Isolation and Characterization of Salmonella Typhi Vi-Specific Bacteriophages from Urine Samples: A Prospective Cross-Sectional Study.

Abstract

Background:

Typhoid fever remains a major public health concern in many low- and middle-income countries. Rising antimicrobial resistance has renewed interest in bacteriophage-based diagnostics and therapeutics. This prospective observational study aimed to isolate and characterize Salmonella Typhi Vi-specific bacteriophages from urine samples collected over six months.

 Methods:

Fifty urine samples were collected from patients with either clinically suspected or microbiologically confirmed typhoid. Following centrifugation and filtration, samples were enriched using host strains of Salmonella Typhi that were Vi-positive. Spot and double-layer agar plaque assays were used to detect phages. Plaque morphology, host range, heat stability, pH tolerance, and chloroform sensitivity were used to describe isolated phages.

 Results:

Out of 50 samples, 18 (36%) had Vi-specific bacteriophages. Compared to clinically suspected cases, isolation was substantially higher in culture-confirmed typhoid cases (52.0% vs. 18.2%, p=0.018). Turbid plaques made up 38.9% of the total, whereas clear plaques predominated (61.1%). At pH 6–8 and temperatures as high as 50°C, the majority of isolates were stable. 72.2% of isolates showed narrow host specificity toward bacteria that expressed Vi.

 Conclusion:

These findings demonstrate that urine is a feasible non-invasive source for recovering Vi-specific bacteriophages. Such phages may have future utility in rapid diagnostics, environmental surveillance, and adjunctive phage therapy against drug-resistant typhoid fever.

 Recommendation

Urine-based isolation of Vi-specific bacteriophages should be further explored as a non-invasive approach for typhoid diagnostics and surveillance. Larger multicenter studies incorporating molecular characterization are recommended before clinical application.