Plastic debris facilitates the survival of multidrug-resistant bacterial pathogens in an urban agricultural environment.

Abstract

Rapid urbanisation in Low- and Middle-Income Countries (LMICs) has driven the expansion of urban and peri-urban farming to enhance food security. However, these systems are highly vulnerable to contaminated irrigation waters, urban runoff, open defecation and inadequate sanitation, and anthropogenic pollution, such as plastic and microplastic waste. Here, we investigated the role of plastic debris as a reservoir and vector for multidrug-resistant (MDR) enteric bacterial pathogens in a real-world agronomic setting. Focusing on two peri-urban agricultural sites in Dar es Salaam, Tanzania, we analysed 140 environmental samples (soil, water, vegetation, and surface and buried plastic debris) for the presence of four key enteric pathogens: E. coli, Salmonella spp., V. cholerae, and K. pneumoniae. The concentration of total culturable pathogens was higher on plastic debris compared to soil, water and vegetation, with presumptive E. coli loads of ∼1 × 103 CFU per individual piece of plastic debris. Importantly, plastic debris harboured a greater proportion of MDR strains; specifically, 69% of E. coli isolates were resistant to two or more antimicrobials, with plastics at one site accounting for over half of all MDR E. coli. While MDR E. coli were absent from soil, plastic debris supported strains of E. coli and K. pneumoniae that were resistant to critically important antimicrobials (e.g., ciprofloxacin and cefixime).This study provides robust evidence that in a real-world setting, plastic waste can act as an ecological reservoir which concentrates and facilitates the survival of MDR pathogens. Therefore, the widespread presence of contaminated plastic in agricultural systems could pose significant occupational health risks for farmers, in addition to a potential environment-to-food risk for consumers.