We have evaluated the effectiveness of API 20E, Biolog testing, plasmid profiling, ribotyping, and enteric repetitive intergenic consensus (ERIC)-PCR to characterize, classify, and differentiate nine bacterial isolates of the common brewery contaminant Obesumbacterium proteus. Of the five typing techniques, Biolog testing, plasmid profiling, and ERIC-PCR provided the most differentiation, and API 20E testing and ribotyping were relatively indiscriminate. The molecular biology approach of ERIC-PCR offered the ideal combination of speed, simplicity, and discrimination in this study. Overall, the results are supportive of the view that 0. proteus can be subdivided into two biogroups, biogroup 1, which has considerable biochemical and genetic homology to Hafnia alvei, and biogroup 2, which is relatively heterogeneous.
A plasmid-borne transcriptional fusion between the Escherichia coli nitrate reductase (narG) promoter and the Photorhabdus luminescens lux operon provides E. coli with a highly bioluminescent phenotype in the presence of nitrate. This E. coli biosensor can detect nitrate to a level of 5×10 −5 mol l −1 (0·3 ppm), levels relevant to those levels encountered in brewing water. Since induction of the narG promoter requires NarL, the plasmidbased sensor can also be used to interrogate enteric bacteria for the presence of functional homologues of this E. coli regulatory protein. Obesumbacterium proteus, an important bacterial brewery contaminant, failed to provide nitrate-dependent bioluminescence demonstrating divergence in this organism from E. coli in the mechanism of nitrate reductase regulation.
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