Modified crystal violet pectate medium (CVP) based on a new polypectate source (Slendid) for the detection and isolation of soft rot erwinias

Summary The selective-diagnostic crystal violet pectate (CVP) medium for the detection and isolation of soft rot erwinias was modified and improved to allow the use of a new source of sodium polypectate (Slendid type 440), as the previous polypectate (Bulmer) is no longer available. Two formulations were developed: CVP-S1 medium was less transparent but otherwise similar to the Bulmer polypectate-based CVP medium (CVP-B) except that NaOH was added and CaCl₂ concentration reduced. CVP-S2 medium was prepared by mixing equal volumes of two double strength preparations containing 1) polypectate and NaOH, and 2) all other ingredients, both sterilised separately. Although erwinia cavity formation was slower, it showed a number of advantages over CVP-B and CVP-S1 media, thereby facilitating colony/cavity detection and enumeration. These included the absence of precipitate, greater firmness and a reduced risk of liquefaction in the presence of large erwinia numbers, and a reduction in the number of saprophytic bacteria.