Prevalence and survival of Escherichia coli during onion production and postharvest storage: Influence of soil amendment, field curing, and storage temperature

ABSTRACT : Biological soil amendments of animal origin (BSAAO) can introduce foodborne pathogens into vegetable production soils and are frequently applied during onion production, a commodity associated with multiple foodborne outbreaks in recent years. This study assessed the prevalence of Escherichia coli ( E. coli ) on onions grown in heat-treated poultry pellets (HTPP) amended plots, its survival during field curing, and the influence of temperature on its survival during subsequent storage. Vidalia onion seedlings were transplanted into E. coli inoculated field plots that were either unamended or amended with HTTP. E. coli populations in the field plots were monitored through harvest (133 days) and after a 14-day field curing period. Inoculated onions were stored at 20 and 30°C and sampled at pre-determined time points (0-96 h) to assess survival. Samples were enumerated for E. coli using standard plating and most probable number (MPN) methods, followed by enrichment for confirmation. Onions from HTPP-amended plots had a significantly higher prevalence of E. coli (80.00%) at harvest compared to onions in unamended plots (13.33%) (p = 0.0007), as determined by Fisher’s exact test. Curing significantly reduced E. coli prevalence on the onions in HTPP plots from 80.00% to 6.67% (p = 0.0001). Storage temperature, time and their interaction significantly influenced E. coli reduction (p<0.05), with a faster die-off at 30°C than at 20°C. These suggest that higher temperatures can favor a faster E. coli decline on onions over time.