Quantification of residual antibiotics in cow manure being spread over agricultural land and assessment of their behavioral effects on antibiotic resistant bacteria.

Antibiotic resistant bacteria (ARB) in livestock manure used as fertilizer and spread over agriculture land, may pose a threat to the health of humans. Considering this, the concentrations of tetracycline (TC), oxytetracycline (OTC), and sulfathiazole (STZ) in the surface soil were quantified using LC-MS. These antibiotics have been used in livestock and are found in fertilizer produced from livestock excretions. Species of ABR were identified using 16S rDNA. Soil samples were collected at depths of 0, 7, and 15 cm from farmland in Incheon (South Korea). In the surface soil, three compounds were detected: TC (17.74 μg/kg), OTC (0.78 μg/kg), and STZ (0.23 μg/kg). However, except for STZ, antibiotics were not detected in the deeper samples. Overall, TC can form a chelated complex with cations, which consequently enhances its adsorption to the organic matter and metals in soil. This property can significantly reduce the mobility of TC (to lower than that of STZ). The result of 16S rDNA gene analysis indicated that Pseudomonas spp., Arthrobacter spp., and Rhodococcus spp. showed persistent resistance to the three antibiotics tested. DNA quantification results revealed strong resistance of Pseudomonas spp. to STZ, whereas Arthrobacter spp. and Rhodococcus spp. had resistance to TC and OTC. Antibiotics biodegradation suggested ability of ARB to grow in soil samples in presence of residual antibiotics during 13 days incubation. The concentrations of STZ, TC, and OTC reduced as much as 23.53, 35.60 and 66.88%, respectively.