Module 10 - Antimicrobials

Question 1

Disinfectants vs Antimicrobials:

Answer 1

-disinfectants are chemical compounds that am be able to eliminate microorganisms but are usually too toxic for human use other than topicals
-examples: alcohol,chlorhexidine,mercurials, iodine, ammonia
-soap can eliminate some microbes

Question 2

Ideal antimicrobial:

Answer 2

-something that is hard for pathogen to develop antibiotic resistance to
-broadspectrum (kills all organisms including microbiome) vs target antibiotics (ex. Only gram negative bacteria)
-different administration - needle/IV vs taking a pill
-something that is stable in multiple temperatures (thermostable)
-easily readable and inexpensive
-lethal to pathogen or atleast inhibits its growth
-harmless to person
-stable for storage (no allergens or toxicity)
-long half life (less frequent dosing)
-low plasma-protein binding
-no interference with other drugs

Question 3

What is an Antibiotic?

Answer 3

-traditionally, it refers to a natural metabolic product that will kill or inhibit growth of microorganisms
-antibiotics used today are derived from natural products of fermentation and are chemically modified (semi-synthetic) to improve their antimicrobial properties
-some agents are totally synthetic

Question 4

We’re Developing Less and Less Antibiotics:

Answer 4

-each year, less antibiotics are approved
-2018, 26% of infections were resistant to the drugs generally used to treat them- this converts to 5400 lives lost due to antimicrobial resistance (AMR)
-2050, this is likely to be 40%-, this converts to 13,700 lives lost due to AMR
-most resistant infections are musculoskeletal infection, skin and soft tissue infections, UTIs, Pneumonia/Intra-abdominal infection

Question 5

Antibiotic Resistance:

Answer 5

-a resistant organism is one that will not be inhibited or killed by an antibacterial agent at the concentrations of the drug achievable in the body after a normal dose
-can happen from Involves the synthesis of new or altered proteins by the microorganism

–Single chromosomal mutation: single amino acid change → lowers affinity to antibiotic

–Series of mutations: changes on penicillin binding proteins → penicillin resistance

Question 6

Mechanisms of Resistance:

Answer 6

-Altered target site: Drugs need to bind a particular receptor/site. This lower affinity of the target for the antibacterial. Receptor/site still functions for cell processes

-Altered uptake/increased efflux: Reducing the amount of drug that reaches the target (decreasing cell wall permeability, pumping drug out of cell)

-Drug inactivation:
-Enzymes that modify or destroy the drug
-E.g. Penicillin-β lactamases made be bacteria break down beta lactam ring so it can’t work

Question 7

Ways HCPs can Prevent Antibiotic Resistance:

Answer 7

-only prescribing when necessary - can sometimes see if infection clears on its own
-making sure people take the full course of antibiotics and not stopping if they feel better
-choosing narrow spectrum antibiotics when possible
-confirm its a bacterial infection before prescribing antibiotics
-make sure people NEVER share antibiotics and never using leftover antibiotics

Question 8

Ways to Classify Antibacterial Agents:

Answer 8

1.Bactericidal or Bacteriostatic
–Bactericidal → Kills a microorganism
–Bacteriostatic → Halts the growth of microorganisms, the immune system can then eliminate them (Not effective if immunity is suppressed)

2.Mechanism of action

3.Chemical structure
–Not of practical use when used alone
–When combined with target site can be useful to organise antimicrobial agents into specific families

Slide 15 → different classes of antibiotics:

Question 9

Bactericidal vs. Bacteriostatic (1/ways to classify antibacterial agents)

Answer 9

-Bactericidal
–E.g. penicillin can cause holes in the cell walls of bacteria, so they die
– Immune system is responsible for cleaning up cellular fragments

-Bacteriostatic
- E.g. tetracycline or erythromycin keep bacteria from dividing further by inhibiting protein synthesis necessary for division
- Immune system must actively be fighting disease or theinfection will not resolve

Question 10

Mechanism of Action (2/ways to classify antibacterial agents)

Answer 10

A) Cell wall synthesis
B) Protein synthesis
C) Nucleic acid synthesis (DNA, Folic acid synthesis inhibition
**Selective toxicity of the antimicrobial allows inhibition of the bacterial cell without harming the host cell

-inhibitors of cell wall synthesis: cell wall is made of peptidoglycan that is unique to bacteria and is optimum target for selective toxicity

Question 11

Penicillins (β-lactam):

Answer 11

-Penicillin V and G, amoxicillin, ampicillin, methicillin, dicloxacillin
-Prototype for penicillin was discovered in 1929, but therapeutic importance and large scale production occurred in the 1940’s
-Penicillins (and cephalosporins) are called β- lactam drugs because of the importance of the β-lactam ring
-An intact ring structure is essential for antibacterial activity
–Cleavage of the ring by penicillinases (β-lactamases) inactivates the drug

Question 12

How Penicillins Work (Mechanism of Action):

Answer 12

-Penicillin binds to receptors - penicillin- binding proteins (PBP’s)
-This interferes with the formation of the peptidoglycan cell wall
–Inhibit transpeptidases (PBP)- which normally catalyse the final step in synthesis of peptidoglycan
-The above can lead to activation of autolytic enzymes that cause cell lysis (some unresponsive to penicillin, because these enzymes are not activated)
-Penicillin is bactericidal, but it kills cells only when bacteria are growing →more active during the log phase of bacterial cell growth than during the stationary phase

Question 13

Activity of Selected Penicillins Chart

Question 14

Penicillins Disadvantages:

Answer 14

Limited effectiveness against many gram-negative rods
-Need frequent doses for most B-lactams
-Can be inactivated by β-lactamases
-We have developed drug defences against β-lactamases through inhibitors such as clavulanic acid and sulbactam
–Inhibitors that have little antibacterial activity, but bind strongly to β-lactamases and protect the penicillin
-Combinations, such as amoxicillin and clavulanic acid (Augmentin) are in clinical use
-penicillin allergies (true anaphylaxis) are very rare but serious (slide 25 chart)

Question 15

Cephalosporins (also B-Lactam Group):

Answer 15

-Cefotaxime, Ceftriaxone, cefazolin
-Has a 6-sided ring attached to beta-lactam group
-The first-generation cephalosporins are active primarily against gram-positive cocci
-Second- third- and fourth-generation cephalosporins are active against Gram positive and negative bacteria
-can be administered parenterally and orally
-Often given prophylactically before and after surgery
-Treatment of choice for gonorrhoea
-Cefazolin is the second choice for GBS infections after penicillin

Question 16

Resistance and Beta Lactams:

Answer 16

-Resistance to penicillins /beta- lactams falls into several categories: Production of beta-lactamases by staphylococci, gram-negative bacteria, gonococci
–More than 50 different
-lactamases are known, most of them produced under the control of bacterial plasmids
–Can be specific for one antibiotic or broad spectrum
-Lack of penicillin receptors (PBPs) or altered PBPs (e.g., pneumococci, enterococci) or inaccessibility of receptors because of permeability barriers of bacterial outer membranes
-Failure of activation of autolytic enzymes in cell wall, which can result in inhibition without killing bacteria (e.g., tolerance of some staphylococci)
-Failure to synthesise peptidoglycans, e.g., in mycoplasmas => metabolically inactive bacteria

Question 17

Glycopeptides:

Answer 17

-Vancomycin
-Bactericidal agent
-Active only against Gram Positive bacteria
-Inhibits the addition of subunits to the peptidoglycan backbone (cell wall)
-These agents act at an earlier stage than β lactams
-Not useful to combine them
-Slower killers than Beta lactams
-Used against Gram pos. cocci and rods that are resistant to beta-lactam drugs: S. aureus (MRSA)
-Used in people allergic to beta-lactams
-It is the treatment for Clostridium difficile
-Some resistance is appearing:
-Gram neg are naturally resistant as glycopeptides are too large to move through the outer membrane
-Glycopeptide resistance has been described

Question 18

Inhibitors of Protein Synthesis:

Answer 18

-Inhibit protein synthesis in bacteria without significantly interfering with protein synthesis in human cells
-This selective toxicity due to the differences between bacterial and human ribosomes
-Bacteria have 70S ribosomes with 50S and 30S subunits
-Human cells have 80S ribosomes with 60S and 40S subunits

-These antibacterial agents can be Grouped:
-30S subunit of the ribosome:
-Aminoglycosides (gentamicin/streptomycin) and
Tetracyclines

Question 19

Aminoglycosides:

Answer 19

-A family of related molecules with bactericidal activity
-Very effective against aerobic gram negative bacteria
Important against facultative anaerobe(Often used in combination with beta-lactams to broaden spectrum)
-They must be given intravenously or intramuscularly for systemic treatment
-Commonly administered to women with prolonged rupture of membranes and babies with suspected sepsis
-Production of aminoglycoside-modifying enzymes is the most important mechanism of resistance
-Examples are: streptomycin, neomycin, gentamicin
-mechanisms of action:
-Binding to specific proteins in the 30S subunit
-Inhibition of the initiation complex → important
for the bactericidal activity of the drug
-Misreading of messenger RNA (mRNA) - results in inhibition of initiation & misreading, membrane damage occurs and the bacterium
dies

Question 20

Aminoglycosides Toxicity:

Answer 20

-Potentially ototoxic (may damage inner ear) or nephrotoxic (damage kidney) (discussion of this but is category C/D by FDA)
-Use in pregnancy not recommended, especially in 1St trimester
-Gentamicin is category C

Question 21

Tetracyclines:

Answer 21

Tetracycline, doxycycline
-Action: inhibit the binding of tRNA to the ribosome
–Prevent protein synthesis
-Bacteriostatic action
-Administered orally: Doxycycline is completely absorbed → higher serum concentrations and less GI upset
-Used in the treatment of infections caused by chlamydia, mycoplasma
-Widespread resistance: Bacteria make new cytoplasmic membrane proteins capable of pumping tetracycline out of resistant cells

Question 22

Tetracyclines: Side effects:

Answer 22

Should be avoided in pregnancy and in children under 8 years of age – teratogenic
-resulting in permanent staining (dark yellow- grey teeth with a darker horizontal band that goes across the top and bottom rows of teeth)
-Possibly affect the growth of teeth and bones
-Photosensitive allergic reaction - increases the risk of sunburn under exposure to UV light from the sun or other sources
-Suppress normal gut flora
-Results in GI upset and diarrhoea
-Superinfection can occur
-Because normal flora is disrupted
-New infection caused by an organism other than the one which caused the initial infection
-Microbe responsible is usually resistant to the treatment given for the initial infection (E.g. S. aureus Or Candida)
-Pseudomembranous colitis
-Colitis associated with antibiotic therapy
-C. difficile

Question 23

Macrolides:

Answer 23

-Erythromycin, Azithromycin, Clarithromycin
-Mechanism of action: prevents the release of tRNA after peptide formation
-Bacteriostatic
-Useful in treatment of sexually transmitted infections, especially during pregnancy when tetracyclines are contraindicated

Question 24

Macrolides Resistance:

Answer 24

-Plasmid-encoded genes
→ Active pump mechanism for efflux of macrolides
→ Can protect the ribosome from action of macrolides by production of methylase enzymes that alter the binding site

Question 25

Erythromycin (a Macrolide):

Answer 25

-Active against Gram-positive cocci
-Alternative treatment for streptococcus in patients allergic to Penicillin
-Active against chlamydia and mycoplasma
-Given for prolonged rupture of membranes in penicillin allergic clients
-Good against Gram positive microbes (GBS prevention)
-Given orally/IV
-Side effects: Epigastric pain, nausea, vomiting

Question 26

Azithromycin (another Macrolide):

Answer 26

-Azithromycin penetrates into most tissues (except CSF)
-It is slowly release which permits once-daily dosing and shortening of the duration of treatment in many cases
-A single 1-g dose of azithromycin is as effective as a 7-day course of doxycycline for chlamydial cervicitis and urethritis

Question 27

Lincosamides: Clindamycin:

Answer 27

-Inhibits peptide formation (binding 50S ribosomal subunit)
-Primarily active against aerobic gram-positive bacteria and anaerobic bacteria
-Active against Chlamydia trachomatis, Neisseria gonorrhoeae,GBS and Gardnerella vaginalis (BV)
-Used vaginally in the treatment of women with bacterial vaginosis during pregnancy

Question 28

Ask friend for jeopardy notes on condition and what we would prescribe

Question 29

Lincosamides: Clindamycin

Answer 29

-Common side effects of systemic treatment: Diarrhoea, nausea, and skin rashes
-Facilitates pseudomembranous colitis: produced by Clostridium difficile

Question 31

Inhibitors of DNA Replication: Quinolones

Answer 31

-Nalidixic acid, Ciprofloxacin, Ofloxacin
-Synthetic agents, Bactericidal
-Action : inhibits bacterial DNA gyrase
-DNA gyrase – ensures DNA has proper conformation for efficient replication
-When it is inhibited, DNA gets twisted and is unreadable
-Able to interfere with this enzyme in bacteria without affecting it in humans

Question 32

Resistance in Quinolones:

Answer 32

-Resistance is chromosomally mediated
-Change in target enzymes → affects quinolone binding
-Change in cell wall permeability →decrease uptake
-In general very effective against Gram negatives
-Second and third generation cover some Gram positive (ciprofloxacin, norfloxacin, levofloxacin)

Question 33

Quinolones:

Answer 33

-Administered orally
-Used to treat UTIs (ciprofloxacin)
-Ofloxacin has been used to treat chlamydia and gonorrhoea
-Side effects: Nausea, vomiting, abdominal pain
-Fluoroquinolones not recommended for children, pregnant or lactating women because of possible effect on cartilage development (especially 1St trimester)

Question 34

Folic acid synthesis inhibition- Sulfonamides:

Answer 34

-Synthetic agents,Bacteriostatic
-Have a spectrum of activity primarily against Gram negative
-Action: Inhibits bacterial metabolic pathways which produce precursors for nucleic acid synthesis

Question 35

Sulfonamides:

Answer 35

-Act in competition with para-aminobenzoic acid (PABA) for the active site on an enzyme that catalyses an essential reaction in the pathway producing nucleic acid precursors
-Tetrahydrofolic acid(THFA) is the biologically active form of folic acid → If bacteria cannot make folic acid …they die
-Selective toxicity
-Bacteria make their own folic acid
-These drugs do not affect the human pathway

-Administered orally
-Useful in the treatment of UTIs
-Resistance is widespread
-Not used near end of term (affect bilirubin in foetus)
-Avoided in 1st trimester due to possible effect on folic acid
-Side Effects: Rashes, Bone marrow suppression → anaemia, If there is dehydration, crystals in urine may form (crystalluria)

Question 36

Trimethoprim (& sulfamethoxazole (TMP+SMX)):

Answer 36

-Like sulfonamides prevents THFA synthesis by inhibiting the dihydrofolate reductase
-Enzyme is present in mammalian, bacterial and protozoan cells
-Administered orally alone or combined with sulfonamide
-Effective against Gram negative
-Useful in the treatment of UTIs
-Resistance is provided by plasmid

Combination of Trimethoprim/Sulfamethoxazole is not recommended in late pregnancy or in neonates- increased unconjugated bilirubin and risk of kernicterus in foetus or neonate.
Avoided in early pregnancy. Unless benefit outweighs harm (HIV infected).

Question 37

Other Agents that Affect DNA: Metronidazole:

Answer 37

-AKA FLAGYL
-Only effective against anaerobic organisms
-This is a prodrug that when taken up by the microorganism leads to the buildup of free radicals in the organism that damages it
-Active against a wide range of protozoa → T. vaginalis (trichomoniasis), Toxoplasma gondii (toxoplasmosis), Giardia lamblia (gastroenteritis), Entamoeba histolytica (amoebic dysentery) and Gardnerella vaginalis (BV)

Question 38

Condition = GBS:

Answer 38

-caused by: group b strep - strep agalactiae
-possible treatment:
1st = penicillin - good choice because its cheap, readily audible and narrow spectrum, bad choice because of antibiotic resistance and allergy
2nd = if sensitive/mildly allergic to penicillin, opt for cefazolin
3rd = clindamycin.erythromycin (if seriously allergic to penicillin so no Beta lactam group)

Question 39

Condition = UTI:

Answer 39

-caused by: E. coli, GBS, staph-epidermidis/saprophyticus, enterococci
-possible treatment:
1st = nitrofurantoin for e coli (not in last trimester as it may cause hemolytic anaemia)
2nd = for GBS sulfamethoxazole-trimethoprim (1st trimester - folic acid/neural tube defects, near terms is hyperbilirubinemia so blue bib does not bind to albumin)
3rd = staph-epidermidis/saprophyticus is ciprofloxacin but cant used in 1st trimester as it alters cartilage development