Evaluation of plating media for recovering Salmonella from thermally treated egg albumen

Abstract

Salmonella spp. present in pasteurized egg albumen are often difficult to recover by direct plating because of thermal injury and the presence of innate iron binding and other antimicrobials in egg white. The literature has reported a multiplicity of selective and nonselective media used to recover heat-injured Salmonella, to measure the proportion of injured cells, or both. This study compared the proficiency of selective and nonselective plating media for supporting colony development or for assessing bacterial injury of heat-stressed Salmonella from egg albumen. A 6-strain composite of Salmonella was added to albumen (pH 9.0), heated at 53.3°C for 3.1 min, and plated on 26 nonselective and 22 selective media. Recovery of heat-injured salmonellae varied little (≤0.52 log cfu/mL) among the nonselective media tryptic soy agar, plate count agar, dextrose tryptone agar, or brain heart infusion agar, regardless of the manufacturer. Selective media that were optimal for recovery of salmonellae from albumen included 3 brilliant green agars, Levine eosin methylene blue agar, and bismuth sulfite agar, which recovered more cells (P ≤ 0.05) than selenite-cystine, tetrathionate, xylose-lysine-tergitol-4, xylose lysine deoxycholate, or Rappaport-Vassiliadis agars. The results of this study may assist in choosing selective or nonselective media to maximize the recovery of Salmonella from thermally treated albumen.