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PubMed2001

Critical role for tumor necrosis factor alpha in controlling the number of lumenal pathogenic bacteria and immunopathology in infectious colitis.

Infection of mice with the intestinal bacterial pathogen Citrobacter rodentium results in colonic mucosal hyperplasia and a local Th1 inflammatory response similar to that seen in mouse models of inflammatory bowel disease. In these latter models, and in patients with Crohn's disease, neutralization of tumor necrosis factor alpha (TNF-alpha) is of therapeutic benefit. Since there is no information on the role of TNF-alpha in either immunity to noninvasive bacterial pathogens or on the role of TNF-alpha in the immunopathology of infectious colitis, we investigated C. rodentium infection in TNFRp55(-/-) mice. In TNFRp55(-/-) mice, there were higher colonic bacterial burdens, but the organisms were cleared at the same rate as C57BL/6 mice, showing that TNF-alpha is not needed for protective antibacterial immunity. The most striking feature of infection in TNFRp55(-/-) mice, however, was the markedly enhanced pathology, with increased mucosal weight and thickness, increased T-cell infiltrate, and a markedly greater mucosal Th1 response. Interleukin-12 p40 transcripts were markedly elevated in C. rodentium-infected TNFRp55(-/-) mice, and this was associated with enhanced mucosal STAT4 phosphorylation. TNF-alpha is not obligatory for protective immunity to C. rodentium in mice; however, it appears to play some role in downregulating mucosal pathology and Th1 immune responses.

Animals↗
PubMed2003

CesD2 of enteropathogenic Escherichia coli is a second chaperone for the type III secretion translocator protein EspD.

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli are extracellular pathogens that employ a type III secretion system to export translocator and effector proteins, proteins which facilitates colonization of the mucosal surface of the intestine via formation of attaching and effacing (A/E) lesions. The genes encoding the proteins for A/E lesion formation are located on a pathogenicity island, termed the locus of enterocyte effacement (LEE), which contains eae encoding intimin as well as the type III secretion system and effector genes. Many type III secreted proteins are stabilized and maintained in a secretion-competent conformation in the bacterial cytosol by specific chaperone proteins. Three type III chaperones have been described thus far within the EPEC LEE region: CesD, for the translocator proteins EspB and EspD; CesT, for the effector proteins Tir and Map; and CesF, for EspF. In this study we report the characterization of CesD2 (previously Orf27), a second LEE-encoded chaperone for EspD. We show specific CesD2-EspD protein interaction which appears to be necessary for proper EspD secretion in vitro and pathogenesis in vivo as demonstrated in the A/E-lesion-forming mouse pathogen Citrobacter rodentium.

Amino Acid Sequence↗
PubMed2005

EspJ is a prophage-carried type III effector protein of attaching and effacing pathogens that modulates infection dynamics.

Enterohemorrhagic Escherichia coli, enteropathogenic E. coli, and Citrobacter rodentium are highly adapted enteropathogens that successfully colonize their host's gastrointestinal tract via the formation of attaching and effacing (A/E) lesions. These pathogens utilize a type III secretion system (TTSS) apparatus, encoded by the locus of enterocyte effacement, to translocate bacterial effector proteins into epithelial cells. Here, we report the identification of EspJ (E. coli-secreted protein J), a translocated TTSS effector that is carried on the 5' end of the cryptic prophage CP-933U. Infection of epithelial cells in culture revealed that EspJ is not required for A/E lesion activity in vivo and ex vivo. However, in vivo studies performed with mice demonstrated that EspJ possesses properties that influence the dynamics of clearance of the pathogen from the host's intestinal tract, suggesting a role in host survival and pathogen transmission.

Animals↗
PubMed2005

Regulation of type III secretion hierarchy of translocators and effectors in attaching and effacing bacterial pathogens.

Human enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and the mouse pathogen Citrobacter rodentium (CR) belong to the family of attaching and effacing (A/E) bacterial pathogens. They possess the locus of enterocyte effacement (LEE) pathogenicity island, which encodes a type III secretion system. These pathogens secrete a number of proteins into culture media, including type III effector proteins and translocators that are required for the translocation of effectors into host cells. Preliminary evidence indicated that the LEE-encoded SepL and Rorf6/SepD may form a molecular switch that controls the secretion of translocators and effectors in CR. Here, we show that SepL and SepD indeed perform this function in A/E pathogens such as EHEC and EPEC. Their sepL and sepD mutants do not secrete translocators but exhibit enhanced secretion of effectors. We demonstrate that SepL and SepD interact with each other and that both SepL and SepD are localized to the bacterial membranes. Furthermore, we demonstrate that culture media influence the type III secretion profile of EHEC, EPEC, and CR and that low-calcium concentrations inhibit secretion of translocators but promote the secretion of effectors, similar to effects on type III secretion by mutations in sepL and sepD. However, the secretion profile of the sepD and sepL mutants is not affected by these culture conditions. Collectively, our results suggest that SepL and SepD not only are necessary for efficient translocator secretion in A/E pathogens but also control a switch from translocator to effector secretion by sensing certain environmental signals such as low calcium.

Bacterial Outer Membrane Proteins↗
PubMed1978

Comparative immunological studies on arylsulfatase in bacteria of the family Enterobacteriaceae: occurrence of latent arylsulfatase protein regulated by sulfur compounds and tyramine.

The arylsulfatases of 21 strains of the family Enterobacteriaceae were compared by measuring their enzymatic activities and immunological reactivities. Enzyme formation under repressing, nonrepressing, and derepressing conditions was tested. Antiserum prepared against pure arylsulfatase from Klebsiella aerobgenes W70 was tested against the enzyme extracts from the strains using double diffusion, quantitative precipitation, and immunoelectrophoresis. No close relationship was found between arylsulfatase activity and immunological cross-reactionship was found between arylsulfatase activity and immunological cross-reactivity. The strains in the family Enterobacteriaceae could be divided into two groups on the basis of the immunological properties of their enzyme. Antisera formed a precipitin band with both active and inactive enzyme proteins from Escherichia, Citrobacter, Salmonella, Klebsiella, and Enterobacter, but not with the proteins from Serratia, Proteus, and Erwinia, even though some strains of these species had enzyme activity. It was also found that the formation of arylsulfatase proteins, irrespective of whether they had enzyme activity, were under regulation by sulfur compounds and tyramine.

Arylsulfatases↗
PubMed1980

Regulation of hydrogenase activity in enterobacteria.

Proteus vulgaris, Escherichia coli, and Citrobacter freundii cells were devoid of hydrogenase activity when grown on complex medium or minimal medium plus glucose in the presence of saturating levels of dissolved oxygen. Anaerobically grown cells had appreciable hydrogenase activity. Cells grown anaerobically in the presence of CO (an inhibitor of hydrogenase) or nitrate (an electron acceptor) lacked hydrogenase activity. To make hydrogenase essential for anaerobic growth, cells were grown on fumarate, a nonfermentable carbon source. P. vulgaris and C. freundii evolved H2 gas under these conditions, and the hydrogenase-specific activity was 8 to 10 times greater than that in cells grown on glucose. Cell growth was inhibited by CO, and the cells grew but lacked hydrogenase activity when grown in the presence of nitrate. E. coli grew on fumarate plus H2, and the specific activity was five times greater than that in cells grown on glucose. Thus, hydrogenase activity is inducible and is expressed maximally when the enzyme is essential for cellular growth. Under conditions of growth where the enzyme would not be catalytically active, cells contain little active hydrogenase. Under anaerobic conditions where the enzyme is not essential for growth, the level of hydrogenase activity is intermediate.

Anaerobiosis↗
PubMed1981

Translocatable resistance to mercuric and phenylmercuric ions in soil bacteria.

Of a sample of 42 gram-negative Hg-resistant bacteria, three (a Pseudomonas fluorescens, a Klebsiella sp. and a Citrobacter sp.) contained translocatable elements conferring resistance to Hg2+ (all three) and to Hg2+ and phenylmercuric acetate (P. fluorescens). The discovery of transposable phenylmercuric acetate resistance extends the range of known resistance "transposons" from heavy metals and antibiotics to organometallic compounds.

Bacteria↗
PubMed1983

Comparison of the overlapping frd and ampC operons of Escherichia coli with the corresponding DNA sequences in other gram-negative bacteria.

Specific DNA probes from Escherichia coli K-12 were used to analyze the sequence divergence of the frd and ampC operons in various species of gram-negative bacteria. These operons code for the fumarate reductase complex and the chromosomal beta-lactamase, respectively. We demonstrate that the two operons show the same general pattern of divergence, although the frd operon is considerably more conserved than is the ampC operon. The major exception is Salmonella typhimurium LT2, which shows a strong homology to the E. coli frd probe but none to the E. coli ampC probe. The operons from Citrobacter freundii and Shigella sonnei were cloned and characterized by physical mapping, Southern hybridization, and protein synthesis in minicells. In S. sonnei, as in E. coli K-12, the frd and ampC operons overlap (T. Grundström and B. Jaurin, Proc. Natl. Acad. Sci. U.S.A. 79:1111-1115, 1982). Only minor discrepancies between the two operons were found over the entire frd-ampC region. In C. freundii, the ampC and frd operons do not overlap, being separated by about 1,100 base pairs. Presumably the inducible property of the C. freundii chromosomal beta-lactamase is encoded by this 1,100-base-pair DNA segment.

Base Sequence↗
PubMed1987

Cloning of genes from members of the family Enterobacteriaceae with mini-Mu bacteriophage containing plasmid replicons.

An in vivo cloning system that uses derivatives of the Escherichia coli bacteriophage Mu with plasmid replicons has been extended to five different species of the family Enterobacteriaceae. Mu and these mini-Mu replicon elements were introduced into strains of E. coli, Shigella flexneri, Salmonella typhimurium, Citrobacter freundii, and Proteus mirabilis by infection, by transformation, or by conjugation with newly constructed broad-host-range plasmids containing insertions of these elements. Lysates from these cells, lysogenic for Mu and mini-Mu elements, were used to infect sensitive recipient strains of E. coli, S. typhimurium, and C. freundii. Drug-resistant transductants had mini-Mu replicon elements with inserts of different DNA sequences. All of the lysogens made could be induced to yield high phage titers, including those coming from strains that were resistant to Mu and Mu derivatives. Clones of 10 particular genes were isolated by their ability to complement specific mutations in the recipient strains, even in the presence of the E. coli K-12 restriction system. Some of the mini-Mu replicon elements used contained lac gene fusing segments and resulted in fusions of the lac operon to control regions in the cloned sequences.

Citrobacter↗
PubMed1988

Distribution and diversity of hsd genes in Escherichia coli and other enteric bacteria.

We screened Salmonella typhimurium, Citrobacter freundii, Klebsiella pneumoniae, Shigella boydii, and many isolates of Escherichia coli for DNA sequences homologous to those encoding each of two unrelated type I restriction and modification systems (EcoK and EcoA). Both K- and A-related hsd genes were identified, but never both in the same strain. S. typhimurium encodes three restriction and modification systems, but its DNA hybridized only to the K-specific probe which we know to identify the StySB system. No homology to either probe was detected in the majority of E. coli strains, but in C. freundii, we identified homology to the A-specific probe. We cloned this region of the C. freundii genome and showed that it encoded a functional, A-related restriction system whose specificity differs from those of known type I enzymes. Sequences immediately flanking the hsd K genes of E. coli K-12 and the hsd A genes of E. coli 15T- were shown to be homologous, indicating similar or even identical positions in their respective chromosomes. E. coli C has no known restriction system, and the organization of its chromosome is consistent with deletion of the three hsd genes and their neighbor, mcrB.

Citrobacter↗
PubMed2005

A positive regulatory loop controls expression of the locus of enterocyte effacement-encoded regulators Ler and GrlA.

The formation of attaching and effacing (A/E) lesions on intestinal epithelial cells is an essential step in the pathogenesis of human enteropathogenic and enterohemorrhagic Escherichia coli and of the mouse pathogen Citrobacter rodentium. The genes required for the development of the A/E phenotype are located within a pathogenicity island known as the locus of enterocyte effacement (LEE). The LEE-encoded transcriptional regulators Ler, an H-NS-like protein, and GrlA, a member of a novel family of transcriptional activators, positively control the expression of the genes located in the LEE and their corresponding virulence. In this study, we used C. rodentium as a model to study the mechanisms controlling the expression of Ler and GrlA. By deletion analysis of the ler and grlRA regulatory regions and complementation experiments, negative and positive cis-acting regulatory motifs were identified that are essential for the regulation of both genes. This analysis confirmed that GrlA is required for the activation of ler, but it also showed that Ler is required for the expression of grlRA, revealing a novel regulatory loop controlling the optimal expression of virulence genes in A/E pathogens. Furthermore, our results indicate that Ler and GrlA induce the expression of each other by, at least in part, counteracting the repression mediated by H-NS. However, whereas GrlA is still required for the optimal expression of ler even in the absence of H-NS, Ler is not needed for the expression of grlRA in the absence of H-NS. This type of transcriptional positive regulatory loop represents a novel mechanism in pathogenic bacteria that is likely required to maintain an appropriate spatiotemporal transcriptional response during infection.

Base Sequence↗
PubMed2005

The Flag-2 locus, an ancestral gene cluster, is potentially associated with a novel flagellar system from Escherichia coli.

Escherichia coli K-12 possesses two adjacent, divergent, promoterless flagellar genes, fhiA-mbhA, that are absent from Salmonella enterica. Through bioinformatics analysis, we found that these genes are remnants of an ancestral 44-gene cluster and are capable of encoding a novel flagellar system, Flag-2. In enteroaggregative E. coli strain 042, there is a frameshift in lfgC that is likely to have inactivated the system in this strain. Tiling path PCR studies showed that the Flag-2 cluster is present in 15 of 72 of the well-characterized ECOR strains. The Flag-2 system resembles the lateral flagellar systems of Aeromonas and Vibrio, particularly in its apparent dependence on RpoN. Unlike the conventional Flag-1 flagellin, the Flag-2 flagellin shows a remarkable lack of sequence polymorphism. The Flag-2 gene cluster encodes a flagellar type III secretion system (including a dedicated flagellar sigma-antisigma combination), thus raising the number of distinct type III secretion systems in Escherichia/Shigella to five. The presence of the Flag-2 cluster at identical sites in E. coli and its close relative Citrobacter rodentium, combined with its absence from S. enterica, suggests that it was acquired by horizontal gene transfer after the former two species diverged from Salmonella. The presence of Flag-2-like gene clusters in Yersinia pestis, Yersinia pseudotuberculosis, and Chromobacterium violaceum suggests that coexistence of two flagellar systems within the same species is more common than previously suspected. The fact that the Flag-2 gene cluster was not discovered in the first 10 Escherichia/Shigella genome sequences studied emphasizes the importance of maintaining an energetic program of genome sequencing for this important taxonomic group.

Aeromonas↗
PubMed1975

Evaluation of tyrosine medium for the identification of Enterobacteriaceae.

Use of the tyrosine medium in the identification of members of the family Enterobacteriaceae form the basis of this paper. Six hundred and twenty-three strains were tested for their property of tyrosine degradation. Three hundred and seventy-two strains were positive in 24 h and an additional eight strains were positive in 48 to 72 h. These positive strains consisted of all 344 strains of the Proteus-Providencia group, all 25 strains of Citrobacter diversus, and three strains of atypical C. freundii. Our findings suggest that tyrosine degradation is a useful property for separating out the Proteus-Providencia group and in specific identification of C. diversus.

Citrobacter↗
PubMed1982

Comparison of three automated systems for antimicrobial susceptibility testing of gram-negative bacilli.

Several instruments for automated or semiautomated susceptibility testing are currently available. Three of these instruments, Autobac (General Diagnostics, Warner-Lambert Co., Morris Plains, N.J.), MS-2 (Abbott Laboratories, Dallas, Tex.), and AutoMicrobic system (AMS) (Vitek, Inc., Hazelwood, Mo.) were compared for antimicrobial susceptibility testing of gram-negative bacilli. A total of 207 isolates representing 29 species of gram-negative bacilli were tested simultaneously by each instrument and by a standardized disk diffusion reference method. Nine antimicrobial agents, including ampicillin, carbenicillin, cephalothin, gentamicin, tobramycin, amikacin, tetracycline, trimethoprim-sulfamethoxazole, and nitrofurantoin were tested. Discrepancies between the results of the automated and reference disk diffusion methods were resolved by agar dilution testing. Overall, 93% of the Autobac and MS-2 results and 83% of the AMS results were in agreement with the results obtained by the reference methods. The results of the Autobac, MS-2, and AMS systems respectively included 3.3, 2.3, and 4.2% major and very major discrepancies. Excessive testing discrepancies were found for certain drugs, including ampicillin, tetracycline, and nitrofurantoin, and for certain organisms, including species of Providencia, Serratia, and Citrobacter. The results of this comparison of three automated systems for antimicrobial susceptibility testing indicate that the Autobac and MS-2 instruments provided highly reliable results. The AMS need further development of its susceptibility testing capability to eliminate an unacceptably high number of minor discrepancies.

Ampicillin↗
PubMed1975

Thin-layer chromatographic technique for rapid detection of bacterial phospholipases.

Silica gel thin-layer chromatography was employed to detect lecithinase activity induced from bacterial resting cell preparations induced from bacterial resting cell preparations incubated at 37 C for 4 h in the presence of purified egg yolk lecithin. Bacillus subtilis, Bacillus cereus, Serratia marcescens, and Pseudomonas aeruginosa hydrolyzed lecithin with the formation of free fatty acids as the sole lipid-soluble product. In none of the Escherichia coli and Citrobacter freundii strains tested could lecithinase activity be detected. Four among eight strains of Enterobacter aerogenes and one among 12 strains of Proteus tested produced negligible amounts of free fatty acid.

Bacillus cereus↗
PubMed1985

Biochemical identification of new species and biogroups of Enterobacteriaceae isolated from clinical specimens.

In 1972 there were only 11 genera and 26 species in the family Enterobacteriaceae. Today there are 22 genera, 69 species, and 29 biogroups or Enteric Groups. This paper is a review of all of the new organisms. It has a series of differential charts to assist in identification and a large chart with the reactions of 98 different organisms for 47 tests often used in identification. A simplified version of this chart gives the most common species and tests most often used for identification. The sources of the new organisms are listed, and their role in human disease is discussed. Fourteen new groups of Enterobacteriaceae are described for the first time. These new groups are biochemically distinct from previously described species, biogroups, and Enteric Groups of Enterobacteriaceae. The new groups are Citrobacter amalonaticus biogroup 1, Klebsiella group 47 (indole positive, ornithine positive), Serratia marcescens biogroup 1, and unclassified Enteric Groups 17, 45, 57, 58, 59, 60, 63, 64, 68, and 69.

Adult↗
PubMed1987

Production of Vi monoclonal antibodies and their application as diagnostic reagents.

Serum antibodies to Vi antigen were detected in mice immunized with the purified antigen but not with Vi-bearing Salmonella typhi whole cells. Fusion of the spleen cells from one of the Vi antibody-producing mice with NSI myeloma cells produced four stable hybridomas that secreted antibodies to Vi. Monoclonal antibodies from these four clones were all of the immunoglobulin G class and, as determined by competition, appeared to have the same epitope specificity. Despite their immunoglobulin G nature, mouse ascitic fluids induced by one of the hybridomas strongly agglutinated the Vi-positive strains of S. typhi, S. dublin, and Citrobacter strain 5396/38. Thus, 10 clinical isolates of S. typhi but not 98 strains of other bacteria were reactive in slide agglutination tests with the monoclonal antibodies.

Agglutination Tests↗
PubMed1988

Application of optical properties of the Vi capsular polysaccharide for quantitation of the Vi antigen in vaccines for typhoid fever.

The capsular polysaccharide of Salmonella typhi and of Citrobacter freundii (Vi) is a linear homopolymer of alpha 1,4-linked N-acetylgalactosaminuronic acid, variably O-acetylated at the C-3 position. Vaccines composed of Vi confer protection against typhoid fever with an efficacy of about 70%; Vi has recently been conjugated to proteins to increase its immunogenicity and effectiveness (I.L. Acharya, R. Tapa, V.L. Gurubacharya, M.B. Shrestha, C.U. Lowe, D.D. Bryla, R. Schneerson, J.B. Robbins, T. Crampton, B. Trollfors, M. Cadoz, D. Schulz, and J. Armand, N. Engl. J. Med. 317:1101-1104, 1987; K.P. Klugman, I. Gilbertson, H.J. Kornhof, J.B. Robbins, R. Schneerson, D. Schulz, M. Cadoz, and J. Armand, Lancet ii:1165-1169, 1987; S.C. Szu, A.L. Stone, J.D. Robbins, R. Schneerson, and J.B. Robbins, J. Exp. Med. 166:1510-1524, 1987). Vi, however, cannot be measured by conventional colorimetric methods. Two optical techniques were adapted to quantitate Vi in vaccines. The first, Fourier-transformed infrared spectroscopy, was performed on salt-free, freeze-dried samples. The intensities of the absorbance peaks of Vi were proportional to the amount of Vi within the range of 0.25 to 2.0 mg. The amount of Vi was determined from integrated absorptions at the 1,235- or 1,417-cm-1 band. The second technique, spectrophotometric titration, was more sensitive than the Fourier-transformed infrared spectroscopy and could be performed on dilute solutions. The metachromatic effect of the reaction between the aromatic cationic dye acridine orange and the carboxyl groups of Vi was quantitative within +/- 2% in the range of 20 to 700 micrograms of Vi per ml. The accuracy of the titration of Vi in the vaccines was within +/- 8%. These two methods may be applicable to measure other capsular polysaccharides in vaccines.

Acridine Orange↗