• YAKHAK HOEJI
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• v.26 no.3
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• pp.169-174
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• 1982

Several strains of bacteria having resistance to macrolide antibiotics were isolated. EMR-1, one of them, exhibited the induced resistance to macrolide antibiotics and this microorganism was identified as a bacterium belong to Bacillus species. The subinhibitory concentration of erythromycin or oleandomycin induced strong resistance to both erythromycin and oleandomycin themselves and to other macrolide antibiotics such as leucomycin, spiramycin and josamycin. The effective concentration of inducer, erythromycin was $0.0016-0.2\mu$g/ml. The inactivating enzyme of these antibiotics was not produced by EMR-1.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.4
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• pp.605-616
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• 2004

Subinhibitory concentrations (sub-MICs) refer to concentrations below minimum inhibitory concentrations (MICs). The antimicrobial agents may be present at relatively high concentration, at least higher than bacterial MIC and thereafter be deserted off a surface and function at sub-MICs, perhaps by interfering with bacterial metabolism. Consequently, the aim of this study was to determine the effects of growth, in the presence of sub-MICs of antimicrobial agents, on the cell surface properties and virulence factors of mutans streptococci and to investigate the efficacy of a chemical approach in vitro. Streptococcus mutans Ingbritt and Streptococcus sobrinus 6715-7 were used. Eight antimicrobial agents (Sanguinaria extract;SG, Chlorhexidine digluconate;CHX, Fluoride;F, Propolis;PP, Hydrogen peroxide;HP, Triclosan;TC, Sodium dodecyl sulfate;SDS Cetylpyridinium chloride; CC) were diluted serially in broth to determine MICs and to compare the growth rate, acid production, hydrophobicity, adhesion activity to saliva coated hydroxyapatite, glucan synthesis and cellular aggregation of experiment groups (in the presence of sub-MICs) with those of control (in the absence of antimicrobial agents). Sub-MICs of antimicrobial agents affected the growth of cells, hydrophobicity, and adhesion of bacteria to saliva coated hydroxyapatite and glucan synthesis. They also resulted in a significant reduction in pH after 12 hours (p<0.05). By cells pretreated with proteinase K, either the aggregation induced by antimicrobial agents was completely inhibited or the aggregation titers were markedly increased. According to the results of the present study, each antimicrobial agent at sub-MICs could affect similar as its known action mechanism and could continually inhibit cariogenic bacteria at such concentrations. Thus, the use of these antimicrobial agents would be one of the effective methods to prevent dental caries.

• YAKHAK HOEJI
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• v.52 no.3
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• pp.219-224
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• 2008

Clinically isolated methicillin-resistant Staphylococcus aureus strains were exposed to subinhibitory concentration of DW286, DW-224a, gemifloxacin, trovafloxacin, sparfloxacin and ciprofloxacin during 26- to 39-days period. Subculturing led to resistance development, and most of the selected mutants were above susceptible breakpoints. Selected mutants had broad cross resistance to other quinolone antibiotics and only one mutant was completely susceptible to all fluoroquinolones. Twenty five among 42 mutants revealed mutations on DNA gyrase and topoisomerase IV by sequencing. Also 16 mutants had fluoroquinolones MICs that were 4-32 times lower in the presence of reserpine. In conclusion, alterations in DNA gyrase or topoisomerase IV and action of efflux pumping out system are the resistance mechanisms of DW-224a.

• Journal of Ginseng Research
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• v.45 no.1
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• pp.75-85
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• 2021

Background: Invasive infections due to foodborne pathogens, including Salmonella enterica serovar Typhimurium, are prevalent and life-threatening. This study aimed to evaluate the effects of ginsenoside Rg3 (Rg3) on the adhesion, invasion, and intracellular survival of S. Typhimurium. Methods: The impacts of Rg3 on bacterial growth and host cell viability were determined using the time kill and the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assays, respectively. Gentamicin assay and confocal microscopic examination were undertaken to determine the effects of Rg3 on the adhesive and invasive abilities of S. Typhimurium to Caco-2 and RAW 264.7 cells. Quantitative reverse transcription polymerase chain reaction was performed to assess the expression of genes correlated with the adhesion, invasion, and virulence of S. Typhimurium. Results: Subinhibitory concentrations of Rg3 significantly reduced (p < 0.05) the adhesion, invasion, and intracellular survival of S. Typhimurium. Rg3 considerably reduced (p < 0.05) the bacterial motility as well as the release of nitrite from infected macrophages in a concentration-dependent manner. The expression of genes related to the adhesion, invasion, quorum sensing, and virulence of S. Typhimurium including cheY, hilA, OmpD, PrgK, rsgE, SdiA, and SipB was significantly reduced after Rg3 treatment. Besides, the compound downregulated rac-1 and Cdc-42 that are essential for actin remodeling and membrane ruffling, thereby facilitating Salmonella entry into host cells. This report is the first to describe the effects of Rg3 on "trigger" entry mechanism and intracellular survival S. Typhimurium. Conclusion: Rg3 could be considered as a supplement agent to prevent S. Typhimurium infection.