Antibacterial activity of selected plant essential oils against carbapenemase-producing multidrug-resistant bacteria

Infections caused by carbapenemase-producing multidrug-resistant (MDR) bacteria represent a major global health challenge, highlighting the urgent need for alternative antimicrobial agents.

In this study, MDR isolates of Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa were obtained from the microbial bank of Ahvaz Jundishapur University of Medical Sciences, Iran. The presence of carbapenemase genes (blaKPC, blaIMP, blaNDM, blaVIM-1, and blaOXA-48) was determined by polymerase chain reaction (PCR) in Gram-negative isolates. Essential oils (Eos) of Zataria multiflora, Mentha pulegium, Cinnamomum verum, and Zingiber officinale were extracted by hydrodistillation. Antibacterial activity was evaluated using the agar disc diffusion method and a modified disc-based concentration gradient approach to estimate minimum inhibitory concentrations (MICs).

The K. pneumoniae isolate harbored blaKPC and blaOXA−48, while P. aeruginosa carried blaIMP and blaNDM. No carbapenemase genes were detected in S. aureus. Among the tested EOs, Z. multiflora exhibited the strongest antibacterial activity, with inhibition zones up to 40 mm. C. verum demonstrated notable activity, particularly against K. pneumoniae (MIC: 1.56 mg/mL). M. pulegium showed moderate activity, whereas Z. officinale displayed no detectable antibacterial effect under the tested conditions. P. aeruginosa demonstrated comparatively higher resistance to all EOs.

Selected plant essential oils, particularly Z. multiflora and C. verum, demonstrated promising in vitro antibacterial activity against carbapenemase-producing MDR bacteria. Further investigations, including in vivo studies and chemical characterization of the oils, are warranted.