Hypermutable bacteria isolated from humans--a critical analysis.

Hypermutable bacteria of several species have been described among isolates recovered from humans over the last decade. Interpretation of the literature in this area is complicated by diversity in the determination and definition of hypermutability, and this review outlines the different methods used. Inactivation of the mismatch repair gene mutS is often implicated in the mutator phenotype; the reported effect of mutS inactivation on mutation frequency varies widely between species, from under 10-fold to nearly 1,000-fold, but also varies among different reports on the same species. Particularly high proportions of mutators have been reported among Pseudomonas aeruginosa and other species in the cystic fibrosis lung, epidemic serogroup A Neisseria meningitidis, and Helicobacter pylori. Aspects of the biology of these infections that could be relevant to hypermutability are discussed, and some future directions that may increase our understanding of mutators among bacteria isolated from humans are considered.