Submitted to: International Poultry Forum Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 11/27/2017
Publication Date: 1/29/2018
Citation: Richardson, K.E., Cox Jr, N.A., Cosby, D.E., Berrang, M.E. 2018. Dry and heat stress affects h2s production of Salmonella on selective plating media [abstract]. International Poultry Forum Proceedings. 97(E-Suppl.1):338.
Interpretive Summary: none
Technical Abstract: t has been shown that the pH of Salmonella pre-enrichment media becomes acidic (pH 4.0 to 5.0) when feeds and ingredients are incubated for 24 hrs. Salmonella in poultry feed have been stressed by heat and desiccation and exhibit different tolerances to the lower pH’s than non-stressed cultures. .Acidic conditions affect the biochemical pathways and injure or kill Salmonella. In this study, eight serotypes, four from feed (S. Montevideo (SMo), S. Senftenberg (SS), S. Tennessee (STn) and S. Schwarzengrund (SSc)) and four from the processing plant (S. Typhimurium (STy), S. Enteritidis (SE), S. Infantis (SI), and S. Heidelberg (SH)), were grown in sterile meat and bone meal for 48hrs at 35oC, centrifuged and the sediment subjected to desiccation and heat exposure (37oC for 36-48 hrs under partial vacuum) to stress them. Isolates were subsequently exposed to acidic pH from 4.0 to 7.0 in 0.5 pH increments (3 replicates/pH increment) in citrate buffer. At 6 and 24 hrs, serial dilutions were plated in duplicate on xylose lysine tergitol 4 (XLT4) agar. Four serotypes (SE, SI, SM and SSc) showed an impaired ability to decarboxylate lysine on XLT4. At a pH of 6, 56.61-57.04% of the colonies of unstressed cultures of SI and SSc were H2S negative within 6 hrs. This percentage significantly (P<0.05) increased for SSC at 24 hrs.Stressed SE and SI resulted in the greatest overall change in the ability of the isolate to decarboxylate lysine on XLT4. At a pH of 6, 92.51% of the SE colonies were H2S positive at 6 hrs, however, at 24 hrs, 87.54% of the colonies were H2S negative. In the case of SI, 90.24% of the colonies were H2S negative at 6hrs. 24 Hr results were not significantly different (P<0.05). At a pH of 6, stressed cultures of SM and SSc produced an approximate 50:50 ratio of H2S positive: H2S negative colonies at both 6 and 24 hrs. When further examined using the API20 biochemical test, with the exception of SI, cultures were still able to decarboxylate lysine. This suggests that XLT4 agar contains a biochemical stressor(s) which affects the rate of decarboxylation by Salmonella instead of the isolate losing the ability to decarboxylate lysine. These results suggest that the acidic conditions may influence the detection and confirmation of Salmonella in feed.