Population structure and evolutionary dynamics of pathogenic bacteria

Evidence concerning the significance of recombination within natural bacter ial populations has historically come from two main sources: multilocus enz yme electrophoresis (MLEE) and nucleotide sequence data. Here we discuss ev idence from a third method, multilocus sequence typing (MLST), which is a d evelopment of MLEE based on nucleotide sequencing that combines the advanta ges of both approaches. MLST has confirmed both the existence of clones and the high rates of recombination for several bacterial pathogens. The data are consistent with "epidemic" population structures, where clones are supe rimposed upon a backdrop of frequent recombination, thus, in the short term , resisting the homogenising effect of recombination. The nature of the sel ective advantage of clones, however, and how this advantage relates to viru lence are unclear. The current evidence also has broader implications conce rning bacterial species definition, the management of antibiotic-resistant bacteria and the assessment of the dangers of releasing genetically modifie d organisms into the environment. (C) 2000 John Wiley & Sons, Inc.