Evaluation of the stability of biochemical phenotypes of Escherichia coli upon subculturing and storage.

Stability of the biotypic characters of 72 enteropathogenic Escherichia coli (EPEC) and 21 faecal E. coli strains was evaluated after storage and after subculturing using a computerized biochemical fingerprinting method. Sixteen (22%) EPEC strains and nine (43%) faecal strains exhibited changes in their biochemical reactions after subculturing. In contrast, strains stored at -70 degrees C and 4 degrees C did not show any measurable changes. Of 23 biochemical markers tested, eight were subject to changes in at least one of these strains. Changes in lactulose fermentation was most frequent, occurring in 17 (18%) strains. A decrease or loss of activity in the fermentation of 5-ketogluconate, arbutin and methyl beta-D-glucoside in six strains (6%), and an increase in the ability to ferment sucrose, raffinose, melibiose and D-arabinose in 20 strains (22%) were observed. Mean similarity of the strains, when compared pairwise before and after subculturing, was slightly affected by these changes, but the overall biochemical phenotypes of the strains remained constant.