Patent ID: 8481281

Claim:
A method for determining the resistance of a microorganism to a drug by detecting growth of the microorganism in the presence of the drug, comprising: (a) incubating the microorganism in i) an isotopically-labeled growth medium comprising at least one drug and an isotopic label, wherein the microorganism incorporates the isotopic label into one or more biomarker molecules of the microorganism during growth in the medium; and ii) a control growth medium that lacks the drug and the isotopic label, wherein the one or more biomarker molecules of the microorganism remain unlabeled during growth in the medium; (b) applying a sample comprising the biomarker molecules of(a)(i) and applying a sample comprising the biomarker molecules of (a)(ii) to a mass spectrometry system and producing ion mass fragments of the biomarker molecules of (a)(i) and (a)(ii); (c) analyzing the ion mass fragments of tile biomarker molecules of (a)(ii) and using such analysis to determine a predicted mass for the one or more biomarker molecules of a(i) using an algorithm that determines a predicted mass based on the incorporation of the isotopic label into the one or more biomarker molecules of (a)(ii); (d) comparing the predicted mass of (c) with an observed mass of the one or more biomarker molecules of the microorganism growing in the isotopically-labeled medium with drug of (a)(i) using an algorithm based on which a probability that the biomarker molecules in the two media match can be determined, thereby indicating if growth of the microrganism has occurred in the isotopically-labeled medium with drug if the biomarkers have a high probability of matching; and (e) determining the microorganism to be resistant to the drug if the biomarkers have a high probability of matching.