Survival of Salmonella enterica and Enterococcus faecium on Abiotic Surfaces During Storage at Low Relative Humidity

Yucen Xie; Xiaonuo Long; Yoonbin Kim; Linda J Harris; Nitin Nitin

doi:10.1016/j.jfp.2024.100292

Survival of Salmonella enterica and Enterococcus faecium on Abiotic Surfaces During Storage at Low Relative Humidity

J Food Prot. 2024 May 6;87(7):100292. doi: 10.1016/j.jfp.2024.100292. Online ahead of print.

Authors

Yucen Xie¹, Xiaonuo Long², Yoonbin Kim³, Linda J Harris⁴, Nitin Nitin⁵

Affiliations

¹ Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address: yucxie@ucdavis.edu.
² Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address: xnlong@ucdavis.edu.
³ Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address: csbkim@ucdavis.edu.
⁴ Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA; Western Center for Food Safety, University of California, Davis, CA 95616, USA. Electronic address: ljharris@ucdavis.edu.
⁵ Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA; Department of Agricultural and Biological Engineering, University of California, Davis, CA 95616, USA. Electronic address: nnitin@ucdavis.edu.

PMID: 38718984
DOI: 10.1016/j.jfp.2024.100292

Abstract

Currently, there is limited knowledge on the survival of bacteria on surfaces during postharvest handling of dry products such as onions. Extended survival of microorganisms, coupled with a lack of established and regular, validated cleaning or sanitation methods could enable cross-contamination of these products. The aim of the study was to evaluate the survival of a potential surrogate, Enterococcus faecium, and Salmonella enterica on typical onion handling surfaces, polyurethane (PU), and stainless steel (SS), under low relative humidity. The influence of onion extract on the survival of E. faecium and Salmonella on PU and SS was also investigated. Rifampin-resistant E. faecium NRRL B-2354 and a five-strain cocktail of Salmonella suspended in 0.1% peptone or onion extract were separately inoculated onto PU and SS coupons (2 × 2 cm), at high, moderate, or low (7, 5, or 3 log CFU/cm²) levels. The inoculated surfaces were stored at ∼34% relative humidity and 21°C for up to 84 days. Triplicate samples were enumerated at regular intervals in replicate trials. Samples were enriched when populations fell below the limit of detection by plating (0.48 log CFU/cm²). Scanning electron microscopy was used to observe the cell distribution on the coupons. Reductions of E. faecium of less than ∼2 log were observed on PU and SS over 12 weeks at all inoculum levels and with both inoculum carriers. In 0.1% peptone, Salmonella populations declined by 2 to 3 log over 12 weeks at the high and moderate inoculum levels; at the low inoculum level, Salmonella could not be recovered by enrichment at 84 days. Survival of E. faecium and Salmonella was significantly (P < 0.05) enhanced over 84 days of storage when suspended in onion extract, where cells were covered by a layer of onion extract. E. faecium might have utility as a conservative surrogate for Salmonella when evaluating microbial survival on dry food-contact surfaces.

Keywords: Desiccation stability; Dry environment; Food contact surfaces; Pathogens; Produce extract.