Altering the length of the lipopolysaccharide O antigen has an impact on the interaction of Salmonella enterica serovar Typhimurium with macrophages and complement - PubMed (original) (raw)

Altering the length of the lipopolysaccharide O antigen has an impact on the interaction of Salmonella enterica serovar Typhimurium with macrophages and complement

Gerald L Murray et al. J Bacteriol. 2006 Apr.

Abstract

A panel of isogenic Salmonella enterica serovar Typhimurium strains that vary only in the length of the O antigen was constructed through complementation of a wzz double mutant (displaying unregulated O-antigen length) with one of two homologous (wzzST and wzzfepE) or three heterologous (wzzO139 of Vibrio cholerae and wzzSF and wzzpHS-2 of Shigella flexneri) wzz genes. Each gene was functional in the S. enterica serovar Typhimurium host and specified production of O-antigen polymers with lengths typical of those synthesized by the donor bacteria (ranging from 2 to >100 O-antigen repeat units). By use of this panel of strains, it was found that O-antigen length influences invasion/uptake by macrophage cells; this is the first time this has been shown with Salmonella. O-antigen length was confirmed to be related to complement resistance, with a minimum protective length of >4 and <15 repeat units. O antigen of 16 to 35 repeat units was found to activate complement more efficiently than other lengths, but this was unrelated to complement resistance. No evidence was found to suggest that modifying the length of the O-antigen polymer affected expression of the O1, O4, or O5 antigenic factors.

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Figures

FIG. 1.

FIG. 1.

Analysis of LPS from S. enterica serovar Typhimurium C5 Oag modal-length variants and the wbaP (rough) mutant. Each lane corresponds to LPS from 2 × 108 bacteria, except lanes 3 and 4 (2 × 107 bacteria). The number of Oag RUs in each band is indicated on the left of the figure. A bracket denotes the zone of modal regulation for each strain. Lane 10 corresponds to C5Δ_wbaP_ (pGEM-T Easy-wbaP).

FIG. 2.

FIG. 2.

Competition invasion/uptake assays using RAW264.7 macrophages. Mixtures of bacteria with different Oag modal lengths and C5 (input ratio of 1:1) were used in invasion/uptake assays, and the competitive index was subsequently calculated (input ratio/output ratio). The horizontal line (competitive index of 1) indicates the strains that have a level of uptake equivalent to that of C5 under the conditions tested. Values below this line indicate strains with reduced uptake. Histograms show means ± standard errors from three assays (statistical analysis between histograms is indicated by horizontal lines; *, P < 0.05; **, P < 0.01; Student's t test).

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