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

<b>Background:</b> The rapid emergence of antibiotic resistance in <i>Acinetobacter baumannii</i> 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. <b>Objectives:</b> To clone, over-express, and characterize a novel endolysin, LysTAC1, from <i>Acinetobacter</i> phage TAC1 for its antibacterial efficacy against multidrug-resistant bacteria. <b>Methods:</b> A 24 kDa endolysin featuring a glycoside hydrolase Family 19 chitinase domain was tested against carbapenem-resistant <i>Acinetobacter baumannii</i> clinical isolates and various <i>Escherichia coli</i> strains following outer membrane permeabilization with Ethylenediaminetetraacetic acid (EDTA). Stability assays and molecular docking studies were performed. <b>Results:</b> LysTAC1 demonstrated potent lytic activity against Gram-negative bacteria but showed no activity against Gram-positive bacteria (<i>Staphylococcus aureus</i> ATCC 29213 and <i>Enterococcus gallinarum</i> 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. <b>Conclusions</b>: LysTAC1 shows significant potential as a targeted therapeutic agent against <i>A. baumannii</i> with robust stability under physiological conditions.