The catalase reaction of Shigella species and its use in rapid screening for epidemic Shigella dysenteriae type 1.

As epidemic dysentery caused by Shigella dysenteriae type 1 is associated with high mortality, early identification of outbreaks is important. Since S. dysenteriae type 1 differs from most of the Enterobacteriaceae in that it does not produce catalase, a test for catalase may provide a useful screening method. The ability of a catalase test to provide rapid identification of S. dysenteriae type 1 has now been assessed, using isolates of this pathogen from five continents, Shigella of other species, and entero-invasive (EIEC) and Shiga-toxin-producing Escherichia coli (STEC). All of the isolates of S. dysenteriae type 1, as well as S. dysenteriae of types 3, 4, 6, 9, 11 and 12 and S. boydii of type 12, were found catalase-negative. All the other bacteria tested were positive for catalase. In an epidemic setting in South Africa, 406 xylose-negative and lysine-decarboxylase-negative isolates, collected from xylose-lysine-deoxycholate (XLD) agar, were tested for catalase. All 356 of the catalase-negative isolates were confirmed to be of S. dysenteriae type 1. None of the catalase-positive isolates were of S. dysenteriae type 1. The catalase test is useful in the rapid, presumptive identification of S. dysenteriae type 1, from appropriate culture media, because of its high predictive value, simplicity and speed. It would be particularly useful during dysentery outbreaks, when other Shigella would be uncommon. There was no association between the absence of catalase activity and the production of Shiga toxin.