Research in Plant Metabolites

Research in Plant Metabolites

Alteration of exo gene expression in clinical isolates of antibiotic-resistant Pseudomonas aeruginosa treated with plant metabolites (allicin and thymol)

Document Type : Original Article

Authors
somayeh ataei jaliseh
houra Pourghafar
Department of Biology, Ra.C., Islamic Azad University, Rasht, Iran
10.22034/jrpsm.2026.574356.1108
Abstract
Background and Objective: Pseudomonas aeruginosa is a common cause of hospital-acquired infections due to its high pathogenicity potential. The spread of antibiotic resistance, especially in gram-negative bacteria, has led to the development of plant antibiotic compounds for the treatment of infections caused by these bacteria. In this study, the antimicrobial effects of the active ingredient allicin in garlic and thymol in a number of medicinal plants, including thyme, on the expression of exoA, exoS, and exoT genes of P. aeruginosa as important pathogenic factors were investigated.
Materials and Methods: Fifty clinical isolates from different patients were studied along with the Standard strain of P. aeruginosa ATCC27853. Various biochemical tests were performed to purify the bacteria, including the ability to produce hemolysin, oxidase, catalase, urease, growth ability at 42 °C, growth profile in Mac Conkey, TSI, SIM, and Mueller Hinton media, and Gram staining. Antibiogram tests were performed on Mueller Hinton agar culture medium along with determination of P. aeruginosa sensitivity by disk diffusion method on antibiotics Cefepime, Gentamicin, Amikacin, Ceftazidime, Imipenem, and Ciprofloxacin (based on CLSI) and disks impregnated with the active ingredient allicin and thymol in the culture medium. After that, the zone of inhibition of bacterial growth was measured. Then MBC and MIC were performed, and DNA and RNA extraction, cDNA synthesis, and finally, Real-time PCR was performed to determine the effect of the active ingredients allicin and thymol on the expression of exoA, exoS, and exoT at subMIC concentrations.
Results: Out of 50 clinical isolates studied, 40 isolates of P. aeruginosa were identified and confirmed. The mean diameter of the inhibition zone of P. aeruginosa isolates at 10 mg.ml-1 allicin and thymol were 19.2 and 17 mm, respectively. The highest resistance of bacteria to the antibiotics Ceftazidime and Imipenem, and the lowest to Amikacin and Gentamicin. The MIC was represented by a dilution of 1:8 and a concentration of 1.25 mg.ml-1 allicin and thymol, and the MBC was represented by a dilution of 1:2 and a concentration of 2.5 mg.ml-1 allicin and thymol. The presence of the studied exo genes in clinical isolates of P. aeruginosa was confirmed in the PCR product of the bacterial genome extracted with primers specific for each gene. The results obtained from real-time PCR showed that allicin at a subMIC concentration (0.6 mg.ml-1) in this study reduced the expression of exoA, exoS and exoT genes in P. aeruginosa isolates. Data analysis showed that the expression of exoT and exoS genes in P. aeruginosa isolates treated with allicin was significantly reduced (P<0.001) and the exoA gene was significantly reduced (P<0.01). Also, the expression of exoA and exoS genes in Pseudomonas isolates treated with the active ingredient thymol at a subMIC concentration (0.6 mg.ml-1) was significantly reduced (P<0.001).
Conclusion: This study showed that the active ingredient allicin in garlic and thymol in thyme, with a significant bactericidal effect, reduce the expression of exo genes in P. aeruginosa. It is hoped that the results obtained in the future, after conducting standard clinical research, will lead to the production of a drug containing the active ingredients allicin and thymol with a strong antibacterial effect.
Keywords
Real-Time PCR
subMIC
‌‌exoA
exoS
exoT
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