Genetic relationships and clonal structure of strains of Escherichia coli causing neonatal septicemia and meningitis.

Genetic diversity and relationships among 63 isolates of Escherichia coli from infants in Finland with septicemia or meningitis were assessed by analyzing electrophoretic variation in 21 enzymes encoded by chromosomal genes. Thirty-nine multilocus genotypes (electrophoretic types) were distinguished, 23 of which formed a closely related, distinctive subset (group 1) of five or six clones represented by 40 (63%) of the isolates. The remaining isolates represented a second subset of 16 electrophoretic types (group 2) that were, on the average, rather more distantly related to one another. Although the number of electrophoretic types causing neonatal systemic disease is smaller than that occurring in healthy intestinal floras, the pathogenic electrophoretic types are only slightly less diverse genetically. Isolates of group 1 were characterized by relatively high incidences of hemolysin production and S, type 1, type 1C, and P fimbriae. However, because phenotypic characters, considered individually or in combination, did not adequately reflect the overall genetic relationships of isolates, it is recommended that the genetic structure of populations be defined on the basis of multilocus chromosomal genotypes.