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Microbiology/Lab Medicine > Bacterial Structure and Classification > Flashcards

Bacterial Structure and Classification Flashcards

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Biology 101 flashcards
1
Q

Classification of bacteria is largely determined by what?

A

structure

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2
Q

pathogenic properties of bacteria can be dependent on specific structure such as ___

A

pili and capsules

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3
Q

the structures unique to bacteria are also the bases and targets of ____

A

antimicrobial therapy

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4
Q

what are the 2 major shapes of bacteria?

A

rods (bacilli) and spheres (cocci)

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5
Q

chains of cocci =

A

streptococci

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6
Q

cocci in pairs =

A

diplococci

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7
Q

cocci in grape-like clusters =

A

staphylococci

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8
Q

which type of cocci is most infectious?

A

staphylococci

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9
Q

comma-shaped bacteria =

A

vibrio

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10
Q

corkscrew shape bacteria =

A

spirilli and spirochetes

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11
Q

the bacterial genome usually comprises what?

A

single, circular DNA chromosome that lacks introns and is not bound by histone proteins

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12
Q

do bacteria have cell walls?

A

yes

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13
Q

what are bacterial cell walls composed of?

A

peptidoglycan

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14
Q

the cell wall provides ___ for the bacteria and also serves as ___ for antimicrobial therapy

A

provides rigidity; major target

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15
Q

how do the cell walls of gram positive and gram negative bacteria differ?

A

gram positive: very thick, heavily cross-linked, lies external to cytoplasmic membrane, contains teichoic and lipoteichoic acid (up to 50%)
gram negative: thin, lightly cross-linked, lies bw inner cytoplasmic and outer membrane in periplasmic space

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16
Q

the bacterial lipid membrane lacks what?

A

sterols

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17
Q

what is special about the membrane of gram negative bacteria?

A

they have 2 lipid membranes

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18
Q

what is the role of pili (fimbrae)?

A

1) attach bacteria to host cell surfaces (major)

2) ‘sex pilus’ used to transmit genetic material from one bacterium to another during conjugation

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19
Q

what is the role of flagella?

A

allow motile bacteria to swim

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20
Q

flagella bear what antigen which is used in serotyping?

A

H

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21
Q

do all bacteria have pili? flagella?

A

no; no

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22
Q

what are capsules?

A

external structures composed of either polysaccharide or polypeptides

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23
Q

what is the role of capsules?

A

protect encapsulated bacteria from phagocytosis

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24
Q

not all bacteria are encapsulated, but nearly all bacterium causing ___ contains a capsule

A

meningitis

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25
Q

how can capsules be visualized?

A

by their ability to exclude dyes from immediate proximity of bacterium

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26
Q

what are spores?

A

dehydrated, dormant forms of bacteria that allow them to survive during harsh conditions

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27
Q

can both gram negative and gram positive bacteria form spores?

A

only gram positive rods

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28
Q

the cytoplasmic membrane of gram pos/neg bacteria contains many ___ necessary to bring in nutrients.

A

transport proteins

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29
Q

the outer membrane of gram negative bacteria serves as an additional ___

A

permeability barrier

30
Q

is the outer membrane of gram negative bacteria charged? why or why not?

A

yes, negatively charged which helps bacteria evade phagocytosis, hinder antibiotic uptake, and avoid action of complement

31
Q

the outer membrane of gram negative bacteria contains ___ to allow import of nutrients

A

porins

32
Q

the periplasm is home to ___ some of which destroy antibiotics

A

degradative enzymes

33
Q

unique to the outer membrane of gram neg. bacteria is ___, found in the outer leaflet of the membrane.

A

lipopolysaccharide (LPS)

34
Q

what does LPS contain?

A 
lipid A (toxic phospholipid, aka endotoxin)
core polysaccharide
O antigen polysaccharide (major surface antigen of gram neg. bacteria)
35
Q

lipid A is recognized by the ___ which elicits what response?

A

innate immune system –> cytokine storm leading to septic shock

36
Q

the successful pathogenesis by some bacteria depends on their ability to ___

A

secrete proteins or other substances from the cell

37
Q

describe the Type I protein secretion system

A
  • members of ABC transporter family
  • encoded by all gram neg bacteria
  • proteins are directly secreted into EC environment from cytoplasm
38
Q

what is the significance of the type I secretion system with regards to bacterial pathogenesis?

A

antimicrobial drugs can be expelled from the cell using these systems, thus promoting resistance to the antibiotic

39
Q

describe the Type II protein secretion system

A
  • found in all gram negative bacteria
  • serve as the general secretory pathway, used to deliver proteins to periplasm and EC spaces
  • proteins first secreted to the periplasm before being secreted across outer membrane
40
Q

describe the Type III protein secretion system

A
  • found only in pathogens
  • hydrophobic segments of the Type III
    system span cytoplasmic and outer
    membranes of gram negative cell as well as
    plasma membrane of animal cell
41
Q

why are type III secretion systems referred to as molecular syringes?

A

bc their structure allows direct injection of toxins and other virulence factors into cytosol of a targeted animal cell

42
Q

what are the bases for gram staining?

A

differing peptidoglycan depths and extent of cross-linking

43
Q

in gram staining, the extensive cell wall of Gram ___ bacteria retains the crystal violet while the thin layer of peptidoglycan found in Gram ___ bacteria does not.

A

positive; negative

44
Q

peptidoglycan is a major target for ___

A

antimicrobial therapy

45
Q

Peptidoglycan is composed of a backbone of repeating disaccharides comprising ___

A

N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG)

46
Q

what enzyme links the disaccharides in peptidoglycan to form long chains?

A

transglycosylase

47
Q

what is attached to the NAM residue of

each disaccharide?

A

pentapeptide composed of L- and D-isomers of amino acids;

48
Q

what enzymes are involved in cross-linking?

A

transpeptidases (penicillin-binding proteins) and carboxypeptidases

49
Q

how does the cross-linking differ bw gram

positive and gram negative bacteria?

A

simple bond in Gram negative bacteria, but in Gram positive bacteria, a pentaglycine interpeptide links the polypeptides

50
Q

NAM-pentapeptides contain a terminal D-alanine pair which is critical for what?

A

crosslinking process making them a target for antimicrobials

51
Q

cell wall assembly begins where?

A

cytoplasm

52
Q

what are the steps of cell wall assembly that occur in the cytoplasm?

A

individual NAM-NAG disaccharides linked to a pentapeptide side chain are synthesized and attached via a diphosphate linkage to a lipid carrier

53
Q

how do the cytoplasmic cell wall components make it out of the cytoplasm?

A

the lipid carrier is localized in the cytoplasmic membrane and is used to transport individual disaccharide pentapeptide subunits across the membrane to the external face of the cytoplasmic membrane

54
Q

once external to the cytoplasmic membrane, what happens to the cell wall components?

A

subunit is incorporated into the growing
cell wall by the action of glycosidases and
transpeptidases

55
Q

once external to the cytoplasmic membrane, what happens to the lipid carrier? why is this significant?

A

lipid carrier recycles to
the interior leaflet of the cytoplasmic membrane to recharge with new cargo, but only after dephosphorylation –> dephos. is antimicrobial target

56
Q

what is lysozyme?

A

a glycosidase that hydrolyzes the bond bw NAM and NAG, which disrupts the sugar backbone (instead of the pentapeptide cross-links)

57
Q

where can lysozyme be found?

A

tears, saliva, in lysosomes of phagocytic cells

58
Q

what was the first beta-lactam that was discovered?

A

penicillin

59
Q

what is a beta-lactam? why is it important?

A

drugs containing a beta-lactam ring, which structurally resembles the D-alanine D-alanine terminal pair of the pentapeptide side chains; bc of this resemblance, the beta-lactams are bound by the transpeptidases (i.e., penicillin-binding proteins) of the bacteria and prevent cross-linking from occurring

60
Q

how does the mechanism of action of the glycopeptide vancomycin differ from beta-lactams?

A

directly binds the D-alanine D-alanine pair while the cell wall subunit is still attached to its lipid carrier, blocking its availability for subsequent incorporation into the growing cell wall.

61
Q

what is problem with beta-lactams and glycopeptides?

A

resistance

62
Q

how do bacteria resist beta-lactams?

A

the beta-lactam ring is cleaved by beta-lactamases produced in resistant
bacteria; other resistant bacteria produce
mutated transpeptidases that no longer bind beta-lactams

63
Q

how do bacteria resist glycopeptides like vancomycin?

A

D-alanine D-lactone is synthesized by bacteria instead of D-alanine D-alanine. The new pair is still recognized by transpeptidases, but not vancomycin

64
Q

beta-lactams require what for activity?

A

cell growth

65
Q

when beta-lactams inhibit the cross-linking of new subunits, cells ___ due to a loss of structural
integrity

A

lyse

66
Q

what is the growth property of bacteria most associated with classification?

A

response to oxygen

67
Q

aerobic bacteria =

A

require oxygen and use respiration for growth

68
Q

anaerobic bacteria =

A

inhibited or killed in the presence of oxygen and use fermentation exclusively for metabolism

69
Q

facultative bacteria =

A

represent the majority of pathogens and use respiration in the presence of oxygen and use fermentation in its absence

70
Q

microaerophilic baceria =

A

grow in the absence of oxygen, but grow optimally at low oxygen concentrations (5-10%)

71
Q

the basis of classification of bacteria includes:

A 
 Morphology
 Arrangement
 Staining properties
 Growth properties
 Fermentation properties
 Other enzymatic and virulence properties
 Antigenicity
 Genotype

Microbiology/Lab Medicine (3 decks)

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