A novel colorimetric strategy based on canine IgM for ultrasensitive and selective detection of Staphylococcus aureus

Conventional methods for Staphylococcus aureus (S. aureus) detection using mammalian immunoglobulins could yield false positive results, owing to the presence of the protein G-producing Streptococcus. In this study, because canine IgM can bind to protein A but not to protein G, we firstly designed a colorimetric platform based on canine IgM to identify S. aureus. Magnetic beads (MBs) functionalized with canine IgM acted as captors to enrich S. aureus, relying on the binding interaction between the Fc region of canine IgM and protein A in the bacterial cell wall, while horseradish peroxidase (HRP)-labeled rabbit anti-S. aureus IgG served as a tracer in the sandwich-type immunoassay, catalyzing the colorimetric reaction. Under optimal conditions, the proposed strategy achieved a satisfactory analytical performance with a broad linear range from 1.6 × 103 CFU/mL to 1.0 × 105 CFU/mL, a colorimetric minimum resolution of as low as 1.4 × 102 CFU/mL in 100 μL phosphate-buffered saline (PBS), and good selectivity in differentiating target from protein G-producing Streptococcus. Moreover, the proposed approach successfully identified S. aureus in various application scenarios (except for samples containing IgG), can be completed in less than 90 min, and was not dependent on any specialized equipment.