D/PVA/I-1 as an Antibiotic Adjuvant: In Vitro Synergy and Membrane Permeabilization in MDR Bacteria

Background: Antimicrobial resistance (AMR) is among the most pressing challenges in modern infectious medicine, driving progressive failure of standard antibacterial therapy and rising mortality from infections caused by multidrug-resistant (MDR) pathogens. Antibiotic potentiation through adjuvant compounds capable of restoring the activity of existing drugs represents a promising strategy to overcome resistance without developing fundamentally new antibacterial molecules. This study aimed to evaluate the antibiotic-potentiating activity of a dextrin/polyvinyl alcohol/iodine complex (D/PVA/I-1), developed at the Scientific Center for Anti-Infectious Drugs JSC (Almaty, Kazakhstan), against clinically relevant MDR reference strains. Methods: Nine reference strains, Staphylococcus aureus (ATCC 33591, BAA-39), Escherichia coli (ATCC BAA-196, BAA-2523), Klebsiella pneumoniae (ATCC BAA-2524, 700603), Acinetobacter baumannii (ATCC BAA-1790), Streptococcus pneumoniae (ATCC BAA-660), and Haemophilus influenzae (ATCC 33930), and two clinical isolates, P. aeruginosa SCAID PHRX1-2019 and E. coli SCAID WND1-2021, were tested. Antibiotic-potentiating activity was assessed by checkerboard assay with calculation of the fractional inhibitory concentration index (FICI); bactericidal kinetics were evaluated by time-kill analysis. The effect of D/PVA/I-1 on cytoplasmic membrane permeability was investigated using a crystal violet uptake assay. Results: Of 45 D/PVA/I-1–antibiotic combinations tested across nine antibiotics, synergy (FICI ≤ 0.5) was demonstrated in 44.4% of cases, partial synergy in 48.9%, and additive effects in 6.7%; no antagonistic interactions were detected. The most pronounced potentiating effect occurred against Gram-positive pathogens, particularly MRSA strains (66.7% synergistic combinations). Time-kill analysis confirmed suppression of the regrowth phenotype characteristic of MDR strains under monotherapy and restoration of bactericidal activity against antibiotics to which strains exhibited intrinsic resistance. D/PVA/I-1 induced a dose- and time-dependent increase in membrane permeability in both Gram-positive and Gram-negative organisms. Conclusions: D/PVA/I-1 is an effective broad-spectrum antibiotic potentiator and represents a promising basis for combination therapy regimens against MDR infections.