Comparison of enrichment techniques for the isolation of Salmonella sp. from swine feces

Abstract

From July 1998 to November 1999, 1541 pre-slaughter fecal samples, 428 post-slaughter cecal/rectal content samples, and 430 ileocecal lymph node samples were cultured for Salmonella sp. A total of 371 isolates of Salmonella were recovered using seven comparative techniques for isolation. A standard protocol, consisting of xylose lysine tergitol-4 agar (XLT4) paired with a primary enrichment in tetrathionate broth with iodine (TTH) and secondary enrichment in Rappaport-Vassiliadis R10 broth (RV), was used on all samples. This standard protocol was compared with seven different protocols for Salmonella isolation. The first experiment compared the standard protocol to a procedure utilizing xylose lysine desoxycholate agar (XLD) paired with enrichment in malachite green-mannitol-selenite broth (MMS). The second experiment compared XLD agar to XLT4 agar using the standard protocol. The third and fourth experiments compared the standard protocol a similar protocol that varies of the amount of TTH added to the experimental RV. The fifth and sixth experiments compared the standard protocol to a deviation of the same protocol that varies the amount of iodine solution added to the TTH. The seventh experiment compared the standard protocol to the use of RV as primary enrichment broth alone. Experiments one, four, and seven demonstrated that the standard protocol was significantly superior. Experiments two, three, five, and six were equivocal with no significant difference found. However, in experiment six there was a trend toward significance for improved salmonella recovery by the addition of 1.0 ml of iodine to the TTH. Using the standard protocol, the secondary enrichment in RV was found to be greatly beneficial when used with pre-slaughter fecal samples and post-slaughter cecal/rectal content samples. Significance was established with a p-value <0.05.