The intra-species differentiation of was analysed by comparing the polymorphism of esterases by conventional polyacrylamide-agarose gel electrophoresis, the physicochemical properties of the variants of the major esterase P and the restriction fragment length polymorphism of ribosomal RNA gene regions (ribotyping) to O-serotyping for several panels of strains selected from among a series of 257 clinical isolates and two references strains, (ATCC nos. 10145 and 27853). The electrophoretic variation of four main kinds of esterase (P-P) and 11 additional esterases distinguished by their spectra of hydrolytic activity with synthetic substrates and by their sensitivity to di-isopropyl-fluorophosphate, allowed the discrimination of 67 zymotypes. Thirty-two esterase P variants were characterised by their pI, electrophoretic mobilities and titration curve analyses. They were distributed into two groups which, by these molecular criteria, seem to be distantly related. Combination of the patterns resulting from III, RI and I. restriction endonuclease digestions allowed the discrimination of 33 ribotypes among 134 strains. The strains exhibiting esterase P variants of group 2 presented a distinct ribotype and belonged to serotype O12. They could constitute a distinct group within the species. For the majority of the strains, the absence of correlation between zymotype, ribotype and serotype argues for a high level of heterogeneity within and indicates that the parallel use of the first two methods represent a potential tool for epidemiological study.


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