Antibiotic Mechanism And Resistance

Question 1

How were antibiotics invented?

Answer 1

Micro organisms first produced antibiotics in order to protect their ecological niche from other organisms.

Question 2

What are bactericidal drugs?

Answer 2

Antimicrobials that kill bacteria such as penicillin.

Question 3

What are bacteriostatic drugs?

Answer 3

Antimicrobials that inhibit the growth of bacteria such as erythromycin.

Question 4

What does it mean if an organism is sensitive to a drug?

Answer 4

It means they are inhibited or killed by the antimicrobial at the site of infection.

Question 5

What does it mean if an organism is resistant to a drug?

Answer 5

It means they are not killed or inhibited by the antimicrobial at the site of infection.

Question 6

What does MBC mean?

Answer 6

Minimum bactericidal concentration

Minimum concentration of antimicrobial needed to kill an organism.

Question 7

What does MIC mean?

Answer 7

Minimum inhibitory concentration

The minimum concentration of antimicrobial needed to inhibit the growth of the organism.

Question 8

What are three ways of administering antimicrobials?

Answer 8

Topical is applying to a surface such as skin or to mucous membranes.
Systemic is taken internally such as orally or parenterally.
Parenteral is administered intravenously or intramuscularly and sometimes subcutaneously.

Question 9

What are three different areas of metabolism that antimicrobials can target?

Answer 9

Cell wall synthesis
Nucleic acid synthesis
Protein synthesis

Question 10

Name two types of beta lactams and how they work

Answer 10

Penicillins and cephalosporins have beta lactam rings that allow them to inhibit cell wall synthesis.
They disrupt peptidoglycan synthesis by inhibiting enzymes (penicillin binding proteins) that cross link the carbohydrate chains.

Question 11

How do glycopeptides work? Name two examples and how they are administered. Which one is more toxic?

Answer 11

They inhibit the cell wall synthesis.
Vancomycin and teicoplanin can only act on gram positive organisms and can only be given parenterally.
Vancomycin can be very toxic so needs to be monitored carefully.

Question 12

How do aminoglycosides work?

Name an example of one and some of its qualities

Answer 12

They inhibit the protein synthesis by making the tRNA misread the codon.
Gentamicin is useful for the treatment of gram negative infections but is also toxic so needs careful monitoring.

Question 13

How do macrolides work? Name an example of one and what it is useful in treating

Answer 13

They inhibit protein synthesis by affecting the peptide bond between proteins.
Erythromycin is useful to treat gram positive infections when patients are allergic to penicillin.

Question 14

How do tetracyclines work?

Answer 14

They inhibit protein synthesis by not allowing tRNA to bind.
Many strains of bacteria are resistant like S. Aureus.

Question 15

How do oxazolidinones work? Name an example and how it is taken

Answer 15

They inhibit protein synthesis.

Linezolid can be taken orally and is held in reserve to treat serious infections.

Question 16

How do cyclic lipopeptides work? Name an example of one and what it acts on

Answer 16

They inhibit protein synthesis.
Daptomycin is a new antimicrobial that acts against gram positive organisms (MRSA in particular).
Used in serious infections on specialist advice.

Question 17

What are two drugs that inhibit nucleic acid synthesis and how do they work? What kind of infections are they useful for?

Answer 17

Trimethoprim and sulphamethoxazole inhibit different steps in purine synthesis. They are used in combination as co-trimoxazole.
Trimethoprim is used to treat UTIs. Also useful to treat chest infections.

Question 18

How do fluoroquinolones work? Name two types and what they are useful against. What age range should they not be used in and why?

Answer 18

They inhibit nucleic acid synthesis by inhibiting DNA synthesis directly.
Ciprofloxacin and levofloxacin are useful against gram negative organisms like pseudomonas. They can’t be used in children as they interfere with cartilage growth.

Question 19

Which antimicrobial is always resistant to aminoglycosides?

Answer 19

Streptococci

Question 20

What are two ways that resistance of bacteria to an antimicrobial can be acquired?

Answer 20

Spontaneous mutations are a change in structure or function so the antimicrobial doesn’t work.
Spread of resistance is when genes for resistance spread from organisms or species by plasmids or transposons (packets of DNA that insert themselves into chromosome).

Question 21

What can some gram negative bacilli and staphylococcus aureus produce which let them be residents to antimicrobials like penicillin?

Answer 21

They produce enzymes called beta lactamases which cleave the beta lactam Ring and render it inactive.

Question 22

How can beta lactamase be combatted?

Answer 22

By producing a second component to the antibiotic which will inhibit the beta lactamase and allow the antibiotic to work such as co-amoxiclav (amoxicillin and clavulanic acid).
Or modify the antibiotic side chain to make the antibiotic resistant to beta lactamase such as flucloxacillin.

Question 23

What are ESBLs and what are they produced by?

Answer 23

Extended spectrum beta lactamase produced by gram negative organisms.

Question 24

What are CPE and CRE?

Answer 24

Carbapenemase producing enterobacteriaceae
Carbamem resistant enterobacteriaceae
Gram negative organisms
Some cases there is no antimicrobial treatment

Question 25

How can microorganisms change themselves structurally to avoid beta lactams? Name an example

Answer 25

They can change their penicillin biding protein target sites so beta lactams can’t inhibit cell wall synthesis.
Staphylococcus aureus is resistant to meticillin through this mechanism (MRSA)

Question 26

What two gram positive bacteria have recently become resistant to the glycopeptide vancomycin?

Answer 26

Enterococcus faecalis
Enterococcus faecium
Vancomycin resistant enterococci (VRE)