Reports of disease caused by enteropathogenic E. coli and its relative, Salmonella, usually include a description of the responsible serotype. For example, in 1993, hundreds of infections from Shiga-toxin-producing E. coli resulted from undercooked hamburgers sold by Jack-in-the-Box restaurants. The outbreak was caused by the now-infamous E. coli strain O157:H7. The "O" in this designation refers to an antigen on which of the following molecules?
A. osmoregulatory proteins
B. capsular oligosaccharide
C. lipopolysaccharide
D. outer membrane lipoprotein
E. outer membrane porins

E. coli strain O157:H7 is known to cause the shiga toxin and proves to be pathogenic for the organisms. O stands for the kind of antigen associated with enteropathogenecity.

The O antigen is present on the lipopolysaccharides of the bacterial cellwall. O-antigen flippase enzyme is responsible for the presence of antigenss on the lipopolysaccharidre. The gnd gene is involved in the antigenicity of the E. coli strain O157:H7.

Thus, the correct answer is option (C).