PA 20, a semi-selective medium for isolation and enumeration of Pantoea ananatis

A semi-selective medium, PA 20, was developed for the isolation and enumeration of Pantoea ananatis from plant material, specifically from onion seed. The medium has a pH of 8.0 and contains NH4H2PO4, K2HPO4, magnesium sulphate, NaCl, d (+) arabitol, crystal violet, bromothymol blue and thallium nitrate. All P. ananatis strains from a variety of hosts produced characteristic yellow colonies in 6–7 days at 25 °C. Plating efficiencies on PA 20 in comparison to nutrient agar ranged from 92 to 112%. Recovery from naturally infested and artificially contaminated onion seed was high, with an almost total reduction of saprophytes.