Enzyme polymorphism in Escherichia coli : genetic structure of intestinal populations : relationships with urinary tract infection strains and with Shigella / Dominique A. Caugant.

Tese (doutor) - University of Göteborg, 1983

The genetic diversity and population structure of Escherichia coli and Shigella was investigated by starch gel electrophoresis to examine variation in genes encoding enzymes. The electrophoresis technique was described and compared with other methods detecting genetic variation in Enterobacteriaceae: The numbers of allozyme differences among pairs of strains was correlated to the genetic divergence measured by DNA reassociation experiments. Strains with the same O, K or H antigens were genetically heterogeneous. The technique was applied as follows: 1) The fecal E.coli population of a human host was surveyed over an 11 month period. 53 distinct electrophoretic types (ETs) were identified. Three were present over extended periods of time (residents). Transient ETs were replaced in two weeks time. Only a minor part of the genetic diversity was generated by recombination in situ. It was concluded that the temporal variation in the E.coli population of the host was due to successive invasions of E.coli genotypes from external sources. 2) The analysis of fecal samples from members of 5 families demonstrated that associated hosts, in average, shared more E.coli ETs than unassociated hosts. Some E.coli genotypes were geographically widespread and temporally stable. In more than 1500 E.coli isolates from human and animal sources, 279 ETs were distinguished. A principal component analysis of allozyme profiles revealed three overlapping clusters among the E.coli genotypes reflecting strong non-random associations of alleles. 3) The analysis of multilocus genotypes confirmed the close affinity between Shigella and E.coli with 77% of the allozymes of Shigella identical to those of E.coli. Little correspondance was shown between the current classification of Shigella into four species and the similarity of the genotypes determined by enzyme electrophoresis. All the Shigella sonnei strains analysed were genetically homogeneous. 4) E.coli strains causing urinary tract infections, UTI, wore compared to the fecal E.coli flora of a control population. Strains causing symptomatic UTI had a lower genetic diversity than fecal strains. The frequency distribution of genotypes was significantly different between the fecal and symptomatic UTI samples. 5) The relationship between fecal carriage and UTI reinfections was analyzed in patients sequentially sampled for rectal and urinary E.coli. In 16 patients with recurrent UTI, most of the strains infecting the urinary tract were present in the intestine for several months. It was suggested that resident strains were more "uropathogenic" than transient fecal E.coli strains.