Understanding a foodâs ability to support the growth and/or survival of a pathogen throughout the supply chain is essential to minimizing large-scale contamination events. The purpose of this study was to examine the behavior (growth and/or survival) of Listeria monocytogeneson broccoli and cauliflower florets stored under different post-harvest temperatures utilized along the supply chain. Broccoli and cauliflower samples were inoculated at approximately 3 log CFU/g and stored at temperatures: 23Â±2, 12Â±2, 4Â±2, and -18Â±2Â°C. Samples were enumerated at 0, 0.167 (4 h), 1, 2, 3, and 4 (23Â±2Â°C); 0, 0.167, 1, 2, 3, 4, 7, 10 and 14 (12Â±2Â°C); 0, 0.167, 1, 2, 3, 4, 7, 10, 14, 21 and 28 (4Â±2Â°C); and 0, 1, 7, 28, 56, 84, 112, 140 and 168 (-18Â±2Â°C) d. L. monocytogenes populations were determined from plating samples onto tryptic soy agar and modified Oxford agars supplemented with nalidixic acid. Broccoli and cauliflower supported the growth of L. monocytogenes at 23, 12, and 4Â°C, with higher growth rates observed at higher temperatures. Populations of L. monocytogenes on broccoli and cauliflower samples significantly increased within 1 d at 23Â°C (1.6 and 2.0 log CFU/g, respectively) (P â¤ 0.05). At 12Â°C, populations of L. monocytogenes on broccoli and cauliflower samples significantly increased over 14 d by 1.4 and 1.9 log CFU/g, respectively (P â¤ 0.05). No significant difference over time was observed in L. monocytogenes populations on broccoli and cauliflower samples held at refrigeration, until populations began to grow by d 10 for both commodities (P> 0.05). Under frozen storage (-18Â°C),populations of L. monocytogenes survived on broccoli and cauliflower at least up to 168 d. Broccoli and cauliflower may be stored at lower temperatures to minimize L. monocytogenes growth potential, as growth rates were lower at 4Â°C, compared to at 12 and 23Â°C.
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.