Screening assays that allow for the identification of agents that increase acyl homoserine lactone (AHL) acylase expression and/or AHL acylase activity in .gamma.-proteobacteria such as Pseudomonas aeruginosa. Such agents are useful, for example, for inhibiting quorum sensing activity of such bacteria by increasing degradation of long chain, but not short chain, AHLs and, therefore, can be useful for treating infections by such bacteria.