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ID Week 2 > LM 2.1: Bacteria Growth & Cell Walls > Flashcards

LM 2.1: Bacteria Growth & Cell Walls Flashcards

1
Q

how fast does bacteria grow?

A

it can be extremely rapid

high surface-to-volume ratio

exponential growth

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2
Q

how does surface-to-volume ratio effect bacteria growth?

A

surface to volume ratios limit metabolic efficiency

a bacteria’s need for nutrients, and rate of waste generation, are proportional to volume

its rate of taking up nutrients, or pumping out waste products, is proportional to surface area

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3
Q

what is the lag phase of the bacterial growth curve?

A

bacteria adapting to new environment

little to no growth

large changes in gene expression

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4
Q

what is the logarithmic/exponential phase of the bacterial growth curve?

A

period of most rapid increase in cell mass

growth is balanced, constant growth rate

gene expression is constant
Most bacterial studies involve this phase

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5
Q

what is the stationary phase of the bacterial growth curve?

A

nutrient(s) become limiting – cells begin to starve

genes necessary for starvation survival are transcribed

the most common state of existence for most bacteria

cell growth balances cell death (loss of VIABILITY)

in many cases, this is when toxins are produced

some bacteria begin to sporulate

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6
Q

what is the death phase of the bacterial growth curve?

A

rapid cell death

new cell growth begins to balance cell death (“cannibalism”)

bacteria become more resistant to environmental stresses

some cells become persisters

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7
Q

which bacteria are spore-forming bacterial pathogens?

A
  1. bacillus

2. clostridium

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8
Q

what are the characteristics of bacterial endospores?

A

very resistant to high temperatures (survives boiling >1h)

resistant to desiccation, low and high pH

sSensitive to irradiation

multilayered spore coat

can remain viable for >1000s of years

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9
Q

what are the 3 ways you can kill bacteria?

A
  1. sterilization
  2. disinfection
  3. antisepsis
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10
Q

what is sterilization?

A

use of physical or chemical agents to destroy all microbial forms, including bacterial spores

  1. heat = >120 C for 15 minutes wet or hours if dry
  2. ionizing radiation
  3. filtration = removes cell, spores from liquids
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11
Q

what is disinfection?

A

use of physical procedures or chemical agents to destroy most microbial forms

bacterial spores and other relatively resistant organisms (e.g., mycobacteria, some viruses, fungi) may remain viable

  1. alcohols
  2. phenols
  3. detergents
  4. halogens
  5. UV irradiation
  6. ethylene oxide
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12
Q

what is antisepsis?

A

use of chemical agents on skin or other living tissue to inhibit or eliminate microbes; not sporocidal

  1. soaps
  2. isopropanol
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13
Q

what is the function of the bacterial cell wall?

A
  • mediates adherence to target cells (adhesins, fimbriae, pili)
  • mediates invasion of target cells
  • mediates motility and chemotaxis
  • contains export machinery for toxins
  • in many cases contains intrinsic toxins
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14
Q

what is a major target for antibiotics?

A

bacterial cell wall

it’s because there’s no similar structure that exists in human cells

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15
Q

what is the cytoplasmic membrane of bacteria?

A

phospholipid bilayer with proteins

they’re mechanically weak but they’re an effective barrier against ion diffusion

they are really similar to animal cells so they’re difficult antibiotic targets

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16
Q

what are the two approaches to resisting osmotic pressure?

A
  1. strengthen membrane itself like with sterols

2. surround membrane with a retaining wall = this is what most bacteria do!

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17
Q

what are the roles of the retaining wall?

A
  1. hold in cytoplasmic membrane

confer cell shape:

  • spheres
  • rods
  • spirals
  1. permit rapid diffusion of small molecules
    - entry of nutrients
  • exit of waste products
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18
Q

what shape are cocci?

A

spheres

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19
Q

what shape are bacilli?

A

rods

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20
Q

what are the characteristics you’d want in a cell wall?

A
  1. strong to resist osmotic pressure
  2. flexible to change sape during cell division
  3. open to permit rapid diffusion of small molecules
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21
Q

what are the two basic bacterial cell wall structures?

A
  1. gram positive

2. gram negative

22
Q

what is the structure of gram negative cell walls?

A

periplasm = space between inner and outer membranes

outer membrane = outer leaflet is lipopolysaccharide (LPS) also called endotoxin –> OM borders periplasm, is shed in vesicles and contains LPS

thin peptidoglycan layer surrounded by a second bilayer membrane with porins

23
Q

what is the structure of gram positive bacteria?

A

lipoteichoic acid (LTA)

super thick peptidoglycan layer

24
Q

what is the function of periplasm in gram negative bacteria?

A

can include enzymes important for virulence and antibiotic resistance

25
Q

what is the function of the outer membrane in gram negative bacteria?

A

OM vesicles:

  1. can deliver toxins by fusing to host cell membrane
  2. increase dispersion of endotoxin
26
Q

what gets through outer membrane porins

A

small <600 Da

uncharged

hydrophilic

27
Q

what is the structure of peptidoglycan?

A
  1. chain-link fence = strong yet porous
  2. long chains of sugar copolymer = NAG-NAM

NAG = N-acetyl glucosamine

NAM = N-acetyl muramic acid = NAG + O-lactyl ether

  1. amino acid tails (5 AA long) on O-lactyl ether on NAM portion

3rd AA is lysine or DAP; both have free NH2 in side-chain

4th and 5th are both D-alanine

28
Q

what do fosfomycin drugs do?

A

take out the O-lactyl ether part of NAM in peptidoglycan

PEP analog; inhibits PEP O-lactyl ether on UDP-NAG

29
Q

what do cycloserine drugs do?

A

take out the D-ala part of the NAM in peptidoglycan

D-alanine analog; inhibits Ala racemase & D-ala-D-ala ligase

30
Q

what makes peptidoglycan strong?

A

NAM-NAG chains crosslinked to one another

without crosslinking, PG is weak (like a beaded curtain)

corsslinking happens through Lys/DAP on one chain (–NH2) bonded to penultimate D-Ala (–COOH) on another chain

31
Q

how does peptidoglycan get crosslinked?

A

DAP on one chain is bonded to D-ala on the other

this causes the terminal D-ala to be released during formation of crosslink

this provides entropic drive to make reaction efectively irreversible

B-lactam and glycopeptides act on this step!

32
Q

what are the steps in peptidoglycan summary?

A

Precursors are synthesized, yielding NAG, and peptidyl-NAM-UDP. [Inhibitors of these steps include fosfomycin and cycloserine.]

  1. pNAM-PO4 is transferred to bactoprenol-PO4, releasing UMP.
  2. In a concerted reaction, NAG is added to pNAM-P-P-bactoprenol and the resulting product is exported across the cytoplasmic membrane (by “flippase”).
  3. One product of step 3 is bactoprenol diphosphate, which must be recycled by removing the second PO4 . [This step is blocked by bacitracin.]
  4. One of the PBPs (“penicillin-binding proteins”, responsible for peptidoglycan biosynthesis) takes the pNAM-NAG from bactoprenol, and adds it to a growing NAM-NAG chain (transglycosylation). [This step is blocked by some glycopeptide antibiotics.]
  5. A crosslink is formed between two NAM-NAG chains, directly or indirectly linking the DAP/Lysine on one to the penultimate D-Ala on the other (transpeptidation) The terminal D-Ala is released. [This crosslinking is inhibited by glycopeptides and β-lactams.]
33
Q

what happens during step 1 peptidoglycan synthesis?

A

precursors of NAG are made in the cytoplasm of the bacteria

NAG and pNAM are synthesized then carried around the cell on UDP carriers

34
Q

what happens during step 2 peptidoglycan synthesis?

A

pNAM group is carried from carrier UDP to C-55 (bactoprenol)-PO4

35
Q

what happens during step 3 peptidoglycan synthesis?

A

pNAM-NAG transferred across cytoplasmic membrane and released from carrier protein

36
Q

what happens during step 4 peptidoglycan synthesis?

A

C55-PP carrier protein is recycled into C55-P so that it can go back and take another pNAM-NAG group across the membrane

37
Q

what does bacitracin do?

A

antibiotic found in neosporin!

it inhibits the step where the C55-PP carrier protein is recycled into C55-P so that it can go back and take another pNAM-NAG group across the membrane

38
Q

what happens during step 5 peptidoglycan synthesis?

A

transglycosylation

pNAM-NAG disacharrides are added to the growing chain outside the cell

39
Q

what do glycopeptides do?

A

inhibit step 5 of peptidoglycan synthesis

that’s the step where pNAM-NAG disacharrides are added to the growing chain outside the cell

they also inhibit the corss-linking step!

ex. vancomycin and teichoplanin

40
Q

what happens during step 6 peptidoglycan synthesis?

A

cross-linking

3rd AA on one acid gets crosslinked to the 4th on another

B-lactams and glycopeptides inhibit this step

41
Q

what’s the difference in crosslinking between gram - and gram + bacteria?

A

gram - has direct cross-linking between 3rd DAP and 4th D-ala of the other chain

gram + can have either direct or indirect crosslinking

indirect would be 5 glycine residues that crosslink the two chains in the same spot

42
Q

what’s the difference in peptidoglycan thickness between gram - and gram + bacteria?

A

gram + have super thick peptidoglycan layer than gram - bactiera

43
Q

how does gram staining work?

A

stain the bacteria first with crystal violet that will bind peptidoglycan layer

quick wash with ethanol will strip the purple stain from gram - but it can’t do the same from gram + unless you treat for a longer time

so they use sachranine for gram - bacteria which is pink in color

so bacteria under the microscope will be pruple for gram + and pink for gram -

44
Q

what’s the difference in attachment to cell between gram - and gram + bacteria?

A

gram - bacteria have a direct linkage between outermembrane lipoprotein by DAP to anchor the peptidoglycan to the outer membrane

in gram + bacteria, LTA is used to anchor peptidoglycan to cytoplasmic membrane and it weaves its way through peptidoglycan layer – the LTA is weaved through peptidoglycan layer and anchored to phospholipids in cytoplasmic membrane

45
Q

which TLRs target gram - lipoproteins?

A

lipoproteins in gram - bacteria link bacterial peptidoglycan to the outermembrane

they’re recognized by TLR2

46
Q

which TLRs target LTA of gram + bacteria?

A

TLR2 and TLR6

47
Q

what is lysozyme?

A

lysozyme is produced by humans during nonspecific, intrinsic defenses

it’s present in a lot of seromucous secretions

48
Q

what does lysozyme do?

A

chips the NAM-NAG backbone of peptidoglycan into individual pNAM-NAG disaccharides

49
Q

how do bacteria protect themselves against lysozyme?

A

chips the NAM-NAG backbone of peptidoglycan into individual pNAM-NAG disaccharides

  1. bacteria can cover PG with outermembrane like in gram -
  2. produce capsule on the outside of bacterium to produce PG
  3. some bacteria have a high degree of crosslinking
50
Q

what is chemotaxis important for during infection?

A

if a bacteria wants to penetrate the gut, they have to get through mucous that protects intestinal epithelium

epithelium produces chemicals that the bacteria can sense and they are attracted to it despite peristalsis trying to move the bacteria through the gut

51
Q

what is flagellum?

A

flagellum is anchored in the inner and outer membrane of bacteria

it moves bacteria around

bacteria can have 1 or more flagellum

they are super strong!

52
Q

what anchors PG to the cell?

A

gram - = lipoprotein

gram + = lipoteichoic acids (LTA)

ID Week 2 (20 decks)

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