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Study reveals bacteria’s competitive nature

In a new study, researchers have found that bacteria living in close proximity may have competitive interactions. (Photograph: CooperP/Shutterstock)

Fri. 27. July 2018

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NEW HAVEN, Conn., U.S.: With between 100 and 200 different strains of bacteria in the human mouth at any one time, the oral cavity can be a highly contested space. In a new study, scientists have suggested that the effects of antibiotics on particular bacterial communities throughout the entire body depend on whether neighboring species have competitive or cooperative relationships, as well as their spatial arrangement.

Bacteria living in close proximity may have competitive interactions, such as fighting for limited resources; or cooperative (mutualistic) interactions, such as one species producing a product that serves as food for the other. In the study, which was conducted by researchers from Yale University in New Haven and the Georgia Institute of Technology in Atlanta, the scientists set out to understand the role of mutualistic relationships.

“Too little is known about the ecology of microbial infections, especially what pathogens do and how they interact with their host’s resident microbes,” said co-author of the study Dr. Sylvie Estrela, from the Department of Ecology and Evolutionary Biology at Yale.

As part of the study, Estrela and co-researcher Dr. Sam Brown, associate professor at Georgia Tech’s School of Biological Sciences, modified an existing model of bacterial growth so that it could be used to predict how competitive or mutualistic interactions between antibiotic-resistant and -sensitive species might influence a two-species community’s response to antibiotic treatment. According to the study’s results, simulations showed that, between two competing species, antibiotic treatment suppressed the sensitive species while favoring growth of the resistant species. However, in the context of a mutualistic relationship, hitting the sensitive species with antibiotics also suppressed the resistant species, owing to their interdependency.

Additionally, Estrela and Brown found that spatial arrangement of individual bacterial cells influenced their response to antibiotics, with some resistant species able to deploy detoxification strategies against antibiotics, which can result in cross-protection of nearby sensitive cells. According to the researchers, this showed that such cross-protection is more effective among a mutualistic pair of sensitive and resistant species because mutualists tend to mix as they grow, while competing or noninteracting species tend to segregate.

Moving forward, Estrela and Brown will test their simulated predictions in the laboratory and use the results to refine the model in order to test new ideas and generate new hypotheses. “We hope our results will help draw attention to the fact that the community ecological and spatial context in which antibiotics are applied matters for treatment success,” said Estrela.

The study, titled “Community interactions and spatial structure shape selection on antibiotic resistant lineages,” was published in PLOS Computational Biology on June 21, 2018.

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