Antibiotics are critical treatments for bacterial infections, but antibiotic resistance is a growing problem. Wastewater treatment plants may foster resistance development, since sewage contains both human pathogens and antibiotics or their metabolite. The activated sludge (AS) stage commonly used to treat sewage at these plants is especially microbe-rich and may encourage transfer of antibiotic resistance genes (ARGs) through reproduction (vertical transfer) or movement of mobile genetic elements (horizontal transfer). To learn more, a recent study profiled ARGs and their neighboring genes at five wastewater treatment plants on three continents. Overall, ARG abundance was lower in AS than in incoming sewage (IN). In addition, ARGs tended to colocalize with plasmids and other mobile genetic elements to a greater extent in IN than AS, indicating decreased horizontal transfer potential. Chromosomal ARGs generally had the same hosts in both AS and IN despite the different ARG and bacterial profiles of the two sources, which suggests that most chromosomal ARG dissemination comes from vertical transfer rather than horizontal. The results of this study imply that the AS stage helps protect against the proliferation of most ARGs. Nevertheless, the persistent or proliferating ARGs deserve further research.