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11.
王云 《中国环境管理干部学院学报》2012,22(2):68-72
研究了短时游离氯后转氯胺的联合消毒方法对大肠杆菌的灭活作用,并对其协同作用以及pH值和温度对协同作用的影响进行了探讨。结果表明:pH值在6.5~8范围内,温度不超过30℃时,短时游离氯后转氯胺的消毒方法对大肠杆菌的灭活具有协同作用,且随pH值的降低而加强,在低温下该方法的协同效果更加明显。 相似文献
12.
将大肠杆菌E.coli ATCC8739置于12.0 T超强静磁场(ultra-strong static magnetic field,SMF)中进行处理,获得了磁场处理0.5、1、2、4和8 h的菌株E.coli-SMFn(n=0.5、1、2、4、8)。在37℃、pH 7、静置的条件下,菌株对偶氮染料AR14(I.C.Acid Red 14)的脱色结果指出,当反应进行到4、6和8 h时,E.coli-SMF8的脱色效率分别为18%、55%和96%,远高于E.coli ATCC8739的3%、19%和50%,表明SMF作用显著地增强了菌株的脱色效率。基因组DNA提取、PCR扩增、分子克隆以及基因测序的实验结果进一步表明,全部6例E.coli ATCC8739菌株的偶氮还原酶基因(acpD)序列均与GenBank中报道的完全一致;而E.coli-SMF8菌株的acpD-SMF8核酸序列中缺失了第99位的胞嘧啶。该缺失突变不仅使acpD-SMF8的核酸序列与acpD的存在显著不同,同时得到了具新活性中心的偶氮还原酶AzoR-SMF8。这个新的活性中心具有更强的黄素(FMN)结合能力,因此使该酶与偶氮染料的亲和力大大增加,促进了脱色效率的提高。 相似文献
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14.
Hector Gutierrez-Bañuelos William E. Pinchak Byeng R. Min Gordon E. Carstens Robin C. Anderson Luis O. Tedeschi 《Journal of environmental science and health. Part. B》2013,48(4):360-365
Pathogenic bacteria attached to the hide or shed in the feces of cattle at slaughter can contaminate carcasses intended to be processed for human consumption. Therefore, new pre-harvest interventions are needed to prevent the carriage and excretion of foodborne pathogens in cattle presented to the processing plant. The objectives of this study were to examine the antimicrobial effects of hydrolysable tannin-rich chestnut and condensed tannin-rich mimosa extracts on bacterial indicators of foodborne pathogens when applied as a hide-intervention and as a feed additive to feedlot cattle. Water (control) or solutions (3 % wt/vol) of chestnut- and mimosa-extract treatments were sprayed (25 mL) at the left costal side of each animal to a 1000 cm2 area, divided in four equal quadrants. Hide-swabs samples obtained at pre-, 2-min, 8-h, and 24-h post-spray application were cultured to enumerate Escherichia coli/total coliforms and total aerobic plate counts. In a second experiment, diets supplemented without (controls) or with (1.5 % of diet dry matter) chestnut- or mimosa-extracts were fed during a 42–day experimental feeding period. Weekly fecal samples starting on day 0, and rumen fluid obtained on days 0, 7, 21 or 42 were cultured to enumerate E.coli/total coliforms and Campylobacter. Tannin spray application showed no effect of treatment or post-application-time (P> 0.05) on measured bacterial populations, averaging 1.7/1.8, 1.5/1.6 and 1.5/1.7 (log10 CFU/cm2) for E. coli/total coliforms, and 4.0, 3.4 and 4.2 (log10CFU/cm2) in total aerobes for control, chestnut and mimosa treatments, respectively. Mean (± SEM) ruminal E. coli and total coliform concentrations (log10 CFU/mL) were reduced (P< 0.01) in steers fed chestnut-tannins (3.6 and 3.8 ± 0.1) in comparison with the controls (4.1 and 4.2 ± 0.1). Fecal E. coli concentrations were affected by treatment (P< 0.01), showing the highest values (log10 CFU/g) in fecal contents from mimosa-fed steers compared to controls (5.9 versus 5.6 ± 0.1 SEM, respectively). Total coliforms (log CFU/g) showed the highest values (P< 0.01) in feces from chestnut- and mimosa-fed steers (6.0 and 6.1 ± 0.1 respectively) in comparison with controls (5.7 ± 0.1). Fecal Campylobacter concentrations (log10CFU/g) were affected by treatment (P< 0.05), day (P< 0.001) and their interaction (P< 0.01) with the controls having lower concentrations than chestnut- and mimosa-fed steers (0.4, 1.0, and 0.8 ± 0.3, respectively). It was concluded that under our research conditions, tannins were not effective in decreasing measured bacterial populations on beef cattle hides. Additionally, chestnut tannin reduced E. coli and total coliforms within the rumen but the antimicrobial effect was not maintained in the lower gastrointestinal tract. Further research is necessary to elucidate the possible antimicrobial effects of tannins at site-specific locations of the gastrointestinal tract in beef cattle fed high-grain and high-forage diets. 相似文献
15.
Most probable number (MPN) and colony-forming unit (CFU) estimates of fecal indicator bacteria (FIB) concentration are common
measures of water quality in aquatic environments. Thus, FIB intensively monitored in Yeongsan Watershed in an attempt to compare
two di erent methods and to develop a statistical model to convert from CFU to MPN estimates or vice versa. As a result, the significant
di erence was found in the MPN and CFU estimates. The enumerated Escherichia coli concentrations in MPN are greater than those in
CFU, except for the measurement in winter. Especially in fall, E. coli concentrations in MPN are one order of magnitude greater than
that in CFU. Contrarily, enterococci bacteria in MPN are lower than those in CFU. However, in general, a strongly positive relationship
are found between MPN and CFU estimates. Therefore, the statistical models were developed, and showed the reasonable converting
FIB concentrations from CFU estimates to MPN estimates. We expect this study will provide preliminary information towards future
research on whether di erent analysis methods may result in di erent water quality standard violation frequencies for the same water
sample. 相似文献
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17.
采用批实验研究了蒙脱石对左氧氟沙星的吸附机理及对左氧氟沙星抗菌作用的影响。结果表明,中性条件下存在培养基时,左氧氟沙星在蒙脱石上前2 h即达到吸附平衡,吸附等温线符合Langmuir吸附方程,吸附率达90%以上;蒙脱石吸附左氧氟沙星存在阳离子交换作用、氢键作用、疏水作用、阳离子键桥作用、静电吸附作用等物理化学过程;蒙脱石本身不具有抑菌、杀菌活性,且由于蒙脱石增大了微生物附着的比表面积,在特定情况下可以促进微生物的生长;扣除其对微生物生长的促进作用后,蒙脱石吸附左氧氟沙星降低了后者的毒性效应,其抑菌率降低约25%。上述结果为进一步研究抗生素在环境中的毒理效应提供了基础依据。 相似文献
18.
Bacterial systems have not had success predicting metal carcinogenicity. Hypotheses explaining this failure are examined. Using a broad genetic endpoint, λ prophage induction, under sub‐toxic growing conditions, genotoxicity is seen for compounds of chromium, manganese, lead, molybdenum and tungsten. Copper, manganese, arsenic and molybdenum compounds enhanced UV mutagenesis in E. coli WP2. The toxicity of metal compounds to cultured mammalian cells correlates well with rat oral LD50 values. Whereas insolubility can present problems in bacterial studies, concentrations of metal compounds toxic to mammalian cells can be determined even in the presence of precipitate, and sometimes [Pb(NO3)2, BaCl2 and BeCl2] occurs only in its presence. PbS and MnS, which are insoluble, are much more toxic than the more soluble compounds Pb(NO3)2 and MnCl2. These results demonstrate the importance of cellular phagocytosis of insoluble metal compounds as a factor in studying the toxicity and genotoxicity of metal compounds. 相似文献
19.
通过测定在各种条件下Ag(Ⅰ)对大肠杆菌Escherichia coli的生长的抑制作用,系统分析了各参数对Ag(Ⅰ)毒性的影响。结果表明:好氧、厌氧状态下,Ag(Ⅰ)对E.coli的抑制能力基本相同;在LB培养基、氨基酸基本培养基和标准基本培养基中Ag(Ⅰ)开始抑制E.coli生长的浓度差异较大,分别为10、0.5、0.1μmol/L;LB组分中的酵母粉的加入完全消除了Ag(I)对E.coli的抑制作用;此外,菌体浓度越高抑制其生长所需的Ag(Ⅰ)浓度也越高。因此Ag(I)对E.coli生长的抑制作用与氧化应激无关,而与培养基种类、培养基组分及菌体浓度高度相关。 相似文献
20.
抗生素滥用所导致的环境问题日益受到人们的关注,抗生素在环境中常以低剂量的形式暴露,生物体在低浓度的抗生素作用下通常会表现出毒物兴奋效应(hormesis)。因此,研究抗生素的hormesis,对抗生素的生态风险评价极其重要。为了研究抗生素的hormesis,本文选取4种磺胺类抗生素为研究对象,观测了不同浓度培养基下磺胺对大肠杆菌能否产生hormesis。结果表明,磺胺对大肠杆菌在原倍和0.8倍浓度的培养基下不产生hormesis,在0.6和0.4倍浓度的培养基下产生hormesis;并且,结合我们之前对另一种革兰氏阴性菌——费氏弧菌hormesis的研究可知,对于具有不同群体感应系统的2种革兰氏阴性菌,都存在hormesis,磺胺可以通过作用群体感应系统使革兰氏阴性菌产生hormesis,只是hormesis的大小不同。上述研究结果为抗生素的生态风险评价提供了依据,为hormesis的相关研究提供了参考。 相似文献