Antimicrobial effect of alexidine and chlorhexidine against Enterococcus faecalis infection

A previous study demonstrated that alexidine has greater affinity for the major virulence factors of bacteria than chlorhexidine.The aim of this study was to compare the antimicrobial activity of 1%alexidine with that of 2%chlorhexidine using Enterococcus faecalis-infected dentin blocks.Sixty bovine dentin blocks were prepared and randomly divided into six groups of 10 each.E.faecalis was inoculated on 60 dentin blocks using the Luppens apparatus for 24 h and then the dentin blocks were soaked in 2%chlorhexidine or 1%alexidine solutions for 5 and 10 min,respectively.Sterile saline was used as a control.The antimicrobial efficacy was assessed by counting the number of bacteria adhering to the dentin surface and observing the degradation of bacterial shape or membrane rupture under a scanning electron microscope.Significantly fewer bacteria were observed in the 2%chlorhexidine-or 1%alexidine-soaked groups than in the control group(P<0.05).However,there was no significant difference in the number of bacteria adhering to the dentinal surface between the two experimental groups or between the two soaking time groups(P>0.05).Ruptured or antiseptic-attached bacteria were more frequently observed in the 10-min-soaked chlorhexidine and alexidine groups than in the 5-min-soaked chlorhexidine and alexidine groups.In conclusion,10-min soaking with 1%alexidine or 2%chlorhexidine can be effective against E.faecalis infection.

Estimating the production and mortality of fine roots using minirhizotrons in a Pinus densiflora forest in Gwangneung,Korea

The aim of this study was to estimate fine root production （FP） and fine root mortality （FM） at 0-10, 10-20, and 20-30 cm soil depths using minirhizotrons in a 75-year-old Pinus densiflora Sieb. et Zucc. forest located in Gwangneung, Korea. We developed the conversion factors （frame cm-2） of three soil depths （0.158 for 0-10 cm, 0.120 for 10-20 cm, and 0.131 for 20-30 cm） based on soil coring and minirhizotron data. FP and FM were estimated using conversion factors from March 26, 2013 to March 2, 2014. The annual FP and FM values at the 0-30 cm soil depth were 3200.2 and 2271.5 kg ha-1 yr -1, respectively. The FP estimate accounted for approximately 17 % of the total net primary production at the study site. FP was highest in summer （July 31-September 26）, and FM was highest in autumn （September 27-November 29）. FP was positively correlated with seasonal change in soil temperature, while FM was not related to that change. The sea- sonality of FP and FM might be linked to above-ground photosynthetic activity. Both FP and FM at the 0-10 cm depth were significantly higher than at 10-20 and 20-30 cm depths, and this resulted from the decrease in nutrient availability with increasing soil depth. The minirhizotron approach and conversion factors developed in this study will enable fast and accurate estimation of the fine root dynamics in P. densiflora forest ecosystems.

Soil depth- and root diameter- related variations affect root decomposition in temperate pine and oak forests

Aims Assessment of factors regulating root decomposition is needed to understand carbon and nutrient cycling in forest ecosystems.the ob-jective of this study is to examine the effects of soil depth and root diameter on root decomposition and to analyze the relationship of root decomposition with factors such as soil environmental conditions and initial litter quality.Methods two decomposition experiments were conducted in natural pine(Pinus densiflora)and oak(Quercus serrata)forests over a 2-year period using the litterbag technique.For the soil depth experiment,216 litterbags containing fine roots(∅=0-2 mm)were buried at 0-10-,10-20-and 20-30-cm soil depths.Soil properties and soil enzyme activities and microbial biomass at each soil depth were analyzed.For the root diameter experiment,216 litterbags containing roots 0-1-,1-2-and 2-3-mm in diameter were buried at 10-cm soil depth.the initial litter qualities(carbon(c),nitrogen(N),calcium(ca)and phosphorus(P)concentrations)for each of the root diameter classes were analyzed.Litterbags were retrieved after 3,6,12 and 24 months in each forest type.Important Findingsthe root decomposition rate was significantly altered by soil depth and root diameter.After 2 years,the root decay constant at 0-10-cm depth(pine:0.35 and oak:0.41)was significantly higher than that at 10-20-cm(0.31 and 0.37)and 20-30-cm(0.32 and 0.33)depths in the P.densiflora and Q.serrata forests.Enzyme activities and microbial biomass declined with soil depth,which may be associated with decreasing soil moisture and organic matter.the decay constant for the 0-1-mm roots(pine:0.32 and oak:0.37)was higher than that of 1-2-mm(0.29 and 0.33)and 2-3-mm roots(0.26 and 0.33)for the P.densiflora and Q.serrata forests.Difference in initial P concentration and c/N ratio among the different diameter roots were linearly related with root decomposition.In particular,the increasing c/N ratio with root diameter resulted in decreases in the decomposition rate.these results indicate the surface soil microbial activities and initial c/N ratio of root litter as important drivers of c dynamics in temperate pine and oak forests.