Abstract
Cuminum cyminum L. (cumin) is valued for its aromatic and medicinal properties. There are several reports of antibacterial activity of C. cyminum essential oil (CcEO). Accordingly, the present study was conducted to investigate the mechanism(s) of action of the CcEO against multidrug-resistant (MDR) Staphylococcus aureus. Therefore, 10 S. aureus MDR isolates, obtained from different sources, were selected based on the antibiotic susceptibility patterns and the Clinical and Laboratory Standards Institute definition and subjected to the examinations. Our results exhibited promising bacteriostatic and bactericidal properties of the CcEO. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration values ranged from 5 to 10 and 10 to 20 μL ⋅ mL–1, respectively. Scanning electron microscope was used to assess the bacterial cell structure and morphology after the induction with 1/2 MIC concentration of the CcEO. The observed morphological changes appeared to be deformation of the cell membrane and destruction of the cells. In the case of quorum sensing inhibitory potential, treatment of S. aureus isolates with the sub-MIC concentrations (1/2 MIC) of the CcEO significantly reduced the hld expression (3.13-fold downregulation), which considerably controls S. aureus quorum-sensing accessory regulator system. Another virulence factor influenced by the CcEO was the polysaccharide intercellular adhesion production system, as an important component of cell–cell adhesion and biofilm formation. Consequently, the expression level of the intercellular adhesion (ica) locus in the S. aureus cells was examined following treatment with CcEO. The results showed significant decrease (−3.3-fold) in ica expression, indicating that the CcEO could potentially interfere with the process of biofilm formation. Using the ethidium bromide efflux inhibition assay, the S. aureus NorA efflux pump was phenotypically but not genotypically (in quantitative polymerase chain reaction assay) affected by the CcEO treatment. Using gas chromatography–mass spectrometry analysis, cuminic aldehyde (38.26%), α,β-dihydroxyethylbenzene (29.16%), 2-caren-10-al (11.20%), and γ-terpinene (6.49%) were the most detected compounds. The antibacterial and antivirulence action of the CcEO at sub-MIC concentrations means that no microbial resistance will be promoted and developed after the treatment with this agent. These findings revealed that the CcEO is a promising antibacterial agent to control infections caused by the MDR S. aureus strains.
Highlights
Infectious diseases are known as the second leading cause of death in the world
In vitro bacteriostatic and bactericidal properties of the C. cyminum EO (CcEO) were evaluated against S. aureus bacteria (Figure 1)
The antibacterial, quorum sensing (QS) inhibitory, polysaccharide intercellular adhesion (PIA) production inhibitory properties, and NorA efflux pump inhibitory of the CcEO were investigated against MDR S. aureus
Summary
Infectious diseases are known as the second leading cause of death in the world. One of the most important causes of infectious diseases is Staphylococcus aureus, which has the ability to cause various diseases from minor skin and soft tissue infections to life-threatening diseases such as pneumonia, severe sepsis, and fatal infections (Bezerra Filho et al, 2020; Guo et al, 2020). The emergence and the spread of MDR S. aureus bacteria are a global threat for the therapeutic management of staphylococcal infections (Guo et al, 2020; Xu et al, 2020). Plant essential oils (EOs) are aromatic oily liquids that are well known for their different biological activities such as antibacterial activities. They contain various bioactive compounds with destructive effects on different parts of pathogen and MDR bacteria. This property makes them attractive to be used for therapeutic and food preservative purposes (Fridman, 2006; Tongnuanchan and Benjakul, 2014)
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