Affordable and accessible sequencing technologies have ushered in an unprecedented age for infectious disease surveillance, requiring new tools to harness these data. The population genetic statistic Fu’s Fs has previously identified the gene porA as a locus of interest after experimental studies showed that a mutation in porA was necessary and sufficient for an expansion-associated phenotype in Campylobacter jejuni. In this project, I utilised Fu’s Fs to identify loci carrying signals of positive selection in Escherichia coli ST131-C, a rapidly expanding clone associated with antibiotic resistance.
These loci include a gene regulating a well described efflux pump, a sigma-54 transcriptional activator, and various yersiniabactin genes. The efflux regulator's mutational profile stands out as atypical, and is closely tied to the expanding clades within ST131. There does not appear to be a particular “beneficial” mutation within this gene, but rather continued evolutionary pressure for it to accumulate premature stop codons and frameshifts.
This project has verified that Fu’s Fs can identify genetic loci that appear to be under selection, or evolving in a manner consistent with driving a population expansion. It may be useful as a complementary and easily generalizable method to prioritize specific genes, particularly in the case of emerging phenotypes like virulence, for further experimental validation.