A comparison of isolation procedures for salmonellas from polluted water using two forms of Rappaport's medium.

The efficiency of Rappaport's broth ( RB10 ) and Rappaport's broth containing novobiocin ( NRB10 ) were compared for the isolation of salmonellas from polluted water, both as direct enrichment media and after pre-enrichment in buffered peptone water. Ninety samples were examined and 41 were found to contain salmonellas by at least one of the procedures used. Direct inoculation of the sample into RB10 resulted in the recovery of salmonellas from only 29.3% of the samples found to be positive. The use of NRB10 as a direct enrichment medium increased the percentage recovery to 78.0% of the total positive samples. Pre-enrichment in buffered peptone water allowed the recovery of salmonellas from a total of 41 samples whereas direct enrichment recovered them from only 32. No significant difference was demonstrated in the efficiencies of RB10 and NRB10 in recovering salmonellas after pre-enrichment in buffered peptone water. Three selective agars were used: no significant difference in their ability to recover salmonellae was demonstrated.