Antibacterial activity of clove (Syzygium aromaticum) and cinnamon (Cinnamomum burmannii) essential oil against extended-spectrum β-lactamase-producing bacteria

Background and Aim: Extended-spectrum β-lactamase (ESBL) is an enzyme produced by the family of Enterobacteriaceae,
especially Escherichia coli and Klebsiella pneumoniae, which can hydrolyze β-lactam antibiotics, such as penicillins,
cephalosporins, cephamycin, and carbapenem. ESBL-producing bacteria are widely distributed from farms to slaughterhouses until food products originating from animals are available in the market, which plays an important role as a pathway for the exposure and transmission of ESBL-producing bacteria from food products of animal origin to humans. This study aimed to determine the antibacterial activity of Syzygium aromaticum (clove) and Cinnamomum verum (cinnamon) essential oils against strains resistant to ESBL-producing E. coli and K. pneumoniae isolates.

Materials and Methods: The antibacterial activity of clove and cinnamon essential oils was tested against three strains
of tested bacteria using the disk diffusion method. The minimum inhibitory concentration (MIC) of clove and cinnamon
essential oils was determined using the broth microdilution method. The minimum bactericidal concentration (MBC)
was determined using the MIC. Morphological changes on each tested bacteria were observed through scanning electron
microscopy (SEM).

Results: Both essential oils exhibited inhibitory effects toward all test organisms, indicated by inhibition zones around the disk. The MIC values of clove essential oil were 0.078% (v/v) for all tested bacteria, whereas the MICs of cinnamon essential oil ranged from 0.039% (v/v) to 0.156% (v/v) for all tested bacteria. MBC values of clove and cinnamon essential oils ranged from 0.078% (v/v) to 0.156% (v/v) for all tested bacteria. There were morphological changes in each tested bacterial cell that was observed through SEM. Each tested bacteria treated with clove and cinnamon essential oils showed shrinkage and cells lysis.
Conclusion: It was concluded that clove and cinnamon essential oils have emerged as effective antibacterial agents by showing high antibacterial activity against ESBL-producing E. coli and K. pneumoniae isolates, as evidenced by the inhibition zone diameter and MIC value.