The epidemiology of Escherichia coli strains isolated from food handlers of 4 cafeteria in a factory was studied by using plasmid analysis, restriction endonuclease analysis, incompatibility grouping of conjugative R plasmid, and DNA
hybridization
in
conjunction with biotyping and antibiogram pattern. Fifty-three(62.4%) of 85 E. coli isolates were resistant to antimicrobial drugs and 43.4% of resistant strains carried conjugative R plasmids ranging 31 to 126 megadaltons. Most isolates(85%)
harbored
1 to 4 plasmids ranging 2 to 100 megadalton. By incompatibility grouping, 35 conjugative R plasmids were classified into IncFI(7), IncFIV(2), and IncIa(6), and the remaining 20 were untypable. Two IngFIV plasmids which were obtained from strains
with
identical plasmid profile, antibiogram, biotype, and same source showed identical fragment pattern generated by restriction endonuclease EcoRI and HindIII. Three IncFI plasmids which derived from strains of similar plasmid profile, antibiogram,
different biotype, and the same source showed nearly identical or similar fragment pattern one another by same endonuclease, and high degree of homology(95% and 88%) by southern hybridization method but three IncFI plasmids derived from strains
of
different sources exhibited quite different fragment patterns from them. Some plasmids and strains with common phenotype derved from the same source exhibited identical or nearly identical fragment patterns but plasmids from different source
never
showed similar pattern. These results suggested that there seemed to be exchange of floral strains of E. coli harboring R plasmids among the personnels working in same cafeteria, and during this process, there could be molecular evolution of
plasmid.
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