Clinical Gastroenterology: Investigation of Fidaxomicin Resistance Mechanisms in Clostridium difficile

Clostridium difficile is a leading pathogen in healthcare-associated diarrheal infections. C. difficile has a plastic genome with multiple mobile genetic elements and recognized capacity to acquire genes involved in resistance and virulence. Antibiotic treatment is a major risk factor for C. difficile infection (CDI), with resistance to multiple antibiotics becoming frequent in newly emergent strains. CDI antibiotic treatment is currently limited to vancomycin and fidaxomicin, with the later showing high CDI resolution rates and reduced risk of recurrent infection1. Fidaxomicin is the first new antimicrobial agent licensed for use in CDI treatment for 30 years. This antibiotic can persist in the faeces for ~3 weeks following the cessation of dosing, and does not necessarily lead to eradication of C. difficile spores in patients. Furthermore, a recent novel extended dosage of fidaxomicin has been trialled, which involves a 25 day administration period (as opposed to the current standard 10 day regimen). Thus, there is a potential for C. difficile exposure to the antibiotic for ~9 weeks, increasing the risk of resistance emergence. We need to understand why resistance may develop in clinical C. difficile strains and what the potential implications are for clinical treatment of the disease.  

Clinical strains with increased minimum inhibitory concentration (MIC) consistent with in vitro resistance or reduced susceptibility to fidaxomicin are emerging. In a pan-European surveillance study1, we identified one isolate showing and MIC of >4 mg/L to fidaxomicin, with one further isolate showing an MIC of 0.5 mg/L. Laboratory selection assays have implicated the RNA polymerase gene rpoB, and a transcriptional regulator gene marR, in fidaxomicin resistance in vitro2. However, it is unknown whether the same mechanisms occur in vivo, and their clinical implications in the treatment of CDI remain unclear. This project will investigate fidaxomicin resistance in clinical C. difficile isolates, assessing the stability of fidaxomicin resistance using MIC assays, and will use whole-genome sequencing to identify potential gene mutations associated with the high MIC phenotype. The student will also create mutants in fidaxomicin susceptible C. difficile strains for the genes of interest rpoB, marR and others possibly identified by the whole-genome sequencing analysis, and study the resulting phenotype. Mutations in multidrug efflux transporters can confer increased tolerance to macrocyclic antibiotics in other microorganisms. By over-expressing these systems in fidaxomicin susceptible strains, we will be able to infer other mechanisms or stress responses that may occur in C. difficile down the line. The fitness cost of these mutations regarding toxin production, sporulation and competitive growth will also be investigated.  

In order to understand the clinical implications of fidaxomicin resistance, the student will use a clinically reflective chemostat model of the human colon, developed by the HCAI group3. This model accurately represents the human gut microbiota and has been used in multiple studies resulting in >30 publications, helping define the UK prescribing regulations for CDI. Fidaxomicin resistant C. difficile strains will be inoculated in this model to investigate their potential to cause CDI in presence of drug concentrations equivalent to those found in the human colon. 

Techniques associated with project:

Bacterial culture and microbial identification, MIC determination, whole-genome sequencing analysis, genetic modification of class II microorganisms, assembly and use of a chemostat model. 

This project is available as part of the International PhD Academy: Medical Research

Eligibility:

You should hold a first degree equivalent to at least a UK upper second class honours degree in a relevant subject.

Candidates whose first language is not English must provide evidence that their English language is sufficient to meet the specific demands of their study. The Faculty of Medicine and Health minimum requirements are:

• British Council IELTS - score of 7.0 overall, with no element less than 6.5
• TOEFL iBT - overall score of 100 with the listening and reading element no less than 22, writing element no less than 23 and the speaking element no less than 24.

How to apply:

Applications can be made at any time. To apply for this project applicants should complete an online application form and attach the following documentation to support their application. 

• a full academic CV
• degree certificate and transcripts of marks
• Evidence that you meet the University's minimum English language requirements (if applicable)

To help us identify that you are applying for this project please ensure you provide the following information on your application form;

• Select PhD in Medicine, Health and Human Disease as your programme of study
• Give the full project title and name the supervisors listed in this advert

Any queries regarding the application process should be directed to fmhpgradmissions@leeds.ac.uk