Optimizing Salmonella Detection in Beijing's Surface Water: Unveiling Rare Serotypes with a Modified Moore Swab (MMS) Method.

Background: Salmonella, a notorious foodborne pathogen with a wide range of hosts, poses a significant public health concern globally. Contaminated surface water acts as a potential source of Salmonella transmission.

Objective: To optimize a Salmonella detection method from large-volume water and analyze surface water samples in Beijing and characterize Salmonella isolates from these samples by whole genome sequencing.

Methods: A microbial enrichment device based on the modified Moore swab (MMS) design was optimized and validated. Thirty-five water samples were collected and analyzed for Salmonella from 11 park lakes, two rivers, and two farms. Multiple characteristics of isolates were analyzed using antibiotic antimicrobial testing and whole genome sequencing.

Results: The optimized MMS unit showed high efficiency (over 80% recovery) and a low detection limit (100 cells) for enriching and isolating Salmonella from large-volume water (10 L). Compared to the conventional method, the MMS device significantly improved Salmonella detection efficiency (62.86 versus 8.57%) in Beijing's surface water. Most of the Salmonella isolates from surface water belonged to rare serotypes from water wildlife susceptible to all the tested antimicrbials.

Conclusion: The study demonstrates the optimized MMS's effectiveness for on-site enrichment of pathogens from large-volume water, validates the accuracy and sensitivity of a Salmonella detection method for surface water, and reveals previously unknown information about Salmonella contamination in Beijing's public water system.

Highlights: Salmonella concentrations in water are typically very low: implementation of this method would successfully realize large-volume water sampling and on-site pathogen enrichment, and significantly improve Salmonella detection efficiency in surface water.