Taxonomy of the genus Serratia

One hundred and fifty-six strains of Serratia and related bacteria including representatives of Enterobacter liquefaciens, Enterobacter cloacae, Enterobacter aerogenes, Erwinia carotovora, Erwinia chrysanthemi, Erwinia herbicola and Erwinia nimipressuralis were studied using 223 morphological, physiological, biochemical and carbon source utilization tests. The results were subjected to computer analysis. At the 80% similarity level all strains, except two, grouped into eight phenons representing: (A) Serratia marcescens with the neotype CCM303 (ATCCI3880); (B) S. marinorubra with the monotype NCTC10912 (ATCC27614); (CI) S. liquefaciens with the type ATCCI4460; (C2) S. plymuthica with the monotype CCM640 (ATCC183); (D) Erwinia herbicola with the neotype of Enterobacter agglomerans NCTC9381; (E) Enterobacter cloacae with the neotype NCTCI0005 and Erwinia nimipressuralis; (F) Erwinia carotovora with the type ATCC495, Erwinia atroseptica and Erwinia chrysanthemi; (G) Klebsiella mobilis with the neotype NCTCI0006. At the 70% similarity level the phenons formed two groups: (A, B, CI, C2) and (D, E, F, G). The following conclusions were drawn. (I) There are three species of enterobacteria producing prodigiosin: S. marcescens, S. plymuthica and S. marinorubra. (2) There are four species of Serratia, one colourless (S. liquefaciens). (3) Subphenons (biovars) are described within the four species of Serratia. (4) Non-pigmented wild-type strains of S. marcescens can generally be differentiated from pigmented strains by characters other than pigmentation, because subphenons are homogeneous with respect to pigmentation. This survey raised some problems of nomenclature because old descriptions could be found that could loosely fit the present phenons. Comparison with an authentic culture was considered to be the most objective way of identifying these phenons with earlier named species.