"Swab-and-Stain" Nanoparticle Assay for Detection of PBP2a-Expressing Methicillin-Resistant Staphylococcus aureus Toward Point-of-Need Environmental Surveillance.

Surveillance of methicillin-resistant Staphylococcus aureus (MRSA) in the environment is crucial for reducing its transmission, particularly in hospitals, nursing homes, and high-contact public areas. Rapid Point-of-Need (PON) tools at healthcare facilities, without involving prolonged bacterial culture in sophisticated laboratories, are needed for environmental surveillance of MRSA. We have developed a gold nanoparticle (AuNP)-based "Swab-and-Stain" assay for rapid and on-site detection of PBP2a-expressing MRSA from environmental surfaces. The assay utilizes anti-PBP2a antibody immobilized on cotton swabs to specifically capture PBP2a-expressing MRSA and anti-MRSA antibody conjugated on AuNPs to detect the captured MRSA on the swabs via sandwiched complex formation. In the presence of PBP2a-expressing MRSA, the swabs were stained in red, as seen with the naked eye. The color intensity of the stain can be quantified by smartphone image analysis for MRSA quantification. Using PBP2a-expressing MRSA samples spiked in real hospital sink and drain matrices, this pilot study demonstrated a "Swab-and-Stain" assay as a proof-of-concept method for detecting MRSA at a concentration as low as 12 CFU/mL. The assay was validated to specifically detect MRSA spiked in real hospital sink and drain matrices. This "Swab-and-Stain" assay provides a rapid, portable, and easy-to-use platform with potential application for PON environmental surveillance of MRSA.