The genus Serratia.

The genus Serratia a member of the Enterobacteriaceae (see Introduction to the Family Enterobacteriaceae from the second edition.), is comprised of a group of bacteria that are related both phenotypically and by DNA sequence. The type species of the genus is Serratia marcescens. Some species and biotypes of Serratia produce a nondiffusible red pigment, prodigiosin, or 2-methyl-3-amyl-6-methoxyprodigiosene (Williams and Qadri, 1980). The multiplication of redpigmented Serratia was incriminated in the appearance of bloodlike spots (e.g., on bread, consecrated wafers [sacramental Hosts], and polenta) with rather disastrous sociological consequences. In this context, several scholars have traced the history of the genus Serratia back to antiquity (Gaughran, 1969; Harrison, 1924; Reid, 1936). However, several bacterial species outside the genus Serratia produce prodigiosin or prodigiosin-like pigments (Williams and Qadri, 1980) or many other kinds of red pigments, and the identity of microorganisms involved in these striking phenomena can only be surmised. Bizio (1823) named the red-pigmented microorganism he observed on polenta Serratia marcescens. Ehrenberg (1848) named a motile bacterium isolated from red spots on food “Monas prodigiosa.” No cultures of these organisms were preserved, but the name Serratia marcescens was preferred over the name “Erythrobacillus pyosepticus”—a culture of which was preserved as ATCC 275 (Fortineau, 1904)—by Breed and Breed (1924, 1927) and by the editors of Bergey’s Manual of Determinative Bacteriology (Bergey et al., 1923). The name Serratia marcescens is now universally accepted, and a neotype strain has been designated (Martinec and Kocur, 1961a). At the start of this century, more than 76 nomenspecies had been described with red or pink pigmentation (Hefferan, 1904), and 23 Serratia species were listed in the first edition of Bergey’s Manual (Bergey et al., 1923). This number progressively decreased to five in the fifth edition of Bergey’s Manual (Breed et al., 1957), and later to one species: S. marcescens (Ewing et al., 1959; Martinec and Kocur, 1960, 1961a, 1961b, 1961c, 1961d). The only Serratia species recognized in the eighth edition of Bergey’s Manual was S. marcescens (Sakazaki, 1974). Then, new objective approaches, such as numerical taxonomy and DNA relatedness applied to strains recovered from diverse habitats, delineated an increasing number of species in the genus Serratia. Five and seven species, respectively, were mentioned in the first edition of The Prokaryotes (Grimont and Grimont, 1981) and in Bergey’s Manual of Systematic Bacteriology (Grimont and Grimont, 1984). Ten species are presently known to belong in the genus Serratia. These species (and synonyms) are: