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Plague Causing Bacteria Yersinia Pestis Was Once Harmless

Examining the genetic evolution of the Yersinia Pestis, the bacteria that caused epidemics like the Black Death, researchers found that acquisition of just one gene turned it deadly from being harmless.

A team of researchers from Northwestern University’s Feinberg School of Medicine examined the effect of ancestral strains of the bacteria in mouse models to find that the ancestral bacteria could colonize the lung but did not cause the deadly infection that pneumonic plague is.  This ability to infect the lung early on helped it find it new environments.