New Strategies for Inhibition of Listeria monocytogenes and Klebsiella pneumoniae Biofilm Formation and Persistence

Objective: This study aimed to find new strategies for the prevention of bacterial biofilms and investigate the effect of some plant extracts on the biofilm formation by certain pathogenic bacterial strains in-vitro. Methods: Fourteen different biofilm forming bacterial isolates were collected   and their biofilm were quantitatively measured under different temperature, pH and growth medium using Crystal violet staining method.  Exopolysaccharides (EPS) produced by the isolates were estimated and a comparison between the tested isolates was made. The effect of some plant extracts on bacterial growth, biofilm formation and exopolysaccharide quantity was determined. Results: The two isolates, Listeria monocytogenes (ATCC13932) and Klebsiella pneumoniae (ATCC700613) were among the most active biofilm forming bacterial isolates.  The optimum temperature, pH and media for EPS production and biofilm formation were determined. The effect of some plant extracts of Cranberry; Pomegranate peel and, Arak on growth and formation of biofilm and EPS were recorded. Moreover, minimum inhibition concentration of each plant extract was performed. Conclusion: EPS quantity produced from the tested isolates depends on some effective factors such temperature, media contents and pH. Aqueous-Cranberry, aqueous-Pomegranate Peel and methanolic-Arak extracts have antibacterial and antibiofilm activities on L. monocytogenes and K.  pneumonia. Thus, application of new natural approaches for inhibiting bacterial biofilm is important to prevent persistent and recurrent biofilm related infections.