antimicrobial chemotherapy mechanisms of action and resistance

Question 1

bactericidal

Answer 1

An antimicrobial that kills bacteria (e.g. the penicillins).

Question 2

Bacteriostatic

Answer 2

An antimicrobial that inhibits growth of bacteria

e.g. erythromycin

Question 3

Sensitive

Answer 3

An organism is considered sensitive if it is inhibited or killed
by levels of the antimicrobial that are available at the site of
infection.

Question 4

Resistant

Answer 4

An organism is considered resistant if it is not killed or inhibited
by levels of the antimicrobial that are available at the site of
infection.

Question 5

MIC

Answer 5

Minimal inhibitory concentration is defined as the minimum
concentration of antimicrobial needed to inhibit visible growth
of a given organism.

Question 6

MBC

Answer 6

Minimal bactericidal concentration is defined as the minimum

concentration of the antimicrobial needed to kill a given organism.

Question 7

routes of administration of antimicrobial agents

Answer 7

topical
systemic
parenteral

Question 8

Topical

Answer 8

Applied to a surface, usually skin or to mucous membranes e.g.
conjunctiva.

Question 9

Systemic

Answer 9

Taken internally, either orally or parenterally

Question 10

Parenteral

Answer 10

Administered either intra-venously (iv) or intra-muscularly (im),
occassionally subcutaneously

Question 11

sites of antibiotic action

Answer 11

1. inhibition of cell wall synthesis
2. inhibition of protein synthesis
3. inhibition of nucleic acid synthesis

Question 12

drug groups that inhibit cell wall synthesis

Answer 12

1. β-lactams

2. glycopeptides

Question 13

β-lactams examples

Answer 13

• penicillins and cephalosporins

- benzyl penicillin

Question 14

action of penicillins and cephalosporins

Answer 14

inhibit the synthesis of cell wall by binding to penicillin binding proteins, this inhibits the enzymes that produce cross bridges between carbohydrate.

Question 15

benzyl penicillin

Answer 15

original form of penicillin isolated, less useful than derivatives

Question 16

β-lactamases

Answer 16

enzymes produced by bacteria resistant to β-lactams, they breakdown the functional group, turning them from a toxin to a food.

Question 17

glycopeptides examples

Answer 17

• vancomycin

- teicoplanin

Question 18

vancomycin and teicoplanin action

Answer 18

inhibit the assembly of peptidoglycan precursor

Question 19

vancomycin toxicity

Answer 19

toxicity is very common with vancomycin as small therapeutic range

Question 20

drugs types that inhibit protein synthesis

Answer 20

• aminoglycosides
• macrolides and tetracyclines
• oxazolidinones
• cyclic lipoprotein

Question 21

aminoglycosides use

Answer 21

eg, gentamicin used to treat gram negative infections

Question 22

gentamicin toxicity

Answer 22

it is toxic to requires a careful dosing regime and monitoring of levels

Question 23

examples of macrolides

Answer 23

erythromycin. clarythromycin

Question 24

macrolides and tetracyclines use

Answer 24

used as an alternative to penicillin and used against gram positive bacteria

Question 25

Trimethoprim and sulphamethoxazole action

Answer 25

inhibit different steps in purine

synthesis, and are used in a combined form in the drug co-trimoxazole

Question 26

Oxazolidinones example

Answer 26

Linezolid

Question 27

Linezolid use

Answer 27

used to treat MRSA infections

Question 28

cyclic lipopeptide example

Answer 28

Daptomycin

Question 29

Daptomycin use

Answer 29

used against MRSA and gram positives in general

Question 30

drugs that inhibit nucleic acid synthesis

Answer 30

• Trimethoprim and sulphamethoxazole

- Fluoroquinolones

Question 31

fluoroquinolone example

Answer 31

ciprofloxacin

levofloxacin

Question 32

fluoroquinolones action

Answer 32

act directly on nucleic act synthesis, binding to dna-protein complex.

Question 33

bacteria ciprofloxacin

Answer 33

gram negative

Question 34

bacteria levofloxacin acts on

Answer 34

gram negative but also some pneumonia causing gram positives

Question 35

what is the selection pressure for the selection of bacteria resistant to antibiotics

Answer 35

the wide spread (sometimes uncontrolled) use of antibiotics

Question 36

ways in which bacteria can be resistant to β-lactams

Answer 36

• they can produce β-lactamase

- they can alter there penicillin binding protein target site

Question 37

which genus of bacteria are always resistant to aminoglycosides?

Answer 37

streptococci

Question 38

what type of bacteria are always resistant to vancomycin?

Answer 38

gram negative organsims

Question 39

what is inherent/ intrinsic resistance

Answer 39

all strains of a given species are naturally resistant to an antibiotic

Question 40

how does acquired resistance come about?

Answer 40

1. spontaneous mutation

2. spread of resistance eg. using plasmids or transposons

Question 41

transposons

Answer 41

packets of DNA which insert themselves into the chromosome

Question 42

ways to combat β-lactamase production

Answer 42

1. introduce a second component to the antibiotic
   (β-lactamase inhibitor) protecting the antibiotic
   from enzymatic degradation eg. co-amoxiclav
2. modify the antibiotic side chain producing new antibiotic resistant to the actions of β-lactamase eg. flucloxacillin

Question 43

extended spectrum β-lactamase producing organisms

Answer 43

gram negative organisms resistant to all β-lactams.

Question 44

Carbapenemase Producing Enterobacteriaceae (CPE) and

Carbapenem Resistant Enterobacteriaciae (CRE)

Answer 44

gram negative organisms resistant to the carbapenems

Question 45

how vancomycin resistant enterococci are resistant

Answer 45

they have an altered peptidoglycan precursor