What concentration is used to test high-level gentamicin resistance?

What concentration is used to test high-level gentamicin resistance?

• A. 500 ug/ml
• B. 128 ug/ml
• C. 2000 ug/ml
• D. 1000 ug/ml

Answer: (A)

High-level gentamicin resistance is detected by exposing the organism to a fixed, high concentration of gentamicin to see if it can still grow. For Enterococcus and similar bacteria, 500 μg/mL is the established screening concentration. If the organism grows at this level, it’s considered high-level gentamicin resistant, meaning the drug won’t work in synergistic combinations with a cell-wall–active agent. This threshold helps clinicians decide that alternative therapies are needed. The other listed concentrations don’t align with the standard HLAR screening breakpoint: they are either below the HLAR threshold or far above the accepted screening level, so they don’t reliably indicate HLAR.

High-level gentamicin resistance is detected by exposing the organism to a fixed, high concentration of gentamicin to see if it can still grow. For Enterococcus and similar bacteria, 500 μg/mL is the established screening concentration. If the organism grows at this level, it’s considered high-level gentamicin resistant, meaning the drug won’t work in synergistic combinations with a cell-wall–active agent. This threshold helps clinicians decide that alternative therapies are needed. The other listed concentrations don’t align with the standard HLAR screening breakpoint: they are either below the HLAR threshold or far above the accepted screening level, so they don’t reliably indicate HLAR.