Green Fluorescent Protein Expressing Salmonella Stanley to Investigate Survival Spatial Location and Control On Sprouts

Useof Green Fluorescent Protein Expressing Salmonella Stanley To InvestigateSurvival, Spatial Location, and Control on Alfalfa Sprouts

Journalof Food Protection: Vol. 64, No. 12, pp. 1891-1898.

MeghaGands, Sherene Golding, Sima Yaron, and Karl R. Matthews

CookCollege, Department of Food Science, Rutgers, The State University of New Jersey

Abstract-Laser scanningconfocal microscopy (LSCM) was used to observe the interaction of SalmonellaStanley with alfalfa sprouts. The green fluorescent protein (gfp) gene wasintegrated into the chromosome of Salmonella Stanley for constitutiveexpression, thereby eliminating problems of plasmid stability and loss ofsignal. Alfalfa seeds were inoculated by immersion in a suspension of SalmonellaStanley (ca. 107 CFU/ml) for 5 min at 22°C. Epifluorescencemicroscopy demonstrated the presence of target bacteria on the surface ofsprouts. LSCM demonstrated bacteria present at a depth of 12 um within intactsprout tissue. An initial population of ca. 104 CFU/g seed increasedto 7.0 log CFU/g during a 24-h germination period and then decreased to 4.9 logCFU/g during a 144-h sprouting period. Populations of Salmonella Stanley onalfalfa seeds decreased from 5.2 to 4.1 log CFU/g and from 5.2 to 2.8 log CFU/gfor seeds stored 60 days at 5 and 22°C, respectively. The efficacy of 100, 200,500, or 2,000 ppm chlorine in killing Salmonella Stanley associated with sproutswas determined. Treatment of sprouts in 2,000 ppm chlorine for 2 or 5 min causeda significant reduction in populations of Salmonella Stanley. Influence ofstorage on Salmonella Stanley populations was investigated by storing sprouts 4days at 4°C. The initial population (7.76 log CFU/g) of Salmonella Stanley onmature sprouts decreased (7.67 log CFU/g) only slightly. Cross-contaminationduring harvest was investigated by harvesting contaminated sprouts, thendirectly harvesting noncontaminated sprouts. This process resulted in thetransfer of ca. 105 CFU/g Salmonella Stanley to the noncontaminatedsprouts.