Effect of heavy metal-sulfamethoxazole complexes on the sulfanilamide resistance gene Sul1

Both heavy metals and antibiotics in the environment might be affecting the environmental behaviour of antibiotic resistance gene (ARGs). However, little attention has been paid to the effect of heavy metal-antibiotic complexes on the performance of ARGs. Therefore, in the present work, four heavy metals (Cu, Zn, Pb, Cd) and sulfamethoxazole (SMX) were selected as candidates to explore the effect of heavy metal-SMX complexes on the sulfanilamide resistance gene sul1. The results showed that Pb could inhibit the ampli�cation of sul1, but Zn could stimulate it, as well as Cu and Cd stimulated the ampli�cation of sul1 at low concentrations but inhibited at high concentrations (> 0.50 mg/L). Meanwhile, SMX could stimulate the ampli�cation of sul1at high concentrations. Most importantly, it was discovered for the �rst time that the complexes of SMX with Pb, Zn, Cu, and Cd showed positive effects on the ampli�cation of sul1 at ratios of 1:1, 1:1, 2:1, and 1:2, respectively, and the positive effects of the four complexes on sul1 were consistently higher than that of SMX or any of the heavy metals alone. These results reveal that heavy metal-antibiotic complexes could affect the existence and distribution of ARGs.