# NeuO-mediated O-acetylation of uropathogenic Escherichia coli K1 capsule enhances resistance to phage and neutrophil killing

## TL;DR

This study shows that O-acetylation of the K1 capsule in uropathogenic E. coli helps it resist phage and neutrophil attacks, but makes it more vulnerable to human serum.

## Contribution

The study reveals the role of phase-variable O-acetylation in enhancing UPEC survival against phage and neutrophils.

## Key findings

- NeuO-mediated O-acetylation increases resistance to lytic K1 phage and human neutrophils.
- O-acetylation increases susceptibility to human serum.
- The neuO gene is prevalent in the pandemic ST95 UPEC clone.

## Abstract

Uropathogenic Escherichia coli (UPEC) strains that express the K1 capsule are associated with severe invasive disease, including pyelonephritis, urosepsis, and neonatal meningitis. The K1 capsule can be modified by NeuO, a phage-encoded phase-variable O-acetyltransferase. The role of O-acetylation in pathogenesis of K1 UPEC remains to be fully elucidated. Here, we assessed the prevalence of the neuO gene in a K1 E. coli data set comprising 8,659 genomes and observed that 43.5% of genomes harbor neuO, with a high prevalence (88.1%) in the pandemic UPEC clone sequence type (ST) 95. We generated an isogenic ∆neuO mutant in the reference ST95 strain MS7163 and complemented this with a phase-ON locked version of the neuO gene, resulting in constitutive O-acetylation of the K1 capsule. The phase-variable rate of neuO in MS7163 was measured by fragment analysis at 93% phase-ON with 21 heptanucleotide repeats. NeuO acetylated the K1 sialic acid into O-acetylated forms, including Neu5,7Ac2, Neu5,8Ac2, and Neu5,9Ac2. We demonstrate that O-acetylation increased survival of K1 UPEC to lytic K1 phage and human neutrophils, yet increased susceptibility to human serum. O-acetylation of the K1 capsule did not influence bladder colonization in a murine model of urinary tract infection. Overall, we hypothesize that phase-variable O-acetylation is a niche-specific adaptive mechanism that enhances survival of UPEC in different ways, including protection against K1 phage and resistance to neutrophil-mediated killing.

The K1 polysialic acid capsule is a key virulence factor of uropathogenic Escherichia coli (UPEC). A subset of K1 UPEC possesses the phage-encoded phase-variable neuO gene, which mediates O-acetylation of the capsule. However, the prevalence, phase dynamics, and biological consequences of this modification remain to be fully elucidated. Here, we show that the neuO gene exhibits variable distribution among K1 UPEC, with a high prevalence in the global ST95 clone and evidence for active phase switching. We further demonstrate that K1 O-acetylation confers resistance to phage and neutrophil killing, suggesting a role associated with enhanced survival in infection and environmental settings.