Lactobacillus acidophilus expressing recombinant K99 adhesive fimbriae has an inhibitory effect on adhesion of enterotoxigenic Escherichia coli

The most common enteric colibacillosis in neonatal and newborns is caused by enterotoxigenic Escherichia coli(ETEC). Colonization of ETEC in the small intestine is associated with adhesions using fimbriae, which is known as a specific adhesion factor and provides highly specific means for anchoring and prerequisite for an infectious agent. In the present study we have engineered Lactobacillus acidophilus to produce recombinant K99 fimbriae, which is used for the colonization to the intestine of pigs. The expression of K99 fimbrial protein was confirmed using SDS-PAGE, immunoblot and agglutination analyses. To evaluate a function of the K99 fimbrial protein, inhibition and competition tests were performed on pre-screened intestinal brush border from pigs. The tests showed that recombinant L. acidophilus, not control L. acidophilus, had a significant inhibitory effect to and competition against K99+ E. coli in a dose dependent manner. In conclusion, we demonstrated that recombinant K99 fimbriae producing L. acidophilus was able to prevent E. coli binding to intestinal brush border.     

大肠杆菌K99噬菌体的分离鉴定及在小鼠上的防治效果

【背景】产肠毒素大肠杆菌K99是引起仔猪腹泻的主要致病菌之一,目前对该病的治疗主要依赖于抗生素,但大量抗生素的长期使用造成了病原菌耐药性的增强,亟待寻求一种新的产品来解决这一问题。【目的】以一株产肠毒素大肠杆菌K99为宿主菌,从畜禽粪水中分离噬菌体并对其基本生物学特性进行研究,同时在小鼠上检验噬菌体对小鼠大肠杆菌感染的防治效果。【方法】双层平板法分离筛选烈性噬菌体并观察噬菌斑形态;纯化后进行电镜观察、核酸类型鉴定;测定噬菌体热稳定性、p H稳定性、最佳感染复数及一步生长曲线;通过小鼠体内实验检测噬菌体对小鼠大肠杆菌感染的防治效果。【结果】从畜禽粪水中分离出1株产肠毒素大肠杆菌K99强裂解性噬菌体,命名为ФK99-1,经电镜观察及核酸类型鉴定,应属于肌尾噬菌体科(Myoviridae)。噬菌体能耐受50°C左右的高温,在p H 3.0-10.0范围内效价稳定。最佳感染复数为0.000 01,暴发量为108 333 PFU/cell;运用噬菌体ФK99-1预防和治疗小鼠产肠毒素大肠杆菌K99感染,结果显示小鼠发病症状较阳性对照组明显减轻,小鼠血液内大肠杆菌K99含量也显著低于阳性对照组,通过病理切片观察显示脏器发病情况也较阳性对照组减轻。【结论】ФK99-1是一株在不同温度、不同酸碱性环境中有较强适应能力,且在小鼠大肠杆菌感染上表现出良好防治效果的裂解性肌尾科大肠杆菌噬菌体。     

Detection and purification of the free A subunit of heat-labile enterotoxin produced by enterotoxigenic Escherichia coli

After removal of total B subunit and heat-labile enterotoxin (LT) from crude cell extracts of enterotoxigenic Escherichia coli (HB 101-EWD 299) by Bio-gel A 5 m column chromatography, the crude cell extract was shown to contain a free A subunit (A' subunit) that did not bind to the coligenoid of the B subunits. The A' subunit was found to be immunologically identical to the A subunit of holo-LT and was purified to show only one band in SDS-poly-acrylamide gel electrophoresis (PAGE). The mobility of the A' subunit was identical to that of the A subunit of holo-LT. The pI value of the A' subunit was also the same as that of the A subunit of holo-LT. These data suggest that in enterotoxigenic E. coli there is free A subunit which may be involved in formation of holo-LT, analogously to free B subunit (coligenoid), and that the free A subunit is physicochemically and immunologically identical to the A subunit of holo-LT.     

A recombinant Escherichia coli heat-stable enterotoxin (STa) fusion protein eliciting anti-STa neutralizing antibodies

A recombinant fusion protein consisting of native Escherichia coli heat-stable enterotoxin (STa) and a dimer of a synthetic IgG-binding fragment (ZZ), derived from Staphylococcus aureus protein A was produced in E. coli. The fusion protein (ZZSTa) was secreted in large quantities into the growth medium and recovered by affinity chromatography on IgG-Sepharose. Rabbits immunized with the fusion protein responded by producing high serum levels of anti-STa antibodies that also effectively neutralized STa toxicity in infant mice. The fusion peptide ZZSTa had a substantially decreased toxicity as compared with native STa. A polymeric form of ZZSTa separated by size fractionation was about 100 times less toxic than the monomeric fusion protein, yet both forms had the same capacity to induce neutralizing antibodies. This suggests that modified non-toxic forms of ZZSTa with retained immunogenicity may be produced and tested for their usefulness as functional components in a vaccine against diarrhoea caused by enterotoxigenic E. coli.     

Synthesis of the K5 (group II) capsular polysaccharide in transport-deficient recombinant Escherichia coli

Abstract The genes directing the expression of group II capsules in Escherichia coli are organized into three regions. The central region 2 is type specific and thought to determine the synthesis of the respective polysaccharide, whilst the flanking regions 1 and 3 are common to all group II gene clusters and direct the surface expression of the capsular polysaccharide. In this communication we analyze the involvement of region 1 and 3 genes in the synthesis of the capsular KS polysaccharide. Recombinant E. coli strains harboring all KS specific region 2 genes and having various combinations of region 1 and 3 gene were studied using immunoelectron microscopy. Membranes from these bacteria were incubated with UDP[¹⁴C]GlcA and UDPG1cNAc in the absence or presence of KS polysaccharide as an exogenous acceptor. It was found that recombinant strains with only gene region 2 did not produce the K5 polysaccharide. Membranes of such strains did not synthesize the polymer and did not elongate K5 polysaccharide added as an exogenous acceptor. An involvement of genes from region 1 (notably kps C and kps S) and from region 3 (notably kps T) in the K5 polysaccharide synthesis was apparent and is discussed.     

A recombinant Escherichia coli heat-stable enterotoxin b (STb) fusion protein eliciting neutralizing antibodies

Abstract STb is a heat-stable enterotoxin elaborated by enterotoxigenic Escherichia coli strains associated with weaning piglets and is responsible for diarrhoea in those animals. The maltose binding protein (MBP) of E. coli was used as a carrier for STb, a poorly immunogenic molecule. Constructions were produced where the gene coding for mature STb toxin (MBP-STb) and a fragment of the gene spanning the major epitopic region of STb (AA8–AA30)(MBP-STb₂) were fused to malE gene coding for MBP. The fusion proteins accumulated in the periplasm and were detected with a polyclonal antibody raised against the purified toxin. MBP-STb induced secretion in the biological model whereas MBP-STb₂ was non-toxic. Immunization of rabbits evoked an antibody response to STb for these two fusion proteins. However, only MBP-STb elicited antibodies that effectively neutralized the toxicity of pure STb toxin as determined in the rat loop assay.     

Expression and immunogenicity of an <Emphasis Type="Italic">Escherichia coli</Emphasis> K99 fimbriae subunit antigen in soybean

Enterotoxigenic Escherichia coli (ETEC) cause acute diarrhea in humans and farm animals, and can be fatal if the host is left untreated. As a potential alternative to traditional needle vaccination of cattle, we investigated the feasibility of expressing the major K99 fimbrial subunit, FanC, in soybean (Glycine max) for use as an edible subunit vaccine. As a first step in this developmental process, a synthetic version of fanC was optimized for expression in the cytosol and transferred to soybean via Agrobacterium-mediated transformation. Western analysis of T₀ events revealed the presence of a peptide with the expected mobility for FanC in transgenic protein extracts, and immunofluorescense confirmed localization to the cytosol. Two T₀ lines, which accumulated FanC to levels near 0.5% of total soluble protein, were chosen for further molecular characterization in the T₁ and T₂ generations. Mice immunized intraperitoneally with protein extract derived from transgenic leaves expressing synthetic FanC developed significant antibody titers against bacterially derived FanC and produced antigen-specific CD4⁺ T lymphocytes, demonstrating the ability of transgenic FanC to function as an immunogen. These experiments are the first to demonstrate the expression and immunogenicity of a model subunit antigen in the soybean system, and mark the first steps toward the development of a K99 edible vaccine to protect against ETEC.     

产肠毒素大肠杆菌亚单位疫苗3STaM(G)-K99和3STaM(S)-K99的纯化及其免疫学性质的研究

产肠毒素大肠杆菌(ETEC)是一种导致新生犊牛和仔猪腹泻的主要病原体之一.ETEC的毒力因子主要有黏附素(CFs)、不耐热性肠毒素(LT)和耐热性肠毒素(ST)三种.在前期研究中,利用PCR和酶切连接技术成功构建了两种ETEC亚单位疫苗3STaM (G)-K99和3STaM(S)-K99,且在大肠杆菌中获得高效表达.本研究利用阴离子交换层析纯化融合蛋白3STaM (G)-K99 and 3STaM(S)-K99,辅以弗氏佐剂免疫新西兰大白兔,通过Elisa分析其免疫学性质,并利用肠毒素中和实验在昆明系乳鼠中评价其激发抗STa中和抗体的能力.实验结果表明:亚单位疫苗3STaM(G)-K99 and 3STaM (S)-K99能够激发相对较高水平、可针对天然STa、ETEC和融合蛋白STa-K99的特异性抗体.其次,亚单位疫苗中STa突变体(STaM)组分的肠毒素活性显著降低,且其所激发的特异性抗体属于中和抗体,能有效抑制天然STa的肠毒素活性.亚单位疫苗3STaM (G)-K99 and 3STaM(S)-K99为研制预防ETEC感染性腹泻的多价基因工程疫苗提供了基本素材和理论指导.     

Linker insertion analysis of the FimH adhesin of type 1 fimbriae in an Escherichia coli fimH-null background

Abstract The gene encoding the Escherichia coli FimH adhesin of type 1 fimbriae has been subjected to linker insertion mutagenesis. Amino acid changes were introduced at a number of positions spanning the entire sequence in order to probe the structure-function relationship of the FimH protein. The effect of these mutations on the ability of bacteria to express a D-mannose binding phenotype was assessed in a fimH null mutant (MS4) constructed by allelic exchange in the E. coli K-12 strain PC31. Mutations mapping at amino acid residues 36, 58 and 279 of the mature FimH protein were shown to completely abolish binding to D-mannose receptors. Differences in the level of fimbriation were also observed as a result of some of the mutations in the fimH gene. These mutants may prove useful in dissecting receptor-ligand interactions by defining regions of the FimH protein that are important in erythrocyte binding.     

The nucleotide sequence of a regulatory gene present on a plasmid in an enterotoxigenic Escherichia coli strain of serotype O167:H5

A DNA fragment that can functionally substitute for cfaD, the positive regulatory gene involved in expression of CFA/I fimbriae, has recently been cloned from an Escherichia coli strain of serotype O167:H5 that produces CS5 fimbriae. Nucleotide sequence determination showed that the fragment contained a gene, csvR (Coli Surface Virulence factor Regulator) homologous to the cfaD gene, which encoded for a protein of 301 amino acid residues. The csvR gene was found to be located between two different insertion sequences. Comparison of the amino acid sequence of the CsvR and CfaD proteins showed that CsvR is 34 amino acid residues longer at the C-terminus and, in the sequence, it also contains an insertion of two amino acid residues. The similarity between CfaD and Rns, the positive regulator of CS1 and CS2 expression, is much higher (97%) than between CsvR and CfaD (87%). This is reflected by the fact that the level of expression of CFA/I fimbriae induced by CsvR is not as high as when expression is induced by CfaD or Rns.     

Passive protective effect of egg-yolk antibodies against enterotoxigenic Escherichia coli K88+ infection in neonatal and early-weaned piglets

The protective effects of egg-yolk antibodies obtained from hens immunized with fimbrial antigens from a local strain (Escherichia coli K88+ MB, Manitoba, Canada) of K88+ piliated enterotoxigenic E. coli (ETEC) were evaluated in 3- and 21-day-old piglets in which ETEC diarrhea was induced and also in early-weaned piglets in a commercial farm. The results demonstrated that the E. coli K88+ MB-induced diarrhea in 3-day-old piglets was cured 24 h after treating with egg-yolk antibodies while those treated with egg-yolk powder from conventional hens continued to have diarrhea and 62.5% of them died of severe diarrhea. For 21-day-old weaned piglets, those fed egg-yolk antibodies had transient diarrhea, positive body weight gains and 100% survival during the period of the experiment, whereas control piglets that were treated with placebo had severe diarrhea and dehydration and some died within 48 h after infection. In the field trial, the incidence and severity of diarrhea of 14-18-day-old weaned piglets fed egg-yolk antibodies were much lower than in those fed a commercial diet containing an antibiotic. These results indicate that the neonatal and early-weaned piglets that received the egg-yolk antibodies were protected against ETEC infection.     

Sequences related to the major subunit gene fedA of F107 fimbriae in porcine Escherichia coli strains that express adhesive fimbriae

Abstract Porcine Escherichia coli strains isolated from cases fo postweaning diarrhea or edema disease were analysed for the presence of fedA , the major subunit gene of F107 fimbriae. The E. coli isolates were known to contain colonisation factor '8813', or to express F107, 2134P or other fimbriae, different from F4, F5, F6, and F41. PCR with fedA -specific primers, restriction enzyme digestion of the PCR product, and nucleotide sequence analysis demonstrated that 2134P pili, colonisation factor '8813' and fimbriae identified on Australian strains of the O141 serotype belong to one family of F107 fimbrial antigens.     

L(-)-carnitine production using a recombinant Escherichia coli strain

The L(-)-carnitine production by biotransformation using the recombinant strain Escherichia coli pT7-5KE32 has been studied and optimized with crotonobetaine and D(+)-carnitine as substrates. A resting rather than a growing cells system for L(-)-carnitine production was chosen, crotonobetaine being the best substrate. High biocatalytic activity was obtained after growing the cells under anaerobic conditions at 37°C and with crotonobetaine or L(-)-carnitine as inducer. The growth incubation temperature (37°C) was high enough as to activate the heat-inducible λp_L promoter inserted in the plasmid pGP1-2. The best biotransformation conditions were with resting cells, under aerobiosis, with 4 g l⁻¹ and 100 mM biomass and substrate concentrations respectively. Under these conditions the biotransformation time (1 h) was shorter and the L(-)-carnitine yield (70%) higher than previously reported. Consequently productivity value (11.3 g l⁻¹h⁻¹) was highly improved when comparing with other published works. The resting cells could be reused until eight times maintaining product yield levels well over 50% that meant to increase ten times the L(-)-carnitine obtained per gram of biomass.     

Chromosomal mapping of genes encoding mannose-sensitive (type I) and mannose-resistant F8 (P) fimbriae of Escherichia coli O18:K5:H5

DNA hybridization experiments demonstrated that the gene clusters encoding the F8 fimbriae (fei) as well as the type I fimbriae (pil) exist in a single copy on the chromosome of E. coli O18:K5 strain 2980. In conjugation experiments with appropriate donors, the chromosomal site of these gene clusters was determined. The pil genes were mapped close to the gene clusters thr and leu controlling the biosynthesis of threonine and leucine, respectively. The fei genes were found to be located close to the galactose operon (gal) between the position 17 and 21 of the E. coli chromosomal linkage map.     

Hemagglutinating activity of the B subunit(s) of the heat-labile enterotoxin isolated from chicken enterotoxigenic Escherichia coli

The hemagglutinating activity of the B subunit(s) of the heat-labile enterotoxin (LTc-B) produced by chicken enterotoxigenic Escherichia coli was studied by hemagglutination and hemagglutination inhibition. No or weak hemagglutination of intact human erythrocytes was found by the LTc-B at the highest concentration used, whereas strong hemagglutination of both neuraminidase- and pronase-treated human erythrocytes was found. Enhancement in hemagglutination of treated human erythrocytes induced by the LTc-B was over 2 to 120-fold for type A and B erythrocytes and over 8-fold for type O erythrocytes, respectively. With intact and treated sheep erythrocytes, on the other hand, no hemagglutination was found by the LTc-B at the highest concentration used. Hemagglutination of pronase-treated human type B erythrocytes by the LTc-B was inhibited by methyl-alpha-D-galactopyranoside, galactose, melibiose, hog A + H, asialo-bovine salivary mucin and asialo-thyroglobulin among mono-, di- and polysaccharides and glycoproteins used as inhibitors. These results suggest that the LTc-B is a galactose-specific bacterial lectin.     

Hemagglutinating activity of the B subunit(s) of the heat-labile enterotoxin isolated from human enterotoxigenic Escherichia coli

Abstract The hemagglutinating activity of the B subunit(s) of the heat-labile toxin (LT_h - B) produced by human enterotoxigenic Escherichia coli was studied by hemagglutination and hemagglutination inhibition. Very strong hemagglutination of both neuraminidase- and pronase-treated human erythrocytes was induced by the LT_h - B whereas that of intact ones was induced weakly or not at all by the LT_h - B at the highest concentration used. Enhancement in hemagglitination of these human erythrocytes by the LT_h - B was about 8- to 512-fold for type A and B erythrocytes and 16-fold for type O erthrocytes, respectively. On the other hand, no hemagglutination of intact and treated sheep erythrocytes was found by the LT_h - B at the highest concentration used. Hemagglutination of pronase-treated human type B erythrocytes by the LT_h - B was inhibited by galactose and melibiose among mono-, di- and polysaccharides used as inhibitors. These findings suggest that the LT_h - B is a bacterial lectin specific for galactose-linked residues.     

Identification by Tn10 transposon mutagenesis of host factors involved in the biosynthesis of K99 fimbriae of Escherichia coli: Effect of LPS core mutations

Abstract Tn 10 transposon mutagenesis of Escherichia coli producing K99 fimbriae was carried out to identify host factors involved in regulation or biosynthesis of fimbriae. Two chromosomal mutants were obtained that showed a strongly reduced cell surface expression of K99 fimbriae upon colony blotting and ELISA. Analysis by inversed PCR and nucleotide sequencing showed that one mutant (EP14) contained the Tn 10 transposon in rfaQ , affecting theexpression of the rfaQGP gene cluster, whereas the other mutant (EP35) was affected in a, to date, unknown region of the genome. Immunoblotting analysis confirmed a Rd₁ type of LPS of mutant strain EP14. These findings for the first time indicated an effect of LPS core biosynthesis on the biogenesis of fimbriae at the cell surface. Preliminary experiments indicated that K99 major subunits, in contrast to K88 subunits, strongly bind LPS molecules.     

Deletion and duplication of specific sequences in the K88ab fimbrial subunit protein from porcine enterotoxigenic Escherichia coli.

Summary Small, defined in-frame deletions and in-frame duplications of specific sequences were made within the faeG gene encoding the K88ab fimbrial subunit protein from porcine enterotoxigenic Escherichia coli. The cellular localization and proteolytic stability of the different mutated fimbrial subunit proteins were determined, and compared with those of the wild-type protein. Based upon these results, we predict a functional role of specific structures in the K88ab fimbrial subunit protein in subunit-subunit interactions as well as in interactions between FaeG and the other proteins encoded by the K88ab operon. The results obtained were further compared with results obtained from operon deletions, linker insertion mutagenesis and the current model for biogenesis of K88 fimbriae. One of the mutated fimbrial subunit genes was used to construct a secreted in-frame fusion between FaeG and a characterized epitope (lacking cysteine) from the Hepatitis B pre-S2 protein. Such fusion proteins might be useful in the design of recombinant vaccines.