Development of a rapid, point-of-care assay for detecting bacterial pathogens is crucial to reduce the overuse of antibiotics and the spread of multidrug resistance. Herein, we describe a rapid, colorimetric assay based on the precipitation of nanobeads in the presence of Gram-positive bacteria. Vancomycin was immobilized onto colored polystyrene nanobeads to induce specific and multivalent binding with the Gram-positive bacterial cell wall and subsequent agglomeration. Without any pre-processing steps, the addition of various types of Gram-positive pathogens to the nanobeads resulted in the formation of blue precipitates, which could be observed with the naked eye in ~30 min. We also utilize a porous filter system to the assay, which allowed more clear discrimination of the positive signals of the formed precipitates, by reducing background signals from nonspecific agglomeration. We anticipate that the colorimetric nanobead assay can be potentially applied as a rapid and simple sensing platform, and enable point-of-care diagnosis of Gram-positive infections.