Exopolysaccharides of lactic acid bacteria as protective agents against bacterial and viral plant pathogens.

In this study, 25 exopolysaccharides produced by lactic acid bacteria (LAB) were screened for their effect on plant pathogens. The molecular masses of EPS were found to be 3,8-5,0 × 104 Da. The GC-MS analysis revealed that EPSs were majorly composed of glucose (85.85-97.98 %). The FT-IR spectra of EPSs were in agreement with the typical absorption peaks of polysaccharides. EPSs showed a hydroxyl radical scavenging ability. The scavenging rate of EPS ranged from 20 to 50 % at a concentration of 5.0 mg/mL. Significant growth delay of phytopathogenic bacteria was observed after 3-6 h of cultivation. Optical density values of indicator cultures growing in the medium with EPS (1 mg/mL) were lower compared to the control by 24-100 % for Pseudomonas fluorescens, 9-46 % for P. syringae, 47-79 % for Pectobacterium carotovorum, 14-90 % for Clavibacter michiganensis, 9-100 % for Xantomonas campestris, and 45-100 % for X. vesicatorium. EPS retained their inhibitory effect on the growth of X. campestris, X. vesicatorium and C. michiganensis strains after 24-48 h of cultivation, but stimulating effect on the growth of some strains also was observed. LAB EPS showed antibiofilm activity against P. carotovorum, P. syringae, and P. fluorescent, decreasing their biofilm formation by 16-50 %, 14-39 %, and 29-59 %, respectively. Also, stimulation of biofilm formation by X. campestris (by 8-29 %), X. vesicatorium (by 3-32 %) and C. michiganensis (by 31-41 %) strains was observed. EPSs showed antiviral activity against tobacco mosaic virus (TMV). At a concentration of 100 µg/mL, they decreased the infective ability of TMV by 61-92 %. This is the first study demonstrating that LAB EPS exhibited in vitro antibacterial and antibiofilm activity against phytopathogenic bacteria and anti-viral activity against TMV. Thus, LAB EPSs could have great potential for plant protection strategies.

Screening of bacteriocin-producing dairy Enterococcus strains using low-cost culture media.

This study was carried out to select the bacteriocinogenic strains among Enterococcus strains isolated from Ukrainian traditional dairy products using a low-cost media for screening, that containing molasses and steep corn liquor. A total of 475 Enterococcus spp. strains were screened for antagonistic activity against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes indicator strains. The initial screening revealed that 34 Enterococcus strains during growth in low-cost medium containing corn steep liquor, peptone, yeast extract, and sucrose produced metabolites with inhibition activity against at least of the indicator strains used. Enterocin genes entA, entP, and entB were detected in 5 Enterococcus strains by PCR assay. Genes of enterocins A and P were found in E. faecalis 58 and Enterococcus sp. 226 strains, enterocins B and P - in Enterococcus sp. 423, enterocin A - in E. faecalis 888 and E. durans 248 strains. Bacteriocin-like inhibitory substances (BLIS) produced by these Enterococcus strains were thermostable and sensitive to proteolytic enzymes. To our knowledge, this is the first report on the isolation of enterocin-producing wild Enterococcus strains from traditional Ukrainian dairy products using a low-cost media for screening bacteriocinogenic strains. Strains E. faecalis 58, Enterococcus sp. 423, and Enterococcus sp. 226 are promising candidates for practical use as producers of bacteriocins with inhibitory activity against L. monocytogenes using molasses and steep corn liquor as cheap sources of carbon and nitrogen, that can significantly reduce the cost of industrial bacteriocin production. Further studies will be required to determine the dynamic of bacteriocin production, its structure, and mechanisms of antibacterial action.

Lactobacillus species mediated synthesis of silver nanoparticles and their antibacterial activity against opportunistic pathogens in vitro.

Introduction: Application of lactic acid bacteria for synthesis of silver (AG) nanoparticles (NPs) could be a good ecological friendly alternative to chemical and physical methods. The objective of this study was to investigate the biosynthesis of silver NPs using Lactobacillus strains and to compare their monosaccharide composition of capsular exopolysaccharides and the antibacterial activity of synthesized nanoparticles. Methods: The washed cells of 22 Lactobacillus strains were used for in vitro silver nanoparticle biosynthesis from silver nitrate solution. The NPs formation was confirmed by UV-visible spectroscopy and transmission electron microscopy (TEM) analysis. TEM micrographs were used for the evaluation of NPs size. The monosaccharide composition of capsular exopolysaccharides was determined using GC/MS analysis. The antimicrobial activity was determined by agar well diffusion assay. Results: The capsular layers of Lactobacillus strains contained heteropolysaccharides that were composed mostly of glucose, mannose, galactose and rhamnose in a different molar ratio. It was found that Ag NPs with large size (30.65 ± 5.81 nm) obtained from L. acidophilus 58p were more active against S. epidermidis, E. coli, K. pneumonia,S. flexneri and S. sonnei compared with Ag NPs from L. plantarum 92T (19.92 ± 3.4 nm). Conclusion: The size and antibacterial activities of Ag NPs were strain-dependent and such characteristics may be due to the capsular biopolymer composition of Lactobacillus strains used for Ag NPs synthesis.