J Bacteriol 2019 Apr 8. Epub 2019 Apr 8.
Department of Microbial Infection and Immunity, The Ohio State University College of Medicine, Columbus, Ohio, USA.
Typhoid fever, a human-specific disease, is primarily caused by the pathogen serovar Typhi ( Typhi). It is estimated that 3-5% of people infected with typhoid fever become chronic carriers. Studies have demonstrated that a mechanism of chronic carriage involves biofilm formation on gallstone surfaces. In the course of a previous study using a chronic carriage mouse model, a Typhimurium isolate was recovered from a mouse gallstone that exhibited a 2-fold increase in biofilm formation over the wild type. In order to identify the gene(s) responsible for the phenotype, the genomic sequence of this isolate and others were determined and compared. These sequences identified SNPs in 14 genes. Mutations in the most promising candidates, and were created but neither showed increased biofilm-forming ability separately or in combination. The hyper-biofilm isolate did however, present variations in cellular appendages observable using different techniques and a preferential binding to cholesterol. The isolate was also examined for systemic virulence and the ability to colonize the gallbladder/gallstones in a mouse model of chronic infection, demonstrating a systemic virulence defect and Finally, to determine if the appearance of hyper-biofilm isolates could be replicated and if this was a common event, wild type was grown long-term in gallbladder-mimicking conditions, resulting in a high proportion of isolates that replicated the hyper-biofilm phenotype of the original isolate. Thus, acquire random mutations in the gallbladder/gallbladder-simulating conditions that may aid persistence but negatively affect systemic virulence.Chronic carriers are the main reservoirs for the spread of typhoid fever in endemic regions. Typhi forms biofilms on gallstones in order to persist. A strain with enhanced biofilm-forming ability was recovered after a nine-month chronic carriage mouse study. After sequencing this strain and recreating some of the mutations we could not duplicate the phenotype. The isolate did show a difference in flagella, a preference to bind to cholesterol and a systemic virulence defect. Finally, gallbladder conditions were simulated After 60 days, there was a 4.5-fold increase in hyper-biofilm isolates when a gallstone was present. These results indicate that can undergo genetic changes that improve persistence in gallbladder albeit at the cost of decreased virulence.