A Gram-negative bacterium that is the cause of plague. The genus gets its name from Alexandre Yersin, a colleague of Pasteur, who isolated the bacterium in 1894. Bubonic plague is maintained in rat populations and transmitted to humans by the bites of rat fleas. Pneumonic plague occurs under crowded conditions where infected persons spread the bacteria in respiratory droplets which are directly inhaled by nearby people. Y. pestis appears to have been a relatively harmless gut pathogen until about 1,500 years ago when it picked up genes that allowed it to colonize fleas and to multiply in the bloodstream of humans. Its genome has been sequenced and found to consist of a 4.65 Mb chromosome and three plasmids of 96.2 kb, 70.3 kb, and 9.6 kb. See Classification, Bacteria, Proteobacteria.
Subjects: Genetics and Genomics.