Effect of different plasmids on colonization of mouse tissues by the aromatic amino acid dependent Salmonella typhimurium SL 3261

The stability of plasmids pBR322, pUC19 and pBluescript and their effect on bacterial colonization of mice was determined. S. typhimurium SL 3261 carrying high copy number plasmids colonized spleen and liver tissues poorly compared to low copy number plasmids. After inoculation into mice, the stability of the plasmids appeared to be inversely related to the plasmid's size and complexity. Mouse-passaging a pBluescript-based recombinant plasmid expressing the Protective Antigen of Bacillus anthracis selected for a mutant S. typhimurium strain (designated G3) that colonized at high levels and more stably maintained plasmids than S. typhimurium SL 3261. S. typhimurium G3 down-regulated the copy number of ColE1 plasmids. The significance of these data for vaccine design is discussed.

Rapid identification of flaviviruses based on conserved NS5 gene sequences

Two conserved regions in the sequence of the NS5 gene of Flaviviruses were identified. Primers were designed from the consensus sequence of these regions and were used in a reverse transcription/polymerase chain reaction (RT/PCR) to amplify a region of the central european tick-borne encephalitis virus Kumlinge NS5 gene. The authenticity of the amplified fragment was confirmed by nucleotide sequencing. A band of the expected size was also obtained when this RT/PCR was applied to 13 other flaviviral RNAs. This method may be useful for characterisation of the NS5 genes of flaviviruses and as a potential pan-flavivirus diagnostic tool.

A genetically engineered vaccine against the alpha-toxin of Clostridium perfringens protects mice against experimental gas gangrene

Fragments of the alpha-toxin of Clostridium perfringens have been produced using genetic manipulation techniques. Antibody which cross-reacted with the alpha-toxin was induced after immunization with fragments representing the N- (Cpa1-249) and C-terminal (Cpa247-370) domains of the toxin. Smaller fragments of the alpha-toxin did not induce cross-reacting antibody. Anti-Cpa1-249 serum neutralized phospholipase C activity but not haemolytic activity of the toxin. Anti-Cpa247-370 serum neutralized both the phospholipase C and haemolytic activities. Only immunization with Cpa247-370 induced protection against the lethal effects of the toxin. Immunization with Cpa247-370 also provided protection in a mouse model against at least 10 LD100 doses of C. perfringens type A. This result confirms the essential role of this toxin in the pathogenesis of gas gangrene.

Molecular genetic analysis of beta-toxin of Clostridium perfringens reveals sequence homology with alpha-toxin, gamma-toxin, and leukocidin of Staphylococcus aureus

Oligonucleotide probes designed on the basis of the N-terminal sequence of Clostridium perfringens beta-toxin were used to isolate the encoding gene (cpb). The nucleotide sequence of cpb was determined, and on the basis of DNA hybridization experiments it was shown that the gene is found only in type B and C strains of C. perfringens. The deduced amino acid sequence of the beta-toxin revealed homology with the alpha-toxin, gamma-toxin, and leukocidin of Staphylococcus aureus. The beta-toxin purified from C. perfringens appeared to exist in monomeric and multimeric forms. Recombinant beta-toxin, produced in Escherichia coli, appeared to be mainly in the multimeric form.

Analysis of a cloned Francisella tularensis outer membrane protein gene and expression in attenuated Salmonella typhimurium

We have determined the nucleotide sequence of fopA from Francisella tularensis. Using the polymerase chain reaction fopA was detected in high and low virulence biotypes of F. tularensis. fopA was stably maintained in pBluescript in attenuated Salmonella typhimurium where FopA was expressed and located in the outer membrane. This recombinant will be suitable for studies on the role of FopA in immunity against tularaemia.

Biochemical and immunological properties of the C-terminal domain of the alpha-toxin of Clostridium perfringens

The C-terminal domain of the alpha-toxin (cpa247-370) of Clostridium perfringens has been expressed in Escherichia coli and purified. Antiserum raised against cpa247-370 reacted in an identical manner to anti-alpha-toxin serum when used to map epitopes in the C-terminal domain, suggesting that cpa247-370 was immunologically and structurally identical to this region in the alpha-toxin. The isolated cpa247-370 was devoid of sphingomyelinase activity or haemolytic activity and was not cytotoxic for mouse lymphocytes. Haemolytic activity was detected when cpa247-370 was tested with the N-terminal domain of the alpha-toxin (cpa1-249), confirming that cpa247-370 confers haemolytic properties on the phospholipase C activity of the alpha-toxin. Haemolytic activity was not detected if cpa247-370 was tested with the Bacillus cereus phosphatidylcholine phospholipase C, nor if cpa1-249 and cpa247-370 were incubated sequentially with erythrocytes.

Bacterial phospholipases C

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.

Comparison of the nucleotide sequence and development of a PCR test for the epsilon toxin gene of Clostridium perfringens type B and type D

The sequence of the epsilon toxin gene of Clostridium perfringens type D was determined and compared with that of the previously reported type B sequence. It showed two nucleotide changes in the open reading frame, giving rise to one amino acid substitution. The promoter sequences were not homologous, and different putative -35 and -10 regions have been identified in each. The sequence information was used to develop PCR primers which were specific for the epsilon toxin gene. The utility of this system for identifying type B or D strains of C. perfringens was demonstrated.

Detection of spores of Bacillus anthracis using the polymerase chain reaction

The polymerase chain reaction (PCR) was used to identify spores of Bacillus anthracis. By using an assay capable of amplifying a 1247-bp fragment from the gene that encodes the edema factor of B. anthracis, as few as 10(3) copies of a plasmid containing the edema factor gene and as few as 2 x 10(4) spores were detected. Subjecting the product of this PCR to a second PCR designed to amplify a 208-bp fragment nested within the 1247-bp product improved detection to a single plasmid copy per PCR and to two spores of B. anthracis per PCR.

Cloning and nucleotide sequencing of the Clostridium perfringens epsilon-toxin gene and its expression in Escherichia coli

The sequence of 20 amino acids from the N terminus of Clostridium perfringens epsilon-toxin was determined. Some differences between this sequence and the previously published sequence (A. S. Bhown and A. F. S. A. Habeeb, Biochem. Biophys. Res. Commun. 78:889-896, 1977) were found. A degenerate 23-bp pair oligonucleotide probe was designed from the amino acid sequence data and used to isolate a DNA fragment containing the gene encoding epsilon-toxin (etx) from C. perfringens type B. The gene encoded a protein with a molecular weight of 32,981. Upstream of the gene, promoter sequences which resembled the Escherichia coli sigma 70 consensus sequences were identified. The gene was expressed in E. coli, and the cloned gene product reacted with epsilon-toxin-specific monoclonal antibodies and had a molecular weight and isoelectric point similar to those of the native protein. Downstream of etx, two overlapping open reading frames were identified. Each encoded part of a protein which was homologous to the transposase from Staphylococcus aureus transposon Tn4001. Southern hybridization experiments indicated that the etx gene was found only in C. perfringens types B and D, the types which produce epsilon-toxin.

Epitope mapping of the alpha-toxin of Clostridium perfringens

A panel of monoclonal antibodies specific for the Clostridium perfringens alpha-toxin was produced by the fusion of X63.Ag8-653 cells with splenocytes from mice immunized either intrasplenically or intraperitoneally with an alpha-toxoid. The toxin-binding activity of each monoclonal antibody was evaluated. The monoclonal antibodies were also screened for their toxin-neutralizing potential in vitro, as determined by the inhibition of phospholipase C and hemolytic activities. In vivo inhibition of toxicity was assessed by the survival of mice challenged with preincubated alpha-toxin-antibody mixtures. Only one monoclonal antibody (3A4D10) was protective in vivo and neutralizing in both in vitro assays. Since 3A4D10 could inhibit both activities, the evidence suggests that these are colocated in the same area of the toxin molecule. This paper identifies a significant continuous linear binding region for 3A4D10 at positions 193 to 198 in the primary amino acid sequence of alpha-toxin.

Hemolytic and sphingomyelinase activities of Clostridium perfringens alpha-toxin are dependent on a domain homologous to that of an enzyme from the human arachidonic acid pathway

The N-terminal domain of Clostridium perfringens alpha-toxin, homologous with the nontoxic phospholipase C of Bacillus cereus, was expressed in Escherichia coli and shown to retain all of the phosphatidylcholine hydrolyzing activity of the alpha-toxin, but not the sphingomyelinase, hemolytic, or lethal activities. The C-terminal domain of alpha-toxin showed sequence and predicted structural homologies with the N-terminal region of arachidonate 5-lipoxygenase, an enzyme from the human arachidonic acid pathway which plays a role in inflammatory and cardiovascular diseases in humans.

The role of histidine residues in the alpha toxin of Clostridium perfringens

The alpha-toxin (phospholipase C) of Clostridium perfringens has been reported to contain catalytically essential zinc ions. We report here that histidine residues are essential for the co-ordination of these ion(s). Incubation of alpha toxin with diethylpyrocarbonate, a histidine modifying reagent, did not result in the loss of phospholipase C activity unless the protein was first incubated with EDTA, suggesting that zinc ions normally protect the susceptible histidine residues. When the amino acid sequences of three phospholipase C's were aligned, essential zinc binding histidine residues in the non-toxic B. cereus phospholipase C were found in similar positions in the toxic C. perfringens enzyme and the weakly toxic C. bifermentans phospholipase C.

Molecular cloning and nucleotide sequence of the alpha-toxin (phospholipase C) of Clostridium perfringens

A fragment of DNA containing the gene coding for the phospholipase C (alpha-toxin) of Clostridium perfringens was cloned into Escherichia coli. The cloned DNA appeared to code only for the alpha-toxin and contained both the coding region and its associated gene promoter. The nucleotide sequence of the cloned DNA was determined, and an open reading frame was identified which encoded a protein with a molecular weight of 42,528. By comparison of the gene sequence with the N-terminal amino acid sequence of the protein, a 28-amino-acid signal sequence was identified. The gene promoter showed considerable homology with the E. coli sigma 55 consensus promoter sequences, and this may explain why the gene was expressed by E. coli. The cloned gene product appeared to be virtually identical to the native protein. A 77-amino-acid stretch that was close to the N terminus of the alpha-toxin showed considerable homology with similarly located regions of the Bacillus cereus phosphatidylcholine, preferring phospholipase C and weaker homology with the phospholipase C from Pseudomonas aeruginosa.

Factors affecting the germination of spores of Bacillus anthracis

Spores of Bacillus anthracis germinated poorly at high cell densities unless the alanine racemase inhibitor O-carbamyl-D-serine was added to the germination medium. Spores derived from a variety of strains of B. anthracis germinated optimally at 22 degrees C. No correlation was found between rate of spore germination and virulence or between susceptibility of animal species to anthrax and spore germination rate using sera from those animals as the germination medium.

Role of caseinase from Aeromonas salmonicida in activation of hemolysin

Mutants of the bacterial fish pathogen Aeromonas salmonicida selected for inability to digest casein concomitantly lost hemolytic activity against horse erythrocytes under certain conditions. Mixtures of wild-type with mutant culture supernatants indicated that mutants produce an inactive precursor of a hemolysin which was activated by autogenous caseinase and, with less efficiency, by other serine proteases. Selective inhibition or repression of caseinase production in the wild-type strain also resulted in the production of an inactive precursor of a hemolysin. The precursor of hemolysin was also activated by a serum factor which appeared to exert its maximum effect at the bacterial surface or after entry into the bacterial cell. These results could affect the interpretation of studies evaluating the role of individual extracellular products in the pathogenesis of A. salmonicida infections.

The purification and some properties of H-lysin from Aeromonas salmonicida

H-lysin from Aeromonas salmonicida has been purified 1770-fold by freeze fractionation, ammonium sulphate precipitation, ion exchange chromatography and gel filtration chromatography. The purified material was predominantly H-lysin, devoid of detectable T-lysin, caseinase or gelatinase activity, although glycerophospholipid: cholesterol acyltransferase (GCAT) activity was present. The results suggested that H-lysin and GCAT activities were due to different extracellular products. Studies of the kinetics of haemolysis indicated that the H-lysin had an enzymic mode of action, and that initial erythrocyte damage appeared to precede lysis of the cell. The H-lysin was lethal to cultured rainbow trout gonad cells and leucocytes, but when it was injected intravenously in rainbow trout no pathological effects were observed.