• Journal of Microbiology and Biotechnology
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• v.11 no.1
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• pp.160-163
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• 2001

In order to investigate the role of bacterial chemotaxis in root colonization, the chemotaxis potential of bacteria isolated from spinach roots was compared with that of bacteria from nonhizosphere soil, with reference to the plant age (1,000 isolates), soil moisture conditons (1,400 isolates), and part of the root (200 isolates). The % CT (% occurrence of chemotaxis (+) isolates among total bacterial isoltes) of the root isolates significantlyfluctuated during the plant growth period, reaching a maximum after 10-15 days of growth. At this time period, the maximum % CT for the root isolates was around 70-80% CT under a soil moisture 50% WFP (% volume of water-filled pores in total soil pores), and then gradually reduced with an increasing % WFP. The results of the chemotaxis potential of each of the 100 islates from the spinach roots and nonrhizosphere soil under various % WFP demonstrated that the % CT of the root isolates were significantly higher than those of solates from the nonrhizosphere soil under a wide range of soil moisture content (35-80% WFP). Furthermore, the % CT value (80%) from the upper root was significantly higher than tht (55%) from the lower root. Compared with the % CT values of the roots, the values from the nonrhizosphere soil did not significantly vary relative to the plant age of % WFP. These results indicate that chemotaxis would appear to be a major factor in bacterial root colonization.

• Journal of Veterinary Science
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• v.22 no.2
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• pp.24.1-24.16
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• 2021

Background: Bovine tuberculosis (TB) is caused by Mycobacterium bovis, a well-known cause of zoonotic tuberculosis in cattle and deer, and has been investigated in many physiological and molecular studies. However, detailed genome-level studies of M. bovis have not been performed in Korea. Objectives: To survey whole genome-wide single-nucleotide polymorphism (SNP) variants in Korean M. bovis field isolates and to define M. bovis groups in Korea by comparing SNP typing with spoligotyping and variable number tandem repeat typing. Methods: A total of 46 M. bovis field isolates, isolated from laryngopharyngeal lymph nodes and lungs of Korean cattle, wild boar, and Korean water deer, were used to identify SNPs by performing whole-genome sequencing. SNP sites were confirmed via polymerase chain reaction using 87 primer pairs. Results: We identified 34 SNP sites with different frequencies across M. bovis isolates, and performed SNP typing and epidemiological analysis, which divided the 46 field isolates into 16 subtypes. Conclusions: Through SNP analysis, detailed differences in samples with identical spoligotypes could be detected. SNP analysis is, therefore, a useful epidemiological tracing tool that could enable better management of bovine TB, thus preventing further outbreaks and reducing the impact of this disease.

• Journal of Microbiology and Biotechnology
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• v.23 no.5
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• pp.731-737
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• 2013

Seventy-four Shiga toxin-producing Escherichia coli (STEC) isolates belonging to the serotype O91:H21 were isolated from 1,643 asymptomatic human carriers in a STEC outbreak at Gwangju in Korea. Although the isolates did not cause any symptoms, all of them produced Shiga toxins 1 (Stx1) and 2 (Stx2). In order to determine why these strains cause no symptoms, we explored the differences in virulence potential between the asymptomatic STEC O91:H21 isolates and symptomatic STEC O91:H21 strains (ATCC 51435 and ATCC 51434). The asymptomatic STEC O91:H21 isolates showed strongly reduced cytopathic effects compared with the symptomatic strains when intact bacterial cells were used as an inoculant. Moreover, we found a reduced adherence phenotype when testing asymptomatic strains on HeLa cells. Real-time quantitative PCR results suggest that transcriptional repression of the genes encoding type-1 fimbriae occurs in the asymptomatic isolates but not in the symptomatic strains.

• Clinical and Experimental Pediatrics
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• v.56 no.8
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• pp.332-337
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• 2013

Purpose: To identify the frequency of bacterial isolates in early-onset neonatal sepsis (EONS) and their antimicrobial resistance pattern. Methods: A retrospective study of EONS was conducted at the Beni Suef University Hospital from September 2008 to September 2012. A case of EONS was defined as an infant who had clinical signs of infection or who was born to a mother with risk factors for infection, and in whom blood culture obtained within 72 hours of life grew a bacterial pathogen. Results: Of 673 neonates screened, there were 138 positive blood cultures (20.5%) (confirmed EONS). Of the recovered isolates, 86.2% were gram-negative pathogens. Klebsiella pneumoniae (42.8%), Enterobacter cloacae (22.5%), and Escherichia coli (13.8%) were the commonest isolated organisms. The most common gram-positive microorganism was Staphylococcus aureus accounting for only 12 isolates (8.7%). All Klebsiella isolates and 93% of Enterobacter isolates were resistant to ampicillin. Gram-negative pathogens had the maximum overall sensitivity to imipenem, cefepime, and ciprofloxacin; whereas, gram-positive isolates were most susceptible to vancomycin, imipenem, and piperacillin. Conclusion: K. pneumoniae was the predominant causative bacteria of EONS followed by E. cloacae and E. coli. There was a high resistance to ampicillin. Imipenem had the maximum overall activity against the causative bacteria. Continuous surveillance is needed to monitor the changing epidemiology of pathogens and antibiotic sensitivity.

• Journal of Microbiology
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• v.39 no.2
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• pp.133-138
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• 2001

We investigated the antagonism of indigenous bacteria isolated from stressed mussels and their extracellular metabolites on the adult zebra mussel, Dreissena polymorpha. Selective bacterial isolates including Aeromonas media, A. salmonicida, A. veronii, and Shewanella putrefaciens, showed strong lethality against adult mussels and 100% mortality was observed within 5 days of incubation. Bacterial metabolites, fractionated and concentrated from stationary-phase culture supernatants of these bacterial isolates, displayed varying degrees of antagonistic effects on zebra mussels. Among the three size fractions examined, <5, 5-10, and >10 kDa, the mast lethal fraction seems to be >10 kDa for three of the four isolates tested. Further chemical analyses of these size fractions revealed that the predominant constituents were polysaccharides and proteins. No 2-keto-3-deoxyoctanoic acid (2-KDO), deoxyribonucleic acids (DNA) or uranic acid were detectable. Extraction of supernatants of two antagonistic isolates with polar solvent suggested that polar molecules are present in the active fraction. Our data suggest that extracellular metabolites produced by antagonistic bacteria are also involved in disease development in zebra mussels and elucidation of the mechanisms involved may offer a novel strategy for control of biofouling invertebrates.

• Mycobiology
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• v.34 no.2
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• pp.67-72
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• 2006

Efficacy of resistance induction by the bacterial isolates Pseudomonas putida (TRL2-3), Micrococcus luteus (TRK2-2) and Flexibacteraceae bacterium (MRL412), which were isolated from the rhizosphere of plants growing in Jeju Mountain, were tested in a greenhouse. The disease severity caused by Phytophthora infestans was effectively reduced in the potato plants pre-inoculated with bacterial isolates compared with those of the untreated control plants growing in a greenhouse. In order to estimate the level of protection by the bacterial isolates, Mancozeb WP (Diesen $M^{(R)}$, Kyong nong) and DL-3-amino butyric acid (BABA) were pre-treated, whereas Dimethomorph WP ($Forum^{(R)}$, Kyong nong) and phosphonic acid ($H_{3}PO_{3}$) were post-treated the challenge inoculation with the pathogen. Disease severities of chemical pre-treated as well as post-treated plants were reduced compare to those of the untreated. The disease reduction in the plants pre-treated with Mancozeb WP was the highest, whereas that of post-treated with Dimethomorph WP was the lowest. The yields of plants pre-inoculated with three bacterial isolates were greatly increased than those of control plants. These results suggest that biological control by bacterial isolates might be an alternative strategy against late blight disease in potato plants growing in greenhouse.

• Research in Plant Disease
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• v.25 no.4
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• pp.179-187
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• 2019

This study was carried out to test the antimicrobial activities of nano metal hybrid materials produced by plasma technologies (radio frequency-thermal plasma system and direct current sputtering system) against microbes isolated from cucurbit (watermelon, pumpkin, and gourd) seeds. Eight different nano metal hybrid materials and four carriers were tested against five different fungal and ten different bacterial isolates in vitro. Among the tested nano metal hybrid material, Brass/CaCO₃ (1,000 ppm) exhibited 100% antimicrobial effect against all the five tested fungi. However, nano metal hybrid material Brass/CaCO₃ (1,000 ppm) inhibited only four bacterial isolates, Weissella sp., Rhodotorula mucilaginosa, Burkholderia sp., and Enterococcus sp. at 100% level, and did not inhibited other six bacterial isolates. Nano metal hybrid material graphite-nickel (G-Ni) showed 100% inhibition rate against Rhizopus stolonifer and 52.94-71.76% inhibition rate against four different fungal isolates. Nano metal hybrid material G-Ni did not show any inhibition effects against tested ten bacterial isolates. In summary, among the tested eight different nano metal hybrid materials and four carriers, Brass/CaCO₃ showed inhibition effects against five fungal isolates and four bacterial isolates, and G-Ni showed variable inhibition effects (52.94-100%) against five fungal isolates and did not show any inhibition effects against all the bacterial isolates.

• The Plant Pathology Journal
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• v.36 no.1
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• pp.29-42
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• 2020

Acidovorax citrulli causes bacterial fruit blotch in Cucurbitaceae, including watermelon. Although A. citrulli is a seed-borne pathogen, it can cause diverse symptoms in other plant organs like leaves, stems and fruits. To determine the infection routes of A. citrulli, we examined the virulence of six isolates (Ac0, Ac1, Ac2, Ac4, Ac8, and Ac11) on watermelon using several inoculation methods. Among six isolates, DNA polymorphism reveals that three isolates Ac0, Ac1, and Ac4 belong to Clonal Complex (CC) group II and the others do CC group I. Ac0, Ac4, and Ac8 isolates efficiently infected seeds during germination in soil, and Ac0 and Ac4 also infected the roots of watermelon seedlings wounded prior to inoculation. Infection through leaves was successful only by three isolates belonging to CC group II, and two of these also infected the mature watermelon fruits. Ac2 did not cause the disease in all assays. Interestingly, three putative type III effectors (Aave_2166, Aave_2708, and Aave_3062) with intact forms were only found in CC group II. Overall, our results indicate that A. citrulli can infect watermelons through diverse routes, and the CC grouping of A. citrulli was only correlated with virulence in leaf infection assays.

• Ocean Science Journal
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• v.42 no.4
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• pp.247-254
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• 2007

Marine bacteria, actionmycetes and fungal strains were isolated from continental slope sediment of the Bay of Bengal and studied for fatty acid profile to investigate their involvement in the benthic food-web. Fifteen different saturated and unsaturated fatty acids from bacterial isolates, 14 from actinomycetes and fungal isolates were detected. The total unsaturated fatty acids in bacterial isolates ranged from 11.85 to 37.26%, while the saturated fatty acid ranged between 42.34 and 80.74%. In actinomycetes isolates, total unsaturated fatty acids varied from 27.86 to 38.85% and saturated fatty acids ranged from 35.29 to 51.25%. In fungal isolates unsaturated fatty acids ranged between 44.62 and 65.52% while saturated FA ranged from 20.80 to 46.30%. The higher percentages of unsaturated fatty acids from the microbial isolates are helpful in anticipating the active participation in the benthic food-web of Bay of Bengal.

• Journal of Microbiology
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• v.37 no.4
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• pp.193-199
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• 1999

Fifty-eight strains showing different colony morphological characteristics on various media were isolated from marine coral (Plexauridae sp.) and ambient seawater near Mun-Sum, Cheju-Island in 1998. Bacterial diversity was studies by phylogenetic analysis of the partial 16S rRNA gene sequences. All isolates representing the bacterial domain included affiliates of the high G+C (59%) and los G+C (3%) subdivision of Gram positive bacteria, and the alpha (33%) and gamma (5%) subdivision of the Proteobacteria. The 16S rDNA sequence similarity of the isolates was in the 88.3 to 100% range (average, 95.6%) to reported sequence data. In the comparison of the isolates from marine coarl and ambient seawater, more diverse groups belonging to ${\alpha}$-Proteobacteria were preferentially obtained from seawater.