Interference with Pseudomonas quinolone signal synthesis inhibits virulence factor expression by Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen that controls numerous virulence factors through intercellular signals. This bacterium has two quorum-sensing systems (las and rhl), which act through the intercellular signals N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C(12)-HSL) and N-butyryl-l-homoserine lactone (C(4)-HSL), respectively. P. aeruginosa also produces a third intercellular signal that is involved in virulence factor regulation. This signal, 2-heptyl-3-hydroxy-4-quinolone [referred to as the Pseudomonas quinolone signal (PQS)], is a secondary metabolite that is part of the P. aeruginosa quorum-sensing hierarchy. PQS can induce both lasB (encodes LasB elastase) and rhlI (encodes the C(4)-HSL synthase) in P. aeruginosa and is produced maximally during the late stationary phase of growth. Because PQS is an intercellular signal that is part of the quorum-sensing hierarchy and controls multiple virulence factors, we began basic studies designed to elucidate its biosynthetic pathway. First, we present data that strongly suggest that anthranilate is a precursor for PQS. P. aeruginosa converted radiolabeled anthranilate into radioactive PQS, which was bioactive. We also found that an anthranilate analog (methyl anthranilate) would inhibit the production of PQS. This analog was then shown to have a major negative effect on elastase production by P. aeruginosa. These data provide evidence that precursors of intercellular signals may provide viable targets for the development of therapeutic treatments that will reduce P. aeruginosa virulence.

Falsely increased immunoassay measurements of total and unbound phenytoin in critically ill uremic patients receiving fosphenytoin.

BACKGROUND: Fosphenytoin, a phosphate ester prodrug of phenytoin, is metabolized to phenytoin in vivo. Phenytoin metabolites accumulate in renal insufficiency and cross-react in some phenytoin immunoassays. Our aim was to determine the accuracy of phenytoin immunoassays in renal patients treated with fosphenytoin. METHODS: We measured phenytoin with HPLC and with the aca, ACS:180, TDx phenytoin II, Vitros, and AxSYM methods. Specimens were collected 2-120 h after fosphenytoin administration from 17 patients with renal insufficiency. RESULTS: The AxSYM, TDx phenytoin II, ACS:180, and Vitros assays displayed falsely increased phenytoin results up to 20 times higher than the HPLC results. The aca Star results for these specimens were comparable to the HPLC results. Although fosphenytoin can cross-react with phenytoin immunoassays, no fosphenytoin was detected by a sensitive HPLC method in any sample that was tested for its presence. CONCLUSION: These results are consistent with the formation of one or more novel metabolites or adducts of fosphenytoin that accumulate in some critically ill patients with renal insufficiency and that display significant cross-reactivity with some, but not all, phenytoin immunoassay methods.

Metabolic fate and hepatocyte toxicity of reverse amide analogs of conjugated ursodeoxycholate in the rat.

Reverse amide analogs of conjugated bile acids were tested for their effects on the viability of cultured primary rat hepatocytes, for their transport and metabolism in the intact rat, and for their susceptibility to hydrolysis by intestinal bacteria. Succinylnorursodeoxycholanylamide (SNUDCN) and its parent C23 amine showed the same general lack of toxicity toward hepatocytes as the normal conjugates of ursodeoxycholic acid, at concentrations up to 500 microM. The 3alpha,7alpha,12alpha-trihydroxy analog and its parent amine were more toxic than the corresponding dihydroxy compounds, although their effects were similar to those observed for the normal conjugates of cholic acid. Following intraduodenal infusion, greater than 80% of administered SNUDCN appeared in the bile of bile fistula rats. Analysis of bile fractions indicated the presence of SNUDCN (81.5 mol% of original amount) and two metabolites, the taurine conjugate of SNUDCN (9.4 mol%) and SNUDCN containing an additional hydroxy group (9.1 mol%). Although SNUDCN underwent an efficient first pass enterohepatic circulation, it displayed a shorter biological half life than taurocholate (T1/2: 8.9 h vs 39.6 h, respectively). The reverse amide analogs were not hydrolyzed by any of a variety of intestinal bacteria known to hydrolyze normal conjugated bile acids. Despite the shorter half-life, the reverse amide analogs may be of potential use in the targeting of therapeutic bile acids to the colon.

Oxidative stress response in an anaerobe, Bacteroides fragilis: a role for catalase in protection against hydrogen peroxide.

Survival of Bacteroides fragilis in the presence of oxygen was dependent on the ability of bacteria to synthesize new proteins, as determined by the inhibition of protein synthesis after oxygen exposure. The B. fragilis protein profile was significantly altered after either a shift from anaerobic to aerobic conditions with or without paraquat or the addition of exogenous hydrogen peroxide. As determined by autoradiography after two-dimensional gel electrophoresis, approximately 28 newly synthesized proteins were detected in response to oxidative conditions. These proteins were found to have a broad range of pI values (from 5.1 to 7.2) and molecular weights (from 12,000 to 79,000). The hydrogen peroxide- and paraquat-inducible responses were similar but not identical to that induced by oxygen as seen by two-dimensional gel protein profile. Eleven of the oxidative response proteins were closely related, with pI values and molecular weights from 5.1 to 5.8 and from 17,000 to 23,000, respectively. As a first step to understanding the resistance to oxygen, a catalase-deficient mutant was constructed by allelic gene exchange. The katB mutant was found to be more sensitive to the lethal effects of hydrogen peroxide than was the parent strain when the ferrous iron chelator bipyridyl was added to culture media. This suggests that the presence of ferrous iron in anaerobic culture media exacerbates the toxicity of hydrogen peroxide and that the presence of a functional catalase is important for survival in the presence of hydrogen peroxide. Further, the treatment of cultures with a sublethal concentration of hydrogen peroxide was necessary to induce resistance to higher concentrations of hydrogen peroxide in the parent strain, suggesting that this was an inducible response. This was confirmed when the bacterial culture, treated with chloramphenicol before the cells were exposed to a sublethal concentration of peroxide, completely lost viability. In contrast, cell viability was greatly preserved when protein synthesis inhibition occurred after peroxide induction. Complementation of catalase activity in the mutant restored the ability of the mutant strain to survive in the presence of hydrogen peroxide, showing that the catalase (KatB) may play a role in oxidative stress resistance in aerotolerant anaerobic bacteria.

Continuous spectrophotometric assay of conjugated bile acid hydrolase.

Conjugated bile acid hydrolase (CBAH) refers to a class of enzymes which catalyze the cleavage of the amino acid moieties from conjugated bile acids. These enzymes are significant because of their role in providing substrates for further microbial metabolism in the gastrointestinal tract. They also are used in research laboratories for the deconjugation of bile acids prior to structural analyses. A continuous spectrophotometric assay for CBAH activity was developed using a conjugate of cholic acid and the chromophore, 5-amino-2-nitro-benzoic acid. The free chromophore is detected by virtue of its absorbance at 410 nm. The CBAH from Clostridium perfringens displayed a Km for this substrate of 120 microM. These results demonstrate that this new compound functions as an effective substrate of the enzyme and forms the basis for a convenient and rapid method to monitor CBAH activity.

Cloning and characterization of a conjugated bile acid hydrolase gene from Clostridium perfringens.

The gene encoding a conjugated bile acid hydrolase (CBAH) from Clostridium perfringens 13 has been cloned and expressed in Escherichia coli, and its nucleotide sequence has been determined. Nucleotide and predicted amino acid sequence analyses indicated that the gene product is related to two previously characterized amidases, a CBAH from Lactobacillus plantarum (40% identity) and a penicillin V amidase from Bacillus sphaericus (34% identity). The product is apparently unrelated to a CBAH from C. perfringens for which N-terminal sequence information was determined. The gene product was purified from recombinant E. coli and used to raise antibody in rabbits. The presence of the protein in C. perfringens was then confirmed by immunoblot analysis. The protein was shown to have a native molecular weight of 147,000 and a subunit molecular weight of 36,100, indicating its probable existence as a tetramer. Disruption of the chromosomal C. perfringens CBAH gene with a chloramphenicol resistance cartridge resulted in a mutant strain which retained partial CBAH activity. Polyacrylamide gel electrophoresis followed by enzymatic activity staining and immunoblotting indicated that the mutant strain no longer expressed the cloned CBAH (CBAH-1) but did express at least one additional CBAH (CBAH-2). CBAH-2 was immunologically distinct from CBAH-1, and its mobility on native polyacrylamide gels was different from that of CBAH-1. Furthermore, comparisons of pH optima and substrate specificities of CBAH activities from recombinant E. coli and wild-type and mutant C. perfringens provided further evidence for the presence of multiple CBAH activities in C. perfringens.

Synthesis and characterization of novel analogs of conjugated bile acids containing reversed amide bonds.

New analogs of amino acid-conjugated bile acids were synthesized in which the amide bond was reversed from its normal configuration. These structural isomers of the beta-alanyl conjugates of cholic acid and ursodeoxycholic acid were synthesized by reaction of succinic anhydride with the 24-nor-23-amine derivatives of cholic acid and ursodeoxycholic acid. The chemical and physical properties of these reverse amide conjugated bile acid analogs were compared with those of the normal glycine and beta-alanine conjugates. The reverse amide analogs comigrated with their isomeric beta-alanine conjugates during thin-layer chromatography using a variety of solvent systems. However, the isomeric pairs could be resolved by reversed-phase high performance liquid chromatography, with the reverse amides having greater retention times compared to the beta-alanine conjugates. Critical micelle concentrations, solubility of undissociated forms, and acid dissociation constants were similar for the isomeric pairs. Significant differences in melting points were observed, however, While the isomeric pairs showed no significant differences in sensitivity to base hydrolysis, the reverse amides were not hydrolyzed by the cholylglycine hydrolase from Clostridium perfringens, even after long incubation periods.

Characterization and regulation of the NADP-linked 7 alpha-hydroxysteroid dehydrogenase gene from Clostridium sordellii.

A bile acid-inducible NADP-linked 7 alpha-hydroxysteroid dehydrogenase (7 alpha-HSDH) from Clostridium sordellii ATCC 9714 was purified 310-fold by ion-exchange, gel filtration, and dye-ligand affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the purified enzyme showed one predominant peptide band (30,000 Da). The N-terminal sequence was determined, and the corresponding oligonucleotides were synthesized and used to screen EcoRI and HindIII genomic digests of C. sordellii. Two separate fragments (4,500 bp, EcoRI; 3,200 bp, HindIII) were subsequently cloned by ligation to pUC19 and transformation into Escherichia coli DH5 alpha-MCR. The EcoRI fragment was shown to contain a truncated 7 alpha-HSDH gene, while the HindIII fragment contained the entire coding region. E. coli clones containing the HindIII insert expressed high levels of an NADP-linked 7 alpha-HSDH. Nucleotide sequence analyses suggest that the 7 alpha-HSDH is encoded by a monocistronic transcriptional unit, with DNA sequence elements resembling rho-independent terminators located in both the upstream and downstream flanking regions. The transcriptional start site was located by primer extension analysis. Northern (RNA) blot analysis indicated that induction is mediated at the transcriptional level in response to the presence of bile acid in the growth medium. In addition, growth-phase-dependent expression is observed in uninduced cultures. Analysis of the predicted protein sequence indicates that the enzyme can be classified in the short-chain dehydrogenase group.

Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708.

Eubacterium sp. strain VPI 12708 is a human intestinal isolate which has an inducible bile acid 7-dehydroxylation activity. At least two cholic acid-induced polypeptides, with molecular masses of 27,000 and 45,000 daltons, respectively, coelute with bile acid 7-dehydroxylation activity. The 45,000-dalton polypeptide appears to be encoded by a cholic acid-induced mRNA species of greater than 6 kilobases, which suggests that the gene coding for this polypeptide is part of a larger operon. A gene has been cloned which flanks the gene encoding the 45,000-dalton polypeptide, in the upstream (5') direction. This gene appears to encode a second 27,000-dalton polypeptide. The gene bears striking homology at both the nucleotide (80%) and deduced amino acid sequence (89%) levels with the gene which encodes the 27,000-dalton polypeptide that has been shown previously to be involved in the bile acid 7-dehydroxylation reaction sequence. The implications of this homology and the possible function(s) of the two homologous genes in bile acid 7-dehydroxylation are discussed. Evidence is presented which suggests that the two homologous genes involved in bile acid 7-dehydroxylation may be part of a larger multigene family in Eubacterium sp. strain VPI 12708.

Nucleotide sequence and regulation of a gene involved in bile acid 7-dehydroxylation by Eubacterium sp. strain VPI 12708.

Eubacterium sp. strain VPI 12708 is an anaerobic intestinal bacterium that has inducible bile acid 7-dehydroxylation activity. At least four new polypeptides were synthesized after addition of primary bile acids to the growth medium. One of these, of molecular weight 27,000 (P-27), was shown to be involved in the 7-dehydroxylation reaction sequence. The gene coding for P-27 was cloned, and the entire DNA sequence for the protein-coding region was determined. In addition, sequence information was obtained for 294 bases upstream from the translational start codon and 329 bases downstream from the stop codon. Induction studies with a synthetic oligonucleotide probe (16-mer) revealed the presence of a cholic acid-inducible mRNA species approximately 900 bases long. A 5' terminus of this mRNA was detected by primer extension analysis, and the location of the 3' terminus of the mRNA was estimated by using S1 nuclease mapping. The 3' terminus of the mRNA contained a large element with dyad symmetry of unknown function. The open reading frame contained 249 codons, and the corresponding polypeptide had a calculated molecular weight of 26,745. The amino acid sequence of P-27 showed significant homology to several previously described alcohol-polyol dehydrogenases ("nonzinc" dehydrogenases), especially in the region believed to contain a pyridine nucleotide-binding domain. The implications of this homology and the possible function of P-27 in bile acid 7-dehydroxylation are discussed.

Affinity-purified antibodies to ring-infected erythrocyte surface antigen do not correlate with merozoite invasion inhibition in Plasmodium falciparum.

We affinity purified, from malaria-immune serum, antibody to the ring-infected erythrocyte surface antigen (RESA), using petri dishes containing a monolayer of Plasmodium falciparum ring-infected erythrocytes. Except for one out of eight samples, the purified antibody positive by RESA-immunofluorescent assay was not inhibitory to the in vitro invasion of merozoites into erythrocytes in three geographically distinct strains of P. falciparum. However, the initial high level of merozoite-inhibiting antibodies of the intact serum samples remained in the immunoglobulin G fraction from which the RESA antibodies had been removed by affinity chromatography. These results suggest that, although in some cases RESA-immunofluorescent assay-positive antibodies may be inhibitory to merozoite invasion, there are more important antibodies capable of merozoite invasion inhibition.

Molecular cloning of a gene encoding a 45,000-dalton polypeptide associated with bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708.

Eubacterium sp. strain VPI 12708 is an intestinal anaerobic bacterium which possesses an inducible bile acid 7-dehydroxylation activity. Two cholic acid-induced polypeptides with apparent molecular weights of 27,000 and 45,000, respectively, coeluted with bile acid 7-dehydroxylation activity upon anaerobic high-performance gel filtration chromatography of crude cellular protein extracts. The 45,000-dalton polypeptide was purified to greater than 95% homogeneity by high-performance liquid chromatography gel filtration and high-performance liquid-DEAE chromatography. The first 28 amino acid residues of the N terminus of this polypeptide were determined by gas-phase sequencing, and a corresponding mixed oligonucleotide (20-mer) was synthesized. Southern blot analysis of EcoRI total digests of chromosomal DNA showed a 2.6-kilobase fragment which hybridized to the 32P-labeled 20-mer. This fragment was enriched for by size fractionation of an EcoRI total digest of genomic DNA and ligated into bacteriophage lambda gt11. Recombinant phage containing the putative gene encoding the 45,000-dalton polypeptide were detected with the 32P-labeled 20-mer by plaque hybridization techniques. The insert was 2.6 kilobases in length and may contain the entire coding sequence for the 45,000-dalton polypeptide. The 2.6-kilobase insert was subcloned into pUC8 and transformed into Escherichia coli DH5 alpha. However, the 45,000-dalton polypeptide was not detected in cell extracts of this organism when specific antibody was used. Preliminary nucleic acid sequence data correlated exactly with the amino acid sequence. A cholic acid-induced mRNA species of greater than 6 kilobases in size was identified by Northern (RNA) blot analysis of total RNA, suggesting that the gene coding for this polypeptide is part of a larger operon.

Molecular cloning of bile acid 7-dehydroxylase from Eubacterium sp. strain VPI 12708.

Eubacterium sp. strain VPI 12708 is a human intestinal bacterium which contains an inducible bile acid 7-dehydroxylase. Two-dimensional polyacrylamide gel electrophoresis showed that at least four new polypeptides were synthesized after exposure of growing cells to sodium cholate. One of these, of molecular weight 27,000 (PP-27), was implicated in 7-dehydroxylase catalysis. PP-27 was purified to greater than 95% homogeneity by DEAE-cellulose chromatography, high-pressure liquid chromatographic gel filtration, high-pressure liquid chromatography-DEAE chromatography, and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The first 33 amino acid residues of the N terminus of PP-27 were determined with a gas-phase sequencer, and a corresponding mixed oligonucleotide (17-mer) was synthesized. Southern blot analysis of EcoRI total digests of chromosomal DNA showed a 2.2-kilobase fragment which hybridized to the 32P-labeled 17-mer. This fragment was enriched for by size fractionation of an EcoRI total digest of genomic DNA, ligated into the bacterial plasmid pUC8, and used to transform Escherichia coli HB101. Transformants containing the putative 7-dehydroxylase gene were detected with the 32P-labeled 17-mer by colony hybridization techniques. The insert was 2.2 kilobases in length and contained the first 290 bases of the PP-27 gene. Preliminary nucleic acid sequence data correlate with the amino acid sequence. The entire gene was cloned on a 1,150-base-pair TaqI fragment. Western blot analysis of E. coli strains containing these plasmids indicated that PP-27 is expressed in E. coli but is not regulated by bile acids under the conditions used.

Biosynthesis of a novel bile acid nucleotide and mechanism of 7 alpha-dehydroxylation by an intestinal Eubacterium species.

Eubacterium species V.P.I. 12708 has inducible bile acid 7-dehydroxylase activity that can use either 7 alpha or 7 beta bile acids as substrates. Cell extracts prepared from bacteria grown in the presence of cholic acid catalyzed the rapid conversion of free bile acids into a highly polar bile acid metabolite (HPBA). This conjugation activity co-eluted with bile acid 7-dehydroxylase activity on high performance gel filtration chromatography (GFC). The HPBA was purified by a combination of high performance GFC and reverse-phase high performance liquid chromatography (HPLC). The intact HPBA eluted earlier from reverse-phase HPLC than deoxycholyl-CoA and had a Mr of 1102 by Bio-Gel P-2 (GFC). The HPBA had an absorption peak at 255 nm and was sensitive to treatment with phosphodiesterase I or nucleotide pyrophosphatase. The HPBA has a free phosphate as shown by an increase in elution volume on reverse-phase HPLC following treatment with alkaline phosphatase. Treatment of the purified HPBA with nucleotide pyrophosphate plus alkaline phosphatase yielded adenosine, whereas, treatment with nucleotide pyrophosphatase alone generated 5',3'-ADP. A bile acid metabolite was also generated by nucleotide pyrophosphatase treatment. The bile acid metabolite had different chromatographic properties (HPLC and TLC) than the corresponding free bile acid. Gas liquid chromatography-mass spectrometry showed the bile acid metabolite to be 12 alpha-hydroxy-3-oxo-4-cholenoic acid. We hypothesize that the HPBA is an intermediate in 7-dehydroxylation and consists of this compound linked at the C-24 with an anhydride bond to the beta phosphate (5') of ADP-3'-phosphate. These results suggest a novel mechanism of bile acid 7 alpha/7 beta-dehydroxylation in Eubacterium sp. V.P.I. 12708.

Purification and characterization of the secondary alcohol dehydrogenase from propane-utilizing Mycobacterium vaccae strain JOB-5.

Mycobacterium vaccae strain JOB-5 cultured in the presence of propane contained an inducible secondary alcohol dehydrogenase. The enzyme was purified 198-fold using DEAE-cellulose, omega-aminopentyl agarose and NAD-agarose chromatography. The Mr of the enzyme was approximately 136000, with subunits of Mr 37000. The pH optimum for the reaction oxidizing propan-2-ol to propanone was 10-10.5 while the optimum for the reverse reaction was 7.5-8.5. The isoelectric point was 4.9. NAD but not NADP could serve as electron acceptor. The apparent Km values for propan-2-ol and NAD were 4.9 X 10(-5)M and 2.8 X 10(-4)M, respectively. The enzyme was inhibited by thiol reagents and metal chelators. It appears to play an essential role in the metabolism of propane by this bacterium.

Fate of the C1 product of propane dissimilation in Mycobacterium vaccae.

Mycobacterium vaccae catabolizes propane through a C2 + C1 cleavage. Radiorespirometric and 14C-substrate incorporation studies were conducted to ascertain the fate of the C1 product. Results presented indicate that it is directly assimilated through the cellular reduced C1 pool.

Purification and characterization of the amine dehydrogenase from a facultative methylotroph.

Strain RA-6 is a pink-pigmented organism which can grow on a variety of substrates including methylamine. It can utilize methylamine as sole source of carbon via an isocitrate lyase negative serine pathway. Methylamine grown cells contain an inducible primary amine dehydrogenase [primary amine: (acceptor) oxidoreductase (deaminating)] which is not present in succinate grown cells. The amine dehydrogenase was purified to over 90% homogeneity. It is an acidic protein (isoelectric point of 5.37) with a molecular weight of 118,000 containing subunits with approximate molecular weights of 16,500 and 46,000. It is active on an array of primary terminal amines and is strongly inhibited by carbonyl reagents. Cytochrome c or artificial electron acceptors are required for activity; neither NAD nor NADP can serve as primary electron acceptor.