Antimicrobials

Question 1

Generally, discuss how bacteria differ from human cells

Answer 1

Bacteria have no nucleus

Ribosomes are the only internal organelles

Rapidly reproduce –> binary fission, recombination

Question 2

Explain Obligate aerobes

Answer 2

Only aerobic growth, req O2

Only grow in areas where large [O2] have fused into medium

Question 3

Explain facultative anaerobes

Answer 3

Both aerobic and anaerobic growth

Grow best when O2 is present but can grow in absence

Question 4

Explain obligate anaerobes

Answer 4

Obligate anaerobes can only grow in the absence of O2

Question 5

Explain Aerotolerant anaerobes

Answer 5

Only anaerobic growth but continues in the presence of oxygen

Question 6

Where would you find aerobic bacteria on the body?

Answer 6

Skin

Some parts of the respiratory system

Question 7

Where would you commonly find anaerobic bacteria?

Answer 7

Found in mucosal membranes and soils

Skin, brain, blood, intrabdominal, pelvic, skin and soft tissue

They’re unable to deal with the O2 radicals such as peroxides

Question 8

Discuss the difference between Gram +ve and Gram -ve bacteria

Answer 8

Gram +ve (STaph, STrep) have a thick peptidoglycan layer whilst Gram -ve bacteria dont have a thick peptidoglycan layer on the surface of the cell

Question 9

Which antibiotic mechanism would work better on Gram +ve bacteria compared to Gram -ve? Why?

Answer 9

Gram +ve bacteria are prone to cell wall disruption due to thick peptidoglycan layers in comparison to Gram -ve bacteria

Question 10

Name some Gram+ve Cocci aerobic bacteria

Answer 10

staphylococci
streptococci
Enterococci

Question 11

Name some Gram+ve rod-shaped anaerobic bacteria

Answer 11

Acintomyces
Clostridium

Question 12

Name some Gram-ve Cocci aerobic facultative anaerobic bacteria

Answer 12

Neisseria

Question 13

List the mechanistic targets of antibacterials (generally)

Answer 13

Nucleic acid synthesis (DNA gyrase)

RNA polymerase

Folate synthesis

Protein synthesis (50s and 30s subunits)

Cell wall synthesis

Question 14

What factors influence the pharmacokinetics of antibiotics?

Answer 14

Bioavailability, clearance, vol of dist, ability to reach infection site and have desired concentration in target tissue

Question 15

Which antibiotics target nucleic acid synthesis?

Answer 15

Quinolones

Question 16

Which antibiotics target RNA polymerase?

Answer 16

Rifamyxins

Question 17

Which antibiotics target folate synthesis?

Answer 17

Sulfonamides

trimethoprim

Question 18

Which antibiotics target cell wall synthesis?

Answer 18

Penicillins
Cephalosporins
Carbapenems
Monobactams
Glycopeptides

Question 19

Which antibiotics target Protein synthesis?

Answer 19

50s = macrolides, chloramphenicol
30s = aminoglycosides, tetracyclines

Question 20

What do bactericidal antibiotics do?

Answer 20

Kill the bacteria, is bacteriocidal at low doses

e.g. penicillin, cephalosporins, monobactams, carbapenems, glycopeptides

Question 21

What do bacteriostatic antibacterials do

Answer 21

Prevent the replication/duplication of bacteria

e.g.Tetracycline, spectinomycin, macrolides, trimethoprim, chrloamphenicol

Question 22

Outline the principles of the antimicrobial creed

(Hint: MIND ME)

Answer 22

M = microbiology guides therapy wherever possible
I = indication should be evidence-based
N = narrowest spectrum therapy required
D = dosage individualised to patient and site/type of infection

M = minimise therapy duration
E = ensure oral therapy used where clinically possible

Question 23

Describe prophylactic antibiotic use

Answer 23

Aims to prevent infection when significant risk of developing infection is present, basing antimicrobial choice on likely pathogen

Restrict only to indications for which there is evidence of efficacy/consequences of infection are sig

Question 24

Discuss empirical antibiotic therapy

Answer 24

Treats an established infection when causative organism has not been identified, treatment guided by clinical presentation (most likely cause)

Restricted to clear indication and clinical benefit, using narrowest therapy possible , review after 28-72 hrs

Question 25

Under which circumstances is empirical antibiotic therapy warranted?

Answer 25

When treatment must be started before culture sus results available

When clinical situation not serious enough to warrant taking culture

Sample culture cannot be obtained

Question 26

Discuss directed antibiotic therapy

Answer 26

Treats established infection where the pathogen has been identified

Ensure culture is critically evaluated, accounting: antimicrobial susceptibility, direct therapy in accordance w/ guidelines, use most effective/least toxic, narrowest spectrum drug available

Duration of therapy as short as possible, do not exceed 7 days

Question 27

When is combination antibiotic therapy used? How does it work?

Answer 27

Used for = polymicrobial infections, minimise the development of resistance

Works through synergy = e.g. one antibiotic breaks cells wall whilst the other (that can’t break wall) enters bacteria and works

Question 28

What are some direct ADRs of antibiotics?

Answer 28

hypersensitivity, toxicity (in preg, breastfeeding), drug interaction

Question 29

What are some indirect ADRs of antibiotics?

Answer 29

Effect on commensal flora (w/ clostridium infections) = candidiasis, inc risk of colonisation and/or infection w/ drug-resistant pathogens

Effect on environmental flora = inc risk of C. difficile or drug-resistant pathogens spreading to env/other people

Question 30

Discuss penicillin hypersensitivity

Answer 30

Caused not by the beta-lactam ring but by R-group side chains

Patients hypersensitive to penicillins may be allergic to structurally similar drugs, mainly limited to carbapenems (1%) and cephalosporins (2.5%)

Can use desensitisation = up-titrating dose over 15 mins

Question 31

Briefly discuss the use of antibiotics in pregnancy

Answer 31

Plasma [drug] dec in preg women –> less effective

Many antibiotics appear in breast milk of nursing mothers, may cause ADRs in infant

Sulfonamides may lead to toxic bilirubin accumulation in new-born’s brain

Question 32

Briefly discuss the use of antibiotics in pregnancy

Answer 32

Plasma [drug] dec in preg women –> less effective

Many antibiotics appear in breast milk of nursing mothers, may cause ADRs in infant

Sulfonamides may lead to toxic bilirubin accumulation in new-born’s br

Question 33

When is parental antibiotic administration required?

Answer 33

Oral admin not tolerated/not possible

GI absorption sig red

oral antimicrobial is not available

higher doses than can be easily administered oraaly are required for site of infection

urgent treatment is required

Question 34

What are the mechanism of antimicrobial resistance?

Answer 34

Inactivation = add a phosphate grp on antibiotic –> dec ability to bind to bact ribosomes

Pumping out = inc active efflux of the drug

Modification = modified the drug’s target

impermeability = modify cell wall protein