Anti-S. flexneri type 5 Polyclonal antibody

The O antigen (Oag) component of lipopolysaccharides (LPS) is crucial for virulence and Oag chain-length regulation is controlled by the polysaccharide co-polymerase class 1 (PCP1) proteins. Crystal structure analyses indicate that structural conservation among PCP1 proteins is highly maintained, however the mechanism of Oag modal-chain-length control remains to be fully elucidated. Shigella flexneri PCP1 protein WzzB(SF) confers a modal-chain length of 10-17 Oag repeat units (RUs), whereas the Salmonella enterica Typhimurium PCP1 protein WZZB(ST) confers a modal-chain length of similar to 16-28 Oag RUs. Both proteins share >70% overall sequence identity and contain two transmembrane (TM1 and TM2) regions, whereby a conserved prolineglycine-rich motif overlapping the TM2 region is identical in both proteins. Conserved glycine residues within TM2 are functionally important, as glycine to alanine substitutions at positions 305 and 311 confer very short Oag modal-chain length (similar to 2-6 Oag RUs). In this study, WzzB(SF) was co-expressed with WzzB(ST) in S. flexneri and a single intermediate modal-chain length of similar to 11-21 Oag RUs was observed, suggesting the presence of Wzz:Wzz interactions. Interestingly, co-expression of WzzB(SF) with WzzB(G305A/G311A) conferred a bimodal LPS Oag chain length (despite over 99% protein sequence identity), and we hypothesized that the proteins fail to interact. Co-purification assays detected His(6)-WzzB(SF) co-purifying with FLAG-tagged WzzB(ST) but not with FLAG-tagged WzzB(G305A/G311A), supporting our hypothesis. These data indicate that the conserved glycine residues in TM2 are involved in Wzz:Wzz interactions, and provide insight into key interactions that drive Oag modal length control.

The combination of salt and acid is commonly used in the production of many foods, including pickles and fermented foods. However, in our previous studies, the addition of salt significantly reduced the inhibitory effect of acetic acid on Escherichia coli O157: H7 in laboratory media and pickled cucumbers. Therefore, this study was conducted to determine the mechanism by which salt confers resistance against acetic acid in E. coli O157: H7. The addition of high concentrations (up to 9% or 15% [w/v]) of salt increased the resistance of E. coli O157: H7 to acetic acid treatment. Combined treatment with acetic acid and salt showed varying results among different bacterial strains (an antagonistic effect for E. coli O157: H7 and Shigella and a synergistic effect for Listeria monocytogenes and Staphylococcus aureus). The addition of salt increased the cytoplasmic pH of E. coli O157: H7, but decreased the cytoplasmic pH of L. monocytogenes and S. aureus on treatment with acetic acid. Therefore, the addition of salt increases the acid resistance of E. coli O157: H7 possibly by increasing its acid resistance response and consequently preventing the acidification of its cytoplasm by organic acids. (C) 2015 Elsevier Ltd. All rights reserved.