Evaluation of enrichment techniques for the isolation of Salmonella choleraesuis from swine feces

To improve the isolation of Salmonella choleraesuis from swine feces, we compared the isolation of a field isolate of S. choleraesuis var kunzendorf after primary and delayed secondary enrichments in five broths: a laboratory performed medium (3MC; Blessman et al., 1981; Greenwood et al., 1980), Rappaport-Vassiliadis soya peptone (RVSP), selenite brilliant green-sulfa (SBG), selenite cysteine (SC), and tetrathionate with iodine (TTI). For each enrichment broth, S. choleraesuis was added, serial dilutions were made, swine feces were added, and the greatest dilution that resulted in the recovery of S. choleraesuis from each medium/enrichment combination was determined. None of the media inhibited S. choleraesuis growth in the absence of porcine feces; S. choleraesuis grew to 10(8) colony forming units (cfu) within 12 h in all media tested. Optimal recovery of S, choleraesuis in the presence of feces was with RVSP combined with delayed secondary enrichment. With this combination, S. choleraesuis was isolated consistently from 180 mi of RVSP enrichment broth containing porcine feces that had an initial inoculum of 4 cfu (0.02 cfu/ml). Delayed secondary enrichment did not enhance the recovery of S. choleraesuis from any of the other media. Primary enrichment in RVSP broth for 12 or 24 h or in SBG broth for 24 h gave the next best results, consistently allowing identification of S. choleraesuis from media initially inoculated with 360 bacteria/180 mi (2 cfu/ml). However, primary enrichment did not enhance the isolation of S. choleraesuis from porcine feces in SC, 3MC, and TTI. With these combinations, 10(2) to 10(4) bacteria/ml were required in the initial inocula to consistently detect S. choleraesuis. (C) 1998 Elsevier Science B.V.