HIGH MUTATION FREQUENCIES AMONG ESCHERICHIA-COLI AND SALMONELLA PATHOGENS

Here it is reported that the incidence of mutators among isolates of p athogenic Escherichia coli and Salmonella enterica is high (over 1 per cent). These findings counter the theory, founded on studies with labo ratory-attenuated strains, that suggests mutators are rare among bacte rial populations. Defects in methyl-directed mismatch repair underlie all mutator phenotypes described here. Of nine independently derived h ypermutable strains, seven contained a defective mutS allele. Because these mutant alleles increase the mutation rate and enhance recombinat ion among diverse species, these studies may help explain both the rap id emergence of antibiotic resistance and the penetrance of virulence genes within the prokaryotic community.