Macrolide resistance genes and mobile genetic elements in waterways from pig farms to the sea in Taiwan

•Pig farm wastewater in Taiwan showed a high rate of erythromycin-resistant bacteria.•Seawater was less contaminated with the resistant bacteria.•Aquaculture ponds separated from pig farms have few macrolide resistance genes.•IntI1 was abundant in pig farms, rivers, and aquaculture ponds.•IntI1 was positively related to mef(A), erm(B), and mph(B) but not mef(C)-mph(G).