In our current world, antibiotic resistance among pathogenic microbes keeps getting worse with few new antibiotics being pursued by pharmaceutical companies. Modern-day immunotherapies, reminiscent of the serotherapy approaches used in the early days of antimicrobial treatments, are a potential counter-measure, but are usually limited by the narrow spectrum against target antigens. Surprisingly, many multidrug-resistant (MDR) bacteria share a common surface polysaccharide, poly-β-1,6-N-acetylglucosamine (PNAG). Natural antibodies to PNAG are present in normal human sera, but are not protective. However, human monoclonal antibodies (MAbs) or polyclonal antisera raised to a deacetylated glycoform of PNAG mediate opsonic killing and protect mice against infections due to all PNAG-positive MDR pathogens tested. An MAb is currently in Phase II clinical trials. These discoveries could lead to utilization of antibodies to PNAG for either therapeutic use in patients infected by PNAG-producing MDR bacteria or prophylactic use in patients at risk of developing MDR infections.