Determination of Antibiotic Resistance Flashcards
What is antimicrobial resistance?
A natural phenomenon accelerated by use of antimicrobial medicines
Resistant strains survive and aggregate
How does AMR develop?
Microbes acquire mutations
Microbes acquire genetic information from other microbes to develop resistance
What are the types of AMR?
Antibacterial resistance
Antiviral resistance
Antiparasitic resistance
Antifungal resistance
Why is AMR a global concern?
Increases mortality
Challenges control of infectious diseases
Threatens a return into the pre-antibiotic era
Increases costs of healthcare
Jeopardises healthcare gains to society
What are the 3 main mechanisms that lead to drug resistance?
Modify drug target
Modify drug
Modify efflux and influx of drug
How does modification of drug target lead to drug resistance?
gyrase A mutation cause fluoroquinolone resistance
How are drugs modified?
Aminoglycoside modifying enzymes
Beta lactamases degrade B-lactam antibiotics
How does modification of efflux and influx of the drug lead to drug resistance?
Efflux pumps pump drug out the cells
Influx via porins
What are genetic mechanisms of resistance?
Chromosome-mediated - due to spontaneous mutation in the target molecule or the drug uptake system - mutants are selected, not induced
Mobile gene-mediated - common in gram -ve rods, multiple mechanism of transfer e.g. plasmids, carry genes conferring multidrug resistance
What is meant by selection of mutants?
Random mutation occurs causing resistance in that mutant
When antibiotic added to the population, the mutants are selected for and survive, creating a resistant species
Describe genetic transfer in bacteria
Mechanism for genetic heterogeneity and evolution
Rapid, cross-species
Virulence (toxins), drug resistance, antigens (immune evasion)
Give examples of fluoroquinolones
Ciprofloxacin
Moxifloxacin
Ofloxacin
What do fluoroquinolones do?
Bind to DNA gyrase (gyrA) and topoisomerase IV (parC)
Inhibits DNA replication
How does resistance to fluoroquinolones occur?
Mutations in the target gyrA and parC genes
Mutations usually in quinolone resistance-determining region (QRDR)
Give examples of aminoglycosides
Tobramycin
Gentamicin
Amikacin
What di aminoglycosides do?
Irreversibly bind to 16S rRNA in 30S subunit of ribosome
Inhibits protein synthesis
How does resistance to aminoglycosides occur?
Mutations in target rrs gene (16S rRNA)
Aminoglycoside modifying enzymes
What are the aminoglycoside modifying enzymes?
N-Acetyltransferase (AAC)
O-Adenyltransferase (ANT)
O-Phosphotransferase (APH)
What does AAC do?
Catalyses acetyl CoA-depedent acetylation of an amino group
What does ANT do?
Catalyses ATP-dependent adenylation of hydroxyl group
What does APH do?
Catalyses ATP-dependent phosphorylation of a hydroxyl group
Give examples of beta-lactams
Penicillins
Carbapenems
Cephlasporins
Give examples of penicillins
Ampicillin
Amoxicillin
Give examples of cephalosporins
Cefazolin
Ceftriaxone
Give examples of carbapenems
Meropenem
Ertapenem
Give examples of monobactams
Aztreonam
Tigemonam
What is the active structure in penicillin?
Beta-lactam ring
What do beta-lactams do?
Bind to penicillin binding proteins (PBPs)
The bound PBPs are then unable to crosslink peptidoglycan chains
Bacteria unable to synthesis cell wall and bacteria are lysed
How does resistance to beta-lactams develop?
Mainly due to beta-lactamase enzymes
What do beta-lactamases do?
Hydrolyse and break the beta-lactam ring, inactivating beta-lactam
Can be overcome by adding beta lactamase inhibitors
Give examples of beta-lactamase inhibitors
Tazobactam
Clavulanic acid
What are extended spectrum beta-lactamases (ESBLs)?
Carried on plasmids that have other resistance genes - results in multidrug resistance
Give an example of an ESBL
Carbapenemases - they inactivate carbapenems, penicillins and extended spectrum cephalosporins
What do efflux pumps do?
Transport proteins that can expel toxic substances from the cell
Where are efflux pumps found?
In gram +ve and -ve species
What are the 5 families of efflux transporters in bacteria?
Major facilitator (MF)
Multidrug and toxic efflux (MATE)
Resistance nodulation division (RND)
Small multidrug resistance (SMR)
ATP binding cassette (ABC)
What is the genetic basis of antibiotic resistance in Neisseria gonorrhoeae?
Acquired genes
Mutations
Gene mosaics with or without superimposed mutations
What mutations of Neisseria gonorrhoeae provide resistance to penicillin?
penA - PBP2
ponA - PBP1
penB - outer membrane porin
mrR regulator - controls mtrCDE efflux pump operon
penC - secretin PilQ of the type IV pilin
What acquired genes in Neisseria gonorrhoeae provide resistance to penicillin?
plasmid-mediated TEM-1 penicillinase - blaTEM-1
How are N. gonorrhoeae resistant to tetracycline?
Acquisition of plasmid-mediated tet(M) ribosomal protection protein
A combination of mtrR, penB and rpsJ gene mutations
What makes N. gonorrhoeae resistant to fluroquinolones?
Mutations in gyrA and parC in QRDR
What makes N. gonorrhoeae resistant to cephalosporin?
Multiple alterations in penA (PBP2), often + mosaic gene exchange with other Neisseria species
High level ceftriaxone resistance - point mutations superimposed upon mosaics
What makes N. gonorrhoeae resistant to azithromycin?
Mutations to multiple 23S rRNA gene copies - single mutation + internal recombination (high level resistance)
What gives N. gonorrhoeae low level resistance to azithromycin?
mtr mutations
acquired mphA
mefA-E (efflux pumps)
ermABCF (ribosomal methylases)
How can drug resistance phenotype be determined?
Culture based methods
Molecular diagnostics
Genome sequencing
