Manure application led to higher antibiotic resistance risk in red soil compared with black soil and fluvo-aquic soil

Abstract

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) that originated in manure application increased antibiotic resistance in soil bacterial communities. Our previous work showed that the abundance of ARB and ARGs obviously reduced after composting, and further investigation was still required about their fate in soil after manure application. Soil types were suggested to play a role in ARB and ARGs and thus it was important to identify their influence on the occurrence and development of antibiotic resistance. Compared with black soil and fluvo-aquic soil, the absolute abundance of chlortetracycline-resistant bacteria (CRB) significantly increased to 1.97 × 106, 2.75 × 106 CFU/g after manure and chlortetracycline-manure application in red soil, respectively (p < 0.05), which then induced antibiotic resistance of soil indigenous microbes (Streptomyces and Rhodococcus). Manure application had a higher risk of pathogenic transmission in red soil than that in the other soils. In addition, the relative abundance of multidrug resistance genes increased the most in red soil (1.07-1.41 times) with chlortetracycline-manure treatment. Further analysis indicated that the range of potential ARGs host bacteria was larger in treatments with chlortetracycline. Based on structural equation model analysis, soil microbial community directly influenced ARGs, and soil properties indirectly affected ARGs by influencing the microbial community. Overall, soil types and properties should be considered in manure application in order to control antibiotic resistance risk effectively.