Lecture 5: antibiotic resistance Flashcards
What are antibiotics
compounds that can kill or inhibit the growth of the bacteria
how was the antibiotics found
-found to be produced by mold aka penicilium
true or false: antibiotiocs can be synthetic or natureal
truewhat are the
what are the main routes of administration for antibioticvs
oral or intraveinous
what makes a drug antibacterial
-spectrum of activirty: gram + vs _ and aerobes vs anaerobes, specific sopecies
-bacteriostatic vs bactericidal
-mechanism of action, drug target
-pharmacology: potency, delivery and side effects
what does bacteriostatic mean
-interferes with a process required for cell replication (ex: protein synthesis) causing an arrest in growth
what does bactericidal mean
-interferes with a process required for cell survival (ex: lysis of cell wall, dna damage etc) causing cell death
cell wall synthesis inhibiotors
-b lactams and glycopeptide abx mechanisms
-binds d-ala-d-ala terminal
-structure is similar do d-ala-d-ala terminal portion
-bind to PBPactive domain (penicilin binding proteins)
True or false: cell wall synthesis is conserved across many species and has multiple steps that can be inhiboted by different types of compound
true
many cell wall synthesis inhibitors are not active against….
gram - bacteria because they can’t penetrate the outer membrane
what makes beta lactams easy to differenciate
they have a common beta lactam ring
true or false: all beta lactams are all the same
nah different classes of beta lactams with different susceptibility to bete lactamase degredation and spectrum of activity
true or false: resistance is increasing but newer generations are hydrolyzed by certain beta lactamases
false; they are not hydrolyzed
what is the mechanism of resistance of the beta lactams
-hydrolysis of beta lactamase
-expression of alternate PBP with low binding affinity
name protein synthesis inhibitors
-chloramphenicol
-macrolides, clindamycin and streotogramins
-aminoglycosides
-tetracyclines
-linezolid
all protein synthesis inhibitors, except for…. are bacteriostatic
aminoglycosides
what inhibits peptidyl transferase centre (50S inhibitor)
chloramphenicol
what inhibits peptide exit tunnel (50S inhibitor)
mecrolides
what inhibits trna delivery (30S inhibitor)
tetracyclines
what inhibits trna translocation (30S inhibitor)
aminoglycosides
what is the mechanism of action and antibiotic resistance of protein synthesis
-expression of aminoglycosides modifying enzymes (acetylation, phosphorylation)
-modification of ribosomal
-reduced uptake/permeability
aminoglycosides structure:
-structurally varied with natural and semi synthetic compound with a central aminocyclitol ring
-with numerous hydroxyl and amine group
aminoglycosides: broad spectrum with ……
excellent activity against gra, - and some gram +
clinical use of aminoglycosides
-no oral drug
-has significant systemic toxiciyu
-usually used for multi drug resistant or severe gram - infections or topical use
mechanism of action of aminoglycosides
- Binding to 30S ribosomal subunit, inhibits protein translation at the translocation reaction and prevent the subunit splitting
- Induce mistranslation by stabilizing the binding of non cognate tRNA to the mRNA; Mistranslation of membrane proteins likely indirectly causes loss of cell-wall integrity
what are antibiotics that target nucleic acid synthesis
-dna gyrase: quinolones
-rna polymerase: rifampin
what is the spectrum pf action in quilonoles
-bactericidal drug with broad spectrum with activity against gram + and - bacteria, mycobacteria
is quinolones natural
-synthetic drug but derived from natural compounds
are quilonoles well tolerated?
- Highly effective and well tolerated treatment and widely used for a wide range of human infections (e.g. GI, urinary, respiratory infections), even Mycobacteria (including TB)
why is there resistance with fluoro quinolones
due to widespread use
mechanism of action of quinolones
- Inhibits bacterial gyrase and Topoisomerase IV, which relaxes DNA supercoils
- Causes DNA fragmentation due to residual nuclease activity
mechanism of resistance in quinolones
Mechanisms of resistance
* point mutation of binding site
* efflux pumps
* porin expression and membrane permeability
mechanism of action of rifampin
Rifampin inhibits transcription by binding to the β subunit (encoded by the rpoB gene) of the prokaryotic RNA polymerase (RNAP) which facilitate the direct blocking of the elongating RNA.
mechanism of resistance with rifampin
point mutations of binding site
hiw to assess antibiotic susceptibility
Conventionally defined by growth at high drug concentration by MIC (Minimal Inhibitory Concentration), zone of inhibition or E-test
resistance to multiple compounds=…
multidrug resistance
The outer membrane of Gram negative bacteria and mycobacterial cell wall are highly……
hydrophobic and impermeable and acts as a selective barrier.
hydrophilic molecules and some hydrophobic molecules must enter through…..
size limited pores
low permeability account for resistance to drugs such as…
- Low permeability account for resistance to drugs such as beta lactams, glycopeptides (vancomycin) in gram-negatives
- Typically responsible for intrinsic resistance but can also be acquired through differential expression or mutations of certain porins.
Antibiotic resistance due to drug efflux
- Antibiotics are pumped out of the cell (outer and inner membrane) and therefore cannot reach their targets
- Major mechanism in gram negative bacteria
- Complex “multi-purpose” efflux pumps
- Can cause multi-drug resistance
which type of pump resists to multipledrugs
acrb (rnd family) and lmrA (ABC superfamily)
Antibiotic resistance due to target mutation
- Can be due to genetic mutation of the target gene
- Example: gyrB (gyrase) mutations reduce the binding affinity of quinolones to GyrA and confer quinolone resistance
- Can be due to enzymatic modification of the target structure
- Erm genes which encore methyl transferases that can modify of 50S subunit and confer macrolide resistance
name beta lactams
-penicilins
-monobactam
-cephalosporins
-carbapene,
enzymes secreted in… are highly effective at cleaving beta lactam rings
periplasm
Different beta-lactamases exist with different spectrum… now there are extended
spectrum (ESBL) that can cleave cephalosporins and metallo-beta lactamases (MBL) that cleave carbapenems.
where are esbl and mbls are encoded
Encoded on plasmids (acquired resistance) or on the chromosome of some gramnegative bacteria (eg. intrinsic resistance in Pseudomonas).
Aminoglycoside modification
-This inactivation of antibiotics depends on the modifying enzymes’ function, i.e., the addition of chemical groups to vulnerable sites of the antibiotic molecule or antibiotic targets.
* Various different chemical groups can be transferred, including acyl, phosphate, nucleotidyl, ribitoyl, glycosyl , and thiol groups.
* This prevents proper binding of aminoglycosides to the 30S subuni
what does intrinsic resistance
Intrinsic resistance: resistance to an antimicrobial is inherent to a bacterial
species ( “natural resistance”)
-ex: absence of target
-low permeability
-low affinity target
what is aquired resistance
Acquired resistance: Strain is typically susceptible to a given antimicrobial drug and becomes resistant.
-ex: inactivation of druh
how does antibiotic resistance spread withinm a population
vertical and horizontal gene transfet
Vertical genetic transfer of resistance
mutations
This selects an advantageous mutation (resistance mutation) that occurred as a random genetic event into a major genetic allele through clonal expansion
Horizontal genetic transfer of
resistance genes or mutations
- Major mechanism spread within and
across hosts, different environments and bacterial species - Plasmid-borne transfers can allow multiple resistance genes to be spread at once
true or false: resistance genes often originate from antibiotic producing species or other resistant bacteria
true
true or false: newly acquired resistance genes can be selected for under antibiotic treatment
TRUE
NAME the eskape pathogens
Enterococci faecium
Staphylococcus aureus
Klebsiella pneumoniae
Acinetobacter baumannii
Pseudomonas aeruginosa
Enterobacter sp.
who top priorities
- Tuberculosis
- Gram negative bacteria
- Resistance to antibiotics of “last resort”:
- ESBL (extended spectrum betalactamase) and MBL (metallo
beta-lactamase) - Colistin resistance
AMR outside the clinic
- Antibiotic use for growth promotion, disease prevention and treatment
- Use of medically used antibiotics
- Off label use of antibiotics highly similar to human antibiotics
antibiotic resistance; what can you do
-only take antibiotics when have to
-tajke full prescription
-never use left over antibiotivs
-never share antibiotiocs
-wash your hands and don’t tal;k to sick people
true or false: no new class of antibiotics discovered since 1987 has yet led
to new drugs
true
No new antibiotics introduced between … and ….
2003-2011tr
true ot false: the antibiotic pipeline is less bad npw
true
total approved antibiotics since 2014:
14
total discontinued antibiotics since 2014
19
Penicillin, the 1st antibiotic (1928, Sir Fleming) produced by the …
mold Penicillium
Streptomycin, the first screen for antibiotics (1943, Selman Waksman) what was done
- Screened >10,000 soil organisms
- Streptomycin, first aminoglycoside produced by Streptomyces griseus
Antibiotic-producing micro-organisms: soilorganisms such as ….
Actinomyces and Streptomyces, fungi/mold
Antibiotic have been made by bacteria for over …` millions years
40
Natural products; strategies
- Natural compound libraries
- Libraries of micro-organisms (natural isolates)
- Screen natural samples for antibacterial activity: soil and marine bacteria, fungi, marine invertebrates (e.g. sponges, corals)
- Probably need to screen many strains (107 ?) to find one compound
Screening of synthetic molecule libraries
- hundreds of thousands/millions of molecules
- In vitro screening yielded little success
- Whole cell assays more difficult
Synthetic biology
- genome mining for biosynthetic clusters
- “natural” or recombinant expression of antibiotic-producing operons
Chemical optimization:
- Improve penetration inside cells: increased membrane penetration or
uptake, greater stability, better activity against target - Improve pharmacokinetic/pharmacodynamic
- Overcome resistance mechanisms: reduced efflux, drug degradation or
modification
Combination therapy (with adjuvants)
- Add another antibiotic: e.g. trimethoprim-sulfadiazine, multi-drug TB regimens
- Molecule to overcome resistance: e.g. ampicillin + clavulanic acid
- Molecule that increases penetration: e.g. cephalosporin siderophore
Repurposing of drugs already approved
Non-antibiotics which show antibacterial activity: e.g. antipsychotics
target protein+chemical library..
=target specific assay (high throughput screening)=phenotypic evaluation
cell/ organism model+ chemical library…
=phenotypic assay(high content screeniong)=target devolution
teixobactin
Teixobactin kills bacteria by a two-pronged attack on the cell envelope
without resistance
Cefiderocol
Cefiderocol for the Treatment of Infections Due to Metallo-B-lactamase–Producing Pathogens in the CREDIBLE-CR and APEKS-NP Phase 3 Randomized Studies
