The applicability of fluorescent optotracers for in vitro and in vivo Staphylococcus aureus detection and quantification

A sensitive and specific method for assessing microbial contamination is crucial in many sectors of our society like the medical field. Optotracers that trigger fluorescence upon binding to bacterial cell surfaces offer a novel approach. Several studies have highlighted limitations in the specificity of these optotracers with respect to their molecular targets, but, to the best of our knowledge, none did in vivo studies with the same bacterial strain as the in vitro studies. In this study, we compared the activatable optotracer EbbaBiolight 680 for bacterial detection, both in vitro and in vivo with the same Staphylococcus aureus bacterial strain, while analyzing the sensitivity and specificity of the probe against this strain. In vitro the probe's fluorescence correlated strongly with the number of bacterial colony-forming units, both in planktonic suspension and biofilms. However, in vivo results from a mouse model demonstrated limited specificity for S. aureus, as the probe also binds to repetitive component motifs in the extracellular matrix of the tissue. This resulted in a substantial background signal that obscured bacterial detection. In conclusion, while EbbaBiolight 680 effectively detects S. aureus in planktonic suspension and biofilms in vitro, the probe has unfortunately limited specificity in vivo, which can hinder accurate bacterial detection.