War between bacteria, phages benefits humans

In our battle with cholera bacteria, we may have an unknown ally in bacteria-killing viruses known as phages. In a new study, researchers from Tufts University, Massachusetts General Hospital, Partners In Health, Haiti's National Public Health Laboratory, and elsewhere, report that phages can force cholera bacteria to give up their virulence in order to survive.

Importantly, the study -- published in eLife -- found that cholera's mutational escape from phage predation occurs during human infection.

First author Kimberley Seed, Ph.D., and corresponding author Andrew Camilli, Ph.D., both of Tufts University School of Medicine, and their co-authors analyzed phage resistance properties and DNA sequences of cholera bacteria taken from phage-positive stool samples from patients with cholera in Haiti and Bangladesh, two countries where cholera outbreaks are common at present.

They first determined that cholera bacteria from Haiti changed its DNA in order to fight phages. They compared the bacteria from Haiti to bacteria from Bangladesh collected over many years to determine if the changes were happening on multiple occasions in both countries or only in isolated groups or cases.

The research team discovered that across both time and geography, the cholera bacteria mutated during human infection in order to trade their virulence, or ability to persist and make a human sick, for the ability to defend against the phages. Alternatively, in some patients, the cholera bacteria mutated in a more conservative manner to retain virulence, yet sacrificed the ability to grow optimally in the environment. In either scenario, the cholera bacteria appear to have traded something important in order to survive the onslaught from phages.