Hydrolysis of urea in the gastrointestinal tract of "monoxenic" rats: effect of immunization with strains of ureolytic bacteria.

Axenic rats, in whose feces urea is ordinarily excreted, were inoculated with ureolytic strains of Lactobacillus or Actinobacillus originally derived from the microflora of "holoxenic" rats. In these "monoxenic" animals, harboring one or another of the bacterial strains, fecal urea was hydrolyzed, with a more rapid onset of ureolysis in the case of Actinobacillus as compared with Lactobacillus. In vitro, a parallel difference between the two strains with regard to the onset of ureolysis was observed, hydrolysis beginning at the onset of growth in the case of Actinobacillus and only at the end of the exponential growth phase in the case of Lactobacillus. Extracellular urease activity was demonstrated in cultures of Lactobacillus, whereas none was found extracellularly with Actinobacillus. The pH optimum for the Lactobacillus urease in vitro was found to be 3.0, whereas the corresponding value for Actinobacillus was 6.0. In the two types of monoxenic rats, urea was consistently present in the small intestine and virtually absent from cecum and colon. Hydrolysis of urea in stomach was almost complete in rats bearing Lactobacillus but much less so in animals monoxenic with Actinobacillus, despite essentially equal numbers of organisms in that location. When rats carrying a monoflora of ureolytic Lactobacillus were immunized with either whole cells or soluble extract of the same organism, urea appeared in cecum and feces, indicating suppression of ureolytic activity. Immunization with an extract of nonureolytic Lactobacillus failed to produce such a result. Similar immunization techniques applied to animals monoassociated with ureolytic Actinobacillus did not alter ureolysis, and no appreciable quantity of urea appeared in feces. These studies demonstrate that it is indeed possible to inhibit the ureolytic activity of some bacteria in vivo by immunological means, but that the urease system of other organisms may not be as amenable to such manipulation.