Escherichia coli is a naturally occurring inhabitant of both the human and animal gastrointestinal tracts. Among the maladies it triggers, diarrhoea, aerobic vaginitis (AV) and urinary tract infections are amongst the most impactful.
Once this bacterium infiltrates the digestive or urogenital system, it swiftly adheres to and takes root in cells, effectively eluding the host’s immune system and assaulting host cells through toxin production.
In this regard, E. coli frequently incites biofilm-associated opportunistic infections such as endometritis, diarrhoea, and mastitis.
While antibiotics can mitigate disease symptoms and duration, numerous strains of E. coli have developed resistance to these drugs over the past five decades, primarily due to excessive use. Therefore, Cinnamomum has been employed to impede E. coli attachment and biofilm formation as a means to manage infections caused by this bacterium.
Pourkhosravani et al.1 unveiled that essential oil derived from the trunk bark of Cinnamomum could effectively thwart E. coli from forming biofilms.
In anti-adhesion tests, as determined through a crystal violet assay, Cinnamomum completely blocked the bacterium’s adhesion.
Additionally, assessments of biofilm metabolic activity and biomass quantification demonstrated that Cinnamomum suppressed E. coli‘s metabolic activity and biofilm formation by 99% and 100%, respectively.
Worth noting is the fact that gas chromatography-mass spectrometry (GC-MS) analysis identified E-cinnamaldehyde, α-terpinyl acetate, and copaene as comprising 91.31% of Cinnamomum‘s essential oil composition.
Another investigation also observed that C. camphora essential oil (CCEO) effectively eradicated clinical isolates of E. coli from dairy cows afflicted with clinical endometritis, whether in planktonic or biofilm communities2.
Furthermore, the researchers scrutinised the kinetics of CCEO’s impact on E. coli in both suspension and biofilm communities, and the results showed that the most rapid bacterial killing transpired within the first 5 minutes of treatment, with the lowest level of viable bacteria detected approximately an hour after treatment.
These findings suggest that CCEO’s efficacy wanes over time, with its pharmacodynamic duration falling short of 24 hours, and its inhibitory effects on biofilms manifesting early on. Microscopic analyses corroborated these results, confirming CCEO’s substantial inhibition and eradication of E. coli biofilms1.
Recent investigations have lent support to these findings, reporting that Cinnamomum extract, in a dose-dependent manner, curtailed extracellular polymeric substance (EPS) secretion and biofilm metabolic activity, leading to a suppression of E. coli strain ATCC 25922 biofilms from 24.45% to 98.09%.
In tests on pre-existing biofilms, various concentrations resulted in reductions ranging from 16.20% to 46.14%. Microscopic analyses aligned with these findings, demonstrating that Cinnamomum extract markedly hindered and eliminated E. coli biofilms3.
Furthermore, Olszewska et al.4 reported that cinnamaldehyde diminished nearly 60% of cell metabolic activity and the biofilm cell cultivability of E. coli strain CECT 434.
Notably, the authors hypothesised that cinnamaldehyde might disrupt the membrane integrity of biofilm cells, as evidenced by various bacterial cell morphologies, including filamentous cells and decreased substrate coverage.
A recently published study also noted that Cinnamomum extract and cinnamaldehyde inhibited 60% and 86.7% of biofilm production by E. coli isolated from colon cancer patients, respectively5. Thus, recent research underscores Cinnamomum‘s antibiofilm activity against diverse E. coli strains, even though the exact antibiofilm mechanism of these substances remains unreported.
Additionally, other researchers have assessed Cinnamomum‘s inhibitory effects on E. coli O157:H7 (EHEC) biofilms. This bacterium, classified under the attaching and effacing (A/E) E. coli group, is responsible for bloody diarrhoea.
Antibiotics are not recommended for its treatment, as they induce the SOS response and activate prophages, causing the release of Shiga toxins. EHEC’s propensity to adhere to various surfaces and form biofilms, combined with the lack of effective therapies for EHEC-biofilm-related infections, has spurred efforts to develop new antibiofilm agents.
Recent experiments demonstrated that C. verum essential oil (CVEO) effectively inhibited the biofilm formation of clinical EHEC isolates. Microscopic analysis revealed distinctive characteristics of biofilm cells in the presence of CVEO: sparser microcolonies, individual cells with fewer and shorter interconnecting meshes, but no discernible morphological changes.
In a 2019 study6, sub-lethal concentrations of cinnamaldehyde were found to increase the expression of tnaA and bssS genes, negative regulators of biofilm formation in EHEC. Notably, tnaA encodes the enzyme tryptophanase, leading to indole production, a signalling molecule that suppresses E. coli biofilm formation.
Moreover, BssS reduces bacterial biofilm formation by influencing cell signalling7,8. Interestingly, cinnamaldehyde concurrently suppressed the expression of virulence-associated genes, including Type III secretion systems (T3SSs) (sepD and escC), flagellar biosynthesis and functions (fliA and motA), and chemotaxis (cheA and cheZ).
Subsequently, the authors assessed the connection between changes in virulence gene expression and observable phenotypic alterations. They observed that cinnamaldehyde significantly diminished EHEC’s biofilm-forming ability, efflux pump activity, and motility, all without inducing antibiotic resistance in the bacterium.
Kim et al.9 found that Cinnamomum bark oil and its constituents inhibited the formation of EHEC biofilms and virulence.
Their research demonstrated that coating biodegradable poly (lactic-co-glycolic acid) surfaces with cinnamaldehyde or Cinnamomum bark oil significantly impeded EHEC biofilm formation. These compounds also reduced the expression of csgAB and stx2 genes, responsible for curli formation and Shiga-like toxin production, respectively.
Interestingly, Cinnamomum bark oil did not exert significant effects on the expression of other biofilm-related genes.
References
- 1.Pourkhosravani E, Dehghan Nayeri F, Mohammadi Bazargani M. Decoding antibacterial and antibiofilm properties of cinnamon and cardamom essential oils: a combined molecular docking and experimental study. AMB Expr. Published online October 26, 2021. doi:10.1186/s13568-021-01305-6
- 2.Wang L, Zhang K, Zhang K, et al. Antibacterial Activity of Cinnamomum camphora Essential Oil on Escherichia coli During Planktonic Growth and Biofilm Formation. Front Microbiol. Published online November 12, 2020. doi:10.3389/fmicb.2020.561002
- 3.Lu C, Liu H, Shangguan W, Chen S, Zhong Q. Antibiofilm activities of the cinnamon extract against Vibrio parahaemolyticus and Escherichia coli. Arch Microbiol. Published online August 9, 2020:125-135. doi:10.1007/s00203-020-02008-5
- 4.Olszewska MA, Gędas A, Simões M. The Effects of Eugenol, Trans-Cinnamaldehyde, Citronellol, and Terpineol on Escherichia coli Biofilm Control as Assessed by Culture-Dependent and -Independent Methods. Molecules. Published online June 6, 2020:2641. doi:10.3390/molecules25112641
- 5.Kosari F, Taheri M, Moradi A, Hakimi Alni R, Alikhani MY. Evaluation of cinnamon extract effects on clbB gene expression and biofilm formation in Escherichia coli strains isolated from colon cancer patients. BMC Cancer. Published online March 30, 2020. doi:10.1186/s12885-020-06736-1
- 6.Yuan W, Yuk HG. Effects of Sublethal Thymol, Carvacrol, and trans -Cinnamaldehyde Adaptation on Virulence Properties of Escherichia coli O157:H7. Müller V, ed. Appl Environ Microbiol. Published online July 15, 2019. doi:10.1128/aem.00271-19
- 7.Isaacs H, Chao D, Yanofsky C, Saier MH. Mechanism of catabolite repression of tryptophanase synthesis in Escherichia coli. Microbiology. Published online August 1, 1994:2125-2134. doi:10.1099/13500872-140-8-2125
- 8.Domka J, Lee J, Wood TK. YliH (BssR) and YceP (BssS) Regulate Escherichia coli K-12 Biofilm Formation by Influencing Cell Signaling. Appl Environ Microbiol. Published online April 2006:2449-2459. doi:10.1128/aem.72.4.2449-2459.2006
- 9.Kim YG, Lee JH, Kim SI, Baek KH, Lee J. Cinnamon bark oil and its components inhibit biofilm formation and toxin production. International Journal of Food Microbiology. Published online February 2015:30-39. doi:10.1016/j.ijfoodmicro.2014.11.028
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