Seasonal and spatial variability of antibiotic resistance genes and Class I integrons in the rivers of the Mekong delta, Vietnam

Aquaculture activities continue to expand in Vietnam, covering an estimated 700,000 ha, with 89% of these culture ponds located in the Mekong Delta. Since 2009, large-scale bacterial outbreaks have spread in response to this intensive farming. Antibiotics, even those considered a last resort, have only partially mitigated this problem. A side effect of the massive use of these chemicals is the appearance of mobile genetic elements associated with antibiotic resistance genes (ARGs). The large-scale emergence of a diverse bacterial resistome, accompanied by severe economic losses, has posed significant health risks to local residents. In this study, the seasonal and spatial distributions of the class I integrase (CL1) intl1 and the ARGs sul2 (sulfonamide), BLA-oxa1 ({beta}-lactams), and ermB (erythromycin) were quantified from water and sediment samples collected during two consecutive seasons along the Vam Co River and its tributary (Long An province, Vietnam). Results showed that CL1 was present in all river compartments, reaching 2.98x104 copies/mL and 1.07x106 copies/g of sediment, respectively. The highest relative copy abundances to the 16S rDNA gene were measured in water samples, with up to 3.02% for BLA-oxa1, followed by sul2 (1.16%) and ermB (0.46%). Strong seasonal (dry season vs. rainy season) and spatial trends were recorded for all resistance genes. Higher amounts of ARGs in river water could be associated with higher antibiotic use during the rainy season. In contrast, higher amounts of ARGs were recorded in river sediments during the dry season, making this habitat a potential reservoir of transient genes. Finally, the observations made in this study allowed us to clarify the environmental and anthropogenic influences that may promote the dispersal and persistence of ARGS in this riverine ecosystem. ABSTRACT ART O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=99 SRC="FIGDIR/small/469999v2_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@16b09fborg.highwire.dtl.DTLVardef@5c6da7org.highwire.dtl.DTLVardef@22fe83org.highwire.dtl.DTLVardef@1736e6e_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIIn Vietnam, inland aquaculture massively relies on antibiotics to prevent epidemics C_LIO_LIResistance genes were quantified along two rivers of the Mekong delta C_LIO_LISeasonal (dry and rainy seasons) and spatial distributions were registered by qPCR C_LIO_LIBLA-oxa1and sul2 reached highest abundances among bacterial communities C_LIO_LIStrong seasonal patterns and local variabilities were measured for CL1s and ARGs C_LI