Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2007
Publication Date: 2/1/2008
Citation: Danyluk, M.D., Brandl, M., Harris, L.J. 2008. Migration of Salmonella Enteritidis PT 30 through almond hulls and shells. Journal of Food Protection. 71:397-401
Interpretive Summary: There have been multiple outbreaks associated with raw almonds. These have generated interest in potential modes of contamination of this nutmeat. We have investigated the ability of Salmonella Enteritidis PT 30 to migrate through almond hulls and shells. S. Enteritidis was isolated from the inside of the shells of almond fruits that were previously soaked in the bacterial suspension. GFP-Salmonella cells were detected on almond kernels, outer and inner shells, and on and within the hull by confocal laser scanning microscopy. These combined data provide direct evidence that wet conditions allow for Salmonella multiplication and migration through the hull and the shell, thus providing a means by which almonds kernels may become contaminated.
Technical Abstract: The ability of Salmonella to migrate from an external aqueous environment through the almond hull and shell, and to colonize the kernel, was evaluated in two ways. First, the outer surface of shell halves from five varieties of almonds that differed in shell hardness were placed in contact with a suspension of Salmonella enterica serovar Enteritidis Phage Type (PT) 30 for 24 h at 24 degree C. Salmonella Enteritidis was isolated from the inside of these almond shells in 46% and 100% of the samples by direct swabbing of the inner surface of the shell and by enrichment from the swab, respectively. These findings suggested that hardness of the shell is not a significant factor in the migration of the pathogen through that tissue. In addition, both motile and non-motile strains of S. enterica serovar Typhimurium migrated through the almond shells to the same extent under the conditions of this assay, indicating that bacterial migration through the wet shell may be a passive process. Second, whole almonds (intact hull, shell, and kernel) were soaked for 24 to 72 h at 24 degree C in a suspension of S. Enteritidis PT 30 labeled with the green fluorescent protein (GFP). GFP-labeled Salmonella cells were observed on the outer and inner surfaces of both the almond hull and shell, and on the kernel, by confocal laser scanning microscopy. Our data provide direct evidence that wet conditions allow for Salmonella migration through the hull and shell and onto the almond kernel, thus providing a means by which almond kernels may become contaminated in the field.