● Antimicrobial = drugs w activity against microorganisms
● Antibiotic = chemical compound made by microorg that inhibits/kills other microorgs at
low conc. Doesn’t include synthetic agents
Selection Pressure
● Mutation is rare but rapid growth rate of bacteria means it doesn’t take long for
resistance to occur
● Resistance genes develop → transferred directly to all bacteria’s progeny
during DNA replication (vertical gene transfer) OR transferred via pilius
(horizontal gene transfer)
Resistance Mechanisms
● Prevent key from getting to lock - biofilm formation / pump antimicrobial out via efflux
pumps
● Destroy key - antimicrobial inactivation (modification/degradation)
● Change lock - bacterial target site modification
Antimicrobial Susceptibility Testing (AST)
● To confirm dx & justify prescription
● Available if pt not responding to empirical choice
●
● Minimum Inhibitory Conc (MIC): lowest conc of abx req to stop organism growth
● Clinical Breakpoint: chosen conc of abx which defines whether bacterial species are
susceptible/resistant. If MIC </= CB bacteria is susceptible. If MIC > CB bacteria is resistant
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