Phenotypic and metabolic diversity of Salmonella isolates from agricultural creek sediment

Authors: Oh, Sookyung; Patel, Jitendra

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2026
Publication Date: 5/7/2026
Citation: Oh, S., Patel, J.R. 2026. Phenotypic and metabolic diversity of Salmonella isolates from agricultural creek sediment. Journal of Food Protection. 89(7). Article e100807. https://doi.org/10.1016/j.jfp.2026.100807.
DOI: https://doi.org/10.1016/j.jfp.2026.100807

Interpretive Summary: Foodborne outbreaks associated with bacterial pathogen contamination of fresh produce have been reported. Salmonella, a pathogen present in creek sediment can survive for a long time and contaminate fresh produce via irrigation water. We studied 16 Salmonella isolates from sediment in a Conococheague creek in the Mid-Atlantic region of the U.S. The research showed different behavior of these isolates under environmental stress conditions. Hydrophobicity, a water repellent trait of bacteria which can help bacteria in surface attachment, varied significantly among these isolates. Salmonella serovar Typhimurium was resistant to acidic conditions, while serovar Holcomb was sensitive to harsh alkaline and oxidative stress. Bacterial growth pattern identified as metabolic heat rate revealed potential use of alternative energy sources to survive in fluctuating environmental conditions. While most isolates were susceptible to antibiotics, serovar Holcomb showed resistance to cefoxitin. These critical findings are helpful to farmers in improving food safety and reducing the risk of fresh produce contamination at the farm.

Technical Abstract: Salmonella is an important foodborne pathogen and its outbreaks are increasingly linked to environmental contamination in preharvest systems. Sediment in agricultural watersheds can provide a critical long-term microbial reservoir. However, the phenotypic and metabolic diversity in Salmonella populations hampers effective control. We assessed growth characteristics of 16 Salmonella isolates recovered from sediment of the Conococheague Creek, in Mid-Atlantic USA. We tested hydrophobicity, tolerance to acidic (pH 3.0), alkaline (pH 10.0), and oxidative (H2O2) stress, metabolic activity using isothermal calorimetry, and antimicrobial susceptibility. Isolates showed variable hydrophobicity levels of 15% to 81%. Notably, Newport serotype isolates were grouped into two distinct clusters, indicating clonal variation. Isolate 5 (Typhimurium) exhibited a high degree of acid resistance, whereas isolate 4 (Holcomb) was highly susceptible to alkaline and oxidative stresses, indicating isolate-specific stress tolerance. Calorimetry analysis revealed variation in peak heat flow from 49.6 to 63.0 µW across isolates. In a subset of isolates, a secondary metabolic shift was observed at 24–26 h, pointing to the fact that these strains may adapt to fluctuating environmental conditions by utilizing alternative energy sources. Most isolates were susceptible to antimicrobials tested, while isolate 4 (Holcomb) showed intermediate resistance to cefoxitin (MIC = 16 µg/mL), suggesting a potential mobile ß-lactamase in this isolate, linking environmental survival to antimicrobial resistance (AMR) threats. We demonstrated distinctive characteristics of Salmonella isolates from the environment and this research provides a basis for improving risk assessment and preharvest food safety strategies.