title: Clonal structure and virulence factors in strains of Escherichia coli of the classic serogroup O55.
abstract: Virulence properties and genetic variation as determined by multilocus enzyme electrophoresis were studied in 70 strains of Escherichia coli 055, a common serogroup of enteropathogenic E. coli (EPEC), a major cause of infantile diarrhea in developing countries. Nearly 40% of the strains were originally isolated in Brazil and represented serotypes 055:H6, 055:H7, and 055:H51 and nonmotile (055:H-) strains. The analysis of electrophoretic variants of 20 enzymes defined seven distinct electrophoretic types (ETs). ET 1 was represented by 41% of the strains, including strains which usually hybridized with DNA probes for the intimin gene (eaeA), the EPEC adherence plasmid (EAF), and the gene for the pilin subunit of the bundle-forming pilus (bfpA). The ET 1 strains were also typically serotype 055:H6, displayed localized adherence (LA) in tissue culture assays, and were positive in the fluorescent-actin staining test for intimate cell adherence. These same characteristics were observed in the closely related ETs 2 to 4, which clustered in the same branch as ET 1. No known virulence marker could be identified in ET 6. ET 5 included 23 strains, all of which carried the eaeA gene but otherwise displayed a striking array of distinct virulence traits. This ET was represented by 055:H7 strains with phenotypes as diverse as the simultaneous expression of LA and diffuse adherence and the ability to form a newly described adherence pattern, called LA-like adherence. The results suggest that ET 5 marks a special pathogenic clone with a propensity to acquire virulence factors which may facilitate the emergence of new pathogenic strains.
authors.affiliation: Departamento de Microbiologia, Instituto de Clências Biomédicas, Universidade de São Paulo, Brasil.
authors.forename: J
authors.initials: J
authors.lastname: Rodrigues
authors.forename: I C
authors.initials: IC
authors.lastname: Scaletsky
authors.forename: L C
authors.initials: LC
authors.lastname: Campos
authors.forename: T A
authors.initials: TA
authors.lastname: Gomes
authors.forename: T S
authors.initials: TS
authors.lastname: Whittam
authors.forename: L R
authors.initials: LR
authors.lastname: Trabulsi
mesh_terms: D001938:Brazil; D003967:Diarrhea / Q000382:microbiology; D004798:Enzymes / Q000235:genetics; D004926:Escherichia coli / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology; D005798:Genes, Bacterial; D014644:Genetic Variation; D006801:Humans; D007223:Infant; D011110:Polymorphism, Genetic; D012703:Serotyping; D014774:Virulence / Q000235:genetics
chemical_list: D004798:Enzymes