Efficiency of different enrichment and isolation procedures for the detection of Salmonella serotypes in edible offal

Abstract

Rapid detection systems for Salmonella in foodstuffs are currently being developed. However, existing standards still call for application of traditional methods employing pre-enrichment followed by selective enrichment and isolation. The efficacy of various methods was tested using 264 chicken and lamb organ meats. Pre-enrichment was carried out in Tryptone Soy Broth (TSB) and enrichment in Tetrathionate Brilliant Green Broth (TTB) at 37 degrees C, Selenite Broth with Brilliant Green and Sulphapyridine at 37 degrees C and 43 degrees C, and Rappaport-Vassiliadis Broth (RV 10) at 42 degrees C. The isolation media were Brilliant Green Agar (BGA), Deoxycholate Citrate Agar, Hektoen Enteric Agar (HEA) and Salmonella-Shigella Agar. Enrichment in RV/42 degrees C followed by isolation on BGA as recommended by ISO standard no. 6579 and enrichment in TTB/37 degrees C followed by isolation in HEA, no longer recommended by that standard, produced the best results. Low percentages of positive samples and difficulties in detecting Salmonella are the result of interference by competing organisms (Enterobacteriaceae) and the number of salmonellas present after enrichment. A total of 528 samples (TSB, eggs, lamb liver and chicken liver) were inoculated with Salm. enteritidis, Salm. kapemba and Salm. virchow, and the preceding experiment was repeated. All the TSB and egg samples tested positive, but the percentage of positive samples from the lamb and chicken liver was only 81-92%. Recovery of the salmonellas did not depend upon the method employed or the serotype inoculated but instead on interference by competing flora and the numbers of Salmonella present in the samples.

Scientific Opinion on a quantitative estimation of the public health impact of setting a new target for the reduction of Salmonella in laying hens

“…During testing of samples competing organisms are the main limiting factor in detection (Arroyo and Arroyo, 1995) and it is important to allow enough free enrichment media around the sample for Salmonella to migrate away from the sample matrix (McCrea et al, 2005). Low numbers of Salmonella organisms, e.g.…”

Immunomagnetic separation and conventional culture procedure for detection of naturally occurring Salmonella in raw pork sausages and chicken meat

“…The most Pre-enrichment cultures were subjected to IMS as described frequently isolated serotypes were Salm. derby (five isolates), previously (Mansfield and Forsythe 1993). One ml of BPW Salm.…”

“…The supernatant fluid was removed by monella serotypes. Arroyo and Arroyo (1995) also reported aspiration and the Dynabeads ® were washed in 1 ml of differences in serotype detection using RV, SC and tetramaximum recovery diluent (MRD, Oxoid) containing 0·05% thionate broth. Tween 20, and separated again in the MPC.…”

“…However, the data presented here support the results of other studies which showed that IMS give similar isolations plate). Isolations on RA and BGA following IMS were quite difficult because of the large numbers of competing bacteria to SC and RV (Mansfield and Forsythe 1993) and that use of SC recorded more salmonellae than RV (Cudjoe et al 1994).…”

“…Indeed, conventional culture methods require at least biological methods or by rapid detection techniques such 4 d to obtain negative results and 6-7 d for identification of as microscopy, ELISA and PCR (Skjerve and Olsvik 1991; Salmonella-positive samples. Accordingly there is a need to Vermunt et al 1992;Mansfield and Forsythe 1993; Safarik develop more rapid Salmonella testing methods for the detecet al 1995). tion of Salmonella in foods (Blackburn 1993;Swaminathan Aims of the present study were to compare IMS and 1994).…”