antibiograms

An antibiogram is a laboratory-generated summary of the antimicrobial susceptibility of bacterial isolates collected within a defined setting over a specified period, typically one year. It is used to guide empiric antibiotic therapy, monitor resistance trends, and support antimicrobial stewardship. The most common form is the institutional cumulative antibiogram, though ward- or unit-specific antibiograms may also be produced to reflect local practice.

Construction and content: Data come from routine susceptibility testing performed by clinical microbiology laboratories. For each species and antibiotic, the percent of isolates susceptible is calculated. Duplicates are typically removed (for example, excluding repeat isolates from the same patient within a single infection episode). Results are aligned to standardized breakpoints according to guidelines such as CLSI or EUCAST. The output lists organism–drug combinations with susceptibility percentages, usually stratified by specimen type and sometimes by infection site.

Uses and applications: Clinicians use antibiograms to select empiric therapy while awaiting susceptibility results, especially in severe infections. Hospitals and stewardship programs rely on them to update local guidelines and formularies, track resistance trends, and identify emerging resistance patterns or outbreaks. They also inform public health surveillance and regional comparisons.

Limitations: Antibiograms summarize aggregate data and may not reflect local variation across wards or specific patient populations. They depend on testing practices, specimen types, and breakpoint changes over time. They do not predict individual outcomes and may be biased by which isolates are collected or tested. Not all organisms or antibiotics are represented, especially when isolate numbers are low.