Assembly and performance of a cholera RDT prototype that detects both Vibrio cholerae and associated bacteriophage as a proxy for pathogen detection

Cholera rapid diagnostic tests (RDTs) are vulnerable to virulent bacteriophage predation. We hypothesized that an enhanced cholera RDT that detects the common virulent bacteriophage ICP1 might serve as a proxy for pathogen detection. We previously developed a monoclonal antibody (mAb) to the ICP1 major capsid protein. Our objective was to design and assemble a first-of-its-kind RDT that detects both a bacterial pathogen (Vibrio cholerae) and associated virulent bacteriophage (ICP1). Candidate mAbs were expanded to increase design options and evaluated by immunological assays (ELISA; western blot). A subset of mAbs were selected for gold conjugation and printing on the RDT. The detection limit of the prototype RDTs was determined in diarrheal stools with the addition of ICP1. Three mAb candidates were developed and evaluated for the capsid decoration protein (ORF123) and tail fiber protein (ORF93), and the prior mAb for the major capsid protein (ORF122). A single mAb sandwich RDT prototype for ORF122 was able to detect ICP1; RDTs with mAbs to ORF123 and ORF93 failed to detect ICP1 in single- or dual-sandwich configurations. Biologically relevant concentrations for ICP1 were detected only after boiling the stool with ICP1; analysis by electron microscopy (EM) suggested increased epitope availability after boiling. In this study, we demonstrate a proof of concept for a functional RDT that can detect both the primary pathogen and a common virulent bacteriophage as a proxy for pathogen detection. Further optimization is required before scaled production and implementation.IMPORTANCEThis paper represents an important step forward to address the vulnerability of cholera RDTs to the effects of phage predation on the target Vibrio cholerae. The assembly and evaluation of an RDT that detects both the primary pathogen and a phage as a proxy for the primary pathogen is an innovative solution. When optimized and evaluated in clinical studies, this tool may become critical in the cholera response tool kit as well as represent a diagnostic proof-of-concept for other infectious agents.