• 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.40 no.1
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• pp.35-39
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• 2015

Minimal inhibitory concentration (MIC) is the lowest concentration of antibiotics that inhibits the visible growth of bacteria. It has been reported that sub-MIC of antibiotics may result in morphological alterations, along with the biochemical and physiological changes in bacteria. The purpose of this study was to examine morphological changes of Aggregatibacter actinomycetemcomitans, after the treatment with sub-MIC metronidazole and penicillin. The bacterial morphology was observed with scanning electron microscope, after incubating with sub-MIC antibiotics. The length of A. actinomycetemcomitans was increased after the incubation with sub-MIC metronidazole and penicillin. Sub-MIC metronidazole and penicillin inhibited bacterial division and induced long filaments. Our study showed that metronidazole and penicillin can induce the morphological changes in A. actinomycetemcomitans.

• 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.

• International Journal of Oral Biology
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• v.39 no.2
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• pp.115-120
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• 2014

Minimal inhibitory concentration (MIC) is the lowest concentration of antibiotics that inhibits the visible growth of a microorganism. It has been reported that sub-MIC of antibiotics may result in morphological alterations along with biochemical and physiological changes in bacteria. The purpose of this study was to examine morphological changes of periodontal pathogens after treatment with sub-MIC antibiotics. Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, and Porphyromonas gingivalis were used in this study. The MIC for amoxicillin, doxycycline, metronidazole, penicillin, and tetracycline were determined by broth dilution method. The bacterial morphology was observed with bright field microscope after incubating with sub-MIC antibiotics. The length of A. actinomycetemcomitans and F. nucleatum were increased after incubation with metronidazole; penicillin and amoxicillin. P. gingivalis were increased after incubating with metronidazole and penicillin. However, F. nucleatum showed decreased length after incubation with doxycycline and tetracycline. In this study, we observed that sub-MIC antibiotics can affect the morphology of periodontal pathogens.

• Biomedical Science Letters
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• v.30 no.1
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• pp.32-35
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• 2024

In vitro antimicrobial activities of hot water extracts of Chamaecyparis obtuse, for methicillin-resistant Staphylococcus aureus (MRSA) was compared to commonly used conventional antimicrobial agents. All MRSA was susceptible to linezolid or vancomycin, but also to erythromycin. MIC range and MIC₉₀ to erythromycin, clindamycin, levofloxacin, tetracycline for MRSA were each 4 ㎍/mL, 2 ~ >128 ㎍/mL, ≤0.06 ~ >128 ㎍/mL, 0.25 ~ >128 ㎍/mL, 0.25~64 ㎍/mL and 4 ㎍/mL, .128 ㎍/mL, >128 ㎍/mL, >128 ㎍/mL, 64 ㎍/mL. The hot water extracts of leaf of C. obtuse had the lowest MIC range, MIC₅₀, and MIC₉₀ (0.125 µL/mL) for the MRSA tested, and it was possible more potent than various conventional antimicrobial agents. Screen antibacterial drug candidate with high antibacterial activity such as derivatives of C. obtuse leaf extract such as terpinen-4-ol or using combined therapy with commercialized antibacterial agents will likely be helpful in treating refractory MRSA infections.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1281-1292
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• 2014

Photovoltaic (PV) solar systems with series-connected module integrated converters (MICs) are receiving increased attention because of their ability to create high output voltage while performing local maximum power point tracking (MPPT) control for individual solar panels, which is a solution for partial shading effects in PV systems at panel level. To eliminate the partial shading effects in PV system more effectively, sub-MICs are utilized at the cell level or grouped cell level within a PV solar panel. This study presents the results of a series-output-connection MPPT (SOC-MPPT) controller for sub-MIC architecture using a single sensor at the output and a single digital MPPT controller (sub-MIC SOC-MPPT controller and architecture). The sub-MIC SOC-MPPT controller and architecture are investigated based on boost type sub-MICs. Experimental results under steady-state and transient conditions are presented to verify the performance of the controller and the effectiveness of the architecture.

• International Journal of Oral Biology
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• v.30 no.2
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• pp.59-63
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• 2005

Postantibiotic effects (PAE) refer to suppression of the bacterial growth following limited periods of exposure to an antibiotic and subsequent to the removal of the antibiotic agent. Fusobacterium nucleatum and Porphyromonas gingivalis are Gram-negative anaerobic bacteria associated with several periodontal diseases. In this study, postantibiotic effects (PAE), postantibiotic sub-MIC effect (PA SME) and sub-MIC effect (SME) of antibiotics on F. nucleatum ATCC 25586 and P. gingivalis W50 were investigated. The PAE was induced by 10X the MIC of antibiotic and antibiotic was eliminated by washing. The PA SMEs were studied by addition of 0.1, 0.2 and 0.3X MICs during the postantibiotic phase of the bacteria, and the SMEs were studied by exposition of the bacteria to antibiotic at the sub-MICs only. Amoxicillin, doxycycline and tetracycline induced PAE for F. nucleatum ATCC 25586 and P. gingivalis W50. But metronidazole and penicillin induced PAE for only F. nucleatum ATCC 25586. Metronidazole and doxycycline induced PA SME and SME for both species of anaerobic bacteria used in this study. The PA SME values for both strains were substantially longer than the SME values. The present study showed the existence of PAE, PA SME and SME for various antibiotics against F. nucleatum ATCC 25586 and P. gingivalis W50.

• Journal of Life Science
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• v.30 no.3
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• pp.278-284
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• 2020

Magnolia kobus is known to exert various biological effects, such as antioxidant and hypnotic activity. In this study, we investigated the antimicrobial and anti-inflammatory activity of M. kobus essential oil extracted using steam distillation. Its antimicrobial activity was tested against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa by the paper disk diffusion and minimum inhibitory concentration (MIC) methods. Its anti-inflammatory activity was evaluated by measuring its inhibition ratio on the production of nitric oxide (NO) and PGE₂ in lipopolysaccharide (LPS)-induced RAW264.7 cells. Its composition was analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that M. kobus essential oil exhibited excellent antibacterial activity against S. aureus, with a clear zone of 18 mm and an MIC value of 0.25 mg/ml. Its clear zones against P. aeruginosa and E. coli were 14 mm and 17 mm, respectively, while its MIC values were 1 mg/ml and 0.5 mg/ml, respectively. The essential oil exhibited no cytotoxicity to the RAW264.7 cells at a concentration of 500 ㎍/ml while showing NO (37.7%) and PGE₂ inhibition (24.0%). Its three main fragrance ingredients identified were 3-carene (77.07%), β-elemene (6.92%), and caryphyllene (2.86%). The results suggest that M. kobus essential oil has potential as a cosmetic functional material with antimicrobial and anti-inflammatory effects.

• Journal of Veterinary Science
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• v.22 no.6
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• pp.41.1-41.14
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• 2021

Background: Our previously prepared ceftiofur (CEF) hydrochloride oily suspension shows potential wide applications for controlling swine Streptococcus suis infections, while the irrational dose has not been formulated. Objectives: The rational dose regimens of CEF oily suspension against S. suis were systematically studied using a pharmacokinetic-pharmacodynamic model method. Methods: The healthy and infected pigs were intramuscularly administered CEF hydrochloride oily suspension at a single dose of 5 mg/kg, and then the plasma and pulmonary epithelial lining fluid (PELF) were collected at different times. The minimum inhibitory concentration (MIC), minimal bactericidal concentration, mutant prevention concentration (MPC), post-antibiotic effect (PAE), and time-killing curves were determined. Subsequently, the area under the curve by the MIC (AUC_0-24h/MIC) values of desfuroylceftiofur (DFC) in the PELF was obtained by integrating in vivo pharmacokinetic data of the infected pigs and ex vivo pharmacodynamic data using the sigmoid E_max (Hill) equation. The dose was calculated based on the AUC_0-24h/MIC values for bacteriostatic action, bactericidal action, and bacterial elimination. Results: The peak concentration, the area under the concentration-time curve, and the time to peak for PELF's DFC were 24.76 ± 0.92 ㎍/mL, 811.99 ± 54.70 ㎍·h/mL, and 8.00 h in healthy pigs, and 33.04 ± 0.99 ㎍/mL, 735.85 ± 26.20 ㎍·h/mL, and 8.00 h in infected pigs, respectively. The MIC of PELF's DFC against S. suis strain was 0.25 ㎍/mL. There was strong concentration-dependent activity as determined by MPC, PAE, and the time-killing curves. The AUC_0-24h/MIC values of PELF's DFC for bacteriostatic activity, bactericidal activity, and virtual eradication of bacteria were 6.54 h, 9.69 h, and 11.49 h, respectively. Thus, a dosage regimen of 1.94 mg/kg every 72 h could be sufficient to reach bactericidal activity. Conclusions: A rational dosage regimen was recommended, and it could assist in increasing the treatment effectiveness of CEF hydrochloride oily suspension against S. Suis infections.

• International Journal of Oral Biology
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• v.34 no.3
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• pp.165-168
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• 2009

Postantibiotic effect (PAE) is defined as the length of time that bacterial growth is suppressed following brief exposure to an antibiotic. In this study, the in vitro PAE, postantibiotic sub-MIC effect (PA SME) and sub-MIC effect (SME) of antibiotics on Treponema denticola ATCC 35405 were investigated. The PAE of doxycycline and metronidazole were 20.3 h and 25.0 h, respectively. The PA SMEs examined by addition of 0.1, 0.2 and 0.3X MICs during the postantibiotic phase of the bacteria for metronidazole were longer than those for doxycycline. In contrast, the SMEs for doxycycline were longer than those for metronidazole. The PA-SME and SME values increased as the concentration of antibiotics increased. The present study illustrates the existence of PAE, PA-SME and SME for several antibiotics against T. denticola, thereby extending the pharmacodynamic advantages of these antibiotics.