Nucleic acid methods

Basic principle: detect specific gene(s) or DNA DNA probe: single stranded probe specific for a unique genetic sequence of the target organism - organisms in the food sample fixed to solid support (ex. membrane filter) - cells lysed and DNA denatured - labeled DNA probe added to membrane filter - filter placed on agar surface - microbial colonies transferred to membrane and blotted with probe - probe attaches only to complementary sequence - probe detected by radioactive or enzyme label