# A mouse model for studying chronic Salmonella Typhi infection and anti-biofilm interventions

## TL;DR

Researchers created a mouse model to study chronic Salmonella Typhi infection and test treatments for eliminating the carrier state.

## Contribution

A new murine model of chronic S. Typhi infection is established, enabling in vivo studies of the carrier state and anti-biofilm therapies.

## Key findings

- A murine model using CC003/Unc and CC053/Unc mice supports chronic S. Typhi infection in the gallbladder, liver, and spleen.
- Gallstone-associated biofilms contribute to chronic S. Typhi carriage and can be targeted by anti-biofilm compounds combined with ciprofloxacin.
- Male mice showed increased weight loss and lethality after infection, but no sex difference in bacterial load was observed.

## Abstract

Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), continues to cause significant human disease, especially in endemic regions. Chronic carriers of typhoid fever are a significant contributor to the perpetuation of disease in these communities, and treatments for elimination of the carrier state remain a challenge to clinicians and researchers. S. Typhi is host-restricted to humans and has been shown to be rapidly cleared by immunocompetent mice, which led to the use of S. enterica serovar Typhimurium infection of susceptible mice as a model for S. Typhi and typhoid fever. Thus, the lack of a direct murine model of S. Typhi infection has long been a challenge in the study of the mechanisms of typhoid fever and identification of therapeutics to treat the chronic carrier state. Here, we demonstrate the establishment of a murine model of chronic S. Typhi infection utilizing the immunocompetent Collaborative Cross mouse lines CC003/Unc and CC053/Unc, in which S. Typhi can be recovered in the gallbladder, liver, and spleen up to 21 days post-infection. Cholesterol gallstones foster enhanced S. Typhi gallbladder carriage. While there is no sex difference with regard to CFU recovered in the gallbladder at 21 days post-infection, male mice lost significantly more weight at early time points after infection and showed increased lethality. Bacterial aggregates (biofilms) were identified associated with the gallstone surface, consistent with observations in the S. Typhimurium gallstone mouse model of carriage and in human S. Typhi carriers. Additionally, we show that novel anti-biofilm compounds, in combination with ciprofloxacin, are able to reduce S. Typhi burden within the CC003/Unc gallbladder. Together, these findings support the role of gallstone biofilms in chronic typhoid fever and establish a new murine model that can be used to further interrogate the mechanisms of chronic typhoid fever utilizing the primary etiologic agent, S. Typhi.

Chronic typhoid fever, caused by persistent Salmonella Typhi infection, remains a significant public health concern in multiple regions throughout the world. There is currently no direct animal model utilizing S. Typhi that has been demonstrated to recapitulate the carrier state of typhoid fever. This lack of an animal model has precluded in vivo studies on the mechanisms of infection unique to this serovar. This study establishes and characterizes a new murine model of chronic S. Typhi carriage and demonstrates its utility with the identification of novel anti-biofilm compounds that disperse S. Typhi biofilms from gallbladder gallstones. This new model will provide a means for further studies into S. Typhi chronic infection.