Genetic analysis of Escherichia coli K1 gastrointestinal colonization

Strains of Escherichia coli expressing the K1 polysaccharide capsule coloni ze the large intestine of newborn infants, and are the leading cause of Gra mnegative septicaemia and meningitis in the neonatal period. We used signat ure-tagged mutagenesis (STM) to identify genes that E. coli K1 requires to colonize the gastrointestinal (GI) tract. A total of 2140 mTn5 mutants was screened for their capacity to colonize the GI tract of infant rats, and 16 colonization defective mutants were identified. The mutants have transposo n insertions in genes affecting the synthesis of cell surface structures, m embrane transporters, transcriptional regulators, enzymes in metabolic path ways, and in genes of unknown function, designated dgc ((d) under bar efect ive in (G) under bar I (c) under bar olonization). Three dgcs are absent fr om the whole genome sequence of E. coli K-12, although related sequences ar e found in other pathogenic strains of E. coli and in Shigella flexneri. Ad ditionally, immunohistochemistry was used to define the nature of the colon ization defect in five mutants including all dgc mutants. STM was successfu lly applied to examine the factors involved in E. coli K1 colonization, and the findings are relevant to the pathogenesis of other enteric infections.