# In Vitro Antibacterial Efficacy of Recombinant Phage-Derived Endolysin LysTAC1 Against Carbapenem-Resistant Acinetobacter baumannii

## TL;DR

This study explores a new antibacterial protein, LysTAC1, effective against drug-resistant Acinetobacter baumannii, a major public health threat.

## Contribution

The paper introduces and characterizes LysTAC1, a novel phage-derived endolysin with potent activity against carbapenem-resistant A. baumannii.

## Key findings

- LysTAC1 effectively lyses Gram-negative bacteria like A. baumannii and E. coli but not Gram-positive bacteria.
- The endolysin remains stable across a wide range of pH and temperatures and is minimally affected by certain metal ions.
- Molecular docking studies show strong binding interactions with chitinase substrates, supporting its enzymatic activity.

## Abstract

Background: The rapid emergence of antibiotic resistance in Acinetobacter baumannii has led the World Health Organization (WHO) to designate it as a “high priority” pathogen. The emergence of multidrug-resistant (MDR) and pandrug-resistant (PDR) strains poses considerable treatment challenges. As antimicrobial resistance (AMR) escalates toward a post-antibiotic era, innovative therapeutic solutions are urgently needed. Objectives: To clone, over-express, and characterize a novel endolysin, LysTAC1, from Acinetobacter phage TAC1 for its antibacterial efficacy against multidrug-resistant bacteria. Methods: A 24 kDa endolysin featuring a glycoside hydrolase Family 19 chitinase domain was tested against carbapenem-resistant Acinetobacter baumannii clinical isolates and various Escherichia coli strains following outer membrane permeabilization with Ethylenediaminetetraacetic acid (EDTA). Stability assays and molecular docking studies were performed. Results: LysTAC1 demonstrated potent lytic activity against Gram-negative bacteria but showed no activity against Gram-positive bacteria (Staphylococcus aureus ATCC 29213 and Enterococcus gallinarum HCD 28-1). LysTAC1 maintained activity across pH 6–9 and temperatures 4–65 °C, with differential sensitivity to metal ions where K+ showed no inhibitory effect at any concentration (0.1–100 mM), and Fe2+ was non-inhibitory at lower concentrations (0.1–1 mM), while Mg2+ and Ca2+ demonstrated concentration-dependent inhibition across the tested range (0.1–100 mM). Molecular docking revealed LysTAC1 interactions with chitinase substrates 4-nitrophenyl N-acetyl-β-D-glucosaminide and 4-nitrophenyl N, N-Diacetyl-β-D-chitobioside, with binding energies of −5.82 and −6.85 kcal/mol, respectively. Conclusions: LysTAC1 shows significant potential as a targeted therapeutic agent against A. baumannii with robust stability under physiological conditions.