IN VITRO EVALUATION OF THE ANTIBACTERIAL POTENTIAL OF TRACHYSPERMUM AMMI (AJWAIN) ETHANOLIC EXTRACT AGAINST CLINICAL ACINETOBACTER BAUMANNII ISOLATES

Abstract

Background: Acinetobacter baumannii is a highly resistant Gram-negative pathogen with the decreasing availability of effective antimicrobial agents, which has raised interest in naturally occurring and plant-derived antimicrobial compounds. Trachyspermum ammi (ajwain) is a medicinal aromatic spice with bioactive compounds like thymol and carvacrol, that have shown antimicrobial properties.

 Objective: To assess the in vitro antibacterial activity of the ethanolic extract of T. ammi against clinical isolates of A. baumannii by the agar well diffusion and broth microdilution methods.

 Materials and Methods: Ajwain seed was cleaned, dried, powdered, and extracted with ethanol. The initial screening for the antibacterial activity was done with the agar well diffusion method against standardized bacterial suspensions (0.5 McFarland) on Mueller–Hinton agar. Colistin was used as a positive control and dimethyl sulfoxide (DMSO) was used as a negative control. The minimum inhibitory concentration (MIC) was then calculated by two-fold serial dilutions of the extract in 96-well microtiter plate. Optical density was measured at 600 nm, prior to and after 24 h incubation. Mixed ANOVA was used to evaluate the effect of the extracts and bacterial strains.

Results: Ethanolic extracts were found to have measurable inhibitory effect against all three A. baumannii isolates with the inhibition zone being 15mm, 14mm and 13mm, respectively (mean inhibition zone = 14.0 ± 1.0mm). The MIC values were 50 mg/mL for isolates 2 and 3, and 50 and 100 mg/mL for isolate 1 in two determinations. The concentration of extract had significant impact on the bacterial growth (p<0.001) and significant difference between the strains (p=0.048).

Conclusion: Ethanolic T. ammi extract demonstrated in vitro antibacterial activity against A. baumannii and should be investigated, employing standardized extraction methods, phytochemical characterization, and expanded collections of A. baumannii.