Expression profile of elaD in different E. coli strains.

The gene encoding elaD can be found in all intestinal pathogenic E. coli strains, and in the commensal strain K12. The gene is absent in APEC, NMEC, and two uropathogenic strains, and encoded as a pseudogene in three other strains. Interestingly, all pseudogenes in E. coli and Shigellae begin with the same single-nucleotide deletion, resulting in a frame shift and downstream sequence deterioration. Formally, the strain 53638 also encodes elaD as a pseudogene (indicated with an asterisk), but careful inspection suggests that this is just the result of sequencing slippage in an adenosine-rich region of the elaD gene. APEC, NMEC, and UPEC belong to the group of extraintestinal pathogenic strains (ExPEC).