Targeting Acinetobacter baumannii wound infections: From transcriptional profiling to drug repurposing and bioactive hydrogel development

Abstract

Antimicrobial resistance (AMR) is an increasing public health emergency, driven largely by the overuse and misuse of antibiotics. Among multidrug-resistant pathogens, Acinetobacter baumannii is a major clinical concern due to its ability to survive in hospital environments. Recent studies have shown that artificial sweeteners, including acesulfame potassium (Ace-K), sodium saccharin (SACC), and sodium cyclamate (CYC), can inhibit bacterial growth, motility, and biofilm formation, and may enhance antibiotic activity in vitro. However, effective delivery of these compounds to wound infection sites remains a significant challenge. This thesis investigates alternative non-antibiotic strategies for targeting A. baumannii, with a focus on artificial sweetener-loaded polyvinyl alcohol (PVA)-based hydrogels, behaviour changing in wound-mimic environment, 3D-printable hydrogel development, and screening of FDA-approved drugs that modulate virulence-associated pathways. PVA-Borax and freezethaw PVA hydrogels were formulated with Ace-K, SACC, and CYC and demonstrate strong antimicrobial activity. In addition, this thesis explores how A. baumannii behaves in a woundmimic environment in Lubbock chronic wound biofilm (LCWB) medium. Under LCWB conditions, it induced reduced biofilm formation and iron-starvation responses. With iron supplementation, biofilm formation was restored. This highlights that iron is limited in the LCWB medium and is an important regulator of A. baumannii behaviour. Moreover, a 3Dprintable PVA/hydroxypropyl methylcellulose (HPMC) hydrogel was then developed to improve mechanical properties and control antimicrobial release. The optimised PVA/HPMC/SACC formulation demonstrated improved printability, structural integrity, swelling behaviour, rapid SACC release and antimicrobial activity compared with non-printed formulations. Finally, a high-throughput screen of an FDA-approved drug library identified compounds that regulate pilA expression and biofilm formation in A. baumannii. A cancer drug pomalidomide, was identified as a key hit that suppressed pilA expression, reduced twitching-associated behaviour, enhanced biofilm formation, and increased infection severity in Galleria mellonella and murine infection models. Overall, these findings demonstrate that effective control of A. baumannii wound infections requires more than identifying antimicrobial compounds alone. It also requires wound-relevant testing models, rational biomaterial-based delivery systems, and careful evaluation of how nonantibiotic compounds influence bacterial physiology and virulence.