Fluorescent analysis of Staphylococcus aureus by using daptomycin and immunoglobulin G for dual sites affinity

A dual sites affinity protocol was developed for fluorescent analysis of Staphylococcus aureus (S. aureus) by employing daptomycin and immunoglobulin G (IgG) as the recognition elements. Pig IgG immobilized on microplate was employed as the first recognition element to capture S. aureus owing to the fact that the Fc segment of mammal IgG can selectively bind with protein A on the surface of the target bacteria. Meanwhile, fluorescein isothiocyanate-conjugated daptomycin was employed as the second recognition element as well as the signal tracer for the target bacteria utilizing the binding capability of daptomycin to Gram-positive bacteria. S. aureus can be analyzed within a concentration range of 5.0 × 10³-5.0 × 10⁸ CFU mL^-1 with a detection limit of 3.6 × 10³ CFU mL^-1. The analytical process can be accomplished within 1.5 h by using a pre-coated microplate. The dual sites affinity protocol can exclude the interference led by Gram-negative bacteria and other common Gram-positive bacteria. We have successfully applied it to analyze S. aureus in spiked lake water and physiological saline injection samples, and the recovery values ranged from 88.0% to 120.0%. The results demonstrate its application potential for environmental sanitation and drug safety control.