Rapid detection and enumeration of Salmonella in chicken carcass rinses using filtration, enrichment and colony blot immunoassay

A strategy was developed for 24-h detection and enumeration of Salmonella spp. on processed chicken carcasses. Carcasses were rinsed with saline and the rinses spiked with known numbers of serogroup B, C, D or E Salmonella. The total rinse volume was passed through two filter units of decreasing pore size. These removed most of the extraneous material while permitting rapid passage of more than 77% of the Salmonella. At least 100 mi of the filtrate was passed through a third filter unit containing a nitrocellulose capture membrane. Captured bacteria were selectively enriched by incubating the nitrocellulose membrane on filter pads soaked in Rappaport-Vassiliadis broth and then on pads soaked in brilliant green broth containing sulfadiazine and novobiocin. A colony blot immunoassay using two anti-Salmonella monoclonal antibodies was used to identify and enumerate the captured Salmonella. As few as five Salmonella colony forming units per carcass rinse could be detected. An evaluation of this system with 24 field samples indicated that the specificity was comparable to and the sensitivity higher than that of standard culture procedures.