Molecular Profiling and Phytochemical Approach to Combat Multidrug-Resistant Escherichia coli O157: Insights from (GTG)₅-PCR Genotyping and Melissa officinalis Extract Antibacterial Activity

Document Type : Original Article

Authors
Sedigheh Mokhtari 1
Yahya Tahamtan 2
Mohammad Kargar 1
Keyvan Tadayon 3
1 Department of Microbiology, Zand Institute of Higher Education, Shiraz, Iran.
2 Microbiology Department, Razi Vaccine and Serum Research Institute, Shiraz Branch, Agricultural Research, Education and Extension Organization (AREEO), Shiraz, Iran.
3 Department of Veterinary Aerobic Bacterial Vaccines, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran.
10.22034/zmm.2025.735898
Abstract
Background & Objectives: Industrial The emergence and global spread of multidrug-resistant (MDR) Escherichia coli O157 represents a critical public health challenge, causing severe foodborne outbreaks and life-threatening complications such as hemolytic uremic syndrome (HUS). Rapid adaptation and genetic diversity inof E. coli O157 complicate treatment, while limited efficacy of conventional antibiotics underscores the urgent need for alternative strategies. This study aimed to investigate the genetic diversity of E. coli O157 isolates and evaluate the antibacterial potential of Melissa officinalis extract as a natural therapeutic option for controlling infections caused by this pathogen.
Materials & Methods: Twenty-three E. coli O157 isolates from diverse animal sources were genotyped using (GTG)₅-PCR. Antibiotic susceptibility of each strain was assessed via Kirby–Bauer disk diffusion against Norfloxacin, Tobramycin, Imipenem, Azithromycin, Doxycycline, and Levofloxacin. Antibacterial activity of aqueous-ethanolic leaf extract of M. officinalis leaf extract (100 mg/mL) was tested using agar well diffusion.
Results: (GTG)₅-PCR revealed five distinct genotypic clusters, demonstrating high genetic heterogeneity. Antibiotic testing showed variable susceptibility, with Norfloxacin most effective (32-34 mm) and Tobramycin least (10-19 mm). Clusters D and E exhibited multidrug resistance. M. officinalis extract displayed strong bactericidal activity against all isolates, with an average inhibition zone of 32 mm, exceeding several conventional antibiotics.
Conclusion: E. coli O157 isolates exhibit substantial genetic diversity and variable antibiotic resistance. The potent antibacterial activity of M. officinalis extract highlights its potential as a natural alternative or complementary therapy. Integrating molecular genotyping with phytochemical screening offers a promising approach to combat MDR pathogens.
Keywords
Escherichia coli O157
Antibiotic resistance
Melissa officinalis
Phytochemical antibacterial
Genotyping
(GTG)₅-PCR
Zand Molecular Microbiology
Volume 1, Issue 2
Autumn 2025
Pages 61-68