Olive Leaf Extract Modulates Quorum Sensing Genes and Biofilm Formation in Multi-Drug Resistant Pseudomonas aeruginosa

Nazly R El-Sayed, Reham Samir, Lina Jamil M Abdel-Hafez, Mohammed A Ramadan, Nazly R El-Sayed, Reham Samir, Lina Jamil M Abdel-Hafez, Mohammed A Ramadan

Abstract

Biofilm acts as a complex barrier against antibiotics. In this study, we investigated the inhibitory activities of Olea europaea (olive) leaves Camellia sinensis (green tea), Styrax benzoin, Ocimum basilicum, Humulus lupulus, Ruta graveolens, and Propolis extracts on the biofilm formation, pyocyanin production, and twitching motility of Pseudomonas aeruginosa isolates. Moreover, we investigated the effect of olive leaf extract on the transcription of some biofilm related genes. A total of 204 isolates of Pseudomonas were collected from different Egyptian hospitals. A susceptibility test, carried out using the disc diffusion method, revealed that 49% of the isolates were multidrug-resistant. More than 90% of the isolates were biofilm-forming, of which 26% were strong biofilm producers. At subinhibitory concentrations, green tea and olive leaf extracts had the highest biofilm inhibitory effects with 84.8% and 82.2%, respectively. The expression levels of lasI, lasR, rhlI, and rhlR treated with these extracts were significantly reduced (p < 0.05) by around 97-99% compared to untreated isolates. This study suggests the ability of olive leaf extract to reduce the biofilm formation and virulence factor production of P. aeruginosa through the down regulation of quorum sensing (QS) genes. This may help in reducing our dependence on antibiotics and to handle biofilm-related infections of opportunistic pathogens more efficiently.

Keywords: Pseudomonas; biofilm; green tea; olive leaves; quorum sensing inhibitors; real-time RT-PCR.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Effect of different herbal extracts on biofilm formation of P. aeruginosa. Bar chart showing the absorbance of P. aeruginosa C21 and E81 in absence and presence of the sub-MIC of Camellia sinensis (3.125 mg/mL), Olea europaea (6.25 mg/mL), Styrax benzoin (12.5 mg/mL), Humulus lupulus (6.25 mg/mL), Ocimum basilicum (6.25 mg/mL), Propolis (6.25 mg/mL), and Ruta graveolens (12.5 mg/mL). Biofilm formation was evaluated using the microtiter plate method. Data are an average of three independent experiments. The results are presented by the mean ± SD. ns = nonsignificant; * = p < 0.05; *** = p < 0.001: significance was compared to the respective control.
Figure 2
Figure 2
Effect of different herbal extracts on twitching motility of P. aeruginosa. Bar chart showing the percent inhibition of C21 and E81 twitching motility in the absence and presence of herbal extracts Camellia sinensis (3.125 mg/mL), Olea europaea (6.25 mg/mL), Styrax benzoin (12.5 mg/mL), Humulus lupulus (6.25 mg/mL), Ocimum basilicum (6.25 mg/mL), Propolis (6.25 mg/mL), and Ruta graveolens (12.5 mg/mL). Data are an average of three independent experiments. The results are presented by the mean ± SD. ns = nonsignificant; ** = p < 0.01; *** = p < 0.001: significance was compared to the respective control.
Figure 3
Figure 3
Effect of different herbal extracts on pyocyanin production of P. aeruginosa. Bar chart showing percent inhibition of C21 and E81 pyocyanin production in the absence and presence of herbal extracts Camellia sinensis (3.125 mg/mL), Olea europaea (6.25 mg/mL), Styrax benzoin (12.5 mg/mL), Humulus lupulus (6.25 mg/mL), Ocimum basilicum (6.25 mg/mL), Propolis (6.25 mg/mL), and Ruta graveolens (12.5 mg/mL). Pyocyanin production was evaluated by the chloroform-HCl extraction method. Data are an average of three independent experiments. The results are presented by the mean ± SD. ns = nonsignificant; * = p < 0.05; *** = p < 0.001: significance was compared to the respective control.
Figure 4
Figure 4
Effect of Camellia sinensis and Olea europaea extracts on the transcription of quorum sensing (QS)-regulated genes of P. aeruginosaC21. Bar chart of the qRT-PCR analysis representing the relative transcription levels of lasI, lasR, rhlI, and rhlR genes treated with sub-MIC levels of Camellia sinensis (3.125 mg/mL) and Olea europaea (6.25 mg/mL), normalized with the reference gene 5s RNA and compared to the untreated control. The error bars indicate the standard deviations of three replicates. **** = p < 0.0001: significance was compared to the respective control.
Figure 5
Figure 5
Effect of Camellia sinensis and Olea europaea extracts on the expression of QS-regulated genes of P. aeruginosa (E81). Bar chart of the qRT-PCR analysis representing the relative transcription levels of lasI, lasR, rhlI, and rhlR genes treated with sub-MIC levels of Camellia sinensis (3.125 mg/mL) and Olea europaea (6.25 mg/mL), normalized with the reference gene 5s RNA and compared to the untreated control. The error bars indicate the standard deviations of three replicates. **** = p < 0.0001: significance was compared to the respective control.

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