Ascorbic Acid Undermines Drug-Resistant Acinetobacter baumannii in Lab Tests

Vitamin C, one of the most familiar molecules in medicine, has shown a surprising ability to interfere with one of the hospital’s most stubborn pathogens. In a new laboratory study, ascorbic acid displayed antibacterial, anti-quorum sensing, and antibiofilm activity against multidrug-resistant Acinetobacter baumannii, a bacterium that causes a growing share of healthcare-associated infections and has become increasingly resistant to frontline antibiotics. The work, published in BMC Microbiology, also found that ascorbic acid enhanced the activity of the antibiotic cefepime in combination testing, suggesting a possible role as an adjunctive anti-virulence strategy.

The research team, led by Fatemeh Sabzi, Mohammad Hossein Ahmadi, and Zeinab Fagheei Aghmiyuni, examined ten clinical isolates of A. baumannii along with two reference strains, ATCC 19606 and ATCC 17978, all confirmed by PCR. Every strain tested was resistant to ciprofloxacin, imipenem, and piperacillin/tazobactam, underscoring the clinical challenge these organisms pose. The investigators then measured how ascorbic acid performed against these bacteria using standard microbiological techniques, including broth microdilution to determine the minimum inhibitory concentration, or MIC, and the minimum bactericidal concentration, or MBC.

The results showed that ascorbic acid inhibited bacterial growth at concentrations ranging from 1.367 to 10.938 milligrams per milliliter, with MIC50 and MIC90 values of 5.469 and 10.938 milligrams per milliliter, respectively. Notably, the MIC and MBC values were identical across the panel, a pattern the authors interpret as bactericidal activity, meaning the compound killed the bacteria rather than merely halting their growth. These are laboratory concentrations, and the study did not evaluate whether such levels could be achieved safely in patients, so the findings remain at the preclinical stage.

Beyond direct killing, the researchers probed whether ascorbic acid could weaken the bacterium’s communication system. Quorum sensing, the chemical signaling process by which bacteria coordinate group behaviors such as biofilm formation and virulence factor production, plays a central role in how A. baumannii establishes persistent infections. Because biofilms shield bacteria from antibiotics and immune attacks, disrupting quorum sensing has become an attractive target for alternative infection-control strategies that do not rely on conventional antibiotics alone.

To test this, the team quantified the expression of two quorum sensing genes, abaI and abaR, by real-time PCR. Ascorbic acid significantly downregulated both genes, reducing abaI expression by 68.0 percent and abaR expression by 74.5 percent. This transcriptional suppression indicates that the vitamin interferes with the signaling machinery the bacterium uses to coordinate its virulence behaviors, offering a mechanism that goes beyond simple growth inhibition.

The antibiofilm effects were assessed with the crystal violet microtiter plate method, a standard assay for measuring biofilm biomass. At the MIC, ascorbic acid reduced biofilm formation by 54 to 65 percent across the tested strains. Biofilm inhibition of this magnitude is meaningful in the laboratory context, since biofilms are a major reason why device-associated and chronic A. baumannii infections are so difficult to eradicate with existing drugs.

The study also explored whether ascorbic acid could work alongside existing antibiotics. Using the checkerboard assay, a method for evaluating drug interactions, the researchers combined ascorbic acid with cefepime and found synergistic or additive effects in 72.7 percent of the strains tested. This suggests that, at least in vitro, the vitamin can enhance the antibacterial activity of a beta-lactam antibiotic even against isolates that have accumulated multiple resistance mechanisms.

The authors conclude that ascorbic acid demonstrated antibacterial, antibiofilm, and anti-quorum sensing activities against multidrug-resistant A. baumannii and enhanced the antibacterial activity of cefepime in vitro. They frame these findings as support for further investigation of ascorbic acid as a potential adjunctive anti-virulence strategy rather than as evidence for clinical use. Because the work was conducted entirely with laboratory strains and standard in vitro assays, the concentrations and effects observed do not translate directly into treatment recommendations, and clinical evaluation would be a necessary next step.

Nevertheless, the study adds to a growing interest in repurposing simple, well-characterized molecules to combat resistant bacteria. With A. baumannii increasingly associated with multidrug resistance and limited treatment options, strategies that target virulence and biofilm formation rather than bacterial survival alone could complement existing antibiotics. The precise concentrations required, the mechanisms of gene downregulation, and the safety and pharmacology of achieving effective levels in the body remain open questions that future research will need to address.

Subject of Research: Laboratory evaluation of ascorbic acid against multidrug-resistant Acinetobacter baumannii

Article Title: Antibacterial, anti-quorum sensing, and antibiofilm effects of ascorbic acid against multidrug-resistant Acinetobacter baumannii

Article References: Sabzi, F., Ahmadi, M. H., & Aghmiyuni, Z. F. (2026). Antibacterial, anti-quorum sensing, and antibiofilm effects of ascorbic acid against multidrug-resistant Acinetobacter baumannii. BMC Microbiology. https://doi.org/10.1186/s12866-026-05880-1

Image Credits: AI Generated

DOI: 10.1186/s12866-026-05880-1

Keywords: Acinetobacter baumannii, ascorbic acid, antibiotic resistance, quorum sensing, biofilm, cefepime, MIC, healthcare-associated infections, anti-virulence, in vitro, Antibacterial, anti-quorum