Metal impacts on the persistence and proliferation of β-lactam resistance genes in Xiangjiang River, China.

Currently, the emergence of clinically relevant multi-resistant bacteria and the associated β-lactamases resistance genes which threaten the last frontier for antibiotics presents a major challenge for medical treatment. Xiangjiang River is typically contaminated with heavy metals due to the intensive metal mining activities within this watershed. The occurrence and distribution of several β-lactam antibiotics and ten β-lactam resistance genes (blaTEM, blaVIM, blaSHV, blaGES, blaDHA, blaOXA-1, blaOXA-2, blaOXA-10, blaCMY-2, and blaampC) were investigated in the Xiangjiang River, China. The absolute abundance of bla genes was as high as (7.0 ± 0.6) × 106 copies/mL for surface water and (2.3 ± 0.7) × 108 copies/g for sediment. In contrast, all the detected β-lactam antibiotic compounds were below the detection limit. The distribution of individual bla gene subtypes was correlated with speciation of heavy metals which might affect the bacterial community structure. The principal coordinate analysis (PCoA) and Mantal test reconfirmed that the heavy metals had a correlation with the bla genes and the bla genes were correlated with bacterial community structure, suggesting that heavy metals impacted on the distribution of the bla genes by shifting bacterial community structure under the long-term selective pressure. The microcosm experiments indicated metal-induced persistence of bla genes in the resistant bacteria (Bacillus megaterium, Staphylococcus epidermidis). The persistence of β-lactam resistance under metal selective pressure is beneficial to the survival of resistant bacteria, thereby contributing to the shift of the bacterial community structure, consequently impacts on the distribution of bla genes.