Shifts in spinach microbial communities after chlorine washing and storage at compliant and abusive temperatures

Authors: GU, GANGY - VIRGINIA TECH; OTTESEN, ANDREA - FOOD AND DRUG ADMINISTRATION(FDA); BOLTEN, SAMANTHA; RAMACHANDRAN, PADMINI - FOOD AND DRUG ADMINISTRATION(FDA); REED, ELIZABETH - FOOD AND DRUG ADMINISTRATION(FDA); RIDEOUT, STEVEN - VIRGINIA TECH; Luo, Yaguang - Sunny; Patel, Jitu; BROWN, ERIC - FOOD AND DRUG ADMINISTRATION(FDA); Nou, Xiangwu

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2018
Publication Date: 1/4/2018
Publication URL: https://handle.nal.usda.gov/10113/5918969
Citation: Gu, G., Ottesen, A., Bolten, S.J., Ramachandran, P., Reed, E., Rideout, S., Luo, Y., Patel, J.R., Brown, E., Nou, X. 2018. Shifts in spinach microbial communities after chlorine washing and storage at compliant and abusive temperatures. Food Microbiology. 73:73-84. https://doi.org/10.1016/j.fm.2018.01.002.
DOI: https://doi.org/10.1016/j.fm.2018.01.002

Interpretive Summary: Spinach, like other fresh vegetables, can be a vehicle for the transmission of foodborne pathogens. It harbors large and diverse bacterial populations, potentially including pathogenic bacteria. These bacteria interact with each other to form a community. In the rare case that foodborne pathogens are present, this community can collectively influence the survival and proliferation of bacterial pathogens. This manuscript reports the changes in bacterial population and composition on spinach after washing and storage processes. Fresh spinach was collected from a commercial fresh produce processor before and after washing/packaging process in the factory. The bacterial population on the spinach were quantified, identified, and compared using microbiological and metagenomic analyses. We observed shifts in bacterial community at species and phylum levels in response of chlorine treatment and storages at different temperatures. This study provides insights on the microbial ecology of diverse bacterial community on spinach during production, which can benefit further studies on the interaction of microbes on produce, and the prevention of foodborne pathogens and spoilage.

Technical Abstract: Fresh produce, such as spinach, harbors large, diverse bacterial populations, including spoilage and potentially pathogenic bacteria. This study examined the effects of produce washing in chlorinated water and subsequent storage on the microbiota of spinach. Baby spinach leaves from a commercial fresh-cut produce processor, were assessed before and after washing in chlorine water, and then after one week's storage at 4, 10, and 15 oC. Live bacterial populations were determined using both culture method and quantitative real-time PCR (qPCR) after PMA treatment. Microbiota on spinach samples were analyzed by 16S rDNA amplicon sequencing using MiSeq and Qiime2. Bacterial populations on spinach, averaging at 6.12 ± 0.61 log CFU/g, were reduced by 1.33 ± 0.57 log after washing. However, populations increased by 1.77 - 3.24 log after storage, with larger increases occurring at higher temperature (15 > 10 > 4 oC). The predominant phylum identified on unwashed spinach leaves was Proteobacteria; dominant genera were Pseudomonas and Sphingomonas. Bacterial communities shifted significantly after chlorine washing and storage. Several Proteobacteria species, such as Stenotrophomonas and Erwinia spp., were relatively tolerant of chlorine treatment, while species of Flavobacterium and Pedobacter (phylum Bacteroidetes) grew rapidly during storage, especially at abusive temperatures. Cupriavidus and Ralstonia spp. showed significant increases after chlorine washing. After storage, microbial communities on spinach appeared to shift back toward the pre-washing distributions. This study provides insights into the ecology of microbial communities on fresh produce during processing and storage.