Colorimetric point-of-care diagnostic to monitor Enterococcus faecalis causing urinary tract infection

Abstract

Urinary tract infections (UTIs) are among the most common bacterial infections, affecting approximately 150 million people worldwide each year. Currently, diagnosis is often made using culture-based methods, which are time-consuming and therefore costly. Point-of-care (POC) devices have the potential to provide a rapid and accurate UTI diagnosis, thereby improving treatment efficacy. In this work, we developed a fast, specific, and accurate colorimetric sensor capable of indirectly detecting Enterococcus faecalis in urine samples by targeting its metabolite, L-lactate. The sensing probe consists of silica nanoparticles (SNP) loaded with MnO₂ (MnSNP), functionalised on the surface with the enzyme lactate oxidase (Lac@MnSNP). The sensor enables both qualitative analysis – through a visible colour change – and quantitative analysis, using spectroscopy. The morphology and composition of the probe were characterised at each synthesis step, confirming that the incorporation of MnO₂ into SNP and subsequent enzyme functionalisation did not alter nanoparticle morphology. Lac@MnSNP demonstrated responsiveness to L-lactate, showing a linear decrease in signal up to 50 μM of the analyte, with a limit of detection of 31 μM. The probe successfully detected E. faecalis in artificial urine medium and in complex samples at concentrations as low as 10³ CFU mL⁻¹ within 5 h. These results demonstrate the potential of this probe for fast, accurate, and lactate-specific diagnoses.