In vitro evaluation of the antibacterial effects of Cinnamomum zeylanicum essential oil against clinical multidrug-resistant Shigella isolates

As there are little data about the antimicrobial effects of the cinnamon essential oils (EO) against multidrug-resistant (MDR) Shigella species, this study aimed to evaluate the antibacterial activities of Cinnamomum zeylanicum EO against the clinical MDR Shigella isolates. Totally 50 MDR Shigella isolates including 17 (34%) S. flexneri, 20 (40%) S. sonnei, and 13 (26%) S. boydii were collected. The isolates were identified by standard phenotypic and molecular methods. The MDR phenotypes were determined as resistant to three antibiotic classes using disc diffusion. The C. zeylanicum EO was analyzed by gas chromatography/mass spectrometry (GC/MS). The minimum inhibitory concentration (MIC) of cinnamon EO was evaluated by microtiter broth dilution. The most Shigella isolates 38% (n = 19) were resistant to six antibiotics. The ampicillin-amikacin-cefotaxime-erythromycin-ciprofloxacin-cotrimoxazole resistotype was the most prevalent pattern detected in five S. sonnei, four S. boydii, and three S. flexneri isolates. The result of GC/MS revealed the cinnamaldehyde (84.8%) as the main ingredient of C. zeylanycum EO. The most susceptible strain to the C. zeylanycum EO was S. boydii (MIC range = 0.15-0.62 μl/ml) followed by S. flexneri (MIC range = 0.07-1.25 μl/ml), and S. sonnei (MIC range = 0.15-1.25 μl/ml). The observed ranges of MIC and MBC values of cinnamon EO against Shigella spp. were 0.07-1.25 μl/ml and 0.31-1.25 μl/ml, respectively. The antibacterial effects of cinnamon EO in this study may increase the hope of finding suitable plant compounds to treat infections caused by MDR Shigella isolates.