Detection and differential identification of typhoidal using bacteriophages and resazurin.

This study was aimed at developing an easy to use and inexpensive biosensor for the detection of typhoidal . The technique was designed to be used without expensive instrumentation if necessary. Bacteriophages specifically infecting three typhoidal serovars were isolated and purified. Log-phase cultures were mixed with a high titre of a single phage (10 PFUs) in separate wells of a microtitre plate and incubated at room temperature (30 °C) for 1 h. After incubation, resazurin was added and the plates were incubated further for 1 h. Absorbance at 570 nm of each test well was measured using a commercial microplate reader and compared with that of the control well. A significant difference ( < 0.05) between the absorbance of test and control wells indicated the presence of target bacteria. With visual inspection, a delay in colour change from blue to pink was considered a positive result. The system could detect 5 × 10 CFUs in 120 min without pre-enrichment and 10 CFUs with a pre-enrichment of 6 h.