"Outsmarting superbugs?"
Professor Liz Harry, Professor of Biology, School of Medical and Molecular Sciences, University of Technology Sydney
Wednesday 3 October 2012 at 6.30 pm
Union, University and Schools Club, 25 Bent Street, Sydney
Meeting report by James Kehoe and Jude Allen
Bacterial infections have become increasingly resistant to current antibiotics. The ability of bacteria to adapt rapidly to their environments, including the presence of antibiotics, is outstripping our ability to discover and refine novel agents. Bacterial infections have become increasingly resistant to current antibiotics. The ability of bacteria to adapt rapidly to their environments, including the presence of antibiotics, is outstripping our ability to discover and refine novel agents.
At the 1204th OGM, Professor Liz Harry of the University of Technology Sydney delivered a lively and informative talk concerning the role of bacteria in our lives, the mechanisms by which they adapt, and tests of alternative methods for defeating them without producing resistant strains.
Prof. Harry first provided an overview of bacteria, particularly their prevalence in nearly every possible habitat on Earth. Nearly every surface – large or small – is covered by bacteria, as either free-living individual cells or in multicellular aggregates embedded in a self-produced extracellular polymeric substance, known more colloquially as "slime". These biofilms can be particularly resistant to antibiotics.
In both these forms, bacteria constitute a total biomass that exceeds that of all plants and animals, even though an individual bacterium is typically a few micrometres length. Within human bodies bacteria, living most notably on our skin, in our digestive tracts, and in our respiratory tracts, outnumber human cells, possibly by a factor of ten. Prof. Harry quipped that we are more bacterium than human. Commercial advertisements often paint bacteria as agents of disease that must be eradicated, preferably by the advertiser's product. In fact, the bulk of bacteria in and around humans are harmless or long-ago neutralised by our immune system. An attempt eradicate all bacteria from humans, apart from being futile, is likely to provide an opening for invasion by dangerous species. According to Prof Harry, ordinary cleanliness, especially hand-washing, is sufficient to wash away invaders while retaining our familiar and possibly protective bacteria. The ability of bacteria to adapt rapidly to new antibiotics is enhanced by the multiple ways by which they can introduce genetic variation. On the one hand, the most familiar form of bacterial reproduction is asexual cell division. Through this mechanism, bacteria can proliferate at astonishing rates, but evolution through cell division would have to rely entirely on random mutation to produce variation, which would leave bacteria largely open to attack by antibiotics.
On the other hand, bacteria readily recombine genetic material by a variety of methods, which include:
- Conjugation, sometimes called "bacterial sex," in which DNA is passed from one bacterium to another by a tube called a pilus.
- Transformation, in which bacteria incorporate DNA floating in their environment, often originating from dead bacterial cells.
- Transduction, in which bacteria exchange DNA via viral infection and reproduction.
Notwithstanding attempts to identify new antibiotic agents, bacteria seem to have the upper hand through rapid adaptation to any single agent. The best strategy appears to be a combined approach, in which a diversity of agents simultaneously attack different pathways and structures in bacteria, thus flooding their adaptive capability. Rather than trying to synthesize a joint agent, one answer may already be available in the form of honey, which has long been a traditional remedy for a variety of conditions and injuries. Prof. Harry showed photographs of a case in which honey-impregnated dressings helped to heal infected skin ulcerations that had resisted other antibiotic treatments.
Prof. Harry and her colleagues have been experimentally testing the ability of honey to serve as a topical antibiotic. Honey appears to have a general antibiotic property that allows it to be safely stored by bees and on our kitchen shelves for extended periods. Some honeys seem to possess strong antibacterial properties, including a variety from New Zealand. The unique factor appears to arise from the nectar of certain plants; in Prof. Harry's case, it is the Manuka plant. Prof. Harry suspects that the antibacterial properties of honey rely on the joint effect of a host of factors contained in the honey.
Prof. Harry concluded that, thanks to the effectiveness of antibiotics, modern society has become a bit blasé about basic cleanliness and too reliant on expecting a quick fix. At the same time, research on antibacterial agents of all varieties has languished, because effective antibiotics, which are commonly used for brief periods of time for acute conditions, are relatively unprofitable compared to drugs for managing chronic conditions, for example, hypertension.