Which statement describes a key limitation of rapid molecular diagnostics in guiding therapy?

Which statement describes a key limitation of rapid molecular diagnostics in guiding therapy?

• A. They may miss resistance mechanisms not encoded by known genes.
• B. They always include antibiotic susceptibility testing.
• C. They do not detect resistance genes.
• D. They can fully replace phenotypic testing.

Answer: (C)

Rapid molecular diagnostics work by quickly detecting known genetic determinants of resistance. Their strength is speed, but their limitation is scope: they only pick up what the test panel is designed to detect. If resistance arises from mechanisms not encoded by those known genes, or from chromosomal mutations or regulatory changes not targeted by the assay, the test can miss it. So a pathogen might appear susceptible based on gene targets, but still exhibit resistance in real-world therapy because there are untested mechanisms at play. That’s why molecular tests are powerful for rapid guidance, yet they do not fully replace phenotypic testing, which measures actual growth in the presence of antibiotics and can reveal resistance established through uncharacterized or non-genetic means. It’s also worth noting that many panels do detect resistance genes; saying they do not detect resistance genes is not accurate, and other statements about universal antibiotic susceptibility testing or complete replacement of phenotypic testing don’t hold in practice.

Rapid molecular diagnostics work by quickly detecting known genetic determinants of resistance. Their strength is speed, but their limitation is scope: they only pick up what the test panel is designed to detect. If resistance arises from mechanisms not encoded by those known genes, or from chromosomal mutations or regulatory changes not targeted by the assay, the test can miss it. So a pathogen might appear susceptible based on gene targets, but still exhibit resistance in real-world therapy because there are untested mechanisms at play. That’s why molecular tests are powerful for rapid guidance, yet they do not fully replace phenotypic testing, which measures actual growth in the presence of antibiotics and can reveal resistance established through uncharacterized or non-genetic means. It’s also worth noting that many panels do detect resistance genes; saying they do not detect resistance genes is not accurate, and other statements about universal antibiotic susceptibility testing or complete replacement of phenotypic testing don’t hold in practice.