Characteristics of capsules in enterotoxemic Escherichia coli O139:K12 strains causing swine edema disease

The characteristics of the capsule of the enterotoxemic Escherichia coli (ETEEC) O139:K12 strains that strongly adhere to Hep-2 cells were examined. Electron microscopic studies using the freeze-substitution technique revealed that ETEEC strains had a capsule of approximately 25 nm. These strains show hydrophobic surface properties and strong adherence to human polymorphonuclear leukocytes (PMNs). In contrast, ETEEC strains RK-O139 and ED-1 show weak adherence to HEp-2 cells and fail to express the capsule layer on the cell surface. These ETEEC strains possess hydrophilic surface properties and also adhere to PMNs. The lipopolysaccharide (LPS) analysis by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that ETEEC strains had the same LPS profile and long O-side chains of LPS. Furthermore, all strains were resistant to serum killing activity. These results suggest that the capsule of ETEEC strains does not contribute as an antiphagocytic factor, but as an adherence factor to host cells.     

Escherichia coli strains of serogroup O139 isolated from oedema disease of swine bind fibronectin

Abstract 15 Escherichia coli strains of the serogroup O139, isolated from oedema disease of swine, were examined for their ability to interact with ¹²⁵I-labelled fibronectin. All strains were positive, and all except one showed higher fibronectin binding than Staphylococcus aureus strain Cowan 1 cells (to which fibronectin bound in the order of 15% of total protein added). 7 E. coli strains isolated from diarrhoea in young piglets were also tested, and 3 were positive. 2 of these strains showed higher binding than S. aureus Cowan 1 cells. E. coli strains expressing either K99 or K88 antigen were poor binders, comparable to cells of S. aureus strain Wood 46. There was no correlation between cell surface hydrophobicity, as determined by chromatography on Octyl-Sepharose, and the fibronectin-binding property.     

Monoclonal antibodies against O and K antigens of uropathogenic Escherichia coli O4 : K12 : H− as opsonins

Abstract Monoclonal antibodies of subclasses IgG1 and IgG2b and specific for the O4 antigen of Escherichia coli 20025 (O4 : K12 : H⁻) and the capsular K12 polysaccharide of the same strain (IgM) were obtained with the hybridoma technique using spleen cells from Balb/c mice, immunized with a crude bacterial extract, and Sp2/O-Ag8 myeloma cells. The anti-O4 antibodies reacted exclusively with the O4 lipopolysaccharide and not with those from serologically O-cross reactive E. coli . The anti-K12 antibodies recognized as epitope (part of) the KDO moiety of the capsular K12 polysaccharide. Not only anti-K12, but also anti-O4 antibodies effectively phagoopsonized encapsulated E. coli 20025. The opsonized bacteria were killed in subsequent in vitro phagocytosis by human leokocytes in the presence of human serum complement.     

Molecular cloning and expression in Escherichia coli K-12 of chromosomal genes determining the O antigen of an E. coli O2: K1 strain

Abstract: The rfb gene cluster which determines the biosynthesis of the O2 O antigen has been cloned from an Escherichia coli O2: K1 strain isolated from a case of septicaemia in chickens. The region required for expression of the O antigen in E. coli K-12 was localised to a 10.7 to 14.15-kb segment which was shown to be chromosomal in origin with a close linkage to the gnd and his genetic loci.     

模拟失重环境对大肠杆菌K12表型异质性亚群菌株的影响

【背景】我国未来几年深空探索任务将呈"井喷式"发展,微生物对于航天活动的影响越来越引起关注,而国内外少有表型异质性亚群的研究。【目的】从表型异质性的角度探讨低剪切力模拟失重环境(Low-shearmodeledmicrogravity,LSMMG)和低剪切力正常重力环境(Low-shearnormalgravity,LSNG)对大肠杆菌K12造成的影响。【方法】利用旋转细胞培养系统模拟失重环境对大肠杆菌K12进行连续传代培养,从单克隆形态、颜色以及菌体形态等方面挑选出表型异质性的亚群菌株,对不同菌株进行增殖速率、抗生素耐药性、生物被膜形成、环境压力抵抗力以及细胞毒性的测定,以此评估低剪切力和模拟失重环境对大肠杆菌K12的影响。【结果】利用旋转细胞培养系统连续传代培养,总共分离出4株形态不同的表型异质性亚群菌株,其中2株来自模拟失重组(M1,Ma),另外2株来自正常重力对照组(N1,Na);4株亚群与原始菌株(P)相比,在增殖速率、生物被膜形成、环境压力抵抗力和细胞毒性方面均有增强或减弱的明显变化,对于抗生素的耐药性无明显变化。【结论】低剪切力模拟失重环境以及存在低剪切力的正常重力环境均能引起大肠杆菌表型异质性变化,与原始菌株相比,表型异质性亚群菌株在分化上并没有统一的方向,但仍需警惕那些可能对人类造成危害的变化表型。     

Variations in cell size and buoyant density of Escherichia coli K12 during glycogen accumulation

The effect of glycogen accumulation on buoyant density and volume of Escherichia coli K12 was studied. A procedure consisting of three linear equations is presented. This requires measurement only of three parameters: cell buoyant density, cell volume and specific content of the polymer. Experimental values are then used to calculate intercepts and slopes of the equations by linear regression. From the estimated values of such parameters the in vivo values of several variables of interest can be calculated. These include in vivo density and volume of the glycogen inclusion, as well as density and volume of the structural material in the cell. The results are consistent with the glycogen inclusions being hydrated.     

Fimbriation, surface hydrophobicity and serum resistance in uropathogenic strains of Escherichia coli

Abstract A total of 80 Escherichia coli strains were examined for expression of P-fimbriae, mannose-sensitive haemagglutination (MSHA) and mannose-resistant haemagglutination (MRHA) of human group A erythrocytes and guinea pig erthrocytes, cell surface hydrophobicity and resistance to serum bactericidal activity. Isolates were obtained from urine of children and adults, either with acute pyelonephritis ( n = 15 and n = 12) or lower urinary tract infection (UTI) ( n = 30 and n = 23, respectively). Results obtained showed that, in E. coli strains isolated both from children and adults with lower UTI, significant differences were not found concerning the incidence of P-fimbriae, cell surface hydrophobicity and serum resistance. In pyelonephritogenic E. coli isolated from children and adults, the incidence of P-fimbriae and cell surface hydrophobicity was associated more frequently with the former (87% vs. 42% and 100% vs. 67%, P < 0.05), while serum resistance was associated with the latter (47% vs. 67%, P < 0.05).     

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.     

P fimbriae on uropathogenic Escherichia coli O16:K1 and O18 strains

Abstract The fimbrial composition of 12 P-fimbriate uropathogenic Escherichia coli O16 and O18 strains was analysed by immunoprecipitation with 14 fimbria-specific antisera. All the O16 strains possessed a P fimbrial serovariant with an apparent M _r of 17500. One strain had an additional, serologically closely related P fimbria with an apparent M _r of 19 800. Two groups were found among the O18 strains; one possessing a type 1C fimbria and a 19800-Da P fimbria, the other lacking type 1C fimbriae and possessing a P-fimbrial variant with an apparent M _r of 17 800. Fimbriae on strains within the groups were serologically similar by immunoprecipitation assays. Also, the fimbriae on the O16 and O18 strains were mutually cross-reactive. The grouping of the O18 strains by fimbrial serology corresponded to the previous clonal grouping based on other phenotypic characters.     

模拟失重对大肠杆菌K12基因表达及表型的影响

【目的】通过低剪切力模拟失重(Low-shear modeled microgravity,LSMMG)连续传代培养大肠杆菌,检测大肠杆菌在模拟失重条件下的表型变化及基因改变。【方法】利用旋转细胞培养系统模拟失重环境对大肠杆菌K12进行连续传代培养,对菌株进行增殖速率、耐酸性和生物膜形成的测定,以此评估LSMMG对大肠杆菌K12表型的影响。利用转录组测序检测模拟失重条件下差异表达的基因,与表型作比对。【结果】模拟失重导致大肠杆菌增殖速率降低,耐酸性下降,生物膜形成能力增强;模拟失重条件下,营养代谢相关差异表达基因有25个,其中20个表达下降,2个与耐酸相关基因表达均下降。【结论】模拟失重会引起大肠杆菌表型及相应的基因变化,其中生物膜形成能力的增强可能对航天飞行造成潜在威胁。     

抗菌肽OH-CATH对大肠杆菌Escherichia coli的作用(英文）

OH-CATH是眼镜王蛇中新发现的cathelicidin家族抗菌肽.它在1%NaCI存在的条件下对多种细菌都有较强的抗菌活性,同时,在高浓度下对人红细胞无溶血活性.OH-CATH足开发新型抗菌药物的优良模板.蜊明OH-CATH的作用机理及其对微生物的选择性,对研发以OH-CATH为先导结构的药物研发有十分重要的意义.本文利用扫描电镜以及透射电镜对OH-CATH与革兰氏阴性菌一大肠杆菌ATCC 25922相互作用的效应研究.结果揭示:OH-CATH对大肠杆菌的作用涉及到3个步骤.首先,OH-CATH借助其带正电的氨基酸残基附着到细菌带负电荷的细胞壁:然后,附着的OH-CATH在达剑一定浓度后发生聚集,以孔道彤成的方式破坏细菌的膜结构;最终,由十细菌膜的损坏,膜的渗透性被破坏,胞内内含物释放造成细菌死亡.     

Escherichia coli K12 arabinose-binding protein mutants with altered transport properties.

The arabinose-binding protein (ABP) of Escherichia coli binds L-arabinose in the periplasm and delivers it to a cytoplasmic membrane complex consisting of the AraG and AraH proteins, for uptake into the cell. To study the interaction between the soluble and membrane components of this periplasmic transport system, regions of the ABP surface containing the opening of the arabinose-binding cleft were subjected to site-directed mutagenesis. Thirty-eight ABP variants containing one to three amino acid substitutions were recovered. ABP variants were expressed with wild-type AraG and AraH from a plasmid, in a strain lacking the chromosomal araFGH operon, and the whole cell uptake parameters, Ven (maximum initial velocity of arabinose entry) and K(en) (concentration of arabinose yielding half-maximal entry) were determined. Twenty-four mutants had normal Ven values, 3 mutants had Ven and K(en) values twice wild type, and 11 mutants had Ven and K(en) values 20-50% of wild type. Binding proteins that had altered uptake properties were each expressed, processed, and localized to the periplasm at levels equivalent to wild type. The mutant binding proteins behaved the same as wild type during purification, and each had a Kd (dissociation constant for bound arabinose) comparable to that of wild-type ABP. Mutations that resulted in altered uptake identified nine amino acids surrounding the arabinose-binding cleft, all of which are charged in the wild-type protein, and all of whose side chains project outward from the cleft. The evidence suggests that this surface of the binding protein and these nine charged loci play a major role in ABP interactions with the membrane complex.     

Cell density dependent acid sensitivity in stationary phase cultures of enterohemorrhagic Escherichia coli O157:H7

Escherichia coli O157:H7, the causative agent of hemorrhagic colitis and hemolytic uremic syndrome, can survive in a highly acidic environment. The acid resistance of this organism, as measured by its ability to survive in low pH, depended on the density of the cells present during the assay. At low cell densities (相似文献   

Escherichia coli from retail meats carry genes associated with uropathogenic Escherichia coli, but are weakly invasive in human bladder cell culture

Aims: The aim of this study was to determine the uropathogenic potential of Escherichia coli isolated from retail meats. Methods and Results: Two hundred E. coli isolates recovered from retail meats, which were previously identified molecularly as extraintestinal pathogenic E. coli, were investigated for the presence of 21 uropathogenic E. coli (UPEC) virulence‐associated genes. Twenty‐three E. coli isolates were selected based on their serogroups and the number of virulence genes they contained, and further characterized using multilocus sequence typing, and by tissue culture assays for adherence to and invasion of T‐24 human bladder cells and for their induction of interleukin (IL)‐6 secretion. All virulence genes tested, except afa/dra and hlyD, were detected among the E. coli isolates. Multilocus sequence typing analysis of 23 selected isolates revealed that 17 isolates belonged to STs associated with human UPEC. Nearly all 23 isolates exhibited lower level of adherence and invasion compared to a clinical strain, UPEC CFT073. Conclusions: These observations suggested that a small proportion of E. coli isolates from retail meats carry uropathogenic associated virulence genes and thus may serve as a reservoir of these genes to UPEC in the human intestine. Their virulence potential seemed limited as they were only weakly invasive in human bladder cell culture. Significance and Impact of the Study: These findings support the hypothesis that retail meat E. coli may play a role in relation to urinary tract infection (UTI) and may be considered in development of a UTI prevention strategy.     

Cloning, mapping and gene product identification of rhaT from Escherichia coli K12

Rhamnose utilization requires the function of a specific rhamnose transport system. Rhamnose transport mutants have been isolated and characterized. The structural gene, rhaT, encoding the rhamnose permease has been cloned from Escherichia coli. rhaT has been mapped in the rha locus (87.7 min) by analysis of cotransduction with glpK and other rha markers. The precise location of the gene has been determined by complementation analysis of rhamnose transport mutants transformed with recombinant plasmids containing different fragments of the cloned region. Gene order (counterclockwise) is established as glpK . . . rhaT-rhaR-rhaS-rhaB-rhaA-rhaD. The gene product has been identified by expression of rhaT in a T7 RNA polymerase/promoter system. This 23 kDa protein has been assigned to the rhaT product and has been shown to be located in the cell membrane.     

Role of type 1 fimbriae and mannose in the development of Escherichia coli K12 biofilm: from initial cell adhesion to biofilm formation

The influence of type 1 fimbriae, mannose-sensitive structures, on biofilm development and maturation has been examined by the use of three isogenic Escherichia coli K12 strains: wild type, fimbriated, and non-fimbriated. Experiments with the three strains were done in minimal medium or Luria–Bertani broth supplemented with different concentrations of d-mannose. The investigation consisted of: (1) characterizing the bacterial surface of the three strains with respect to hydrophilicity and surface charge, (2) investigating the effect of type 1 fimbriae on bacterial adhesion rate and reversibility of initial adhesion on glass surfaces, and (3) verifying the role of type 1 fimbriae and exopolysaccharides (EPS) in biofilm maturation. The results suggest that type 1 fimbriae are not required for the initial bacterial adhesion on glass surfaces as the non-fimbriated cells had higher adhesion rates and irreversible deposition. Type 1 fimbriae, however, are critical for subsequent biofilm development. It was hypothesized that in the biofilm maturation step, the cells synthesize mannose-rich EPS, which functions as a ‘conditioning film’ that can be recognized by the type 1 fimbriae.     

Isolation of Escherichia coli O157:H7 strains that do not produce Shiga toxin from bovine, avian and environmental sources

AIMS: To determine the potential for naturally occurring Shiga toxin-negative Escherichia coli O157 to acquire stx(2) genes. METHODS AND RESULTS: Multiple E. coli O157:H7 isolates positive for eae and ehxA, but not for stx genes, were isolated from cattle, water trough sediment, animal bedding and wild bird sources on several Ohio dairy farms. These isolates were experimentally lysogenized by stx(2)-converting bacteriophage. CONCLUSIONS: Shiga toxin-negative strains of E. coli O157 are present in multiple animal and environmental sources. SIGNIFICANCE AND IMPACT OF THE STUDY: Shiga toxin-negative strains of E. coli O157 present in the food production environment are able to acquire the stx genes, demonstrating their potential to emerge as new Shiga toxin-producing E. coli strains.