Sensitivity Testing

The test compares microbial growth after exposure to a defined antibiotic with the expected growth response under the testing conditions. Reduced or absent growth indicates inhibition, while continued growth indicates that the organism is less affected. This response is then interpreted as susceptible, intermediate, or resistant, providing a basis for selecting treatment.

Disk diffusion and dilution testing assess antimicrobial effects through different testing formats. Disk diffusion places antibiotic-containing disks in relation to a cultured pathogen and evaluates growth inhibition, whereas dilution testing exposes the organism to defined antibiotic dilutions. Both approaches support susceptibility interpretation, but they organize the exposure and response assessment differently.

Diagnostic sensitivity concerns how effectively a test detects true cases, so it addresses the test’s ability to identify affected individuals or conditions. Antimicrobial susceptibility instead concerns how a cultured microorganism responds to an antibiotic. Keeping these concepts separate prevents confusion between evaluating a diagnostic test and selecting treatment for an identified pathogen.

A typical workflow begins with a cultured pathogen and a defined antibiotic exposure. The laboratory then assesses whether microbial growth is inhibited using disk diffusion or dilution testing. Finally, the observed response is assigned a susceptibility category such as susceptible, intermediate, or resistant. This sequence converts a laboratory response into information relevant to clinical treatment decisions.

It is particularly useful when clinicians need information for targeted antimicrobial treatment rather than relying on an unnecessary or poorly matched drug. The resulting susceptibility category can guide treatment decisions, while broader use supports infection control by clarifying patterns of microbial response. It also helps reduce avoidable antibiotic use when a more appropriate choice is identified.

Antimicrobial results can inform treatment selection for infections caused by cultured pathogens, while diagnostic sensitivity results help assess how reliably a test detects true cases. Together, these measurements contribute to clinical decision-making and infection control. In research, they provide a structured way to evaluate biological responses to defined treatments, stimuli, or testing conditions.