Antimicrobials

Question 1

naturally occurring substances usually produced by other microorganisms that have the capacity to kill
or inhibit the growth of other microorganisms

Answer 1

Antibiotics

Question 2

synthetically manufactured compounds e.g. sulphonamides, trimethoprim, cotrimoxazole, metronidazole, quinolones

Answer 2

Chemotherapeutic agents

Question 3

naturally occurring compounds that are chemically modified e.g. ampicillin, amoxycillin, methicillin, all cephalosporins

Answer 3

Semi-synthetic antibiotics

Question 4

The process of killing pathogenic organisms or rendering them inert

substances that are used to inhibit microbial organisms on inanimate objects

substances that are too toxic for use inside the body but may be used topically – eyes, ears, skin

Answer 4

disinfection

disinfectant

antiseptics

Question 5

How do B lactams work?

Answer 5

bind to proteins at the cell wall/cell membrane interface (PBPs peptidoglycan binding proteins) that are involved in the cross linking of the peptidoglycan strands
results in cell lysis (all are bactericidal)

Not effective against resting bacteria
* Generally, more active against Gram positives

Question 6

behave like detergents, solubilise lipids in the cell membrane (increasing permeability) resulting in leakage of the cell

Answer 6

Polypeptides (Bacitracin)

Question 7

blocks the incorporation of alanine into the peptide bridges of the cell wall

Answer 7

Cycloserine

Question 8

binds to the terminal D-alanine residues on the ends of the peptide bridge molecules preventing their incorporation into the
growing cell wall

Bactericidal action

Answer 8

Glycopeptides

Question 9

inactivates the enzyme enolpyruvyl transferase, thereby preventing the production of N-acetylmuramic acid

Answer 9

Fosfomycin

Question 10

what is the difference between penicilli v and g?

Answer 10

Both are naturally occurring, bactericidal, high activity low toxicity, narrow spectrum inc resistance but V can be administered orally while G cannot be

Question 11

Led to:
- penicillins active against GNB rather than just GPC - Resistant to penicillinases
* Methicillin (not oral) – led to cloxacillin and flucloxacillin (oral)
* MRSA produce staphylococcal b-lactamase

• Amoxicillin and ampicillin have the same activity but
  amoxicillin has better GIT absorption

Answer 11

Removal of the phenylacetic acid side chain from benzylpenicillin produces aminopenicillanic acid

Question 12

Polymyxins
* Derived from Bacillus polymyxa * Examples:
- Polymyxin B- Polymyxin E (colistin – being used systemically for resistant GNB) * Bactericidal
* Poor tissue distribution systemically and nephrotoxic
* Used topically–eye, ear, skin
* Active against Gram negatives except Proteus sp.
* Not active against Gram positives(no outer membrane)
Bacitracin
* Isolated from Bacillus licheniformis
* topical–creams,sprays * staphylococci and streptococci
* Gram negatives are resistant

Answer 12

polypeptides

Question 13

Bactericidal
* Many are NOT absorbed by the gut – IV only
* Toxicity varies – all have some degree of ototoxicity, nephrotoxicity
* Often used in combination with b-lactams – act synergistically
* Not active against anaerobes or streptococci

Answer 13

amglycosides

Question 14

Binds to the 50 s ribosome to inhibit protein synthesis * Bacteriostatic
* Suitable for oral and parenteral use
* Broad spectrum but can cause toxicity problems
- Aplastic anaemia in bone marrow = decreased everyday use
- Good CSF penetration for use in cases of meningitis
- Not suitable for neonates – causes gray baby syndrome
Morecommonlyusedintopicalpreparations–eyedrops,eardrops

Answer 14

cloramphenicol

Question 15

• Potential antagonism with macrolides – test for inducible resistance - Bacteriostatic
• Primary complication of use is Clostridium difficile colitis
• Antibacterialproperties
• Primarily anaerobes e.g., Bacteroides, Fusobacterium, Prevotella - Some staphylococcal and streptococcal infections
• ?MRSA if a susceptible strain

Answer 15

Clindamycin is a semi-synthetic derivative of lincomycin- lincoasamide

Question 16

Bacteriostatic
* OralandIVuse
* Goodbonepenetration,poorCSFpenetration
* Mostcommonlyusedasanti-staphylococcalagent
- Should be used in combination with another agent, (usually a b-lactam) to prevent the selection of R variants

Answer 16

Fusidic acid

Question 17

Inhibit protein synthesis – reversible binding to 50s ribosomal subunit
- Bacteriostatic
* Examples are erythromycin - E, roxithromycin - RXT, azithromycin - AZM, clarithromycin
* Suitable for oral ingestion, low toxicity
* Most Gram-negative bacteria are Resistant

Answer 17

Macrolides

Question 18

Bactericidal
* Antagonistic with quinolones–NOTtobeprescribedtogether
* Oraluseonly
* OnlyusedforUTI

Answer 18

Nitrofurans

Question 19

Inhibit protein synthesis by blocking tRNA
* Examples are tetracycline-TE,doxycycline-DO,minocycline-MH
* Bacteriostatic
* Suitable for oral use only
- Stain teeth during calcification (avoid in children <8-9 yrs old)
- Avoid during pregnancy
- Not to be taken with Ca2+, Mg2+, Fe2+ supplements, drugs (↓ gut absorption)

Answer 19

Tetracyclines

Question 20

Restricted to use against staphylococci and streptococci
* Inactivated in vivo
* Only used topically–creams/ointments,drops,sprays

Answer 20

Mupirocin

Question 21

Reduced(reduction)inside the host bacterial cell to cytotoxic compounds
- Breakdown products disrupt the bacterial DNA
- Reduction only occurs in anaerobes (facultative orgs not affected) - Human cells not affected but can cause significant nausea, v+d
* Antibacterialproperties
- anaerobes only e.g. Bacteroides
* Antiparasiticproperties
- Trichomonas vaginalis
- Giardia lamblia (intestinalis) - Entamoeba
* Orally, rectally, IV
* GoodtissueandCSFpenetration

Answer 21

Nitroimidazoles - Metronidazole - MTZ

Question 22

Bactericidal for mycobacterium tuberculosis(susceptible strains)
* Oral and parenteral administration
* Active against staphylococci and streptococci(but rapid development of R)
- often combined with other antibacterial agents e.g. Trimethoprim for UTI
- can treat MRSA if used with another drug
* Gram negative bacteria are intrinsically resistant

Answer 22

Rifamycins