# Loss of LafB activity reverses daptomycin resistance in E. faecium

## TL;DR

Disabling the lafB gene in E. faecium makes daptomycin-resistant bacteria more sensitive to the antibiotic, offering a new way to combat resistance.

## Contribution

Loss of lafB function prevents or reverses daptomycin resistance in E. faecium, suggesting LafB inhibition as a novel therapeutic strategy.

## Key findings

- Daptomycin-resistant mutants do not emerge in vitro when lafB is nonfunctional.
- Clinical daptomycin-resistant strains with lafB mutations become more susceptible to daptomycin.
- LafB is critical for known daptomycin resistance mechanisms and has phenotypic dominance over other resistance mutations.

## Abstract

Infections caused by multidrug-resistant enterococci, particularly vancomycin-resistant Enterococcus (VRE), present significant therapeutic challenges. Daptomycin, a last-line treatment for VRE, often loses efficacy due to the emergence of resistance. In this study, we revealed the critical role of the lafB gene as a key determinant of daptomycin susceptibility and resistance in E. faecium. We showed that in the absence of a functional lafB, daptomycin-resistant mutants did not emerge in vitro, and derivatives of clinical daptomycin-resistant strains engineered to lack functional lafB were rendered even more sensitive to daptomycin than wild-type daptomycin-susceptible strains. These findings indicated that functional lafB is critical for key known mechanisms of daptomycin resistance, and mutations in lafB have phenotypic dominance to those that otherwise confer resistance. Therefore, inhibiting the activity of the lafB gene product is predicted to prevent or reverse resistance, offering a promising new strategy for extending the efficacy of daptomycin for treating enterococcal infections.

Daptomycin is one of the few remaining effective antibiotics for treating vancomycin-resistant enterococcal infections but is limited by the emergence of resistance during protracted therapy. Here, we show that without a functional lafB gene, daptomycin-resistant mutants do not arise under conditions where wild-type strains readily generate daptomycin-resistant mutants. Furthermore, we show that loss of function mutation of the lafB gene in daptomycin-resistant clinical isolates renders them more susceptible to daptomycin than wild-type Enterococcus faecium. This indicates that an effective small molecule inhibitor of LafB activity or lafB gene expression would be a useful adjunctive for extending and restoring the therapeutic utility of daptomycin.