SalmonellaTyphi Haplotype 58 (H58) Biofilm Formation and Genetic Variation in Typhoid Fever Patients with Gallstones in an Endemic Setting in Kenya

Abstract

The causative agent of typhoid fever,Salmonella entericaserovar Typhi, is a human restricted pathogen. Human carriers, 90% of whom have gallstones in their gallbladder, continue to shed the pathogen after treatment. The genetic mechanisms involved in establishing the carrier state are poorly understood, butS. Typhi is thought to undergo specific genetic changes within the gallbladder as an adaptive mechanism. In the current study, we aimed to identify biofilm forming ability and the genetic differences in longitudinal clinicalS. Typhi isolates from asymptomatic carriers with gallstones in Nairobi, Kenya. Whole genome sequences were analyzed from 22S. Typhi isolates, 20 from stool and 2 from blood samples, all genotype 4.3.1 (H58). Nineteen strains were from four patients also diagnosed with gallstones, of whom, three had typhoid symptoms and continued to shedS. Typhi after treatment. All isolates had point mutations in the quinolone resistance determining region (QRDR) and only sub-lineage 4.3.1.2EA3 encoded multidrug resistance genes. There was no variation in antimicrobial resistance patterns among strains from the same patient/household. Non-multidrug resistant (MDR), isolates formed significantly stronger biofilmsin vitrothan the MDR isolates, p<0.001. A point mutation within thetreBgene (treBA383T) was observed in strains isolated after clinical resolution from patients living in 75% of the households. Missense mutations in Vi capsular polysaccharide genes,tviEP263S was also observed in 18% of the isolates. This study provides insights into the role of typhoid carriage, biofilm formation, AMR genes and genetic variations inS.Typhi from asymptomatic carriers.ImportanceAlthough typhoid fever has largely been eliminated in high income countries, it remains a major global public health concern especially among low- and middle-income countries. The bacteria responsible for this infectious disease,SalmonellaTyphi, has limited ability to replicate outside the human host and human carriers serve as a reservoir of infection. Typhoid is a common infection in parts of sub-Saharan Africa and Asia, and is endemic in our study setting. Our research findings on differences inS.Typhi strains causing typhoid fever and carriage will influence public health approaches aimed at reducing carriage and transmission ofS. Typhi.