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

Abstract

SummaryOne hundred and eighty samples of pork sausages were examined after preenrichment in buffered peptone water (P medium), for the presence of salmonellas. From each pre-enrichment four enrichments were made: (1) 0·1 ml of P medium was inoculated into 10 ml of Rappaport's medium, formula R10 (R10/43 °C), (2) 1 ml of the P medium was added to 100 ml of R10 broth (R10/100 ml/43 °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 °C) and (4) 10 ml of P medium were added to 100 ml of MK broth (MK/100 ml/43 °C). All the enrichments were incubated at 43 °C for 48 h. Forty-six and 47 samples were found positive with the first two enrichment methods (R10/43 °C and R10/100 ml/43 °C), while only 16 samples were found positive with the method MK/43 °C, and 27 with the method MK/100 ml/43 °C. The superiority of either one of the two R10 procedures over either one of the two MK methods is statistically highly significant (paired χ2; P < 0·001 in all four comparisons). The superiority of procedure MK/100 ml/43 °C over the method MK/43 °C is also statistically significant (P < 0·005). Both R10/43 °C and R10/100 ml/43 °C procedures had a much stronger inhibitory effect on the competing organisms (lactose- and sucrosenegative) than the two MK methods.