Phenotypic Characterization of Salmonella Isolated from Food Production Environments Associated with Low–Water Activity Foods

Abstract

Salmonella can survive for extended periods of time in low-moisture environments posing a challenge for modern food production. This dangerous pathogen must be controlled throughout the production chain with a minimal risk of dissemination. Limited information is currently available describing the behavior and characteristics of this important zoonotic foodborne bacterium in low-moisture food production environments and in food. In our study, the phenotypes related to low-moisture survival of 46 Salmonella isolates were examined. Most of the isolates in the collection could form biofilms under defined laboratory conditions, with 57% being positive for curli fimbriae production and 75% of the collection positive for cellulose production, which are both linked with stronger biofilm formation. Biocides in the factory environment to manage hygiene were found to be most effective against planktonic cells but less so when the same bacteria were surface dried or present as a biofilm. Cellulose-producing isolates were better survivors when exposed to a biocide compared with cellulose-negative isolates. Examination of Salmonella growth of these 18 serotypes in NaCl, KCl, and glycerol found that glycerol was the least inhibitory of these three humectants. We identified a significant correlation between the ability to survive in glycerol and the ability to survive in KCl and biofilm formation, which may be important for food safety and the protection of public health.

Comparative Genotypic and Phenotypic Analysis of Cronobacter Species Cultured from Four Powdered Infant Formula Production Facilities: Indication of Pathoadaptation along the Food Chain

“…Cronobacter species are by definition a motile genus; nonetheless, few studies have explored this phenotype in a collection of isolates cultured from the PIF production environment. Salmonella Typhimurium DT104 13348 was included for comparison purposes, as it demonstrated a suitable swim and swarm phenotype (39,40). After 8 h of incubation at 37°C, 34 isolates (20.2%) were observed to have an increased swim phenotype, with 1 (0.6%) exhibiting no change in its swimming ability and 133 oth- ers (79.2%) displaying reduced swim activity compared to the reference strain ( Fig.…”

“…5) and cellulose production (see Table S1 in the supplemental material). Salmonella Typhimurium ATCC 14028 was selected as the reference strain (40). Four morphotypes were noted, as shown in Fig.…”

“…The colony morphology of Cronobacter species on Congo red agar was examined for the binding of the Congo red dye as described previously (40). Congo red agar plates were prepared using LB agar without salt as a base and supplemented with 40 g/ml Congo red dye (Sigma-Aldrich, Gillingham, United Kingdom) as well as 20 g/ml of Coomassie brilliant blue (ThermoFisher Scientific, Waltham, MA).…”

“…The production of cellulose by Cronobacter species was examined on calcofluor agar plates as described previously (40). A concentration of 50 g/ml fluorescent brightener 28 (Sigma-Aldrich, Gillingham, United Kingdom) was added into the LB agar without salt.…”

Hydrosol of Thymbra capitata Is a Highly Efficient Biocide against Salmonella enterica Serovar Typhimurium Biofilms

“…Biofilms are consortia of microorganisms adherent to each other and usually to a surface and embedded in a scaffold of self-produced extracellular polymeric substances (EPS) (4,5). Thus, there is extended documentation on the ability of Salmonella to attach to various food-contact surfaces (such as stainless steel, plastic, and cement) and form biofilms under in vitro conditions (6)(7)(8)(9)(10), while Salmonella cells have also been recovered from surfaces and products of various food industries (11)(12)(13)(14). During the past decades, it has become increasingly clear that biofilms are the predominant mode of bacterial life in most environments (15)(16)(17).…”