A highly efficient method was developed for the isolation and purification of the periplasmic Escherichia coli lysozyme inhibitor protein Ivy. After isolation by osmotic shock from an E. coli overexpression strain, Ivy was purified to > 95% purity using a single affinity chromatography step with hen egg white lysozyme as a ligand. Further, the specificity of Ivy against various types of lysozymes (hen egg white lysozyme, c-type; mutanolysine, ch-type; cauliflower lysozyme, not further classified; goose egg white lysozyme, g-type; lambda lysozyme, X-type and T4 lysozyme, v-type) was investigated. Most strongly inhibited was hen egg white lysozyme, followed by goose egg white lysozyme and finally T4 lysozyme, while no inhibition was observed for the other lysozymes. These results clearly indicate that Ivy is a relatively specific inhibitor of vertebrate lysozymes belonging to the c- and g-type and that its inhibition profile corresponds to the structural and evolutionary relatedness of the lysozymes. The availability of pure Ivy and the elucidation of its inhibition profile will contribute to the further identification of its biological function in bacteria. (c) 2005 Elsevier Inc. All rights reserved.