Pacifict microbes in disease treatment may make pathogens stronger

Introducing pacifist microbes into treatment to combat is popular in some circles, yet unproven. It's not as crazy as using a placebo to treat symptoms similar to a disease, as homeopathy charlatans do, but it remains unvalidated. However, in agriculture microbial disease treatment could be beneficial, whereas homeopathy is stupid and inhumane. 

It has been suggested that this approach could also be an effective way of treating cancer, and scientists have already produced encouraging results in the fight against Clostridium difficile infections.

One new paper claims that introducing 'friendlier' less-potent strains into a population of disease-causing microbes can lead to increased disease severity. Instead of being a 'silver bullet' to weaken disease, the pacifist microbes could make the aggressive pathogen stronger, which could hamper disease management.

One strategy being explored to treat infections that resist current drugs involves neutralizing the disease-causing agent. This strategy involves extracting the agent from the patient so that scientists can remove components of the microbe's DNA in order to neutralize the disease.

This new harmless agent is then grown in the lab and re-introduced to the disease site with the expectation that it will out-compete its more harmful cousin by stealing resources the disease needs to proliferate. Such research has proved effective in several lab tests.

The scientists tested this method in rice blast infections, but found more severe disease symptoms.

 The scientists used cooperation theory and mathematical modeling to identify the reason for their surprising result. They found that in some circumstances pacifists "helped" aggressive microbes to be more efficient in utilizing resources obtained from the host.

Professor Ivana Gudelj, who led the research, said, "Our study shows that a promising disease management strategy may not always be effective and indeed may have damaging unforeseen consequences. Importantly, our work also provides a foundation for the analysis of when, and why, this can happen. We find that the mechanisms driving our unexpected findings when treating rice blast infection are pertinent for many diseases involving bacterial and fungal pathogens."

  

Professor Nick Talbot, Professor of Molecular Genetics at University of Exeter said, "The strategy of introducing less aggressive microbes to fight more aggressive ones may prove effective to control some crop disease, but our study shows that they are not a silver bullet and caution needs to be exercised. We need to understand how microbes interact with each other in natural settings, before we can try to alter their ability to cause disease in this way. Our study also shows why mathematicians and biologists need to work together more often, because we would not have understood this phenomenon at all without the mathematical analysis carried out."

The scientists tested this strategy using a plant pathogen, the devastating rice blast disease. They introduced a mixed population of the fungus that causes this disease into rice, where the mixture included an aggressive strain and a pacifist mutant. They expected that the overall disease severity would decrease because of the presence of the pacifist strain. However, they found the opposite. The rice plants succumbed to much more severe disease.

The research shows that the therapy can in some circumstances have the opposite effect, and that the way the pathogen will behave can be unpredictable, leading to more severe disease.