Proposition of a phagosensor with a unique Teseptimavirus SAL_R1S on a carbon nanotube platform for efficient detection of typhoid pathogen

The detection of the typhoid pathogen, Salmonella enterica serotype Typhi (S. Typhi), holds massive clinical, public health, and epidemiological significance around the globe. Conventional diagnosis relies on bacterial isolation having a set of challenges when it comes to accurate detection, therapeutic intervention and disease management. Substantial reviews and reports exist on the advantages of bacteriophage-based biosensors (phagosensors) concerning Salmonella. However, phagosensor for Salmonella Typhi point of care detection at a lower limit of detection (LOD) has yet to be reported. This study is the earliest endeavor to develop a multi-wall carbon nanotubes (MWCNTs) based electrochemical phagosensor utilizing a unique bacteriophage SAL_R1S as a biomolecular recognition element, selectively binding S. Typhi DMS_A1 at LOD of 1 CFU/ml. S. Typhi DMS_A1, retrieved from patient's blood, consists of 10 pathogenicity islands and a wide range of efflux pump genes in its whole genome, which has not yet been documented for Salmonella. Subsequent screening for its specific bacteriophage from a sewage sample pinpointed the phage SAL_R1S of class Caudoviricetes, family Autographiviridae and genus Teseptimavirus. The whole genome- and tail-fiber protein- based alignment was close to Salmonella phage Vi06 covering 88.8 % and 90 % similarity, respectively. SAL_R1S exclusively binds S. Typhi in a specific manner and also possess excellent genetic feature as a candidate for developing a highly sensitive electrochemical phagosensor. Therefore, it was covalently immobilized onto a modified SPE/MWCNT/PANI-based electrode surface, allowing charge-directed, oriented immobilization which then confirmed through scanning electron microscopy. The electrode surface was featured via field emission scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The pathogen detection process of the phagosensor is quick (∼ 20 min). It has exceptional selectivity for typhoid pathogens from blood, wastewater or within mixed populations, indicating the application of this proposed phagosensor in clinical settings as a rapid, alternative to available conventional detection techniques, and low-cost surveillance tool.