Juan F González Baileigh Laipply Victoria A Sadowski Matthew Price John S Gunn ^*

• Abigail Wexner Research Institute, Nationwide Children's Hospital, Columbus, United States

Typhoid fever is an infectious disease primarily caused by Salmonella enterica sv. Typhi (S. Typhi), a bacterium that causes as many as 20 million infections and 600,000 deaths annually. Asymptomatic chronic carriers of S. Typhi play a major role in the transmission of typhoid fever, as they intermittently shed the bacteria and can unknowingly infect humans in close proximity. An estimated 90% of chronic carriers have gallstones; biofilm formation on gallstones is a primary factor in the establishment and maintenance of gallbladder carriage. CsgD is a central biofilm regulator in Salmonella, but the S. Typhi csgD gene has a mutation that introduces an early stop codon, resulting in a protein truncated by 8 amino acids at the C-terminus. In this study, we investigate the role of role of CsgD in S. Typhi. We introduced a fully functional copy of the csgD gene from S. Typhimurium into S. Typhi under both a native and a constitutive promoter. We demonstrate that although CsgD-regulated curli and cellulose production were partially restored, the introduction of the S. Typhimurium csgD did not induce the red, dry and rough (Rdar) colony morphology. Interestingly, we show that CsgD does not have a significant role in S. Typhi biofilm formation, as biofilm-forming capacities depend more on the isolate than the CsgD regulator. This data suggests the presence of an alternative biofilm regulatory process in this human-restricted pathogen.