Antibiotic resistance Flashcards
What are common causes of antibiotic therapy failure?
Unjustified therapy
Poor antibiotic selection.
Incorrect dose or regimen.
Suppressed host response.
Resistance.
What does C&AST stand for?
Culture and Antibiotic sensitivity testing
What are the methods for assessing resistance?
Liquid culture MIC determination
Disk diffusion (Kirby-Bauer) where diameter of zone inhibition for a genus is matched to a break point for MIC.
Detection of know resistance genes or mutations
What is the role of clinical breakpoints in determining antibiotic resistance?
Clinical breakpoints define whether bacteria are sensitive or resistant to antibiotics based on:
MIC (Minimum Inhibitory Concentration):
Sensitive: MIC < breakpoint.
Resistant: MIC > breakpoint.
Zone diameter in disc diffusion tests:
Sensitive: Diameter > breakpoint.
Resistant: Diameter < breakpoint.
Describe intrinsic resistance
An innate ability to resist activity of a particular antimicrobial agent through inherent structural or functional characteristics which allow tolerance of the drug
Describe acquired resistance
When a microorganism obtains the ability to resist the activity of a drug. Can be mutation or new gene acquisition.
Give examples of intrinsic bacteria
Poor permeability: Gram- -ve bacteria resist vancomycin
Lack of target: Mycoplasmas lack cell wall, making them resistant to beta-lactams
Different target: Enterococci resist cephalosporins due to low PBP affinity.
What are the mechanisms of acquired resistance?
Gene mutation: Alters antibiotic binding sites
Gene acquisition: Horizontal transfer via plasmids or other methods
Efflux pumps: Actively remove antibiotics from bacterial cells (e.g., tetracyclines)
Enzymatic degradation: Break down antibiotics (e.g., beta-lactamases)
Modification of targets: Changes to binding sites (e.g., methylation in ribosomal RNA).
What are common resistance mechanisms by antibiotic group?
Beta-lactams: Cleavage by beta-lactamases, altered PBPs.
Aminoglycosides: Enzymatic modification, efflux pumps.
Quinolones: Efflux, target mutations.
Tetracyclines: Efflux.
Rifamycins: Altered RNA polymerase.
What are factors that increase risk of selection?
Underdosing: Suboptimal concentrations fail to kill bacteria completely.
Length of selective exposure: Prolonged exposure increases resistance development.
Presence of resistant bacteria: Allows selection of resistant strains.
What is the difference between MDR, XDR, and PDR?
MDR (Multi-Drug Resistant): Resistant to ≥1 agent in ≥3 antimicrobial categories.
XDR (Extensively Drug Resistant): Resistant to ≥1 agent in all but ≥2 categories.
PDR (Pan-Drug Resistant): Resistant to all antimicrobial agents tested.
What are the key principles of good antibiotic stewardship?
Limit antibiotic use to necessary cases.
Use cytology and sensitivity testing where possible.
Prefer first-line agents over second-line or broad-spectrum antibiotics.
Administer concentration-dependent antibiotics at the highest effective dose.
Avoid underdosing or irregular administration.
Implement a practice-wide PROTECT plan.
What does the sensitivity grading “sssrR” indicate in an antimicrobial report?
It indicates very resistant sensitivity.
What is the significance of the disk content in antibiotic susceptibility testing?
It determines the breakpoints; changes in disk content can affect interpretive criteria.
What is the benefit of using Convenia (Cefovecin) in veterinary practice?
It is a long-acting injectable antibiotic, useful for hard-to-dose patients and treating skin and soft tissue infections.
