细菌质粒的消除*

利用化学消除剂或改变生长条件可以消除细菌中的质粒。除宿主菌的特性及其所含质粒分子量大小之外 ,消除率还与消除剂浓度、作用时间有关。嵌合染料适用于消除大肠杆菌中的质粒。十二烷基硫酸钠对具有性纤毛的细菌作用效果较好。适当提高培养温度可消除一些细菌中的质粒 ,胸腺嘧啶限量法仅适用于其营养缺陷型菌株的质粒消除。利用原生质体的形成与再生及反复冻融菌体均可消除细菌中的质粒。     

黄芩与止痢灵对大肠杆菌R质粒消除作用的研究

本研究从中药黄芩与止痢灵为质粒消除剂,用携带Ｒ质粒的多重耐药性大肠杆菌Ｅ．Ｏ１０株为靶细菌,进行了体外Ｒ质粒消除作用的实验研究。同时,观察了黄芩与止痢灵联合应用对Ｒ质粒消除的影响。实验结果表明：黄芩和止痢灵对大肠杆菌携带的Ｒ质粒具有消除作用。其消除率为２．４２％和２．１４％。从Ｒ质粒的消除表型来看：单用黄芩或止痢灵,绝大多数消除了表现为单一耐药性的丢失。黄芩和止痢灵联合应用,其消除率可提高至１８．１４％。而且细菌不仅表现为单一耐药性的丢失,还表现对ＳＭ＋ＴＣ,ＡＰ＋ＴＣ多重耐药性的丢失。     

黄芩甙对铜绿假单胞菌R质粒的消除作用

测定黄芩甙对铜绿假单胞菌R质粒的消除作用 ;以携带R质粒的铜绿假单胞菌株PA16为靶细菌 ,以黄芩甙作为R质粒消除剂 ,进行R质粒体内外消除试验 ;体外消除实验结果表明 ,黄芩甙对PA16的消除率为 5 .1% ,明显高于空白对照组 ,也高于EB对照组的结果 ;体内R质粒消除率为 12 .0 % ,明显高于对照组 ;黄芩甙在体内外对铜绿假单胞菌R质粒具有较强的消除作用 ,为其实际应用提供实验依据。     

中药三黄汤对家兔金黄色葡萄球菌R质粒消除的实验研究

中药三黄汤(黄苓、黄柏、黄连)作为R质粒消除剂,以家兔金黄色葡萄球菌作为靶细菌,进行R质粒的体外、体内消除实验。     

黄芩甙对痢疾杆菌R质粒体外消除作用的实验研究

以携带R质粒的痢疾杆菌F_(13)株为靶细菌,以黄芩甙作为R质粒消除剂,进行R质粒体外消除试验。实验组R质粒的消除率为0.3%,对照组中SDS的消除率为0.6%,吖啶橙的消除率0.42%。琼脂糖凝胶电泳结果显示,消除子都丢失了相应的质粒带。     

中药对R质粒消除作用的研究

由于 R质粒的传播和耐药菌株的增加 ,临床抗菌药物的敏感性下降 ,为临床治疗带来极大的困难。人们试图寻找出一种有效的方法把 R质粒从宿主菌中消除掉 ,使其重新恢复对药物的敏感性。许多理化因素均可消除质粒 ,如高温培养、紫外线照射 ,常用的化学消除剂有 SDS、溴化乙啶与口丫啶橙等。但由于这些因素对人体均有较强的毒副作用 ,不能投入临床应用。目前耐药 R质粒的消除仍是一个国际性难题 ,到现在为止还没有一个较好的可供体内使用的消除 R质粒的方法。而中草药具有天然、低毒甚至无毒的特点 ,人们希望从我国传统中药中选择出非常适合…     

细菌内源质粒消除研究进展北大核心CSCD

为了探究细菌内源质粒的功能,包括细菌耐药性、细菌共生、细菌荚膜形成、细菌的重金属抗性等方面,需要对细菌的内源质粒进行消除。本文综述了基于物理学、化学及分子生物学的细菌内源质粒消除方法,阐明了质粒消除的原理。结合笔者自身的研究对质粒消除技术进行了展望。     

银离子抗性细菌质粒的分离与鉴定

通过对不同化工厂废水处理池的活性污泥进行富集、不同浓度银离子驯化后,分离得到30株银离子抗性细菌,最大硝酸银耐受量可达80 mg·ml^-1.对这些细菌进行质粒抽提与鉴定,质粒检出率为76.67％.40 mmol·L^-1的苯甲酸钠对HAg4细菌质粒的消除率可达98.75％;而350 μg· ml^-1的吖啶橙对HAg4细菌质粒的消除率只有77.78％.细菌质粒与银离子抗性密切相关.     

艾迪注射液细菌内毒素检查方法探讨

目的:建立艾迪注射液细菌内毒素检查方法。方法:根据《中华人民共和国药典》2005年版Ⅱ部收载的细菌内毒素检查法进行。结果:将艾迪注射液稀释至1/6后可消除干扰因素,用标示灵敏度为0.25 EU/mL的鲎试剂检测细菌内毒素是有效的。结论:细菌内毒素检查法准确、可靠,适用于检测艾迪注射液中的内毒素。     

抗干扰微生物检测技术研究

在检测细菌、真菌和大肠菌群时,抗防腐剂型微生物培养基可消除样品中浓度为 ２．０ｇ／Ｌ（Ｋｇ）的山梨酸、山梨酸钾、苯甲酸及苯甲酸钠的干扰;抗消毒剂型微生物培养基可分别消除１５０ｍｇ／ Ｌ二氧化氯、４００ｍｐ／ Ｌ过氧乙酸、７００ｍｇ／ Ｌ次氯酸钠及１８０ｍｐ／ Ｌ过氧化氢的干扰;抗臭氧型微生物培养基可以消除１０．０ｍｇ／Ｌ的臭氧和余氯的干扰。大样倾注平板法可以取５ｍＬ的样品,适用所有样品的检测;液体大样法可以取１００ｍＬ的样品,适用于所有样品的检测及增菌,特别适用于无色液体样品;最小近似数法可以检出次大样中     

Role of plasmids in mercury transformation by bacteria isolated from the aquatic environment.

Eight mercury-resistant bacterial strains isolated from the Chesapeake Bay and one strain isolated from the Cayman Trench were examined for ability to volatilize mercury. Mercury volatilization was found to be variable in the strains tested. In addition, plasmids were detected in all strains. After curing, two of the bacterial strains lost mercury resistance, indicating that volatilization is plasmid mediated in these strains. Only two cultures demonstrated ability to methylate mercuric chloride under either aerobic or anaerobic conditions. Methylation of mercury, compared with volatilization, appears to be mediated by a separate genetic system in these bacteria. It is concluded that mercury volatilization in the estuarine environment can be mediated by genes carried on plasmids.     

Role of plasmids in mercury transformation by bacteria isolated from the aquatic environment

Eight mercury-resistant bacterial strains isolated from the Chesapeake Bay and one strain isolated from the Cayman Trench were examined for ability to volatilize mercury. Mercury volatilization was found to be variable in the strains tested. In addition, plasmids were detected in all strains. After curing, two of the bacterial strains lost mercury resistance, indicating that volatilization is plasmid mediated in these strains. Only two cultures demonstrated ability to methylate mercuric chloride under either aerobic or anaerobic conditions. Methylation of mercury, compared with volatilization, appears to be mediated by a separate genetic system in these bacteria. It is concluded that mercury volatilization in the estuarine environment can be mediated by genes carried on plasmids.     

Curing of plasmid pXO1 from Bacillus anthracis using plasmid incompatibility

The large plasmid pXO1 encoding the anthrax toxin is important for the virulence of Bacillus anthracis. It is essential to cure pXO1 from B. anthracis to evaluate its role in the pathogenesis of anthrax infection. Because conventional methods for curing plasmids (e.g., curing agents or growth at elevated temperatures) can induce mutations in the host chromosomal DNA, we developed a specific and reliable method to eliminate pXO1 from B. anthracis using plasmid incompatibility. Three putative replication origins of pXO1 were inserted into a temperature-sensitive plasmid to generate three incompatible plasmids. One of the three plasmids successfully eliminated the large plasmid pXO1 from B. anthracis vaccine strain A16R and wild type strain A16. These findings provided additional information about the replication/partitioning of pXO1 and demonstrated that introducing a small incompatible plasmid can generate plasmid-cured strains of B. anthracis without inducing spontaneous mutations in the host chromosome.     

Plasmid-mediated horizontal gene transfer is a coevolutionary process

Conjugative plasmids are key agents of horizontal gene transfer (HGT) that accelerate bacterial adaptation by vectoring ecologically important traits between strains and species. However, although many conjugative plasmids carry beneficial traits, all plasmids exert physiological costs-of-carriage on bacteria. The existence of conjugative plasmids, therefore, presents a paradox because non-beneficial plasmids should be lost to purifying selection, whereas beneficial genes carried on plasmids should be integrated into the bacterial chromosome. Several ecological solutions to the paradox have been proposed, but none account for co-adaptation of bacteria and conjugative plasmids. Drawing upon evidence from experimental evolution, we argue that HGT via conjugation can only be fully understood in a coevolutionary framework.     

Plasmid curing of Oenococcus oeni

Two strains of Oenococcus oeni, RS1 (which carries the plasmid pRS1) and RS2 (which carries the plasmids pRS2 and pRS3), were grown in the presence of different curing agents and at different temperatures. Sublethal temperature together with acriflavine generated all possible types of cured strains, i.e., lacking pRS1 (from strain RS1), and lacking pRS2, pRS3, or both (from strain RS2). Sublethal temperature together with acridine orange only generated cured strains lacking pRS3. These results suggest that acriflavine is a better curing agent than acridine orange for O. oeni, and that pRS3 is the most sensitive to these curing agents. We also observed spontaneous loss of pRS2 or both pRS2 and pRS3 by electroporation. The ability to cure O. oeni strains of plasmids provides a critical new tool for the genetic analysis and engineering of this commercially important bacterium.     

Plasmid profiling and curing of Lactobacillus strains isolated from the gastrointestinal tract of chicken

In this study, we assessed the susceptibility of 12 Lactobacillus strains, all of which had been isolated from the gastrointestinal tracts of chicken, to three antibiotics (chloramphenicol, erythromycin and tetracycline) used commonly as selective markers in transformation studies of lactic acid bacteria. Among these strains, 17%, 58%, and 25% were found to exhibit a high degree of resistance to 200 microg/ml of tetracycline, erythromycin, and chloramphenicol, respectively. Seven of the 12 Lactobacillus strains exhibiting resistance to at least 50 microg/ml of chloramphenicol or erythromycin, and five strains exhibiting resistance to at least 50 microg/ml of tetracycline, were subsequently subjected to plasmid curing with chemical curing agents, such as novobiocin, acriflavin, SDS, and ethidium bromide. In no cases did the antibiotic resistance of these strains prove to be curable, with the exception of the erythromycin resistance exhibited by five Lactobacillus strains (L. acidophilus I16 and I26, L. fermentum I24 and C17, and L. brevis C10). Analysis of the plasmid profiles of these five cured derivatives revealed that all of the derivatives, except for L. acidophilus I16, possessed profiles similar to those of wild-type strains. The curing of L. acidophilus I16 was accompanied by the loss of 4.4 kb, 6.1 kb, and 11.5 kb plasmids.     

Curing of the killer character of Saccharomyces cerevisiae with acridine orange

Acridine orange, an intercalating dye usually employed in the curing of bacterial plasmids, was tested for its ability to cure K1 and K2 killer strains (laboratory and wine strains). The results showed a high curing percentage of the killer character. This was demonstrated by the loss of M1 or M2 dsRNAs (responsible for toxin production and resistance to it) and because the meiotic products exhibited non-Mendelian segregation. The curing percentages varied, depending on the strain but not on the killer type, and showed similar efficiency as compared with other known curing agents.     

Drug resistance plasmids in Lactobacillus acidophilus and Lactobacillus reuteri.

Sixteen strains of Lactobacillus reuteri and 20 strains of Lactobacillus acidophilus were tested for resistance to 22 antibiotics by using commercially available sensitivity disks. Evidence suggesting linkage of these resistances to plasmids was obtained by "curing" experiments with acridine dyes and high growth temperatures. Examination of plasmid patterns of agarose gel electrophoresis provided further evidence of loss in plasmid DNA under curing conditions in some of the strains examined.     

Bicarbonate-stimulated dark fermentative growth of a phototrophic purple nonsulfur bacterium

Abstract Two strains of soil bacteria, Pseudomonas cepacia and Pseudomonas alcaligenes , which degrade herbicides have been isolated. Both contain plasmids whose presence is correlated with the capacity to metabolise phenylcarbamates. Successive subculturing in the absence of herbicide or curing my mitomycin C leads to the loss of small plasmids from both strains associated with modifications in herbicide degradation. Further, the level of the smallest plasmid of P. cepacia increases when CIPC is the sole carbon source. This plasmid hybridises to several larger molecular species, suggesting a certain degree of structural rearrangement in response to the presence of the herbicide.