Usefulness of trehalose fermentation and L-glutamic acid decarboxylation for identification of biochemically aberrant Providencia stuartii strains.

A total of 849 Providencia isolates were collected during a 4-year period when an increased incidence of nosocomial Providencia stuartii infection was noted in urologic wards. Of these isolates, 630 were identified as P. stuartii, 206 were identified as Providencia rettgeri, and 1 was identified as Providencia alcalifaciens. Twelve inositol-positive isolates from 10 patients (10 strains) resembled P. stuartii in fermenting trehalose but resembled P. rettgeri in fermenting D-arabitol or meso-erythritol or both. The latter traits, however, were not stable in all cases. These aberrant strains were identified as P. stuartii on the basis of their O antigens and DNA hybridization experiments. All isolates were tested for L-glutamic acid decarboxylase activity by a qualitative thin-layer chromatography method. All P. stuartii isolates, including the aberrant ones, were trehalose positive and L-glutamic acid decarboxylase negative. None of the P. rettgeri isolates fermented trehalose, while 99.0% of them and the single P. alcalifaciens strain were L-glutamic acid decarboxylase positive. Thus, trehalose fermentation and L-glutamic acid decarboxylation are more useful for separating P. stuartii from P. rettgeri than are D-arabitol and meso-erythritol fermentation.