Esculin hydrolysis by Enterobacteriaceae

Abstract

Literature reports disagree concerning esculin hydrolysis in the family Enterobacteriaceae. A total of 2490 strains of the family were investigated for esculin hydrolysis by 2 methods, the esculin spot test and the PathoTec incubation strip, which measure constitutive enzyme, and 5 growth-supporting methods, which determine constitutive and inducible enzymes. The 5 growth-supporting media studied were: Vaughn-Levine, the standard esculin hydrolysis medium, Vaughn-Levine without Fe, Vaughn-Levine without Andrade''s indicator and bile-esculin medium. Growth media were incubated at 35.degree. C and checked every 24 h for 120 h. On growth media, 0.3% of hscherichia coli were positive in 24 h, 34% in 48 h and 61% in 120 h. No strains were positive on the nongrowth tests. It appeared that the esculin hydrolysis enzyme(s) of E. coli was inducible rather than constitutive. All esculin hydrolyzers, which yielded positive tests on constitutive tests and 24 h tests, were limited to the genera Klebsiella, Enterobacter and Serratia and species Proteus vulgaris, P. rettgeri and Citrobacter diversus. When used with standardized inoculum size and incubation time, the esculin hydrolysis test is very useful for differentiation within the family Enterobacteriaceae.