Antibacterial activity and modulation of antibiotic action of citral against Acinetobacter baumannii strains

Abstract

Antimicrobial resistance represents one of the major public health challenges of the contemporary era, driving the search for new therapeutic strategies, including the use of natural compounds as antimicrobial agents or antibiotic activity modulators. Citral, a monoterpene present in Cymbopogon citratus, has demonstrated antimicrobial potential against different bacterial pathogens. Therefore, this study aimed to evaluate the intrinsic antibacterial activity of citral and its ability to modulate the action of antibiotics against Acinetobacter baumannii. The minimum inhibitory concentration (MIC) of citral was determined by the broth microdilution method, using resazurin as a bacterial viability indicator. The modulatory activity was assessed by combining citral at a sub-inhibitory concentration with the antibiotics ciprofloxacin, gentamicin, and oxacillin. All assays were performed in triplicate and statistically analyzed using one-way ANOVA followed by Tukey’s post hoc test. The results demonstrated that citral exhibited moderate intrinsic antibacterial activity, with MIC values ranging from 512 to 1024 µg/mL. However, the combinations of citral with the tested antibiotics did not produce significant changes in MIC values and were therefore classified as showing an indifferent effect. These findings suggest that although citral exerts direct antimicrobial activity, its ability to potentiate antibiotic efficacy against A. baumannii is limited under the experimental conditions evaluated, likely due to the complex resistance mechanisms and low permeability of the outer membrane characteristic of this pathogen. In conclusion, citral shows potential as a natural antimicrobial agent; however, further studies are required to investigate alternative therapeutic combinations and strategies to enhance its effectiveness against multidrug-resistant bacteria.