Antibiotic Resistance Flashcards
Definition of antibiotic resistance?
Ability of bacteria to survive and grow in presence of antibiotic concentration safely achievable in patients at site of infection
Two types of antibiotic resistance?
Acquired and intrinsic
Acquired when previous susceptible population becomes resistant
Intrinsic from inherent features e.g Mycoplasmae have no peptidoglycan wall so intrinsically resistant to b-lactams and glycopeptides
E.coli is intrinsically resistant to vancomycin and Mupirocin as can’t get through outer membrane
Many g-ve species resistant to linezolid as actively effluvia out
What does O’Neil report say on Ab resistance?
By 2050 antibiotic resistance will be largest cause of death, taking 10 million a year
With economic impact of $100.2 trillion dollars
Consequence of antibiotic resistance
Increased mortality
- resistance can be more fatal
Increased morbidity
- prolonged illness
- great opportunities to for resistant organisms to grow
Increased cost
- Longer stays in hospitals
- newer, more costly drugs will be used
Mechanisms of resistance all the ways to alter target site
Mutation of target
Recombination
Modification of target
Target overexpression
Example of recombination resistance
Example of target modification resistance
Neisseria spp and Streptococcus spp can have beta lactam resistance by taking DNA from eDNA of intrinsically resistant species
Methylation of ribosomal RNA
Enterococci can confer resistance to vancomycin by switching out D-ala-D-ala for D-ala-D-lactate
Resistance mechanisms by decreased uptake?
Reduced permeability
Mainly feature of g-ve, by loss of porins( has fitness cost)
Active efflux
Several different families of efflux pump
May be specific or broad
Confer resistance to multiple classes of Antibiotics
May arise from upregualtion of endogenous pump or horizontal acquisition of new one
Structure of AcrAB/TolC system in E. coli
Tripartite pump
Efflux transporter connected to adaptor protein linked to OM channel protein
Drug crosses OM and or CM
Transporter pumps drug out bypassing OM
Enzyme inactivation or modification?
Example
Destruction of target
B-lactamases mediate resistance to beta-lactam Antibiotics
Cyclic amide bonds of beta lactam rings are hydrolysed
Open ring forms cannot bind to target site
Problem as g-ve produce several B-lactamases
What enzymes modifiy aminoglycosides ?
As form of resistance
Aminoglycoside adenyltransferase ANT
–catalysed ATP-dependant adenylation of hydroxyl group
Aminoglycoside acetyltransferases AAC
–Catalyses acetyl CoA-dependant acetylation of an amino group
Aminoglycoside phosphotransferases APH
–Catalyse ATP-dependant phosphorylation of hydroxyl group
Bulk up sites important for binding to the 16s ribosomal unit
Target bypass?
And example?
Acquisition of alternative target
MRSA has acquired MecA gene that encodes an alternative PBP2. It’s a transpeptidase resistant to B-lactam
Trimethoprim resistance by resistant dihydrofolate dedicates that can discriminate between the drug and dihydrofolate
Multiple mechanisms of resistance can operate for single drug class?
What drug classes have 3 mechanisms of resistance
B-lactams
Aminoglycosides
How long has Fusidic acid been in clinicl use
Since 1962
Systemically and topically
Fusidic acid hydrolyses
GTP
How does FusA resistance arise
Consequence of point mutations in gene that encode this protein
Huge diversion of mutation that can cause this
What is fusB type resistance
Less we’ll known or characterised
Associated to strains that’s carry plasmid associated with resistance of Fusidic acid
How was genetic basis of fusB type resistance?
Shotgun cloning performs on plasmid responsible for Fusidic acid resistance and fragments were cloned into staph
Single small gene (FusB) was 642bp
- –bioinformatics analysis shows encodes as small proteins that is cytoplasmic and hydrophilic
- –no known homologues
- -part of family of unknow functions
Homologise collectively know as FusB type proteins
Number of resistance isolates in MRSA
And percentage
N=291
FusB=67%
FusA=13%
FusC=20%
Vast majority of strains horizontally acquire
Resistance emerges due to succesful clones spreading from one patient to another
FusB binds to?
Ef-G
Binds to EF-g without need for other components
Highly affinity binds
1 mole of FusB bind to 1 mole of EF-G
FusB binds to EF-g whether or not in the presence of Fusidic acid
What are the routes to Antibiotic resistance?
Spontaneous mutations to resistance
Depends on fidelity of DNA polymerase.
Horizontal acquisition by
- natural competence
- transposition
Most resistance is spontaneous event without need for Antibiotics
But are cases Antibiotics can cause mutations due to stress
Mutation frequencies to Antibiotics
Mutation rare event but bacteria can increase their rate of mutation and become hyper mutable
Biofilms can become hypermutable due to oxidative stress
Adding catalase removes hydrogen peroxide and detoxifies biofilm lowering mutation rate
Best seen in CF infections
How do Antibiotics cause mutations?
Due to stress
Bacteria initiate SOS response
This is DNA repair by low fidelity polymerase
Which increases rate of horizontal acquisition
How can resistance be transferred horizontally
Plasmids
Transposons
Staph cassettes
Known as ICE integrative conjugating elements By transduction(phages), conjugation and transformation
Where do acquired resistance genes originate ?
Antibiotics used for under a century but bacteria millions of years
Many antibiotics are naturally produced metabolites. So bacteria would have encountered and and obtained resistance in nature.
Vancomycin resistance can be found in environmental strains
Origins of B-lactamases
PBPs and b-lactamases very similar
Both have serine group in active sites and can perform nucleophilic attack on ring structure of the beta-lactam
Ring structure is broken and would covalently bind to PBP but with B-lactams those intermediates are released
FusB resistance could be due to resistance being conferred accidentally by household genes
How do resistances spread?
Once emerged can grow and expand by
Global expansion
Horizontal dissemination of resistance genes
Antibiotic resistance is evolutionary process and antibiotic usage drives an increase to resistance frequencies. Survival of fitness
Inadvertent directed evolution
Why is Enterobacteriacea current cause of concern
Has resistance to Aminoglycosides, beta-lactams and fluoroquinolones
Extended spectrum beta-lactamase ESBL. CTX-M enzymes –seriously threatens use of 3rd generation cephalosporins
Shift to carbapenems: cost, parenteral administration, destruction of commensal flora and selection for carbapenem resistance
International spread of NDM-1 beta-lactamases which confer resistance to all b-lactams
Concerns over Pseudomonas aeruginosa and Acinetobacter baumannii?
Environmental bacteria have evolved vast methods of survival strategies, efflux pumps and large complex genomes
Are very adaptable
Tuberculosis has three diff types of resistant strains. Which are?
mdr TB
edr TB
XDR TB
Concerns about Neisseria gonorrhoea
Common Bacterial infection
Not fatal but can lead to sterility
People don’t pay attention to non lethal disease
Ciprofloxacin was common treatment
In 2011 3rd gen cephalosporin and azithromycin
Not proved effective new resistance gonorrhea first outbreak in Leeds
How to address resistance. Problem
Better training of people prescribeing drugs
Better coordination of international surveillance of resistance arising in animals and humans
Better guideline
-cycling Antibiotics to reduce the selective pressure
Restriction on use of antibiotic as growth promoters
Improve infection control practice
Ultimately need new antibiotics drugs to circumvent the problem
