Bacteria that render colistin, a "last resort" antibiotic, ineffective are lurking in SoCal's wastewater. While bacteria resistant to colistin have been found elsewhere in the world, this marks the first detection in Los Angeles wastewater. The bacteria and associated genes that provide resistance to colistin were discovered at the county's two largest wastewater plants. One treatment center serves 4 million residents, the other serves 3.5 million.