ORIGINAL ABSTRACT

Intensive pesticide use drives antimicrobial resistance (AMR) in agriculture, yet the effects of specific practices remain poorly understood. This study evaluated the impact of dairy manure and agrochemicals (glyphosate, copper, streptomycin, and propiconazole) on the composition of culturable AMR bacteria (CARB), AMR genes (ARGs; n = 87), and the microbiome in a processing tomato field (n = 64 experimental plots). Glyphosate-treated plots harbored the lowest levels of CARB, but the highest prevalence of ARGs (especially tetA, tetB, OXA-50, and OXA-58) in the tomato leaves (P < 0.05). Manure-treated plots had the highest levels of CARB and ARGs in the soil and in tomato leaves (especially ACT-1, LAT, MIR, aadA1, and aphA6). The prevalence of multiple ARGs (IMP-12, ACT-1, DHA, MIR, MOX, OXA-58, OXA-60, ermB, oprj, and oprm) was lower in streptomycin- or propiconazole-treated plots compared to non-treated plots. Shifts in the soil and leaf microbiome correlated with changes in ARG composition, particularly aminoglycoside-, fluoroquinolone-, and beta-lactamase-associated genes. These findings show that dairy manure, glyphosate, and propiconazole significantly alter the tomato field microbiome and ARG landscape, indicating that fungicide and herbicide applications may contribute to AMR development and dissemination similar to conventional antibacterial agents in agricultural ecosystems.IMPORTANCEPlant agricultural practices are commonly used by farmers to assure the yield and quality of crops; however, they are also associated with the emergence and dissemination of antimicrobial-resistant (AMR) pathogens. AMR is a critical concern in plant agriculture, as it can affect food safety, security, and sustainability. To combat this issue, it is critical to understand the impact of agricultural practices on AMR. Our study demonstrated that biological amendment (dairy manure) and pesticides (glyphosate, copper, streptomycin, and propiconazole) significantly exacerbated the AMR burden in the applied tomato field, which could increase the food safety risk of the fruit. Findings from this study will raise awareness among farmers, policymakers, and consumers, promote responsible and judicious use of antimicrobial agents in plant agriculture, and prioritize the development of sustainable practices to mitigate current and future AMR challenges.