Anti-biofilm activity of new low molecular weight compounds produced by Lactiplantibacillus plantarum SJ33 against Klebsiella pneumoniae

Community-acquired infections are partly attributed to biofilms formed by drug resistant bacteria signifying major health problems. Hence, there is a critical need for the development of new antibiotics with antibacterial activities. In this study, we investigated the biofilm inhibiting characteristics of antibacterial compounds C1 and C2 confirmed as (3-amino-5-hydroxy-6-(hydroxymethyl)-4-(1-hydroxyprop-2-yn-1-yl)-3,3a,4,5,6,7a-hexahydro-7H-indazol-7-one) and (1-(dimethylamino)-3-hydroxy-3-((2-hydroxypropan-2-yl)oxy)-1 (methylamino)butan-2-one) which were previously characterized and identified by our group. This compound exhibits antibacterial activity against Gram-negative bacteria including activity against clinical isolates of Klebsiella pnemoniae and Escherichia coli. Bactericidal activity against K. pnemoniae was revealed by scanning electron microscopic (SEM) images that showed cellular leakage by C1 and C2 which is probably the major cause of its antibacterial activity. These findings were supported by antibacterial assays of susceptible as well as resistant pathogens. Biofilm assays also proved anti-biofilm activity of C1 and C2 on biofilm inhibition as well as dispersion of mature biofilms using crystal violet assay and the results were confirmed by fluorescence and SEM observation. In conclusion, our results showed that C1 and C2 exert bactericidal action on target cells by membrane disruption. Biofilm inhibition and dispersion of preformed biofilms was also revealed by microscopic images, making it an interesting alternative for commercial antibiotics for the development of new antibacterial therapies. The bioactive compounds C1 and C2 not only inhibit K. pnemoniae growth but also eradicate the biofilm formation thus reducing the virulence of K. pnemoniae pathogen.