• KSBB Journal
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• v.27 no.1
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• pp.9-15
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• 2012

Antimicrobial peptides are widely used in various organisms as a defense system against infection. The peptides are lethal towards bacteria and fungi, however have minimal toxicity in mammalian and plant cells. In this aspect, it is considered that antimicrobial peptides are new alternative materials for defensing against microbial infection. Here, we describe overall characteristics of antimicrobial peptides based on the mechanism of action, classification of the peptides, report detection/screening methods and chemical/biological production. It is expected that understanding of innate immune system based on antimicrobial peptides tends to develop novel natural antimicrobial agents, which might be applied for defensing pathogenic microorganisms resistant to conventional antibiotics.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1135-1142
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• 2010

A series of N(2)-benzothiazolyl substituted tetrahydroindazoles has been synthesized via cyclic ${\beta}$ keto esters. Optimum reaction condition was found as acidic toluene and effect of higher acidity towards substituted hydrazines in situ was described. Synthesized compounds have been achieved as single isomer and characterized by using 1D and 2D NMR spectral reports. Antimicrobial screening was carried out for the synthesized compounds along with a series of N(2)-pyridyl tetrahydroindazoles.1 The results of the in vitro antimicrobial screening studies revealed that compounds 13, 16 against Staphylococcus aureus, 11 against Escherichia coli, 10-12, 16 against Pseudomonas aeruginosa and 12 against Klebsiella pneumoniae recorded almost two-fold better activity compared to the standard drug used.

• Archives of Pharmacal Research
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• v.21 no.3
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• pp.278-285
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• 1998

The microdilution assay recommended by NCCLS (National Committee for Clinical Laboratory Standards) is one of the standardized methods of antibiotic susceptibility test. This method has been widely used clinically to obtain MIC values of antibiotics on pathogenic microorganisms. It is more convenient, rapid and simple to test many samples than other test methods such as agar diffusion assay and broth macrodilution assay. The screening of antimicrobial agents from microbial extracts is too laborious in its process. Therefore, a number of screening methods having more simple procedure have been developed. In our laboratory, we applied microdilution assay for screening the antimicrobial agents. This assay showed dose-response results and was more sensitive than disc diffusion assay in our system. We tested 200 samples of microbial extracts originated from 100 microbial strains and selected several samples as potential candidates. In this report, we show that the microdilution assay is more convenient method in screeing of antibiotic susceptibility than those previously reported.

• Journal of Microbiology and Biotechnology
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• v.23 no.6
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• pp.850-855
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• 2013

Finding new antimicrobial activities by functional metagenomics has been shown to depend on the heterologous host used to express the foreign DNA. Therefore, efforts are devoted to developing new tools for constructing metagenomic libraries in shuttle vectors replicatable in phylogenetically distinct hosts. Here we evaluated the use of the Escherichia coli-Bacillus subtilis shuttle vector pHT01 to construct a forest-soil metagenomic library. This library was screened in both hosts for antimicrobial activities against four opportunistic bacteria: Proteus vulgaris, Bacillus cereus, Staphylococcus epidermidis, and Micrococcus luteus. A new antibacterial activity against B. cereus was found upon screening in B. subtilis. The new antimicrobial agent, sensitive to proteinase K, was not active when the corresponding DNA fragment was expressed in E. coli. Our results validate the use of pHT01 as a shuttle vector and B. subtilis as a host to isolate new activities by functional metagenomics.

• Microbiology and Biotechnology Letters
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• v.35 no.4
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• pp.278-284
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• 2007

A novel screening strategy for salt-resistant antimicrobial peptides from a M13 peptide library was developed. Fusion of MSI-344, a magainin derivative and indolicidin to pIII coat proteins did not significantly affect viability of the recombinant phages, which indicated that the pIII could neutralize toxicity of the antimicrobial peptides and therefore it is possible to construct antimicrobial peptide library in Escherichia coli. On the basis of the conserved sequence of ${\alpha}$-helical antimicrobial peptides, a semi-combinatorial peptide library was constructed in which the peptides were displayed by pIII. To remove hemolytic activity from the library, the phages bound to red blood cells were removed, and the subtracted phage library was screened for binding to target bacteria Pseudomonas aeruginosa and Staphylococcus aureus under high salt concentrations. The screened peptides showed relatively low antimicrobial activity against the target bacteria. However, antimicrobial activities of the screened peptides P06 and S18 were not affected by the cation concentrations of 150 mM $Na^+$, 2 mM $Mg^{2+}$ and 2 mM $Ca^{2+}$ without significant hemolytic activity. This screening strategy that is based on binding capacity to target cells provides new potential to develop salt-tolerant antimicrobial peptides.

• Journal of the Korean Society of Food Science and Nutrition
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• v.25 no.6
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• pp.1080-1086
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• 1996

Monascus strains were isolated from Ang-Khak for the screening of antimicrobial activity. Two Monascus isolates, No.116 and No.481, were selected because they showed strong antimicrobial activity. Effect of various nutrients and incubation conditions on antimicrobial activity were different between two isolates. Strong antimicrobial activity of isolate No.116 was observed in the medium with 8% sucrose and $0.8%(NH_4)_2SO_4,$ 0.5% $KH_2PO_4and$ 0.5% $MgSO_4,$ while isolate No.481 required 8% sucrose, 1.6~2% $(NH_4)_2SO_4,$ 0.5% $MgSO_4and$ 0.5% $FeSO_4for$ the highest activity. The strong antimicroial activity was observed when both isolates were incubated on rice extract broth with initial pH of 5.3. The optiimum incubation temperature for the highest antimicrobial activity was $32.5^{\circ}C.$ With optimal conditions for the highest antimicrobial activity, isolate No.116 and No. 481 were both active for 51 hours or longer against test organisms Bacillus subtilis, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecium.

• Proceedings of the Korean Society of Food and Cookery Science Conference
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• 1998.11a
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• pp.461-461
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• 1998

• International Journal of Oral Biology
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• v.32 no.2
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• pp.75-78
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• 2007

The periodontal diseases and dental caries are major infectious diseases in oral cavity. Many of the preventive and therapeutic dental products contain the antimicrobial and anti-inflammatory components. But some of these antimicrobial have weak points such as coloration, burning sensation and insolubility in water. We have screened the therapeutic herbal extracts of the Plant Extract Bank for the antimicrobial activity on the major dental pathogens by growth inhibition assay. For the Porphyromonas gingivalis, 8 herbal extracts had an antimicrobial activity, 11 herbal extracts for the Prevotella intermedia, 43 herbal extracts for the Haemophilus actinomycetemcomitans and 61 herbal extracts for the Streptococcus mutans. Among these extracts, 6 herbal extracts had an antimicrobial activity for more than 3 species of dental pathogens. These extracts are Araliae Cordatae Radix, Crassirhizomae Rhizoma, Mori Radicis Cortex, Psoraleae Semen, Pini Ramulus and Sieges- beckiae Herba. All of effective extracts were CA group, ethanol extracts. Among these 6 herbal extracts, only Crassirhizomae is known to have a antibacterial effects. Therefore these herbal extracts have a possibility to be a candidate for a major antibacterial components in dental products.

• Journal of Microbiology and Biotechnology
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• v.16 no.11
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• pp.1706-1712
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• 2006

Because of the need for new antimicrobial substances with novel mechanisms of action, we report here the use of an Acinetobacter reporter system for high-throughput screening of active antimicrobial agents. The bioreporter Acinetobacter strain DF4/PUTK2 carrying luciferase genes luxCDABE was chosen because of its ecological importance and it is widespread in nature. This bioreporter is genetically engineered to emit light constitutively that can be measured in real time by luminometry. Hence, this reporter system was employed to determine the bacteriostatic actions of spent-culture supernatants derived from twelve bacterial isolates. Out of the results, the strongest bioluminescence inhibitory effect of the supernatants was recorded with Bacillus cereus strain BAC (S5). Subsequently, ethyl acetate extracts of extracellular products of strain BAC (S5) were separated by a thin-layer chromatography (TLC). Based on the bioluminescence inhibitory assay, three fractions were found to have antimicrobial activity. One fraction (C) having the strongest antimicrobial activity was further purified using TLC and characterized by IR, $^1H$ NMR, mass spectrometry, SDS-PAGE, and amino acid composition analysis. The results predicted the presence of 2-pyrrolidone-S-carboxylic acid (PCA) and the octadeconic-acid-like fatty acid. Fraction C also demonstrated a broad inhibitory activity on several Gram-negative and Gram-positive bacteria. In conclusion, the Acinetobacter reporter system shows great potential to be a reliable, sensitive, and real-time indicator of the bacteriostatic actions of the antimicrobial agents.

• Journal of Plant Biotechnology
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• v.47 no.1
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• pp.90-99
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• 2020

This study aimed to screen for plants with antimicrobial potential among the evergreen woody species of South Korea that are used for horticulture and landscaping and to provide basic information about plants with proven antimicrobial activity to underpin future research. The plant materials were extracted under various conditions, and the antimicrobial activities of the extracts were evaluated by agar diffusion assay. The screening tests demonstrated that the crude extracts of 43 species had inhibitory effects against S. aureus. The inhibitory activities of four species (Elaeocarpus sylvestris, Camellia japonica, Cleyera japonica, and Quercus salicina) were relatively higher than that of the synthetic antimicrobial agents methylparaben and phenoxyethanol. The highest inhibitory activity was observed with the leaf extracts (extracted with methanol for 30 minutes) of E. sylvestris, based on induction of the largest inhibition zone of 23.3 mm in size. In addition, solvent fractions of E. sylvestris were evaluated. The largest inhibitory zone of 23.1 mm was observed for the n-butanol fraction, which is likely to contain effective compounds that exhibit inhibitory activity against S. aureus. In contrast, n-hexane and residual aqueous fractions showed no antimicrobial activity. Overall, our findings confirm that evergreen woody plants native to South Korea have potential antimicrobial activity.