Assessment of synergistic antibacterial activity of combined biosurfactants revealed by bacterial cell envelop damage

Abstract

Besides potential surface activity and some beneficial physical properties, biosurfactants express antibacterial activity. Bacterial cell membrane disrupting ability of rhamnolipid produced by Pseudomonas aeruginosa C2 and a lipopeptide type biosurfactant, BS15 produced by Bacillus stratosphericus A15 was examined against Staphylococcus aureus ATCC 25923 and Escherichia coli K8813. Broth dilution technique was followed to examine minimum inhibitory concentration (MIC) of both the biosurfactants. The combined effect of rhamnolipid and BS15 against S. aureus and E. coli showed synergistic activity by expressing fractional inhibitory concentration (FIC) index of 0.43 and 0.5. Survival curve of both the bacteria showed bactericidal activity after treating with biosurfactants at their MIC obtained from FIC index study as it killed >90% of initial population. The lesser value of MIC than minimum bactericidal concentration (MBC) of the biosurfactants also supported their bactericidal activity against both the bacteria. Membrane permeability against both the bacteria was supported by amplifying protein release, increasing of cell surface hydrophobicity, withholding capacity of crystal violet dye and leakage of intracellular materials. Finally cell membrane disruption was confirmed by scanning electron microscopy (SEM). All these experiments expressed synergism and effective bactericidal activity of the combination of rhamnolipid and BS15 by enhancing the bacterial cell membrane permeability. Such effect of the combination of rhamnolipid and BS15 could make them promising alternatives to traditional antibiotic in near future.

Microbial biosurfactants: current trends and applications in agricultural and biomedical industries

“…Sana et al . () showed that both E. coli and S. aureus were sensitive to rhamnolipid and that because of its’ hydrophilic and hydrophobic parts it interacts with the nonpolar part of the cell membrane. The membrane disintegrates leading to the penetration of the cell wall and plasma membrane by pore formation and subsequent leakage of inner cytoplasmic materials leading to cell death (Meincken et al .…”

“…These mechanisms might help explain how the LP produced by B. stratosphericus (Sana et al . ) has an antibacterial effect against both S. aureus and E. coli .…”

“…Another suggestion is that rhamnolipids cause cell membrane damage by insertion of acyl tails causing cell leakage of cytoplasmic components (Yalc ßin and Ergene 2009). Sana et al (2018) showed that both E. coli and S. aureus were sensitive to rhamnolipid and that because of its' hydrophilic and hydrophobic parts it interacts with the nonpolar part of the cell membrane. The membrane disintegrates leading to the penetration of the cell wall and plasma membrane by pore formation and subsequent leakage of inner cytoplasmic materials leading to cell death (Meincken et al 2005;Ortiz et al 2006).…”

“…In terms of SLs, the vigorous membrane-distorting potentiality of SUR is dependent on the size of the peptide ring with the peptide moiety penetrating into the cell membrane and generating a variance of charge at the site of action on the membrane surface (Heerklotz and Seelig 2001). These mechanisms might help explain how the LP produced by B. stratosphericus (Sana et al 2018) has an antibacterial effect against both S. aureus and E. coli.…”

Antibacterial activity of a hexahydro‐β‐acids/methyl‐β‐cyclodextrin inclusion complex against bacteria related to foodborne illness

“…Instead, E. sakazakii cells were seen to have shrunk, producing a ruffled appearance to their membranes. The difference in these two results is likely attributable to the difference in cell membrane structure between the gram‐positive S. aureus and the gram‐negative E. sakazakii (Sana, Datta, Biswas, & Sengupta, ; Szabó et al, ).…”