Contribution of AIDA-I to the pathogenicity of a porcine diarrheagenic Escherichia coli and to intestinal colonization through biofilm formation in pigs

In order to evaluate the role of the AIDA-I of porcine diarrheagenic Escherichia coli strain PD20 serogroup O143 (AIDA-I⁺, STb⁺), a mutant strain PD20M (AIDA-I⁻, STb⁺) was generated from strain PD20 by an allelic exchange procedure. In addition, the full-length aidA gene was reintroduced into strain PD20M to generate the complemented strain PD20C (pTaidA, AIDA-I⁺, STb⁺). A non-pathogenic E. coli strain PD71 was used as negative control. Each strain was inoculated to newborn pigs via stomach tube. Severity of diarrhea was evaluated clinically and intestinal colonization was assessed by histology, immunohistochemistry (IHC), and transmission electron microscopy (TEM) including immunogold electron microscopy (IGEM). The adhesion pattern to HeLa cells, bacterial auto-aggregation and biofilm formation were evaluated in vitro. Pigs infected with strains PD20 or PD20C developed diarrhea 16 and 28 h after inoculation, respectively, in contrast to pigs infected with strains PD20M or PD71. Histology, IHC, TEM and IGEM examinations showed heavy bacterial colonization with biofilm formation in the large intestine, and marked in vivo expression of AIDA-I protein in pigs infected with strains PD20 or PD20C in contrast to pigs infected with strains PD20M or PD71. The in vitro assays showed marked diffuse adherence to HeLa cells, enhanced bacterial auto-aggregation and significant biofilm formation (p < 0.05) by the AIDA-I⁺ strains, when compared to AIDA-I⁻ strains. These results demonstrate that expression of AIDA-I is essential for intestinal colonization and in vitro bacterial autoaggregation and biofilm formation. Thus, AIDA-I may be considered a significant virulence determinant in development of diarrhea caused by porcine diarrheagenic AIDA-I⁺ E. coli PD20 in piglets.     

Adherence of Pasteurella multocida to fibronectin

For many pathogens, adherence and/or invasion involve association with host extracellular matrix molecules, such as fibronectin (Fn). Pasteurella multocida was found to bind significantly to Fn and collagen type IX but not to laminin and collagen types IV and X. The binding of P. multocida to Fn was dose-dependent and was inhibited by heparin (Hep). Removal of polysaccharide capsule enhanced the binding capacity of the bacterium to Fn and inhibition by Hep. Protease treatment of bacteria decreased binding, implicating surface protein(s) as adhesive components. Investigation of the binding domain(s) of P. multocida on the Fn molecule revealed preferential binding to the N-terminal Hep-binding domain of Fn but not to the carboxyl-terminal Hep-binding domain. Furthermore, Fn, and anti-Fn antibodies inhibited P. multocida adherence to Madin-Darby bovine kidney cells, suggesting the involvement of Fn in the bacterium adherence to host cells. Ligand blotting, batch affinity purification and MALDI-TOF mass spectrometry implicated several proteins as putative adhesins of P. multocida in the Fn-mediated adherence. Taken together, the data suggest that P. multocida-Fn interaction may play a role in the bacterium adherence to host cells, and this may be mediated by bacterial surface proteins with preferential affinity for the Hep-1 binding domain of Fn.     

鸡TGF-β1对大肠杆菌和鸡白痢沙门菌黏附DF1细胞的影响

旨在研究鸡转化生长因子-β1（transfer growth factor-β1,TGF-β1）对大肠杆菌和鸡白痢沙门菌黏附DF1细胞的影响。通过ELISA方法检测鸡新城疫病毒（Newcastle disease virus,NDV）感染DF1细胞后鸡TGF-β1表达量的变化,参考GenBank中鸡TGF-β1序列构建鸡TGF-β1的过表达和干扰表达载体,将构建成功的TGF-β1重组表达载体转染DF1细胞后48 h在荧光显微镜下观察其转染效率,荧光定量PCR检测鸡TGF-β1 mRNA水平表达量的变化,ELISA方法检测鸡TGF-β1胞外蛋白表达量的变化,通过黏附试验检测鸡TGF-β1对致病性大肠杆菌和鸡白痢沙门菌黏附DF1细胞的影响。结果显示,NDV感染DF1细胞后,鸡TGF-β1胞外表达量显著高于未感染细胞的表达量（P<0.05）,经酶切测序鉴定TGF-β1干扰表达和过表达重组载体构建成功。转染鸡TGF-β1重组过表达载体细胞的TGF-β1 mRNA和胞外蛋白表达量均显著高于未转染细胞（P<0.01）,致病性大肠杆菌和鸡白痢沙门菌对细胞的黏附率均显著高于未转染细胞（P<0.01）,转染鸡TGF-β1重组干扰表达载体细胞的mRNA和胞外蛋白表达量均显著低于未转染细胞（P<0.01）,致病性大肠杆菌和鸡白痢沙门菌对细胞的黏附率均显著低于未转染细胞（P<0.01）。综上,NDV感染DF1细胞后,鸡TGF-β1的表达量增加,鸡TGF-β1可促进致病性大肠杆菌和鸡白痢沙门菌黏附DF1细胞,这为进一步研究鸡TGF-β1在家禽病毒感染继发细菌性疾病中的作用提供试验基础。     

A comparison of virulent and avirulent strains of Salmonella choleraesuis and their ability to invade Vero cell monolayers.

The mechanisms of invasion used by virulent and avirulent Salmonella choleraesuis were compared using a Vero cell invasion assay. Mouse virulent S. choleraesuis strain 38 and avirulent strain 9 were examined for their ability to invade and survive in Vero cells. The assay was performed by S. choleraesuis infection of the Vero cell monolayer alone and in the presence of various treatments applied to the Vero cell monolayers. Intracellular S. choleraesuis colony forming units were then counted to characterize the mechanism of bacterial uptake. Invasion was not affected by colchicine, but was significantly inhibited in the presence of cytochalasins B and D, chloroquine, and dansylcadaverine. Inhibition by the above substances suggested the importance of microfilaments and of receptor recycling in receptor mediated endocytosis. Both bacterial strains had decreased invasion in the presence of mannose and after enzymic treatment with trypsin. Mannose exposure caused a significant 48% decrease in the uptake of virulent S. choleraesuis 38 and a 28% decrease in avirulent S. choleraesuis 9. Inhibition of endosome acidification did not affect the virulent strain 38 as much as it affected avirulent strain 9. Results from these experiments suggested that Vero cell invasion by S. choleraesuis was due to host uptake by receptor mediated endocytosis, and was mediated in part by mannosesensitive adhesins. Outer membrane proteins were extracted from the virulent and avirulent strain and compared using SDS-PAGE following surface protein labeling with ¹²⁵I. Virulent S. choleraesuis 38 had a unique 35 kD protein. The outer membrane proteins of both strains were then examined by radio-immunoprecipitation and western blot using guinea pig polyclonal antisera and the 35 kD protein was again found to be unique to the virulent strain 38. Antisera against the 35 kD protein significantly inhibited invasion of Vero cells by S. choleraesuis strain 38.     

A recombinant chimera composed of repeat region RR1 of Mycoplasma hyopneumoniae adhesin with Pseudomonas exotoxin: in vivo evaluation of specific IgG response in mice and pigs

Using the binding and translocation domain of Pseudomonas exotoxin A [domain III deleted PE termed PE(ΔIII)] as a vehicle, this study characterized and evaluated a novel application of PE toxin in Mycoplasma hyopneumoniae adhesin used as an immunogen. PCR and sequence analysis revealed that 16 copies of AAKPV(E) in tandem repeat region 1 (RR1) of M. hyopneumoniae 97 kDa adhesion were successfully fused to the downstream of PE(ΔIII) to create a subunit vaccine, i.e. PE(ΔIII)-RR1. This chimeric protein, over-expressed in inclusion bodies of E. coli BL21(DE3)pLysS, was characterized by a monoclonal antibody (MAb) F2G5 prepared against RR1 of the 97 kDa adhesin and was readily purified. The data indicated that the epitope recognized by MAb F2G5 was located in the structure of PE(ΔIII)-RR1. Using ELISA and Western blot analyses, the specific IgG immune response against RR1 and whole adhesin in mice immunized with PE(ΔIII)-RR1 was found more marked than that in mice immunized with the M. hyopneumoniae whole cells. Similarly, PE(ΔIII)-RR1 also stimulated a remarkable IgG response against RR1 in pigs compared to that in pigs immunized with the conventional M. hyopneumoniae vaccine. The PE(ΔIII)-RR1 would be potentially useful for the future development of a M. hyopneumoniae adhesin vaccine.     

A 39 kDa protein mediates adhesion of avian Pasteurella multocida to chicken embryo fibroblast cells

To clarify the role of avian Pasteurella multocida capsule in pathogenesis, adhesion of capsulated strains P-1059, X-73 and Pm-18, and noncapsulated strains P-1059B, Pm-1 and Pm-3 to chicken embryo fibroblast (CEF) cells was compared. Number of adherent organisms of the capsulated strains to CEF cells were approximately three times as much as noncapsulated strains indicating that adhesive properties were enhanced by the presence of bacterial capsule. Pretreatments of the bacterial cells with heat, trypsin, or with antiserum caused a marked decrease in adhesion of capsulated strain P-1059 and its noncapsulated variant P-1059B. However, depolymerization of capsular hyaluronic acid with high dose of hyaluronidase enhanced adhesion of these strains. Combined treatments of the bacterial cells with both hyaluronidase and trypsin significantly (P < 0.05) inhibited the adherence of strain P-1059 as compared to the treatment only with trypsin, but strain P-1059B was not affected. SDS-PAGE profiles of crude capsular extract (CCE) prepared from capsulated strain P-1059 and its noncapsulated variant P-1059B grown on dextrose starch agar (DSA) plates by heating at 56 degrees C in a 2.5% NaCl solution demonstrated eight protein bands of 28, 34, 36, 39, 52, 56, 63 and 93 kDa. The 28, 34 and 36 kDa proteins were commonly major for both strains, and the 39 kDa protein was major only for strain P-1059 but poor in strain P-1059B. Outer membrane protein (OMP) profiles were identical with a major protein at 34 kDa and four minor proteins between the two strains. The adhesion of strain P-1059 and strain P-1059B to CEF cells was inhibited significantly (P < 0.01) by treatment with rabbit antisera against P-1059, P-1059B, CCE or 39 kDa protein of strain P-1059 as compared to the treatment with either PBS or with normal rabbit serum. These results indicated that an antigenic 39 kDa protein in the capsule may be responsible for adhesion of avian P. multocida type A strains to CEF cells as a virulence factor.     

Effect of cyclosporin A on murine experimental Salmonellosis

Investigations were undertaken to evaluate the effect of cyclosporin A (CyA) on primary infection of mice with Salmonella typhimurium. Further, its effect on delayed-type hypersensitivity (DTH) and antibody response to porin, an outer membrane protein of S. typhimurium, has been characterized under different CyA regimen. When mice were infected i.p. with 5 × 10⁴ live medium virulent organisms, the bacterial growth increased by about 2 log₁₀ in CyA treated mice. CyA administered daily for 2 weeks following immunization with porin caused profound suppression of DTH and both IgM and IgG antibody responses. Given a single dose of CyA 24 h before DTH elicitation, the drug had a marked suppressive effect on DTH, but not on the antibody response to porin. Treatment on days 0–5 following immunization had no effect on the manifestation of the DTH response nor on the anti-porin IgM response whereas an enhanced level of IgG was observed in this group.     

新疆地区2株驴源马流产沙门菌的分离鉴定及致病性分析

【目的】研究确定导致新疆地区2个规模化驴场出现流产的疑似病原沙门菌,并探究其致病能力和耐药性情况。【方法】通过细菌分离培养、形态学观察、生化试验对分离菌进行了鉴定,并对分离菌的鞭毛基因FliC进行了PCR扩增及序列分析,通过致病性测定、荷菌量检测及病理组织学观察,鉴定和分析了分离菌的致病性,并通过药敏试验分析其耐药性。【结果】通过细菌分离培养、形态学观察、生化试验,确定分离到的2株细菌均为马流产沙门菌,分别命名为G1-1和XD1-2。对这2个分离株的鞭毛基因FliC的遗传进化分析结果显示,2株分离菌FliC氨基酸序列之间的相似性为99.0%,2株分离菌FliC氨基酸序列与爱尔兰马源马流产沙门菌分离株Ireland-HE801373、Ireland-HE801378株相似性均最高,且均为99.3%;分离株G1-1与爱尔兰马源马流产沙门菌分离株Ireland-HE801373和Ireland-HE801378及国内马源马流产沙门菌分离株China-KJ486797.1和China-KJ486769.1亲缘关系较近,分离株XD1-2则与美国肠炎沙门菌分离株USA-EBQ1214032.1亲缘...     

Serotype, hemolysin production, and adherence characteristics of strains of Escherichia coli causing urinary tract infection in dogs.

Virulence factors were studied in 82 strains of Escherichia coli isolated from the urine of dogs with urinary tract infections. The most frequently expressed O antigens were 2, 4, 6, 25, and 22/83. Most strains were K nontypeable. Mannose-sensitive hemagglutination (MSH) with canine erythrocytes was observed in 71 strains and mannose-resistant hemagglutination (MRH) was observed in 32 strains. Strains that caused MSH of erythrocytes from dogs also caused MSH of erythrocytes from guinea pigs. Most strains that caused MRH of human A1P1 erythrocytes also reacted with erythrocytes of dogs. Of 22 strains (27%) that agglutinated human A1P1 erythrocytes, but not A1p erythrocytes, 17 (77%) had specificity for globo A, but did not react with the galactose alpha 1----4galactose beta disaccharide receptor. The remaining 5 strains and 2 others that simultaneously expressed an X adhesin agglutinated galactose alpha 1----4galactose beta-coated latex beads. Bacterial adherence to canine uroepithelial cells from the bladder was most often observed in strains expressing MSH, less often observed in strains expressing MRH, and least often observed in strains that failed to induce hemagglutination. Adherence of MSH strains to canine uroepithelial cells was inhibited by alpha-methyl-D-mannoside. As a group, MRH strains expressing globo-A- and galactose alpha 1----4galactose beta-specific adhesins did not have strong adherence. Strains of E coli isolated from dogs with urinary tract infections most commonly expressed type-1 fimbriae, and the main mechanism of in vitro adherence to canine uroepithelial cells involved a mannose-sensitive mechanism. Overrepresentation of globo-A-specific adhesins did not appear to be related to adherence of canine uroepithelial cells.     

Inducible nitric oxide synthase expression in Leishmania-infected dog macrophages

Nitric oxide (NO) production by the inducible NO synthase (iNOS or NOS2) represents one of the main microbicidal mechanisms of murine macrophages, but its role in other animal models is poorly investigated. Therefore, the aim of this work was to evaluate NOS2 expression in dog macrophages infected with Leishmania infantum. Macrophages obtained from peripheral blood of healthy dogs were activated with recombinant human interferon (rhIFN)-γ and bacterial lipopolysaccharide (LPS) and then infected with L. infantum promastigotes, zymodeme MON1. For the immunofluorescence assay fixed macrophages were incubated with polyclonal rabbit anti-NOS2 and then with rhodamine F(ab′)₂ goat anti-rabbit IgG. For immunoblotting, cell lysates were submitted to SDS–PAGE and blots were incubated with polyclonal rabbit anti-NOS2 and then with horseradish peroxidase-conjugated goat anti-rabbit IgG. Results demonstrated that L. infantum-infected cells, after stimulation with rhIFN-γ and LPS, displayed high levels of fluorescence for the NOS2 in their cytoplasm, unlike unstimulated uninfected macrophages. In western blotting, polyclonal anti-NOS2 reacted specifically with a protein band corresponding to 130 kDa. The signal produced in Leishmania-infected cells stimulated with rhIFN-γ and LPS was higher than that produced in Leishmania-infected unstimulated cells. No band was detected in cellular lysates from uninfected unstimulated cells. These results indicate that dog macrophages can express NOS2, and suggest a role for IFN-γ and LPS in NOS2 induction also in this animal model.     

Salmonella enterica level in French pig farms effluents: Experimental and field data

The study aimed to (1) validate the mini-MSRV-MPN method to quantify Salmonella enterica in pig slurry, (2) estimate the effect and interaction on temperature, time and initial Salmonella load on the survival of the 2 strains of Salmonella typhimurium (PF 1690 and DT104 100/706/037) during slurry storage and (3) identify Salmonella contaminated finishing pig batches and assess the level of contamination of their slurry. The mini-MSRV-MPN method was compared to direct isolations on brilliant green agar supplemented with rifampicin to quantify Salmonella in pig slurry. Doelhert uniform shell design was used to study the effect of different parameters on the survival of the 2 strains of Salmonella in pig slurry. Environmental samples of faecal material and a sample of the slurry of 50 batches of finishing pigs were analysed by bacteriological classical method to identify Salmonella. Quantification was performed on pools of faeces and in slurry using the mini-MSRV-MPN technique. This method proved to be suited to quantify Salmonella in pig slurry. Temperature, time of slurry storage and their interaction influenced Salmonella decrease. 12 batches of pigs tested Salmonella positive. Quantification was possible in 5 batches of faecal samples (2.4–350 MPN g^− 1 of Salmonella). Quantification was achieved in 2 out of 6 positive samples of slurry (1.6 and 110 MPN mL^− 1 of Salmonella).     

Development of a molecular diagnostic test applied to experimental abattoir surveillance on bovine tuberculosis

Biofilm formation where bacterial cells adhere to a surface and surround themselves in a polysaccharide matrix is thought to be an important factor in disease initiation and persistence for many bacterial species. We have examined biofilm formation by Mycoplasma mycoides subsp. mycoides small colony using a simple model without an air/liquid interface and have found that adherent Mmm SC was more resistant to many stresses, including heat, osmotic shock and oxidative stress. Biofilms of Mmm SC also exhibited remarkable persistence and were able to survive for up to 20 weeks in stationary phase. Significant variation was seen between Mmm SC strains in their ability to form a biofilm and the morphology of the biofilm produced with some strains unable to produce microcolonies. Proteomic analysis found that a number of proteins linked to adherence were over-expressed in biofilms compared with planktonic cells.     

Characterization of a 39kDa capsular protein of avian Pasteurella multocida using monoclonal antibodies

The role of a 39kDa protein of avian Pasteurella multocida in pathogenesis of fowl cholera was investigated using monoclonal antibodies (Mabs). Mabs were prepared by immunization of BALB/c mice with a crude capsular extract (CCE) of P. multocida strain P-1059 (serovar A:3). Totally eight hybridomas producing Mab were obtained. Immunoblot analysis of the hybridomas revealed that all the Mabs recognized a 39kDa protein of CCE. Treatment of CCE antigen with proteinase K or periodic acid indicated that the epitope recognized was proteinaceous. The Mabs reacted with a major 39kDa protein of CCE from encapsulated strains but not with any protein of non-capsulated strains indicating that a direct correlation between encapsulation and the 39kDa protein. Immunoelectron microscopy on strain P-1059 and the non-capsulated derivative P-1059B (serovar -:3) reacting with the Mabs and gold-labeled anti-mouse IgG indicated that the protein is associated with the capsule. The Mabs significantly inhibited the adherence of encapsulated P. multocida strains to chicken embryo fibroblast cells, but only slightly that of non-capsulated strains. Mice passively immunized with the Mabs were protected from lethal challenge with virulent strains P-1059 and X-73 (serovar A:1). Thus the capsular 39kDa protein was determined to be an adherence factor and a cross-protective antigen of avian P. multocida type A strains.     

基于转录组测序筛选鼠伤寒沙门菌hfq基因缺失菌的差异表达基因

旨在鼠伤寒沙门菌hfq基因缺失株转录组测序中分析适应环境变化及细菌分泌通路，筛选相关基因。通过使用实时荧光定量PCR对鼠伤寒沙门菌hfq基因缺失株转录组测序结果进行验证，从而对鼠伤寒沙门菌hfq基因缺失株的细菌趋化性通路、细菌双组分通路、细菌分泌通路进行深入分析，筛选相关的重要调控基因。结果显示：在细菌趋化性通路中筛选出yiaD、STM3138、STM3216和malE等4个共表达基因；在细菌分泌通路中筛选出spaP、invA、prgH、invE、spaS、invG和ssaV等7个共表达基因；在细菌双组分通路中筛选出ybfM、htrA、pagO、STM3138、STM3031、ttrB、hilD、pstS、STM1530、hilA、pgtC、hydH、pocR、STM3216、ttrR和fljB等16个共表达基因。在鼠伤寒沙门菌hfq基因缺失株的趋化性通路、细菌双组分通路、细菌分泌通路中筛选出差异表达基因，hfq能够对这些基因进行调控，从而影响如运动性、毒力等相关作用，为沙门菌中的sRNA与hfq后续研究及沙门菌的防治奠定一定基础。     

Detection of Escherichia coli strains producing cytotoxic necrotizing factor type two (CNF2) by enzyme-linked immunosorbent assay

Sheep and rabbit antisera were produced against lysates of E. coli strain 711 (pVir). This K-12 strain carries the Vir plasmid which codes for Cytotoxic Necrotizing Factor type 2 (CNF2). Immunoglobulin G (IgG) fractions of both immune sera were subsequently purified by a two-step precipitation method. To increase the specificity for CNF2, the sheep IgG preparation was extensively adsorbed against both a sonicated extract of isogenic K-12 strain 711 and intact phenol-treated cells of vaccine strain 711 (pVir). An enzyme-linked immunosorbent assay (ELISA) was developed to detect clinical isolates of E. coli producing CNF2, using the final preparations of rabbit and sheep IgG in a double sandwich technique. The results obtained with this CNF2-ELISA were compared to those obtained with the conventional HeLa cell cytotoxicity assay. The testing of 133 E. coli strains (49 CNF2 positive strains and 84 negative strains) resulted in no false-negative and no false-positive. Therefore, the CNF2-ELISA offers a good alternative to the HeLa cell culture assay for the detection of CNF2-producing strains where facilities for and experience with cell cultures is lacking.     

In vitro adhesion of K88ac+ Escherichia coli to Peyer''s patch and peripheral blood lymphocytes, buccal and rectal epithelial cells or intestinal epithelial brush borders of weaned pigs

Escherichia coli adhesion assays were conducted using isolated porcine peripheral blood lymphocytes, Peyer's patch lymphocytes, rectal epithelial cells or brush borders, buccal epithelial cells and brush borders from small intestinal epithelial cells. The cells and brush borders were tested for their ability to bind K88-piliated exterotoxigenic E. coliStrain M1823B (K88ac) and E. coli Strain 1476 (K-12, K88ac). Comparison of adhesive phenotypes of 37 weaned pigs as determined by the adhesion assay with small intestinal brush borders and the adherence of K88ac⁺ enterotoxigenic E. coli to peripheral blood lymphocytes, Peyer's patch lymphocytes and rectal epithelial cells or brush borders, revealed no correlation. In vitro adhesion of K88ac-bearing E. coli was always negative with buccal epithelial cells. K88ac strains varied in their ability to adhere to lymphocytes and rectale pithelial cells or brush borders, indicating that the mechanism of adherence is unrelated to K88-mediated adhesion observed in animals that had the receptors on small-intestinal epithelial-cell brush borders. The non-piliated control E. coli Strain 123 adhered to fresh peripheral blood lymphocytes, and less intensively to frozen-thawed peripheral blood lymphocytes or Peyer's patch lymphocytes. It was concluded that none of the cell types or brush borders, except small-intestinal epithelial-cell brush borders, could be used as targets for phenotyping pigs for the presence of the K88 receptors that have been associated with adhesion and colonization of K88⁺ enterotoxigenic E. coli in the porcine small intestine.     

The possible influence of LuxS in the in vivo virulence of rabbit enteropathogenic Escherichia coli

Attaching and effacing (A/E) organisms, such as rabbit enteropathogenic Escherichia coli (EPEC), human EPEC or enterohemorrhagic E. coli (EHEC) share attaching and effacing phenotype and LEE pathogenicity island responsible for A/E. The present study was undertaken to investigate the impact of the LuxS quorum sensing (QS) signaling system in vitro and in vivo pathogenicity of A/E organisms using rabbit EPEC (rEPEC) strain E22 (O103:H2). Analysis of the bioluminescence indicated abolished production of the QS signal AI-2 by luxS mutant (E22DeltaluxS). Strain E22Deltalux also exhibited impaired expression of several normally secreted proteins and reduced adherence to cultured HeLa cells. Complementation of the intact luxS gene to E22DeltaluxS restored secreted protein expression comparable to the WT type but not adherence to HeLa cells. In experimentally infected rabbits, the isogenic luxS mutant induced clinical illness and intimate adherence to the intestinal mucosa, albeit to a less extent, comparable to that seen with the parent virulent strain. It is worth noting that reduced fecal bacterial shedding, mucosal adherence and improved cumulative weight gain were seen for the mutant strain complemented with luxS when compared to the WT. It appears that the luxS gene is not essential for in vivo pathogenicity by rEPEC where exogenous QS signals are present in the gut. The impact of AI-2 provided by multicopy plasmid on bacterial virulence is discussed.     

Control of Salmonella enteritidis phage type 4 experimental infection by fosfomycin in newly hatched chicks

One hundred and twenty 1-day-old broiler chickens were divided into four groups: group I unmedicated and orally challenged with 1.5×10⁸ cfu of Salmonella enteritidis phage type 4; group F infected and treated with 300 ppm of fosfomycin in their drinking water; group CF uninfected and treated, and group C maintained as a control group. Their performance, clinical signs, S. enteritidis PT4 reisolation and biochemistry variables were compared. Group F showed fewer symptoms and gross lesions than those from group I. Fosfomycin treatment at 300 ppm improved body weight at 7 days of age by 42.3%. S. enteritidis PT4 reisolation in group I was higher than in the treated group, but total decontamination of challenged birds was not achieved. There was an increase in the levels of total protein and globulins in group I but not in the treated group. Fosfomycin caused no adverse effects on chickens from group CF, assessed by performance and biochemical variables. The results indicate that fosfomycin could be used in the treatment of S. enteritidis PT4 experimental infection.     

Factors influencing the adherence of strains of Streptococcus bovis and Escherichia coli isolated from ruminal epithelium

Two strains of Streptococcus bovis (A1 and A5) and one strain of Escherichia coli (0141: H28) isolated from the surface of bovine ruminal mucous epithelium were examined for adherence to isolated and cultured ruminal epithelial cells. The E. coli adhered to the target cell by means of fimbriae, which had several common properties with type 1 common fimbriae and caused mannose-sensitive haemagglutination. The A1 strain of S. bovis was devoid of fimbriae and its adherence to the epithelial surface was not inhibited by treatment with sugars or phenol-treated bacterial membrane from the same organism. It was therefore postulated that the bacterial glycocalyx of the S. bovis organisms acted as ligand. The extent of bacterial adherence depended on the state of differentiation of the target cell in both the isolated and the cultured ruminal cell systems. The receptors for both adherent bacterial species were in all probability associated with the glycocalyx of the target cells.     

Adherence of streptococcal isolates from cattle and horses to their respective host epithelial cells

Adherence of Streptococcus dysgalactiae isolates from cattle and S equi isolates from horses to their respective host epithelial cells was compared with the adherence of S pyogenes to human epithelial cells. The adherence was quantitatively determined by use of fluorescein-labeled streptococci. All 3 streptococcal species adhered selectively to their respective host cells. The mechanism of adherence was evaluated by binding studies with adhesive plasma protein, fibronectin. Although all 3 streptococcal species bound fibronectin, S dysgalactiae and S equi interacted preferentially with a 210-kilodalton (kD) C-terminal fragment of fibronectin, whereas S pyogenes bound only a 29-kD N-terminal fragment. A synthetic peptide Gly-Arg-Gly-Asp-Ser, representing the host cell attachment site of fibronectin, partially inhibited the binding of fibronectin and of its 210 kD fragment to S dysgalactiae, but not to S equi. The binding of fibronectin and its 29-kD fragment to S pyogenes was not inhibited by Gly-Arg-Gly-Asp-Ser. These differences in binding activities corresponded to the ability of fibronectin to mediate the adherence of the streptococci to the epithelial cells: fibronectin strongly inhibited the adherence of S pyogenes and S equi to the epithelial cells, but only weakly inhibited that of S dysgalactiae.