Abstract
Proteus mirabilis is a prevalent pathogen of the catheterised urinary tract, isolated in up to 44 % of catheter-associated urinary tract infections (CAUTIs). Infections with P. mirabilis are often complex as a result of crystalline biofilm formation which can occlude urine flow and result in catheter blockage. Infection control strategies to prevent CAUTI often include the use of biocides, such as chlorhexidine (CHD), however, numerous past studies have documented clinical isolates of P. mirabilis with reduced CHD susceptibility. In this study, we aimed to elucidate mechanisms of reduced CHD susceptibility in P. mirabilis, and investigate the clinical relevance of reduced CHD susceptibility in the CAUTI niche.Screening a mutant library of the previously high CHD minimum inhibitory concentration (MIC) P. mirabilis clinical strain RS47 revealed one stable mutant designated RS47-2 with an ~8 fold reduction in CHD susceptibility. Genotypic and phenotypic analysis of this mutant revealed the importance of intact LPS structure in a number of key aspects of P. mirabilis virulence, including motility, human serum evasion and crystalline biofilm formation. Additionally, complementation studies highlighted the important interplay between efflux and LPS structure in modulating susceptibility to cationic biocides in P. mirabilis.
In vitro bladder model assays were utilised to investigate the clinical relevance of reduced CHD susceptibility in clinical isolates of P. mirabilis as predicted by standard antimicrobial susceptibility testing (AST) techniques. No correlation was observed between AST assay results and survival, or time to block urinary catheters following treatment with a clinically relevant CHD containing product, the 1:5000 CHD Uro-Tainer® bladder irrigation solution, in the in vitro bladder model, suggesting that standard AST methods do not reliably predict the performance of CHD containing products.
A CHD adapted derivative of the low CHD MIC clinical strain RS50a, designated RS50aCHD10 was utilised to determine whether adaptation to CHD would impact virulence and CAUTI pathogenesis in P. mirabilis. Mutations in genes associated with cell envelope structure were not associated with any changes in fitness in a five-member polymicrobial in vitro bladder model community or a novel proposed Manduca sexta virulence model. However, these mutations were shown to reduce susceptibility to a wide range of cationic antimicrobials including biocides and polymyxin B, as well as human serum, highlighting the potential for CHD adaptation to impact P. mirabilis survival and pathogenesis in the CAUTI niche.
| Date of Award | 26 Jun 2024 |
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| Original language | English |
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| Supervisor | Brian Jones (Supervisor) & Susanne Gebhard (Supervisor) |