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Biomedical subjects

J E Samuel

Publications and source records attributed to J E Samuel.

At least 19 recordsLinked to original sources
PubMed2006

Clinical and pathologic changes in a guinea pig aerosol challenge model of acute Q fever.

Acute Q fever is a zoonotic disease caused by the obligate intracellular bacterium Coxiella burnetii and can manifest as a flu-like illness, pneumonia, or hepatitis. A need exists in Q fever research for animal models mimicking both the typical route of infection (inhalation) and the clinical illness seen in human cases of Q fever. A guinea pig aerosol challenge model was developed using C. burnetii Nine Mile phase I (RSA 493), administered using a specialized chamber designed to deliver droplet nuclei directly to the alveolar spaces. Guinea pigs were given 10(1) to 10(6) organisms and evaluated for 28 days postinfection. Clinical signs included fever, weight loss, respiratory difficulty, and death, with the degree and duration of response corresponding to the dose of organism delivered. Histopathologic evaluation of the lungs of animals infected with a high dose showed coalescing panleukocytic bronchointerstitial pneumonia at 7 days postinfection that resolved to multifocal lymphohistiocytic interstitial pneumonia by 28 days. Guinea pigs receiving a killed whole-cell vaccine prior to challenge with the highest dose of C. burnetii were protected against lethal infection and did not develop fever. Clinical signs and pathological changes noted for these guinea pigs were comparable to those seen in human acute Q fever, making this an accurate and valuable animal model of human disease.

Acute Disease↗
PubMed2003

Identification and cloning potentially protective antigens of Coxiella burnetii using sera from mice experimentally infected with Nine Mile phase I.

Coxiella burnetii is an obligate intracellular bacterium that causes acute Q fever and occasional chronic infections in humans. To determine the immunodominant antigens during infection with C. burnetii, sera from mice experimentally infected with Nine Mile phase I were tested by immunoblotting. The mouse sera recognized antigens with a variety of molecular weights, including proteins of 14, 22, 28, 34, and 60 kDa as immunodominant antigens. In order to clone potential protective antigens, a genomic DNA library of Nine Mile phase I was constructed in the expression vector Lambda ZAP Express and screened with sera from mice that recovered from C. burnetii infection. A total of 102 immunoreactive clones with various signal intensities were identified from about 8,000 plaques. These clones were purified and expressed in the excised plasmid pBK-CMV. The proteins expressed by these recombinant plasmids were analyzed by SDS-PAGE and immunoblotting. Fifty-four clones expressed immunoreactive proteins of molecular masses ranging from approximately 14 to 60 kDa. Sequence analysis and BLAST search of the recently completed genome sequence identified a variety of novel immunoreactive proteins. These proteins are logical vaccine candidates for testing protective activity against C. burnetii challenge. We established a sublethal challenge model in BALB/c mice with protection from the development of severe splenomegaly as an indicator of vaccinogenic activity. Further characterization of these proteins will provide essential information for developing novel, specific diagnostic reagents and potential subunit vaccine candidates against C. burnetii infection.

Animals↗
PubMed2003

Molecular pathogenesis of Coxiella burnetii in a genomics era.

The agent of acute and chronic Q fever, Coxiella burnetii, occupies a unique niche among intracellular pathogens. The mechanisms the organism employs to cause disease are unclear but involve persistence in a parasitophorous vacuole and the subsequent host response. Studies designed to model molecular mechanisms of pathogenesis have relied upon indirect evidence for testing the role of virulence factors since methods for generation of defined mutations have not been developed. Evidence suggests replication involving a developmental lifecycle is critical for intra- and extracellular survival but this cycle is incompletely defined. It has been proposed that survival in the phagolysosomal-like parasitophorous vacuole requires specific iron uptake systems, secretion of enzymes to detoxify the compartment (catalase and SOD), and down-regulation of an oxidative burst (acid phosphatase). Studies to test these potential virulence mechanisms can be accelerated with the recent development of the complete genome sequence for the prototype acute disease isolate, Nine Mile. Proteins differentially expressed during the developmental cycle can more readily be identified with MALDI-TOF description of proteomic profiles. Genes encoding secreted Cu/Zn SOD, catalase, and acid phosphatase are predicted and can be tested for function and expression. An iron regulon is predicted based upon Fur-regulated open reading frames. The specific role the iron-regulated genes play in iron acquisition can be tested. Confirmation of the iron regulon and others can be tested using microarrays based upon the genomic ORF predictions. These are examples of how we are rapidly changing the experimental approaches used to investigate C. burnetii to improve our understanding of the biology of this unusual and highly adapted organism.

Coxiella burnetii↗
PubMed2001

Characterization of a stress-induced alternate sigma factor, RpoS, of Coxiella burnetii and its expression during the development cycle.

Coxiella burnetii is an obligate intracellular bacterium that resides in an acidified phagolysosome and has a remarkable ability to persist in the extracellular environment. C. burnetii has evolved a developmental cycle that includes at least two morphologic forms, designated large cell variants (LCV) and small cell variants (SCV). Based on differential protein expression, distinct ultrastructures, and different metabolic activities, we speculated that LCV and SCV are similar to typical logarithmic- and stationary-phase growth stages. We hypothesized that the alternate sigma factor, RpoS, a global regulator of genes expressed under stationary-phase, starvation, and stress conditions in many bacteria, regulates differential expression in life cycle variants of C. burnetii. To test this hypothesis, we cloned and characterized the major sigma factor, encoded by an rpoD homologue, and the stress response sigma factor, encoded by an rpoS homologue. The rpoS gene was cloned by complementation of an Escherichia coli rpoS null mutant containing an RpoS-dependent lacZ fusion (osmY::lacZ). Expression of C. burnetii rpoS was regulated by growth phase in E. coli (induced upon entry into stationary phase). A glutathione S-transferase-RpoS fusion protein was used to develop polyclonal antiserum against C. burnetii RpoS. Western blot analysis detected abundant RpoS in LCV but not in SCV. These results suggest that LCV and SCV are not comparable to logarithmic and stationary phases of growth and may represent a novel adaptation for survival in both the phagolysosome and the extracellular environment.

Alternative Splicing↗
PubMed2000

Intervention with Shiga toxin (Stx) antibody after infection by Stx-producing Escherichia coli.

Shiga toxins (Stxs) produced by Escherichia coli (STEC) cause systemic vascular damage, manifested as hemolytic uremic syndrome in humans and as edema disease in pigs. Edema disease, a naturally occurring disease of pigs, was used to determine whether Stx antibodies, administered after infection and after the onset of Stx production, could prevent the systemic vascular damage and clinical disease caused by Stxs. A total of 119 STEC-infected pigs were treated with low, medium, or high doses of Stx antibody or with placebo. After inoculation with STEC, antibodies or placebo was injected intraperitoneally at 2 days postinoculation (DPI; low dose) or 4 DPI (medium and high doses). Edema disease was prevented with the low- and high-dose Stx antibody treatments administered at 2 and 4 DPI, respectively. High-dose antibody treatment also reduced the incidence and extent of vascular lesions. The degree of protection depended on the dose of antibody and the time of administration.

Animals↗
PubMed2000

Cattle lack vascular receptors for Escherichia coli O157:H7 Shiga toxins.

Escherichia coli O157:H7 causes Shiga toxin (Stx)-mediated vascular damage, resulting in hemorrhagic colitis and the hemolytic uremic syndrome in humans. These infections are often foodborne, and healthy carrier cattle are a major reservoir of E. coli O157:H7. We were interested in knowing why cattle are tolerant to infection with E. coli O157:H7. Cattle tissues were examined for the Stx receptor globotriaosylceramide (Gb(3)), for receptivity to Stx binding in vitro, and for susceptibility to the enterotoxic effects of Stx in vivo. TLC was used to detect Gb(3) in tissues from a newborn calf. Gb(3) was detected by TLC in kidney and brain, but not in the gastrointestinal tract. Immunohistochemistry was used to define binding of Stx1 and Stx2 overlaid onto sections from cattle tissues. Stx1 and Stx2 bound to selected tubules in the cortex of the kidney of both newborn calves (n = 3) and adult cattle (n = 3). Stx did not bind to blood vessels in any of the six gastrointestinal and five extraintestinal organs examined. The lack of Gb(3) and of Stx receptivity in the gastrointestinal tract raised questions about the toxicity of Stx in bovine intestine. We found that neither viable E. coli O157:H7 nor Stx-containing bacterial extracts were enterotoxic (caused fluid accumulation) in ligated ileal loops in newborn calves. The lack of vascular receptors for Stx provides insight into why cattle are tolerant reservoir hosts for E. coli O157:H7.

Animals↗
PubMed2000

Shiga toxin-producing Escherichia coli infection: temporal and quantitative relationships among colonization, toxin production, and systemic disease.

Edema disease, a naturally occurring disease of swine caused by Shiga toxin-producing Escherichia coli (STEC), was used as a model for the sequence of events that occur in the pathogenesis of STEC infection. The mean time from production of levels of Shiga toxin 2e (Stx2e) detectable in the feces (day 1) to the onset of clinical disease (neurologic disturbances or death) was 5 days (range, 3-9). Bacterial colonization and titers of Stx2e in the ileum peaked at 4 days after inoculation in pigs without signs of clinical disease and at 6 days after inoculation in clinically affected pigs. Animals with the greatest risk of progressing to clinical disease tended to have the highest fecal toxin titers (>/=1:4096). Stx2e was detected in the red cell fraction from blood of some pigs showing clinical signs of edema disease but was not detected in the serum or cerebrospinal fluid.

Animals↗
PubMed1999

Edema disease as a model for systemic disease induced by Shiga toxin-producing E. coli.

Edema disease (ED) is a naturally occurring disease of weaned pigs caused by host adapted strains of E. coli that produce Shiga toxin (STEC). We determined the temporal and quantitative relationships between intestinal colonization by STEC, levels of Shiga toxin (Stx2e) in the gut, in the blood, and clinical manifestations of ED. Bacterial colonization (10(8) CFU/cm ileum) was highest 4 days post inoculation (pi) in animals that did not develop clinical disease and 6 days pi in animals with clinical signs of ED. The mean time for the development of clinical signs of ED was 6 days pi (range 4-10). Average peak titers of Stx2e in the ileum were 1:16,384 in asymptomatic animals and 1:32,768 in clinical animals. Titers of Stx2e in the feces reflected the toxin titers in the ileum but were lower. Intestinal titers of Stx2e and the density of bacterial colonization were predictive of clinical ED for a group of animals but not for individuals. Approximately 50% of the pigs that had Stx2e titers of > or = 1:4096 and a bacterial density of > or = 10(6) CFU/cm in their ileum, had clinical ED. Pigs that had intestinal Stx2e titers < 1:4096 were asymptomatic. Stx2e was detected in the red cell fraction of blood from some of the pigs with clinical ED and in some that were asymptomatic. Stx2e was not detected in the serum of any animals. ED may be a useful model for predicting the temporal and quantitative relationships between bacterial colonization, Stx levels in the gut and blood and systemic disease for STEC in other species.

Animals↗
PubMed1999

Developmental biology of Coxiella burnettii.

The obligate intracellular bacterial agent of human Q fever, Coxiella burnetii, has a remarkable ability to persist in the extracellular environment. It replicates only when phagocytosed and delivered to the phagolysosome, where it resists degradation. Different morphological forms of the bacterium have different resistance properties and appear to be stages of a developmental cycle. Despite the lack of genetic systems, the molecular events surrounding C. burnetii development are now being unraveled.

Bacterial Proteins↗
PubMed1999

Interaction of Shiga toxins with human brain microvascular endothelial cells: cytokines as sensitizing agents.

Neurologic abnormalities are among the most serious extraintestinal complications of infection with Shiga toxin (Stx)-producing bacteria. Histopathologic examination of tissues from patients with extraintestinal sequelae suggested that Stxs damage endothelial cells. It is shown here that human brain microvascular endothelial cells (HBMECs) are relatively resistant to purified Stxs (50% cytotoxic doses [CD50s] >/=10 microgram/mL). Pretreatment of HBMECs with tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, n-butyric acid, or a cAMP analogue resulted in a 103- to 104-fold decrease in CD50 values and a 2- to 4-fold increase in fluoresceinated Stx binding to HBMECs. Treatment of HBMECs with lipopolysaccharides did not significantly alter cytotoxicity or toxin binding. TNF-alpha and IL-1beta treatment was associated with the increased HBMEC expression of the toxin-binding glycolipid globotriaosylceramide. HBMECs did not produce IL-1beta and produced only trace amounts of TNF-alpha when stimulated with purified Stx1 in vitro.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1999

Differential expression of translational elements by life cycle variants of Coxiella burnetii.

Coxiella burnetii replicates as distinct morphological forms, which may allow potential life cycle variants to survive the harsh environment of the phagolysosome. Monoclonal antibodies (MAbs) were compared by Western blotting for reactivity with large cell variant (LCV) and small cell variant (SCV) antigens to characterize proteins differentially expressed by C. burnetii. MAb NM7.3 reacted with a approximately 32-kDa LCV-upregulated antigen, and MAb NM183 reacted with a approximately 45-kDa LCV-specific antigen. MAb NM7.3 was used to screen a lambdaZapII C. burnetii DNA expression library, and an immunoreactive clone was identified with sequence similarity to the Escherichia coli tsf gene, which encodes elongation factor Ts (EF-Ts). Since a similar screen with MAb NM183 did not identify immunoreactive clones, an alternate strategy was devised to clone the reactive antigen based on observations of cross-reactivity with the 45-kDa elongation factor Tu (EF-Tu) protein from Chlamydia trachomatis. The highly conserved nature of EF-Tu among eubacteria allowed PCR amplification of a tuf gene fragment (encoding approximately 95% of the predicted EF-Tu open reading frame) from C. burnetii using degenerate primers. The product of the cloned tuf gene fragment reacted with MAb NM183 in Western blot analysis, confirming the identity of the 45-kDa LCV-specific antigen. Identification of two proteins differentially expressed by C. burnetii, EF-Tu and EF-Ts, both essential components of the translational machinery of the cell, supports the hypothesis that LCVs are metabolically more active than SCVs.

Amino Acid Sequence↗
PubMed1996

Vaccination with genetically modified Shiga-like toxin IIe prevents edema disease in swine.

Escherichia coli strains producing Shiga-like toxin II variant (SLT-IIe, formerly called SLT-IIv) cause edema disease in weaned pigs. Vaccination of pigs with a genetically modified form of Shiga-like toxin IIe, SLT-IIe(E167Q), has been previously shown to be nontoxic and to induce antibodies to SLT-IIe (V.M. Gordon. S.C. Whipp, H.W. Moon, A.D. O'Brien, and J.E. Samuel, Infect, Immun. 60:485-502, 1992). Fifty micrograms of SLT-IIe(E167Q) toxin was used to vaccinate suckling pigs at 1 and 2 weeks of age. Both vaccinated and nonvaccinated pigs were orally inoculated with an SLT-IIe-producing strain of E. coli after weaning (3 to 4 weeks of age). Pigs fed a low-protein diet that were not vaccinated with SLT-IIe(E167Q) developed subclinical edema disease, histologically evident as vascular necrosis. Pigs fed a high-protein diet that were not vaccinated with SLT-IIe(E167Q) developed clinical edema disease manifested as vascular necrosis, reduced weight gain, ataxia, palpebral edema, lateral recumbency, and death. Pigs vaccinated with SLT-IIe(E167Q) had a reduction in the incidence of subclinical edema disease and never developed clinical edema disease. These data demonstrate that vaccination with a genetically modified form of SLT-IIe prevents edema disease and are consistent with the notion that diet influences susceptibility to edema disease.

Animals↗
PubMed1994

Evidence that proteolytic separation of Shiga-like toxin type IIv A subunit into A1 and A2 subunits is not required for toxin activity.

The role for proteolytic activation of Shiga-like toxin type II variant (SLT-IIv) A subunit was examined using site-directed mutagenesis. Processing of the enzymatically active A subunit by trypsin results in cleavage at an arginine residue(s) (Arg247 and/or Arg250) located between two cysteines. After reduction of the disulfide bond, the processed A subunit separates into an enzymatically active A1 and an A2 peptide. Substitution mutations were created in SLT-IIv that replaced each or both of the two arginines with either glutamic acid (R247E, R250E, or R247E/R250E) or histidine (R247H, R250H, or R247H/R250H). The products of all glutamic acid substitution mutations were immunoreactive but were not cytotoxic due to an inability to assemble into holotoxin. The products of all histidine substitution mutations had cytotoxic activities, enzymatic activities, and a lethal dose for mice similar to that of native toxin. R247H and R250H were susceptible to proteolytic cleavage while R247H/R250H was resistant to processing by exogenously added trypsin. Native toxin incubated with Vero cells was completely cleaved while only a fraction of R247H/R250H was cleaved. These results demonstrate that cleavage of SLT-IIv can be mediated by proteases with different specificities and suggest efficient cleavage is not required for toxicity.

Amino Acid Sequence↗
PubMed1994

Age-related resistance to 987P fimbria-mediated colonization correlates with specific glycolipid receptors in intestinal mucus in swine.

Strains of enterotoxigenic Escherichia coli that produce 987P fimbriae (987P+ strains) colonize the small intestines and cause diarrhea in neonatal (< 6-day-old) pigs but not in weaned pigs. However, 987P+ E. coli strains adhere in vitro to intestinal epithelial cells from pigs of both ages. Two intestinal components, designated 987R and 987M, bind 987P fimbriae (987P) on Western blots (immunoblots). We examined brush borders (BB) and intestinal washes (IW) from pigs to determine if they contain glycolipids which bind 987P. Total glycolipid extracts from BB and IW of 4-week-old pigs were separated on thin-layer chromatograms and overlaid with purified 987P. Bound 987P were detected with 987P-specific antiserum. 987P bound to at least one moiety in both BB and IW glycolipids and also bound to several purified glycolipids, including gangliotetraosylceramide, lactosylceramide (CDH), sulfatide (SFT), gangliotriaosylceramide, and galactosylceramide (listed in order of decreasing affinity). Strain 987, but not the isogenic 987P- strain I36, bound to these same glycolipids, indicating that the fimbriae contain the adhesin required for binding to these lipids. Glycolipids extracted from BB and IW isolated from 3- and 4-week-old pigs and from BB isolated from 1-day-old pigs contained similar amounts of glycolipids like CDH and SFT that bound 987P. Finally, 987P bound to CDH, SFT, and total BB glycolipids separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to Immobilon, and these glycolipids had mobilities similar to that of 987M. Thus, 987M may contain 987P-binding glycolipids. We hypothesize that glycolipid receptors for 987P, most likely CDH or SFT, in the mucus of older pigs bind 987P and inhibit 987P- mediated intestinal colonization by preventing the attachment of 987P+ E. coli to 987P receptors on the intestinal epithelium.

Adhesins, Escherichia coli↗
PubMed1994

Purified Shiga-like toxins induce expression of proinflammatory cytokines from murine peritoneal macrophages.

Infections with Shiga toxin-producing Shigella dysenteriae type 1 and Shiga-like toxin (SLT)-producing Escherichia coli cause outbreaks of bloody diarrhea in which patients are at risk for developing life-threatening complications involving the renal and central nervous systems. Histopathology studies and in vitro experiments suggested that the toxins damage toxin receptor-expressing endothelial cells (EC) lining glomerular and central nervous system capillaries. In the presence of inducible host factors (cytokines), EC sensitivity to SLT toxicity was increased approximately 1 million-fold. We hypothesized that to manifest the vascular lesions characteristic of infection with toxin-producing bacteria, two signals were needed: systemic toxins and elevated proinflammatory cytokines (tumor necrosis factor alpha [TNF-alpha], interleukin 1 [IL-1], and IL-6). Human EC do not secrete these cytokines when stimulated with SLTs in vitro, suggesting that additional cells may be involved in pathogenesis. Therefore, we carried out comparative analyses of the capacity of purified (endotoxin-free) SLTs and lipopolysaccharides (LPS) to induce cytokine mRNA and proteins from murine macrophages. The cells were essentially refractory to SLT cytotoxicity, expressing low to undetectable levels of toxin receptor. SLTs and LPS induced TNF activity and IL-6 expression from macrophages, although dose response and kinetics of cytokine induction differed. LPS was a more effective inducing agent than SLTs. SLT-I-induced TNF activity and IL-6 expression were delayed compared with induction mediated by LPS. IL-1 alpha production required approximately 24 h of exposure to SLTs or LPS. Macrophages from LPS-hyporesponsive C3H/HeJ mice produced low levels of TNF activity when treated with SLT-I, suggesting that LPS and SLTs may utilize separate signaling pathways for cytokine induction.

Animals↗
PubMed1994

The specific activities of Shiga-like toxin type II (SLT-II) and SLT-II-related toxins of enterohemorrhagic Escherichia coli differ when measured by Vero cell cytotoxicity but not by mouse lethality.

Characteristically, enterohemorrhagic Escherichia coli (EHEC) strains produce Shiga-like toxin type I (SLT-I), SLT-II, or both of these immunologically distinct cytotoxins. No antigenic or receptor-binding variants of SLT-I have been identified, but a number of SLT-II-related toxins have been described. Because EHEC O91:H21 strain B2F1, which produces two SLT-II-related toxins, is exquisitely virulent in an orally infected, streptomycin-treated mouse model (oral 50% lethal dose [LD50], < 10 organisms), we asked whether the pathogenicity of strain B2F1 was a consequence of SLT-II-related toxin production. For this purpose, we compared the lethality of orally administered E. coli DH5 alpha (Strr) strains that produced different cytotoxic levels of SLT-II, SLT-IIvha (cloned from B2F1), SLT-IIvhb (also cloned from B2F1), or SLT-IIc (cloned from EHEC O157:H7 strain E32511) on Vero cells. We also calculated the specific activities of purified SLT-IIvhb and SLT-II in intraperitoneally injected mice and on Vero cells. The two purified toxins were equally toxic for mice, but SLT-IIvhb was approximately 100-fold less active than SLT-II on Vero cells and bound to the glycolipid receptor Gb3 with lower affinity than did SLT-II. In addition, characterization of SLT-II-related toxin-binding (B) subunit mutants generated in this study revealed that the reduced in vitro cytotoxic levels of the SLT-II-related toxins were due to Asn-16 in the B subunit. Taken together, these findings do not support the idea that B2F1 is uniquely virulent because of the in vivo toxicity of SLT-II-related toxins but do demonstrate differences in in vitro cytotoxic activity among the SLT-II group produced by human EHEC isolates.

Animals↗