Antimicrobial Resistance Flashcards
What is the link between antibiotic development and resistance development?
Most antibiotics exist for 5-15 years after development and clinical use before resistance occurs
The use of the antibiotic promote resistant to developme
What is meant by intrinsic resistance in terms of AMR?
When a species of microrganism is naturally resistant (or not susceptible) to an antibiotic or antibiotic class, without the need to acquire new genes or mutations.
What antibiotics are bacteroides intrinsically resistant to?
Aminoglycosides
Many Beta lactams
Quinolones
bacteriodes = gram negative anaerobes
What antibiotics are all gram negative and/all all gram positive organisms resistant to?
Gram negative - glycopeptides and lipopetides
Gram positive - aztreonam
Give some examples of specific gram positive microbes and what antibiotics they are intrinsically resistant to
Enterococci - aminoglycosides, cephlasporins, lincosamides
Listera monocytogenes - cephlasporins
Give some examples of specific gram negative microbes and what antibiotics that are intrinsically resistant to.
E.coli - macrolides
Klebsiella spp - ampicillin
Serratia marcescens - macrolides
Pseudomonas aeruginose - sulfonamides, amipicllin, 1st and 2nd gen cephlasporins, chloramphenicol, tetracylcine
Stentophomonas maltophilia - amingoglycosides, beta lactams, carbapenems, quinolones
Acinetobacter spp - ampicillin, glycopeptides
What is meant by acquired antibiotic resistance?
An evolutionary process by which bacteria acquire resistance to an antibiotic , by adopting properties or features or functions that they did not originally have.
What are the different methods by which cells can acquired antibiotic resistance?
Transfer of resistant genes
Mutation
Selection due to antibiotic pressure
Growth conditions - biofilms
What is meant by phenotypic resistance in terms of antibiotic resistance?
Resistance is achieved without genetic alteration.
Normally occurs due to environmental changes in specific growing conditions causing physiological changes.
This resistance tends to be transient (hence reversible) but is difficult to identify on susceptibility tests (when the environmental conditions are often different).
What are the three different methods of phenotypic resistance?
Persistence
Biofilm growth
Swarming
What is persistence as a method of phenotypic resistance?
When an a bacterial subpopulation is not killed by an antibiotic at normally lethal concentrations but the majority of the population are killed, tends to do this by transiently stopping growth.
When the antibiotic is removed this subpopulation repopulates the colony
Note population continues to behave as a susceptible organism, and will reproduce in susceptible and persistent organisms.
What is the key difference between bacterial persistence and resistance?
Persistence - growth stops to avoid death
Resistance - growth continues
Both appear in presence of antibiotics.
What is meant by biofilm growth as a method of phenotypic resistance?
Biofilm - bacteria surface-associated growth and become embedded in a matrix containing polysaccharides.
Bacteria in biofilm are less susceptible to antibiotics - ECM can alter antibiotic function by affecting diffusion and access to microbes
Regions of the biofilm will have different levels of oxygen and nutrients altering their metabolism - so some subpopulation less susceptible
What is swarming as a method on phenotypic antimicrobial resistance?
Swarming is the pattern of movement of bacterial cell population, many bacteria gather and growth together on top of a surface.
Can rapidly migrate together across a moist surface
Tend to be hyperflagellated cells in nutrient rich environments.
Resistance is transient and may be due to altered cell surface and permeability to drug.
What is meant by an intrinsic resistome in terms of antibiotic resistance?
A set of elements of characteristics that contributes directly or indirectly to how bacteria develop resistant to antibiotics and does not involve previous antibiotic exposure or gene transfer.
How can genetic influence the intrinsic resitome?
The metabolic genes that a cell posses alters the different phenotypes it can possess
This is further modified by regulators that alter which genes are expressed
Does not always require to acquisition of new genes (hence intrinsic)
What are the classical determinants of resistance on bacteria?
Antibiotic inactivation
Target modification
Changes in bacterial permeability (drug uptake)
Efflux pump
This can occur due to intrinsic or acquired resistance.
What are the methods of spreading acquired resistance to antibiotics?
Horizontal genes transfer
Mutation.
What is meant by the halo effect of bacteria in terms of antibiotic resistance?
When the presence of one antibiotic-resistant microbe in a population also provides benefit to other non resistant microbes in that colony indirectly be reducing antibiotic concentration.
May also cause people to negative under treat or perceive non resistant strains as a threat. Leading to ineffective care.
What environments contribute to an antibiotic resistant gene pool?
Antibiotics or antibiotic residues and bacteria are found in high concentrations in clinical settings, wastewater and soil (from use on plants).
This creates a highly concentrated environment where antibiotic use is a selective pressure, microbes in these environments rapidly develop resistance
Creates an antibiotic resistance gene pool, where genes are exchanged and spread quickly between different microbes.
What are the methods of horizontal gene transfer to acquire antibiotic resistance?
Conjugation - cell to cell contact mediated by pillia allows gene exhcnage between bacteria, often mediated by plasmid
Tranformation - bacteria takes up pieces of DNA floating in its environment often from other bacteria that has died and released content
Transduction - bacteriophages move resistance between the bacteria they infect.
How do selection pressures affect the development of antibiotic resistance?
Selecitive pressure - can cause epigentic changes in an organism, evolutionary change where adaptive changes persist in the population
Antibiotic use acts as a selective pressure, bacteria that epigenetic changes enable resistance survive whilst other rest die
Post antimicrobial growth is dominated by resistant bacteria.
What are some of the mechanisms of resistance to beta lactams?
- Limited uptake due to decreased number of porins or has no outer cell wall
- Gram pos alter PBPs so low affinity
- Gram pos and neg have beta lactamses that can inactivate drug
- Presence of END efflux pumps
What are some mechanisms of resistance against carbapenems?
Changed selectivity of porins alter drug uptake.
What are some mechanism of resistance against cephalosporins?
Changed selectivity of porins alter drug uptake
What are some mechanisms of resistance against glycopeptides?
- Thickened cell wall or no outer cell wall - alters drug uptake
- Modified target peptidoglycan
What are some mechanisms of resistance against lipopetides?
Modified net cell surface charge -alters drug target.
What are some mechanisms of resistance against aminoglycosides?
- Change cell wall polarity to alter uptake
- Ribosomal mutation or methylation to alter drug target
- Aminoglycoside modifying enzymes inactive drug by acetylation, phosphorylation or adenylation
- RND efflux pumps
What are some mechanisms of resistance against tetracyclines?
- Decreased number of porins alters drug uptake
- Ribosomal protection altedrs drug target
- Oxidate and inactive antibiotic
- MFS and RND efflux pumps
What are some mechanisms of resistance against chloramphenicol?
- Ribsomal methylation alters drug target
- Acetylation of drug inactive it
- MFS and RND effluc pump
What are some mechanisms of resistance against lincoamides?
Gram positive bacteria can methylate ribosomes altering the drug target
ABC and RND efflux pumps
What are some mechanism of resistance against macrolides?
- Ribosomal mutation or methylation alters drug target.
- ABC, MFS and RND effluc pumps
What are some mechanisms of resistance against oxazolidinones?
- Ribosomal methylation - alters drug target
- RND efflux pumps.
What is the detailed mechanism of resistance to beta lactams?
Beta lactamases mediate resistance against beta lactams
Beta lactamases contain a ser-OH group and Lys as found in the transpeptidase target site (targeted by beta lactam)
Ser-OH forms a bond with the beta lactam, the associated electron donation to the beta lactam from the serine open the beta lactam ring by destorying the amide bond, this forms an acyl-enzyme intermediate.
This is eventually release as an inactive molecule, now unable to interact with target site.
What are Ambler class A of beta lactamases?
What are they useful for?
- Narrow spectrum - such as TEM-1, SHV-1 - target pencillines and narrow spec cephlasporins
- Extended spectrum - SHV-2, PER-1- target narrow and exepnted spectrum beta lactams
- Serine carbapenemase - KPC-1, IMI-1, SME-1 - target carbapenems
What are Ambler class B beta lactamases?
Metallo-beta-lactamases
For example VIM-1, IMP-1 and NDM-1
Target most beta lactams including carbepenems
What are Ambler class C beta lactamases?
Cephalosporinases
Such as AmpC, ACT-1 and FOX-1
Target cephalosporins
What are Ambler class D beta lactamses?
OXA-type enzymes
Target penicillins, oxacillines and carbapenems.
What is the mechanism by which bacteria enzymatically modify aminoglycosides?
By enzymatic modification
Phosphotransferase activity - mainly targets amikacin, gentamicin and kanamycin
Acetyltransferase activity - mainly targets amikacin, netilimicin, sisomicin, tobramycin
Adenyltransgerase activity - mainly targets gentamicin, kanamycin, sisomicin, tobramycin.
What is function of ABC efflux pump?
In inner cell membrane
Drug out into intermembrane space
Requires ATP hydrolysis
What is the function of the MFS efflux pump?
Located in the inner cell membrane
Drug out into intermembrane space in return for H+
What is the function of the SMR efflux pump?
Located in the inner cell membrane
Drug out into intermembrane space in return for H+
What is the function of the RND efflux pump?
Across the inner and outer cell membrane
Removes drug from intermembrane space and cytoplasm into external environment
In exchange for H+ into the cytoplasm from the intermembrane space.
What is the function of the MATE efflux pump?
Located in inner membrane
Removes drug into intermembrane space in return for Na+
What is a negative consequence for the bacteria of having an efflux pump?
Expression can require a lot of energy and by taxing on resources
Can reduce bacterial growth/replication as less available energy.
How does mechanism of resistance against aminoglycosides vary between gram negative and gram positive bacteria?
Gram positive - have MATE efflux pumps
Gram negative - have RND efflux pumps
Enzymatic modification such as phosphotransferase activity can occur in gram negative and gram positive bacteria.
Give a specific example of how the presence of antibiotics acts to transient cause bacteria to become antibiotic resistance.
**
In absence of antibiotic: ErmC (erythromycin ribosomal methylation) leader peptide is produced, and forms two hairpins in mRNA transcript for ermC preventing the ribosome from recognising the ribosomal binding site for ermC - so not translated as initial codon is hidden.
After exposure to erythromycin, the antibiotic interacts with the ribosome and binds tightly to the leader peptide stalling the progression of the translation, this releases ermcC RBS by stopping double hairpin formation and permits translation of the functional section of the mRNA as initiation codon exposed
Note ErmC leader peptide and ermC are located on the same mRNA molecule.
What gram positive cocci are multi-drug resistant?
Staph aureus (MRSA)
Pneumococci
Enterococci
What gram positive rods show multi drug resistance?
Clostridium difficile
Corynebactera
What gram negative coccis show multi drug resistance?
Gonococci
What gram negative rods show multi drug resistance?
E.coli
Klebsiella
Enterobacter
Pseudomonas
Acinetobcater
Strentrophomonas
Helicobacter
Many more…
What are some of the mechanisms that gram negative robs show multi drug resistance?
Enterobacteriaceae produce ESBL (extend spectrum beta lactamase) provides resistance against penicillins and cephalosporins
Carbapenem resistant Enterobacteriaceae tend to be resistant against penicillines, cephlasporings and carbapenems.
What are the different classification of MDR species by WHO?
Priority 1 - critical
Priority 2 - high
Priority 3 - medium
Based on level of threat to human health
What species are considered a critical or priority 1 threat by the WHO for MDR?
Gram -ve
Acinteobacter baumanni - carbapenem resistant
Pseudomonas aeruginose - carbapenem resistant
Enterobacteriacea - carbapenem resistant, 3rd gen cephalosprin resistant
What species are considered a high or priority 2 threat by the WHO for MDR?
Gram +ve
Enterococcus faecion - vancomycin R
Staphy. aureus - methicilllin and vancomycin R
Gram -ve
H.pylori - clarithromycin
Camplyobacter - fluoroquinolone
Salmonella spp - fluoroquinolone
Neisseria gonorrhoeae - 3rd gen cephalosporin and fluoroquinolone
What species are classified as a medium threat or priority 3 threat for MDR by the WHO?
Gram +ve
Streptococcus pneumoia - penicillin
Haemophilius influenza - amipicillin
Shigella spp - fluoroquinolone.
How can acinetobacter baumannii be diagnosed in a lab?
Gram negative rob (may be cocci if old culture)
Grow on range of agars.
May identify by API (aerobic, catalise positive, indole neg, oxidase neg, mostly encapsulated)
Why is acinetobacter baumannii a problem?
Low virulence - mainly affects immunocompromised, neutropenic or ventilated patients.
High morbidity and mortality in sick patients with multi-organ disease
Increasing numbers of resistance - with mortality of patient up to 70%.
What is the pattern of resistance agsint carbepenems and acinteobacter baumannii?
May be used as treatment as effective against many bacterial species and less vulnerance to most beta lactam determinants, often used as reliable last resort.
However resistance is growing
EUCAST breakpoints for impenem and meropenem MIC against acinetbacter ar more than 16mg/L
Why is methicillin resistant staphylococcus aureus (MRSA) a problem?
Leading cause of hospital and community acquired infection
Signficant morbidity and mortality.
Often requires long hospital stay and high cost burden.
Infects wide variety of tissues and sites including skin and lungs.
What mechanism of resistance does MRSA use?
Resistant to all beta lactams
Express mecA gene - produced PBP2a with a low affinity for beta lactams
Alters drug affinity for target
What is the mechanism of lab diagnosis for MRSA?
gram positive coccus - often in clusters
MRSA oxacillin MIC of greater than or equal to 4 mg/mL
Use oxacillin as resistance aginst is rare and better induced mec A gene - sensitive and specific test results.
What are the different methods of monitoring for antimicrobial resistance?
Culture methods - Diffusion disk array, AMT ring or E-test
DNA based methods - scush as PCR or NGS (note gene may be present but not necessarily expressed)
What are the different methods of testing for antimicrobial susceptibility?
Phenotypic methods - dilution, diffusion, gradient test, chromogenic media
Molecular based methods - PCR, qPCT, cycle sequencing ot NGS
Mass spectrometry - compare bacterial growth and bacterial fingerprints.
What factors has led to a rise in antibiotic resistance?
Increase use of antibiotics
Prescriptions taken incorrectly
Sold iwhtout medical supervision
Prophylatic use before surgery
Antibiotic use for viral infection
Spread of resistant microbes in hospitals due to lack of hygiene
Patients who do not complete antibiotic course
Antibiotics in animal feeds.
What is the key ideas of infection prevention and control for antimicrobial resistance?
Minimise the transmission of organisms with successful antimicrobial resistance.
Avoid infection and exposure to resistant organmis (hard to do for most vulnerable population who tend to be found in hospitals)
How does antimicrobial usage relate to antimicrobial resistance?
Antimicrobial exposure exerts a selective pressure to enable organisms with inherent or acquired resistance to proliferate.
Any reduction in antimicrobial usage will reduce the risk of resistance.
This may include reducing broad spectrum antibiotics, reduce treatment duration (still effective coarse) and reduce antibiotic when no infection is present.
What is meant by antibiotic stewardship?
A set of coordinated stratergies to improve the use of antimicrobial medications with the goal of enhancing patient health outcomes, reduce antimicrobial resistant and decrease unnecessary costs.
What is the origin on antimicrobial stewardship?
Resposne to C.diff infections - 10 to 15 years previously
Linked to excessive and inappropriate antimicrobial usage.
Caused a rise in local and secondary care responses to ensure hollistis approach to prevent antimicrobial resistance.
What are the two different methods of behavioural change meant to tackle antibiotic resistance?
Enabling behaviours - provide more feedback on antibiotic effectiveness, better and faster diagnosistic methods
These methods tend to be more acceptable professional and inc sustainability of the intervention
Restrictive behaviours - reduce antibiotic use. This has been shown to reduce C.diff rate in short term, however may delay 1st dose antibiotics (fatal in meningitis), also creates a negative professional culture with little trust or communication.
Minimal evidence shows either method is effective.
How is the ermC gene regulated in the absence of antibiotics?
Asbence of macrolide
Ribosome binds to RBS1 site on mRNA and translation occurs producing leader peptide
This secondary structure causes the ermC mRNA to form two hairpin loops concealining the ribosomal binding site for erm.
Ribosome does not bind to, so ermC is not translated, instead terminates after leader peptide.
No ermC no methyltransferase activity hence no resistance against antibiotics.
How does ermC provide resistance against erythromycin ?
Has methyl transferase activity
Alters drug binding site (methylates ribosome)
