Comparative Antibacterial and Antibiofilm Potential of Syzygium aromaticum and Melaleuca alternifolia Methanolic Extracts Against Antibiotic-Resistant Clinical Escherichia coli Isolates

Abstract

Multidrug resistance and biofilm formation are challenging the treatment of Escherichia coli infections, and plant extracts are being investigated as complementary antimicrobial agents. Methods: The methanolic extracts of clove, Syzygium aromaticum, and tea tree, Melaleuca alternifolia, were compared with 4 clinical isolates of E. coli, 3 from Al-Ramadi Teaching Hospital and 1 from Heet General Hospital. The antibiotic susceptibility testing was performed by the Kirby-Bauer disk diffusion method (ceftriaxone, ciprofloxacin, amikacin, ceftazidime). The antibacterial activity was evaluated using the agar well diffusion method; biofilm production was evaluated using the Congo red agar (CRA), and the effect on biofilm production was evaluated using the crystal violet microtiter plate (CV-MP) method read at 450 nm. Results: Ciprofloxacin was the most active antibiotic (zone up to 48 mm), while most other zones were in the resistant zone (Heet isolate). Inhibition zones of 15- 28 mm were produced in the case of tea tree extract and 9- 13 mm in the case of clove extract. All isolates produced dark brown to black colonies, which indicates the production of biofilm on CRA. In the microtiter assay, the wells treated with extract were stained lighter than the untreated wells, and the OD450 readings were in the range of 0.045 – 0.419. Conclusions: In these conditions, tea tree extract produced larger inhibition zones, and both extracts were effective at inhibiting crystal violet staining. Due to the limited number of isolates, lack of replicate statistics, and lack of a methanol-matched control in the biofilm assay, the results are preliminary and require further evaluation by MIC/MBC and sub-inhibitory antibiofilm and phytochemical evaluation.