Survival of Salmonella Newport on Whole and Fresh-Cut Cucumbers Treated with Lytic Bacteriophages

Abstract

Salmonella enterica associated with consumption of cucumbers ( Cucumis sativus ) has led to foodborne outbreaks in the United States. Whole and fresh-cut cucumbers are susceptible to S. enterica contamination during growing, harvesting, and postharvest handling. The application of lytic bacteriophages specific for S. enterica was evaluated to reduce Salmonella populations on cucumbers. Unwaxed cucumbers ('Lisboa' variety, or mini-cucumbers purchased at retail) were inoculated with Salmonella Newport (5 log CFU per cucumber) and were sprayed with 3.2 mL of phosphate-buffered saline (control) or 10 log PFU/ml of SalmoFresh, a Salmonella-specific bacteriophage preparation (phage), to deliver 4.76 × 10 PFU/cm. Cucumbers were stored at 10 or 22°C for 7 days. Inoculated mini-cucumbers were sliced with a sterile knife to investigate Salmonella transfer to mesocarp, and cut pieces were stored at 4°C for 2 days. Populations (log CFU per cucumber) of Salmonella Newport on phage-treated whole cucumbers were significantly (P < 0.05) smaller (2.44 ± 0.94) than on control-treated cucumbers (4.27 ± 0.37) on day 0. Populations on phage-treated cucumbers stored at 10°C were 1.72 ± 0.77 and 1.56 ± 0.46, which were significantly lower than those on control-treated cucumbers (3.20 ± 0.48 and 2.33 ± 0.25) on days 1 and 4, respectively. Between days 0 and 1, populations on control-treated cucumbers stored at 10 and 22°C declined by 1.07 and 2.47 log CFU per cucumber, respectively. At 22°C, Salmonella Newport populations declined by 2.37 log CFU per cucumber between days 0 and 1. Phage application to whole cucumbers before slicing did not reduce the transfer of Salmonella Newport to fresh-cut slices. Lytic phage application may be a potential intervention to reduce Salmonella populations on whole cucumbers.

Isolation and Characterization of Two Lytic Bacteriophages Infecting a Multi-Drug Resistant Salmonella Typhimurium and Their Efficacy to Combat Salmonellosis in Ready-to-Use Foods

“…Previous studies detected a significant reduction in the recovered S. Enteritidis by up to 3 log10 while using phage cocktail at an MOI of 10000 and 1000 in milk, chicken breast, and cabbage detected [62,83], and the application of phage cocktails has also been shown to reduce Salmonella spp. in different food matrices [26,39,[90][91][92][93][94][95].…”

Effectiveness of Bacteriophages Against Biofilm-Forming Shiga-ToxigenicEscherichia colion Leafy Greens and Cucumbers

“…34 The concept of LO could also be applicable when phage-treated produce is stored at low temperatures (4°C), where the growth of many pathogenic bacteria is halted, leading to incomplete lytic cycle of bacteriophage. 21 This would explain the immediate reduction in pathogen populations on phage-treated greens stored at 4°C.…”

“…The marked areas (1 • 6 cm) on each cucumber received 10 inoculum spots (10 lL each) of the multiserotype STEC cocktail and placed in a biosafety cabinet for 1 h to facilitate bacterial attachment. 21 Three cucumbers were set aside as the positive control, whereas the remaining were sprayed with appropriate volumes of either PBS control or phage treatment (*7 logs PFU/cucumber). Each cucumber was placed and stored in a 55 oz.…”

“…On each sampling day, one whole cucumber was suspended in 100 mL PBS and hand massaged for 1 min. 21 Appropriate dilutions were then plated on MAC agar and incubated at 37°C for 24 h. For all the experiments (with leafy greens and cucumbers), 1 mL of the stomached solution was also enriched in 9 mL TSB (37°C; 24 h) to recover any injured cells. To determine phage populations on fresh produce during storage, 1 mL of the stomached solution was filtered using 0.2 lm syringe filter, serially diluted in PBS, and plated using plaque assay.…”

“…Significant reduction in other foodborne pathogens such as Salmonella Typhimurium, Campylobacter jejuni, and L. monocytogenes was also reported in various fresh-cut produce or meat products treated with bacteriophages. [21][22][23][24] Bai et al 22 revealed a reduction (4.7-5.8 logs CFU/cm 2 ) in Salmonella Typhimurium populations on iceberg lettuce and cucumber surfaces after 12 h at 25°C. Another study documented a reduction in L. monocytogenes populations on melon and pear slices (1-1.5 log CFU/plug) after 8 days of storage (10°C).…”