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Title: Optimizing buffering chemistry to maintain near neutral pH of broiler feed during pre-enrichment for Salmonella

item Berrang, Mark
item Cosby, Douglas
item Cox Jr, Nelson
item CASON, JOHN A. - Former ARS Employee
item RICHARDSON, K.E. - Anitox Corp

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2015
Publication Date: 12/16/2015
Citation: Berrang, M.E., Cosby, D.E., Cox Jr, N.A., Cason, J., Richardson, K. 2015. Optimizing buffering chemistry to maintain near neutral pH of broiler feed during pre-enrichment for Salmonella. Poultry Science. 94(12):3048-3051.

Interpretive Summary: Salmonella is human pathogen that can be associated with poultry and poultry meat products. It has been suggested that an effective means to eliminate this organism from processed poultry is to prevent its presence in the growing birds on the farm. One source of Salmonella to the live birds could be feed. Feed may have low numbers of Salmonella cells and those cells may be injured due to the dry nature of pelleted poultry feed. This makes it necessary to use a pre-enrichment method to recover Salmonella. During standard pre-enrichment of feed in buffered peptone broth, the pH of the broth is lowered due to acidic byproducts of extraneous bacteria. This can make it difficult to detect Salmonella, perhaps leading to a false negative result and a false sense of security. We tested a variety of chemical buffering systems added to peptone broth to prevent the pH change during pre-enrichment of feed. Increasing the concentration of standard phosphate buffer up to four fold did not fully prevent the shift to an acidic pH. A combination of phosphate, carbonate and TRIS buffers was the most effective means to control pH and keep it in a range favorable for the growth and detection of Salmonella in feed. We recommend the use of this combination buffering chemistry when assaying poultry feed for the presence of Salmonella.

Technical Abstract: Salmonella is a human pathogen that can accompany live broilers to the slaughter plant contaminating fully processed carcasses. Feed is one potential source of Salmonella to growing broilers. Monitoring feed for the presence of Salmonella is part of good agricultural practices. The first step in culturing feed for Salmonella (which may be at low numbers and sub-lethally stressed) is to add it to a pre-enrichment broth which is incubated for 24 h. During the course of pre-enrichment, extraneous bacteria metabolize carbohydrates in some feed and excrete acidic byproducts causing the pH to drop dramatically. An acidic pre-enrichment pH can injure or kill Salmonella resulting in a failure to detect even if it is present and available to infect chickens. The objective of this study was to test an array of buffering chemistries to prevent formation of an injurious acidic environment during pre-enrichment of feed in peptone water. Five g of feed were added to 45 mL of peptone water buffered with carbonate, TRIS pH 8 and phosphate buffering ingredients individually and in combination. Feed was subjected to a pre-enrichment at 35oC for 24 h; pH was measured at 0, 18 and 24 h. Standard phosphate buffering ingredients at concentrations up to 4 times the normal formulation were unable to fully prevent acidic conditions. Likewise, carbonate and TRIS pH 8 were not fully effective. The combination of phosphate, carbonate and TRIS pH8 was the most effective buffer tested. It is recommended that a highly buffered pre-enrichment broth should be used to examine feed for the presence of low numbers of Salmonella.