Detection ofSalmonellaTyphi andbla_CTX-MGenes in Drinking Water, Wastewater, and Environmental Biofilms in Sindh Province, Pakistan

Typhoid fever poses a significant public health risk, particularly in low- and middle-income countries where access to clean water and improved sanitation may be limited. In Pakistan, this risk is especially serious given the emergence of an extensively drug-resistant (XDR)SalmonellaTyphi strain, a strain attributed toS. Typhi acquisition of thebla_CTX-M-15gene. The now-dominant XDRS. Typhi strain, non-XDRS. Typhi, andbla_CTX-Mgenes are readily disseminated via drinking water and wastewater in Pakistan and may also be present in biofilms associated with these environmental sources. This study investigates the presence ofS. Typhi andbla_CTX-Mgenes within these environmental compartments. Drinking water (n=35) or wastewater samples (n=35) and samples of their associated biofilms were collected from Karachi and Hyderabad, Pakistan. Samples were tested by PCR forS. Typhi andbla_CTX-Mgroup 1 genes as a proxy forbla_CTX-M-15. Heterotrophic plate counts (HPC) were conducted to assess microbial load.S. Typhi was detected by PCR in one bulk wastewater sample and one drinking water biofilm.Bla_CTX-Mgroup 1 genes were detected in all sample types and were detected more frequently in bulk wastewater (n=13/35) than in drinking water (n=2/35) and more frequently overall in biofilm samples (n=22/70) versus bulk water (n=15/70). Detection ofbla_CTX-Min biofilm was not significantly associated with detection in the associated bulk water sample. This study marks the first detection ofS. Typhi in drinking water biofilms and the first report ofbla_CTX-Mgenes in environmental biofilms in Pakistan. Environmental biofilms, particularly in drinking water systems, may serve as reservoirs for human exposure toS. Typhi and drug resistance genes. This study underscores the importance of expanding surveillance strategies to include biofilm sampling, providing valuable insights into pathogen dissemination in water systems, and informing targeted public health interventions to prevent waterborne diseases.