Do uropathogenic E. coli require changes before it can spread into the bloodstream?

Uropathogenic Eschericha coli are the leading cause of urinary tract infections (UTIs). The microbe can spread from bladder to kidney and finally to blood. We wished to determine whether genetic changes accompany the passage of these infections from urine to blood.

12 paired urine and blood samples were collected from patients in Greater Glasgow and Clyde; the interval between sample collection time between pairs was less than 48 h. Whole genomic sequencing of these paired samples was performed using the Illumina MiSeq platform. De novoassembly of reads was carried out using Shovill assembler; whereas SNPs were identified using SMALT, VarScan and Gubbins tools.

Urine and blood samples in each pair had the same MLST type. Surprisingly, however, there were multiple differences in the presence of plasmid genes, phage elements and insertion sequences within pairs, as well as numerous SNPs. For example, the mercury reductase merAgene and mercuric transport protein merPhave been acquired in a plasmid of a blood isolate compared to the contemporaneous urine sample. We also identified missense mutations in genes involved in several metabolic pathways in bloodstream isolates. Several of the observed gene deletions/insertions and SNPs were found in more than one of the paired blood and urine isolates.

The observed sequence differences between contemporaneous blood and urine isolates suggests that genomic differences accumulate within the urinary bladder prior to blood stream invasion. The observed blood stream variants may thus possess a selective advantage in invasion and/or survival within blood.