principles of antibiotic resistance Flashcards
What are the possible causes of antibiotic therapy failure?
Unjustified therapy
Poor selection
Wrong dose
Supressed host response
Resistance
What does C&AST stand for?
Culture and Antibiotic sensitivity testing
What methods are there 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
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 innate resistance
Gram -ve bacteria are generally resistant to Vancomycin which can not penetrate the outer membrane of the bacteria.
Mycoplasmas lack cell wall so cell wall targeting antibiotic will not work on them..
How can resistance be acquired?
Gene mutations
Gene Acquisition
Co-resistance
e.g., reduced permeability of membrane, modification/new/breakdown of enzymes, altered target sites
Describe resistance of beta-lactams
Bacteria developed an enzyme that could breakdown penicillin but not methicillin
Bacteria then developed a new protein (MecA) which has the same function as peptide binding protein but has a low affinity for methicillin
What are the major mechanisms of resistance to aminoglycosides?
enzymatic modification of the drug and target site
Ribosomal mutations
What are the major mechanisms of resistance of quinolones?
target mutations
What are the major mechanisms of resistance of tetracyclines?
efflux
What are the major mechanisms of resistance of pleuromutilins?
Mutations prevent binding to target
What factors increase the risk of selection?
underdosing
length of selection level
presence of resistant bacteria to select
What does MDR mean?
Multidrug resistance
What does XDR mean?
extensive drug resistancer - less available antibiotics that can be used, often need to use CIAs
