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

Abstract

Salmonella enterica is a leading causeof foodborne illness in the U.S. In this study, three S. entericastrains (serovars Cerro, Montevideo, and Typhimurium) were isolated from a beefprocessing plant with a history of Salmonella recurrence. Floor drainsof the hotbox area and storage cooler of the same plant were sampled forenvironmental microorganisms. Biofilm formation on stainless steel (SS) surfaceby the isolated S. enterica strains and the microorganisms recoveredfrom the drains were assessed. Pathogen survival and community compositionsafter sanitization (quaternary ammonium compound, QAC) were examined. Alone theCerro strain formed greater (p<0.05) biofilm mass (5.4 Log10CFU/SS chip) than the Montevideo or Typhimurium strains (4.6 and 4.8 Log10CFU/SS chip, respectively). The Typhimurium strain was the most QAC tolerant(0.3 log reduction) while the Cerro and Montevideo strains exhibited similar sensitivities(1.6 log and 1.1 log reduction, respectively). The environmental microorganismsfrom the drain samples all developed biofilms ranging from 5.7 to 6.0 Log10CFU/SS chip. All S. enterica strains were efficiently integrated intothe drain biofilms where the Montevideo and Typhimurium strains ranged from 3.8to 4.7 Log10 CFU/chip, and the Cerro strain at 4.0 to 5.8 Log10CFU/chip. Enhanced QAC tolerance was only exhibited by the Montevideo strainwhen integrated into the drain biofilms. Metagenomic analysis of the drainbiofilms showed the most abundant genus was Pseudomonas (57.7%), followedby Brochothrix (28.6%), Serratia (7.2%), Lactococcus (4.2%),and Carnobacterium (1.1%), with all varying significantly among thedifferent biofilm samples and their response to QAC treatment. Thus, various factorsunderlie the survival advantages of the S. enterica strains allowingthem to tolerate stress, outcompete and coexist with environmental companionbacteria for protection, which might lead to pathogen prevalence and recurrentproduct contamination.