Antibacterials & Antibiotics Flashcards
(39 cards)
What does antibacterial mean?
A substance that kills bacteria or inhibits bacterial growth
What is an antibiotic?
A substance produced by a living organism that is capable of destroying or inhibiting the growth of microorganisms
What is an antimicrobial?
A substance that kills microorganisms or inhibits their growth
Where do antibiotics come from in nature and why do they work?
Mainly from soil, are secreted to kill or slow competitors
How does clinical resistance form?
When resistance genes are mobilised and moved as a consequence of genetic transfer to organisms that cause infections
What does bactericidal mean?
Antibiotics that kill bacteria, but at low concentrations can be bacteriostatic
What does bacteriostatic mean?
Slow bacterial growth without killing them, but at high concentrations can be bactericidal
Main points of cell wall synthesis inhibitors
- more effective against gram +ve
- disrupt bacterial maintenance of osmotic pressure
- selective, as there is no cell wall in mammals
- generally bactericidal
What are beta-lactams and how do they work?
Drugs that target cell components within the cell wall and destroy integrity
How does Fosfomycin work?
Inhibits phosphoenolpyruvate which is essential for peptioglycan synthesis, limiting the conversion of NAG to NAM and the cross linking between them
How does cycloserine work?
- 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
How does bacitracin work?
Interferes with isoprenylphosphate which carries and transports peptidoglycan molecules, meaning the cell wall can’t be build
How does Vancomycin and Teicoplanin work?
Pretends to be D-Ala-D-Ala in gram +ve bacteria, replacing the residue in the NAM-NAG peptide, stopping peptidoglycan being produced
How is synthetic penicillin made?
- stripping side chains from natural penicillin and adding new ones
- stopping penicillin synthesis early and purifying the central B-lactam ring core
How does Rifampicin work?
- it interferes with the RNA polymerase/DNA complex, preventing separation of the DNA strands and inhibiting transcription
What is Rifampicin?
It is an RNA synthesis inhibitor, which targets the DNA dependent RNA synthesis pathway which uses different RNA polymerases to humans
What are fluoroquinalones?
DNA synthesis inhibitor with low MIC, which target enzymes in bacteria similar to humans
How do fluoroquinalones work?
- 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
What is Metronizadole?
A DNA synthesis inhibitor which is selectively absorbed by anaerobic bacteria
What does Metronizadole do?
Once activated in area of anaerobiosis, the formation of unstable intermediates interact with bacterial DNA and poke holes
Benefits of antibiotic combinations
- delays emergence of resistance
- synergy between the 2 drugs
- act in sequential steps in the pathway
- bactericidal in combination
How does Colistin work?
Interacts and disrupts the plasma membrane of gram -ve bacteria
How does 2 complement system of coliston work?
Sense antibiotic on surface, and trigger changes through a regulator, alter production and presentation of LPS on the microbe surface
How do beta lactamases work?
- beta lactam antibiotic diffuses through porins of the outer membrane and enter periplasmic space
- beta lactamases degrade the antibiotic
