Variation in urease activity of endemic hospital strains of Proteus rettgeri and Providencia stuartii.

Both urease-positive and urease-negative Proteeae isolated from cross-infected patients in the same hospitals and, in three cases, from the same patients were examined for their biochemical reactions and somatic (O-) antigens. All isolates gave the same reactions in 17 biochemical tests and possessed O-antigens characteristic of Providenic O-type strains 4 or 17. Study of the isolates indicated that endemic strains are capable of undergoing variation in urease activity. In the current classification urease-positive and urease-negative strains are classified as Proteus rettgeri and Providencia stuartii, respectively. The observed variation in urease activity of nosocomial isolates of Proteeae suggests that taxonomy should be modified so that all such strains would be accommodated in a single group.