• Journal of Microbiology and Biotechnology
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• v.29 no.8
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• pp.1177-1183
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• 2019

Grapefruit seed extract (GSE) is a safe and effective preservative that is used widely in the food industry. However, there are few studies addressing the anti-biofilm effect of GSE. In this study, the anti-biofilm effect of GSE was investigated against biofilm-forming strains of Staphylococcus aureus and Escherichia coli. The GSE minimum inhibitory concentration (MIC) for S. aureus and E. coli were $25{\mu}g/ml$ and $250{\mu}g/ml$, respectively. To investigate biofilm inhibition and degradation effect, crystal violet assay and stainless steel were used. Biofilm formation rates of four strains (S. aureus 7, S. aureus 8, E. coli ATCC 25922, and E. coli O157:H4 FRIK 125) were 55.8%, 70.2%, 55.4%, and 20.6% at $1/2{\times}MIC$ of GSE, respectively. The degradation effect of GSE on biofilms attached to stainless steel coupons was observed (${\geq}1$ log CFU/coupon) after exposure to concentrations above the MIC for all strains and $1/2{\times}MIC$ for S. aureus 7. In addition, the specific mechanisms of this anti-biofilm effect were investigated by evaluating hydrophobicity, auto-aggregation, exopolysaccharide (EPS) production rate, and motility. Significant changes in EPS production rate and motility were observed in both S. aureus and E. coli in the presence of GSE, while changes in hydrophobicity were observed only in E. coli. No relationship was seen between auto-aggregation and biofilm formation. Therefore, our results suggest that GSE might be used as an anti-biofilm agent that is effective against S. aureus and E. coli.

• Journal of Microbiology and Biotechnology
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• v.31 no.10
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• pp.1420-1429
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• 2021

The safety of the probiotic strain Q180, which exerts postprandial lipid-lowering effects, was bioinformatically and phenotypically evaluated. The genome of strain Q180 was completely sequenced, and single circular chromosome of 3,197,263 bp without any plasmid was generated. Phylogenetic and related analyses using16S rRNA gene and whole-genome sequences revealed that strain Q180 is a member of Lactiplantibacillus (Lp., formerly Lactobacillus) plantarum. Antimicrobial resistance (AMR) genes were bioinformatically analyzed using all Lp. plantarum genomes available in GenBank, which showed that AMR genes are present differently depending on Lp. plantarum strains. Bioinformatic analysis demonstrated that some mobile genetic elements such as prophages and insertion sequences were identified in the genome of strain Q180, but because they did not contain harmful genes such as AMR genes and virulence factor (VF)- and toxin-related genes, it was suggested that there is no transferability of harmful genes. The minimum inhibition concentrations of seven tested antibiotics suggested by the European Food Safety Authority guidelines were slightly lower than or equal to the microbiological cut-off values for Lp. plantarum. Strain Q180 did not show hemolytic and gelatinase activities and biogenic amine-producing ability. Taken together, this study demonstrated the safety of strain Q180 in terms of absence of AMR genes and VF- and toxin-related genes as a probiotic strain.

• Food Science and Preservation
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• v.14 no.2
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• pp.194-200
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• 2007

In order to enhance the functionality and storage period of traditional fermented foods, the strain CH-14, which To enhance the quality of traditional fermented foods, and to lengthen acceptable storage periods, a bacterial strain, CH-14, showing potent enzyme activities and antibacterial capabilities, was isolated and characterize4 The bacterium wn Gram-positive, catalase-positive, oxidase-negative, formed endospores, expressed flagella, was rod-shaped, and had dimensions of 0.5 0.7m and 3.5 4.2m. The bacterium CH-14 was identified as Bacillus subtilis using Bergey's Manual of Systematic Bacteriology, Bergey's Manual of Determinative Bacteriology, and an API 50 CHL Carbohydrate Test Kit. An optimum growth medium contained 2% (w/v) cellobiose as a carbon source, a mixture of 0.5% (w/v) yeast extract and 0.5% (w/v) peptone as nitrogen sources, and 0.05% (w/v) $MgSO_4{\cdot}7H_2O$. The optimal culture temperature and the optimal initial pH were in the ranges of 30 $45^{\circ}C$ and 4.5 10.0, respectively. Maximum production of the antibacterial substance occurred after 24h of culture. The minimum inhibitory concentrations of the antibacterial substance were 5mg bacterial dry weight/mL against E. coli and P. mirabilis, and 10 mg/mL against S. aureus, S. enteritidis and V. parahaemolyticus.

• Journal of Microbiology and Biotechnology
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• v.30 no.4
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• pp.571-582
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• 2020

Quorum sensing (QS)-mediated infections cause severe diseases in human beings. The control of infectious diseases by inhibiting QS using antipathogenic drugs is a promising approach as antibiotics are proving inefficient in treating these diseases. Marine fungal (Pestalotiopsis sydowiana PPR) extract was found to possess effective antipathogenic characteristics. The minimum inhibitory concentration (MIC) of the fungal extract against test pathogen Pseudomonas aeruginosa PAO1 was 1,000 ㎍/ml. Sub-MIC concentrations (250 and 500 ㎍/ml) of fungal extract reduced QS-regulated virulence phenotypes such as the production of pyocyanin, chitinase, protease, elastase, and staphylolytic activity in P. aeruginosa PAO1 by 84.15%, 73.15%, 67.37%, 62.37%, and 33.65%, respectively. Moreover, it also reduced the production of exopolysaccharides (74.99%), rhamnolipids (68.01%), and alginate (54.98%), and inhibited the biofilm formation of the bacteria by 90.54%. In silico analysis revealed that the metabolite of P. sydowiana PPR binds to the bacterial QS receptor proteins (LasR and RhlR) similar to their respective natural signaling molecules. Cyclo(-Leu-Pro) (CLP) and 4-Hydroxyphenylacetamide (4-HPA) were identified as potent bioactive compounds among the metabolites of P. sydowiana PPR using in silico approaches. The MIC values of CLP and 4-HPA against P. aeruginosa PAO1 were determined as 250 and 125 ㎍/ml, respectively. All the antivirulence assays were conducted at sub-MIC concentrations of CLP (125 ㎍/ml) and 4-HPA (62.5 ㎍/ml), which resulted in marked reduction in all the investigated virulence factors. This was further supported by gene expression studies. The findings suggest that the metabolites of P. sydowiana PPR can be employed as promising QS inhibitors that target pathogenic bacteria.

• Journal of the Korean Society of Food Science and Nutrition
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• v.33 no.2
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• pp.229-235
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• 2004

Soy protein was hydrolyzed by 5 different pretenses and determinated antimicrobial activity of each hydrolysate. The soy protein hydrolysate treated by pretense from Aspergillus saitoi showed the highest antimicrobial activity among the protease studied and was used for further analysis. Soy protein hydrolysate was fractionated by ultrafiltration for M.W. 10,000,3,000 and 1,000. The M.W 1,000∼3,000 showed the highest antimicrobial activity. The minimum inhibition concentrations of obtained fraction were 0.5∼0.8 mg/mL for gram positive and negative microbials, and its activity was even observed after heating at 121$^{\circ}C$ for 10 min, suggesting that hydrolyzed protein having antimicrobial activity is quite heat-stable. Reverse-phase HPLC was further applied to separate the fraction and 8 peaks were found. Each 8 peaks were separated and pooled and measured antimicrobial activity. Among them, retention time of peak at 16.02 min showed the prominent antimicrobial activity.

• Research in Plant Disease
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• v.23 no.2
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• pp.177-185
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• 2017

Bacillus amyloliquefaciens LM11 was isolated from the feces of larvae of the rhino beetle and showed strong antifungal activities against various phytopathogenic fungi by producing biosurfactants. In this study, our overall goal was to determine relationship between biosurfactants produced from the LM11 strain and its role in growth inhibition of phytopathogenic fungi. Production and expression levels of B. amyloliquefaciens LM11 biosurfactants were significantly differed depending on growth phases. Transcriptional and biochemical analysis indicated that the biosurfactants of the LM11 strain were greatly enhanced in late log-phase to stationary phase. Inhibitions of phytopathogenic mycelial growth and spore germination were directly correlated (P<0.001, R=0.761) with concentrations of the LM11 cell-free culture filtrates. The minimum inhibitory surface tension of the culture filtrate of the B. amyloliquefaciens LM11 grown in stationary phase to inhibit mycelial growth of the phytopathogenic fungi was 38.5 mN/m (P<0.001, R=0.951-0.977). Our results indicated that the biosurfactants of B. amyloliquefaciens LM11 act as key antifungal metabolites in biocontrol of plant diseases, and measuring surface tension of the cell-free culture fluids can be used as an easy indicator for optimal usage of the biocontrol agents.

• Food Science and Preservation
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• v.13 no.1
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• pp.88-94
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• 2006

This study was carried out to produce antimicrobial peptides from casein using various proteases. To examine whether the hydrolysis of casein would produce antimicrobial substance and the application as natural antimicrobial material, casein was hydrolyzed by five different proteases. The casein hydrolysate was fractionated with regenerated membrane filter (molecular weight cut-off 30,000 10,000 and 3,000) and antimicrobial activity was measured for each fraction. Antimicrobial activity appeared great in the fraction below 3,000 molecular weight The fraction was re-fractionated by high performance liquid chromatography and substance of main peak (retention time: 13.2 min) collected was used as a sample to measure antimicrobial activity. Among the casein hydrolysates produced by protease, antimicrobial activity was observed the greatest in hydrolysate treated with Aspergillus oryzae protease. The minimum inhibition concentrations of the Asp. oryzae protease hydrolysate were 1.0-1.5 mg/mL. This hydrolysate was a heat stable peptide since antimicrobial activity was maintained after treating with heat for 20 min at $121^{\circ}C$.

• Korean Journal of Organic Agriculture
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• v.22 no.3
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• pp.469-481
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• 2014

IIn vitro antimicrobial and anti-inflammatory activities of nargenicin and its derivatives were investigated. Nargenicin, an unusual macrolide antibiotic with potent anti-MRSA (methicilin-resistant Staphylococcus aureus) activity, was purified from the culture broth of Nocardia sp. CS682. And variety of novel nargenicin derivatives was synthesized from nargenicin. Two compounds (4 and 5) exhibit a broad spectrum of antimicrobial activities against infectious bacteria. The antimicrobial activity of derivatives against fifteen organisms was assessed using the minimum inhibitory concentration (MIC). The MIC values were in the ranges of $0.15{\sim}80{\mu}g/mL$ (w/v) for compound 1 and 2, $5{\sim}80{\mu}g/mL$ (w/v) for compound 3, $1.25{\sim}40{\mu}g/mL$ (w/v) for compound 4, and $1.25{\sim}80{\mu}g/mL$ (w/v) for compound 5, depending on the pathogens studied. In vitro, we investigated cytotoxicity and inhibition of nitric oxide (NO) production of synthesized compounds 1-5 in Raw 264.7 cells. LPS-induced nitric oxide releases were significantly blocked by compound 3, 4 and 5 in a dose-dependent manner. At high concentrations ($5{\mu}g/mL$) compound 5 inhibited the NO production by 95%. Compound 4 inhibited the release of NO in LPS-activated Raw 264.7 cells by 75% at the concentration of $10{\mu}g/mL$. Compound 3 inhibited the release of NO in LPS-activated Raw 264.7 cells by 65% at the concentration of $100{\mu}g/mL$. On the other hand, nargenicin, compound 1 and 2 did not inhibit NO production. These results demonstrated that compound 4 and 5 displayed antimicrobial activity and blocked LPS-induced pro-inflammatory mediators such as NO in macrophages, which might be responsible for its therapeutic application.

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.75-84
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• 2009

The effect of various SNPs (silver nanoparticles) on the growth of Microcystis aeruginosa was investigated in laboratory and field experiment. Four SNPs, namely JS47N, JS47N-K2, JS47N/3-1 and JS47N/3-2 were used to this study. The Ag size, concentration and color of these solutions were about $20{\sim}40nm$, $200mg\;L^-1$ and brown, respectively. At 0.01 and $0.1mg\;L^-1$, SNPs inhibited the growth of unicellular M. aeruginosa by 99.4% and 99.9%, respectively. However, SNPs of $1mg\;L^-1$ inhibited the growth of colonial M. aeruginosa by 98.5%, whereas the other three concentrations (0.001, 0.01 and $0.1mg\;L^-1$) had little inhibitory effect. In experimental enclosures from eutrophic lake, cyanobacteria including M. aeruginosa were found to be more sensitive to the SNPs than green algae and diatoms. In conclusion, our study indicates that SNPs has a selective cyanocidal potential when used to M. aeruginosa. We believe that future studies need to test on various other organisms, and determine minimum concentration for field application.

• Korean Journal of Food Science and Technology
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• v.33 no.5
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• pp.611-618
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• 2001

The ethanol extract of Dryopteris crassirhizoma Nakai showed strong growth inhibition against 5 strains of Listeria monocytogenes at the concentrations of $100{\sim}500$ ppm and the minimum inhibitory concentration of n-hexane fraction was under 50 ppm. The D8-2-5 fraction isolated from n-hexane fraction of Dryopteris crassirhizoma Nakai showed a strong bactericidal activity on 5 strains of L. monocytogenes at 20 ppm level in tryptic soy broth medium. At the level, the viable count was reduced $4{\sim}6$ log cycle compared to initial cell number. Observation by the measurement of adenosine triphosphate (ATP) contents and transmission electron microscope showed that disruptions of the cell wall and elution of intracellular ATP are assumed to be due to the bactericidal activity. In addition, the n-hexane fraction of Dryopteris crassirhizoma Nakai showed the strong growth inhibitions at 50 ppm on Vibrio parahaemolyticus and Bacillus cereus, and at 25 ppm on Staphylococcus aureus.