Transferable urease activity in Providencia stuartii

Six urea-positive Providencia stuartii strains were tested for transmissible urease determinants. Two strains, when implanted with "helper" conjugative plasmids, were found to be capable of transferring urease genes to Escherichia coli or urea-negative P. stuartii. Recombination of the urease genes with the helper plasmid in P. stuartii was noted in one case. One of the urea-positive P. staurtii strains was found to harbor a conjugative plasmid which mediated both urease activity and ampicillin resistance. This large plasmid (molecular weight, approximately 140 x 10(6)) was transmissible to and stably maintained in E. coli strains. The demonstration of transmissible genes for urease activity in P. stuartii is significant in that it accounts for previous problems associated with classifying urea-positive strains of this species.