The lipopolysaccharide of the mastitis isolate Escherichia coli strain 1303 comprises a novel O-antigen and the rare K-12 core type

Abstract

Mastitis represents one of the most significant health problems of dairy herds. The two major causative agents of this disease areEscherichia coliandStaphylococcus aureus. Of the first, its lipopolysaccharide (LPS) is thought to play a prominent role during infection. Here, we report the O-antigen (OPS, O-specific polysaccharide) structure of the LPS from bovine mastitis isolateE. coli1303. The structure was determined utilizing chemical analyses, mass spectrometry, and 1D and 2D NMR spectroscopy methods. The O-repeating unit was characterized as -[→4)-β-d-Quip3NAc-(1→3)-α-l-Fucp2OAc-(1→4)-β-d-Galp-(1→3)-α-d-GalpNAc-(1→]- in which theO-acetyl substitution was non-stoichiometric. The nucleotide sequence of the O-antigen gene cluster ofE. coli1303 was also determined. This cluster, located between thegndandgalFgenes, contains 13 putative open reading frames, most of which represent unknown nucleotide sequences that have not been described before. The O-antigen ofE. coli1303 was shown to substitute O-7 of the terminalld-heptose of the K-12 core oligosaccharide. Interestingly, the non-OPS-substituted core oligosaccharide represented a truncated version of the K-12 outer core – namely terminalld-heptose and glucose were missing; however, it possessed a third Kdo residue in the inner core. On the basis of structural and genetic data we show that the mastitis isolateE. coli1303 represents a new serotype and possesses the K-12 core type, which is rather uncommon among human and bovine isolates.