Micro: Bacterial Structure & Classification

Question 1

What are the two major shapes of bacteria?

Answer 1

rods (bacilli) and spheres (cocci)

Question 2

What is streptococci?

Answer 2

chains of cocci bacteria

Question 3

What are comma-shaped bacteria called?

Answer 3

vibrio

Question 4

Describe the bacterial genome.

Answer 4

single circular ring of DNA, no introns, no histones

Question 5

What composes bacterial cell walls?

Answer 5

peptidoglycan

Question 6

Bacterial cell membranes are notable for lacking what?

Answer 6

sterols

Question 7

Components of bacteria that differ enough from animal cells to be used as antibiotic targets include:

Answer 7

cell wall, ribosome, RNA polymerase, topoisomerase

Question 8

What is the major gross difference between gram positive and gram negative bacteria?

Answer 8

gram negative has an additional outer membrane

Question 9

What is the major role of pili in pathogenesis?

Answer 9

to attach bacteria to host cell surfaces

Question 10

What is the composition and role of the bacteria’s capsule?

Answer 10

composed of either polysaccharides or polypeptides; serves to protect against phagocytosis; visualized by its ability to exclude dye from its immediate surroundings; all organisms causing meningitis characteristically have a capsule

Question 11

What is a spore or endospore?

Answer 11

dehydrated, dormant forms that allow potential pathogens (certain Gram positive rods) to survive in harsh conditions for a long time; typically formed in response to stress or nutrient limitation

Question 12

Up to 50% of the Gram positive cell wall is composed of ____ acid or ____ acid.

Answer 12

teichoic acid; lipoteichoic acid

Question 13

Describe the differences between peptidoglycan walls of Gram positive and negative cells in terms of layers thick, amount of cross-linking, and location.

Answer 13

Gram+: >40 layers thick, heavily cross-linked, lies between cytoplasmic membrane and capsule
Gram-: 2 layers thick, lightly cross-linked, lies between the cytoplasmic membrane and the outer membrane in region called periplasmic space

Question 14

What is the role of the outer membrane in Gram negative bacteria?

Answer 14

additional permeability layer, is negatively charged thereby helping avoid phagocytosis, hinder antibiotic uptake, and avoid action of complement

Question 15

What structure allows the import of nutrients into the Gram-negative cell?

Answer 15

porins in the outer membrane

Question 16

What is lipopolysaccharide (LPS)?

Answer 16

component unique to Gram-negative bacteria outer membrane that contain 3 components: lipid A (aka endotoxin), a core polysaccharide, and O antigen polysaccharide (major surface antigen of Gram-neg bacteria)

Question 17

What is the role of Lipid A in sepsis?

Answer 17

lipid A is recognized by the innate immune system to elicit a cytokine storm which leads to septic shock

Question 18

Describe the Type I secretion system for Gram-negative bacteria.

Answer 18

ATP binding cassette transporters connected to a channel-tunnel via adaptor proteins secrete proteins; through this system antimicrobial drugs can be expelled, promoting resistance

Question 19

Describe the Type II secretion system for Gram-negative bacteria.

Answer 19

two-step secretion system for delivering proteins first to the periplasm and then EC space

Question 20

Describe the Type III secretion system for Gram-negative bacteria.

Answer 20

hydrophobic segments extend through cytoplasmic and outer membranes, as well as the membrane of the targeted animal cell, allowing direct injection of toxins and virulence factors into the target cell

Question 21

Describe the staining difference between Gram negative and positive bacteria.

Answer 21

extensive cell wall (thick heavily cross-linked peptidoglycan layers) in Gram positive cells retain the stain

Question 22

What is peptidoglycan composed of?

Answer 22

backbone of repeating disaccharides, NAM and NAG; the NAM residue of each disaccharide also has a pentapeptide attached

Question 23

What is transglycosylase?

Answer 23

an enzyme that links disaccharides to form long chains of peptidoglycan

Question 24

What are the targets of penicillin?

Answer 24

transpeptidases, also known as penicillin-binding proteins

Question 25

What do the enzymes transpeptidase and carboxypeptidase catalyze?

Answer 25

cross-linking of pentapeptides between peptidoglycan chains

Question 26

Cross-linking is a simple bond in Gram ____ bacteria peptidoglycan.

Answer 26

negative

Question 27

A pentaglycine interpeptide cross-links the polypeptides in Gram _____ bacteria peptidoglycan.

Answer 27

positive

Question 28

Cell wall assembly begins in what part of the cell?

Answer 28

cytoplasm; lipid carrier

Question 29

Describe the location and function of lipid carriers.

Answer 29

localized in the cytoplasmic membrane; used to transport individual disaccharide pentapeptide subunits across the membrane to the external face of the cytoplasmic membrane for incorporation into the growing cell wall

Question 30

What is the major regulatory step of the lipid carrier that can serve as the target of antimicrobials such as bacitracin?

Answer 30

dephosphorylation of the carrier, to allow for recycling and reloading with new cargo

Question 31

What is lysozyme?

Answer 31

a naturally occurring glycosidase that hydrolyzes the NAM-NAG bond, thereby defending against microbes; present in tears, saliva, lysosomes of phagocytes, and is particularly effective against Gram-positive bacteria

Question 32

What is the action of vancomycin?

Answer 32

it directly binds the D-alanine D-alanine pair while the cell wall is subunit is still attached to the carrier, thereby preventing cell wall growth (aka peptidoglycan chain elongation)

Question 33

What is the action of beta-lactams?

Answer 33

because the beta-lactam ring is structurally similar to D-alanine D-alanine terminal pair of pentapeptide side chains, they get bound by the transpeptidases and cross-linking is prevented; requires cell growth to have an effect because it must interfere with cross-linking of new subunits

Question 34

What two genera of bacteria fail to stain using the Gram method?

Answer 34

mycoplasma and chlamydia

Question 35

True or false: aerobic bacteria use fermentation for growth, and anaerobic bacteria use respiration.

Answer 35

False (it’s actually the other way around)

Question 36

What process(es) do facultative anaerobes use for growth?

Answer 36

respiration in the presence of oxygen; fermentation in the absence of oxygen

Question 37

Microaerophillic bacteria can grow in the absence of oxygen, but grow optimally in what concentrations of oxygen?

Answer 37

low, i.e. 5-10%

Question 38

Serotyping classifies bacteria of one genus based on what?

Answer 38

the expression versus the lack of a specific antigen

Question 39

The E. coli strain O157:H7 causes severe diarrhea. The O and H refer to antigens located where, respectively?

Answer 39

O antigen found on the lipopolysaccharide (LPS), and H antigen found on the flagellum

Question 40

What is the utility of serotyping a bacterial infection?

Answer 40

to identify the specific strain; for food-borne illnesses to identify the origin or source of the infection

Question 41

What portion of LPS leads to sepsis?

Answer 41

Lipid A, aka endotoxin

Question 42

“A polysaccharide polymer joined by peptide chains” describes what component of bacterial cell walls?

Answer 42

peptidoglycan

Question 43

Which bacterial secretion system is often termed “the molecular syringe”?

Answer 43

Type III