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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 #316973
Title: Injury and death of various Salmonella serotypes due to acidic conditions

Author
item Cox Jr, Nelson
item RICHARDSON, KURT - Anitox Corp
item Cosby, Douglas
item Berrang, Mark
item CASON, JOHN - Former ARS Employee
item Rigsby, Luanne
item HOLCOMBE, NICOLE - Anitox Corp
item DEROME, L - Anitox Corp

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2015
Publication Date: 3/25/2016
Citation: Cox Jr, N.A., Richardson, K., Cosby, D.E., Berrang, M.E., Cason, J., Rigsby, L.L., Holcombe, N., Derome, L. 2016. Injury and death of various Salmonella serotypes due to acidic conditions. Journal of Applied Poultry Research. 25(1):62-66. https://doi.org/10.3382/japr/pfv062.
DOI: https://doi.org/10.3382/japr/pfv062

Interpretive Summary: The first step in the isolation of Salmonella from relatively dry material such as animal feed is to preenrich the sample in a nonselective broth to allow small numbers of sublethally stressed Salmonella to recover and multiply. Should the material being sampled contain fermentable substrates and an assortment of acid producing non-Salmonella bacteria a large amount of acids can be produced and the acidity can reach levels capable of injuring or killing the target organism (Salmonella). This paper shows the effect of this acidity to kill and injure Salmonella thereby reducing the chance of recovery from these samples. Current protocols may not be detecting Salmonella in these types of samples and need to be further evaluated and possibly modified since feed and feed ingredients are considered to be a very important source of Salmonella in animals including poultry

Technical Abstract: Acid injury of Salmonella could prevent detection of Salmonella in feed and feed-type samples. A previous study showed that after incubation in commonly used pre-enrichment media, mixed feeds and feed ingredients reached a pH (4.0 to 5.0) capable of injuring or killing Salmonella. Approximately 105 colony forming units (CFU) of S. Enteritidis, S. Heidelberg, S. Kentucky or S. Typhimurium were individually placed into 50 mL of a citrate buffer at pH of 4, 4.5 or 5.0 for 6 or 24 hours at 37oC. After holding at 37oC, each serotype was serially diluted in sterile physiological saline and plated onto xylose lysine tergitol 4 (XLT4) for injury and nutrient agar (NA) for death. These plates were enumerated and percent injury and/or death determined. The injury and death confirmed that pH 4.0 was detrimental to these Salmonella serotypes. After 24 hours at pH 4.0, 60% or more of all 4 serotypes were killed with 100% of SK killed. At pH 5.0, 65-75% of these organisms were uninjured with death between 15-20%. Researchers testing feed/feed ingredients for Salmonella may not be aware of the acidic nature of the pre-enrichment step and the subsequent injury or death of any Salmonella present, whether healthy or stressed. Current protocols that are considered the “gold standard” may not be detecting Salmonella in samples containing fermentable substrates and extraneous microorganisms which prevent the accurate detection of Salmonella. Injury or death of a few Salmonella cells could reduce the chance of recovery from any sample. More research is needed with additional Salmonella serotypes and strains to fully understand the challenges of isolating Salmonella from feed.