Intro to antibacterial agents Flashcards
difference between bacteriostatic and bactericidal?
Bacteriostatic: Kill microbe
Bactericidal: Inhibits growth of microbe
difference between an antiseptic and a disinfectant?
Antiseptic: kill microbes topically on surface
Disinfectant: Kill microbes on inanimate objects
The basic target sites for the action of antibacterial agents?
- Cell wall synthesis: effective w GPos
- DNA synthesis
- RNA synthesis
- Protein synthesis (50S + 20S ribosomes)
- Antimetabolites: biochem. pathways
Difference between the MIC and the MBC for an antimicrobial agent?
MIC: Min. Inhibitory Conc. = no growth in tube
MBC: Min. Bactericidal Conc. = no growth in tube & culture plate
List 5 ideal qualities for an antimicrobial agent and explain the benefit of each? (7)
- Non-toxic to eukaryotic cells: selective toxicity
- Broad spectrum: targets range of microbes
- Bactericidal: Kills microbes
- No acquired or intrinsic resistance: antimicrobial effective & not gain genetic material
- Slow clearance time: not degraded quickly
- Effective @ low dose: less harmful to person
- Min. impact to host’s NF:
Define drug Autonomy, antagonism, synergism
Autonomy: 2x anti-b have no effect on each other if tog.
Antoagonism: 2x anti-b that cancel each other if tog.
Synergism: 2x anti-b have a better effect when tog.
What bacterial genus has been the source of many antimicrobial agents?
Streptomyces sp.
Why would norfloxacin/nitrofuranstoin NOT be prescribed for septicaemia or meningitis?
bc the kidney rapidly excretes it (can’t get to the site of infection) = only suitable for treating UTI
Why should nitrofurans not be prescribed with quinolones?
bc antagonistic to each other i.e. cancel the effect of each other
Adv & disadv. of nitrofurans
Adv: bactericidal
Disadv: antogonistic w/ quinilones; Only oral use; Only use for UTI
Why is tetracycline not used in children (unless it were a treatment of last resort)?
stain teeth of kids <8-9 yrs old during calcification
Adv & disadv. of tetracycline
Adv: inhibit protein synthesis; variable resistance in GPos & GNeg (susceptible)
Disadv: bacteriostatic; oral use only; stain kid’s teeth;
Why is chloramphenicol primarily only used as a topical agent?
bc broad spectrum - can cause toxixity problems
Adv & disadv. of chloramphenicol
Adv: inhibit protein synthesis; suitable for oral & parenteral (IV), topical use
Disadv: bacteriostatic; broad spectrum => toxicity problems
What is the similarities & difference b/w ampicillin and amoxicillin?
Both: have the same bacterial activity
Amoxillin: absorbed better by GIT
How would aminoglycosides be administered?
IV only bc not absorbed by gut
Adv & disadv. of aminoglycosides
Adv: bactericidal; active against staph (not MRSA), Enterobacteria, most aerobic GNB (e.g. P. aeruginosa) inhibit protein synth.
Disadv: IV only; not active against anaerobes or streptococci;
Why are some bacterial agents suitable for oral ingestion and others are not?
bc it can be absorbed in GIT and remain a good concentration when reach target area.
Others are not suited as can be toxic in the body or easily excreted out by the kidneys
Name and define the three methods of expression of enzyme induced antibacterial resistance? (Inducible, Constitutive)
- Inducible: enzyme only produced if organism is EXPOSED to corresponding B-lactam anti-b
- Constitutive: produced CONSTANTLY
- Constitutive-inducible: produced CONTANTLY @ LOW lvls & INC. as EXPOSED to anti-bact.
Why don’t sulphonamides, trimethoprim or their combination affect humans but do affect bacteria?
Bc these antibacterials inhibit folate pathway = bact. can’t make folate ≠ make dNTP ≠ make DNA. Humans not affected bc get folate from diet
Explain how the CDS (Calibrated dichotomous sensitivity) method of disc susceptibility are performed.
- Fresh colony is picked & mixed in saline.
- innoculum is distributed evenly on sensitised agar media with excess removed.
- It is let to dry then anti-b disk are placed on the media & inoculated for 18 hrs.
- The radius of the disks are measured and interpreted. if <6 = Resistant. ≥6= susceptible
Explain how the CLSI/EUCAST method of disc susceptibility are performed.
- Fresh colony of test organism is suspended to a density of ~0.5 McFarland std.
- A lawn Innoculum is spread on MH agar plate in 3x directions w/ a swab dipped once in inoculum.
- Incubated in air or CO2 for 18-24hrs.
- Zone diameter measured in mm & use a table to determine result = susceptible, intermediate or resistant
Explain how to set up and read an E-test strip so as to report an MIC for gentamicin?*
- Make 0.5 Mcfarland standard w/ test organism
- A lawn Innoculum is spread on MH agar plate in 3x directions w/ a swab dipped once in inoculum.
- Incubated in air or CO2 for 18-24hrs.
- Read MIC where zone intersect strip (always go to next highest value if in b/w values)
What is _ & what is it caused by
a) Colitis
b) Thrush
a) Colitis: inflammation of LI bc of Clostridium deficile
b) Thrush: yeast infection caused by Candida albicans
What is the therapeutic index?
Ratio of a reagent that causes toxicity to the dose that causes a therapeutic effect.
TD50 / ED50
TD50: toxic dose where 50% of pop respond
ED50: therapeutic dose where 50% of pop respond
=> Lo diff = dangerous bc easily overdose = need regular monitor in biochem
Define these terms:
a) Antibiotic:
b) CHemotherapeutic agents
c) Semi-synthetic antibiotics
a) naturally occurring substances produced by micro-o to kill/inhibit other micro-o
b) Synthetically made - completely artificial
c) chemically modified from natural compoun
Similarities & differences of Penicillin G, V (B-lactams)
Adv: bactericidal, high activity, low toxicity
Dis: Not oral (bc inactivated by gastric acid), narrow spectrum, inc bact. resistance
Diff: Penicillin V can be administered orally
Similarities & differences of Amoxicillin & ampicillin
Sim: works against Enterobacteria
Diff: Amoxicillin better GIT absorption
What does Clauvanic acid do?
inhibits PLASMID encoded B-lactamases = allows Antibiotic to work
