Title: Evaluation of plating media for recovering Salmonella from thermally treated egg albumen Author
Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 26, 2009
Publication Date: June 2, 2009
Citation: Gurtler, J. 2009. Evaluation of plating media for recovering Salmonella from thermally treated egg albumen. Journal of Applied Poultry Research. 18:297-309. Interpretive Summary: Salmonella is known to contaminate a small percentage of egg products, although it is often difficult to recover the pathogen from liquid egg white. This study compared 49 different microbiological agar media to determine those best suited to recover Salmonella from liquid egg white that had been heat-treated. While a number of media were found to effectively recover heat-injured Salmonella, a number of commonly used media were shown to inhibit the growth of the bacterium. This information will assist in choosing appropriate microbiological agar media used to accurately determine the numbers of Salmonella in heat-processed liquid egg white.
Technical Abstract: A study was conducted to determine the performance of plating media for supporting resuscitation and colony development by heat-stressed cells of Salmonella from liquid egg white (albumen). A six-strain-composite of Salmonella was added to albumen (pH 9.0) at a population of 7.74 log CFU/ml, heated at 53.3C for 3.1 min to induce ca. 2 log CFU/ml inactivation, and plated on twenty-seven non-selective and twenty-two selective media. Media were prepared according to directions or supplemented with NaCl, KMnO4, ethylenediamine tetraacetic acid (EDTA), sodium deoxycholate, or calcium hypochlorite, and enrichment broths were solidified with 1.5 percent agar. Variations in oxidation-reduction potential (80 – 263 mV) and pH (5.34 – 8.37) of media had little effect on cell recovery. More cells recovered (P < 0.05) on five non-selective (tryptic soy agar [TSA] plus 0.01 or 0.1 percent EDTA, Difco plate count agar [PCA], TSA, and dextrose tryptone agar), than on brain heart infusion agar, PCA (Oxoid), PCA (Sigma), Davis minimal agar, or the following solidified broths: tryptic soy, Luria Bertani, buffered peptone water no. 1 and no. 2, DE neutralizing, or brain heart infusion. Slightly greater numbers of cells recovered on TSA with EDTA than on TSA alone, possibly due to chelation of toxic hydroxyl-generating metals. More cells recovered (P < 0.05) on six selective agar (brilliant green, Levine eosin methylene blue, brilliant green with phosphates, bismuth sulfite, and TSA with 1.5 percent NaCl) than on XLD, XLT4, TSA with 3 percent NaCl, solidified selenite cystine broth, Rappaport Vassiliadis broth, and tetrathionate broth. Although the addition of KMnO4 has been shown to enhance the recovery of heat-injured Salmonella, those findings could not be replicated in recovering the pathogen from heated egg white in this study. These results may assist in choosing a selective or non-selective plating medium to maximize the recovery of Salmonella from thermally-treated egg white.