Escherichia coli K12 regains its O antigen

DNA hybridization and DNA sequencing revealed the rough phenotype of the extant Escherichia coli K12 strain, attributed to the presence of certain independent mutations in the rfb gene cluster. The strain EMG2, which symbolized most K12 mutation that had an IS5 insertion at the downstream and rfb. This rfb-50 mutation, together with a complemented strain, generated O antigen, which was typed as O16 with cross reaction to O17.