Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2009
Publication Date: 7/12/2009
Citation: Gurtler, J., Jordan, J.S. 2009. Thermal resistance of thirty strains of Salmonella in liquid whole egg: are the optimal bacterial strains being used in challenge studies?. [abstract]. International Association for Food Protection, 96th Annual Meeting. p.1.
Technical Abstract: Introduction: Bacterial inactivation studies are conducted to determine the survival of a target pathogen, such as Salmonella, to any number of intervention treatments (e.g., high pressure, antimicrobials, UV light, gamma irradiation, heat, etc.). Resistance of a species of pathogen, such as Salmonella enterica, to these treatments can be very large between strains. Proper selection of bacterial strains to be used in inactivation challenge studies is a critical experimental criterion if relevant results are desired. Purpose: The goal of this study was to screen thirty strains of Salmonella for thermal resistance in commercially-processed liquid whole egg (LWE). Methods: Thirty strains of Salmonella were grown in Tryptic Soy broth at 37C, with one 24 h transfer, concentrated ten-fold by centrifugation, and resuspended in 0.1% peptone water. Each inoculum was added to LWE and mixed thoroughly, resulting in a final population of ca. 8 log CFU/ml. Inoculated LWE was injected into sterile glass capillary tubes, flame-sealed and heated in a water bath at 58C for up to twelve min. Capillary tubes were ethanol sanitized, rinsed twice in sterile water and contents were extracted. The LWE was diluted, surface plated onto Tryptic Soy agar + 0.1% sodium pyruvate and incubated at 37C for 24 h before colonies were enumerated Results: Twenty-three of thirty strains were considered heat-sensitive with asymptotic D58 values of less than 1.00 min. The D58 values of three strains (two Enteritidis phage type 8 and one Oranienburg) were 2.11 – 2.61 min. Four more strains (Enteritidis PT 4, PT 13, Oranienburg, and St. Paul) demonstrated similar D58 values of from 1.85 to 1.90 min. Significance: The four most heat-resistant strains (Salmonella Enteritidis PT 8, 8, 13, and Oranienburg) are being used in ongoing ARS/FSIS liquid egg pasteurization studies. These results highlight the importance of carefully selecting optimal bacterial strains to be used in inactivation challenge studies.