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Medical Microbiology > Antibacterials & Antibiotics > Flashcards

Antibacterials & Antibiotics Flashcards

1
Q

What does antibacterial mean?

A

A substance that kills bacteria or inhibits bacterial growth

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2
Q

What is an antibiotic?

A

A substance produced by a living organism that is capable of destroying or inhibiting the growth of microorganisms

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3
Q

What is an antimicrobial?

A

A substance that kills microorganisms or inhibits their growth

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4
Q

Where do antibiotics come from in nature and why do they work?

A

Mainly from soil, are secreted to kill or slow competitors

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5
Q

How does clinical resistance form?

A

When resistance genes are mobilised and moved as a consequence of genetic transfer to organisms that cause infections

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6
Q

What does bactericidal mean?

A

Antibiotics that kill bacteria, but at low concentrations can be bacteriostatic

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7
Q

What does bacteriostatic mean?

A

Slow bacterial growth without killing them, but at high concentrations can be bactericidal

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8
Q

Main points of cell wall synthesis inhibitors

A
  • more effective against gram +ve
  • disrupt bacterial maintenance of osmotic pressure
  • selective, as there is no cell wall in mammals
  • generally bactericidal
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9
Q

What are beta-lactams and how do they work?

A

Drugs that target cell components within the cell wall and destroy integrity

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10
Q

How does Fosfomycin work?

A

Inhibits phosphoenolpyruvate which is essential for peptioglycan synthesis, limiting the conversion of NAG to NAM and the cross linking between them

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11
Q

How does cycloserine work?

A
  • is an analog of D-Ala, which prevents activity of enzymes (alanine racemase) involved in peptidoglycan synthesis
  • alanine racemase cannot convert L-Ala into D-Ala, so peptidoglycan synthesis is inhibited
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12
Q

How does bacitracin work?

A

Interferes with isoprenylphosphate which carries and transports peptidoglycan molecules, meaning the cell wall can’t be build

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13
Q

How does Vancomycin and Teicoplanin work?

A

Pretends to be D-Ala-D-Ala in gram +ve bacteria, replacing the residue in the NAM-NAG peptide, stopping peptidoglycan being produced

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14
Q

How is synthetic penicillin made?

A
  • stripping side chains from natural penicillin and adding new ones
  • stopping penicillin synthesis early and purifying the central B-lactam ring core
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15
Q

How does Rifampicin work?

A
  • it interferes with the RNA polymerase/DNA complex, preventing separation of the DNA strands and inhibiting transcription
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16
Q

What is Rifampicin?

A

It is an RNA synthesis inhibitor, which targets the DNA dependent RNA synthesis pathway which uses different RNA polymerases to humans

17
Q

What are fluoroquinalones?

A

DNA synthesis inhibitor with low MIC, which target enzymes in bacteria similar to humans

18
Q

How do fluoroquinalones work?

A
  • Inhibit Topoisomerase 2&4 which are critical for DNA replication
  • Gyrase bind DNA and hold the strands in place, quinoline arrests the DNA/gyrase complex so DNA can’t be repaired and released
19
Q

What is Metronizadole?

A

A DNA synthesis inhibitor which is selectively absorbed by anaerobic bacteria

20
Q

What does Metronizadole do?

A

Once activated in area of anaerobiosis, the formation of unstable intermediates interact with bacterial DNA and poke holes

21
Q

Benefits of antibiotic combinations

A
  • delays emergence of resistance
  • synergy between the 2 drugs
  • act in sequential steps in the pathway
  • bactericidal in combination
22
Q

How does Colistin work?

A

Interacts and disrupts the plasma membrane of gram -ve bacteria

23
Q

How does 2 complement system of coliston work?

A

Sense antibiotic on surface, and trigger changes through a regulator, alter production and presentation of LPS on the microbe surface

24
Q

How do beta lactamases work?

A
  • beta lactam antibiotic diffuses through porins of the outer membrane and enter periplasmic space
  • beta lactamases degrade the antibiotic
25
Q

What does penicillin binding protein do?

A
  • if any antibiotic passed through the beta lactamase system, pbp interacts with the molecules and inhibits them
26
Q

What is vertical acquisition?

A

When a species acquires a plasmid which spreads, causing cross infection between patients in a specific environment

27
Q

What is horizontal acquisition?

A

A plasmid spreads into diverse species ubiquitously and continues spreading

28
Q

What are extended spectrum beta lactamases?

A

Beta lactamases which can degrade 3rd generation cephelasporins like cefotaxime and ceftazidine

29
Q

What are the 4 types of beta lactams?

A

Penicillins, cephelasporins, carbapenems, and monobactams

30
Q

How do beta- lactamases work against amoxicillin?

A

Cleaves the amide ring in penicillin/beta lactam molecule, flipping the conformation and making it useless

31
Q

How does the TEM-1 beta lactamase work?

A

Small amoxicillin molecules enter and bind directly with the ser70 active site, which cleaves the amide ring and renders it impotent

32
Q

What antibiotics does TEM-1 not work against and why?

A

Cephelasporins, as they are too large of a molecule to fit into the ser70 binding site

33
Q

What antibiotics does TEM-1 not work against and why?

A

Cephalosporins, as the molecules are too large to fit in the Ser70 active site

34
Q

How does dual resistance to fluoroquinalones and cephalosporin arise?

A
  • plasmid resistant to both
  • expansion of a strain with chromosomal mutation for quinalone resistance and contains a plasmid encoding beta lactamase
35
Q

The process of plasmid genes inserting into bacterial genome?

A

Plasmids carry integrons, which can insert into transposon, which can be inserted into a different plasmid. The integron and transposon can excise themselves from the plasmid and insert into chromosome.

36
Q

What is OmpC?

A

Is a porin that aids permeability of carbapenem, when it is absent the drug is not fast enough to act on the bug

37
Q

What are transposons?

A

Jumping genes that can move into a chromosome OR into another plasmid in the strain

38
Q

What is conservative transposition?

A
  • cut & paste method -
    Transposon from donor is excised, then inserted into the recipient, mediated by transposase
39
Q

What is replicative transposition?

A
  • copy & paste
  • DNA synthesis happens from open ends via DNA polymerase
  • tnpA causes ligation at nicked ends
  • cointegrate has 2 copies of the transposon. 1 copy is resolved through tnpR to stay within donor, while second moves on to target replicon

Medical Microbiology (13 decks)

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