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Module Key Points

  • Antimicrobial resistance is the ability of a microorganism to survive and multiply in the presence of an antimicrobial agent that would normally inhibit or kill this species of microorganism.
  • It is not a new phenomenon, but in the recent years the global increase in incidence and prevalence of antimicrobial resistance has raised concerns.  More bacterial pathogens have also developed multiple drug resistance, severely limiting therapeutic options for infections in both animals and people.
  • Bacteria are able to resist the effects of antimicrobials through preventing intracellular access, immediately removing antimicrobial substances through efflux pumps; modifying the antimicrobial agent through enzymatic breakdown or modifying the antimicrobial targets within the bacterial cell to render the substance ineffective.  Successful development of resistance often results from a combination of two or more of these strategies
  • Antimicrobial resistance traits are genetically coded, and can either be intrinsic or acquired. 
  • Intrinsic resistance is due to innately coded genes which create natural “insensitivity” to a particular antibiotic. Innate resistance is normally expressed by virtually all strains of that particular bacterial species. 
  • Acquired resistance is gained by previously susceptible bacteria either through mutation or horizontally obtained from other bacteria possessing such resistance via transfrormation, transduction or conjugation. Acquired resistance is limited to subpopulations of a particular bacterial species and may result from selective pressure exerted by antibiotic usage.
  • Antimicrobial susceptibility testing (AST) methods are in vitro procedures used to detect antimicrobial resistance in individual bacterial isolates.  Because these laboratory detection methods can determine resistance or susceptibility of an isolate against an array of possible therapeutic candidates, AST results can be a useful guideline in selecting the best antibiotic treatment option for each particular patient. 
  • Examples of AST methods are: broth (and agar) dilution methods, disk-diffusion test, E-test, automated detection using various commercially available detection kits, mechanism-specific methods such as those which detect specific enzymes that bring about resistance, and by applying genotypic methods which detect antibiotic resistance genes.




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