Recovery of Salmonella from Frozen Shrimp: Evaluation of Short-Term Selective Enrichment, Selective Media, Postenrichment, and a Rapid Immunodiffusion Method

Abstract

Frozen shrimp was used as a high-moisture food matrix to evaluate the effect of the following conditions and media on the recovery of Salmonella: comparative efficiency of 6 and 24 h selective enrichment incubation periods; efficiency of Rappaport-Vassiliadis (RV) medium relative to selenite cystine (SC) and tetrathionate (TT) selective enrichment broths; need for postenrichment; and reliability of the immunodiffusion method (Salmonella 1–2 TEST) as a rapid screening procedure. From a total of 244 Salmonella-positive, samples, recoveries at 6 h for selective enrichments SC, TT, RV(1) receiving 1 ml of inoculum, and RV(2) receiving 0.1 ml of inoculum, were 147, 149, 200, and 169, respectively; at 24 h, recoveries were 148, 142, 193, and 205, respectively. As a selective enrichment, RV medium was generally more productive than either SC or TT broths. Postenrichment reduced method sensitivity. Test kit reactions were read independently by three analysts to evaluate the immunodiffusion method. Examination of 200 shrimp samples by standard cultural and 1–2 TEST methods detected 52.5–57% and 56.5–60.5% positive samples, respectively.