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SUMMARY: The ability of pre-enrichment media to buffer pH changes that occur during incubation is essential for recovery and detection of Salmonella from feed/ingredients. Depending on feed/ingredient type, the pH of the pre-enrichment media can decrease during incubation to a pH 4.0–5.0. Acidic conditions can: 1) injure Salmonella, 2) kill Salmonella, and/or 3) affect their biochemical pathways. Most strains of Salmonella produce hydrogen sulfide (H2 S) from thiosulfate and/or sulfide on selective agars which is utilized to differentiate Salmonella from other microorganisms. The ability of isolates to produce H2 S on xylose-lysine-tergitol 4 agar (XLT4) is dependent on the acidic conditions that can occur during pre-enrichment, the strain of Salmonella, and the stress status of the isolate. Enrichment media are often used to recover injured Salmonella with respect to cell multiplication but have not been examined for their ability to repair damage to biochemical pathways. In this study, isolates of Salmonella that had previously been exposed to acidic conditions and lost the ability to produce H2 S on XLT-4 agar were grown in various enrichment media. After 24 h of enrichment, H2 S-positive and negative colonies were enumerated. The impact of enrichment media on cell multiplication was dependent on enrichment media, incubation temperature, Salmonella strain, stress status, and H2 S status. None of the enrichment media restored the ability of the isolate to produce H2 S on XLT-4 agar at 24 h. After an additional 24-h incubation, (48 h total), the ability of some isolates to produce H2 S was restored. |
