Improved Recovery of Salmonella spp. and Cronobacter spp. in Dry Milk Powders Enriched in Brilliant Green Water Compared to Buffered Peptone Water

Introduction:  Salmonella and Cronobacter are two pathogens of concern in infant nutritionals, with one major ingredient being milk powders. The ISO methods for Salmonella and Cronobacter, as well as the FDA method for Cronobacter, enrich milk powders in Buffered Peptone Water (BPW). Previous studies have shown improved recovery of Salmonella in milk powders when enriched in Brilliant Green Water (BGW), prompting the FDA to enrich milk powders in BGW. It is important to determine for milk powders if BGW also improves recovery of the Salmonella and Cronobacter when compared to the standard enrichments in BPW.

Purpose:  To evaluate the recovery of Salmonella and Cronobacter in milk powders enriched in BGW compared to BPW.

Methods: Each lyophilized organism was inoculated into bulk dry milk powder, stabilized at room temperature for minimum of two weeks, then diluted for partial recovery. To create composite sized samples (either 100 g or 375 g), 25 g of base inoculated milk powder was mixed with uninoculated dry milk to achieve the final size. Samples were enriched 1:10 in media for 20 to 24 h.

Results:  For Salmonella, 24 milk powder samples were enriched in BPW and BGW. The recovery in BPW was 13, while the recovery in BGW was 17 of 24 samples. For Cronobacter, 38 samples were enriched in BPW and BGW. The recovery in BPW was 20 while the recovery in BGW was 38 of 38 samples. While recovery in BGW was complete for Cronobacter, much lower partial recovery occurred when enriched in BPW.

Significance:  The improved recovery of Salmonella and more dramatically for Cronobacter in BGW is important to achieve the maximum recovery and detection in milk powders. Given the use of milk powders as a key ingredient in the manufacture of infant nutritionals, this new enrichment condition should be considered superior for microbiological analysis of milk powders. Further, BGW is an economic, simple and well-established medium, increasing its acceptance.