Biofilms of Salmonella enterica

Salmonella enterica (S. enterica) can form multicellular structures, commonly called biofilms, on various occasions. Biofilms can be formed on diverse surfaces/interfaces such as at the epithelial cell layer of a vertebrate host, on plant surfaces, or on abiotic surfaces, at the air–liquid interface and on gallstones. In this way, S. enterica is thought to achieve environmental persistence, transmission, and colonization of host organisms. Characterization of biofilm formation at the molecular level revealed different types of biofilms that have common and distinct regulatory and structural components. The so-called “rdar morphotype,” a multicellular behavior of S. enterica on agar plates is characterized by the expression of the master regulator CsgD, which controls expression of the extracellular matrix components curli fimbriae, the large surface-associated protein BapA, the exopolysaccharide cellulose and a capsular polysaccharide. Colonization of abiotic surfaces, plant surfaces and epithelial cell layers partly require the same factors as rdar morphotype formation, while the biofilm formed by Salmonella on gall stones seems to be substantially distinct from rdar morphotype formation. Introduction Salmonella enterica, in particular serovar Typhimurium (S. Typhimurium) and Enteritidis (S. Enteritidis) have mainly been studied as pathogens in the process of causing disease (Hensel, 2004; Hurley and McCormick, 2003). However, often S. enterica is a regular colonizer of warmand coldblooded animals without causing disease. Although animals and humans act as host organisms for salmonellae, the life cycle of S. enterica is complex and includes stages outside of the host (Winfield and Groisman, 2003). For example, S. enterica has to be effectively transmitted between hosts either by close contact, or through animate or inanimate vehicles such as water, food and produce. Effective survival outside a host is consequently an essential component of the life cycle of S. enterica. Since life outside and inside a host is fundamentally different, S. enterica has to tightly regulate gene expression in order to survive in both environments (Mouslim et al., 2002). A multicellular behavior, commonly called biofilm-formation, is expressed by almost all bacteria and can play roles in virulence and host colonization as well as for the survival outside a host. In this review, current knowledge about biofilm formation in S. enterica is summarized. S. enterica caister.com/biofilmsbooks Römling et al. 128 | forms biofilms on different surfaces in the host such as at the epithelial cell layer or on gall stones; is able to colonize plant surfaces for transmission of the pathogen and colonizes abiotic surfaces such as stainless steel and glass. Elucidation of the molecular basis of biofilm formation has revealed that similar and distinct components are required for biofilm formation on different surfaces. Definition of biofilm