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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Poultry Microbiological Safety and Processing Research Unit » Research » Publications at this Location » Publication #340655

Research Project: Production and Processing Intervention Strategies for Poultry Associated Foodborne Pathogens

Location: Poultry Microbiological Safety and Processing Research Unit

Title: The effect of environmental poultry samples on the pH of typical salmonella pre-enrichment and enrichment media following incubation

item Cox Jr, Nelson
item Cosby, Douglas
item Berrang, Mark
item RICHARDSON, K - Anitox Corp
item HOLCOMBE, N - Anitox Corp
item WELLER, C - Anitox Corp

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2018
Publication Date: 10/5/2017
Citation: Cox Jr, N.A., Cosby, D.E., Berrang, M.E., Richardson, K.E., Holcombe, N., Weller, C. 2017. The effect of environmental poultry samples on the pH of typical salmonella pre-enrichment and enrichment media following incubation. Journal of Applied Poultry Research. 27(1):112-115.

Interpretive Summary: Poultry samples that have fermentable substrates and an assortment of non-Salmonella bacteria capable of turning those compounds into acid produce a highly acidic environment in these samples in the various media used to detect Salmonella. The low pH injures and kills the Salmonella, which results in false negative observations. Researchers analyzing these types of samples should be made aware of the inherent weaknesses in the presently used laboratory procedures.

Technical Abstract: The first step to detect Salmonella in feed and other dry contaminated samples is a pre-enrichment broth which can assist in the recovery of small numbers of stressed Salmonella cells. A previous study demonstrated that incubation of feed and feed ingredients in commonly used pre-enrichment media resulted in a low pH that injured or killed the Salmonella. The objective of this study was to determine which environmental samples and pre-enrichment and selective broths could interfere with the accuracy of Salmonella detection by allowing pH to drop. Samples were collected from commercial poultry operations. Triplicate 10 gram subunits were dispensed into sterile 18 oz Whirl Pak bags and 90 mL of each of the media [lactose broth (LB), buffered peptone water (BPW), Universal Pre-enrichment (UP), minimal salts (M-9), tetrathionate broth (TT) and Rappaport-Vassiliadis broth (RV)] were added to the bags and incubated 24 h at 37°C (or 42°C for RV and TT). The pH was measured after incubation. With turkey litter, fluff and eggshells, regardless of media the pH never went below 5.7. Regardless of sample type, the lowest pH was 6.1, 6.2 and 6.4 for UP, M-9 and BPW, respectively. For the pre-enrichment medium commonly used in the US, (LB) the pH dropped to 4.7 - 4.9 with broiler litter and 4.2 for boot covers used in turkey or broiler houses. Many researchers testing these sample types are unaware of this potential for pH change during pre-enrichment and may be underestimating the presence of Salmonella.