Population structure of pathogenic bacteria revisited.

This minireview summarizes the historical development of bacterial population genetic concepts since the early 1980s. Initially multilocus enzyme electrophoresis was used to determine population structures but this technique is poorly portable between laboratories and was replaced in 1998 by multilocus sequence typing. Diverse population structures exist in different bacterial species. Two distinctive structures are described in greater detail. "Young" organisms, such as Yersinia pestis, have evolved or undergone a severe bottleneck in recent millennia and have not yet accumulated much sequence diversity. "genoclouds" in subgroup III Neisseria meningitidis arise because of the accumulation of diversity due to herd immunity, which is then purified during subsequent epidemic spread.