Biosensor diagnosis of urinary tract infections: a path to better treatment?

Abstract

Urinary tract infection (UTI) is among the most common bacterial infections and poses a significant healthcare burden. The standard culture-based diagnosis of UTI has a typical delay of two to three days. In the absence of definitive microbiological diagnosis at the point of care, physicians frequently initiate empirical broad-spectrum antibiotic treatment, and this has contributed to the emergence of resistant pathogens. Biosensors are emerging as a powerful diagnostic platform for infectious diseases. Paralleling how blood glucose sensors revolutionized the management of diabetes, and how pregnancy tests are now conducted in the home, biosensors are poised to improve UTI diagnosis significantly. Biosensors are amenable to integration with microfluidic technology for point-of-care (POC) applications. This review focuses on promising biosensor technology for UTI diagnosis, including pathogen identification and antimicrobial susceptibility testing, and hurdles to be surpassed in the translation of biosensor technology from bench to bedside.

Figure 1

A biosensor is a molecular sensing device composed of a recognition element and transducer. Specific binding of the target analyte to the recognition element generates a measurable signal (e.g. light, electrical current) that is detectable via the transducer (e.g. CCD camera, photodiode, electrode). Common examples of recognition elements include enzymes, antibodies, and DNA that are able bind specifically to target analytes, including glucose, ions, protein, and nucleic acids which are indicative of the state of health or disease. The matrix is the biological medium (e.g. blood, urine, saliva) with varying biochemical parameters and nonspecific cells and molecules that may impact the performance of the biosensor.

Figure 2

Multiplex pathogen detection scheme using an array of 16 electrochemical biosensors (UTI Sensor Array). Each sensor is composed of 3 electrodes: working, reference, and counter. A. Lysis of pathogens in urine samples releases the 16S rRNA target. B. Hybridization of the 16S rRNA targets with a cocktail of detector probes labeled with fluorescein (orange sphere). C. Deposition of the 16S rRNA-detector probe hybrid onto the sensor surface (working electrode) for sandwich hybridization with the capture probes. Biotin-labeled (gray sphere) capture probes of different specificities are tethered to the surface of each sensor. D. Binding of the anti-fluorescein horseradish peroxidase (HRP) enzyme tag to the sandwich hybrid. E. Oxidation of the HRP substrate H₂O₂ and electron mediator TMB under a fixed voltage generates an electroreduction current. The magnitude of the signal output corresponds to the starting concentration for each pathogen. The limit of detection is 10⁴ cfu/ml. Modified from Reference [47], with permission from copyright holder, Elsevier.

Figure 3

Biosensor diagnosis of UTI is significantly faster than standard culture-based approach. Pathogen identification (ID) and biosensor-based antimicrobial susceptibility test (b-AST) may be completed within 1 and 3.5 hours, respectively, compared to 1–3 days for standard culture. Reprint with permission from copyright holder, Elsevier [48].