ABSTRACT
Vibrio cholerae can cause a range of symptoms in infected patients, ranging from severe diarrhea to asymptomatic infection. Previous studies using whole genome sequencing (WGS) of multiple bacterial isolates per patient have shown that Vibrio cholerae can evolve a modest amount of genetic diversity during symptomatic infection. Little is known about V. cholerae genetic diversity within asymptomatic infected patients. To achieve increased resolution in the detection of Vibrio cholerae diversity within individual infections, we applied culture-based population genomics and metagenomics to a cohort of symptomatic and asymptomatic cholera patients. While the metagenomic approach allowed us to detect more mutations in symptomatic patients compared to the culture-based approach, WGS of isolates was still necessary to detect V. cholerae diversity in asymptomatic carriers, likely due to their low Vibrio cholerae load. We found that symptomatic and asymptomatic patients contain similar levels of within-patient diversity, and discovered V. cholerae hypermutators in some patients. While hypermutators appeared to generate mostly selectively neutral mutations, non-mutators showed signs of convergent mutation across multiple patients, suggesting V. cholerae adaptation within hosts. Our results highlight the power of metagenomics combined with isolate sequencing to characterize within-patient diversity in acute V. cholerae infection and asymptomatic infection, while providing evidence for hypermutator phenotypes within cholera patients.
IMPORTANCE Pathogen evolution within patients can impact phenotypes such as drug resistance and virulence, potentially affecting clinical outcomes. V. cholerae infection can result in life-threatening diarrheal disease, or asymptomatic infection. Here we describe whole-genome sequencing of V. cholerae isolates and culture-free metagenomic sequencing from stool of symptomatic cholera patients and asymptomatic carriers. Despite the acuteness of cholera infections, we found evidence for adaptive mutations in the V. cholerae genome that occur independently and repeatedly within multiple symptomatic patients. We also identified V. cholerae hypermutator phenotypes within 6 out of 14 patients, which appear to generate mainly neutral or deleterious mutations. Our work sets the stage for future studies of the role of hypermutators and within-patient evolution in explaining the variation from asymptomatic carriage to symptomatic cholera.
Competing Interest Statement
The authors have declared no competing interest.
