Characteristics of spontaneously agglutinating Proteus mirabilis strains from bacteriuric patients.

Out of 210 Proteus mirabilis isolates from bacteriuric patients a total of eight spontaneously agglutinating strains were found. SDS-PAGE analysis of their lipopolysaccharides (LPS), the separation of polysaccharide fractions (PS) by gel filtration, and chemical characterization of PSs were performed. Out of the eight strains one S form and one mutant classified as Rc were detected. The remaining six strains were recognized as Ra and intermediate forms. When tested in a hematogenous infection model in mice, the P. mirabilis Rc mutant survived in kidneys for at least two weeks, while the Re mutant used as control was eliminated within 20 h after the challenge. These data indicated that strains of P. mirabilis may be pathogenic even if they express very incomplete LPS.