Assay systems and methods are provided for detecting a target pathogen, such as a microorganism (e.g., bacterium, bacterial toxin) which may be present in a fluid or other location. The method can include linking a magnetic microparticle to a first epitope of the target microorganism in a fluid via a first antibody; utilizing a magnetic field to separate the magnetic microparticle and linked targeted microorganism from at least a portion of other components in the fluid, thereby forming a test sample; linking a glucose molecule to a second epitope of the target microorganism via a second antibody; and detecting the glucose in the test sample to determine the presence or concentration of the target microorganism in the fluid. The glucose detection preferably is one that can be done rapidly, e.g., with a conventional glucometer, and may include measuring the electrical resistance, color, or pH of the test sample.