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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Food Safety and Enteric Pathogens Research » Research » Publications at this Location » Publication #198078


item Muraoka, Wayne
item Wesley, Irene

Submitted to: American Society for Microbiology Branch Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/22/2005
Publication Date: 9/23/2005
Citation: Lechtenberg, T., Muraoka, W.T., Wesley, I.V. 2005. Quantification of Salmonella enterica via the revised RX tube method [abstract]. North Central Branch of the American Society for Microbiology. p.78.

Interpretive Summary:

Technical Abstract: Several different methods of quantifying Salmonella enterica have been developed, of which the most common method is the most probable number (MPN) technique. However, this is a labor and media intensive method. The RX tube (modified semi-solid RV and XLT) was originally designed by Gailey et al. (2004) to replace the MPN technique, but was difficult to produce accurately. In this experiment, the RX method was refined and then compared to a traditional MPN to enumerate Salmonella in a sample. Modifications to the RX tube included varying the concentration of the agar in the modified semi-solid RV when used with mixed cultures and removing the addition of tetrathionate broth when used with pure cultures. With these modifications, the RX tubes were more stable and user-friendly. Both pure cultures of Salmonella and artificially-contaminated turkey cloacal samples were used to compare the RX tube and MPN methods. The RX tubes, MPN method, and plate counts were all performed simultaneously. Visual interpretation of the RX tubes was validated using conventional PCR and the Qualicon BAX PCR system. The RX tubes were found to have a specificity of 98.7% and a sensitivity of 97.3% when compared to conventional PCR. Findings indicated that the RX method produced bacterial counts similar to that of the MPN technique, thus allowing less technician time and media to produce the same result.