COMPARISON OF A MEMBRANE FILTRATION PROCEDURE AND A MPN PROCEDURE FOR ENUMERATING SALMONELLA IN WHOLE CARCASS RINSE SAMPLES1

Abstract

A membrane filtration method using hydrophobic grid membrane filters was developed to enumerate salmonellae in postchill chicken carcass rinse samples. The entire sample volume (100 ml) was filtered utilizing a 0.1% peptone/1% Tween 80 rinse solution which was digested prior to filtration with 2% trypsin. Samonella colonies were countable on XLD agar supplemented with 20 ppm novobiocin and 1% sodium pyruvate after 24 to 30 h of incubation. The filtration method was compared to a modified 3‐tube MPN procedure (utilizing volumes of 30 ml, 3 ml, 0.3 ml, and 0.03 ml) for recovery of thermally stressed salmonellae that had been inoculated into carcass rinse fluid. Presumptive Salmonella levels were obtained in 30 h by membrane filtration method and in 72 h using the MPN procedure. Membrane filtration did not allow for complete recovery of the inoculated, thermally‐stressed Salmonella. The MPN method recovered significantly higher levels of the inoculated organism, however, levels recovered using this procedure were extremely varied from sample to sample.