Salmonella isolation with Rappaport's enrichment medium of different compositions

One hundred samples of feces of normal pigs were examined for the presence of salmonellae. The feces were pre-enriched for 18 h in peptone water and then, 0.1 ml of the pre-enrichment medium was inoculated in 10 ml of the original Rappaport medium (R30), and two modifications (R25 and R10) of this medium. Two of the broths (R30 and R25) were incubated at 37 degrees C (R30/37 degrees C and R25/37 degrees C) while the R10 medium was incubated at 43 degrees C (R10/43 degrees C). In addition 100 ml of R10 medium (R10/100 ml/43 degrees C) and 100 ml of the standardized Muller Kauffmann's tetrathionate broth (MK/100 ml/43 degrees C) (Edel and Kampelmacher, 1969) were inoculated with 1 ml and 10 ml, respectively, of the pre-enrichment medium, and incubated at 43 degrees C. With the method R10/100 ml/43 degrees C, 37 samples were found positive while with the method MK/100 ml/43 degrees C only 22 positive samples were detected (P less than 0.001). With the Rappaport media in 10 ml volumes, the modification R10 yielded 26 positive samples, while the R30 and R25 broths yielded only 15 and 19 positive samples. All Rappaport procedures had a much stronger inhibition of the competing organisms, particularly those giving Salmonella-like colonies (lactose and sucrose negative), than the MK/100 ml/43 degrees C method, a fact of considerable importance in everyday's practice.