A semi-selective differential medium for identifying strains of <i>Pantoea</i> from environmental samples

The genus Pantoea of the Erwinaceae is a genetically and metabolically diverse group whose representatives span a broad range of clinical and nonclinical environments. We sought to develop a culturing medium to facilitate the identification of Pantoea from environmental samples, and to distinguish its members from other closely related Gram-negative genera. We developed a semiselective differential medium, Pantoea Differential Medium (PDM), which contains crystal violet, sodium citrate, tryptone, as well as protease peptone. The efficacy of the medium was evaluated by assessing the growth and phenotype of 42 bacterial strains, including 18 strains of Pantoea along with other representatives of the Enterobacterales. All Pantoea strains, as well as Kosakonia sp. and Duffyella gerundensis formed orange-yellow pigmented colonies on the medium, while all other representative members of the Enterobacterales evaluated formed purple to pink colonies. The medium was also used to distinguish Pantoea from other bacteria in mixed cultures from environmental samples, with 44 of the 48 orange-yellow colonies being identified as members of Pantoea. PDM provides a means for rapidly identifying members of Pantoea from environmental samples, and differentiating them from many of the closely related members of the Erwiniaceae.