Modeling the transmission of β-lactam-resistant Escherichia coli through lettuce: A quantitative microbial exposure assessment integrating environmental and postharvest factors.

Abstract

Livestock production operations can potentially introduce antimicrobial-resistant bacteria (ARB) into soil and environmental water, subsequently contaminating the surrounding cultivation of leafy vegetables through fertilization and irrigation. This study assessed the impact of these contamination sources on the level of human exposure to ARB via consumption of romaine lettuce. A quantitative microbial exposure assessment (QMEA) model was constructed to simulate the transmission of β-lactam-resistant E. coli (BR-EC) from production to consumption. The model estimated human exposure to BR-EC from the consumption of fresh-cut lettuce irrigated with: (i) groundwater distal to livestock operations, (ii) groundwater proximate to livestock operations, (iii) surface water distal to livestock operations, and (iv) surface water proximate to livestock operations, to be -2.97 (95% S.I. -4.57 - -0.68), -2.94 (95% S.I. -4.51 - -0.66), -2.92 (95% S.I. -4.49 - -0.63), and - 2.85 (95% S.I. -4.41 - -0.56) log CFU/serving, respectively. When exposure pathways were disaggregated, manure-amended soil was identified as the dominant contributor to generic E. coli ingestion, whereas irrigation water was the primary source of BR-EC exposure. In addition to pre-harvest BR-EC contamination, post-harvest factors, particularly controlling storage temperatures during retail and home storage, significantly influenced BR-EC levels. These factors reduced ingestion by -1.93 and - 2.23 log CFU/serving, respectively, highlighting the critical importance of post-harvest handling in minimizing consumer exposure to ARB. The present study emphasized the importance of cooperative efforts from various sectors along the fresh produce supply and preparation chain in reducing ARB exposure.