Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2009
Publication Date: 10/1/2009
Citation: Gurtler, J., Kornacki, J.L. 2009. Comparison of supplements to enhance recovery of heat-injured Salmonella from egg albumen. Letters in Applied Microbiology. 503-509.
Interpretive Summary: A low number (approximately 1 in 20,000) eggs from hens are known to contain the bacterium Salmonella. Twenty-four billion eggs each year are pooled into liquid egg products. Liquid egg is then pasteurized to destroy Salmonella before being distributed to the consumer, either as an ingredient in manufactured foods or as eggs served in restaurants, schools and institutions. Microbiological studies are often conducted to test for the effectiveness of pasteurization in recovering and supporting colony development of Salmonella. Recovery compounds are sometimes used to assist in reviving injured Salmonella. This study was conducted to determine the response of sublethally-injured Salmonella to recovery on media supplemented with thirty-nine combinations of resuscitating supplements. We found that out of the thirty-nine combinations of chemical compounds tested, tryptic soy agar plus 1 g per liter of ferrous sulfate, or sodium pyruvate, or 3’3’-thiodipropionic acid recovered the greatest numbers of injured Salmonella. This work will be helpful to researchers in the government and the egg industry to assess the pasteurization of liquid egg products to support safe foods for the public.
Technical Abstract: The recovery of Salmonella from liquid egg white (LEW) is complicated by thermal and innate LEW antimicrobial-induced injury. Numerous supplements have been reported to promote the recovery of injured bacteria. The purpose of this study was to determine the efficacy of twelve media supplements to affect the recovery of heat-injured Salmonella from LEW. A five-strain composite of Salmonella was inoculated in LEW at 7.72 log CFU/ml, heated at 53.3C for 4 min., inducing ca. 2 log CFU/ml inactivation, and serial dilutions were plated on media with or without supplements. Greater numbers of Salmonella (P < 0.05) recovered with the addition of 1g/L ferrous sulfate (FeSO4) to Tryptic Soy agar (TSA) than with the addition of any other supplement, except for 0.5 or 1g/L 3’3’-thiodipropionic acid. Addition of 1g/L sodium pyruvate (CH3COCOONa), or 6g/L yeast extract plus 1g/L CH3COCOONa to TSA supported greater resuscitation than unsupplemented TSA or TSA supplemented with 0.01 or 0.1g/L N-propyl gallate, 10g/L activated charcoal, 0.1g/L KMnO4, or 50mg/L ethoxyquin. Even fewer numbers of Salmonella (P > 0.05) recovered on solidified Fluid Thioglycollate medium or on TSA with addition of the following compounds, ranked in order of performance: 1g/L EDTA > 50g/L sodium thiosulfate (Na2S2O3) > 15g/L NaCl. The remaining supplements supported recovery of equivalent numbers of Salmonella, which was fewer cells than recovered on TSA with 1g/L FeSO4 yet greater populations than recovered on TSA with 50mg/L ethoxyquin. These compounds included 3.5g/L or 6g/L CH3COCOONa, 1 or 5g/L activated charcoal, 0.1 or 0.01g/L FeSO4, 6g/L yeast extract, 1 or 0.5g/L EDTA, 5 or 0.5mg/L ethoxyquin, 0.5 or 5g/L Na2S2O3, 1, 0.1, or 0.01g/L ferric ammonium citrate, as well as unsupplemented plate count agar or TSA. These data suggest that media supplementation with FeSO4, 3’3’-thiodipropionic acid, or CH3COCOONa may aid in recovering sublethally injured Salmonella from LEW.