Serotyping of Serratia marcescens: detection of two new O-antigens (O25 and O26)

Structural and serological characterisation of the O-specific polysaccharide of the lipopolysaccharide from proposed new serotype 029 of Serratia marcescens

The structure of the repeating unit of the O-antigenic polysaccharide from the lipopolysaccharide (LPS) of Serratia marcescens strain 111 was determined by compositional and methylation analyses and NMR spectroscopy as →6)-α-D-Glc p-(1→2)-α-L-Rha p-(1→2)-α-L-Rha p-(1→2)-α-L-Rha p-(1→ (Rha, rhamnose) which represents a new O-antigenic structure in LPS of S. marcescens but is similar to the structure of the repeating unit of the O-antigen of S. marcescens 018 →6)-α-D-Glc pNAc-(1→2)-α-L-Rha p-(1→2)-α-L-Rha p-(1→2)-α-L-Rha p-(1→ (Oxley D., Wilkinson S.G. Structure of a neutral polymer isolated from the lipopolysaccharide of the reference strain for S. marcescens serogroup 018. Carbohydr Res 1989; 195: 111-115). Serological investigations using S. marcescens O- and K-specific ELISA tests and immunoblotting showed that S111 reacted with anti-O18 and anti-K4 sera, and that the anti-S111 serum reacted with serotype strain 018. The K4 reaction was confirmed as capsular by the Quellung reaction. After absorption with the heterologous strain, S. marcescens 018 and strain 111 were shown to be immunologically distinct, probably because of the presence of the GlcNAc residue in 018. We propose to add S111 to the O-serotype strains of S. marcescens as 029.

Lipopolysaccharides fromSerratia marcescens Possess One or Two 4-Amino-4-deoxy-L-arabinopyranose 1-Phosphate Residues in the Lipid A andD-glycero-D-talo-Oct-2-ulopyranosonic Acid in the Inner Core Region

The carbohydrate backbones of the core-lipid A region were characterized from the lipopolysaccharides (LPSs) of Serratia marcescens strains 111R (a rough mutant strain of serotype O29) and IFO 3735 (a smooth strain not serologically characterized but possessing the O-chain structure of serotype O19). The LPSs were degraded either by mild hydrazinolysis (de-O-acylation) and hot 4 M KOH (de-N-acylation), or by hydrolysis in 2 % aqueous acetic acid, or by deamination. Oligosaccharide phosphates were isolated by high-performance anion-exchange chromatography. Through the use of compositional analysis, electrospray ionization Fourier transform mass spectrometry, and 1H and 13C NMR spectroscopy applying various one- and two-dimensional experiments, we identified the structures of the carbohydrate backbones that contained D-glycero-D-talo-oct-2-ulopyranosonic acid and 4-amino-4-deoxy-L-arabinose 1-phosphate residues. We also identified some truncated structures for both strains. All sugars were D-configured pyranoses and alpha-linked, except where stated otherwise.

Re-evaluation of the serotypes of Serratia marcescens and separation into two schemes based on lipopolysaccharide (O) and capsular polysaccharide (K) antigens

Chemical and serological analysis has revealed that many of the 29 O serotype reference strains of Serratia marcescens contain both neutral and acidic polysaccharides which correspond to LPS O antigens and capsular K antigens, respectively. New O and K antigen typing schemes have therefore been devised, based on the known chemical structures of the surface polysaccharides of the organism. These schemes were designed to allow the specific detection of these antigens on unknown strains using ELISAs. O antigens were detected using whole cells cultured in broth then autoclaved to remove capsular material, while K antigens were detected using formolized whole cells which had been cultured on glycerol agar to enhance capsule production. After testing with the 29 reference strains as well as 423 distinct clinical strains, it was apparent that different aspects of chemical structure were associated with different degrees of serological reactivity and the typing schemes were modified further to accommodate this. In general, the O antigen repeating unit structures were chemically simple with di- or trisaccharide backbones. Serological specificity was often provided solely by the presence or absence of an O-acetyl substituent, or a change in the linkage between two sugar residues. Five of the O serotypes in the new scheme were represented by 12 of the 29 reference strains, while three reference strains lacked O antigens altogether, resulting in the elimination of 10 of the original O types. In contrast, the K antigen repeating unit structures were more complex and chemically diverse, having at least four sugar residues. Three K types were each seen in two reference strains while 12 of the 29 reference strains were acapsular. Thus, the resulting schemes contain 19 O types and 14 K types and allow the definitive serotype identification of S. marcescens.

Typing of nosocomial strains of Serratia marcescens: comparison of restriction enzyme cleaved genomic DNA fragment (PFGE) analysis with bacteriocin typing, biochemical profiles and serotyping

Eighty-eight selected clinical isolates of Serratia marcescens, representing 27 putative outbreaks of nosocomial cross-infection encountered during 1980-1995, were tested comparatively by bacteriocin typing, carbon source assimilation tests, serotyping (O and H antigens), and restriction pattern (RFLP) analysis of restriction cleaved (SpeI, XbaI) genomic DNA fragments after pulsed-field gel electrophoresis (PFGE). Serotyping served as the "gold standard" of the phenotypic methods. One pseudo-outbreak (bacteriocin typing incriminated type 26) was uncovered through serotyping as well as the biochemical profile and confirmed by PFGE analysis of genomic DNA. Bacteriocin typing and determination of biochemical profiles disclosed several instances of phenotypic variation; serotyping revealed two episodes of shifts from motility (H12) to nonmotility. Resolution of restricted genomic DNA fragments with the PFGE procedure permitted detection of 27 PFGE patterns (A-M, N-1-N-3, O-1, O-2, P-1-P-3, Q-1-Q-3, R-1-R-3, S-1, and T). Based on the analysis of PFGE patterns against the background of epidemiological data, the number of nosocomically significant strains of S. marcescens could be reduced to 16 (PFGE patterns A-M, N-2, O-1, P-2, and T). It was concluded that PFGE analysis of restricted genomic DNA of S. marcescens was superior to the three phenotypic methods.

Phenotypic variation of clinical Serratia marcescens isolates repeatedly recovered from individual patients

A total of 129 selected isolates of Serratia marcescens which had been recovered from 50 patients during the 1980-1995 period and which revealed phenotypic variation in terms of bacteriocin (phage tail) susceptibility, carbon source assimilation, or serotype, were reexamined with these three phenotypic methods. Seven isolates (5.4%) were bacteriocin nontypable; all 129 isolates utilized carbon sources and could be serotyped. Fourty-eight isolates from 20 patients yielded unambiguous results with these 3 phenotypic methods and were excluded from further analysis. Among the remaining 81 isolates from 30 patients, isolates from 2 patients revealed phenotypic variation in bacteriocin susceptibility only, whereas isolates from 6 patients showed variant bacteriocin types and variant biochemical profiles, but were of identical serotype. Isolates from 20 patients revealed variant biochemical profiles only. Three patients had become superinfected with strains of S. marcescens of different phenotype and genotype. In 4 patients, previously motile (H12) isolates had become nonmotile (H-). PFGE analysis of XbaI and SpeI-restricted genomic DNA of the 81 isolates of the 30 patients demonstrated the isolates of 22 patients to be genotypically identical. The isolates from 3 patients were closely related by genotype, and those from an additional patient proved to be possibly related. PFGE analysis demonstrated one patient to have become infected by two genotypically different strains of S. marcescens of identical serotype, which, however, differed in bacteriocin type and biochemical profile. It was concluded that PFGE analysis of restricted genomic S. marcescens DNA was superior to the three phenotypic methods examined comparatively. Serotyping was more reliable than bacteriocin typing, and the latter technique yielded fewer phenotypic variants than determination of biochemical profiles among consecutively recovered isolates from patients with long-lasting S. marcescens infection.

Ribotyping for use in studying molecular epidemiology of Serratia marcescens: comparison with biotyping

Ribotyping carried out with a nonradioactive probe (acetylaminofluorene ribosomal RNA kit I from Eurogentec, Seraing, Belgium) was performed for the characterization of 139 hospital strains of Serratia marcescens. These strains, which belonged to 11 biotypes and 1 nontypeable group, were isolated in seven hospitals in Belgium between 1986 and 1992. EcoRI and HindIII were used to obtain cleavage patterns. Analysis of the results produced 27 different patterns with EcoRI and 23 patterns with HindIII. Typeability reached 100%. Combination of the patterns obtained with each enzyme produced 38 distinct ribotypes. Percent similarity values, calculated by using the Dice coefficient and unweighted-pair group average linkage clustering, showed four main clusters and nine subclusters of ribopatterns at a similarity rate of approximately 80% or less. These groups did not coincide with those delimited by biotyping, although a rather good correlation was observed. The simultaneous use of the two methods has potential value in epidemiological studies.

Structural and serological studies of lipopolysaccharides from proposed new serotypes (O25 and O26) of Serratia marcescens

The surface polysaccharides of the two most recently proposed O-serotype strains of Serratia marcescens, O25 and O26, were characterised in terms of their chemical structure and immunological reactions. No polymer was isolated from O25, which was shown to lack both capsular K-antigen and smooth, O-antigenic lipopolysaccharide. A neutral polysaccharide was isolated from O26 and shown to be a polymer of rhamnose and N-acetylgalactosamine of the type previously found in the O9 and O15 reference strains. Serological cross-reactions among all three strains were demonstrated by using both whole-cell enzyme-linked immunosorbent assay and immunoblotting of lipopolysaccharide resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. No acidic polysaccharide was found in O26 and this was consistent with the absence of an immunogenic capsule. Thus, neither strain qualifies for inclusion as a new serotype in either an O-typing or a K-typing scheme.