• Journal of Environmental Health Sciences
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• v.27 no.1
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• pp.100-105
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• 2001

Microstructural examinations were performed on the anaerobic biofilm from reactor filled with PE support media. Optical microscope, SEM and fluorescent microscope were used for qualitative and morphological studies on the attached microorganism under anaerobic condition. Microorganisms were attached in crevices where protection from shear forces of surfaces where easy to contact with support media surface. A hypothesis for biofilm accumulation occurs on a surface such as polymer support media is presented schematically : 1st step ; cell-support media attachment, 2nd step ; cell-support media attachment and cell-cell attachment, 3rd step ; attached biofilm from neighboring crevices joins together and growing, 4th step ; mature and irregualar biofilm was formed. In SEM photographs, shape and structures of biofilm were observed, but microorganism species and methanogens were not identified. A large number of methanogenic bacteria were identified on the surface of PE substratum by fluorescence under 480nm of radiation and it was estimated that methanogenic bacteria was related to initial attachment of bacteria under anaerobic condition.

• International Journal of Oral Biology
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• v.40 no.4
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• pp.189-196
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• 2015

Minimal inhibitory concentration (MIC) is the lowest antibiotic concentration that inhibits the visible growth of bacteria. Sub-minimal inhibitory concentration (Sub-MIC) is defined as the concentration of an antimicrobial agent that does not have an effect on bacterial growth but can alter bacterial biochemistry, thus reducing bacterial virulence. Many studies have confirmed that sub-MICs of antibiotics can inhibit bacterial virulence factors. However, most studies were focused on Gram-negative bacteria, while few studies on the effect of sub-MICs of antibiotics on Gram-positive bacteria. In this study, we examined the influence of sub-MICs of doxycycline, tetracycline, penicillin and amoxicillin on biofilm formation and coaggregation of Streptococcus gordonii, Streptococcus mutans, Actinomyces naeslundii, and Actinomyces odontolyticus. In this study, incubation with sub-MIC of antibiotics had no effect on the biofilm formation of S. gordonii and A. naeslundii. However, S. mutans showed increased biofilm formation after incubation with sub-MIC amoxicillin and penicillin. Also, the biofilm formation of A. odontolyticus was increased after incubating with sub-MIC penicillin. Coaggregation of A. naeslundii with S. gordonii and A. odontolyticus was diminished by sub-MIC amoxicillin. These observations indicated that sub-MICs of antibiotics could affect variable virulence properties such as biofilm formation and coaggregation in Gram-positive oral bacteria.

• Journal of Microbiology and Biotechnology
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• v.25 no.11
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• pp.1908-1919
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• 2015

This work investigated the potential of curcumin (CCM) and (-)-epigallocatechin gallate (EGCG) to inhibit N-acyl homoserine lactone (AHL)-mediated biofilm formation in gram-negative bacteria from membrane bioreactor (MBR) activated sludge. The minimum inhibitory concentrations (MICs) of CCM alone against all the tested bacteria were 200-350 μg/ml, whereas those for EGCG were 300-600 μg/ml. Biofilm formation at one-half MICs indicated that CCM and EGCG alone respectively inhibited 52-68% and 59-78% of biofilm formation among all the tested bacteria. However, their combination resulted in 95-99% of biofilm reduction. Quorum sensing inhibition (QSI) assay with known biosensor strains demonstrated that CCM inhibited the expression of C4 and C6 homoserine lactones (HSLs)-mediated phenotypes, whereas EGCG inhibited C4, C6, and C10 HSLs-based phenotypes. The Center for Disease Control biofilm reactor containing a multispecies culture of nine bacteria with one-half MIC of CCM (150 μg/ml) and EGCG (275 μg/ml) showed 17 and 14 μg/cm² of extracellular polymeric substances (EPS) on polyvinylidene fluoride membrane surface, whereas their combination (100 μg/ml of each) exhibited much lower EPS content (3 μg/cm²). Confocal laser scanning microscopy observations also illustrated that the combination of compounds tremendously reduced the biofilm thickness. The combined effect of CCM with EGCG clearly reveals for the first time the enhanced inhibition of AHL-mediated biofilm formation in bacteria from activated sludge. Thus, such combined natural QSI approach could be used for the inhibition of membrane biofouling in MBRs treating wastewaters.

• Journal of Microbiology and Biotechnology
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• v.22 no.3
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• pp.385-389
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• 2012

The application of microorganisms in the field of construction material is rapidly increasing worldwide; however, almost all studies that were investigated were bacterial sources with mineral-producing activity and not with organic substances. The difference in the efficiency of using bacteria as an organic agent is that it could improve the durability of cement material. This study aimed to assess the use of biofilm-forming microorganisms as binding agents to increase the compressive strength of cement-sand material. We isolated 13 alkaliphilic biofilmforming bacteria (ABB) from a cement tetrapod block in the West Sea, Korea. Using 16S RNA sequence analysis, the ABB were partially identified as Bacillus algicola KNUC501 and Exiguobacterium marinum KNUC513. KNUC513 was selected for further study following analysis of pH and biofilm formation. Cement-sand mortar cubes containing KNUC513 exhibited greater compressive strength than mineral-forming bacteria (Sporosarcina pasteurii and Arthrobacter crystallopoietes KNUC403). To determine the biofilm effect, Dnase I was used to suppress the biofilm formation of KNUC513. Field emission scanning electron microscopy image revealed the direct involvement of organic-inorganic substance in cement-sand mortar.

• KSBB Journal
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• v.13 no.6
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• pp.638-643
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• 1998

An investigation was made to develop new biofilm medium which could be applied to the Sequencing Batch Biofilm Reactor(SBBR) system for enhanced nutrient removal. 21 kinds of polyurethane media were tested fro adhesion ability for nitrifying bacteria. Nitrification rates were also tested by introducing synthetic wastewater containing ammonium-nitrogen to reactors with biofilm media. It was found that Z96-06 medium had higher selective adhension ability for nitrifying bacteria than the other biofilm media. The nitrification rate was 2.21 mg {{{{ { NH}`_{4 } ^{ +} }}}}-N /L$.$h$.$g MLSS when we operated the SBBR system containing Z96-06. Nitrification rate of the SBBR system increased approximately by 30% compared with that of the Sequencing Batch Reactor(SBR) system which did not contain biological carrier.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.2
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• pp.181-192
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• 2005

This study evaluated the effect of factors influencing the initial biofilm formation in drinking water distribution pipe by running experiments using a $2^{4-1}$ fractional factorial experimental design with a replicate. Important variables used for assessing biofilm formation included BDOC(biodegradable dissolved organic carbon), viable heterotrophic bacteria present in drinking water, water temperature, and shear stress at two levels each. Based on the statistical analysis of biofilm levels measured as attached HPC(heterotrophic plate count) and community-level assay, the main factors that have significant effects on biofilm formation were found to be viable heterotrophic bacteria and BDOC. Water temperature only exhibited significant effect on the levels of attached HPC, while shear stress was not a significant factor under given conditions. Moreover, the statistical analysis revealed that interactions between the important variables were not statistically significant at a 0.05 significance level.

• Journal of Environmental Science International
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• v.28 no.2
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• pp.225-233
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• 2019

In this study, we investigated the in vitro anti-biofilm activities of plant extracts of chives (Allium tuberosum), garlic (Allium sativum), and radish (Raphanus sativus L.) against environment harmful bacteria (gram-positive Staphylococcus aureus and, gram-negative Salmonella typhimurium and Escherichia coli O157:H7). In the paper disc assay, garlic extracts exhibited the highest anti-biofilm activity. The Minimal Inhibitory Concentration (MIC) of all plant extracts was generally higher for gram-negative bacteria than it was for gram-positive bacteria. Gram-negative bacteria were more resistant to plant extracts. The tetrazolium dye (XTT) assay revealed that, each plant extract exhibited a different anti-biofilm activity at the MIC value depending on the pathogen involved. Among the plant extracts tested, garlic extracts (fresh juice and powder) effectively reduced the metabolic activity of the cells of food-poisoning bacteria in biofilms. These anti-biofilm activities were consistent with the results obtained through light microscopic observation. Though the garlic extract reduced biofilm formation for all pathogens tested, to elucidate whether this reduction was due to antimicrobial effects or anti-biofilm effects, we counted the colony forming units of pathogens in the presence of the garlic extract and a control antimicrobial drug. The garlic extract inhibited the E. coli O157:H7 biofilm effectively compared to the control antimicrobial drug ciprofloxacin; however, it did not inhibit S. aureus biofilm significantly compared to ciprofloxacin. In conclusion, garlic extracts could be used as natural food preservatives to prevent the growth of foodborne pathogens and elongater the shelf life of processed foods.

• Journal of Environmental Science International
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• v.21 no.12
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• pp.1455-1462
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• 2012

The vertical distributions of nitrifying bacteria in aerobic fixed biofilm were investigated to evaluate the relationship between nitrification performance and microbial community at different HRT. Fluorescent in situ hybridization (FISH) and portable ion selective microelectrode system were adopted to analyze microbial communities and ions profiles according to the biofilm depth. Cilia media packed MLE (Modified Ludzack-Ettinger) like reactor composed of anoxic, aerobic I/II was operated with synthetic wastewater having COD 200 mg/L and $NH_4{^+}$-N mg/L at HRT of 6 hrs and 4 hrs. Total biofilm thickness of aerobic I, II reactor at 4 hrs condition was over two times than that of 6 hrs condition due to the sufficient substrate supply at 4 hrs condition (6 hrs; aerobic I 380 ${\mu}m$ and II 400 ${\mu}m$, 4 hrs; aerobic I 830 ${\mu}m$ and II 1040 ${\mu}m$). As deepen the biofilm detection point, the ratio of ammonia oxidizing bacteria (AOB) was decreased while the ratio of nitrite oxidizing bacteria (NOB) was maintained similar distribution at both HRT condition. The ratio of AOB was higher at 4 hrs than 6 hrs condition and $NH_4{^+}$-N removal efficiency was also higher at 4 hrs with 89.2% than 65.4% of 6 hrs. However, the ratio of NOB was decreased when HRT was reduced from 6 hrs to 4 hrs and $NO_2{^-}$-N accumulation was observed at 4 hrs condition. Therefore, it is considered that insufficient HRT condition could supply sufficient substrate and enrichment of AOB in all depth of fixed biofilm but cause decrease of NOB and nitrite accumulation.

• International Journal of Oral Biology
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• v.41 no.4
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• pp.209-215
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• 2016

Chlorhexidine has long been used in mouth washes for the control of dental caries, gingivitis and dental plaque. Minimal inhibitory concentration (MIC) is the lowest concentration of an antimicrobial substance to inhibit the growth of bacteria. Concentrations lower than the MIC are called sub minimal inhibitory concentrations (sub-MICs). Many studies have reported that sub-MICs of antimicrobial substances can affect the virulence of bacteria. The aim of this study was to investigate the effect of sub-MIC chlorhexidine on biofilm formation and coaggregation of oral early colonizers, such as Streptococcus gordonii, Actinomyces naeslundii and Actinomyces odontolyticus. The biofilm formation of S. gordonii, A. naeslundii and A. odontolyticus was not affected by sub-MIC chlorhexidine. However, the biofilm formation of S. mutans increased after incubation with sub-MIC chlorhexidine. In addition, cell surface hydrophobicity of S. mutans treated with sub-MIC of chlorhexidine, decreased when compared with the group not treated with chlorhexidine. However, significant differences were seen with other bacteria. Coaggregation of A. naeslundii with A. odontolyticus reduced by sub-MIC chlorhexidine, whereas the coaggreagation of A. naeslundii with S. gordonii remained unaffected. These results indicate that sub-MIC chlorhexidine could influence the binding properties, such as biofilm formation, hydrophobicity and coaggregation, in early colonizing streptococci and actinomycetes.

• International Journal of Oral Biology
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• v.35 no.4
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• pp.203-207
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• 2010

A number of bacterial species coexist in oral cavities as a biofilm rather than a planktonic arrangement. By forming an oral biofilm with quorum sensing properties, microorganisms can develop a higher pathogenic potential and stronger resistance to the host immune system and antibiotics. Hence, the inhibition of biofilm formation has become a major research issue for the future prevention and treatment of oral diseases. In this study, we investigated the effects of pentose on biofilm formation and phenotypic changes using wild type oral bacteria obtained from healthy human saliva. D-ribose and D-arabinose were found to inhibit biofilm formation, but have no effects on the growth of each oral bacterium tested. Pentoses may thus be good candidate biofilm inhibitors without growth-inhibition activity and be employed for the future prevention or treatment of oral diseases.