Anti-microbial Chemotherapy

Question 1

What is MIC

Answer 1

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

Question 2

What is MBC

Answer 2

the minimal bactericidal concentration is defined as the minimum concentration of antimicrobial of the antimicrobial needed to kill the given organism

Question 3

What does it mean for an organism to be sensitive

Answer 3

If it is inhibited or killed by levels of the antimicrobial that are available at the site of action

Question 4

what does it mean for an organism to be resistant

Answer 4

If it is not killed or inhibited by levels of the antimicrobial that are available at the site of the infection

Question 5

What is a Bactericidal

Answer 5

an antimicrobial that kills bacteria

Question 6

What is a Bacteriostatic

Answer 6

An antimicrobial that inhibits growth of bacteria

Question 7

The mechanism of action of antibacterial drugs

Answer 7

inhibition of cell wall synthesis

inhibition of protein synthesis

Inhibition of nucleic acid synthesis

Question 8

Inhibition of cell wall synthesis

Answer 8

Penicillins and cephalosporins - contail B-lactams, inhibit enzymes responsible for cross-linking carbohydrates to form peptidoglycan chains

Glycopeptides - vancomycin and teicoplanin, act on stage prior to when B-lactams act, inhibiting the production os peptidogylcan precursor, only act on gram +ve bacteria

Question 9

Inhibition of Protein synthesis

Answer 9

Aminoglycosudes- gentamicin, mainly used to treat Gram -ve infections

macrolides and tetracyclines - erythromycine, clarithromycin, used in gram +ve infections, mainly used to treat haemophilus influenza

Oxazolidinones - linezolid, used against MRSA

Question 10

inhibition of nucleic acid synthesis

Answer 10

trimethoprim and sulphamethoxazole - inhibit different steps in purine synthesis, ised in combined form, co-trimoxazole for chest infections, trimwethoprim for UTI’s

Fluoroquinolones - ciprofloxacin, inhibit DNA synthesis more directly, effective against gram -ve infection, cannot be used in children due to danger of cartilage growth interference

Question 11

the mechanism of action for antifungal drugs

Answer 11

polyenes, azoles, allylamines, echinocandins

Question 12

action of polyenes

Answer 12

bind to erosterol and make cell wall more permeable

amphoyericin B is used to treat serious fungal and yeast infections but is toxic

nystatin is used topically or in oral suspension

Question 13

action of azoles

Answer 13

inhibit ergosterol synthesis

fluconazole is used to treat yeast infections, but not all are sensitive

voriconazole and itraconazole used to treat aspergilliosis

Question 14

action of allylamines

Answer 14

suprerss ergosterol synthesis but at a differet stage than azoles

terbinafine is the only one in use

mainly used against deratophytes and clinical use is restricted to infection of skin and nail

Question 15

action of echinocandins

Answer 15

inhibit the production of glucan ploysaccharide

casofungin is used in serious candida and aspergillus infection

it is a safe, IV only drug

Question 16

clinically significant resistant mechanisms to combat B-lactam activity

Answer 16

some organisms (staph. aureus) produse B-lactamase enxymes which can break down penicillins and cephalosporins

flucloxallin is lactamase resistant and so can still treat these bacteria

some organisms (MRSA) have altered binding sites to which the drugs cannot adhere rendering MRSA immune to all penicillins and cephalosporins

some gram -ve bacteria produce extended spectrum B-lactamase which renders them resistant to all B-lactams