Two things called an antibiogram
Most clinicians know the cumulative antibiogram: a yearly table, built from culture isolates, showing what percentage of each organism was susceptible to each drug at one institution. It is a stewardship tool. It says nothing about the patient in front of you.
A patient-specific molecular antibiogram starts from the PCR result on a single specimen. CORE-ABR takes the organisms and resistance genes detected, applies what is already known about each organism's intrinsic biology, applies the specimen site, and grades every agent on the panel for every organism found.
What goes into each grade
- The organism. Intrinsic resistance is encoded per organism — Pseudomonas aeruginosa never gets a grade for ceftriaxone, Enterococcus never gets one for a cephalosporin.
- The genes it can actually carry. A detected gene moves only the organisms known to carry it, and only the agents its mechanism defeats. tetB / tetM removes doxycycline and minocycline but spares omadacycline and tigecycline.
- The site. Urinary-only agents are graded for urine and removed for a wound.
- Whether the drug is indicated there. Agents not appropriate for the site are removed rather than listed.
- How much organism is present. Load band and cycles above the limit of detection travel with the grid — see PCR quantification.
The grading scale
| Grade | Meaning |
|---|---|
| ++ | Active, preferred |
| + | Active |
| ± | Variable |
| 0 | Inactive — intrinsic resistance or a detected mechanism |
| — | Not applicable at this site |
Every grade can be explained: the report can show which rule, gene or site restriction produced it. That is what lets a prescriber — or a pharmacist, or an auditor — trust it.
Molecular genotype does not replace phenotypic susceptibility testing. Detection of a resistance gene predicts resistance; absence of a detected gene does not establish susceptibility.
Organisms graded on the antibiogram
Resistance genes
Decision support only. The treating clinician decides. Molecular genotype does not replace phenotypic susceptibility testing, culture, or public-health reporting. Absence of a detected resistance gene does not establish susceptibility. Organism targets vary by panel; CORE-ABR is configured to the assay each laboratory runs.