Imaging of Staphylococcus aureus Infections and Biofilms Using a Selective Covalent Probe for the Unique Serine Hydrolase FphE.

Staphylococcus aureus is the leading cause of soft tissue infections which can often be treated with antibiotics. However, it can also cause significant mortality and morbidity from systemic infections and infections of surgical implants. Implant infections typically require invasive surgery, and treatment often necessitates removal of the implant because S. aureus biofilms are extremely difficult to eradicate with antibiotic treatment alone. Therefore, there is a significant need for improved diagnostic tools for rapid, noninvasive confirmation of S. aureus infections. We recently developed an activity-based probe containing an oxadiazolone electrophile that selectively and covalently labels the S. aureus-specific serine hydrolase, FphE. Here we describe a Cy5-labeled version of the probe, JJ-OX-012, and its characterization as an imaging agent for detecting biofilms both in vitro and in vivo. The probe labeled S. aureus biofilms in vitro, with virtually no background labeling of bacteria that lack FphE expression, such as Escherichia coli. Furthermore, using a mouse surgical implant infection model, we demonstrate that JJ-OX-012 can be used for noninvasive fluorescent imaging to detect S. aureus biofilms in vivo. Overall, these findings support the potential for using covalent probes targeting FphE as imaging agents for rapid detection and diagnosis of staphylococcal infections in vivo.