Microbiome convergence following sanitizer treatment and identification of sanitizer resistant species from spinach and lettuce rinse water

Abstract

Fresh produce, as a known or suspected source of multiple foodbome outbreaks, harbors large populations of diverse microorganisms, which are partially released into wash water during processing. However, the dynamics of bacterial communities in wash water during produce processing is poorly understood. In this study, we investigated the effect of chlorine (FC) and peracetic acid (PAA) on the microbiome dynamics in spinach and romaine lettuce rinse water. Treatments with increasing concentrations of sanitizers resulted in convergence of distinct microbiomes. The resultant sanitizer resistant microbiome showed dominant presence by Bacillus sp., Arthrobacter psychrolactophilus, Cupriavidus sp., and Ralstonia sp. Most of the FC and PAA resistant bacteria isolated from spinach and lettuce rinse water after sanitation were gram positive spore forming species including Bacillus, Paenibacillus, and Brewbacillus spp., while several PAA resistant Pseudomonas spp. were also isolated from lettuce rinse water. Inoculation of foodbome pathogens altered the microbiome shift in spinach rinse water under PAA treatment, but not in lettuce rinse water or FC treated samples. These inoculated foodbome pathogens were not isolated among the sanitizer resistant strains.