Application of oxytetracycline fermentation residue in agriculture: Abundance of resistance genes in soil and transferability to plant

Antibiotic fermentation residues are known to be a potential source of organic fertilizer. However, their impact on the antibiotic resistance genes (ARGs), microbial communities in the rhizosphere, and plant contamination remain poorly understood. In this study, the effects of thermally treated oxytetracycline fermentation residue (OFR) on the dissemination of antibiotic resistance in the rhizosphere of spinach (Spinacia oleracea), changes in the rhizobacterial communities, and contamination of plant tissue were investigated in a pot experiment under greenhouse condition. Raw OFR, animal manure-based compost sourced from a commercial company, and untreated soil (control) were used as reference treatments for the comparison. The experiment was conducted over a period of 2 months, and soil samples were collected at intervals of 15 days. Plant tissues were analyzed at harvest for the presence of tet genes and concentration of antibiotics. The quantification of tet genes including tetA, tetL, tetQ, and tetX indicated that treated OFR did not significantly promote these genes over the control, as determined by qPCR. Plant growth-promoting bacteria showed a significant (p<0.001) increase under the effect of treated OFR. The accumulation of antibiotics and tet genes in spinach tissues was not significantly different from the control (untreated soil), suggesting the potentiality of the treated OFR as an organic source for agricultural application. The findings of this study can help in evaluating the feasibility of other antibiotics fermentation residues in agricultural applications.