Lecture #11 - Antimicrobial Drugs & Drug Resistance

Question 1

Antimicrobial Drugs are used…

Answer 1

Used when immunization has not occurred (no successful vaccine) and the immune system has difficulty to eliminate infection (ex: HIV)
• Useful against bacterial infection (antibiotics), very few antivirals (used for viral infection) are available (& those avail. are so restricted/limited)

Question 2

Antimicrobial Drugs

These are compounds that…

Answer 2

kill (cidal/lytic) or control the growth (static) of microorganisms in the host
• These drugs MUST display SELECTIVE TOXICITY or they will cause damage to the host
- b/c an antibiotic not used topically, is being let loose in body (full access to tissues) - ensure it won’t do non-specific tissue damage

Question 3

Antimicrobial Drugs

Two broad categories

Answer 3

SYNTHETIC (mostly failed - b/c have to design drug that has appro. polarity, size characteristics, no natural transporters exist, therefore, challenging & has to get to min. inhibitory [ ] in tissue (bone, or nervous tissue for ex which is diff) AND NATURAL (out #)
• Large number of naturally occurring antibiotics with no clinical use
- (naturally) Produced by bacteria and fungi (penicillium or straphylosporium for ex)

Question 4

Antimicrobial Drugs

Can also be described based on whether they are:

Answer 4

• Bacteriostatic or bacteriocidal

• Broad spectrum or narrow spectrum
- broad could be: target all gram + & gram - (broad over 1 that only targets gram -), BUT can also be broad if target all gram - (vs. 1 that targets just E. coli)

Question 5

Antibiotic targets include:

Cell wall synthesis

Answer 5

can target cell wall with diff categories of antibiotics & it’ll be impacted

Question 6

Antibiotic targets include:

Targets for nucleic acid syn.

Answer 6

capacity to interfere with DNA replication or prod. of RNA transcripts (intermediates b/t DNA & protein)

Question 7

Antibiotic targets include:

Protein syn.

Answer 7

can interfere with ribosomes –> protein syn.

- prevent bact from syn proteins needed for cell function

Question 8

Antibiotic targets include:

Lipid biosyn.

Answer 8

target anabolic pathways to be able to build things like lipid which is necessary for mem’s; esp. bact. cells b/c don’t have mem. bound organelles (internal mem’s will be impacted)

Question 9

Antibiotic targets include:

Cytoplasmic membrane structure & function

Answer 9

anything that targets cytoplasmic mem, mostly has:

TOXICITY TO US –> NOT AS WIDELY USED
- b/c our PM as Euk cells & their PM as a prok. cell are comparable to 1 another which means not something you can easily target without causing harm to your cell

Question 10

Antibiotic targets include:

Folic acid metabolism

Answer 10

can inhibit pathways for metabolic syn

–> turn down folic acid syn

Question 11

Cell Wall Active Antimicrobial Drugs

Answer 11

Cell wall active agents offer EXCELLENT SELECTIVE TOXICITY 
• MOST WIDELY USED class of antibiotics

• no harm to OUR own cell b/c we lack PD, therefore don’t target anything we have apart of our cell
• but can dev. allergy if it complexes with proteins in our blood for ex, behaving like a hapten & manages to get attention of immune system (not common)

Question 12

Cell Wall Active Antimicrobial Drugs

Largest class are…

Answer 12

beta lactam antibiotics

Question 13

Cell Wall Active Antimicrobial Drugs

Largest class are beta lactam antibiotics

Answer 13

• Common feature is the b-lactam ring
- core for all this category of antibiotic (can be dressed up with diff functional groups –> will determine where drug could go & conseq. for inside of cell & what the targets will be & how will it be given (orally or IV)

• NATURALLY occurring: produced by Penicillium and Cephalosporium fungi

• found as products of microbial metabolism
• each produce diff. categories of B-lactam; *all have ring but dressed up differently

• Example: penicillins and cephalosporins

• Can be MODIFIED in the lab to produce SEMI-SYNTHETIC drugs that have a modified spectrum of activity
- Reason for this: to change spectrum of activity; give it more activity against a gram - or gram +, more activity against a partic. species of bact.

• Susceptible to beta-lactamases

• Enzyme produced by some bugs to cut and inactivate beta-lactams (drug no longer works - good for bact but not for us)
• • THEREFORE, B-lactamase is a FORM OF ANTIBIOTIC RESISTANCE

Question 14

Cell Wall Active Antimicrobial Drugs

Penicillins

Answer 14

Penicillins have a NARROW spectrum of activity
- prod. by penicillum mold (natural)

• Characterized by a FIVE membered ring (thiazolidine) attached to the beta-lactam component

*• Target TRANSPEPTIDATION in GRAM POSITIVE bacteria

• CANNOT PENETRATE outer membrane of GRAM NEGATIVE bacteria (don’t work against gram -)

• SEMI-SYNTHETIC penicillin are modified to provide SOME ACTIVITY AGAINST gram NEGATIVE bugs
• • Example: ampicillin

*(can’t predict these sorts of things, so have to test antimicrobial in lab to see if these drugs will work against gram +/- experimentally)

Question 15

Explain how Penicillins target transpeptidation in gram +’s

Answer 15

transpeptidation: creates perpendicular cross-links using peptide chains

penicillin drug binds to transpeptidase (enzyme respon. for formation of cross-links)

outcome: WEAK CELL WALL
- when H20 rushes into hypertonic envir. of cell, it’ll cause cell to rupture –> bact no longer viable

Question 16

Explain Ampicillin (ex of penicilin)

Answer 16

broadened spectrum of activity (esp. against gram -), acid-stable (maintain acid sensitivity), B-lactamase-sensitive (means B-lactam will be destroyed by B-lactamase if organism has that)

Question 17

Not all penicillins will be…

Answer 17

susceptible to B-lactamase enzymes

Question 18

Cell Wall Active Antimicrobial Drugs

Cephalosporins

Answer 18

• Structurally distinct from penicillins (despite sharing B-lactam ring)
- SIX membered ring is attached to the beta-lactam component

• Also target transpeptidation of peptidoglycan (like penicillin)
• Many semi-synthetic examples (enhance activity & increase spectrum of activity etc.)
• BROADER SPECTRUM of activity than penicillin (cast wider net –> target more than penicillin can target)
• BETTER RESISTANCE against beta lactamases (harder for B-lactamase enzyme to activate & cut same B-lactam ring the penicillum’s had b/c less accessible due to change of chem)
• Grouped into GENERATIONS
• 1st generation cephalosporin, 2nd generation cephalosporin etc.
• • each gen. will have its own characteristic target & outcome - what its able to go after (gen categories play role in est. & understanding what the function of category will be)
• all have cepha as route –> cepha - beginning of each antibiotic
• associate ending with what gen it belongs to & will then associate that with which gen will work against gram -‘s better etc. to choose best for situation

Question 19

Compare & constrast Penicillins & Cephalosporins briefly

Answer 19

biochem of drugs are diff (6-mem ring vs 5 mem ring), process it targets is same (both target transpeptidation)

Question 20

Growth Factor Analogs

Answer 20

Growth factor analogs (drugs) are structurally similar to growth factors but do not function (behave) in the cell
• Analogs similar (resemble) to vitamins, amino acids, and other compounds (necessary in process)

Question 21

Growth Factor Analogs

Example: Sulfa drugs

Answer 21

FULL SYNTHETIC category (man-made)

• recently quite lost efficiency –> don’t use them to same degree as before
• even when might be useful, they have a *lot of resistance (organism may have resistance to drug)

• Discovered by Gerhard Domagk in the 1930s
- Example: sulfanilamide

• Inhibit growth of bacteria by INHIBITING FOLIC ACID SYNTHESIS and thus NUCLEIC ACID SYNTHESIS

• needed for syn of nitrogenous bases; to be able to assemble in bact cell, things like purines & pyrimides & also in biosyn. of some AA’s as well
• • BACT has a biosyn pathway that does this - BUT for humans we get folic acid from our diet to satisfy req’s, therefore safe for us (no issue with toxicity b/c of that –> PERFECT SELECTIVE TOXICITY)

• Often used in COMBINATION with another analog –> TRIMETHOPRIM
- Combination therapy MINIMIZES the LIKELIHOOD of RESISTANCE

Question 22

Describe how Sulfa drugs (ex: sulfanilamide) is carried out as well as how it is in combo with another analog (trimethoprim)

Answer 22

• enzyme necessary in process to make folic acid will be tricked into using sulfa drug instead
• outcome: not folic acid (drug analog is in here) –> problem
• manipulates enzyme to choose to use drug instead of its natural substrate (sulfa drug used in place of PABA)

*trimethoprim is a sub. for other part (now, not only tricking enzyme to take Sulfa drug instead of substrate (called PABA), you also use trimethoprim in for other part & now folic acid is rly not folic acid b/c used 2 substrates that look same but aren’t same (combo = TMP-SMZ) which *decreases likelihood of resistance b/c using 2 things bombarding organism so it doesn’t have capacity to est. resistance to it

Question 23

Growth Factor Analogs

Example: Isoniazid

Answer 23

• EXTREMELY NARROW SPECTRUM cell wall active agent
- b/c targeting mycolic acid syn (1 species)

• ANALOG of MYCOLIC ACID component needed by Mycobacterium spp. (only affected)

Question 24

Nucleic Acid Synthesis Inhibitors

Quinolones

Answer 24

• SYNTHETIC antimicrobials (man-made)
• INHIBIT DNA GYRASE
• Prevents supercoiling of DNA (& has packaging issue with respect to cell size)
• b/c cells so small, you have to supercoil to fit all that DNA into interior compartment of prok. cell
• -PROKARYOTIC ENZYME (WE DON’T HAVE/USE IT - SELECTIVE TOXICITY IS GOOD)

• Active against BOTH Gram-negative and Gram-positive bacteria (BROAD SPECTRUM)

Question 25

Nucleic Acid Synthesis Inhibitors Quinolones Example:

Answer 25

Example: ciprofloxacin (big gun) a fluorinated quinolone (fluoroquinolone) • Useful AGAINST LIFE THREATENING INFECTIONS - drug will be somewhat aggressive but good at what it does - ex: complex chest infection - ex: complicated UTI

Question 26

Nucleic Acid Synthesis Inhibitors Quinolones Example: ciprofloxacin a fluorinated quinolone (fluoroquinolone) PROBLEM:

Answer 26

INTERFERES WITH CARTILAGE DEV. - if any chance woman is PREGNANT, you CAN'T give them cipro - b/c entire fetal skeleton is gonna be laid down 1st as cartilage & then necessary sections meant to become bone will complete ossification process & then parts of skeletal system aren't meant to ossify will stay as carriage (ex: nostrils)

Question 27

Nucleic Acid Synthesis Inhibitors Quinolones Rifampin:

Answer 27

binds to RNA polymerase preventing transcription Outcome: RNA polymerase = inactive

Question 28

Nucleic Acid Synthesis Inhibitors Quinolones Actinomycin:

Answer 28

Binds to DNA template blocking transcription elongation - RNA polymerase can't get on & assemble nucleotides

Question 29

Protein Synthesis Inhibitors

Answer 29

target process of translation! Protein synthesis inhibitors target 70S ribosomes • GOOD SELECTIVE TOXICITY (but not perfect) • SOME ISSUES because human cells have 70S ribosomes in the mitochondrial matrix - kidney's suffer biggest conseq's

Question 30

Protein Synthesis Inhibitors Include:

Answer 30

Aminoglycosides Tetracycline Macrolides

Question 31

Protein Synthesis Inhibitors Include: • Aminoglycosides

Answer 31

• Bind to the 30S subunit (SSU) of 70S ribosomes *• BLOCK TRANSLATION - ability to syn proteins (which are necessary workhorse of cell) are comprimised • NARROW SPECTRUM (no gram + coverage) - Useful AGAINST GRAM NEGATIVE bugs * - (only know if you try experimentally) • Often used as a last resort drug b/c • Damaging to the kidneys (nephrotoxicity) and ears (issues with hearing & balance) • Examples include streptomycin, gentamycin and neomycin

Question 32

Protein Synthesis Inhibitors Aminoglycosides Examples include:

Answer 32

streptomycin, gentamycin and neomycin

Question 33

Protein Synthesis Inhibitors Tetracycline:

Answer 33

* BROAD SPECTRUM * Produced by species of the Streptomyces genus * Bind to the 30S subunit (SSU) - diff. interaction than aminoglycosides * Consist of BOTH natural and modified semisynthetic drugs (& more resis --> capacity to handle other things b/c of modifications that made them more resilient) • BINDS to CALCIUM (removing it from solution, therefore not enough in ECF for things like n.t. exocytosis in NS, cardiac muscle contraction) damaging TEETH and BONE - SHOULDN'T be used in CHILDREN and PREGNANT WOMEN --> these individuals are actively assembling bone; actively undergoing ossification, therefore need for Ca2+ is much higher than normal • Used in VETERINARY MEDICINE and to promote animal growth - Creates PROBLEMS WITH RESISTANCE - - antibiotics can provide diff. attributes of protection - - problem: exposing bacteria unnecessarily to antibiotics which can allow them the opp. to dev. resistance & we can also be exposed to it (can be found in trace amounts in drinking water)

Question 34

For Protein Synthesis Inhibitor - Tetracycline Why would using an antibiotic on a farm animal be associated with the promotion of growth?

Answer 34

kills off normal flora --> means organisms competing for nutrients will be inhibited animals's healthy = can sell meat animal's have bacterial infection = not safe to sell meat

Question 35

Protein Synthesis Inhibitors Macrolides

Answer 35

• Broad spectrum of activity * • Bind to the 50S (LSU) ribosomal subunit - when it binds to LSU, organism has some capacity to translate protein but it'll be reduced --> call it a type of PREFERENTIAL TRANSLATION (translate based on imp./priority now) - Only inhibits translation of some proteins - Some proteins are preferential translated and others are not - - Creates a DETRIMENTAL PROTEIN IMBALANCE inside of the cell (high levels of some protein & low levels of others - detrimental to survival of bact cell) • Useful to treat infection in patients with allergies to beta lactam antibiotics

Question 36

Protein Synthesis Inhibitors Macrolides Example:

Answer 36

erythromycin and azithromycin (naturally occuring) | • Produced by Streptomyces spp.

Question 37

Novel Antibiotics (last ~10 years) Daptomycin

Answer 37

* Produced by Streptomyces spp. * Cyclic lipopeptide - Active AGAINST Gram-POSITIVES - - Pathogenic Staphylococcal spp. and Streptococcal spp. (strep throat, flesh eating disease etc.) - now got backup if vancomycin fails • Forms pores in the plasma membrane causing DEPOLARIZATION (more + in cell) - Cell cannot synthesize necessary biomolecules (like protein, RNA, etc.) - - Cell death occurs • RESISTANCE can occur when bacteria alter plasma membrane composition - effective mode to protect organism

Question 38

Methicillin

Answer 38

= penicillin that's SEMI-SYNTHETIC with MODIFICATIONS to make it RESISTANT to B-lactamase activity (blocks B-lactamase site to cut) MRSA (resistant to our answer (war b/t us & them) methicillin-R staph aureus (up until recently, only drug to treat MRSA) Vancomycin was last resort for it (if immune system didn't work against it, you'd die)

Question 39

Novel Antibiotics Platensimycin

Answer 39

* INHIBITS FATTY ACID BIOSYNTHESIS (inhibits ANABOLISM) * Produced by Streptomyces platensis (hot genus for antibiotic prod. (we like it) • BROAD spectrum of activity against gram POSITIVE bacteria - broad spectrum compared to Isoniazid for ex • Useful AGAINST important RESISTANT gram POSITIVE PATHOGENS - MRSA and VRE - *vancomycin - resistant (resis. to our answer to MRSA) - - Entercocci (enterococcal species are normal flora in our GI tract) - if you've picked up resis. to vancomycin & then MRSA enters into your body: - VRE gives MRSA some vancomycin resistance, so the MRSA will not only be resis. to mycocyin but also vancomycin - therefore exchange of genetic material that they do freely will create serious repercussions to us - having this drug to be able to target those guys is awesome • Does NOT CAUSE TOXICITY in the HOST - safe to use inside us, despite targeting FA anabolism

Question 40

Antibiotic Resistance

Answer 40

Antibiotic resistance occurs when an organism develops a mechanism to elude the activity of an antimicrobial drug that it should otherwise be susceptible to • Genes for antibiotic resistance can either be encoded on a PLASMID (*passed by conjugation - horizontal gene transfer) or directly within the CHROMOSOME

Question 41

Antibiotic Resistance Resistance is prevalent because of

Answer 41

widespread and sometimes incorrect use of antibiotics (can't let immune system do job if it can, otherwise seek antibiotics) – Medicine, veterinary medicine, agriculture

Question 42

Antibiotic Resistance Mechanism's:

Answer 42

- Reduced permeability - Inactivation of antibiotic - Alteration of target - Development of resistant biochemical pathway - Efflux

Question 43

Antibiotic Resistance Mechanism: Reduced permeability

Answer 43

- SPECIFIC Ex: not opening house to someone scary (reducing permeability to something that could cause harm) - sees antibiotic, understands it could be harmful to cell structure/survival so it reduces permeability & choses not to let antibiotic drug into cell Ex: Penicillins

Question 44

Antibiotic Resistance Mechanism: Inactivation of antibiotic

Answer 44

- SPECIFIC - B lactamase (inactivation by cutting B-lactam ring so no longer effective to interfere with transpeptidase of PD layer) Ex: Penicillins, chloramphenicol, aminoglycosides

Question 45

Antibiotic Resistance Mechanism: Alteration of target

Answer 45

- SPECIFIC - b/c just 1 int. won't be possible - antibiotic won't be able to bind the target (antibiotic ineffective) b/c of a modification (mutated away from antibiotic so its able to persist - replicate; repro. success & see larger #'s within pop.) Ex: Erythromycin, streptomycin, norfloxacin

Question 46

Antibiotic Resistance Mechanism: Development of resistant biochemical pathway

Answer 46

- SPECIFIC enzymes used in biochemical pathway, for ex: folic acid syn, maybe able to avoid effects of antibiotic - structure in pathway won't be targeted by antibiotic & still continue to happen despite antibiotic being there Ex: Sulfonamides - lot of resistance to Sulfa drugs (target metabolic pathways) - this a mech that those bact use to avoid sulfa drug elimination

Question 47

Antibiotic Resistance Mechanism: Efflux

Answer 47

let things in, & then open door (efflux pump) & let them out pump in mem. * CAUSES MDR: multi-drug resistance - any drug that'll fit through pump is gonna be ejected; provide resis. to a series of antibiotics ex: Tetracyclines, chloramphenicol, fluoroquinolones

Question 48

Which Antibiotic Resistance mechanisms are VERY SPECIFIC TO A CERTAIN ANTIBIOTIC (resis to that 1 but doesn't provide protection to others)?

Answer 48

- Reduced permeability - Inactivation of antibiotic - Alternation of target - Development of resistant biochemical pathway

Question 49

Which Antibiotic Resistance mechanisms CAUSES MDR: multi-drug resistance (any drug that'll fit through pump is gonna be ejected; provide resis. to a series of antibiotics)?

Answer 49

Efflux ex: Tetracyclines, chloramphenicol, fluoroquinolones

Question 50

Patterns of Antibiotic Resistance

Answer 50

• Emergence of antibiotic resistance in different species of bacteria * MORE we use drugs, MORE we expose bact to them, MORE likely they're to dev. resis. - game of exposure; if you expose them, the opp. to be able to cause probs will be greater b/c bact needs to see the drug to be able to figure a way around it - happens as conseq of spon. mutation, but if mutations are successful the organism is able to stick around • Patterns of antimicrobial resistance - S. aureus had long standing resis. to antibiotic drugs - *as you increase amount of antibiotic used, prevalence of resis. goes up (exposure) - increase over time of % of resis. strains of N. gonarrhaea b/c of increased exposure - yes, there's sociological factors at play, but in add. to that - geography

Question 51

Preventing Antibiotic Resistance

Answer 51

- Infection prevention (have ways to stop spread - understanding & education is critical to min. # of infections) - Rapid and conclusive diagnosis (to quickly identify what a person is infected with so you can chose an antibiotic that at v. least is specific to that infection *step a patient down - don't know what they're infected with but clear that need antibiotics b/c infection is life threatening, so you give them an antibiotic that'll cast a wide net but then when you get conclusive diagnosis you use an antibiotic that's a bit more narrow/tailored to what you have so you can help to preserve some of their good bact & min. resis. b/c not exposing as many organisms to that drug) - Appropriate/prudent use of antibiotics (prescribe antibiotic to appease patient if they are demanding, but if its a viral infection, it'll have 0 utility & patient experiences placebo effect & now allowing bact to dev. resis. that they can pass along to actual organism if ever it does come into body - *1 of the best ways to get resistance) - Prevention of transmission (cough into elbow, use condum etc.)