Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2007
Publication Date: 8/15/2007
Citation: Uesugi, A.R., Danyluk, M.D., Mandrell, R.E., Harris, L.J. 2007. Isolation of Salmonella Enteritidis PT 30 from a single almond orchard over a 4-year period. Journal of Food Protection. 70:1784-9
Interpretive Summary: There have been multiple outbreaks associated with raw almonds. Traceback investigations lead to isolation of the outbreak strain from almond orchard soils. Sampling of orchard soils was conducted over a three year period and resulted in isolation of the Salmonella Enteritidis phage type that caused the first outbreak. Salmonella isolates were selected, confirmed, serotyped, phage typed, and pulsed field gel electrophoresis (PFGE) patterns were determined (Xba I and Bln I). Salmonella was seldom recovered from December through July, but increased during the months of harvesting (August, September, October, and November), probably due to large amounts of dust generated. This study demonstrates the potential for long-term environmental survival of Salmonella in almond orchards.
Technical Abstract: In 2001, Salmonella Enteritidis phage type (PT) 30 was isolated from drag swabs of 17 61-ha almond orchards on three farms linked to an outbreak of salmonellosis associated with consumption of raw almonds. The objective of this study was to evaluate the long-term persistence of Salmonella Enteritidis PT 30 in one of the almond orchards associated with the outbreak. Swabs (gauze saturated with full-strength sterile evaporated skim milk and attached to string) were pulled along the orchard floor in a standardized manner for 55 m. At each sample time, two pooled samples (four swabs each) were collected from each orchard quadrant. Swabs were enriched for Salmonella using a delayed secondary enrichment procedure developed for isolation of Salmonella from poultry houses. Suspect Salmonella isolates were selected, confirmed, serotyped, and phage typed, and pulsed-field gel electrophoresis (PFGE) patterns were determined after cleavage with XbaI and BlnI. Salmonella was recovered infrequently from pooled samples collected from January through July (3 of 56 samples, 5.3%). In general, Salmonella isolation frequency per sample time increased during and immediately after the harvest, when large amounts of dust were generated in or near the orchard: August, 4 (20%) of 20 samples; September, 13 (20%) of 64 samples; October, 27 (42%)of 64 samples; November, 4 (25%) of 16 samples; and December, 2 (25%) of 8 samples. All 53 Salmonella isolates during the 5 years were identified as Salmonella Enteritidis PT 30, and two PFGE patterns that differed by the presence of an approximately 40-kb fragment were identified. These data demonstrate the potential for long-term environmental persistence of Salmonella in almond orchards.