Klebsiella pneumoniae lipopolysaccharide O typing: Revision of prototype strains and O-group distribution among clinical isolates from different sources and countries

We have previously described an inhibition enzyme-linked immunosorbent assa y method for the O typing of O1 lipopolysaccharide from Klebsiella pneumoni ae which overcomes the technical problems end limitations of the classical O-typing method. In this study, we have extended the method to all of the c urrently recognized O types. The method was validated by studying the proto type strains that have defined the O groups by the classical tube agglutina tination O-typing method. Based on these results, we confirmed the O types of 60 of 64 typeable strains, and we propose a revised O-antigenic scheme, with minor but necessary changes, consisting of serogroups or serotypes O1, O2, O2ac, O3, O4, O5, O7, O8, and O12. Application of this typing method t o 638 K. pneumoniae clinical isolates from Denmark, Spain, and the United S tates from different sources (blood, urine, and others) showed that up to 8 0% of these isolates belong to serotypes or serogroups O1, O2, O3, and O5, independently of the source of isolation, and that a major group of nontype able isolates, representing about 17% of the total, consists of half O+ and half O- strains. Differences were observed, however, in the prevalence of the lipopolysaccharide O types or groups, depending on the country and isol ation source.