Controlling microbial biofilms using plant-based extracts and compounds
Microbial biofilms are simply defined as a community of microbes attached to a surface in a self-produced matrix. Biofilms are regarded as the main mode in which most microbes exist, and they occur everywhere microbes do. They enhance the survival and growth of microbes by acting as nutrient traps, enabling genetic exchange, and protecting their inhabitants from harsh environmental conditions including antimicrobials. While they are beneficial for microbes, and sometimes beneficial to humans, they are a substantial issue in many sectors including the food, health, and environmental, such a water and effluent, industries. Here they may act as reoccurring and often recalcitrant sources of spoilage organisms, pathogens, infections and damage to infrastructure.
Controlling or eliminating biofilms can be both labour intensive and costly. Strategies to do this frequently include the use of physical or chemical disruption followed by the application of biocides to the “freed” cells in the food and environmental industries. Similar approaches can be used for medical devices and in some biotic systems such as on teeth, with brushing followed by a mouth wash a good example. In other parts of the human body the use of antibiotics or other antimicrobials is a more frequent approach. With the emergence of antibiotic resistance and a move against the use of harsh and potentially environmentally damaging chemicals, alternative approaches to biofilm control are being developed and applied with success. Two of the most common alternative approaches used are the application of natural plant- or microbe-based extracts or compounds to disrupt biofilms without necessarily acting as a biocide, and the modification of surfaces at the micro- and nano-scale to prevent microbial attachment and growth. While we have worked in both these areas, here I will briefly discuss the former, leaving the latter to another post.
The use of plant-based extracts and compounds at concentrations which are non-lethal to microbes to control biofilms may sound like a fantasy. The truth is that this approach provides a range of elegant mechanisms of control based on biofilm biology without a number of the drawbacks associated with biocides. Specifically, it uses lower concentrations of often innocuous (to humans) compounds while avoiding the potential development of resistance, or of biofilms becoming latent and re-emerging later as an even bigger problem. The way these extracts and compounds work may vary substantially. They may, for example, interfere with the microbial surface attachment process or disrupt inter-microbe communication or enhance dispersal from the biofilm. We have, for example, recently shown how tea extracts modulate biofilm formation of oral bacterial pathogens by changing their surface hydrophobicity and ability to aggregate [1]. We have also demonstrated that betacyanin from dragon fruit can inhibit Staphylococcus aureus and Pseudomonas aeruginosa mixed biofilms [2] and shown that mangosteen extracts can inhibit Listeria monocytogenes adhesion to human intestinal cell lines due to it high proanthocyanidin content [3]. More broadly, we have extensively reviewed the literature on the use of natural compounds to control staphylococcal biofilms in health-related environments [4].
The diversity of naturally occurring compounds from plants and specific biofilm issues is such that a wide range of potential solutions to much particular problems is available. If you are a producer of plant-based products looking for new markets or you have a waste stream looking for a potential value-add or you are an industry with a biofilm problem looking for a more natural solution this is definitely a path worth exploring.
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