For some studies, enrichment was conducted when sample results
were expected to be below the limit of detection (LOD; 10 CFU/nut).
For all pathogens, the sample remaining after plating (remainder of
the 10-ml diluent and the inshell walnut) was added to 50 ml of TSB
and incubated at 37 °C for 24 or 48 ± 3 h. Secondary enrichments for
each pathogen (Salmonella: Rappaport-Vassiliadis R10 broth and
tetrathionate broth, both without Rif; E. coli O157:H7: Brilliant Green
Bile Lactose broth without Rif; L. monocytogenes: UVMModified Listeria
enrichment brothwithout Rif) and confirmations on differential/selective
media (Salmonella: BSA, xylose lysine deoxycholate agar without Rif, and
Hektoen enteric agar without Rif; E. coli O157:H7: BBL CHROMagar O157
(ChromO157; BD Diagnostic Systems); L. monocytogenes: MOX) were
conducted exactly as described in detail previously (Blessington et al.,
2012).