The genotypic diversity of 40 presumably epidemiologically unrelated strains of belonging to nine different O-serotypes was analysed according to ribosomal DNA fingerprints. Ribotyping was performed with a digoxigenin-labelled DNA probe and four restriction endonucleases. Characteristic banding patterns of three to 12 bands were obtained with the different endonucleases. Among the 40 strains, eight, nine, 10 and 29 different ribotypes were differentiated with RI, the combination RI + III, HI and II, respectively. Poor correlations were noted between the results of serotyping and those of ribotyping. With the latter method, indices of discrimination were calculated for each enzyme from the data of the 40 unrelated strains: the values ranged from 0·678 for RI to 0·979 for II. Epidemiologically related samples were also tested; this enabled assessment of whether the method was able to cluster strains from a common origin with each of the enzymes tested. Ribotyping with II endonuclease is proposed for screening large numbers of strains in epidemiological studies. Additional enzymes could be used to further increase the discrimination between isolates found to be indistinguishable with II enzyme.


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