A KLEBSIELLA-PNEUMONIAE STRAIN THAT SHARES A TYPE-SPECIFIC ANTIGEN WITH SHIGELLA-FLEXNERI SEROTYPE-6 - CHARACTERIZATION OF THE STRAIN AND STRUCTURAL STUDIES OF THE O-ANTIGENIC POLYSACCHARIDE

A strain of Klebsiella pneumoniae was found as the only isolate with p athogenic potential from the stool of a two-year old patient with diar rhoea. A strong serological cross-reactivity with Shigella flexneri se rotype 6 was demonstrated. The cross-reacting antigens were shown to r eside in the cell wall lipopolysaccharide. Studies of the pathogenic p otential of the Klebsiella strain showed low level of invasion of HEp- 2 cells. However, tests for adherence to HEp-2 cells as well as tests for toxin production were negative. The strain had several small plasm ids and was multidrug resistant. These data do not form a sufficient b asis for estimating the pathogenic potential of the organism. No K ant igen was detected. The structure of the O-antigenic polysaccharide fro m the K. pneumoniae strain was investigated using methylation analysis , NMR spectroscopy, and Smith degradation as the principal methods. Th e O-antigenic polysaccharide has the following pentasaccharide repeati ng unit: p-(1-->2)-alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->. This struc ture is not identical to any of the previously described O-antigens of K. pneumoniae. The strong serological cross-reactivity with the Shige lla flexneri serotype 6 O-antigen can most likely be attributed to the structural element alpha-L-Rhap-(1-->2)-alpha-L-Rhap present in the O -polysaccharide repeating unit of this serotype. Antiserum raised agai nst the K. pneumoniae strain also agglutinated S. dysenteriae serotype 1 and strains of all different serotypes of S. flexneri. The Shigella strains contain the structural element alpha-L-Rhap-(1-->3)-alpha-L-R hap in their O-antigen polysaccharides which may be responsible for th e observed cross-reactivity.