Esterases of 53 strains of . including five previously defined biotypes, and 30 strains of were analysed by horizontal poly-acrylamide-agarose gel electrophoresis and by isoelectrofocusing in thin-layer polyacrylamide gel. Esterase bands were defined by their range of activity towards several synthetic substrates, their resistance to heat and to di-isopropyl fluorophosphate. The two species were characterized by distinct electrophoretic patterns of their esterases. The apparent molecular weights of the heat-resistant esterase of and of the major heat-resistant esterase of . as determined by polyacrylamide gradient gel electrophoresis, were estimated to be 52000 and 250000, respectively. On the basis of electrophoretic mobilities and isoelectric points of esterases produced by strains of . five principal zymotypes were observed: two for strains of biotype 1, two for strains of biotypes 2 and 3, respectively, and only one for strains of both biotypes 4 and 5. The zymotypes of strains of biotypes 2, 3, 4 and 5 appeared to be more closely related to one another than to zymotypes of strains of biotype 1. Variations in number or mobility of bands observed within each biotype of and within some serotypes of could represent an additional marker for epidemiological analysis.


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