Antibiotics and Antimicrobial Resistance Flashcards
What is antibiotic resistance?
- The ability of bacteria to survive treatment by certain antibiotics.
- Bacteria which are resistant to multiple antibiotics are called multi-drug resistant
Why is the problem of AMR so bad?
Antibiotic use in humans
- People not taking complete courses of antibiotics
- Inappropriate prescriptions or over-prescription of antibiotics
Why is the problem of AMR so bad: Non-therapeutic uses of antibiotics
•To treat sick animals•As growth promoters in
agriculture (Not in the EU!)
- Biocide use (to extend shelf life)
- Brewing
- Veterinary medicine
- Aquaculture
- Anti-fouling (industrial, ships)
Problem of AMR: No new antibiotics!
Golden age of antibiotic discovery was from 1930-1970!
Why do antibiotics stop working?
What doesn’t kill them makes them makes them stronger!
How do bacteria become resistant to antibiotics?
- Make enzymes which alter or destroy the antibiotic
- Alteration of target site
- Prevent antibiotics getting into the cell
- Pump (efflux) the antibiotic out of the cell
- Temporarily change their metabolism (dormancy)
Show how bacteria become resistant to antibiotics?
Enzymes which alter or destroy the antibiotic
- The β-lactamases (penicillinases)
- Adaptive resistance
- Hydrolyse the β-lactam ring
- Broad spectrum resistance mechanism
- Gram –ve β-lactamases excreted
- Some classes can be inhibited by Clavulanic acid (used in combination with β-lactam antibiotic)
Give examples of organisms with enzymes which alter or destroy antibiotics
- Extended spectrum β-lactamases (ESBLs)Discovered in 1980sPlasmid-encoded (HGT)Confer multi-resistance
- Inhibit a wide range of β-lactams
Resistance to penicillins but not extended-spectrum cephalosporins
Carbapenems used (resistance reported)
- Derive from genes for TEM-1, TEM-2 or
SHV-1 by mutations in in the active site
- TEM ESBL: 90% E. coli resistance. Also H. influenzae, K. pneumoniae, N. gonorrhoeae
- SHV ESBL: K. pneumoniae
Pump (efflux) the antibiotic out of the cell
- Energy dependent (active) transport of unwanted substances out of the bacterial cell
- Adaptive resistance
- Located in cytoplasmic membrane
- Primary active transporters are powered by ATP hydrolysis
- Secondary active transporters pump(H+)
Uniporters, symporters, antiporters
- 5 Superfamilies:
- Major facilitator superfamily (MFS)
- ATP-binding cassette superfamily (ABC)
- Small multidrug resistance superfamily (SMR)
- Resistance-nodulation-cell division superfamily (RND)
- Multi-antimicrobial extrusion protein (MATE)
Did efflux pumps evolve to provide resistance to antibiotics?
- Didn’t evolve for antibiotics
- Lipids (pH homeostasis), environmental toxins etc.
- Bacteria pump antibiotics out of the cell using efflux pumps
- Antibiotics present selective pressure for bacteria with these efflux pumps
Explain Efflux pumps
- Chromosomal or on plasmids (HGT)
- Intrinsic and acquired (from HGT) resistance
- Expression of several classes of efflux pump can lead to a broad spectrum of resistance
- Efflux pump inhibitors exist Verapamil/PABN/CCCP
- Mostly function by disrupting H+ motive force – very toxic, no clinical application
- Triclosan – antibacterial and antifungal agent
- Toothpaste, soaps, detergents etc.
- Triclosan elect for broad spectrum efflux pump expressing bacteria (resistant to Triclosan)
- Banned by FDA in 2017
Alteration of the target site
- EXAMPLE: DNA Gyrase and Fluoroquinolone resistance
- DNA Gyrase – DNA synthesis
- Fluoroquinolones block DNA-gyrase-DNA complex formation
- Resistance by chromosomal mutations in both genes
- More common – mutations in GyrA (A subunit of DNA Gyrase)
- Prevent fluoroquinolone binding
Temporarily change their metabolism
- Escape effect of antibiotic without undergoing genetic change
- “Persister” cell formation (because they are persistent)
- Adaptive resistance
- Do not grow in the presence of antibiotic but are tolerant to its presence
- Small fraction of population >1%
- Mechanism not well understood
- Changes to metabolism made possible by metabolomics
- Not really “dormant” although sometimes described as such
- Phenotypic variance
Give examples of bacteria that temporarily change their metabolism
- EXAMPLE: Non-replicating persistence (NRP) in Mycobacterium tuberculosis
- Causes LTBI
- Non-replicating, metabolically active, multi-drug tolerant
- Induced by <pO2 and nutrient starvation
- Can persist for many years
- TB treatment regimen is inactive (isoniazid and rifampicin have acute effect upon re-activation)
- Killed by metronidazole and Pretomanid (PA-824) under NRP
- Limited uptake in granuloma
- We need more NRP-active drugs
Prevent antibiotics getting in to the cell
- Antibiotics require access to bacterial cell machinery to be effective
- Reduce OM permeability
- Adaptive resistance
- Porin channels allow antibiotics to cross Gram –ve outer membrane
- Modifying cell membrane porin channels
- Frequency
- Size
- Selectivity
- Example: aminoglycoside resistance
Prevent antibiotics getting in to the cell: Explain this mechanism
Which bacteria can this be observed in?
- Increase the Outer Membrane Permeability
- Hydrophobic drugs diffuse across lipid bilayer
- Eg. Macrolides
- Increase saturated lipid composition of OM reduces permeability
- Hydrophilic drugs use porins for accessing cell
- Eg. β-lactams, tetracycline, fluoroquinolones
- Down-regulation, loss or functional change of OmpF and OmpC (Outer membrane porin F/C) leads to antibiotic resistance
- Observed in E. coli, P. aeruginosa, N. gonorrhoeae, Enterobacter aerogenes and K. pneumoniae
The future of antibiotic resistance
By 2050 AMR will be the leading cause of death
