Amelioration of Bacterial Genomes: Rates of Change and Exchange

Although bacterial species display wide variation in their overall GC contents, the genes within a particular species' genome are relatively similar in base composition. As a result, sequences that are novel to a bacterial genome—i.e., DNA introduced through recent horizontal transfer—often bear unusual sequence characteristics and can be distinguished from ancestral DNA. At the time of introgression, horizontally transferred genes reflect the base composition of the donor genome; but, over time, these sequences will ameliorate to reflect the DNA composition of the new genome because the introgressed genes are subject to the same mutational processes affecting all genes in the recipient genome. This process of amelioration is evident in a large group of genes involved in host-cell invasion by enteric bacteria and can be modeled to predict the amount of time required after transfer for foreign DNA to resemble native DNA. Furthermore, models of amelioration can be used to estimate the time of introgression of foreign genes in a chromosome. Applying this approach to a 1.43-megabase continuous sequence, we have calculated that the entire Escherichia coli chromosome contains more than 600 kb of horizontally transferred, protein-coding DNA. Estimates of amelioration times indicate that this DNA has accumulated at a rate of 31 kb per million years, which is on the order of the amount of variant DNA introduced by point mutations. This rate predicts that the E. coli and Salmonella enterica lineages have each gained and lost more than 3 megabases of novel DNA since their divergence. Received: 7 July 1996 / Accepted: 27 September 1996     

Intranasal immunization with a peptide conjugated to Salmonella flagellin induces both systemic and mucosal peptide‐specific antibody responses in mice

In this study, the mucosal adjuvant activity of Salmonella flagellin as a carrier in a conjugate of EXP153–rFliC was investigated. EXP153–rFliC was made by conjugation of a synthetic B‐cell epitope peptide derived from Plasmodium falciparum exported protein‐1(EXP153) to recombinant phase 1 flagellin of Salmonella enterica serovar Typhimurium expressed in Escherichia coli (rFliC), and used to immunize BALB/c mice via intranasal instillation. It was found that robust EXP153‐specific serum IgG antibodies were induced without additional adjuvant. EXP153‐specific sIgA antibodies were also induced, these being detected in bronchoalveolar, nasal, vaginal and intestinal washes. These observations demonstrate that Salmonella flagellin as a carrier is an effective mucosal adjuvant in that its conjugated peptide induces antibody responses.     

一株沙门氏菌拮抗菌的筛选及其在污染土壤原位修复中的应用

利用无菌滤纸片平板法从沙门氏菌(Salmonella)污染土壤中筛选到一株有效拮抗沙门氏菌的细菌A45,通过形态学、革兰氏染色和16SrDNA序列同源性分析鉴定为产碱杆菌(Alcaligenes sp.)。温室土培试验和田间原位试验结果都发现,利用该菌株制备的沙门氏菌拮抗菌剂能显著降低土壤中沙门氏菌数量(P0.05),与对照相比土壤中沙门氏菌数量下降2-3个数量级,表明该拮抗细菌可应用于沙门氏菌污染土壤的修复。     

The effect of bovine diet on Salmonella survival in synthetic abomasal fluid

Aims: To investigate the effect of diet on the survival of Salmonella in the bovine abomasum. Methods and Results: Five fistulated cows were randomly assigned to one of five diets denoted as: (i) 100% grass, (ii) grass + 5·3 kg DM concentrate, (iii) 100% grass silage, (iv) 100% hay and (v) maize/grass silage plus concentrates. Rumen fluid was harvested from each dietary treatment and inoculated with nonacid (NA) and acid‐adapted (AA) 5‐strain Salmonella cocktails. After 24‐h incubation period, Salmonella were acid challenged to synthetic abomasum fluid (SAF, pH 2·5) for 5 h to determine their resistance to low pH. The study found that the volatile fatty acids composition and the pH profile of bovine rumen fluid were significantly altered (P < 0·05) by some of the dietary treatments but not others. Regression analysis found that significantly higher numbers of acid‐adapted Salmonella survived in SAF after incubation in rumen fluid from diets 1, 2 and 4, but fewer significant differences were found between diets for nonacid–adapted Salmonella. The results suggest that the acid‐adapted cells were subjected to a higher level of cell injury than the nonadapted cells. Conclusions: Pre‐incubation in rumen fluid did influence the resistance of nonacid and acid‐adapted Salmonella to SAF but it was dependant on the dietary treatment fed to the cows. Significance and Impact of the Study: This study examined the use of diet, as a modulating factor to limit the bovine excretion of Salmonella with a view to providing a scientific basis for the design of dietary management controls in the future.     

Ames试验在水质检测方面的应用

近年来 ,水体污染日趋严重 ,各国学者从氯化后饮水中分离出多种致突变、致癌物质。为此我们采用Ames试验 ,对珠江流域主要取水点的水源水和对应自来水中的有机致突变物污染情况进行了研究。研究表明 ,部分取水点的有机致突变物污染较严重 ,并且氯化消毒后自来水的致突性大于水源水的致突性。因而 ,加强饮水中致突变物质的检测 ,改进净水消毒剂和净水流程很有必要。     

口服型HCV融合抗原DNA疫苗在小鼠诱导免疫应答

将编码一个外源信号肽、一个通用型辅助性T淋巴细胞抗原表位和HCV核心 包膜蛋白E2融合抗原基因的真核表达质粒pST CE2t(DNA疫苗 )转化到减毒鼠伤寒沙门菌SL72 0 7.将该重组菌口服接种BALB c小鼠 3次 .小鼠的抗HCV核心和E2抗体阳转率分别达 6 0 %和 70 % .体外以重组HCV核心或E2抗原刺激小鼠脾细胞 ,均使之发生明显的增殖反应 ,且小鼠脾细胞能有效杀伤表达HCV核心抗原的同系骨髓瘤细胞SP2 0 .这为研制高效免疫、成本低廉、接种方便的HCV疫苗提供了一个新的可行途径     

伤寒沙门氏菌L型易变性及其流行病学意义探讨

本文研究表明,伤寒沙门氏菌在抗生素或胆盐等化学因素诱发下,极易形成Ｌ型缺壁细菌。而且该菌耐受去氧胆酸钠长期作用的现象,解释了伤寒沙门氏菌可以长期存活于胆囊中,成为具有重大流行病学意义的胆囊带菌者。文中还对Ｌ型引起伤寒的临床改变,从菌体变异角度进行了探讨。     

表达SLTEC保护性抗原的重组猪霍乱沙门氏菌C500株的构建及生物学特性

摘要:【目的】 利用平衡致死系统构建表达产类志贺氏毒素大肠杆菌(Shiga-like toxin Escherichia coli , SLTEC)保护性抗原的减毒猪霍乱沙门氏菌。【方法】 构建表达SLT-IIeB－FedF的重组质粒 ,再将其电转入终宿主菌减毒猪霍乱沙门氏菌ΔasdC500株中构建成口服活疫苗株 ,经聚丙烯酰胺凝胶电泳检测SLT-IIeB－FedF融合蛋白的表达情况,并观察重组菌体外培养的稳定性。【结果】 　利用宿主-载体平衡致死系统构建了表达SLTEC保护性抗原的重组减毒猪霍乱沙门氏菌     

An oral Salmonella vaccine promotes the down-regulation of cell surface Toll-like receptor 4 (TLR4) and TLR2 expression in mice

A single oral immunization with the Lon-protease-deficient Salmonella enterica serovar Typhimurium (strain CS2022) induced protective immunity in mice against a subcutaneous challenge with virulent Listeria monocytogenes as well as virulent Salmonella serovar Typhimurium. The populations of cell surface Toll-like receptor 4 (TLR4) and TLR2 on peritoneal macrophages decreased at week 6 after immunization. This population decrease was not reversed after a challenge with either Salmonella or Listeria. These results suggest that oral immunization with CS2022 induced immune tolerance correlated with the down-regulation of cell surface TLR expression. This down-regulation may in part account for the development of cross-protection against a Listeria challenge by immunization with CS2022.