Comparison of Attachment of Salmonella Enteritidis and Typhimurium on Black Pepper, Almond and Hazelnut

Introduction: Salmonella enterica Enteritidis and Typhimurium are the two most common serovars that cause foodborne illness in the U. S. Outbreaks of these serovars have been attributed to low moisture foods such as peanuts, infant formula, and chocolate. However, little is known about the mechanisms of attachment on low moisture food surface.

Purpose: To evaluate the influence of black pepper, almond, and hazelnut surface characteristics on the attachment of Salmonella Enteritidis and Typhimurium.

Methods: Salmonella Enteritidis PT4 and Typhimurium LT2 were inoculated onto the surfaces of black pepper, almonds and hazelnuts at 10⁹ CFU/g. After air drying for 2 h, samples were incubated at 25°C and 60% humidity. At 0, 1, 3, 7 and 14 d, samples were recovered with agitation at 200 rpm to remove loose or non-attached bacteria. To remove more firmly attached bacteria, the samples were then vortexed at 2000 rpm with sterile glass beads. Samples were serially diluted onto BHI and XLD agars. Statistical analyses were conducted using Excel and Prism GraphPad; a P-value less than 0.05 was considered significant.

Results: Significant differences were found in the attachment of Enteritidis and Typhimurium on the surface of black pepper, almonds and hazelnuts. For black pepper, the D-values (in days) were 24.62 ± 4.51 vs. 6.44 ± 0.42 on BHI and 23.34 ± 3.25 vs. 6.22 ± 0.55 on XLD for LT2 vs. PT4, respectively. For attachment on almonds, D-values were 18.12 ± 7.94 vs. 3.53 ± 0.39 on BHI and 15.35 ± 4.69 vs. 3.26 ± 0.28 on XLD for LT2 vs. PT4, respectively. For attachment on hazelnuts, D-values were 7.49 ± 1.37 vs. 4.37 ± 1.15 on BHI and 7.12 ± 1.38 vs. 4.16 ± 0.97 on XLD for LT2 vs. PT4, respectively.

Significance: The data obtained can be used to better understand the physiology of S. enterica on low moisture foods and aid in developing effective control measures to reduce pathogen contamination.