Salmonella enterica Serovar Kentucky Flagella Are Required for Broiler Skin Adhesion and Caco-2 Cell Invasion

Abstract

Nontyphoidal Salmonella strains are the main source of pathogenic bacterial contamination in the poultry industry. Recently, Salmonella enterica serovar Kentucky has been recognized as the most prominent serovar on carcasses in poultry-processing plants. Previous studies showed that flagella are one of the main factors that contribute to bacterial attachment to broiler skin. However, the precise role of flagella and the mechanism of attachment are unknown. There are two different flagellar subunits (fliC and fljB) expressed alternatively in Salmonella enterica serovars using phase variation. Here, by making deletions in genes encoding flagellar structural subunits (flgK, fliC, and fljB), and flagellar motor (motA), we were able to differentiate the role of flagella and their rotary motion in the colonization of broiler skin and cellular attachment. Utilizing a broiler skin assay, we demonstrated that the presence of FliC is necessary for attachment to broiler skin. Expression of the alternative flagellar subunit FljB enables Salmonella motility, but this subunit is unable to mediate tight attachment. Deletion of the flgK gene prevents proper flagellar assembly, making Salmonella significantly less adherent to broiler skin than the wild type. S. Kentucky with deletions in all three structural genes, fliC, fljB, and flgK, as well as a flagellar motor mutant (motA), exhibited less adhesion and invasion of Caco-2 cells, while an fljB mutant was as adherent and invasive as the wild-type strain.IMPORTANCE In this work, we answered clearly the role of flagella in S. Kentucky attachment to the chicken skin and Caco-2 cells. We demonstrated that the presence of FliC is necessary for attachment to broiler skin. Expression of the alternative flagellar subunit FljB enables Salmonella motility, but this subunit is unable to mediate strong attachment. Deletion of the flgK gene prevents proper flagellar assembly, making Salmonella significantly less adherent to broiler skin than the wild type. S. Kentucky with deletions in all three structural genes, fliC, fljB, and flgK, as well as a flagellar motor mutant (motA), exhibited less adhesion and invasion of Caco-2 cells, while an fljB mutant was as adherent and invasive as the wild-type strain. We expect these results will contribute to the understanding of the mechanisms of Salmonella attachment to food products.

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“…Flagellae, the main motor organ system of bacteria, and their motility, the simplest biological behavior, are prerequisites for adhesion and invasion, playing important roles in the early stage of infection (Salehi et al., 2017). With the help of flagella, bacteria can enter an advantageous environment and travel toward the surface of epithelial cells through the viscous mucus barrier (Rivera‐Chavez et al., 2013).…”

Salmonella Typhimurium encoded cold shock protein E is essential for motility and biofilm formation

“…In fact, flagellar genes are indispensable for establishing the initial attachment and movement of bacterial cells on a surface [67,75]. In case of Salmonella, fliC deletion mutants are impaired in their capacity to attach on cholesterol coated surfaces [76], broiler skins [77] or plant cell wall surfaces [78]. It is likely that motility is required until the bacteria encounters a surface, and then aggregates, to form a biofilm, thus changing the lifestyle from motile to lower motility.…”

Salmonella Harborage Sites in Infected Poultry That May Contribute to Contamination of Ground Meat

“…Salmonella optimally express curli when grown at ambient room temperature (Maurer et al, 1998) or starved for nutrients in the chicken cecum (Cheng et al, 2015). Flagella may also be involved in attachment of Salmonella on chicken skin surfaces (Salehi et al, 2017). Expression of these adhesive structures depends on the genetic background of the isolate as well as environmental factors, such as temperature, oxygen, and nutrient availability (Collinson et al, 1993;Maurer et al, 1998;Gerstel and Römling, 2001).…”