Project Lead(s): Josiah Obiero
The World Health Organization (WHO) estimates that, worldwide, 16–33 million cases of Salmonella typhi illnesses, including typhoid, occur each year, resulting in 216,000 deaths.
Most are due to food and water contamination, and would be preventable if water utility operators could reduce lag time between the occurrence of disease and detection of S. typhi.
Current techniques for the rapid detection of S. typhi in samples are complex, time-consuming and expensive. They also lack sensitivity, requiring 10^5 target cells per milliliter (mL) for detection.
A project was undertaken to develop a paper-based test that takes advantage the specificity of phage tail spike proteins in detecting bacteria, by using them to separate, concentrate and detect the bacteria that causes typhoid fever (Salmonella enterica serovar typhi).
A phage host-binding, protein-based system for isolation and concentration of S. typhi, coupled with the adsorbed cells detection assay, would provide a perfect analytical tool for screening S. typhi contamination.
Recombinant production and purification of Salmonella enterica serovar typhi phage Vi phage I/ Vi phage VI tail fiber proteins was done.
There were six constructs designed and all expressed with the shortest constructs showing the highest protein expression.
The ability to agglutinate Salmonella cells was assessed in cell micro-agglutination assays.
Binding of the GFP-labelled PViVI (PViVI-GFP) to Salmonella cells was tested by adding purified PViVI-GFP to strain exponentially growing S. typhi cells.
In brief, the project has been able to prove that the phage tail spike proteins selected for the project are capable of detecting Salmonella typhi. Results showed that Salmonella typhi phage tail fiber proteins do not agglutinate Salmonella cells. The PViVI-GFP was able to direct GFP efficiently to the entire cell surface of susceptible S. typhi cells, resulting in fluorescent decoration of the bacteria.
The team is still in the development phase of the project and a prototype was not developed during the grant period.
The next step will be to try to immobilize these proteins onto a paper strip to develop a viable test, an enterprise that will require an estimated $100,000.