Survival of Salmonella Newport on whole and fresh-cut cucumbers treated with lytic bacteriophages

Authors: Sharma, Manan; DASHIELL, GWENDOLYN - University Of Maryland Eastern Shore (UMES); Handy, Eric; East, Cheryl - Roberts; REYNNELLS, RUSSEL - University Of Maryland Eastern Shore (UMES); WHITE, CHANELLE - University Of Maryland Eastern Shore (UMES); NYARKO, ESMOND - University Of Delaware; HASHEM, FAWZY - University Of Maryland Eastern Shore (UMES); Millner, Patricia

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2016
Publication Date: 3/15/2017
Citation: Sharma, M., Dashiell, G., Handy, E.T., East, C.L., Reynnells, R., White, C., Nyarko, E., Hashem, F., Millner, P.D. 2017. Survival of Salmonella Newport on whole and fresh-cut cucumbers treated with lytic bacteriophages. Journal of Food Protection. 80:668-673.

Interpretive Summary: Cucumbers have been associated with major outbreaks of salmonellosis. Lytic bacteriophages (phages) are non-harmful viruses that have been used to kill foodborne pathogens on produce commodities. Phages directly applied (sprayed) to the surface of whole cucumbers were effective at reducing Salmonella Newport populations. Indirect transfer of phages from the surface of cucumbers to the flesh (through slicing) was less effective in reducing S. Newport on cucumber flesh. Spraying phages provides a higher ratio of bacteriophage particles to target bacterial cells needed to reduce Salmonella populations. The application of phages hastened the decline of Salmonella populations on whole and fresh-cut cucumbers. This study provides insightful information to scientists working on produce safety.

Technical Abstract: Salmonella enterica associated with consumption of cucumbers (Cucumis sativus) has led to foodborne outbreaks in the U.S. Whole and fresh-cut cucumbers are susceptible to Salmonella spp. contamination during growing and harvesting. The application of lytic bacteriophages specific for Salmonella spp. was evaluated to reduce Salmonella populations on cucumbers. Unwaxed cucumbers (greenhouse-grown, ‘Lisboa’ variety, or mini-cucumbers purchased at retail) were inoculated with 5 log CFU/cucumber Salmonella Newport, and sprayed with 3.2 mL of 9 log PFU/ml SalmoFreshTM, a Salmonella-specific bacteriophage preparation (phage), or phosphate-buffered saline (control). Whole cucumbers were stored at 10 or 22°C for 7 days. Mini-cucumbers were sliced with a sterile knife to investigate Salmonella transfer to mesocarp, and fresh-cut pieces were stored at 4°C for 2 days. Salmonella populations from whole and fresh-cut cucumbers were recovered on selective media. Populations (log CFU/cucumber) of Salmonella on phage-treated whole cucumbers stored at 10°C were 2.44, 1.72, and 1.56, which were significantly (p < 0.05) lower than those on control-treated cucumbers (4.27, 3.20, and 2.33) on days 0, 1, and 4, respectively. There were no significant differences in Salmonella populations between phage- and control-treatments of a) whole cucumbers at 22°C, or b) fresh-cut cucumbers stored at 4°C. Direct application (spraying) of lytic bacteriophages to whole cucumbers led to higher phage titer values and multiplicity of infection (MOI) values than those achieved through indirect transfer (slicing) of phages from the surface to flesh of cucumber. Lytic phages were effective at reducing S. Newport populations by 2 log CFU on whole cucumbers compared to controls.