L1 Antibacterial drugs I

Question 1

Why are antibiotics important for modern medicine

Answer 1

modern medicine is often invasive and calls for good control over bacterial infections

Question 2

What is chemotherapy

Answer 2

using chemicals to aim a certain disease or pathogen

Question 3

What is arsanilic acid (atoxyl)

Answer 3

It is an antibiotic used against syphilis

It was later chemically optimized into neosalvarsan which is less toxic and more specific to the bacteria

(syphilis was later treated with penicillin)

Question 4

What are the 4 targets of antibiotics when it comes to gram-negative and gram-positive bacteria (4)

Answer 4

1. DNA inhibitors: sulfonamides, trimethoprim, quinolones, nitrofurans
2. Cell membrane disruptors: polymyxins, daptomycin
3. Protein synthesis inhibitors: aminoglycosides, tetracyclines
4. Cell wall synthesis inhibitors: beta-lactams, vancomycin

Question 5

What is the difference between bacteriostatic and bactericidal

Answer 5

bacteriostatic: inhibits cell division
-immunocompetent host
-non-life threatening, uncomplicated infection

bactericidal: actively kills bacterial cells
-deep-seated infections (endocarditis, meningitis); heart, brain
-where the immune system has a harder time accessing
-life threatening

Question 6

What is CFU (colony-forming units)

Answer 6

It measures the number of live bacteria in a sample

Question 7

TF: there are 2 types of antibiotics; bactericidal or bacteriostatic

Answer 7

False, some antibiotics can be both depending on the context

Question 8

What is MIC (minimal inhibitory concentration)

Answer 8

It is the the minimum amount of antibiotic required to inhibit bacterial growth/division

it is used to find out weather the antibiotic is working or if the bacteria is resistant

Question 9

What is the MBC (minimal bactericidal concentration)

Answer 9

It is the minimum amount of antibiotic required to kill (all) bacteria

This is done by plating the dilution test samples on an agar plate that does not have any antibiotics

Question 10

What is the susceptibility assay

Answer 10

It is to test weather a bacteria is susceptible to an antibiotic

This is done by adding drug-impregnated disks onto an agar plate swabbed with a given bacteria - then incubated. Greater nongrowth diameters indicate greater susceptibility

Question 11

TF: MIC and MBC are considered susceptibility assays

Answer 11

True, they are a part of susceptibility testing

Question 12

In which cases are broad spectrum antibiotics used

Answer 12

when the causative agent cannot rapidly be identified

e.g. tetracyclines, fluoroquinolones, carbapenems

Question 13

Why is the irresponsible use of broad spectrum antibiotics dangerous

Answer 13

it disturbs the microbiota and may promote antimicrobial resistance

Question 13

Why are narrow spectrum antibiotics beneficial in contrast to broad spectrum antibiotics

Answer 13

-it does not target the microbiome
-broad spectrum can confer resistance in bacteria due to selective pressure

Question 13

In which cases are broad spectrum antibiotics used?

Answer 13

when the clinical cause is known

e.g. penicillins, monobactams

daptomycin is very narrow, developed due to MRSA

Question 14

What are the 3 kinds of antimicrobial therapies

Answer 14

1. Definitive drug therapy: ideal scenario where antimicrobial agent is selected based on the organism identified and its susceptibility
2. Empiric therapy: initial approach where antibiotic selection is guided by clinical presentation and knowledge of most common causative agents (cannot wait for susceptibility assay)
3. Prophylactic drug therapy: use of antimicrobial agent to prevent infection

Question 15

Why are aminoglycosides combined with penicillin? What is this an example of?

Answer 15

aminoglycosides require penicillin’s ability to inhibit the cell wall in order to reach their target (ribosomes) and take action

This is an example of synergy

Question 15

What are the 3 possibilities when combining antimicrobial agents

Answer 15

1. synergy
2. indifference
3. antagonism

• synergy can be additive or potentiating

Question 16

Provide an example of antibacterial synergy (that is not aminoglycosides + penicillin)

Answer 16

sulfonamides + trimethoprim: both block folate synthesis but at different pathways

Question 17

How can bacteria develop resistance so quickly

Answer 17

They divide at a high rate i.e. very fast, thus increasing the possibility of resistance developping

Question 18

What are the 7 major mechanisms of bacterial resistance?

Answer 18

1. active efflux of drug via efflux pump
2. target protection via protein blocking the active site of target
3. inactivation of antibiotic via enzyme
4. decreased influx (via porins for example)
5. target site modification
6. target bypass (bacteria makes new pathways to achieve the same metabolic functions inhibited by the drug)
7. Downregulation (of porins for example)

Question 19

How do bacteria gain resistance via gene exchange? (3)

Answer 19

1. plasmid exchange (bacterial conjugation)
2. transduction with virus (bacteriophage)
3. uptake of free DNA from environment