"When a particular phage comes along that can kill certain members of the population, it does so and the resistant bacteria quickly grow out," says Martens as quoted in Phys.Org. Researchers found a hairy-looking sugar coating on the bacteria that defends against attacks from the human immune system and viruses.
Martens team then found that an additional level of resistant can switch on in bacteria called phase variation providing further protection against infection. Other bacteria not detecting the phage's continued presence, "turn off this resistance switch, leaving them susceptible to infection", says the report. Martens believes these insights can lead to treating diseases by altering our gut microbiome.