Understanding the diversity and evolution of complex wound infections

da Silva, Ana C. (2019) Understanding the diversity and evolution of complex wound infections. PhD thesis, University of Nottingham.

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Abstract

Chronic wounds (CW) are a common complication of diabetic ulcers (DUs), which are a major burden to health care systems worldwide and can result in lower limb amputation due to the intractability of the infection. DUs appear because of underlying causes such as peripheral neuropathy, peripheral vascular disease and trauma and often become colonized with multiple microbial species including Staphylococcus aureus and Pseudomonas aeruginosa. Such polymicrobial infections have been suggested to be more virulent, antibiotic resistant and result in worse patient outcomes but the reasons why remain unclear.

In a long-term infections such as DUs, there is a high probability of the infecting bacteria evolving considerable phenotypic and genetic diversity, as has previously been shown for chronic lung infections of cystic fibrosis patients. However, it is not known whether this is also the case for chronic DUs, and whether diversity and/or interactions between strains or species impacts on virulence and antibiotic resistance. To study this, bacterial populations were isolated from bone and soft tissue samples from five patients and six chronic wounds (CWs) from diabetic foot or leg ulcers. Initially phenotypic diversity was investigated in P. aeruginosa CW populations through the analysis of phenotypes traditionally associated with pathogenicity, and through a whole genome study.

Phenotypic variation in P. aeruginosa isolates taken from different patients was observed, but little variation within the same chronic wound (with exception of one patient with a diabetic leg ulcer). Antibiotic resistance was found to increase during the course of infection, and with the genomic analysis it became apparent that P. aeruginosa colonisation in a diabetic CW is via a single strain per ulcer, and potentially per patient, even though some sample-specific phenotypic profiles can arise from a homogenous population, as happened in one of the patients.

For this patient, two distinct phenotypic profiles were found, so a detailed genomic analysis between isolates was done, including a full characterisation of the single nucleotide polymorphisms and a comparison of their transcriptomes using RNAseq. The results suggest that the loss of flagellum due to a fliJ mutation facilitated evasion of the innate immune system, and blood isolates were able to go undetected and were able to spread systemically causing the rapid decline in the patient’s health.

Furthermore, S. aureus isolates from two of the CWs were used to investigate interactions between strains of both species that co-evolved in the same or different ulcers. We observed that S. aureus and P. aeruginosa strains isolated from the same wound can often co-exist when grown together in synthetic wound fluid. In contrast, when such strains were isolated from different wounds, P. aeruginosa often outcompeted S. aureus, possibly because of differences in alkyl quinolone levels. The data presented in this thesis furthers aids our understanding of how ecology influences the evolution of different species within wound infections and how this contributes to virulence and antibiotic resistance in polymicrobial infections.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Diggle, Stephen P.
Williams, Paul
Keywords: Chronic wounds; Diabetic ulcers; Polymicrobial infections; Phenotypic diversity; Wound infections
Subjects: R Medicine > RC Internal medicine
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 56950
Depositing User: Da Silva, Ana
Date Deposited: 26 Apr 2022 09:01
Last Modified: 26 Apr 2022 09:02
URI: http://eprints.nottingham.ac.uk/id/eprint/56950

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