A pathogen found in the mouth becomes more virulent by interacting with an innocuous oral bacterium.

The harmless species Streptococcus gordonii produces hydrogen peroxide as an antimicrobial, but the bacterium also makes lactate that benefits the pathogen Aggregatibacter actinomycetemcomitans, which causes gum disease. Marvin Whiteley of the University of Texas at Austin and his colleagues discovered that the pathogen either fights peroxide with a detoxifying enzyme, or escapes the site where the antimicrobial is produced.

These 'fight-and-flight' responses help the pathogen to move far enough away to be protected from the peroxide, but also to remain close enough to continue feeding on lactate. This results in an infection that is more severe than one caused by the pathogen alone, say the researchers.

Proc. Natl Acad. Sci. USA http://doi.org/sv4 (2014)