Due to the increased emergence of drug-resistant bacteria, the declining efficiency of traditional antimicrobials has generated severe concerns in recent years. Subsequently, more interest in other antimicrobial agents from natural resources draws more attention as an alternative to conventional medications. This study investigated the bactericidal mechanism of monoterpene 1,8-cineol (eucalyptol), a major compound of various essential oils, against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial activity of 1,8-cineol was assessed by an MTT assay against clinical and reference MRSA strains. A cell membrane integrity test, followed by zeta potential (ZP) measurements, was performed to evaluate the disruption of the bacterial membrane integrity. Additionally, the cytotoxic effect of this molecule on MRSA bacteria was investigated by monitoring reactive oxygen species (ROS) generation, lipid peroxidation (MDA), and antioxidant enzyme activities (CAT and SOD). Regarding the anti-staphylococcal effect, the obtained results revealed the antibacterial efficacy of 1,8-cineol wherein the minimum inhibitory concentrations were equal to 7.23 mg/mL. Furthermore, it enhanced membrane permeability, with a 5.36-fold increase in nucleic acid and protein leakage as compared with untreated strains, along with the alteration of surface charge (ZP) in MRSA cells. The tested compound caused an increase in ROS generation reaching 17,462 FU and MDA production, reaching 9.56 μM/mg protein, in treated bacterial cells, along with a decrease in oxidative stress enzymes activities. Our findings suggest that 1,8-cineol has the ability to damage the membrane integrity and induce ROS-mediated oxidative stress in MRSA cells, leading to its antagonistic effect against this pathogen and consequently aiding in the reversal of antibiotic resistance.

In the present study, a phytochemical screening, antioxidant and antimicrobial activity in vitro were studied for the methanolic extract of the leaves of the plant Urtica dioica L. The DPPH method was used to evaluate the antioxidant activity, and the agar disk diffusion method determined the antibacterial power. The results of the qualitative phytochemical analysis show a high content of phenolic compounds characterized by a higher presence of saponins, and a medium richness in tannins with a low content of flavonoids, free quinines and sterols. On the other hand, the absence of alkaloids is observed. For the results of antioxidant activity, the percentage of inhibition of DPPH is 82.76%, 77.85%, and 74.83% for the concentrations 25mg/ml, 12.5mg/ml, and 6.25mg/ml respectively. The lowest percentage of inhibition is noticed for the concentration of 3,15mg/ml with 29, 84%. Our plant shows positive antioxidant activity with an IC50 of 4.69mg/ml. In addition, the antimicrobial activity revealed the most significant effect for Pseudomonas aeruginosa strain with an inhibition zone of 9mm to 10mm, with concentrations of 400mg/ml, 300 mg/ml and 200 mg/ml, respectively. Our results suggest that the methanolic extract of Urtica dioica L, as a pleasant natural antioxidant and antimicrobial agent, can be applied in the preservation of food products while conducting further studies on the bioactive molecules of this plant to determine their mechanism of action.

The proliferation of methicillin-resistant Staphylococcus aureus (MRSA) in food processing is an escalating public health issue. This circumstance has intensified the quest for ecological alternatives to impede pathogen proliferation and avert food degradation. This study firstly investigated the chemical compositions of three essential oils (EOs) sourced from Eucalyptus, Rosemary and Lavender plants using GC-MS. Subsequently, the antibacterial and antibiofilm activities of the tested EOs were assessed against MRSA strains. The effects of these EOs on the expression of antibiotic resistance-related (mecA), virulence regulatory (agrA and sarA), and enterotoxin (sea) genes in MRSA strains were also evaluated by real-time PCR. Concerning the composition analyses performed on the EOs, our results revealed a total of 82 compounds, which accounted for 99.20, 98.10 and 92.78% of Eucalyptus, Rosemary and Lavender EOs, respectively. The anti-staphylococcal activity showed that Eucalyptus EO had the greatest effect, with diameter of inhibition exceeding 41 mm. Moreover, the association between Rosemary EO and the antibiotic (cefoxitin) highlighted the enhancement of the antibacterial effect against the MRSA reference strain. Additionally, Eucalyptus EO showed the highest inhibitory effect against both strains, with MIC values ranging from 0.781 to 1.563 mg/mL, followed by the Rosemary and Lavender EOs. All the tested EOs displayed a bactericidal effect against the tested MRSA strains. Regarding the antibiofilm activity, Rosemary and Lavender EOs had varying impacts on the pre-formed biofilms, with percentage reduction values ranging from 36% to 73% and 37% to 68%, respectively. Finally, the mRNA expression of the MRSA gene A mecA and virulence genes agrA, sarA and sea declined following EO treatment compared with the control. The findings of this study highlighted the efficacy of locally tested EOs in reducing MRSA biofilm formation and the expression of virulence factors and suggested their potential use in food safety and culinary applications.

Raw milk contamination by Methicillin-resistant S. aureus (MRSA) threatens food safety and leads to public health problems. Our study evaluates biofilm formation and virulence factors among 21 MRSA in raw cow’s milk. Methicillin resistance was confirmed by cefoxitin screening using the automated VITEK2 system, with a minimum inhibitory concentration greater than 8 mg/l. Qualitative characterization of biofilm-producing strains was performed on Congo red agar (CRA), with a semi-quantitative adhesion test on 96-well tissue culture plates (TCP). The ability to produce different enzymes was evaluated, such as caseinase, lipase, and phospholipase (lecithinase). The surface hydrophobicity of the bacteria was determined, and the autoaggregation test was used to predict the interactions between bacterial cells. Among the tested strains, 61.9% were biofilm producers in the CRA, developing a positive and variable phenotype. Furthermore, 19.05% and 80.95% of isolates were high and low biofilm formation on TCP. The enzymatic activity showed that lécithinase, caseinase, and lipase activities were detected in 100%, 80.95%, and 80.95% of cases. Highly hydrophilic (85.71%) and weakly hydrophobic (14.29%) were detected in MRSA isolates. The strains showed that 71.43% were moderate autoaggregation and 28.57% were low autoaggregation. No significant difference was found between the CRA method and TCP (P> 0.05). A significant association was found between adhesion capacity and bacterial autoaggregation in S. aureus strains (p>0.05). On the other hand, no statistical association between the hydrophobicity of microbial strains and adhesion capacity (p<0.05) was found. The same result was for the hydrophobicity of microbial strains and autoaggregation (p<0.05). This investigation could be beneficial for developing new control measures, prevention, and effective treatment against staphylococcal bacterial resistance.