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MD1 FBS > Antibiotics > Flashcards

Antibiotics Flashcards

1
Q

ESCaPeM

Which microorganisms produce large amounts of chromosomal β-lactamases?

A

Enterobacter, Serratia, Citrobacter, Pseudomonas and Morganella

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2
Q

What are the two mechanisms of action for antimicrobial drugs?

Label A and B.

A

A- bactericidal

B- bacteriostatic

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3
Q

In an immunocompromised patient, would bactericidal or bacteriostatic antimicorbial txt be better?

A

Bacteriocidal

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4
Q

Describe the spectrum of Penicillin G and V

A

GPC, GPR, GNC

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5
Q

What is the route of administration for penicllin G and penicillin V? What are their oral efficacies?

A

Penicillin G- intravenous (injected; poor oral efficacy)

Penicillin V- orally (good oral efficacy)

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6
Q

List examples 6 penicillins (from the lecture)

A

Penicillin G

Penicillin V

Ampicillin

Methicillin

Flucloxacillin

Carbenicillin

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7
Q

What do the penicillins ampicillin, methicillin, flucloxacillin and carbenicillin all derive from?

A

6-APA from the microorganism Penicilium chrysogenum

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8
Q

Put these in order of toxicity (most to least): methicillin, flucloxacillin and carbenicillin

A

Methicillin (moderate toxicity)

flucloxacilin (low toxicity)

carbenicillin (v. low toxicity)

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9
Q

What spectrum (GNR, GPR, GNC & GNR) do methicillin and flucloxacillin target? Why would you prescribe one over the other?

A

They both target GPC (Staphyloccocus) but methicillin has a weak oral efficacy and a moderate toxicity, so flucloxacilin would generally be preferred.

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10
Q

What is MRSA?

A

Methicillin resistant Staphyloccus aureus; multi-resistant staphylococcus aureus

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11
Q

What specific bacteria do methicillin, flucloxacillin and carbenicillin target?

A

Methicillin- GPC (Staphylococus)

Flucloxacillin- GPC (Staphylococcus

Carbenicillin- GNR (Pseudomonas; especially Pseudomonas aeringinosa)

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12
Q

Am poo

What antibiotic would you generally prescribe for a patient with an E. coli infection?

A

Ampicillin (GNR spectrum)

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13
Q

Salmonella causes food poisoning, which makes you poo….

What antibiotic would you generally prescribe for a patient with an Salmonella typhi infection?

A

Ampicillin (GNR spectrum)

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14
Q

Ampicillin is generally considered the same as ______

A

Amoxycillin

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15
Q

Which penicillin would you use to detect MRSA?

A

Methicillin

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16
Q

What antibiotic would you generally prescribe for a patient with an Pseudomonas aeringinosa infection?

A

Carbenicillin

Dan’s: Car runs into a fake Mona Lisa

Bella: Car runs into a pond

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17
Q

Which penicillin have good oral efficacy?

A

FAPv;
Flucloxacillin, amplicillin, penicillin V

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18
Q

Common causes of gas gangrene

A

Most commonly caused by clostridium perfringens bacterium.
Less commonly by Group A Streptococcus.

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19
Q

Common cause of gonorrhea

A

Neisseria gonorrhoea

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20
Q

What is meant by selective toxicity from antimicrobial agents?

A

The drugs target bacterial components that are absent from our own cells;

E.g.

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21
Q

What do beta lactams and glycopeptides target in the bacterial cell?

A

Cell wall

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22
Q

What do polymyxins and polyenes target in their target cells?

What are the microorganisms eah of these drugs target?

A

Cytoplasmic membrane

Polymyxins- bacteria

Polyenes- fungi (best anti-fungal agent)

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23
Q

What do aminoglycosides and chloramphenicol target in the bacterial cell?

A

Ribosomes

24
Q

What are the antimicrobial agents which target nucleic acid?

Which one is also used as a txt for Tb?

A

quinolones and rifamycins

Rifamycin is used as a txt for tb

mnemonic: DNA looks like a train rail; Queensland Rail
Jon is shooting his rifle (rifamycin) at the train’s back (Tb)

25
Q

True or false:
Unlike us, bacteria synthesis their own folate?

A

True.

26
Q

Sulphonamide and trimethoprim target what bacterial components?

A

Folic acid pathways

Mnemonic: Three meth heads in their prime (trimethoprim) who are pregnant (folic acid) and stink like sulphur armpits (sulphonamide)

27
Q

What component in bacteria determines their shape as rod or cocci?

A

The peptidoglycan in the cell wall

28
Q

True or false; bacteria only contain D amino acids in their cell walls, which we target with trimethoprim and sulphonamide.

A

False; they have alternating D and L amino acids, and as humans only contain L a.a’s, we can target the D a.a’s as an antimicrobial therapy.

29
Q

What is the mechanism of action of Vancomycin?

A

Vancomycin binds to the C terminal a.a’s (D-ala & D-ala) in a peptidoglycan precursor molecule; thereby blocking the formation of peptidoglycan used in cell wall synthesis.

30
Q

What is the basis of Vancomycin resistance in Enterococci (VRE)?

A

Vancomycin works by binding to the C terminal amino acids (D-ala and D-ala) however, when a mutation (which requires 9 genes) occurs in the enterococci, the terminal amino acid changes to D-lac and vancomycin no longer binds to inhibit peptidoglycan synthesis.

31
Q

What is the name of the enzyme which catalyses this reaction?

What drug inhibits its action?

A

Transpeptidases or penicillin binding proteins

β-lactams bind to this enzyme and inhibit its action; resulting in inhibition in cell wall synthesis in the bacteria.

32
Q

β-lactams have a bactericidal or bacteriostatic mechanism of action?

A

Bactericidal;

binds to the transpeptidases catalyses the reaction which forms cross bridges in peptidoglycan. When peptidoglycan is unable to be synthesised, the bacteria die from osmotic lysis.

33
Q

Why can’t you give bacteriostatic and bactericidal drugs together?

A

Bacteria have to be growing/dividing in order for antibiotics (β-lactams) to work; bacteriocidal requires growth whereas bacteriostatic inhibits growth.

34
Q

This bond here is hydrolysed by ____, which leads to ____ resistance

A

Beta lactamase –> beta lactam resistance.

35
Q

Two methods of resistance to β-lactams:

A
  1. β-lactamase

Cell synthesises an enzyme to hydrolyse and destroy the β-lactams

  1. Altered penicillin-binding proteins

The enzyme which penicillin (and beta-lactams) bind to is altered and beta-lactams can no longer inhibit it.

36
Q

Pseudomonas aeringosa is intrinsically resistant against ______. Why? and intrinsically susceptible to ______

It can get an acquired resistance through _____

A

Resistant: Penicillin G, V and amoxycillin (ampicillin) due to the action of chromosomal β-lactamase.

Suscpetible to: Carbenicillin

Acquired resistance: plasmid encoded β-lactamase

37
Q

What is clavulanic acid used for?

E.g.?

A

Clavulanic acid in iteself is poorly anti-bacterial as it poorly binds to well (β-lactam effect) however, it can bind to β-lactamases (particularly plasmid derived) and inhibits their activity, allowing for other antibiotics (β-lactams) to them act on the bacteria; requires another antibiotic for anti-bacterial effect.
Amoxycillin + clavulanic acid = augmentum/co-amoxyclav.

38
Q

What is the required antibiotic treatment for Pseudomonas aeringinosa infections with acquired β-lactamase?

A

Timentin; ticarcillin (β-lactam action –> prevents cross linking of peptidoglycan) + clavulanic acid (inhibits β-lactamase)

39
Q

Protein:
aminoglycosides and tetracyclines

A

Gentamicin, tobramycin, amikacin (only for emergencies)

40
Q

Mechanism of action of aminoglycosides and tetracyclines

A

They inhibit the recognition phase of protein synthesis in the bacterial cell.

Firstly, they bind to the ribosome and distort the reading frame, causing mistakes in translation –> abnormal proteins –> weakened structure in bacteria –> influx of aminoglycosides into permeable cell –> complete stop of protein synthesis

41
Q

What are the 4 mechanisms to resistance against aminoglycosides?

A
  1. Enzymatic modification of the drug –> reduced entry into cell
  2. Modified outer membrane leading to reduced entry (G - bacteria)–> prevents ALL aminoglycoside entry
  3. Efflux
  4. Ribosomal mutuation (ribosomal protein or rRNA)
42
Q

True or false: aminoglycosides are inactivated via covalent modification, not vua hydrolysis.

A

True.

43
Q

True or false: β-lactams are inactivated via covalent modification, not via hydrolysis.

A

False; they are inactivated via hydrolysis (through β-lactamases)

44
Q

Specific examples of altering the target of drug action

A

VISA –> increased peptidoglycan synthesis –> overproducing target
mnemoic: fuzzy, Dan’s lenient VISA card

modified PBP in pneumococcus and MRSA –> modification of the target to a less sensitive form –> binds penicillin less avidly

ribosomal mutations–> modification of the target to a less sensitive form –> aminoglycoside no longer binds –> aminoglycoside resistance

45
Q

Describe a txt against anaerobes which utilises an inactive precursor.

A

Metronidazole;

Inactivated drug is activated via pathogenic nitroreductase enzyme. Active drug then affects a.a synthesis, nucleotise synethesis etc.

46
Q

Describe the mechanism of resistance against Metronidazole.

A

Pathogen loses activity of nitroreductase enzyme –> drug is not activated –> resistance against Metronidazole.

47
Q

What do the following acronyms stand for:

MRSA, PRP, VRE, VISA, MDR-TB, XDR-TB

A

MRSA- methicillin-resistant Staph. aureus

PRP- penicillin-resistant pneumococci

VRE- vancomycin resistant enterococci

VISA- Vancomycin-intermediate Staph. aureus

MDR-TB- Multi-drug resistant Mycobacterium tb

XDR-TB- Extensively drug resistant M. tb

48
Q

Common microorganism of infection post-op in hip joint replacement?

A

Staphylococcus epidermidis

49
Q

Vancomycin is unable to penetrate the membrane of gram __ cells?

A

Negative

50
Q

What are the three mechanisms for the transfer of genes between bacteria?

A
  1. Transformation
    - uptake of naked DNA released from another, closely related bacterium
    - homologous recombination; incorporates DNA fragment into its own genome
  2. Transduction
    - phage mediated DNA recombination
    - Phages are spp. specific, but can occur just between genus (less specific than transformation)
  3. Conjugation
    - plasmid-mediated
    - can occur between completely unrelated bacteria
51
Q

Three factors which favour the development of resistance?

A
  1. Vast numbers
  2. Rapid growth
  3. Promiscuity
52
Q

The MIC/MBC measures the bacteriostatic property of the antibiotic?

The MIC/MBC measures the bacterialcidal property of the antibiotic?

A

MIC (min. inhib, concentration)

MBC (min. bacterialcidal concentration)

53
Q

Which serious infections would illicit the use of intravenous penicillin?

A

Pneumococcal pneumonia, streptococcal cellulitis and syphilis.

54
Q

Jawetz’s Laws

Bacteriostatic + Bacteriostatic=

Bacteriostatic + bacteriocidal=

Bacteriocidal + bacteriocidal=

A

Bacteriostatic + Bacteriostatic= additive (or indifferent)

Bacteriostatic + bacteriocidal= antagonistic

Bacteriocidal + bacteriocidal= synergistic

55
Q

What should you not prescribe in the txt of meningitis?

A

Bacteriostatic + bactericidal drugs which give antagonistic effects; inhibits the action of the bactericidal drug via the bacteriostatic

e.g. tetracycline + β-lactams

56
Q

What does chloramphenicol target in the bacterial cell?

A

Ribosome

MD1 FBS (28 decks)

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