Characterisation of temperature dependent biofilm formed by uropathogenic Escherichia coil in relation to catheter associated urinary tract infections

Abstract

Urinary tract infections (UTI) are extremely common with around half of all women experiencing at least one episode in their lifetime. Most UTIs are caused by uropathogenic Escherichia coli (UPEC). UTIs are the 7th leading cause of death in Singapore and are a major healthcare burden worldwide. Catheter associated UTIs (CAUTI) represent 80% of healthcare associated UTIs and are one of the few infections known definitively to be caused by biofilms. By existing in biofilms, UPEC are able to survive antibiotic treatment and evade the host immune response, complicating treatment and contributing to antibiotic resistance.

Previously, the pathogenesis of UTI and CAUTI were thought to overlap despite the latter being less extensively studied. The adhesins, type 1 pili, are essential for UPEC attachment, invasion and the subsequent formation of intracellular bacterial communities (IBCs). In vitro biofilm assays are commonly used as a model for attachment for both UTI and CAUTI. The standard biofilm assay, however, is performed at 25°C while the in vivo infection occurs at 37°C (a more physiologically relevant temperature). The aim of this thesis was to study and characterise differences in biofilm temperatures at clinically relevant temperatures, both phenotypically and genetically and to assess the relevance of this phenotype in vivo.

A switch in the mechanism of biofilm formation was shown at 37°C in vitro; biofilms grown at 25°C require type 1 pili, but those grown at 37°C do not. This type 1 pili independent biofilm formation at 37°C is shown to be relevant in an in vivo CAUTI model. The disparity in biofilm formation between 25°C and 37°C is relevant to the study of human CAUTI, as different sections of catheters are at different temperatures when they are in clinical use. This raises the possibility that UPEC are able to take advantage of a particular niche along the catheter and create a foothold for infection and that strains unable to cause standard uncomplicated UTI may be able to cause infection in the presence of a catheter.

In order to further characterise biofilm formation at 37°C and elucidate the mechanism behind type 1 pili independent biofilm formation, a high-throughput genomic screen was employed and revealed a potential role for several novel and previously established biofilm factors.

A clear understanding of the pathogenesis of CAUTI, and the models used to study it, will aid future investigations and the possible implementation of more effective interventions than are currently available for CAUTI.

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Identifiers

ORCID for Stuart Clarke: orcid.org/0000-0002-7009-1548

ORCID for Jeremy Webb: orcid.org/0000-0003-2068-8589

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