Aversion Therapy for Bacteria: Repurposing Aurodox

Antibiotics have been used for many years and are central to the treatment of many common bacterial infections. However, because antibiotics kill bacteria, there is a strong selection for mutants, slightly different from the parental type of bacteria, which are not killed: a new resistant form. These resistant cases of bacteria that are no longer susceptible to common antibiotics means that there is a great need for new alternative forms of treatment. Of all the bacteria that causes problems, the gram negative family are the hardest treat because they rapidly develop resistance. One possibility is to render the disease-causing bacteria less dangerous by turning off their offensive weapons. Compounds that "turn off' bacterial weapons are called "anti-virulence" compounds because they don't try to kill the bug, they just render them less dangerous. Imagine taking an army and removing all its key weapons- it's a lot less effective. Using anti-virulence factors is attractive for the following reasons:

(1) Anti-virulence compounds "disarm" bacteria rather than killing them, generating less selection for resistant mutants.

(2) Secondary infections associated with antibiotic treatment such as those caused by Clostridium difficile and Candida albicans should also be dramatically reduced as natural "good" bacteria are not wiped out during treatment.

(3) For toxin-producing bacteria treatment with traditional antibiotics is controversial, with some reports of increased release of toxins and more severe symptoms. By not killing the bacteria, toxin release is avoided.

My lab has been developing and testing new anti-virulence compounds and working out how they function. We "re-discovered" a compound that is safe for animals, called aurodox which was actually found in the early 1970s from other bacteria that live in the soil. When we use aurodox with bacteria that cause serious diseases, specifically the infamous "burger bug" "E. coli O157" we are able to switch off the major weapon the bacteria use to attach to host cells. In effect we are just switching off the anchor used to attach to the gut, which should ensure the bacteria are simply flushed out of the body. In this work we want to show that aurodox can prevent or treat disease and also work out exactly how it works. We also want to see if aurodox has any negative effects on the "good" bacteria in our guts. Answering these questions would pave the way to use aurodox as the first treatment against EHEC and, more widely, show that anti-virulence approaches are a viable alternative to traditional antibiotics.

There is an urgent need to develop new strategies to combat infectious disease against the background of the antimicrobial resistant (AMR) infection crisis. The World Health Organisation (WHO) has identified AMR as one of the greatest threats to global human health and we need to develop new strategies to reduce our reliance on antibiotics. The UK government has produced a five-year strategy to address AMR. In the UK, 17% of Escherichia coli strains isolated in 2009 could be categorized as multi-drug resistant (MDR), that is, resistant to at least three categories of antimicrobials. Moreover, frequently overlooked is the additional problem that some bacterial strains carry potent toxins which further complicates possible treatment with antibiotics. Enterohaemorrhagic E. coli (EHEC) strains carry Shiga toxins that are located on temperate phages. Expression of phage genes occurs when the phage lytic cycle is activated by induction of the SOS response, hence antibiotics are not recommended during these infections.

We are interested in developing ways to efficiently and selectively "switch off" virulence factors central for pathogenesis. Recently we were able to add mechanistic insight to the work of Kimura et al who had shown that aurodox, a specialised metabolite produced by Streptomyces goldiniensis, blocks pathogenesis of the murine pathogen C. rodentium. We demonstrated that aurodox is able to down regulate the type III secretion system (T3SS) in EHEC. In this proposal, we will determine whether aurodox can prevent and treat infections with bacterial strains carrying the Shiga toxin, study the effect aurodox has on the host microbiome and the potential of strains to develop resistance to the compound. We will also exploit the fact we have cloned the entire aurodox biosynthetic cluster, to facilitate the generation of new derivates of aurodox. Our final aim will be to identify the specific target proteins bound by aurodox.