Minimum detectable level of Salmonellae using a binomial-based bacterial ice nucleation detection assay (BIND (R))

A modified bacterial ice nucleation detection (BIND(R)) assay was used for rapid and sensitive detection of several Salmonella species, For the BIND a ssay, Salmonella cells are infected with bacteriophage genetically modified to contain DNA encoding an ice nucleation protein (INP). After infection, de novo protein synthesis occurs and INPs are incorporated into the outer m embrane of the organism. After supercooling (-9.3 degrees C), only buffer s olutions containing transfected salmonellae freeze, causing a phase-sensiti ve dye to change color. This technique, and a probability-based protocol mo dification, provided quantitative detection with a minimum detectable level (MDL) of 2.0 +/- 0.3 S. enteritidis cells/mL in buffer (about 3 h), The MD Ls for S. typhimurium DT104 and S. abaetetuba were 4.2 +/- 0.2 and 111 +/- 0.4 cells/mL, respectively. Using salmonellae-specific immunomagnetic bead separation technology in conjunction with the modified BIND protocol, we ac hieved an MDL of about 4.5 S, enteritidis cells/mL with an apparent capture efficiency of 56%.