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Factors affecting the recovery of low levels of Salmonella enterica from water
Citation:
Kraft, A., S. Kim, B. McConn, A. Franklin, M. Ibekew, J. Frye, L. Hiott, L. Durso, J. Wells, L. Boczek, J. Garland, C. Kabrera, P. McDermott, A. Ottesen, J. Zheng, C. East, K. Cook, AND M. Sharma. Factors affecting the recovery of low levels of Salmonella enterica from water. 2022 Annual Meeting - International Association for Food Protection, Pittsburgh, PA, July 31 - August 03, 2022.
Impact/Purpose:
Antimicrobial resistant Salmonella enterica in surface waters is an emerging food safety issue and its presence signifies environmental contamination. Having effective methods for detecting antimicrobial resistant Salmonella in water is important for public and food safety. This work examine three different methods for isolating Salmonella from surface waters across different laboratories. This work showed that recovery of Salmonella depends on the method used and the laboratory doing the work. This work provides a basis for additional work to optimize detection methods and the importance of validating methods across laboratories. This information is pertinent for anyone working in food safety (research and/or industry).
Description:
Introduction: The presence of antimicrobial-resistant Salmonella enterica in water indicates environmental contamination and is an emergent food safety issue. Identifying and developing effective and sensitive detection methods for antimicrobial-resistant Salmonella from water is part of the National Antimicrobial Resistance Monitoring System (NARMS), supported by EPA, FDA and USDA. Purpose: To compare methods of and identify factors which affect recovery of Salmonella from surface water. Materials and Methods: Volumes of surface water from a site (MA04) were collected in fall 2021 on five different dates. Rainfall data, water temperature, turbidity, pH, and dissolved oxygen were all recorded. Water was shipped and analyzed at CA, GA, NE, and MD locations for recovery of environmentally present or an inoculated, fluorescently-labeled S. Typhimurium (ca. 30 CFU) which was added to each 1 L sample before being subjected to one of three recovery / enrichment methods: bulk water enrichment (BW), vertical Modified Moore Swab (MM), and Standard Method 9260.B3 (SM). Presumptive Salmonella colonies were confirmed by biochemical analysis (environmental) and / or fluorescence (inoculated). Data were analyzed using a Chi-squared test with recovery method (RM), laboratory location (LL), and Salmonella detection (D) as categorical values. Results: Statistical analysis revealed that the RM, LL, and D were not independent (p < 0.001) of each other and all concurrently influenced recovery/detection of environmental and inoculated Salmonella. Across all four LL, SM was the method that most frequently recovered environmental and low levels of inoculated Salmonella from water. Significance: Recovery of low levels of Salmonella is dependent on the method used and the specific laboratory conducting the work. These data support the need to standardize and simplify the recovery methods to reduce variability from different scientists. Standard Method 9260.B3 more frequently recovered low levels of Salmonella from inoculated water samples and should be prioritized for recovery of antibiotic-resistant Salmonella in laboratory settings.
