Isolation and Effectiveness of Antagonistic Serratia plymuthica ED1 against Salmonella Enteritidis Growth on Mung Bean Sprouts

Introduction: There have been a multitude of Salmonella sp. outbreaks associated with the consumption of bean sprouts throughout the world. The use of antagonistic, non-pathogenic organisms may help aid in the reduction of Salmonella sp. on bean sprouts by limiting the incidence of foodborne disease.

Purpose: The purpose of this study was to evaluate the effectiveness of an isolated strain of Serratia plymuthica (ED1) on the reduction of Salmonella Enteritidis (S. Enteritidis) growth on mung beans during sprouting.

Methods: Mung beans were inoculated with either of S. Enteritidis and/or nalidixic acid resistant antagonistic ED1 at various levels.  At times during germination, sprout samples were homogenized and plated on TSA, 100 µg/ml nalidixic acid TSA, and XLD agars to obtain standard plate, S. plymuthica, and Salmonella counts, respectively. Un-inoculated beans were used as controls.

Results : Fresh produce was screened for organisms demonstrating antagonistic properties against Salmonella sp. One organism was isolated and identified as Serratia plymuthica via 16S rDNA sequencing and was designated as strain ED1.  S. Enteritidis (5 or 8 log CFU/g) were inoculated on mung beans with or without a nalidixic acid variant of antagonistic ED1 (8 CFU/g).  After 5 days, the level of S. Enteritidis in sprouts inoculated with ED1 showed a 4 log and 2 log CFU/g reduction than sprouts without ED1. The refrigerated storage life of the ED1 inoculated sprouts was found to be comparable to non-inoculated sprouts, indicating that the presence of the bacterial antagonist did not result in accelerated spoilage.

Significance: The treatment of beans with ED1 may prove an effective method in reducing and potentially eliminate the presence of low numbers of Salmonella sp. on bean sprouts.