Characterization of Salmonella Strains and Environmental Microorganisms Isolated From a Meat Plant With Salmonella Recurrence

Abstract

Salmonella enterica is a leading cause of foodborne illness in the United States. In this study, 3 S. enterica strains (serovars Cerro, Montevideo, and Typhimurium) were isolated from a beef processing plant with a history of Salmonella recurrence. Floor drains of the hotbox area and storage cooler of the same plant were sampled for environmental micro-organisms. Biofilm formation on stainless steel (SS) by the microorganisms recovered from the drains and surface colonization by the isolated S. enterica strains were assessed. Pathogen survival and community compositions after sanitization (quaternary ammonium compound [QAC]) were examined. Alone the Cerro strain exhibited greater (P < 0.05) surface attachment (5.4 log10 CFU/SS chip) than the Montevideo or Typhimurium strains (4.6 and 4.8 log10 CFU/SS chip, respectively). The Typhimurium strain was the most QAC tolerant (0.3 log reduction), whereas the Cerro and Montevideo strains exhibited similar sensitivities (1.6 log and 1.1 log reduction, respectively). The environmental microorganisms from the drain samples all developed biofilms ranging from 5.7 to 6.0 log10 CFU/SS chip. All S. enterica strains were efficiently integrated into the drain biofilms where the Montevideo and Typhimurium strains ranged from 3.8 to 4.7 log10 CFU/chip and the Cerro strain 4.0 to 5.8 log10 CFU/chip. Enhanced QAC tolerance was only exhibited by the Montevideo strain when integrated into the drain biofilms. Metagenomic analysis of the drain biofilms showed that the most abundant genus was Pseudomonas (57.7%), followed by Brochothrix (28.6%), Serratia (7.2%), Lactococcus (4.2%), and Carnobacterium (1.1%), with all varying significantly among the different biofilm samples and their response to QAC treatment. Thus, various factors underlie the survival advantages of the S. enterica strains, allowing them to tolerate stress as well as out-compete and coexist with environmental companion bacteria for protection, which might lead to pathogen prevalence and recurrent product contamination.