Determining how polymyxins kill bacteria
Lead Research Organisation:
Imperial College London
Department Name: Infectious Disease
Abstract
Bacteria cause many different infections, which can rapidly progress from mild to life-threatening. Ordinarily, a short course of antibiotics is sufficient to clear the infection. However, an increasing number of infections are caused by bacteria that can resist many different types of antibiotics. The World Health Organisation has determined that the most worrying types of resistant bacteria are all Gram-negative, which have an outer cell envelope that consists of two lipid membranes separated by a cell wall. These bacteria are resistant to many different classes of antibiotics, including those known as beta-lactams, which are the most commonly used antibiotics globally.
One type of antibiotic that many bacteria are still susceptible to are the polymyxins, of which two are used clinically, polymyxin B and polymyxin E (more commonly known as colistin). Unfortunately, polymyxins don't work as well as other antibiotics and often damage the patient's kidneys. Furthermore, resistance to polymyxins is an ever-increasing problem. This is partly due to increased use of these drugs and also because a type of polymyxin resistance known as MCR can spread between bacteria.
Polymyxins damage the outer membrane by targeting a chemical called LPS on the surface of bacteria. Work from our group revealed that polymyxins also damage the inner membrane by targeting LPS and that this damage is required to kill bacteria. However, the reasons why polymyxin targeting of LPS in the inner membrane causes damage is unclear and will be resolved in this proposal.
Having determined how polymyxins kill bacteria, we will then investigate how polymyxin resistance protects bacteria from this class of antibiotics, as well as the costs associated with resistance.
Finally, we have discovered that an experimental antibiotic called murepavadin can make bacteria very sensitive to killing by polymyxins, including strains that are polymyxin resistant. By understanding how this happens, we can devise strategies to reverse polymyxin resistance.
Combined, this project will provide insight into how polymyxins kill bacteria, how polymyxin resistance functions and how polymyxin resistance can be reversed.
One type of antibiotic that many bacteria are still susceptible to are the polymyxins, of which two are used clinically, polymyxin B and polymyxin E (more commonly known as colistin). Unfortunately, polymyxins don't work as well as other antibiotics and often damage the patient's kidneys. Furthermore, resistance to polymyxins is an ever-increasing problem. This is partly due to increased use of these drugs and also because a type of polymyxin resistance known as MCR can spread between bacteria.
Polymyxins damage the outer membrane by targeting a chemical called LPS on the surface of bacteria. Work from our group revealed that polymyxins also damage the inner membrane by targeting LPS and that this damage is required to kill bacteria. However, the reasons why polymyxin targeting of LPS in the inner membrane causes damage is unclear and will be resolved in this proposal.
Having determined how polymyxins kill bacteria, we will then investigate how polymyxin resistance protects bacteria from this class of antibiotics, as well as the costs associated with resistance.
Finally, we have discovered that an experimental antibiotic called murepavadin can make bacteria very sensitive to killing by polymyxins, including strains that are polymyxin resistant. By understanding how this happens, we can devise strategies to reverse polymyxin resistance.
Combined, this project will provide insight into how polymyxins kill bacteria, how polymyxin resistance functions and how polymyxin resistance can be reversed.
Technical Summary
Polymyxins have been designated as 'highest priority critically important antimicrobials for human medicine' by the World Health Organisation. It is well established that polymyxins target LPS in the outer membrane of Gram-negative bacteria, leading to membrane permeabilization. However, the mechanism by which this leads to bacterial killing is poorly understood.
We have recently taken a big step towards understanding polymyxin mode of action by showing that, after disrupting the outer membrane, these antibiotics damage the inner membrane by targeting LPS as it is trafficked to the outer membrane, and that this damage was required for bacterial killing. Crucially, manipulation of LPS abundance in the inner membrane modulated polymyxin efficacy, including against polymyxin resistant strains. However, the nature of the membrane disruption and the mechanism by which it occurred remains unclear. We have also shown that for E. coli, acquired polymyxin resistance protects the inner but not outer membrane from damage mediated by the antibiotics.
Therefore, the aim of this proposal is to exploit our recent discoveries to fully elucidate the mechanism by which polymyxins disrupt membranes and kill bacteria and determine how polymyxin resistance can be overcome therapeutically.
We will determine how polymyxin interactions with LPS in the inner membrane damages this structure. We will focus on E. coli and P. aeruginosa since infections caused by these bacteria may be treated with polymyxins, they were used to generate the preliminary data and they have well understood, but distinct mechanisms that regulate LPS synthesis. We will then determine how polymyxin resistance mediated by mobile colistin resistance (mcr) functions and how bacteria balance resistance and fitness costs. Finally, we will build on promising preliminary studies with P. aeruginosa to determine how polymyxin resistance can be reversed.
We have recently taken a big step towards understanding polymyxin mode of action by showing that, after disrupting the outer membrane, these antibiotics damage the inner membrane by targeting LPS as it is trafficked to the outer membrane, and that this damage was required for bacterial killing. Crucially, manipulation of LPS abundance in the inner membrane modulated polymyxin efficacy, including against polymyxin resistant strains. However, the nature of the membrane disruption and the mechanism by which it occurred remains unclear. We have also shown that for E. coli, acquired polymyxin resistance protects the inner but not outer membrane from damage mediated by the antibiotics.
Therefore, the aim of this proposal is to exploit our recent discoveries to fully elucidate the mechanism by which polymyxins disrupt membranes and kill bacteria and determine how polymyxin resistance can be overcome therapeutically.
We will determine how polymyxin interactions with LPS in the inner membrane damages this structure. We will focus on E. coli and P. aeruginosa since infections caused by these bacteria may be treated with polymyxins, they were used to generate the preliminary data and they have well understood, but distinct mechanisms that regulate LPS synthesis. We will then determine how polymyxin resistance mediated by mobile colistin resistance (mcr) functions and how bacteria balance resistance and fitness costs. Finally, we will build on promising preliminary studies with P. aeruginosa to determine how polymyxin resistance can be reversed.