Edwardsiella tarda Ivy, a Lysozyme Inhibitor That Blocks the Lytic Effect of Lysozyme and Facilitates Host Infection in a Manner That Is Dependent on the Conserved Cysteine Residue

• Published in: Infection and Immunity
• Main Authors: Wang, Chong, Hu, Yong-hua, Sun, Bo-guang, Li, Jun, Sun, Li
• Other Authors: Payne, S. M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2013
• Subjects: Infectious Diseases; Immunology; Microbiology; Parasitology; Scophthalmus maximus; Turbot
• Online Access: http://dx.doi.org/10.1128/iai.00503-13; https://journals.asm.org/doi/pdf/10.1128/IAI.00503-13

ABSTRACT Edwardsiella tarda is a Gram-negative bacterial pathogen with a broad host range that includes fish and humans. In this study, we examined the activity and function of the lysozyme inhibitor Ivy (named Ivy Et ) identified in the pathogenic E. tarda strain TX01. Ivy Et possesses the Ivy signature motif CKPHDC in the form of 82 CQPHNC 87 and contains several highly conserved residues, including a tryptophan (W55). For the purpose of virulence analysis, an isogenic TX01 mutant, TXivy, was created. TXivy bears an in-frame deletion of the ivy Et gene. A live infection study in a turbot ( Scophthalmus maximus ) model showed that, compared to TX01, TXivy exhibited attenuated overall virulence, reduced tissue dissemination and colonization capacity, an impaired ability to replicate in host macrophages, and decreased resistance against the bactericidal effect of host serum. To facilitate functional analysis, recombinant Ivy Et (rIvy) and three mutant proteins, i.e., rIvyW55A, rIvyC82S, and rIvyH85D, which bear Ala, Ser, and Asp substitutions at W55, C82, and H85, respectively, were prepared. In vitro studies showed that rIvy, rIvyW55A, and rIvyH85D were able to block the lytic effect of lysozyme on a Gram-positive bacterium, whereas rIvyC82S could not do so. Likewise, rIvy, but not rIvyC82S, inhibited the serum-facilitated killing effect of lysozyme on E. tarda . In vivo analysis showed that rIvy, but not rIvyC82S, restored the lost pathogenicity of TXivy and enhanced the infectivity of TX01. Together these results indicate that Ivy Et is a lysozyme inhibitor and a virulence factor that depends on the conserved C82 for biological activity.