No abstract

The emergence of microbial resistance to conventional antibiotics, partially attributed to biofilm formation, has urged for new antimicrobial compounds. Here, we reported two novel low molecular weight (LMW) compounds from Lactiplantibacillus plantarum SJ33 and evaluated their biofilm inhibitory effects on Staphylococcus aureus. The compounds C1 and C2 were purified by RP-HPLC and structurally identified as 3-amino-5-hydroxy-6-(hydroxymethyl)-4-(1-hydroxyprop-2yn-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 by spectroscopic techniques. High ESI-MS data confirmed the molecular weight of C1 and C2 as 254.1141 and 234.1658 Da, respectively. Time-kill assay demonstrated bactericidal action of compounds, whereas scanning electron microscopy revealed morphological changes in treated S. aureus MTCC96 and methicillin-resistant S. aureus (MRSA) cells. The antibacterial compounds reduced biofilm formation in S. aureus MTCC96 and MRSA by crystal violet assay. Further, fluorescence and scanning electron microscopic images exhibited biofilm formation by pathogens and biofilm inhibition by compounds treatment. The Quantitative RT PCR revealed the down-regulation of icaC and icaD genes involved in intercellular adhesion of biofilms. The results confirmed the anti-biofilm activity of novel LMW compounds by eliminating preformed biofilms formed by S. aureus MTCC96 and MRSA.

Biofilm forming pathogens are among the major causes of hospital-acquired infections and are not much affected by antibiotic treatment. Consequently, novel agents and therapeutics are required urgently that possess antibacterial and antibiofilm activities. This study analyzed two bacteriocins from Lactobacillus plantarum subsp. argentoratensis SJ33 strain for their antibacterial and antibiofilm activity as well as cytotoxic properties. BacF1 and BacF2 showed broad spectrum activity against both Gram-positive (Listeria monocytogenes, Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa, Escherichia coli) bacteria. Significant bactericidal action was also observed on S. aureus cells by pore formation. Additionally, bacteriocins disrupted biofilms formed by S. aureus and P. aeruginosa which were shown by crystal violet staining assay and visualized by fluorescence as well as scanning electron microscopy. Quantitative Real-Time PCR study revealed changes in gene expression of biofilm formation in S. aureus (ica) and P. aeruginosa (pelA, psl, rhlA). Cytotoxicity of bacteriocins was further analyzed on normal mammalian cells and Caenorhabditis elegans. Notably, bacteriocins showed no major effect on HEK-293 cell line and enhanced the survival of S. aureus infected HEK-293 cells. Similarly, no cytotoxic effect was visible on C. elegans even after treatment with higher concentration than MIC at different time intervals.