Growth and Survival of Listeria monocytogenes and Salmonella on Whole and Sliced Cucumbers.

ABSTRACT

Cucumbers were associated with four multistate outbreaks of Salmonella in the United States between 2013 and 2016. This study evaluated the fate of Listeria monocytogenes and Salmonella on whole and sliced cucumbers at various storage temperatures. Cucumbers were inoculated with five-strain cocktails of L. monocytogenes or Salmonella, air dried, and stored at 23 ± 2, 4 ± 2, and -18 ± 2°C. Whole and sliced cucumber samples were enumerated on nonselective and selective media at 0, 0.21, 1, 2, 3, and 4 days (23 ± 2°C); 0, 1, 2, 3, 7, 14, and 21 days (4 ± 2°C); and 0, 7, 28, 60, 90, and 120 days (-18 ± 2°C). For Salmonella, additional time points were added at 8 and 17 h (23 ± 2°C) and at 17 h (4 ± 2°C). Population levels were calculated for whole (CFU per cucumber) and sliced (CFU per gram) cucumbers. Both pathogens grew on whole and sliced cucumbers held at ambient temperatures. At 23 ± 2°C, L. monocytogenes and Salmonella populations significantly increased on whole (2.3 and 3.4 log CFU per cucumber, respectively) and sliced (1.7 and 3.2 log CFU/g, respectively) cucumbers within 1 day. Salmonella populations significantly increased on whole and sliced cucumbers after only 5 h (2.1 log CFU per cucumber and 1.5 log CFU/g, respectively), whereas L. monocytogenes populations were not significantly different on whole and sliced cucumbers at 5 h. L. monocytogenes and Salmonella populations survived up to 21 days on refrigerated whole and sliced cucumbers. At 4 ± 2°C, L. monocytogenes populations significantly increased on whole (2.8 log CFU per cucumber) and sliced (2.9 log CFU/g) cucumbers, whereas Salmonella populations significantly decreased on whole (0.6 log CFU per cucumber) and sliced (1.3 log CFU/g) cucumbers over 21 days. Both pathogens survived on frozen whole and sliced cucumbers for at least 120 days. The ability of L. monocytogenes and Salmonella to grow on whole and sliced cucumbers in short amounts of time at ambient temperatures, and to survive on whole and sliced cucumbers past the recommended shelf life at refrigeration temperatures, highlights the need to reduce the likelihood of contamination events throughout the cucumber supply chain.