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

Tan MS, Rahman S, Dykes GA

Appl Environ Microbiol, 2016 01 15;82(2):680-8.
PMID: 26567310 DOI: 10.1128/AEM.02609-15

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.

Matched MeSH terms: Plant Cells/microbiology*
Attachment of bacterial pathogens to a bacterial cellulose-derived plant cell wall model: a proof of concept

Tan MS, Wang Y, Dykes GA

Foodborne Pathog Dis, 2013 Nov;10(11):992-4.
PMID: 23941519 DOI: 10.1089/fpd.2013.1536

This study aimed to establish, as a proof of concept, whether bacterial cellulose (BC)-derived plant cell wall models could be used to investigate foodborne bacterial pathogen attachment. Attachment of two strains each of Salmonella enterica and Listeria monocytogenes to four BC-derived plant cell wall models (namely, BC, BC-pectin [BCP], BC-xyloglucan [BCX], and BC-pectin-xyloglucan [BCPX]) was investigated. Chemical analysis indicated that the BCPX composite (31% cellulose, 45.6% pectin, 23.4% xyloglucan) had a composition typical of plant cell walls. The Salmonella strains attached in significantly (p<0.05) higher numbers (~6 log colony-forming units [CFU]/cm(2)) to the composites than the Listeria strains (~5 log CFU/cm(2)). Strain-specific differences were also apparent with one Salmonella strain, for example, attaching in significantly (p<0.05) higher numbers to the BCX composite than to the other composites. This study highlights the potential usefulness of these composites to understand attachment of foodborne bacteria to fresh produce.

Matched MeSH terms: Plant Cells/microbiology*
Fulltext Role of Fimbriae, Flagella and Cellulose on the Attachment of Salmonella Typhimurium ATCC 14028 to Plant Cell Wall Models

Tan MS, White AP, Rahman S, Dykes GA

PLoS One, 2016;11(6):e0158311.
PMID: 27355584 DOI: 10.1371/journal.pone.0158311

Cases of foodborne disease caused by Salmonella are frequently associated with the consumption of minimally processed produce. Bacterial cell surface components are known to be important for the attachment of bacterial pathogens to fresh produce. The role of these extracellular structures in Salmonella attachment to plant cell walls has not been investigated in detail. We investigated the role of flagella, fimbriae and cellulose on the attachment of Salmonella Typhimurium ATCC 14028 and a range of isogenic deletion mutants (ΔfliC fljB, ΔbcsA, ΔcsgA, ΔcsgA bcsA and ΔcsgD) to bacterial cellulose (BC)-based plant cell wall models [BC-Pectin (BCP), BC-Xyloglucan (BCX) and BC-Pectin-Xyloglucan (BCPX)] after growth at different temperatures (28°C and 37°C). We found that all three cell surface components were produced at 28°C but only the flagella was produced at 37°C. Flagella appeared to be most important for attachment (reduction of up to 1.5 log CFU/cm2) although both cellulose and fimbriae also aided in attachment. The csgD deletion mutant, which lacks both cellulose and fimbriae, showed significantly higher attachment as compared to wild type cells at 37°C. This may be due to the increased expression of flagella-related genes which are also indirectly regulated by the csgD gene. Our study suggests that bacterial attachment to plant cell walls is a complex process involving many factors. Although flagella, cellulose and fimbriae all aid in attachment, these structures are not the only mechanism as no strain was completely defective in its attachment.

Matched MeSH terms: Plant Cells/microbiology*
Fulltext Attachment of Salmonella strains to a plant cell wall model is modulated by surface characteristics and not by specific carbohydrate interactions

Tan MS, Moore SC, Tabor RF, Fegan N, Rahman S, Dykes GA

BMC Microbiol, 2016 09 15;16:212.
PMID: 27629769 DOI: 10.1186/s12866-016-0832-2

BACKGROUND: Processing of fresh produce exposes cut surfaces of plant cell walls that then become vulnerable to human foodborne pathogen attachment and contamination, particularly by Salmonella enterica. Plant cell walls are mainly composed of the polysaccharides cellulose, pectin and hemicelluloses (predominantly xyloglucan). Our previous work used bacterial cellulose-based plant cell wall models to study the interaction between Salmonella and the various plant cell wall components. We demonstrated that Salmonella attachment was favoured in the presence of pectin while xyloglucan had no effect on its attachment. Xyloglucan significantly increased the attachment of Salmonella cells to the plant cell wall model only when it was in association with pectin. In this study, we investigate whether the plant cell wall polysaccharides mediate Salmonella attachment to the bacterial cellulose-based plant cell wall models through specific carbohydrate interactions or through the effects of carbohydrates on the physical characteristics of the attachment surface.
RESULTS: We found that none of the monosaccharides that make up the plant cell wall polysaccharides specifically inhibit Salmonella attachment to the bacterial cellulose-based plant cell wall models. Confocal laser scanning microscopy showed that Salmonella cells can penetrate and attach within the tightly arranged bacterial cellulose network. Analysis of images obtained from atomic force microscopy revealed that the bacterial cellulose-pectin-xyloglucan composite with 0.3 % (w/v) xyloglucan, previously shown to have the highest number of Salmonella cells attached to it, had significantly thicker cellulose fibrils compared to other composites. Scanning electron microscopy images also showed that the bacterial cellulose and bacterial cellulose-xyloglucan composites were more porous when compared to the other composites containing pectin.
CONCLUSIONS: Our study found that the attachment of Salmonella cells to cut plant cell walls was not mediated by specific carbohydrate interactions. This suggests that the attachment of Salmonella strains to the plant cell wall models were more dependent on the structural characteristics of the attachment surface. Pectin reduces the porosity and space between cellulose fibrils, which then forms a matrix that is able to retain Salmonella cells within the bacterial cellulose network. When present with pectin, xyloglucan provides a greater surface for Salmonella cells to attach through the thickening of cellulose fibrils.

Matched MeSH terms: Plant Cells/microbiology*
Sonication reduces the attachment of Salmonella Typhimurium ATCC 14028 cells to bacterial cellulose-based plant cell wall models and cut plant material

Tan MSF, Rahman S, Dykes GA

Food Microbiol, 2017 Apr;62:62-67.
PMID: 27889167 DOI: 10.1016/j.fm.2016.10.009

This study investigated the removal of bacterial surface structures, particularly flagella, using sonication, and examined its effect on the attachment of Salmonella Typhimurium ATCC 14028 cells to plant cell walls. S. Typhimurium ATCC 14028 cells were subjected to sonication at 20 kHz to remove surface structures without affecting cell viability. Effective removal of flagella was determined by staining flagella of sonicated cells with Ryu's stain and enumerating the flagella remaining by direct microscopic counting. The attachment of sonicated S. Typhimurium cells to bacterial cellulose-based plant cell wall models and cut plant material (potato, apple, lettuce) was then evaluated. Varying concentrations of pectin and/or xyloglucan were used to produce a range of bacterial cellulose-based plant cell wall models. As compared to the non-sonicated controls, sonicated S. Typhimurium cells attached in significantly lower numbers (between 0.5 and 1.0 log CFU/cm2) to all surfaces except to the bacterial cellulose-only composite without pectin and xyloglucan. Since attachment of S. Typhimurium to the bacterial cellulose-only composite was not affected by sonication, this suggests that bacterial surface structures, particularly flagella, could have specific interactions with pectin and xyloglucan. This study indicates that sonication may have potential applications for reducing Salmonella attachment during the processing of fresh produce.

Matched MeSH terms: Plant Cells/microbiology*