Isolation of Salmonella with the use of 100 ml of the R10 modification of Rappaport's enrichment medium.

Abstract

One hundred and eighty samples of pork sausages were examined after pre-enrichment in buffered peptone water (P medium), for the presence of salmonellas. From each pre-enrichment four enrichments were made: (1) o.1 ml of P medium was inoculated into 10 ml of Rappaport's medium formula R 10 (R 10/43 degrees C), /2) 1 ml of the P medium was added to 100 ml of R10 broth (R10/100 ml/43 degrees C), (3) 1 ml of P medium was inoculated into 10 ml of Muller-Kauffmann tetrathionate broth (MK medium) prepared in accordance with the International Standards Organization document ISO 3565 (MK/43 degrees C) and (4) 10 ml of P medium were added to 100 ml of MK broth (MK/100 ml/43 degrees C). All the enrichments were incubated at 43 degrees C for 48 h. Forty-six and 47 samples were found positive with the first two enrichment methods (R10/43 degrees C and R10/100 ml/43 degrees C), while only 16 samples were found positive with the method MK/43 degrees C, and 27 with the methods MK/100ml/43 degrees C. The superiority of either one of the two R10 procedures over either one of the two MK methods is statistically highly significant (paired Chi2; P less than 0.001 in all four comparisons). The superiority of procedures MK/100 ml/43 degrees C over the method MK/43 degrees C is also statistically significant (P less than 0.005). Both R10/43 degrees C and R10/100 ml/43 degrees C procedures had a much stronger inhibitory effect on the competing organisms (lactose- and sucrose negative) than the two MK methods.