Differentiation of Shigella species from Escherichia coli by glycerol dehydrogenase activity.

It has been determined that Escherichia coli and the four Shigella species (except S. boydii scrotype 13) form a single genomospecies (Bren-ner, 1984). E. coil and the so-called Shigella species are biochemically and serologically closely related (Ewing, 1986). The "O" antigens of many serotypes of Shigella are either identical to or closely related to those of 17,. coli (Ewing, 1986). The biochemical identification of ShigeUa sometimes presents difficulties in differentiating it from the biochemically atypical E. coil strains. The genus ShigeUa is composed of non-motile bacteria. With the exception of certain biotypes of S. flexneri 6, Shigella do not form gas from fer-mentable carbohydrates and, compared to Esche-richia, ShigeUa are less active in their utilization of carbohydrates. Christensen's citrate, sodium acetate, sodium mucate and decarboxylation of lysinc are of considerable value in the differentiation of members of the genus Shigella from Escherichia, particularly from anaerogenic non-motile biotypes orE. coli (Ewing, 1986). Shigella do not grow fermcntatively on Christensen's cit-rate; sodium mucate is utilized by some cultures of S. sonnei but not by other ShigeUa. Sotfmm acetate is utilized as a sole source of carbon by some biotypes of S. flexneri 4a but not by other ShigeUa. Lysine is not decarboxylated by Shi-gella. The characteristic "invasiveness" of Shi-gella strains in the guinea pig keratocr-:tjunctivitis test (Sereny tes0 (Sereny, 1957) is als ~shown by enteroinvasive E. coli. ~: The diversity of the glycerol pathway has been documented in enterobacterial species (Bouvet et al., 1994, 1995). Species which can grow fer-mentatively on glycerol possess typical enzymes of the anaerobic glycerol pathway (glycerol dehy-drogenase type I (glyDH-I), dihydroxyacetone kinase, glycerol dehydratase and 1,3-propanediol dehydrogenase). E. coil cannot grow fermenta. tively on glycerol because ef the abser.ce of enzymes of the anaerobic glycerol pathway. An NAD+-linked glycerol dehydrogenase, glyDH-ll, induced by glycerol and hydroxyacetone (thus distinct from glyDH-I) responsible for salvaging the glycerol moiety of degradation products of phospholipids and triglycerides, has been described in E. The structural gene of th,~ E. coli glyDH-II has been mapped and cloned (Truniger and Boos, 1994). The identity of glyDH-II of IF,. coil with D-l-amino-2-propanol oxidoreductase has been reported and its participation in vitamin B 12 metabolism has been suggested (Kelley and Dek-ker, 1985). The levels of the glyDH-H activity are markedly induced by oxidized substrates (i.e. aminoacetone, hydroxyacetone, dihydroxyace-tone). GIyDHs from a few bacterial species including Hafnia alvei and "Salmonella enter-ica'" were found to be distinct from …