Developing anti-plasmid compounds to combat drug resistant infections

Antibiotics underpin modern medicine, they are used to treat and prevent bacterial infections. Antibiotics are extremely important for people with reduced immune function such as the young, elderly, transplant recipients, HIV/AIDs and other viral infections, surgery and cancer patients. However, resistance to antibiotics is rapidly growing, reducing their effectiveness. Developing new antimicrobials has proven difficult. With few new classes of antibiotics introduced to the clinic since the 1980s. Therefore, preventing the spread of antibiotic resistance and finding ways to make bacteria susceptible to existing antibiotics are attractive strategies to maintain antibiotic effectiveness.

One reason for the antibiotic resistance crisis is that bacteria easily share genetic information. They can do this through different ways, including "plasmid transmission." Plasmids are pieces of genetic material that can move between bacterial cells. These plasmids often carry the genes needed to mediate their movement, or transmission, into new bacteria. They frequently carry resistance multiple different types of antibiotics; thus, bacteria can become resistant to multiple antibiotics in one step. This sharing of resistance plasmids frequently occurs in locations such as the gastrointestinal tract, and occurs on a global scale. For example, antibiotic resistance plasmids are often acquired by people travelling to different parts of the world, and can then be shared with family members upon return. Importantly, these antibiotic resistance genes often convey resistance to some of our last-line-of-defence antibiotics, which are essential in treating difficult infections.

Globally, huge quantities of antibiotics are used and misused in humans and animals. This exposes the normal bacteria within the gastrointestinal tract to antibiotics, and this encourages the spread of antibiotic resistance. This makes the gut a key location for these antibiotic resistance plasmids. We are only beginning to understand these real-world antibiotic resistance plasmids in the gut, beyond their DNA sequences and high prevalence.

My research aims to develop drugs that will remove antibiotic resistance plasmids from bacterial populations, such as the gut. This would make bacteria treatable using our existing antibiotics, and help to keep them sensitive to new antibiotics in the future. To accomplish this, I have already constructed a system that allows us to "watch" the movement of antibiotic resistance plasmids in bacteria using fluorescence. This system enabled us to look for already-approved drugs and plant-based compounds that reduce the prevalence of antibiotic resistance plasmids. From this we have identified drugs and compounds which effectively reduce plasmid prevalence in bacteria.

During this project we will determine which types of antibiotic resistance plasmids each drug/compound works on and how they work to reduce plasmid prevalence in bacteria. Understanding how they work is an important step in bringing new therapies to market. Drugs/compounds will be tested in models of gastrointestinal infection and inflammation. Using these models, we will measure plasmid movement and prevalence in the gut, and determine if the drugs/compounds are able to reduce antibiotic resistance. My research is based upon finding new ways to remove antibiotic resistance from bacteria found in the mammalian gastrointestinal tract. This could be applied to humans and animals to reduce the incidence of drug resistant bacterial infections.

Antimicrobial resistance (AMR) poses a threat to human and animal health. Developing and introducing new antimicrobials to the clinic has proven difficult, and resistance to new antimicrobials is highly likely. Therefore, new approaches are needed to reduce AMR prevalence. One reason AMR is increasing is that bacteria share plasmids, many of which are self-transmissible and can carry multiple resistance genes. The aim of this project is to characterise FDA-approved drugs and natural product compounds that inhibit the transmission/persistence of AMR plasmids.

I constructed a fluorescence-based reporter system using global AMR plasmids carrying extended spectrum beta-lactamase (blaCTX-M-14) and carbapenemase (blaKPC) genes, which confer resistance to some of our 'last line of defence' antibiotics. These plasmids are located in uropathogenic E. coli and K. pneumoniae, respectively. Using this system, I identified (a) non-antibiotic FDA approved drugs and (b) natural product compounds which inhibit plasmids. In this project, we will determine their range of activity by testing on clinical isolates containing AMR plasmids (UK and China). We will characterise their mechanism of action and determine how they inhibit transmission/persistence. We will then test them in an in vivo mouse model of gut inflammatory infection the natural mouse pathogen Citrobacter rodentium. This will enable us to determine compounds efficacy in vivo (by measuring both transmission/conjugation and persistence) and impact upon the microbiome.

This project will characterise new ways to reduce AMR plasmid prevalence in the intestine. Furthermore, it will broaden our understanding of the complex biology surrounding plasmid dynamics. In the long term, my research will contribute to understanding AMR transmission and reducing global AMR levels.