram stain?

Methods used to stain cells:

• Acid-Fast Bacteria (Mycobacterium):
- Need to use a special stain (diagnosis of TB)
- Cell walls contain long chain fatty acids (mycolic acid), which repels dye
o Gram stain poorly
o Hard to decolorize with acetone/alcohol
- Hot (Ziehl-Neelsen) or Cold (Kinyoun) methods are used to stain these cells

6

G+/- Cell Envelope

CELL ENVELOPE:
• General:

- Gram Positive: cytoplasmic membrane + thick peptidoglycan
- Gram Negative: cytoplasmic membrane + thin peptidoglycan + outer membrane (2 cell membranes)

7

Teichoic acid =

LPS =

Teichoic acid = lipoteichoic acid

LPS = endotoxin

8

Peptidoglycan aka:
Function:

• Cell Wall (Peptidoglycan/Murein Layer):
- Gives bacterial cell shape and resistance to osmotic changes
- Target for antibacterial agents

9

Composition of Peptidoglycan:

Disaccharide-pentapeptide subunits

10

Disaccaride types:

• N-Acetylglucosamine (NAG)
• N-Acetylmuramic acic (NAM)

11

Peptide bridges between:

G+:

G-:

Peptide bridges between NAM cross-link subunits

• Gram Positive: pentaglycine bridge between lysine and D-alanine
• Gram Negative: direct link between D-alanine and diaminopimelic acid

12

B-Lactam MOA:

What form cross-links?

Penicillin structure resembles:

B-Lactam MOA: target peptide bridges

Penicillin binding proteins (PBPs) form cross-link

Penicillin structure resembles D-ala/D-ala intermediate (binds PBP instead, preventing crosslinking)

13

Teichoic (Mycolic) Acids (Gram Positive):

Associated with:

Also found in:

Techoic and lipotechioic acids provide strength to cell wall

- Associated with inflammatory response in some Gram positive infections
- Also found in Acid Fast Bacilli, making them resistant to phagocytic killing, drying

14

Outer Membrane only found in:

Composed of:

Outer Membrane (Only Gram Negative):

- Composed of bilayer of LPS and phospholipids

15

LPS

Composition (3 parts):

What causes endotoxic shock?

o LPS: important virulence factor; key mediator of inflammation (shock)

Composition of LPS:
• Repeating sugar residues (O antigens) useful for bacterial typing
• Core sugars (consistent, not part of pathogenesis)
• Fatty acid moieties (lipid A) is the bioactive portion of LPS (causes endotoxic shock)

16

Where is periplasmic space found?
What is periplasmic space?
Constituents include:

• Periplasmic Space (Only Gram Negative):

- Space between inner and outer membranes (contains peptidoglycan layer)
- Constituents include enzymes that degrade antibiotics (ie. beta-lactamases)

17

Cytoplasmic (Inner) Membrane:

Found where?

Composed of:

Gram Positive and Gram Negative

- Composed of a lipid bilayer heavily laced with protein

18

Beta-lactams interfere with the formation of (2)

Beta-lactams interfere with the formation of D-ala from L-ala

Beta-lactams interfere with the formation of D-ala + Lys or DAP peptide bond

19

Cytoplasmic (Inner) Membrane:

Functions

Functions:
o Transport of solutes
o Housing enzymes involved in outer membrane and cell wall synthesis
o Assembly and secretion of extracytoplasmic and extracellular substances
o Generation of ATP
o Housing molecular sensor that monitor environmental changes

20

Capsule:

Location:
Composition:
Production:
Protects cell from:

• Capsule:

Exterior to peptidoglycan layer (Gram positive) or outer membrane (Gram negative)

- Composition: high molecular weight polysaccharides or amino acids

- Production: depends on environment and growth conditions

- Important Virulence Factor: protects cell from complement mediated killing

21

Pili aka:

Definition:
Composition:
Mediates:
Antigenic and certain bacteria will:

• Pili (Fimbriae): hair like proteinaceous structures extending from cell membrane

- Composition: subunits of protein called pilin, tipped with adhesins

- Important Virulence Factor: mediate adhesion to host tissue

- Antigenic and certain bacteria (gonococcus) will vary the antigenic composition

22

Two Types of Pili

o Common Pili: mediate adhesion to host eukaryotic cells
o Sex Pili: join conjugating bacteria

23

Flagella:

Definition:
Composition:
Function:

Flagella: long, helical filaments extending from cytoplasmic membrane

- Composition: proteins called flagellins (highly antigenic; H antigens)
- Function: cell motility

24

Endospore definition:

Medically Important Endospore Formers:

Endospore: resting phase of bacteria when living conditions get tough

Medically Important Endospore Formers: Bacillus and Clostridium

25

PROTEIN SECRETION:

Type I

Gram +/-?

Sec-dependent or independent pathway?

Mechanism:

Example:

• Type I: GRAM (-)

- Sec-independent pathway

Mechanism:
o No amino-terminal signal sequence
o ABC transporters (ATP-binding cassette); therefore ATP dependent
o Bypasses periplasm, and is extruded through a hole in cytoplasmic and outer membranes

Example: E.coli hemolysin (alpha toxin)

26

PROTEIN SECRETION:

Type II

Gram +/-?

Sec-dependent or independent pathway?

Mechanism:
Recognizes:
Secretes proteins into:

• Type II: GRAM (-) and GRAM (+)

- Sec-dependent pathway

Mechanism:
o Recognizes proteins with signal sequence (~20 aa with conserved cleavage site)

Secretes proteins into:
• Periplasm of Gram (-)
• Extracellular environment of Gram (+)

27

PROTEIN SECRETION:

Type II

Secretes proteins into:

What form pores in outer membrane?
What else is required?

Example:

Secretes proteins into:
• Periplasm of Gram (-)
• Extracellular environment of Gram (+)

From the periplasm, move through outer membrane to exit cell
• Secretins form pores in outer membrane
• Chaperone proteins and ATP are required

Example: several bacterial toxins

28

PROTEIN SECRETION:

Type III

Gram +/-?

Sec-dependent or independent pathway?

Contact-Dependent or Independent?

Mechanism:

Requires:

Examples:

• Type III: GRAM (-)

- Sec-independent pathway

- Contact-Dependent

- Mechanism:
o Pore formed that injected proteins directly into eukaryotic cells
o Requires ATPase and chaperone proteins

Examples: Yesinia pestis (plague) injects Yops to disrupt eukaryotic cell function

29

Nutrient Transport

Passive Diffusion:

Active Transport:

Group Translocation:

Nutrient Transport

Passive Diffusion: enter by concentration gradient (water, CO2, O2, simple sugars)

Active Transport: energy dependent pumps in the cell envelope (sugars, aa, organic acids, inorganic ions)

Group Translocation: nutrient chemically modified before being brought into the cell (sugars, nucleic acids, FAs)

30

EMP Pathway (Glycolysis):

Glucose → pyruate + NAD + CoA → Acetyl CoA