The Escherichia coli argW-dsdCXA genetic island is highly variable, and E. coli K1 strains commonly possess two copies of dsdCXA.

The genome sequences of Escherichia coli pathotypes reveal extensive genetic variability in the argW-dsdCXA island. Interestingly, the archetype E. coli K1 neonatal meningitis strain, strain RS218, has two copies of the dsdCXA genes for d-serine utilization at the argW and leuX islands.

Uropathogenic Escherichia coli use d-serine deaminase to modulate infection of the murine urinary tract.

Although once thought to be unique to bacteria, d-amino acids are also produced by mammals. For example, d-serine is excreted in human urine at concentrations ranging from 3.0 to 40 micro g ml-1.