April 22, 2022

expert reaction to conference abstract looking at organic vegetables and microbes

A conference abstract presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) Annual Meeting looks at microbes present in organic vegetables.

Dr Matthew Child, Group Leader (chemical microbiology), Wellcome Trust & Royal Society Sir Henry Dale Fellow, Imperial College London, said:

“While potentially interesting, this is extremely preliminary.  It also raises interesting questions about how the human gut responds to the amoeba-resident bacteria, as opposed to those same free-living bacteria outside of the trojan horse – for instance, do those bacteria ever manage to escape their trojan horse amoeba?  It’s also important to remember that just because a pathogen can cause disease, it does not mean that it always does.  As for chemicals and drugs, in relation to pathogen expose the adage remains true; the dose makes the poison.

Does the press release accurately reflect the science?

“In its current form, there is no evidence in the abstract of controls and no details provided concerning their experimental methods.  Unfortunately, this means that these data cannot be fairly interpreted in their current state.  Therefore in my view because the data are preliminary the press release is over-reaching in its conclusions.

Is there enough data available to be able to assess the robustness; is this a peer-reviewed paper or more preliminary?

“It’s important to recognise that these data have not been peer-reviewed – the press release states that “All accepted abstracts have been extensively peer reviewed by the congress selection committee” – this is abstract selection based on interest to the community at the conference, and in no way represents the formal process of peer review.

Is this good quality research?  Are the conclusions backed up by solid data?

“In this preliminary form the quality of the research cannot be fairly judged as insufficient data are provided.  There is no evidence of experimental controls and an absence of any details of their methodology that would support interpretation of the data.

How does this work fit with the existing evidence?

“Without additional data from experimental controls it is impossible to tell.  As the work is currently presented, the authors effectively sampled the environment and identified (using an extremely sensitive approach) the presence of DNA that they attribute to a pathogen.  No data is provided to say whether these pathogens are alive or dead – i.e. are they even infectious?

Have the authors accounted for confounders?  Are there important limitations to be aware of?

“No controls – are these pathogens alive or dead?  Are they infectious?  How do non-organic vegetables compare?  Arguably the impact of these pathogens must be negligible – from the press release: “Acanthamoeba castellanii, that can cause blindness and encephalitis were identified in almost two thirds (63%) of samples” – if these pathogens were a serious cause of infection, the associated pathologies would be significantly more common.

What are the implications in the real world?  Is there any overspeculation?

“In my view there is significant overspeculation, predominantly in the press release – the poster and abstract don’t push the somewhat over-reaching interpretation of their findings (which cannot be interpreted with any scientific rigour).”

Prof John Fawell, Visiting Professor at the Cranfield University Water Institute, Cranfield University, said:

“I don’t believe this abstract provides strong evidence of public health risk.  Legionella is a concern but only through inhalation of aerosols.  However, the authors do make an important point and that relates to teaching consumers the way to ensure food hygiene when using fresh vegetables.  The free living amoebae and the ability of some pathogens to protect themselves and multiply is well known, Legionella being a very good example but in water systems, such as air conditioning.  It is useful to obtain data on how frequently these organisms are found on fresh vegetables that are eaten raw and also what domestic preparation can ensure their removal.  The risks of such pathogens are not well characterised and may be small but having good scientific data to inform risk assessment and processing requirements is important – we need better and more systematic data to show how big a problem this is and to take steps to minimise any risks.  Some of the steps would be sensible anyway but simply presence does not necessarily equate to significant risk.  A hazard has been demonstrated, the next stage is to assess how big a risk this poses to consumers and what steps they should take to mitigate that risk.  It’s difficult to judge how robust this study is without a paper.”

Prof Willem van Schaik, Director of the Institute of Microbiology and Infection and Professor of Microbiology and Infection, University of Birmingham, said:

“As vegetables are grown on soil, it is almost unavoidable that organisms from soil (or water that is used for irrigation) are present on leafy greens and this includes amoeba discussed in the abstract of this study.  These organisms are very widespread in the environment and are extremely rare causes of disease in humans.  The results reported here are generally plausible, with the caveat that technical details are lacking in this abstract, so it is difficult to assess whether the technical approach used is entirely valid and whether potential issues with contamination of samples during handling in the laboratory have been sufficiently controlled for.

“In summary, the observations reported here are somewhat unsurprising, but are not unique to organic vegetables as is suggested here.  It is good to read that the researchers have highlighted the advice that all leafy greens should be washed before use, which will greatly reduce the risk of food-borne infections.”

Prof Ian Poxton, Professor of Medical Microbiology, University of Edinburgh, said:

“What’s new about this?  It has long been recognised that vegetables coming out of the soil, especially those coming from manured soil, are likely to be contaminated with faecal microorganisms.  E. coli O157 is a classic example.

“It’s hard to comment on the robustness of the study because there are so few details.”

Abstract title: ‘Microbiome of free-living amoebae (FLA) present in organic vegetables: a potential risk to public health?’ by Y. Moreno et al. is being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) Annual Meeting in Lisbon.

There is no paper.

Declared interests

Prof Willem van Schaik: “I have no conflicts of interests to declare.”

Prof Ian Poxton: “No conflicts of interest.”

No others received.