Control of Listeria monocytogenes on fresh strawberries by lactic acid bacteria

Authors: COLORADO SUAREZ, STEPHANIE - University Of Puerto Rico; YIN, HSIN-BAI - US Department Of Agriculture (USDA); CHEN, CHI-HUNG - US Department Of Agriculture (USDA); Patel, Jitu

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/19/2019
Publication Date: 7/21/2019
Citation: Colorado Suarez, S., Yin, H., Chen, C., Patel, J.R. 2019. Control of Listeria monocytogenes on fresh strawberries by lactic acid bacteria. International Association for Food Protection. 2:196.

Interpretive Summary:

Technical Abstract: Introduction: Foodborne illness outbreaks associated with consumption of raw fruits have gained public attention in recent years. Listeria monocytogenes as an important foodborne bacterial pathogen may contaminate strawberries and threaten the public health. Purpose: The purpose of this study was to investigate the effect of two canine-feces origin lactic acid bacteria (LAB), namely Lactobacillus plantarum and Pediococcus pentosaceus, as post-harvest biocontrol agents against L. monocytogenes on fresh strawberries. Methods: Strawberries (N=144) purchased from the local grocery store were sorted for identical sizes and then dip-inoculated with a three-strain cocktail of L. monocytogenes in phosphate buffered saline (PBS) to obtain 6.0 log CFU/g of Listeria populations on strawberries. After Listeria inoculation and air-drying for 1h, strawberries were dipped in MRS broth containing 9 log CFU/ml cocktail of L. plantarum and P. pentosaceus. Listeria-inoculated strawberries with no further treatment or dipped with fresh MRS broth alone were included as controls. After treatment, strawberries were stored at 4ºC or 10ºC for 7 days. Surviving Listeria and LAB populations on strawberries were determined on 0, 1, 3, and 7 days-post-treatment by serial dilution and spiral plating on Rapid’Lmono and MRS agars, respectively. Results: There was no significant difference in Listeria populations between the control and MRS control, in which ~ 5.0 log CFU/g of Listeria were recovered from the controls on day 7. At both 4ºC and 10ºC of the storage, LAB treatment significantly decreased Listeria populations by 1.5 log, 2.0 log, and 2.5 log CFU/g as compared to the controls on days 1, 3, and 7, respectively (P<0.05). LAB populations remained at ~ 7.5 log CFU/g levels on strawberries at both storage temperatures throughout the entire study. Significance: Results of this study indicate that LAB can be potentially used as post-harvest biocontrol agents against L. monocytogenes on fresh strawberries. Keywords: strawberry, lactic acid bacteria, Listeria monocytogenes, biocontrol