Pectin and Xyloglucan Influence the Attachment of Salmonella enterica and Listeria monocytogenes to Bacterial Cellulose-Derived Plant Cell Wall Models

Abstract

Minimally processed fresh produce has been implicated as a major source of foodborne microbial pathogens globally. These pathogens must attach to the produce in order to be transmitted. Cut surfaces of produce that expose cell walls are particularly vulnerable. Little is known about the roles that different structural components (cellulose, pectin, and xyloglucan) of plant cell walls play in the attachment of foodborne bacterial pathogens. Using bacterial cellulose-derived plant cell wall models, we showed that the presence of pectin alone or xyloglucan alone affected the attachment of three Salmonella enterica strains (Salmonella enterica subsp. enterica serovar Enteritidis ATCC 13076, Salmonella enterica subsp. enterica serovar Typhimurium ATCC 14028, and Salmonella enterica subsp. indica M4) and Listeria monocytogenes ATCC 7644. In addition, we showed that this effect was modulated in the presence of both polysaccharides. Assays using pairwise combinations of S. Typhimurium ATCC 14028 and L. monocytogenes ATCC 7644 showed that bacterial attachment to all plant cell wall models was dependent on the characteristics of the individual bacterial strains and was not directly proportional to the initial concentration of the bacterial inoculum. This work showed that bacterial attachment was not determined directly by the plant cell wall model or bacterial physicochemical properties. We suggest that attachment of the Salmonella strains may be influenced by the effects of these polysaccharides on physical and structural properties of the plant cell wall model. Our findings improve the understanding of how Salmonella enterica and Listeria monocytogenes attach to plant cell walls, which may facilitate the development of better ways to prevent the attachment of these pathogens to such surfaces.

FIG 1

Attachment of Salmonella Enteritidis ATCC 13076 (a), Salmonella Typhimurium ATCC 14028 (b), Salmonella enterica M4 isolated from lettuce (c), and Listeria monocytogenes ATCC 7644 (d) to BC, BCP, BCX, 0.1% BCPX, 0.3% BCPX, and 0.5% BCPX. Different uppercase letters indicate significant differences between types of composites, whereas different lowercase letters indicate significant differences within each type of composite (one-way ANOVA and Tukey's pairwise comparison, P < 0.05). Stippled bars, 0% PCW components (for BC); light gray bars, 0.1% PCW components; medium gray bars, 0.3% PCW components; dark gray bars, 0.5% PCW components added into the growth medium.

FIG 2

Differences in attachment numbers between S. Typhimurium ATCC 14028 (ST) and L. monocytogenes ATCC 7644 (LM) when present individually and at different initial S. Typhimurium/L. monocytogenes inoculum ratios (0.428, 1, or 2.333) on BC composites and abiotic surfaces. SSC, stainless steel coupons. Different uppercase letters indicate significant differences between attachment surfaces, whereas different lowercase letters indicate significant differences between individual attachment and attachment at different initial inoculum ratios for the same attachment surface (two-way ANOVA and Tukey's pairwise comparison, P < 0.05).