A living bacterium under the lens
We start with cells — evolved P. aeruginosa, some resistant to tobramycin, some not. To the eye they look identical. The question: can light alone tell them apart?
A 785 nm laser strikes the cell
A near-infrared beam hits the bacterium. Almost all light bounces back unchanged — but a tiny fraction scatters with a shifted colour, carrying the cell's molecular fingerprint.
Scattered light is fanned into a spectrum
A grating spreads that faint scattered light by wavenumber. The smear of colour resolves into peaks — vibrations of DNA, protein, and lipid inside the cell.
6,900 spectra, averaged
This is the genuine mean Raman trace from our dataset — 6,900 spectra across 33 strains. Not a drawing: every wiggle from 604–1700 cm⁻¹ is measured.
The common method posts a big number
A standard classifier finds a strong resistant−susceptible difference in the spectrum and calls RESISTANT at AUC 0.89. On its own test set it looks brilliant — the kind of number that ends most papers.
Move to new data, and it falls apart
Score that same model on a different dataset — new strains, new conditions it never trained on — and the skill drops toward a coin‑flip. The high number was real, but it measured the wrong thing: a shortcut that lived only in the original data.
Ours stays consistent
Our model holds its skill from one dataset to the next — because it's anchored to the biology of resistance, not to artifacts of a single batch. Same signal, same answer, wherever it's measured.