How effective are studies on novel antimicrobials?
The popular science press, media releases from research institutes and private companies and the formal scientific literature are filled with news about new antimicrobials. This is driven by the emergence of antibiotic resistance, partly because more natural and plant-based compounds are regarded by consumers and marketers as safer, and more recently by a general interest from the public as a result of the COVID-19 pandemic. Nowhere is the burgeoning of novel antimicrobials more apparent than in the food safety and preservation space. A glance through any of the formal or informal science outlets mentioned above will provide numerous examples of a novel plant extract or compound that has been tested against a few foodborne bacteria and now has the potential to revolutionize the industry. There is no doubt that many new antimicrobials have very strong potential and may provide a pathway to safer food or longer shelf-life, but how do we tell which ones? When we look at the literature how do we tell how good the study is? How do we do determine the potential for the new compound to translate into practical outcomes?
As a scientific editor, reviewer of papers and grants, and an experimentalist in this area, one of the key questions I ask is how reproducible is the work? If someone else were to do the same work on an extract from the same plant against a strain of the same bacterial species would they get the same result. If the answer is yes, we are well on our way to making sure that the potential has a chance (although many other hurdles loom) of becoming reality, if not we should go back to the experimental drawing board. The key to good reproducible data is being able to consider, or better measure, as much of the variability associated with the new antimicrobial and its proposed application as possible. So, for example, the questions to ask may be is the plant material being used analysed separately based on different locations, different times of year and different parts of the plant? Why? This is because these may result in different amounts of the compound of interest and the potential value of the work. Another question may be how many strains of a given foodborne bacterial pathogen, say Listeria monocytogenes, has the extract been tested against? Why? This is because different strains may be resistant to the antimicrobial and if only one is tested in a study we still do not know if most are resistant. A large number of studies on novel antimicrobials submitted and published in food science and food microbiology journals still only test the compound or extract against one strain and extrapolate to the species a whole. This is a problem which needs to be addressed. While it does not mean the antimicrobial is ineffective against the species of concern, it does mean we still do not know, and the work may not be reproducible.
What can be done to resolve this issue? Individual journals could have policies in place requiring papers to, for example, test antimicrobial treatments against multiple strains of the same bacteria or to test plant material sourced from different geographic locations. An alternative approach might be for broader guidelines to be developed, both by the scientific and also the industrial or regulatory community, to make sure studies of this sort are valid. The obvious solution at an individual level is to design good reproducible studies for the work in the first place. While it may cost a little more in terms of time and effort it will allow a smoother path through the scientific and regulatory processes should the antimicrobial have practical or commercial potential.
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