Numerical taxonomy of psychrotrophic pseudomonads

The taxonomy of 218 psychrotrophic pseudomonad strains (200 field strains from meat and 18 type and reference strains) was numerically studied by 174 biochemical and physiological tests. All strains were Gram-negative rods, oxidative positive and motile by means of one or more polar flagella. The strains clustered into 15 groups, of which 9 were regarded as major clusters. The major clusters were designated as Pseudomonas fragi (112 strains), P. fluorescens biotype III (7 strains), P. fluorescens biotype I (16 strains). P. aureofaciens/chlororaphis (3 strains), P. fluorescens biotype II (3 strains), P. putida biotype I (4 strains), Alteromonas putrefaciens (10 strains) and Aeromonas hydrophila biotype I (5 strains). One major cluster, containing 21 strains (cluster 2), was left unassigned. The phenotypic data indicate that this cluster might represent a new species. The P. fluorescens/P. putida complex matched closely the descriptions of Stanier et al. (1966), but the two largest clusters (1 and 2) were not in agreement with any species described in the eighth edition of Bergey's Manual of Determinative Bacteriology. Cluster 1 included the type strain (ATCC 4973) of the hitherto incompletely described P. fragi. A simplified scheme for the separation between P. fragi, P. fluorescens, P. putida and cluster 2 is presented.