Edwardsiella tarda MliC, a Lysozyme Inhibitor That Participates in Pathogenesis in a Manner That Parallels Ivy

• Published in: Infection and Immunity
• Main Authors: Li, Mo-Fei, Wang, Chong, Sun, Li
• Other Authors: Bäumler, A. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2015
• Subjects: Turbot
• Online Access: http://dx.doi.org/10.1128/iai.02473-14; https://journals.asm.org/doi/pdf/10.1128/IAI.02473-14

ABSTRACT Edwardsiella tarda , a bacterial pathogen to farmed fish as well as humans, possesses the genes of two lysozyme inhibitors, ivy and mliC ( ivy Et and mliC Et ). We recently studied Ivy Et and found it to be implicated in E. tarda virulence. In the present study, we characterized MliC Et in comparison with Ivy Et in a turbot model. MliC Et contains the FWSKG motif and two cysteines (C33 and C98) that are highly conserved in subgroup 1 MliCs but are of unknown functional importance. To examine the essentialness of these conserved structural features, recombinant MliC Et (rMliC) and its mutants bearing C33S and W79A (of the FWSKG motif) substitutions were prepared. Subsequent analysis showed that rMliC (i) inhibited lysozyme-induced lysis of a Gram-positive bacterium, (ii) reduced serum-facilitated lysozyme killing of E. tarda , and (iii) when introduced into turbot, promoted bacterial dissemination in fish tissues. The C33S mutation had no influence on the activity of rMliC, while the W79A mutation slightly but significantly enhanced the activity of rMliC. Knockout strains of either mliC Et or ivy Et were severely attenuated for the ability of tissue invasion, host lethality, serum survival, and intracellular replication. The lost virulence of the mliC transformant (TXΔ mliC ) was restored by complementation with an introduced mliC Et gene. Compared to the Δ ivy Et or Δ mliC Et single-knockout strains, the Δ mliC Et Δ ivy Et double-knockout strain was significantly impaired in most of the virulence features. Together, these results provide the first evidence that the conserved cysteine is functionally dispensable to a subgroup 1 MliC and that as a virulence factor, MliC Et most likely works in a concerted and parallel manner with Ivy.