Lecture 29 - Antibiotics

Question 1

soluble compounds that are produced and released by microorganisms and that inhibit the growth or kill other microorganisms

Answer 1

antibiotics

Question 2

bacteria can be classified based on three main criteria:

Answer 2

• aerobic vs. anaerobic
• shapes (rods, spheres, spirals)
• cell wall components (gram -ve or gram +ve)

Question 3

how many different types of cell walls can bacteria have?

Answer 3

two (gram +ve or gram -ve)

Question 4

bacterial cell walls are made of polysaccharide chains called:

Answer 4

peptidoglycan

Question 5

posseses a thick cell wall with many layers of peptidoglycan

Answer 5

gram +ve bacteria

Question 6

have relatively thin cell walls with few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins

Answer 6

gram -ve bacteria

Question 7

do most bacteria have a gram +ve or gram -ve cell wall?

Answer 7

gram -ve

Question 8

peptidoglycan structure consists of glycan strands made of alternative _____ and _____ residues cross-linked by polypeptides

Answer 8

N-acetylglucosamine (GlcNAc), N-acetylmuramic acid (MurNAc)

Question 9

peptidoglycan contributes to the overall _____ and _____ of a bacterium

Answer 9

structure, shape

Question 10

individual glycan strands are polymerized into the peptidoglycan chain by the enzyme:

Answer 10

glycosyltransferase (GT)

Question 11

cross links the glycan strands, and is the target for many antibiotics

Answer 11

transpeptidase (TP)

Question 12

we are covered in thousands of microbial species (normal flora), particularly in the:

Answer 12

skin, mouth, large intestine, and genital areas

Question 13

under what scenario do normal flora cause trouble?

Answer 13

if immune systems are weakened or if they gain access to normally sterile parts of the body

Question 14

microbes which do not require the host to be immunocompromised or injured; have developed highly specialized mechanisms for crossing cellular and biochemical barriers and for eliciting specific responses from the host organism that contribute to survival and multiplication

Answer 14

pathogens

Question 15

antibiotic efficacy and potency can be described with the following terms:

Answer 15

1) spectrum of activity
2) bacterial sensitivity
3) therapeutic index
4) ability to penetrate

Question 16

can be narrow or broad depending on the number of different bacterial species against which they exhibit useful activity

Answer 16

spectrum of activity

Question 17

measured by assessing the ability of bacterial strain to replicate following antibiotic exposure

Answer 17

bacterial sensitivity

Question 18

leads to permanent loss of of replicative activity

Answer 18

bacteriocidal antibiotics

Question 19

leads to temporary loss of growth and replication that returns following the removal of antibiotics

Answer 19

bacteriostatic antibiotics

Question 20

ratio of the minimum concentration likely to produce an adverse effect to the minimum concentration needed to produce a desired effect

Answer 20

therapeutic index

Question 21

delivery of antibiotic to the site of infection is the most difficult challenge of antibiotic delivery

Answer 21

ability to penetrate

Question 22

what are the four major classes of antibiotics?

Answer 22

• cell wall inhibitors
• folic acid
• DNA synthesis inhibitors
• protein synthesis inhibitors

Question 23

what was the first antibiotic to be commercially developed?

Answer 23

penicillin

Question 24

why are penicillins and cephalosporins called “beta lactams”?

Answer 24

because they have an unusual four membered ring

Question 25

how do cell wall inhibitors work?

Answer 25

by inhibiting an enzyme (DD-transpeptidase) responsible for cross-linking components of the cell wall

Question 26

are cell wall inhibitors bacteriocidal or bacteriostatic?

Answer 26

bacteriocidal

Question 27

DD-transpeptidase is also known as:

Answer 27

penicillin binding protein

Question 28

do cell wall inhibitors work better on gram +ve or gram -ve bacteria?

Answer 28

gram +ve

Question 29

penicillin and cephalosporins are two common examples of:

Answer 29

cell wall inhibitors

Question 30

bacterial enzymes (penicillases, cephalosporinases) made by most staphylococci and many gram -ve organisms that hydrolyze the beta lactam ring of certain penicillins and cephalosporins (confer resistance)

Answer 30

beta-lactamases

Question 31

potent inhibitors of beta-lactamases used in combinations to protect hydrolyzable penicillins from inactivation

Answer 31

beta-lactamase inhibitors (ie: calvulanic acid)

Question 32

not a beta-lactam, but also inhibits peptidoglycan; produced in nature by actinobacteria species

Answer 32

vancomycin

Question 33

used by bacteria to synthesize nucleic acids that make up their DNA

Answer 33

folic acid

Question 34

a nutrient obtained from the environment that is the precursor for folate in bacteria

Answer 34

para-aminobenzoic acid (PABA)

Question 35

true or false: eukaryotes do not use folic acid to build their DNA

Answer 35

false

Question 36

resemble para-aminobenzoic acid (PABA) and dihydrofolic acid, respectively, and interfere with PABA metabolic pathways

Answer 36

sulfonamides and trimethoprim

Question 37

why are sulfonamides and trimethoprim usually given together?

Answer 37

to block sequential steps in the synthesis of folic acid

Question 38

list three examples of protein synthesis inhibitors

Answer 38

- chloramphenicol - tetracyclines - macrolides

Question 39

bacteria make protein from an mRNA template within the bacterial:

Answer 39

70S ribosomal complex

Question 40

transfers an amino acid amino acid to the growing amino acid chain in a process called transpeptidation

Answer 40

tRNA

Question 41

why is it that eukaryotes are unaffected by protein synthesis inhibitors?

Answer 41

because eukaryotes have an 80S ribosomal complex

Question 42

list two protein synthesis inhibitors that bind to the 50S subunit and block transpeptidation

Answer 42

chloramphenicol and macrolides

Question 43

a protein synthesis inhibitor that binds to the 30S subunit and prevents binding of an incoming tRNA

Answer 43

tetracyclines

Question 44

protein synthesis inhibitors that bind to the 30S ribosomal subunit and block the initiation complex, cause misreading of the mRNA template, and inhibit translocation

Answer 44

aminoglycosides

Question 45

what is bacterial resistance?

Answer 45

the ability of the microbe to resist the effects of antibiotics

Question 46

how does bacterial resistance occur?

Answer 46

it is a consequence of evolution via natural selection; bacteria that have certain advantageous mutations will live on to reproduce

Question 47

what are four main mechanisms that bacteria have evolved in order to resist antibiotics?

Answer 47

1) drug inactivation or modification (ex: beta-lactamases) 2) alteration of binding site (alteration of penicillin binding proteins) 3) alteration of metabolic pathways (using folic acid from the environment rather than making it from PABA) 4) reduced drug accumulation (develop pumps to actively remove antibiotics from the bacterial cell)

Question 48

antibiotic therapy alters the bacterial environment of the body, and can sometimes lead to:

Answer 48

gastrointestinal distress (ex: diarrhea or GI discomfort)

Question 49

can antibiotics cause adverse skin reactions like rashes and photosensitivity?

Answer 49

yes

Question 50

rare conditions in which the skin becomes detached from the underlying tissue and sloughs off the body that can be associated with antibiotics

Answer 50

Stevens-Johnson syndrome and toxic epidermal necrolysis