Gain of ornithine decarboxylase activity by a strain of Shigella flexneri serotype 6 on the introduction of an R plasmid

The introduction of R plasmid S-a into a strain of Shigella flexneri serotype 6 resulted in the strain gaining the ability to decarboxylate ornithine. The possible reasons for the phenomenon are discussed and the result is compared with that obtained previously when the introduction of R plasmids into a different strain of the same species resulted in enhanced gas production from a range of carbohydrates.