Evaluation of universal preenrichment broth and comparison of rapid molecular methods for the detection of Salmonella from spent sprout irrigation water (SSIW)

Jie Zheng; Elizabeth Reed; Anna Maounounen-Laasri; Xiaohong Deng; Shizhen S Wang; Padmini Ramachandran; Christina Ferreira; Rebecca Bell; Eric W Brown; Thomas S Hammack; Hua Wang

doi:10.1016/j.ijfoodmicro.2023.110527

Evaluation of universal preenrichment broth and comparison of rapid molecular methods for the detection of Salmonella from spent sprout irrigation water (SSIW)

Int J Food Microbiol. 2024 Feb 2:411:110527. doi: 10.1016/j.ijfoodmicro.2023.110527. Epub 2023 Dec 14.

Affiliations

¹ U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Regulatory Science, College Park, MD 20740, United States of America. Electronic address: Jie.Zheng@fda.hhs.gov.
² U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Regulatory Science, College Park, MD 20740, United States of America.
³ U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Analytics and Outreach, College Park, MD 20740, United States of America.

PMID: 38118357
DOI: 10.1016/j.ijfoodmicro.2023.110527

Abstract

Sprouts and spent sprout irrigation water (SSIW) present unique challenges for the development of a Salmonella detection method in food matrices. This study aimed to compare universal preenrichment broth (UPB) and lactose broth (LB) as preenrichment media for cultural and rapid screening methods and to compare their abilities to recover Salmonella in SSIW samples from different sprout varieties (i.e., alfalfa, broccoli, and mung bean sprouts). The associated co-enriched microbiota with different sprout varieties using different preenrichment media were also examined using a quasi-metagenomic approach. The performance of media and detection methods was compared using the relative level of detection (RLOD) value, as recommended by ISO 16140-2:2016. The level of detection (LOD) for Salmonella culture method with UPB was similar to that with LB in low aerobic plate count (APC) background samples (the relative LOD, i.e., RLOD, was nearly 1 after adjusting for the effects of SSIW variety and serovar), but significantly lower than that with LB in high APC background samples (RLOD = 0.32). The LOD for Salmonella with selected rapid methods was comparable to each other (RLOD from 0.97 to 1.50) and to the culture method (RLOD from 0.69 to 1.03), and no significant difference was detected between preenrichment broths in low APC background samples with RLOD values between 0.76 and 1.04. In samples with a high APC background, however, a drastic difference in LOD was observed between methods and between preenrichment broths for each method. The RLOD ranged from 0.03 to 0.32 when UPB was compared to LB as preenrichment broth. The composition and relative abundance (RA) of co-enriched microbiota was affected by multiple factors including food matrices, preenrichment media and Salmonella contamination. Altogether, this study validated UPB as a better preenrichment broth than LB for the detection of Salmonella enterica from SSIW. This study also suggested UPB may also be an optimal preenrichment medium for rapid screening methods when APC level is high. The observation of potential exclusion of Salmonella in preenrichment through the overgrowth of competitive microflora from the quasi-metagenomic study provided novel information that may be used to further optimize preenrichment formulations.

Keywords: Detection; Preenrichment broth; Rapid screening methods; Salmonella; Spent sprout irrigation water.

Published by Elsevier B.V.

MeSH terms

Culture Media / analysis
Food Contamination / analysis
Food Microbiology*
Salmonella / genetics
Salmonella enterica*

Substances

Culture Media