Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Y1 - Microbio Exam 2 > 1_Bacteriology I > Flashcards

1_Bacteriology I Flashcards

1
Q

bacteria:

define

A
  1. small, single cell organisms
  2. 0.1-10 micrometers in length
  3. seen w/ light microscope
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how do bacteria differ from eukaryotic cells?

8 differences

A
  • all are:
    • smaller
    • have cell wall
    • different ribosome structure (70S in bacteria vs. 80S in ribosomes)
  • lack
    • nucleus
    • other organelles (membrane bound vesicles)
    • sterols in membranes
  • some can
    • produce flagella and pili/fimbriae
    • produce capsules and extracellular matrix for biofilms
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

describe basic structure of bacterial cell wall

A
  1. composed of peptidoglycan
  2. pattern
    • alternating residues of NAG and NAM
      • NAG: N-acetylglucosamine
      • NAM: N-acetylmuramic
    • peptide chain of 3 variant amino acids w/ a terminal D-Ala, which can be crosslinked to 3rd amino acid of a neighboring chain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

purpose of cross-linking in the bacterial cell wall?

how can the cross-link vary?

A
  • fxn: cross-linking adds strength to the peptidoglycan
  • the cross-link b/w 4th D-Ala and the 3rd amino acid can be either:
    • direct, or
    • via multi-amino acid bridge
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

purpose of gram-staining

A

divides and identifies pathogenic bacteria into two different classes on the basis of cell wall and membrane structure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

steps of gram staining, and colors that result

A
  1. staining with crystal violet
    • both purple: Gram positive and Gram negative cells appear purple under oil-immersion light microscopy
  2. treatment with iodine aggregates the crystal violet
    • both purple: Gram positive and Gram negative cells appear purple
  3. washing with ethanol collapses peptidoglycan and extracts lipids from the outer membrane
    • Purple/Colorless: Gram positive cells appear purple; Gram negative cells are colorless
  4. counterstaining with Safarnin
    • Purple/Red: Gram positive cells appear purple; Gram negative cells appear red
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

after which steps of gram staining will both the gram positive and gram negative bacteria be purple?

A

Steps 1 and 2

  • staining with crystal violet - both purple under oil-immersion light microscopy
  • treatment with iodine aggregates the crystal violet - both purple
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

just list the 4 steps of gram staining, not the color that results

A

“Color Is Everything #Science”

  1. staining with crystal violet
  2. treatment with iodine aggregates the crystal violet
  3. washing with ethanol collapses peptidoglycan and extracts lipids from the outer membrane
  4. counterstaining with Safarnin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

after which step of gram staining yields both purple and red staining?

A

After counterstaining w/ Safarnin

Yields purple gram-positive, and red gram-negative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

compare cell wall of Gram-Positive and Gram-Negative (outer to inner layers)

and example of bacteria

A

Gram-positive:

  • peptidoglycan cell wall
  • inner plasma membrane
  • E.g. S. aureus

Gram-negative:

  • cell wall:
    • outer membrane +
    • periplasmic space containing peptidoglycan layer
  • inner plasma membrane
  • e.g. E. coli
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

which organisms do NOT stain well with Gram reagents?

why?

A
  • Mycobacteria – high lipid content in wall
  • Rickettsia, Chlamydia – obligate intracellular parasites, Gram-negative cell wall structure
  • Mycoplasma, Ureaplasma – lack cell wall –> too small for standard light microscopy
  • Spirochetes – most are too slender for standard LM
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

can growth state affect gram-staining?

A

yes!

e.g. old cultures – stationary phase and some species of bacteria when directly stained in clinical specimens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how to visualize:

mycobacteria

A

acid-fast stain

(cannot be gram-stained due to high lipid content in cell wall)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how to visualize:

rickettsia

A

Giminez stain or acridine orange

(can’t be gram-stained bc it is an obligate parasite; gram negative cell wall structure)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how to visualize:

chlamydia

A

DNA probes used for rapid ID;

intracellular includions may be visualized w/ fluorescent antibody; can also use giemsa, giminez, or other stains

(can’t be gram-stained bc it is an obligate parasite; gram negative cell wall structure)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how to visualize:

mycoplasma or ureaplasma

A

culture and patient serology

(can’t use gram staining bc lacks cell wall; too small for standard LM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how to visualize:

spirochetes

A

darkfield microscopy used to be standard,

but now ELISA is used for treponema and borrelia

(can’t use gram-staining bc most are too slender for standard LM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what factor confers cell shape and arrangement of bacteria?

A

cell wall (specifically peptidoglycan)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

basic bacterial shapes

A
  • cocci: roughly spherical
  • bacillus: rod-shaped
  • vibrio: curved-rod shape (comma shape)
  • fusiform: tapered ends
  • spirochete: flexible spirally twisted
  • filamentous: long, branching structure
  • pleomorphic: alter their shape or size in response to environmental condition
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

basci bacterial arrangements

A
  • diplo: pair
  • tetrad: four
  • sarcinae: arranged cubes of eight
  • strepto-: arranged in chains
  • staphylo-: arranged in irregular, often grape-like clusters
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

how do these bacterial arrangements differ?

sarcinae, strepto-, staphylo-

A
  • sarcinae: arranged cubes of eight
  • strepto-: arranged in chains
  • staphylo-: arranged in irregular, often grape-like clusters
22
Q

under normal conditions, what causes a cell to lyse?

A

cells w/o a cell wall would lyse bc the membrane cannot withstand the internal turgor pressure

23
Q

how can bacteria stay stable even w/o a cell wall?

A

some can undergo a programmed change in their membrane so the membranes are stable w/ a reduced (cell-wall defective form) or no cell wall (L-form)

24
Q

what confers a negative charge to the cell wall?

what determines the amount of this polysaccharide?

A
  • teichoic acids attached to the wall confer a negative charge
  • amount of teichoic acid depends on:
    • bacterial species and the
    • amount of peptidoglycan
25
Q

teichoic acid:

define

A
  • acidic polysaccharide covalently linked to NAM (N-acetylmuramic) –> gives typical negative charge to more abundant Gram+ bacteria
  • can act as barrier to penetration of negatively charged molecules
26
Q

cell-wall associated proteins:

define

A
  • proteins covalently linked to peptidoglycan in place of cross-linking
  • (KC: the cell wall can have proteins covalently attached to the peptide side chain in place of a peptidoglycan crosslink (predominantly in Gram positive bacteria)
27
Q

*steps of cell wall biosynthesis

A
  1. cytoplasmic steps (synthesis of peptidoglycan subunits)
    • NAG –> makes NAM
    • A pentapeptide chain is attached to NAM (AA1-AA2-AA3-D-Ala-D-Ala).D-Ala is derived from L-Ala by a racemase.
  2. cell membrane step
    • an undecaprenyl carrier transfers the NAG-NAM-pentapeptide subunit to the outer leaflet of the cytoplasmic (inner membrane)
  3. cell wall steps
    • existing cell wall is cleaved by autolysins and the addition of new subunits is carried out by penicillin binding proteins (PBPs).
  4. The new subunits are added by transglycosylation (sugar bonds) and transpeptidation (peptide bond) reactions carried out by penicillin binding proteins.
28
Q

Abx that inhibit cell wall synthesis, and where they act

A
  • Phosphomycin/Fosfomycin is a PEP analog that inhibits the synthesis of NAM from NAG.
  • D-cycloserine is an analog of D-Ala and inhibits the racemase reaction and addition of D-Ala to the AA1-AA2-AA3 chain
  • Bacitracin binds undecaprenyl-PP and inhibits recycling of the carrier.
  • Vancomycin (glycopeptide antibiotic) binds D-Ala-D-Ala and sterically hinders PBPs from carrying out transpeptidation and transglycosylation reactions.
  • b-lactams are structurally related to D-Ala and tightly bind PBPs inhibiting their transglycosylation and transpeptidation activity.
29
Q

what conditions are needed for inhibitory antibiotics to work?

A

these require growing cells for activity

  • Growing cells need to increase their cell wall, hence they produce autolysins to cleave the wall prior to inserting new peptidoglycan.
  • In the absence of new subunits, the autolysins will eventually destroy the cell wall. These resulting cells are osmotically fragile.
30
Q

how can bacteria become resistant to cell-wall-inhibitory antibiotics?

A
  1. enter a quiescent state (learn later)
  2. convert to L-forms – undergo programmed change in cell membrane so they don’t lyse
  3. Mycoplasma lacks cell wall
31
Q

key components of bacterial membranes?

what do these membranes lack, as compared to eukaryotes?

A
  1. PHOSPHOLIPIDS, w/ hydrophilic head/ hydrophobic tail:
    • made up primarily of phosphotidylethanolamine and phosphotidylglycerol
  2. LACK sterols
    • *exception is Mycoplasma, which incorporate sterols from their environment into their membranes
32
Q

components of gram-positive membrane

A
  • lipoproteins
  • lipoteichoic acid
  • membrane proteins
33
Q

components of gram-negative membrane

A
  • both leaflets of the cytoplasmic (inner membrane) are made of a mix of phosphotidylglycerol and phosphotidylethanolamine
    • inner leaflet of the outer membrane made of predominantly phosphotidylethanolamine
    • outer leaflet of the outer membrane is composed of LPS (lipopolysaccharide)
34
Q

which leaflets have:

  1. mix of phosphotidylglycerol and phosphotidylethanolamine
  2. predominantly phosphotidylethanolamine
  3. lipopolysaccharide
A
  1. mix of phosphotidylglycerol and phosphotidylethanolamine
    • both inner and outer leaflets of inner membrane
  2. predominantly phosphotidylethanolamine
    • inner leaflet of outer membrane
  3. lipopolysaccharide (LPS)
    • outer leaflet of outer membrane
35
Q

lipopolysaccharide is composed of:

A
  • lipid A
  • core glycolipid
  • O-specific oligosaccharide subunit composed of repeating sugar subunits
36
Q

which bacteria are capable of causing endotoxic shock?

why?

A
  • Only Gram-negative bacteria are capable of causing endotoxic shock, a type of septic shock.
  • Due to presence of Lipopolysaccharide in the outer leaflet of the outer membrane –> upon cell lysis and release of LPS
37
Q

two types of porins, and where are they found?

A
  • types:
    • non-specific, (water-filled channels)
    • specific
  • found in outer membrane of Gram negative bacteria
38
Q

where are transporters located in gram-positive and gram negative bacteria?

A

A number of transporters are located in the cytoplasmic membrane of Gram negative and Gram positive bacteria

39
Q

how does the gram-negative outer membrane affect Abx?

A

acts as an additional barrier;

example of intrinsic antibiotic resistance

40
Q

polymixin:

define and characteristics

A
  • antibiotics, used predominantly as topical antibiotic (due to toxicity for human cells)
  • composed of a fatty acid tail and cyclic peptide head group
  • disrupts bacterial membrane causing release of cytoplasmic components
  • will destroy quiescent or dormant (non-replicating) cells
41
Q

polymixins have a high affinity for…

A

LPS and phosphatidylethanolamine

42
Q

rank the effectiveness of polymixins from high to low:

human cells, gram positive, gram negative

A

High to Low

Gram negative (most effective) > Gram positive > Human cells

43
Q

capsule:

define and functions

A
  • discrete layer assoc. w/ individual cells
  • functions:
    • mediate adherence
    • protect from engulfment by phagocytes
    • protect from drying/ dessication
44
Q

matrix:

define and functions

A
  • (slime layer) secreted layer which embeds cells allowing for biofilm formation
  • functions:
    • carbohydrate reservoir
    • matrix for biofilm formation
45
Q

fimbriae/ pili:

define and functions

A
  • protein structures
  • functions:
    • involved in attachment, adherence, conjugation (DNA exchange)
    • motility (gliding/twitching motility)
46
Q

flagella:

define and functions

A
  • composed of flagellin
  • function:
    • uses the proton motive force to power bacterial motility
    • 3 arrangements:
      • Monotrichous (polar)
      • Lophotrichous
      • Peritrichous
47
Q

describe the DNA organization in bacteria

A
  • Bacterial cells have tightly coiled DNA that can be referred to as a nucleoid.
    • nucleoid has no membrane, so it is not a nucleus
  • Most bacterial chromosomes are circular (supercoiled and compacted; a number of structural maintenance proteins aid in this process)
48
Q

which proteins allow for replication starting at the origin of replication (ORI), and are target of antibiotics?

A
  • DNA gyrase and topoisomerase IV
49
Q

DNA gyrase:

function

A
  • binds to and relaxes DNA, and catalyzes strand cleavage and exchange to affect DNA supercoiling and compaction –> to fit DNA into bacterial cell;
  • makes DNA accessible for transcription and replication
50
Q

which drugs bind to DNA gyrase?

A
  • quinolones and floroquinolines bind the DNA gyrase: ATP complex thus blocking transcription and DNA replication
  • novobiocin inhibits DNA gyrase activity
51
Q

principle behind PCR

A
  • Many pathogens have genes unique to only the single species
  • The ability to PCR amplify that gene can be used as a diagnostic indicator that the specific pathogen is present

Y1 - Microbio Exam 2 (18 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions