Enterococcus faecalis constitutes an unusual bacterial model in lysozyme resistance

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Host-Pathogen Interactions

Background:

• Lysozyme is a key component of innate immunity, targeting bacterial peptidoglycan.
• Enterococcus faecalis exhibits significant resistance to lysozyme, a trait not fully understood.
• Identifying bacterial mechanisms of lysozyme resistance is crucial for understanding pathogenesis and developing therapies.

Purpose of the Study:

• To investigate the roles of two putative lysozyme resistance genes, EF_0783 and EF_1843, in Enterococcus faecalis.
• To determine the impact of these genes on peptidoglycan structure and lysozyme susceptibility.
• To assess the contribution of EF_0783 and EF_1843 to bacterial survival within host immune cells.

Main Methods:

• Genome sequence analysis to identify candidate genes.
• Construction and characterization of single and double deletion mutants (DeltaEF_0783, DeltaEF_1843, DeltaEF_0783 DeltaEF_1843).
• Lysozyme susceptibility assays, peptidoglycan structural analysis, and macrophage survival experiments.

Main Results:

• The DeltaEF_0783 mutant and the double mutant showed increased sensitivity to lysozyme compared to wild-type E. faecalis.
• EF_0783 was identified as a peptidoglycan O-acetyltransferase, modifying N-acetyl muramic acid.
• EF_1843 deletion had no significant effect on peptidoglycan structure or lysozyme resistance.
• Mutations in EF_0783 and EF_1843 impaired E. faecalis survival within murine macrophages.
• Despite increased sensitivity, mutants retained high lysozyme tolerance compared to other bacterial species.

Conclusions:

• EF_0783 plays a role in Enterococcus faecalis lysozyme resistance through O-acetylation of peptidoglycan.
• O-acetylation and de-N-acetylation are not the primary mechanisms for high-level lysozyme resistance in E. faecalis.
• These genes impact bacterial virulence, particularly macrophage survival, suggesting broader roles in pathogenesis.