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

Abstract

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 its utility has not been confirmed for a wide variety of feed and ingredients. Five-gram samples of feed ingredients (8 types) and corn- or wheat-based poultry feeds (10 types) were individually added to 45 mL of each of 5 different pre-enrichment broths: lactose broth (LB), buffered peptone water (BPW), double-strength buffered peptone water (2xBPW), universal pre-enrichment broth (UPB), and TPC. After incubation for 0, 18, 24, and 48 h at 37° C, the pH of each pre-enrichment was measured (5 replicates/treatment). Data were analyzed by the ANOVA and least significant difference T-test. The initial pH of the LB, BPW, 2xBPW, and UPB ranged from 6 to 7 for all ingredients and feeds. The initial pH of ingredients and feed in TPC was 8.0-8.4. After 24 h of incubation, the 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 to 6.4 at 24 h. Tris phosphate carbonate was less variable than 2xBPW or UPB with the pH ranging from 6.5 to 7.4 at 24 h. 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.

Keywords

• poultry feed
• Salmonella
• pre-enrichment