In vitro inhibition and eradication of multidrug-resistant Acinetobacter baumannii biofilms by riparin III and colistin combination.

Acinetobacter baumannii, a prominent emerging pathogen, is responsible for persistent and recurrent healthcare-associated infections (HAIs). Its bacterial resistance and virulence factors, such as biofilm formation, contribute to its survival in hospital environments. Combination therapy has proven to be an effective approach for controlling these infections; however, antimicrobial resistance and compound toxicity can hinder antimicrobial efficacy. Numerous in vitro studies have demonstrated the synergistic effect of antimicrobials and natural products against multidrug-resistant (MDR) A. baumannii biofilm. Riparin III, a natural alkamide derived from Aniba riparia (Nees) Mez., possesses various biological activities, including significant antimicrobial potential. Nonetheless, no reports are available on the use of this compound in conjunction with conventional antimicrobials. Hence, this study aimed to investigate the inhibition and eradication of A. baumannii MDR biofilm by combining riparin III and colistin, along with potential ultrastructural changes observed in vitro. Clinical isolates of A. baumannii, known for their robust biofilm production, were inhibited, or eradicated in the presence of the riparin III/colistin combination. Furthermore, the combination resulted in several ultrastructural alterations within the biofilm, such as elongated cells and coccus morphology, partial or complete disruption of the biofilm's extracellular matrix, and cells exhibiting cytoplasmic material extravasation. At the synergistic concentrations, the riparin III/colistin combination exhibited a low hemolytic percentage, ranging from 5.74% to 6.19%, exerting inhibitory and eradicating effects on the A. baumannii biofilm, accompanied by notable ultrastructural changes. These findings suggest its potential as a promising alternative for therapeutic purposes.