EVALUATION OF TWO NONRADIOACTIVE GENE PROBES FOR THE ENUMERATION OF VIBRIO PARAHAEMOLYTICUS IN CRABMEAT

Abstract

This study evaluated two nonradioactive DNA probe procedures for the detection and enumeration of Vibrio parahaemolyticus in crabmeat by comparing counts obtained by direct plating and by most probable number (MPN) procedures. The nonradioactive probes evaluated were an alkaline phosphatase‐labeled thermolabile direct hemolysin (AP‐tdh) and a digoxigenin‐labeled thermostable direct hemolysin (DG‐tdh) for detection and enumeration of total and pathogenic V. parahaemolyticus, respectively. Inoculated samples (50 g each) of steamed crabmeat were analyzed by nine analysts in seven laboratories. Samples were inoculated with various Vibrio strains and combinations of strains at different levels of inoculation (0 to 92,000 cells/g). The results indicated that the AP‐tlh probe was reliable for identification and enumeration of total V. parahaemolyticus and the DG‐tdh probe was specific for the pathogenic strains. Both probes required less effort and expense than the biochemical testing and hemolysin assays that have previously been used. The MPN and direct plating procedures using the nonradioactive probes were both effective for enumeration of total and pathogenic V. parahaemolyticus in the absence of competing microflora, but direct plating was preferable to MPN for enumeration of V. parahaemolyticus, especially pathogenic strains, in the presence of competitors.