Antibiotic resistome biomarkers and determinants in lettuce planting soil amended with β-lactam pharmaceutical fermentation residues.

As nutrient-rich biosolids generated by the pharmaceutical industry, pharmaceutical fermentation residues (PFRs) pose high potential for recycling, particularly as organic soil amendments after removing drug residues. In this study, the antibiotic resistome profile of the lettuce pot experiment soil amended by two major types of β-lactam pharmaceutical fermentation residues (penicillin and clavulanic acid) and their derived high-temperature spray granulation treated PFRs was investigated using metagenomic sequencing. After treatment, penicillin and clavulanic acid removal ratios achieved 94.2% and 97.3%. The number and TPM abundance of total antibiotic resistance genes (ARGs) in soil amended by treated PFR decreased by 32.1% and 27.9%, compared to soil fertilized with raw PFR, and were not significantly different from those in the control groups (without PFR or treated PFR application). The results implied that a total of 47 ARGs (7 clinical high-risk ARGs), 32 bacterial taxa (13 potential pathogens), and 21 MGEs were identified as biomarkers by the random forest model. Biomarker MGEs (qacEdelta, tnpAB, and IS91) and bacteria (Neisseria, Staphylococcus, Stenotrophomonas, and Clostridium) were closely associated with the abundance of most biomarker ARGs, including those high-risk ARGs. tnpAB and IS91 were proposed as sentinel indicators of ARG mobility risk. Subsequent RDA analysis explored the variation of ARG biomarker determinants across different growth stages. MGEs dominated before seeding, thereafter, the bacterial community gradually became the principal contributor. Collectively, these findings may benefit the safe recycling of PFR and provide valuable theoretical data for antimicrobial risk assessment of pharmaceutical biowaste.