부산대학교 도서관

Background: Environmental surveillance, using detection of Salmonella Typhi DNA, has emerged as a potentially useful tool to identify typhoid-endemic settings; however, it is relatively costly and requires molecular diagnostic capacity. We sought to determine whether S. Typhi bacteriophages are abundant in water sources in a typhoid-endemic setting, using low-cost assays. Methodology: We collected drinking and surface water samples from urban, peri-urban and rural areas in 4 regions of Nepal. We performed a double agar overlay with S. Typhi to assess the presence of bacteriophages. We isolated and tested phages against multiple strains to assess their host range. We performed whole genome sequencing of isolated phages, and generated phylogenies using conserved genes. Findings: S. Typhi-specific bacteriophages were detected in 54.9% (198/361) of river and 6.3% (1/16) drinking water samples from the Kathmandu Valley and Kavrepalanchok. Water samples collected within or downstream of population-dense areas were more likely to be positive (72.6%, 193/266) than those collected upstream from population centers (5.3%, 5/95) (p=0.005). In urban Biratnagar and rural Dolakha, where typhoid incidence is low, only 6.7% (1/15, Biratnagar) and 0% (0/16, Dolakha) river water samples contained phages. All S. Typhi phages were unable to infect other Salmonella and non-Salmonella strains, nor a Vi-knockout S. Typhi strain. Representative strains from S. Typhi lineages were variably susceptible to the isolated phages. Phylogenetic analysis showed that S. Typhi phages belonged to the class Caudoviricetes and clustered in three distinct groups. Conclusions: S. Typhi bacteriophages were highly abundant in surface waters of typhoid-endemic communities but rarely detected in low typhoid burden communities. Bacteriophages recovered were specific for S. Typhi and required Vi polysaccharide for infection. Screening small volumes of water with simple, low-cost (~$2) plaque assays enables detection of S. Typhi phages and should be further evaluated as a scalable tool for typhoid environmental surveillance. Author summary: Typhoid fever is a major health issue in low- and middle-income countries, causing illness and death. The World Health Organization recommends the use of typhoid-conjugate vaccines to combat its spread. However, limited data on typhoid prevalence in these countries hinders effective vaccination programs. Environmental surveillance, which involves detecting Salmonella Typhi DNA in the environment, has emerged as a method to identify high-risk areas for typhoid transmission. Nevertheless, this approach is costly and requires infrastructure often unavailable in many communities. To address this, we conducted a study in Nepal to explore a low-cost and sustainable typhoid surveillance method. We examined typhoid bacteriophages in surface and drinking water across communities with varying population densities and typhoid burdens. Phages were easily detectable in communities with high typhoid burdens but less prevalent in areas with lower burdens. The isolated phages exhibited specificity for S. Typhi and were effective against different bacterial strains in Nepal. This study demonstrates that phage-based assays can be a simple and affordable tool for typhoid environmental surveillance. This method can help identify areas that require vaccination prioritization and interventions for clean water and sanitation. By utilizing phage-based assays, health authorities can better understand typhoid transmission and implement targeted control measures. [ABSTRACT FROM AUTHOR]