Two new effective semiselective crystal violet pectate media for isolation of Pectobacterium and Dickeya

Pectolytic bacteria, including Pectobacterium spp. and Dickeya spp., are best isolated on crystal violet pectate (CVP), a semiselective medium containing pectin. The source of pectin is essential, because pectolytic bacteria are not able to degrade all of them. The aims of this study were to identify a new pectin source and to perfect formulations of semiselective CVP media to isolate the pectolytic bacteria Pectobacterium spp. and Dickeya spp. from different environmental compartments (plants, soil and water). The AG366 pectin, selected after screening six different formulations, was incorporated into single-layer (SL-CVPAG366) and double-layer (DL-CVPAG366) CVP media. Both media were compared with those based on Bulmer, Sigma-Aldrich and Slendid-Burger pectins, using 39 Pectobacterium and Dickeya strains. All strains formed deep cavities on AG366-CVPs, whereas nine did not produce cavities on Bulmer or Sigma-Aldrich media. Recovery rates were similar on DL-CVPAG366, Sigma-Aldrich and Bulmer CVPs for a given taxon, and did not differ significantly between SL- and DL-CVPAG366. Pectolytic bacteria were successfully isolated on both media from field samples of diseased potatoes, carrots, tobacco, onions, radishes and ornamentals. AG366 is thus a high-performance pectin source for the elaboration of CVP media suitable to isolate Dickeya and Pectobacterium. It is also efficient for enrichment purposes in liquid medium. The validation of AG366 as an improved source of pectin to recover the polyphagous Pectobacterium and Dickeya in different environmental compartments is essential given the current worldwide emergence and recrudescence of these bacteria.