Abstract
Adiantum philippense (A. philippense), an ethnomedicinally important fern, has become an interesting herb in the search for novel bioactive metabolites, which can also be used as therapeutic agents. Primarily, in this study, A. philippense crude extract was screened for its phytochemical constituents, antagonistic potential, and effect on bacterial adhesion and biofilm formation against common food pathogens. Phytochemical profiling of A. philippense was carried out by using High Resolution-Liquid Chromatography and Mass Spectroscopy (HR-LCMS) followed by antibacterial activity via agar cup/well diffusion, broth microdilution susceptibility methods, and growth curve analysis. Antibiofilm potency and efficacy were assessed on the development, formation, and texture of biofilms through light microscopy, fluorescent microscopy, scanning electron microscopy, and the assessment of exopolysaccharide production. Correspondingly, a checkerboard test was performed to evaluate the combinatorial effect of A. philippense and chloramphenicol. Lastly, molecular docking studies of identified phytochemicals with adhesin proteins of tested food pathogens, which helps the bacteria in surface attachment and leads to biofilm formation, were assessed. A. philippense crude extract was found to be active against all tested food pathogens, displaying the rapid time-dependent kinetics of bacterial killing. A. philippense crude extract also impedes the biofilm matrix by reducing the total content of exopolysaccharide, and, likewise, the microscopic images revealed a great extent of disruption in the architecture of biofilms. A synergy was observed between A. philippense crude extract and chloramphenicol for E. coli, S. aureus, and P. aeruginosa, whereas an additive effect was observed for S. flexneri. Various bioactive phytochemicals were categorized from A. philippense crude extract using HR-LCMS. The molecular docking of these identified phytochemicals was interrelated with the active site residues of adhesin proteins, IcsA, Sortase A, OprD, EspA, and FimH from S. flexneri, S. aureus, P. aeruginosa, and E. coli, respectively. Thus, our findings represent the bioactivity and potency of A. philippense crude extract against food pathogens not only in their planktonic forms but also against/in biofilms for the first time. We have also correlated these findings with the possible mechanism of biofilm inhibition via targeting adhesin proteins, which could be explored further to design new bioactive compounds against biofilm producing foodborne bacterial pathogens.
Highlights
Since the conception of human civilization, foodborne diseases have been a concern for mankind
Preliminary phytochemical scrutiny of methanolic crude extract of A. philippense revealed the existence of phenolics, terpenoids, alkaloids, tannins, flavonoids, glycosides, saponins, and carbohydrates (Table 1)
S. aureus was found to be more susceptible when compared to E. coli, P. aeruginosa, and S. flexneri (Figure 1E)
Summary
Since the conception of human civilization, foodborne diseases have been a concern for mankind. Over the last few years, the number of diseases caused by foodborne pathogens has been on an increase, and this has turned into a primary and serious global health issue (Zhao et al, 2017). Food contaminating pathogens have garnered significant attention, as they are currently the cause of remarkable mortality and morbidity numbers with a rate of 420,000 deaths per year (World Health Organization [WHO], 2018). The most ordinary symptoms of these food pathogens are diarrhea, vomiting, abdominal cramps, fatigue, nausea, and fever. These pathogens can contaminate foodstuffs at any stage during processing, distribution, and storage. It is extremely crucial that we control the growth and development of food pathogens, though removal of these organisms is challenging since they are capable of forming biofilms on a variety of planes (Bazargani, 2016)
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