Salmonella enterica serovar Typhimurium DT104 displays a rugose phenotype

Rugose phenotypes, such as those observed in Vibrio cholerae, have increase d 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 med ia at 25 degreesC after 3 days of incubation. Incubation at 37 degreesC res ulted in the appearance of the smooth phenotype. Observation of the ultrast ructure of the rugose form and a stable smooth variant (Stv), which was iso lated following a series of passages of the rugose cells, revealed extracel lular substances only in cells from the rugose colony. Observation of the e xtracellular substance by scanning electron microscopy (SEM) was correlated with the appearance of corrugation during development of rugose colony mor phology over a 4-day incubation period at 25 degreesC. In addition, the cel ls also formed a pellicle in liquid broth, which was associated with the ap pearance 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 extrace llular anionic component. The rugose cells, in contrast to Stv, showed resi stance to low pH and hydrogen peroxide and an ability to form biofilms. Bas ed 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. ente rica serovar Typhimurium DT104.