Characterization of Salmonella strains and environmental microorganisms isolated from a meat plant with Salmonella recurrence

Authors: Wang, Rong; DASS, SAPNA - Texas A&M University; CHEN, QIYUE - Texas A&M University; Guragain, Manita; Bosilevac, Joseph - Mick

Submitted to: Meat and Muscle Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2022
Publication Date: 11/8/2022
Citation: Wang, R., Dass, S.C., Chen, Q., Guragain, M., Bosilevac, J.M. 2022. Characterization of Salmonella strains and environmental microorganisms isolated from a meat plant with Salmonella recurrence. Meat and Muscle Biology. 6(1). Article 15442. https://doi.org/10.22175/mmb.15442.
DOI: https://doi.org/10.22175/mmb.15442

Interpretive Summary: In the United States, Salmonella is the second leading cause of bacterial foodborne illness, most of which are related to the consumption of contaminated foods including red meat and poultry. Meat contamination by Salmonella is traditionally attributed to bacterial transfer from animal hides or from lymph nodes, however, this study shows that a processing plant with recurrent Salmonella contamination harbors different Salmonella strains in the processing plant environment. These strains have strong ability to form biofilms which are complex bacterial communities attached to surfaces and also exhibit high tolerance against sanitization or enhanced survival ability through interactions with processing plant environmental biofilms. The Salmonella cells can be effectively mixed into the biofilm community formed by the multiple types of bacteria to colonize on common food contact surfaces. The different types of bacteria in the biofilm communities can either inhibit or protect the Salmonella cells recruited into the community, therefore, understanding this alternant pathway of contamination will help identify new tactics to improve meat safety.

Technical Abstract: Salmonella enterica is the second leading cause of bacterial foodborne illness in the United States. The majority of human salmonellosis cases are related to consumption of contaminated foods including red meat and poultry. While the source of Salmonella contamination is traditionally attributed to animal hides or lymph nodes, recent insights have shown that pathogens may persist in facilities via biofilm formation. In the present study, three Salmonella strains of Cerro, Montevideo and Typhimurium, serovars frequently found in meat contamination, were isolated from the environment at a processing plant with a history of Salmonella recurrence. Floor drain samples containing multispecies environmental microorganisms were collected from the same plant as well. The isolated Salmonella strains and the drain samples were able to form biofilms on common food contact surfaces under processing conditions. The Salmonella cells were integrated into the multispecies biofilms and distributed in the top-middle layers of the 3D biofilm structure as shown by fluorescence microscopy. All floor drain samples contained the same five major species including Pseudomonas, Brochothrix, Serratia, Lactococcus, and Carnobacterium. Overall, samples from the hotbox (where freshly harvested carcasses are cooled) had higher species diversity than samples from the cooler (where chilled carcasses are stored), and the percentage of the species presented in each sample varied based on the drain locations. Our results further revealed various mechanisms underlying the survival advantages of the Salmonella strains, including strong biofilm formation, strong competition capability against background microorganisms, strain – specific high tolerance, and the interspecies interactions with environmental microbes resulting in enhanced stress tolerance via mixed biofilm formation. Our study indicated that various Salmonella strains of different serovars can apply and adapt multiple strategies, either individually or interacting with environmental microorganisms, for increased survival capability. Strains benefiting from the appropriate mechanisms would gain advantages to effectively tolerate stress, outcompete and coexist with environmental companion bacteria for extra protection, and potentially result in product contamination and pathogen recurrence.