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 ku nzendorf after primary and delayed secondary enrichments in five broth s: a laboratory performed medium (3MC; Blessman et al., 1981; Greenwoo d et al., 1980), Rappaport-Vassiliadis soya peptone (RVSP), selenite b rilliant green-sulfa (SBG), selenite cysteine (SC), and tetrathionate with iodine (TTI). For each enrichment broth, S. choleraesuis was adde d, serial dilutions were made, swine feces were added, and the greates t dilution that resulted in the recovery of S. choleraesuis from each medium/enrichment combination was determined. None of the media inhibi ted S. choleraesuis growth in the absence of porcine feces; S. cholera esuis grew to 10(8) colony forming units (cfu) within 12 h in all medi a tested. Optimal recovery of S, choleraesuis in the presence of feces was with RVSP combined with delayed secondary enrichment. With this c ombination, S. choleraesuis was isolated consistently from 180 mi of R VSP enrichment broth containing porcine feces that had an initial inoc ulum of 4 cfu (0.02 cfu/ml). Delayed secondary enrichment did not enha nce the recovery of S. choleraesuis from any of the other media. Prima ry enrichment in RVSP broth for 12 or 24 h or in SBG broth for 24 h ga ve the next best results, consistently allowing identification of S. c holeraesuis from media initially inoculated with 360 bacteria/180 mi ( 2 cfu/ml). However, primary enrichment did not enhance the isolation o f S. choleraesuis from porcine feces in SC, 3MC, and TTI. With these c ombinations, 10(2) to 10(4) bacteria/ml were required in the initial i nocula to consistently detect S. choleraesuis. (C) 1998 Elsevier Scien ce B.V.