In vitro antibacterial activity and GC–MS profiling of ethanolic extract of Artemisia annua against Aeromonas hydrophila isolated from Clarias gariepinus

Abstract

Aeromonas hydrophila is an important bacterial pathogen of cultured fish and is associated with motile Aeromonas septicemia and economic losses in aquaculture. The increasing concern regarding antimicrobial resistance has encouraged the evaluation of plant-derived alternatives. This study evaluated the in vitro antibacterial activity and chemical profile of an ethanolic extract of Artemisia annua against A. hydrophila isolated from Clarias gariepinus in Dutsin-Ma, Katsina State, Nigeria. Clarias gariepinus showing clinical signs compatible with bacterial disease were collected from selected fish farms and markets in Dutsin-Ma and processed under aseptic conditions. The bacterial isolate was identified by cultural morphology, Gram staining, and biochemical tests including oxidase, catalase, indole, motility, urease, and Triple Sugar Iron reactions. A. annua leaves were authenticated, air-dried, powdered, and extracted with 99% ethanol at a 1:5 (weight/volume) ratio using a rotary evaporator. Gas chromatography–mass spectrometry (GC–MS) was used to characterize compounds detected in the extract. GC–MS profiling identified 28 library-assigned compounds. The most abundant detected compounds were 3-dibenzofuranamine (24.0 %), 4-dibenzofuranamine (19.2%), a limonene isomer (9.44%), and 3,5-heptanedione, 2,2,6,6-tetramethyl- (10.1%).  Antibacterial activity was assessed by agar well diffusion, while minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth dilution and subculture, respectively. The isolate displayed the expected phenotypic profile of A. hydrophila: Gram-negative rod, oxidase-positive, catalase-positive, indole-positive, motile, TSI-positive, and urease-negative. The extract inhibited A. hydrophila at the highest concentration tested, with an MIC of 100 mg/mL; no MBC was recorded within the tested range. Thus, the extract was demonstrated to have a bacteriostatic rather than a demonstrably bactericidal effect under the conditions used. Ethanolic A. annua extract showed potential as a plant-derived antibacterial candidate against A. hydrophila. The findings support further standardized phytochemical confirmation, dose optimization, toxicity assessment, and in vivo evaluation before practical application in aquaculture.

Keywords: Artemisia annua; Aeromonas hydrophila; Clarias gariepinus; antibacterial activity