Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/1999
Publication Date: N/A
Interpretive Summary: Salmonella is a human pathogen that has been associated with poultry and poultry products. In the laboratory procedure for isolation of Salmonella, agar plates are streaked and Salmonella produces colony forming units with a particular color. These colonies are different from the non-Salmonella bacteria. When mixed with non salmonellae bacteria found in poultry samples, Salmonella can go un-detected. Seven types of plating media were tested for detection of Salmonella from these extraneous bacteria. Any two of the best three media would have detected 18 of the 19 salmonellae positive samples. Only one sample was found positive with all seven plating media. Even when samples were inoculated with hundreds of Salmonella, these organisms were not detected on most of these plating media. Variation in results should be expected by research and regulatory laboratories. Even when Salmonella is known to be present in samples, these microorganisms frequently are not detected on the best selective plating media available.
Technical Abstract: Broiler carcasses were obtained and rinsed. The rinses underwent pre-enrichment, selective enrichment and were streaked onto seven different Salmonella selective plating media (BG- Sulfa, Bismuth Sulfite, Hektoen Enteric, Modified Lysine Iron, Rambach Plus, Xylose Lysine Desoxycholate, Xylose Lysine T4). Of the 24 rinse samples, 19 were confirmed to be Salmonella positive by one or more of the plating agars. BG-Sulfa and Modified Lysine Iron detected the most of these positive samples, 17, while Rambach Plus was close behind with 16. Hektoen Enteric and Xylose Lysine T4 each detected 11, Xylose Lysine Desoxycholate detected 6 and Bismuth Sulfite was able to detect Salmonella in one of the 19 positive samples. Any two of the best three media would have detected 18 of the 19 salmonellae positive samples. Only one rinse was found to be positive with all of the plating media. Unless laboratories are using identical procedures, variation in results should be expected because some plating media perform significantly better than others. The presence of abundant extraneous bacteria also growing on the plating medium is the primary reason why salmonellae goes undetected on a specific plate. Even when eight batches of 100 ml of chicken rinse fluid each was spiked with a million cells of Salmonella, only Rambach Plus detected Salmonella in all 8 samples. Modified Lysine Iron Agar, BG- Sulfa Agar and Xylose Lysine Desarycholate Agar detected Salmonella in 6, 3 and 2 of the 8 spiked samples, respectively.