AOAC SPADA Meeting

3/11/2020

Antimicrobial Susceptibility Testing • Antimicrobial susceptibility testing by broth microdilution on 96 ‐ well plates – Uses standard methods of the Clinical and Laboratory Standards Institute (CLSI) • Susceptibility testing involves detecting minimum inhibitory concentrations (MIC) – High numbers indicate resistance (µg/L)

Growth No growth

Concentration (µg/mL)

16 32 2 4 8

MIC

5

5

Antimicrobial Resistance Mechanisms

• Resistance can occur by a number of mechanisms – Mutation of target (mutation of DNA gyrase for quinolones) – Efflux of the antibiotic (TetA ‐ D tetracycline efflux pumps) – Cleavage of the antibiotic ( β‐ lactamases) – Modification of antibiotic or its target (aminoglycoside phosphotransferase)

Wild ‐ type

Mutated

Gene acquired

efflux

modification

E. coli

E. coli

6

6

3