Structural and serological studies of the O-polysaccharide of strains from a newly created Proteus O78 serogroup prevalent in Polish patients.

Seven Proteus mirabilis strains from five Polish patients (five isolates from urea and two from feces) appeared to be a bacterial clone widespread in hospitals, most probably due to nosocomial infection and autoinfection. Enzyme-linked immunosorbent assay and Western blot showed that lipopolysaccharides from all strains studied are serologically identical to each other but distinct from Proteus lipopolysaccharides studied earlier and, hence, these strains could not be classified in any of the currently existing 77 Proteus O-serogroups. Accordingly, structural analysis of the O-polysaccharide of a representative strain 1B-m revealed a structure that is typical of Proteus O-antigens but is unique in detail. Based on these data, we propose to classify the strains studied as a new serogroup in the genus Proteus named O78.