Capsular polysaccharide surrounds smooth and rugose types of Salmonella enterica serovar Typhimurium DT104.

The biofilms and rugose colony morphology of Salmonella enterica serovar Typhimurium strains are usually associated with at least two different exopolymeric substances (EPS), curli and cellulose. In this study, another EPS, a capsular polysaccharide (CP) synthesized constitutively in S. enterica serovar Typhimurium strain DT104 at 25 and 37 degrees C, has been recognized as a biofilm matrix component as well. Fluorophore-assisted carbohydrate electrophoresis (FACE) analysis indicated that the CP is comprised principally of glucose and mannose, with galactose as a minor constituent. The composition differs from that of known colanic acid-containing CP that is isolated from cells of Escherichia coli and other enteric bacteria grown at 37 degrees C. The reactivity of carbohydrate-specific lectins conjugated to fluorescein isothiocyanate or gold particles with cellular carbohydrates demonstrated the cell surface localization of CP. Further, lectin binding also correlated with the FACE analysis of CP. Immunoelectron microscopy, using specific antibodies against CP, confirmed that CP surrounds the cells. Confocal microscopy of antibody-labeled cells showed greater biofilm formation at 25 degrees C than at 37 degrees C. Since the CP was shown to be produced at both 37 degrees C and 25 degrees C, it does not appear to be significantly involved in attachment during the early formation of the biofilm matrix. Although the attachment of S. enterica serovar Typhimurium DT104 does not appear to be mediated by its CP, the capsule does contribute to the biofilm matrix and may have a role in other features of this organism, such as virulence, as has been shown previously for the capsules of other gram-negative and gram-positive bacteria.

Salmonella enterica serovar Typhimurium DT104 displays a rugose phenotype.

Rugose phenotypes, such as those observed in Vibrio cholerae, have increased resistance to chlorine, oxidative stress, and complement-mediated killing. In this study we identified and defined a rugose phenotype in Salmonella enterica serovar Typhimurium DT104 and showed induction only on certain media at 25 degrees C after 3 days of incubation. Incubation at 37 degrees C resulted in the appearance of the smooth phenotype. Observation of the ultrastructure of the rugose form and a stable smooth variant (Stv), which was isolated following a series of passages of the rugose cells, revealed extracellular substances only in cells from the rugose colony. Observation of the extracellular substance by scanning electron microscopy (SEM) was correlated with the appearance of corrugation during development of rugose colony morphology over a 4-day incubation period at 25 degrees C. In addition, the cells also formed a pellicle in liquid broth, which was associated with the appearance of interlacing slime and fibrillar structures, as observed by SEM. The pellicle-forming cells were completely surrounded by capsular material, which bound cationic ferritin, thus indicating the presence of an extracellular anionic component. The rugose cells, in contrast to Stv, showed resistance to low pH and hydrogen peroxide and an ability to form biofilms. Based on these results and analogy to the rugose phenotype in V. cholerae, we propose a possible role for the rugose phenotype in the survival of S. enterica serovar Typhimurium DT104.