AIMS: Biofilm formation is important for the persistence of bacteria in hostile environments. Bacteria in a biofilm are usually more resistant to antibiotics and disinfectants than planktonic bacteria. Our laboratory previously reported that low concentrations of zinc inhibit biofilm formation of Actinobacillus pleuropneumoniae. The aim of this study is to evaluate the effect of zinc on growth and biofilm formation of other bacterial swine pathogens. METHODS AND RESULTS: To determine the effect of zinc on biofilm formation, biofilms were grown with or without zinc in 96-well plates and stained with crystal violet. At micromolar concentrations (0-250 μ mol l(-1)), zinc weakly inhibited bacterial growth and it effectively blocked biofilm formation by A. pleuropneumoniae, Salmonella Typhymurium and Haemophilus parasuis in a dose-dependent manner. Additionally, biofilm formation of Escherichia coli, Staphylococcus aureus and Streptococcus suis was slightly inhibited by zinc. However, zinc did not disperse preformed biofilms. To determine whether zinc inhibits biofilm formation when poly-N-acetylglucosamine (PGA) is present, PGA was detected with the lectin wheat germ agglutinin. Only A. pleuropneumoniae and Staph. aureus biofilms were found to contain PGA. CONCLUSION: Zinc used at nonbactericidal concentrations can inhibit biofilm formation by several Gram-negative and Gram-positive bacterial swine pathogens. SIGNIFICANCE AND IMPACT OF STUDY: The antibiofilm activity of zinc could provide a tool to fight biofilms, and the nonspecific inhibitory effect may well extend to other important human and animal bacterial pathogens.