Green Tea Extract (; L.): A Promising Antimicrobial, Anti-Quorum Sensing and Antibiofilm Candidate Against Multidrug-Resistant Species.

Background: Thermophilic species are among the main culprits behind bacterial gastroenteritis globally and have grown progressively resistant to clinically important antimicrobials. Many studies have been carried out to explore innovative and alternative strategies to control antibiotic-resistant campylobacters in animal reservoirs and human hosts; however, limited studies have been performed to develop efficient control schemes against biofilms.

Methods: This study investigated the antimicrobial and antibiofilm activities of some herbal extracts against multidrug-resistant (MDR) species recovered from different sources using phenotypic and molecular techniques.

Results: The overall species prevalence was 21.5%, representing 15.25% and 6.25% for and , respectively. Regarding , the highest resistance rate was observed for amoxicillin-clavulanic acid and colistin (85.25% each), followed by cefotaxime (83.61%) and tetracycline (81.97%), whereas isolates showed absolute resistance to cefotaxime followed by erythromycin (92%) and colistin (88%). Remarkably, all isolates were MDR with elevated multiple antimicrobial resistance (MAR) indices (0.54-1). The antimicrobial potentials of green tea (), rosemary () and ginger () extracts against MDR isolates were assessed by the disk diffusion assay and broth microdilution technique. Green tea extract showed a marked inhibitory effect against tested isolates, exhibiting growth inhibition zone diameters of 8 to 38 mm and a minimum inhibitory concentration (MIC) range of 1.56-3.12 mg/mL, unlike the rosemary and ginger extracts. Our findings reveal a respectable antibiofilm activity (>50% biofilm formation inhibition) of green tea against the preformed biofilms of isolates. Furthermore, real-time quantitative polymerase chain reaction (RT-qPCR) results showed a significant decrease ( < 0.05) in the expression levels of biofilm biosynthesis gene and its regulator ( and , respectively) in isolates treated with the green tea extract in comparison with untreated ones.

Conclusion: This is the first in vitro approach that has documented the inhibitory activity of green tea extract against MDR-biofilm-producing species isolated from different sources. Further in vivo studies in animals' models should be performed to provide evidence of concept for the implementation of this alternative candidate for the mitigation of MDR infections in the future.