A deadly wave of flesh-eating bacteria emerged in the 1980s when a single cell gained a pair of toxin genes from another bacterium.

Infections with group A Streptococcus (GAS) strains, which cause necrotizing fasciitis, spiked worldwide in the late 1980s and early 1990s. To piece together the sequence of molecular events behind this epidemic, James Musser at the Houston Methodist Research Institute in Texas and his team sequenced the genomes of 3,615 GAS strains isolated from Europe and North America between 1969 and 2013.

Analysis of the genomes revealed a series of genetic changes that began to occur in the early 1970s. The final changes that took place before the strain became a voracious flesh-eater happened in around 1983, when less-virulent strains acquired the genes that are needed to produce certain toxins in humans.

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