Evaluation of tris phosphate carbonate Salmonella pre-enrichment medium for poultry feed and feed ingredients

Summary Detecting Salmonella in poultry feed is challenging. Studies have shown that pre-enrichment media lack the buffering capacity to prevent an acidic pH which results in cell injury, death or altered biochemical pathways preventing Salmonella detection. A tris phosphate carbonate (TPC) pre-enrichment medium has been developed to maintain a near neutral pH during incubation of feed but it’s utility has not been confirmed for a wide variety of feed and ingredients. Five gram samples of feed ingredients (8 types) and corn/wheat based poultry feeds (10 types) were individually added to 45mL of each of five different pre-enrichment broths: lactose broth (LB), buffered peptone water (BPW), double buffered peptone water (2xBPW), universal pre-enrichment broth (UPB), and TPC. After incubation for 0, 18, 24, and 48 hours at 37°C, the pH of each pre-enrichment was measured (five replicates/treatment). Data were analyzed by ANOVA and least significant difference T-test. The initial pH of the LB, BPW, 2xBPW and UPB ranged from 6 - 7 for all ingredients and feeds. The initial pH of ingredients and feed in TPC was 8.0-8.4. After 24h of incubation, pH had decreased to 4.6-5.5 for LB and BPW. Variability was observed among feed types incubated in 2xBPW and UPB where the pH ranged from 4.8-6.4 at 24h. TPC was less variable than 2xBPW or UPB with the pH ranging from 6.5-7.4 at 24h. Results suggest that pre-enrichment of a variety of feed in TPC provides a near neutral pH throughout incubation and may improve the ability to recover Salmonella.