Detection of hemolytic Shiga toxin-producing Escherichia coli in fresh vegetables and efficiency of phytogenically synthesized silver nanoparticles by Syzygium aromaticum extract and gamma radiation against isolated pathogens

Abstract

Background: Shiga toxin-producing E. coli (STEC) is a major cause of foodborne diseases accompanied by several clinical illnesses in humans. This research aimed to isolate, identify, and combat STEC using novel alternative treatments, researchers have lately investigated using plant extract to produce nanoparticles in an environmentally acceptable way. At various gamma-ray doses, gamma irradiation is used to optimize the conditions for the biogenically synthesized silver nanoparticles (Ag NPs) using an aqueous extract of clove as a reducing and stabilizing agent. Methods: On a specific medium, 120 vegetable samples were screened to isolate STEC and molecularly identified using real-time PCR. Moreover, the antibacterial and antibiofilm activities of biogenically synthesized Ag NPs against the isolated STEC were examined. Results: Twenty-five out of 120 samples of eight types of fresh vegetables tested positive for E. coli, as confirmed by 16S rRNA, of which three were positive for the presence of Stx-coding genes, and six were partially hemolytic. Seven antibiotic disks were used to determine antibiotic susceptibility; the results indicated that isolate STX2EC had the highest antibiotic resistance. The results demonstrated that Ag NPs were highly effective against the STEC isolates, particularly the isolate with the highest drug resistance, with inhibition zones recorded as 19 mm for STX2EC, 11 mm for STX1EC1, and 10 mm for STX1EC2 at a concentration of 108 µg/mL. MICs of the isolates STX1EC1, and STX1EC2 were 13.5 µg/mL whereas it was detected as 6.75 µg/mL for STX2EC. The percentages of biofilm inhibition for STX1EC2, STX1EC1, and STX2EC, were 78.7%, 76.9%, and 71.19%, respectively. Conclusion: These findings suggest that the biogenic Ag NPs can be utilized as a new promising antibacterial agent to combat biofouling on surfaces.