# Gelatinase regulates the egress of intracellular replicating populations during Enterococcus faecalis infection

## TL;DR

This paper shows how a protease called gelatinase helps bacteria escape from inside host cells during infection, which may explain why some infections persist.

## Contribution

The study identifies gelatinase and its regulator as key factors in the intracellular-to-extracellular transition of E. faecalis during chronic wound infection.

## Key findings

- Gelatinase (GelE) and the Fsr quorum sensing system are essential for E. faecalis to exit host cells after intracellular replication.
- Gelatinase-deficient E. faecalis accumulates inside host cells, potentially evading immune and antibiotic responses.
- The study reveals a new role for gelatinase in regulating bacterial persistence in chronic wound infections.

## Abstract

Enterococcus faecalis is a common opportunistic pathogen, frequently isolated from chronic wounds, yet the mechanisms underlying its virulence and persistence in this niche remain incompletely understood. We previously showed that a subpopulation of E. faecalis can survive intracellularly for several days during murine wound infection and can replicate within macrophages, revealing an unexpected intracellular phase for this traditionally extracellular bacterium. Here, we identify the secreted metalloprotease gelatinase (GelE) and its regulator, the Fsr quorum sensing system, as key modulators of E. faecalis intracellular survival and replication. Mechanistically, Fsr quorum sensing is induced during intracellular replication, promoting GelE-dependent host cell lysis and bacterial egress. In the absence of active GelE, E. faecalis accumulates as large intracellular clusters, a phenotype observed consistently across GelE-deficient wound isolates. In a mouse wound model, GelE-deficient E. faecalis similarly exhibited higher intracellular numbers within wound infection-associated host cells. Together, our study uncovers GelE as a central effector that orchestrates the transition between intracellular and extracellular lifestyles of E. faecalis, providing a possible explanation for its persistence in chronic wound infection.

Pathogenic bacteria are traditionally classified as either “intracellular” or “extracellular”, but growing evidence suggests that many extracellular bacteria also adopt transient intracellular lifestyles that promote persistent and recurrent infection. Enterococcus faecalis, a leading cause of chronic wound infection, exemplifies this duality. We discovered that E. faecalis strains lacking the secreted protease gelatinase accumulate to high numbers inside host cells such as macrophages. Our data indicate that gelatinase facilitates bacterial escape following intracellular replication, regulating the transition between an intracellular and extracellular lifestyle. During infection, gelatinase-deficient bacteria remain hidden within various wound cell types, potentially evading immune clearance and antibiotic treatment. This work reveals a previously unrecognized role for gelatinase in controlling E. faecalis intracellular dynamics, highlighting a mechanism that may underline chronic and persistent infection.