Control of Staphylococcus epidermidis biofilm by surfactins of an endophytic bacterium Bacillus sp. 15 F.

The present paper deals with the preparation and annotation of a surfactin(s) derived from a culture of the endophytic bacterium Bacillus 15 F. The LC-MS analysis of the acetonitrile fraction confirmed the presence of surfactins Leu/Ile7 C15, Leu/Ile7 C14 and Leu/Ile7 C13 with [M+H]+ at m/z 1036.6895, 1022.6741 and 1008.6581, respectively. Various concentrations of the surfactin(s) (hereafter referred to as surfactin-15 F) were used to reduce the adhesion of Staphylococcus epidermidis S61, which served as a model for studying antibiofilm activity on polystyrene surfaces. Incubation of Staphylococcus epidermidis S61 with 62.5 µg/ml of surfactin-15 F resulted in almost complete inhibition of biofilm formation (90.3 ± 3.33 %), and a significant reduction of cell viability (resazurin-based fluorescence was more than 200 times lower). The antiadhesive effect of surfactin-15 F was confirmed by scanning electron microscopy. Surfactin-15 F demonstrated an eradication effect against preformed biofilm, causing severe disruption of Staphylococcus epidermidis S61 biofilm structure and reducing viability. The results suggest that surfactins produced by endophytic bacteria could be an alternative to synthetic products. Surfactin-15 F, used in wound dressings, demonstrated an efficient treatment of the preformed Staphylococcus epidermidis S61 biofilm, and thus having a great potential in medical applications.

A novel perspective on eugenol as a natural anti-quorum sensing molecule against Serratia sp.

Serratia marcescens is commonly noted to be an opportunistic pathogen and is often associated with nosocomial infections. In addition to its high antibiotic resistance, it exhibits a wide range of virulence factors that confer pathogenicity. Targeting quorum sensing (QS) presents a potential therapeutic strategy for treating bacterial infections caused by S. marcescens, as it regulates the expression of various virulence factors. Inhibiting QS can effectively neutralize S. marcescens' bacterial virulence without exerting stress on bacterial growth, facilitating bacterial eradication by the immune system. In this study, the antibacterial and anti-virulence properties of eugenol against Serratia sp. were investigated. Eugenol exhibited inhibitory effects on the growth of Serratia, with a minimal inhibitory concentration (MIC) value of 16.15 mM. At sub-inhibitory concentrations, eugenol also demonstrated antiadhesive and eradication activities by inhibiting biofilm formation. Furthermore, it reduced prodigiosin production and completely inhibited protease production. Additionally, eugenol effectively decreased swimming and swarming motilities in Serratia sp. This study demonstrated through molecular modeling, docking and molecular dynamic that eugenol inhibited biofilm formation and virulence factor production in Serratia by binding to the SmaR receptor and blocking the formation of the HSL-SmaR complex. The binding of eugenol to SmaR modulates biofilm formation and virulence factor production by Serratia sp. These findings highlight the potential of eugenol as a promising agent to combat S. marcescens infections by targeting its virulence factors through quorum sensing inhibition.

Antibacterial, antibiofilm and cytotoxic properties of prodigiosin produced by a newly isolated Serratia sp. C6LB from a milk collection center.

The aim of this work was to produce a red tripyrrole pigment prodigiosin from Serratia sp. C6LB strain, to investigate the promising antimicrobial properties on Gram-positive and Gram-negative bacterial strains. The research was also proposed to evaluate the antibiofilm activity on Staphylococcus epidermidis S61 biofilm and its cytotoxic activity against human cancer cell lines. The production and structural elucidation of prodigiosin was carried out using spectrophotometric scanning, TLC, HPLC, FTIR and NMR analysis. The pigment production was optimized using mannose and peptone as carbon and nitrogen sources, respectively. The study confirmed promising antibacterial properties of prodigiosin on eight Gram-positive and Gram-negative bacterial strains with MICs values ranged from 0.039 to 2.5 mg/mL. Antiadhesive activity test of prodigiosin on Staphylococcus epidermidis S61 biofilm exhibited 99.9% inhibition, whereas maximum biofilm eradication activity reached 65%. Cytotoxic activity showed IC50 of 16 µg/mL and 6.7 µg/mL against breast cancer lines MCF-7 and MDA-MB231, respectively.

Antibacterial, anti-adherent and cytotoxic activities of surfactin(s) from a lipolytic strain Bacillus safensis F4.

The bacterial strain F4, isolated from olive oil-contaminated soil, has been found to produce biosurfactants as confirmed by oil displacement test and the emulsification index results. The identification of the strain F4, by 16S ribosomal RNA gene, showed a close similarity to Bacillus safensis, therefore the strain has been termed Bacillus safensis F4. The Thin Layer Chromatography (TLC) and the High Pressure Liquid Chromatography-Mass Spectrometry (HPLC-MS/MS) demonstrated that the biosurfactant had a lipopeptide structure and was classified as surfactin. The present study showed also that the produced biosurfactant has an important antibacterial activity against several pathogen strains as monitored with minimum inhibitory concentration (MIC) micro-assays. In particular, it presented an interesting anti-planktonic activity with a MIC of 6.25 mg mL-1 and anti-adhesive activity which exceeded 80% against the biofilm-forming Staphylococcus epidermidis S61 strain. Moreover, the produced lipopeptide showed an antitumor activity against T47D breast cancer cells and B16F10 mouse melanoma cells with IC50 of 0.66 mg mL-1 and 1.17 mg mL-1, respectively. Thus, our results demonstrated that Bacillus safensis F4 biosurfactant exhibited a polyvalent activity via a considerable antibiofilm and antitumoral potencies.

The novel cationic cell-penetrating peptide PEP-NJSM is highly active against Staphylococcus epidermidis biofilm.

A cationic cell-penetrating peptide PEP-NJSM was identified in human virus proteomes by a screening of charge clusters in protein sequences generating Cell-Penetrating Peptides (CPP). PEP-NJSM was selectively active against Gram-positive Staphylococcus epidermidis as antibacterial agent with MIC value of 128 µM compared to the Gram-negative Pseudomonas aeruginosa strain with MIC value exceeded 512 µM. The selected peptide exhibited an important anti-biofilm activity even at sub-MIC levels. PEP-NJSM could prevent biofilm formation and increase the mortality of cells inside mature S. epidermidis biofilm. The results demonstrated that PEP-NJSM presented an important anti-adherent activity. It showed a S. epidermidis inhibition of biofilm formation >84% at a concentration of 256 µM (2 X MIC) and remained active even at a concentration of 4 µM with 32% of inhibition. The eradication of the established biofilm was observed at a concentration of 256 µM with 55.7% of biofilm eradication. The peptide was active against mature biofilm even at low concentration of 0.5 µM with approximately 22.9% of eradication. PEP-NJSM exhibited low hemolytic activity and cytotoxicity against mammalian cells. Our results demonstrate that PEP-NJSM could have a potential role in the treatment of diseases related to Staphylococcus epidermidis infection.

Chemical composition, anti-biofilm activity and potential cytotoxic effect on cancer cells of Rosmarinus officinalis L. essential oil from Tunisia.

BACKGROUND: Rosmarinus officinalis L. from Tunisia, popularly known as rosemary, is of a considerable importance for its medicinal uses and aromatic value. The aim of this study was to examine the chemical composition of Rosmarinus officinalis essential oil (ROEO) and to evaluate its antibiofilm activity on biofilm-forming bacterium and its anticancer activity on cancer cell lines. METHODS: The chemical composition of Rosmarinus officinalis essential oil (ROEO) was analyzed by GC-MS and its antibacterial activity was evaluated by micro-dilution method. The antibofilm activity of ROEO was evaluated using the crystal violet test and the cytotoxicity activity was determined by the MTT assay. RESULTS: In this research, thirty-six compounds were identified in ROEO using GC-MS analyses. The main components were 1,8-cineole (23.56%), camphene (12.78%), camphor (12.55%) and ß-pinene (12.3%). The antibacterial activity of ROEO was evaluated by micro-dilution method. The oil exhibited inhibition and bactericidal effect against two strains: Staphylococcus aureus ATCC 9144 and Staphylococcus epidermidis S61. It was found that the minimum inhibitory concentration (MIC) obtained for S. aureus and S. epidermidis ranged from 1.25 to 2.5 and from 0.312 to 0.625 µl ml-1, respectively and the minimum bactericidal concentration (MBC) were in the order of 5 and 2.5 µl ml-1, respectively. Furthermore, this oil showed a S. epidermidis biofilm inhibition more than 57% at a concentration of 25 µl ml-1. The eradication of 67% of the established biofilm was observed at a concentration of 50 µl ml-1 of ROEO, whereas the dose of 25 µl ml-1 removed only 38% of preformed biofilm. ROEO strongly inhibited the proliferation of Hela and MCF-7 cells with IC50 values of 0.011 and 0.253 µl ml-1, respectively. CONCLUSION: Our results demonstrate that ROEO could have a potential role in the treatment of diseases related to infection by microorganisms or proliferation of cancer cells.

Evaluation of biofilm-forming ability of bacterial strains isolated from the roof of an old house.

The bacterial diversity associated with biofilm-forming ability was studied. Eighteen bacterial strains were isolated from a microbial film collected from the roof of an old house located in Sfax, Tunisia. The purity of these microorganisms was confirmed by microscopic observation after repeated streaking on a Tryptic Soy agar medium. Biofilm formation was estimated using preliminary tests including a motility test, microbial adhesion to solvents (MATS), and the Congo Red Agar method (CRA). Since these tests showed no significant result, microplate tests, such as crystal violet and resazurin assays, were used. The results obtained showed that strain S61 was able to form a biofilm within 24 h (OD570 = 4.87). The viability of the S61 biofilm with resazurin assessed with fluorescence measurement was about 1.5 × 103. The S61 strain was identified as Staphylococcus epidermidis. In the biofilm studied here, it was the most biofilm-forming bacterium and will be used as a bacterial model for studying anti-biofilm activity.