A fascinating Italian/Belgian multicentre study introduces us to the idea of “biocontrol” for problematic surface contamination. They test using “live” cleaning products that deliberately seed hospital surfaces with Bacillus species spores in an attempt to reduce the ecological space for pathogenic microbes through a “competitive exclusion” approach. Ridiculous as it sounds, there’s some logic to this idea. We’re just beginning to understand the potential of complementing a depleted microbiome in human health, so perhaps the same theory goes for the “environmentome”?
The study design is on the one hand impressive and ambitious, with more than 20,000 surfaces samples collected from the three hospitals. However, it is also messy and confusing, with different intervention and sampling protocols in the three hospitals. In particular, it’s a real shame that areas were not randomized to receive the “live” vs. conventional cleaning agents. It seems clear that this was not a carefully planned multicentre study using a standardized protocol – it reads more like three separate studies shoe-horned together.
That said, the results are impressive. Areas treated with the “live” cleaning agents were significantly less likely to be contaminated with coliforms, S. aureus, Candida albicans, with a more moderate impact on C. difficile. However, it’s difficult to determine the scale of the reduction since the relative rather than actual load reductions are reported.
A neat sub-experiment at one of the hospitals is perhaps the most convincing part of the study, where conventional and “live” cleaning agents were alternated (Figure). You can clearly see that the microbial load tracked downwards when the “live” agent was used, and rebounded when the conventional agent was reinstated.
Notwithstanding the impressive reductions, this approach is ringing some alarm bells:
- Do we really know what we’re doing by deliberately seeding the hospital environment with bacterial spores? Almost all microbes can be pathogenic to immuno-compromised patients. Plus, whilst you know what you’re putting down, you don’t know what it will become when exposed to the selective pressure of hospitals. The authors did take a look at this, using antibiotic susceptibility testing and a PCR assay to show that Bacillus species identified from the original cleaning agents and from hospitals surfaces during study did not differ in their carriage of antibiotic resistance genes. However, this is only scratching the surface of a complex risk.
- Where do all the pathogens go? Having an environment that is full of Bacillus spores does not make a scrap of difference to the amount of pathogens that are shed into the environment. So, either the Bacillus spores somehow reduce the amount of time that these pathogens survive on surfaces, or offer them a more complex hiding place. I suspect the latter is more likely.
- Related to this, recent work has identified established biofilms on dry hospital surfaces with important implications. Won’t a daily dose of Bacillus spores only serve to promote the buildup of this biofilm?
- The authors proffer some potential reasons for the lower bacterial counts, including competition for nutrients and quorum sensing to destabilize biofilms. I think these are very unlikely, because they rely on the Bacillus spores germinating on the surfaces. I suspect that the spores remain firmly as spores, and the reductions are explained by occlusion and competition for space.
- Ethics can be a pain, but it’s there for a reason – to prevent our patients from unnecessary harm. The outcome of their ethical submission was surprising: “The two Ethics Committees stated that a formal authorization was not necessary because the probiotic products would not be directly administered to patients but exploited for cleaning of hospital surfaces only.” Applying a soup of Bacillus species spores to a patient’s room is pretty much the same thing as applying the soup directly to their skin. Personally, I’d like to choose whether or not I’m admitted to a room deliberately seeded with Bacillus spores!
- The authors insist on calling the “live” cleaning agents ‘probiotics’, which seems misplaced. To me, ‘xxx-biotics’ implies something that is administered to a patient.
The use of “live” cleaning agents provides an interesting alternative approach to antimicrobial surfaces, or chemicals with residual biocidal activity. However, I am not sure I accept the authors stark choice as their final conclusion: ‘When it comes down to risk management, one has to decide whether a patient should stay in an environment dominated by food grade microorganisms or in an environment harboring an elevated level of increasingly resistant pathogens.’ Personally, I’d prefer to be cared for in an environment with minimal levels of bacterial contamination, and free from contamination with pathogens. Is that too much to ask?