High occurrence rate of tetracycline (TC)-resistant bacteria and TC resistance genes relates to microbial diversity in sediment of mekong river main waterway

Abstract

Spatial monitoring of tetracycline (TC)-resistant bacteria in sediments of the Mekong River watershed revealed that the main waterway showed a high occurrence rate of TC-resistant bacteria, whereas Tonle Sap Lake and the Sai Gon estuary did not. The Shannon index (H'), an indicator of ecological diversity, was calculated from denaturing gradient gel electrophoresis (DGGE) profiles, which indicated that the main waterway of the Mekong River had high microbial diversity (high H') compared to Tonle Sap Lake and the Sai Gon estuary; this diversity was positively correlated with the occurrence rate of TC-resistant bacteria. Analysis of ribosomal protection protein (RPP) genes tet(M), tet(S) and tet(W) in the same area also revealed that high diversity was positively correlated with the occurrence rate of RPP genes, suggesting that RPP genes are well conserved across various bacterial species. Further evidence of different genotypes of tet(M) suggests that the drug resistance genes likely have various origins, and are mixed in the sediment. Sediments in this area are therefore potential reservoirs of drug resistance genes.