Cloning and expression in Escherichia coli of the Streptococcus pneumoniae gene encoding pneumolysin

Mini-review: novel therapeutic strategies to blunt actions of pneumolysin in the lungs

Severe pneumonia is the main single cause of death worldwide in children under five years of age. The main etiological agent of pneumonia is the G+ bacterium Streptococcus pneumoniae, which accounts for up to 45% of all cases. Intriguingly, patients can still die days after commencing antibiotic treatment due to the development of permeability edema, although the pathogen was successfully cleared from their lungs. This condition is characterized by a dramatically impaired alveolar epithelial-capillary barrier function and a dysfunction of the sodium transporters required for edema reabsorption, including the apically expressed epithelial sodium channel (ENaC) and the basolaterally expressed sodium potassium pump (Na+-K+-ATPase). The main agent inducing this edema formation is the virulence factor pneumolysin, a cholesterol-binding pore-forming toxin, released in the alveolar compartment of the lungs when pneumococci are being lysed by antibiotic treatment or upon autolysis. Sub-lytic concentrations of pneumolysin can cause endothelial barrier dysfunction and can impair ENaC-mediated sodium uptake in type II alveolar epithelial cells. These events significantly contribute to the formation of permeability edema, for which currently no standard therapy is available. This review focuses on discussing some recent developments in the search for the novel therapeutic agents able to improve lung function despite the presence of pore-forming toxins. Such treatments could reduce the potentially lethal complications occurring after antibiotic treatment of patients with severe pneumonia.

Cloning and optimization of induction conditions for mature PsaA (pneumococcal surface adhesin A) expression in Escherichia coli and recombinant protein stability during long-term storage

The gene corresponding to mature PsaA from Streptococcus pneumoniae serotype 14 was cloned into a plasmid with kanamycin resistance and without a purification tag in Escherichia coli to express high levels of the recombinant protein for large-scale production as a potential vaccine candidate or as a carrier for polysaccharide conjugation at Bio-Manguinhos/Fiocruz. The evaluation of induction conditions (IPTG concentration, temperature and time) in E. coli was accomplished by experimental design techniques to enhance the expression level of mature recombinant PsaA (rPsaA). The optimization of induction process conditions led us to perform the recombinant protein induction at 25°C for 16 h, with 0.1mM IPTG in Terrific Broth medium. At these conditions, the level of mature rPsaA expression obtained in E. coli BL21 (DE3) Star by pET28a induction with IPTG was in the range of 0.8 g/L of culture medium, with a 10-fold lower concentration of inducer than usually employed, which contributes to a less expensive process. Mature rPsaA expressed in E. coli BL21 (DE3) Star accounted for approximately 30-35% of the total protein. rPsaA purification by ion exchange allowed the production of high-purity recombinant protein without fusion tags. The results presented in this work confirm that the purified recombinant protein maintains its stability and integrity for long periods of time in various storage conditions (temperatures of 4 or -70°C using different cryoprotectors) and for at least 3 years at 4 or -70°C in PBS. The conformation of the stored protein was confirmed using circular dichroism. Mature rPsaA antigenicity was proven by anti-rPsaA mouse serum recognition through western blot analysis, and no protein degradation was detected after long periods of storage.

Interaction of phase variation, host and pressure/gas composition: pneumococcal gene expression of PsaA, SpxB, Ply and LytA in simulated middle ear environments

OBJECTIVE

Streptococcus pneumoniae, a leading cause of otitis media (OM), undergoes spontaneous intra-strain variations in colony morphology. Transparent (T) variants are more efficient in colonizing the nasopharynx while opaque (O) variants exhibit greater virulence during systemic infections. This study was intended to delineate the underlying molecular mechanisms by which the predominant S. pneumoniae variant efficiently infects the middle ear (ME) mucosa.

METHODS

Human ME epithelial cells were preconditioned for 24h under one of the three gas/pressure conditions designed to simulate those for (1) normal ME (NME), (2) ME with Eustachian tube obstruction (ETO) and (3) ME with tympanostomy tube placement (TT), and then were incubated with ∼ 10(7)CFU/ml of either T or O variants of S. pneumoniae (6A) for 3h. Relative expression levels of genes encoding virulence factors, PsaA (surface adhesion), SpxB (pyruvate oxidase), Ply (pneumolysin), and LytA (autolysin) were assessed separately in epithelium-attached and supernatant bacteria 3h post infection using real-time PCR.

RESULTS

Basal levels of the virulence molecules in inocula were comparable between two variants. However, relative expression levels of the gene transcripts were significantly induced in epithelium-attached T variants 3h after infection. Comparing with NME and TT conditions, ETO environment produced the largest effect on the differential expression of the virulence genes in the infected ME epithelial cells between T (induced) and O (suppressed) phenotypic pneumococci.

CONCLUSIONS

T variant is a predominant phenotype responsible for the pathogenesis of pneumococcal OM.

Insights into the Mechanism of Action of Hyaluronate Lyase

Hyaluronate lyases (HLs) cleave hyaluronan and certain other chondroitin/chondroitin sulfates. Although native HL from Streptococcus agalactiae is composed of four domains, it finally stabilizes after autocatalytic conversion as a 92-kDa enzyme composed of the N-terminal spacer, middle alpha-, and C-terminal domains. These three domains are independent folding/unfolding units of the enzyme. Comparative structural and functional studies using the enzyme and its various fragments/domains suggest a relatively insignificant role of the N-terminal spacer domain in the 92-kDa enzyme. Functional studies demonstrate that the alpha-domain is the catalytic domain. However, independently it has a maximum of only about 10% of the activity of the 92-kDa enzyme, whereas its complex with the C-terminal domain in vitro shows a significant enhancement (about 6-fold) in the activity. It has been previously proposed that the C-terminal domain modulates the enzymatic activity of HLs. In addition, one of the possible roles for calcium ions was suggested to induce conformational changes in the enzyme loops, making HL more suitable for catalysis. However, we observed that calcium ions do not interact with the enzyme, and its role actually is in modulating the hyaluronan conformation and not in the functional regulation of enzyme.

The role of pneumolysin in pneumococcal pneumonia and meningitis

Diseases caused by Streptococcus pneumoniae include pneumonia, septicaemia and meningitis. All these are associated with high morbidity and mortality. The pneumococcus can colonize the nasopharynx, and this can be a prelude to bronchopneumonia and invasion of the vasculature space. Proliferation in the blood can result in a breach of the blood-brain barrier and entry into the cerebrospinal fluid (CSF) where the bacteria cause inflammation of the meningeal membranes resulting in meningitis. The infected host may develop septicaemia and/or meningitis secondary to bronchopneumonia. Also septicaemia is a common precursor of meningitis. The mechanisms surrounding the sequence of infection are unknown, but will be dependent on the properties of both the host and bacterium. Treatment of these diseases with antibiotics leads to clearance of the bacteria from the infected tissues, but the bacteriolytic nature of antibiotics leads to an acute release of bacterial toxins and thus after antibiotic therapy the patients can be left with organ-specific deficits. One of the main toxins released from pneumococci is the membrane pore forming toxin pneumolysin. Here we review the extensive studies on the role of pneumolysin in the pathogenesis of pneumococcal diseases.

Streptococcus pneumoniae hyaluronate lyase contains two non-cooperative independent folding/unfolding structural domains: characterization of functional domain and inhibitors of enzyme

Hyaluronate lyase contributes directly to bacterial invasion by degrading hyaluronan, the major component of host extracellular matrix of connective tissues. Streptococcus pneumoniae hyaluronate lyase (SpnHL) is built from two structural domains that interact through interface residues, in addition to being connected by a peptide linker. For the first time we demonstrate that the N- and C-terminal domains of SpnHL fold/unfold independent of each other suggesting the absence of any significant cooperative interactions between them. The C-terminal domain of SpnHL is less stable than the N-terminal domain against thermal and guanidine hydrochloride denaturation. The intact N-terminal domain was purified after limited proteolysis of SpnHL under conditions where only the C-terminal domain was unfolded. Isolated N-terminal domain of SpnHL had similar thermal stability as when present in the native enzyme and was found to be enzymatically active demonstrating that it is capable of carrying out enzymatic reaction on its own. Functional studies demonstrated that guanidine hydrochloride, guanidine isothiocyanate, l-arginine methyl ester, and l-arginine inhibit the enzymatic activity of SpnHL at very low concentrations. This provides a lead for new chemical entities that can be exploited for designing effective inhibitors of SpnHL.

The role of clostridial toxins in the pathogenesis of gas gangrene

Clostridium perfringens gas gangrene is, without a doubt, the most fulminant necrotizing infection that affects humans. In victims of traumatic injury, the infection can become well established in as little as 6-8 h, and the destruction of adjacent healthy muscle can progress several inches per hour despite appropriate antibiotic coverage. Shock and organ failure are present in 50% of patients and, among these, 40% die. Despite modern medical advances and intensive-care regimens, radical amputation remains the single best life-saving treatment. Over the past century, much has been learned about the pathogenesis of this disease, and novel therapies are on the horizon for patients with this devastating infection.

Mechanism of hyaluronan degradation by Streptococcus pneumoniae hyaluronate lyase. Structures of complexes with the substrate

Hyaluronate lyase enzymes degrade hyaluronan, the main polysaccharide component of the host connective tissues, predominantly into unsaturated disaccharide units, thereby destroying the normal connective tissue structure and exposing the tissue cells to various endo- and exogenous factors, including bacterial toxins. The crystal structures of Streptococcus pneumoniae hyaluronate lyase with tetra- and hexasaccharide hyaluronan substrates bound in the active site were determined at 1.52- and 2.0-A resolution, respectively. Hexasaccharide is the longest substrate segment that binds entirely within the active site of these enzymes. The enzyme residues responsible for substrate binding, positioning, catalysis, and product release were thereby identified and their specific roles characterized. The involvement of three residues in catalysis, Asn(349), His(399), and Tyr(408), is confirmed, and the details of proton acceptance and donation within the catalytic machinery are described. The mechanism of processivity of the enzyme is analyzed. The flexibility (allosteric) behavior of the enzyme may be understood in terms of the results of flexibility analysis of this protein, which identified two modes of motion that are also proposed to be involved in the hyaluronan degradation process. The first motion describes an opening and closing of the catalytic cleft located between the alpha- and beta-domains. The second motion demonstrates the mobility of a binding cleft, which may facilitate the binding of the negatively charged hyaluronan to the enzyme.

Pneumococcal virulence factors: structure and function

The overall goal for this review is to summarize the current body of knowledge about the structure and function of major known antigens of Streptococcus pneumoniae, a major gram-positive bacterial pathogen of humans. This information is then related to the role of these proteins in pneumococcal pathogenesis and in the development of new vaccines and/or other antimicrobial agents. S. pneumoniae is the most common cause of fatal community-acquired pneumonia in the elderly and is also one of the most common causes of middle ear infections and meningitis in children. The present vaccine for the pneumococcus consists of a mixture of 23 different capsular polysaccharides. While this vaccine is very effective in young adults, who are normally at low risk of serious disease, it is only about 60% effective in the elderly. In children younger than 2 years the vaccine is ineffective and is not recommended due to the inability of this age group to mount an antibody response to the pneumococcal polysaccharides. Antimicrobial drugs such as penicillin have diminished the risk from pneumococcal disease. Several pneumococcal proteins including pneumococcal surface proteins A and C, hyaluronate lyase, pneumolysin, autolysin, pneumococcal surface antigen A, choline binding protein A, and two neuraminidase enzymes are being investigated as potential vaccine or drug targets. Essentially all of these antigens have been or are being investigated on a structural level in addition to being characterized biochemically. Recently, three-dimensional structures for hyaluronate lyase and pneumococcal surface antigen A became available from X-ray crystallography determinations. Also, modeling studies based on biophysical measurements provided more information about the structures of pneumolysin and pneumococcal surface protein A. Structural and biochemical studies of these pneumococcal virulence factors have facilitated the development of novel antibiotics or protein antigen-based vaccines as an alternative to polysaccharide-based vaccines for the treatment of pneumococcal disease.

Structure and molecular mechanism of a functional form of pneumolysin: a cholesterol-dependent cytolysin from Streptococcus pneumoniae

One of the key steps in understanding human disease arising from gram-positive bacteria lies in the mechanisms of the cholesterol-dependent cytolysins (CDCs). Pneumolysin (PLY), a CDC from Streptococcus pneumoniae, is of special importance due to the severe impacts of pneumococcal infections on mortality and morbidity worldwide. We have overexpressed, purified, and characterized PLY in its fully functional complex form with the enzyme bound to its receptor activator on target cells, cholesterol. The circular dichroism studies of PLY in solution with an excess of cholesterol show a change in the far UV spectrum consistent with a decrease in the beta-sheet and an increase in the random coil structures of the enzyme. Pore formation in membranes leading to cell lysis is the functional target for this cytolysin. The sedimentation velocity and equilibrium analyses of the cholesterol-bound enzyme show hydrodynamic properties different from those of the cholesterol-free form. The soluble form of the cholesterol-free enzyme exists in solution as a mixture of monomers and dimers, whereas the cholesterol-bound form exists only as a monomer. A mechanism of formation of PLY pores in the lipid bilayer of the target cells is discussed.

The pathogenesis of clostridial myonecrosis

These pieces of evidence can be assimilated into a molecular and cellular model of pathogenesis which is initiated by direct toxin effects upon venous capillary endothelial cell function, leading to expression of pro-inflammatory mediators and adhesion molecules, and initiation of platelet aggregation. Toxin-induced hyperadhesion of leukocytes (see above section) with enhanced respiratory burst activity (due to toxins directly or to toxin-induced IL-8 or PAF synthesis by host cells) and toxin-induced chemotaxis deficits could result in neutrophil-mediated vascular injury. Direct toxin-induced cytopathic effects on EC may also contribute to vascular abnormalities associated with gas gangrene. Over prolonged incubation periods, PLC at sublytic concentrations causes EC to undergo profound shape changes similar to those described following prolonged TNF or interferon gamma exposure. In vivo, conversion of EC to this fibroblastoid morphology could contribute to the localized vascular leakage and massive swelling observed clinically with this infection. Similarly, the direct cytotoxicity of PFO could disrupt endothelial integrity and contribute to progressive edema both locally and systemically. Thus, via the mechanisms outlined above, both PLC and PFO may cause local, regional and systemic vascular dysfunction. For instance, local absorption of exotoxins within the capillary beds could affect the physiological function of the endothelium lining the postcapillary venules, resulting in impairment of phagocyte delivery at the site of infection. Toxin-induced endothelial dysfunction and microvascular injury could also cause loss of albumin, electrolytes, and water into the interstitial space resulting in marked localized edema. These events, combined with intravascular platelet aggregation and leukostasis, would increase venous pressures and favor further loss of fluid and protein in the distal capillary bed. Ultimately, a reduced arteriolar flow would impair oxygen delivery thereby attenuating phagocyte oxidative killing and facilitating anaerobic glycolysis of muscle tissue. The resultant drop in tissue pH, together with reduced oxygen tension, might further decrease the redox potential of viable tissues to a point suitable for growth of this anaerobic bacillus. As infection progresses and additional toxin is absorbed, larger venous channels would become affected, causing regional vascular compromise, increased compartment pressures and rapid anoxic necrosis of large muscle groups. When toxins reach arterial circulation, systemic shock and multiorgan failure rapidly ensue, and death is common.

Virulence factors and the pathogenesis of disease caused by Streptococcus pneumoniae

Streptococcus pneumoniae is a major pathogen of man causing diseases such as pneumonia, meningitis and otitis media. The mechanisms by which this organism causes these diseases are still largely unknown. The use of molecular approaches to identifying and studying putative virulence factors in combination with the application of animal models has allowed some of the mechanisms of the disease process to be defined.

Biological properties of pneumolysin

Pneumolysin is a thiol-activated membrane-damaging toxin produced by Streptococcus pneumoniae. The toxin plays a role in virulence of the pneumococcus in animal models of infection. Pneumolysin has a range of biological activity including the ability to lyse eukaryotic cells and to interfere with the function of cells and soluble molecules of the immune system. The use of purified native and mutant toxin and of isogenic mutants of the pneumococcus expressing altered versions of the toxin has allowed the contribution of the various activities of this multifunctional toxin to virulence to be defined.

A genomic analysis of two-component signal transduction in Streptococcus pneumoniae

A genomics-based approach was used to identify the entire gene complement of putative two-component signal transduction systems (TCSTSs) in Streptococcus pneumoniae. A total of 14 open reading frames (ORFs) were identified as putative response regulators, 13 of which were adjacent to genes encoding probable histidine kinases. Both the histidine kinase and response regulator proteins were categorized into subfamilies on the basis of phylogeny. Through a systematic programme of mutagenesis, the importance of each novel TCSTS was determined with respect to viability and pathogenicity. One TCSTS was identified that was essential for the growth of S. pneumoniaeThis locus was highly homologous to the yycFG gene pair encoding the essential response regulator/histidine kinase proteins identified in Bacillus subtilis and Staphylococcus aureus. Separate deletions of eight other loci led in each case to a dramatic attenuation of growth in a mouse respiratory tract infection model, suggesting that these signal transduction systems are important for the in vivo adaptation and pathogenesis of S. pneumoniae. The identification of conserved TCSTSs important for both pathogenicity and viability in a Gram-positive pathogen highlights the potential of two-component signal transduction as a multicomponent target for antibacterial drug discovery.

Validation of immune-complex enzyme immunoassays for diagnosis of pneumococcal pneumonia among adults in Kenya

The efficacy of pneumococcal vaccines in protecting against pneumococcal pneumonia can feasibly be measured only with a diagnostic technique that has a high specificity (0.98 to 1.00) and a sensitivity greatly exceeding that of blood cultures (>0.2 to 0.3). In this context immune-complex enzyme immunoassays (EIAs) offer a novel, convenient diagnostic method, and we have investigated three such assays with appropriate study populations in Kenya. Sera from 129 Kenyan adults with pneumococcal pneumonia and 97 ill controls from the same clinics, but without pneumococcal disease syndromes, were assayed with immune-complex EIAs for pneumolysin, C-polysaccharide, and mixed capsular polysaccharides (Pneumovax II). At an optical density (OD) threshold yielding a specificity of 0.95, the sensitivities (95% confidence intervals) of the assays were 0.22 (0.15 to 0.30), 0.26 (0.19 to 0.34), and 0.22 (0.15 to 0.29), respectively. For pneumolysin immune complexes, human immunodeficiency virus (HIV)-positive patients had a higher mean OD than HIV-negative patients (639 versus 321; P < 0.0001), but stratification by HIV infection status did not alter the performance of this test. Combining the results of all three EIAs did not enhance the diagnostic performances of the individual assays. In Kenyan adults the sensitivities of the immune-complex EIAs could exceed that of blood cultures only at levels of specificity that were insufficient for the performance of vaccine efficacy studies.

Presence of the Streptococcus suis suilysin gene and expression of MRP and EF correlates with high virulence in Streptococcus suis type 2 isolates

Nineteen Streptococccus suis type 2 isolates that had been analyzed previously for hemolysin production, ribotype, and virulence in pigs were examined for presence of the gene coding for suilysin by PCR amplification, and southern blot and hybridization techniques. Based on southern blot and hybridization analysis, all isolates tested contained at least a portion of the suilysin gene. PCR amplification of the entire gene resulted in gene fragments from five of the seven highly virulent isolates and none of the moderately virulent or avirulent isolates. Additional PCR analysis showed that mutation or deletions at the 5' end of the suilysin gene in the less virulent isolates prevented amplification of the sly gene fragment from those isolates. The MRP+ (muramidase-released protein) EF+ (extracellular protein) phenotype was also expressed by the same five highly virulent/sly+ isolates.

Novel expansions of the gene encoding dihydropteroate synthase in trimethoprim-sulfamethoxazole-resistant Streptococcus pneumoniae

A study of eight sulfonamide-resistant clinical isolates of Streptococcus pneumoniae revealed chromosomal mutations within the gene encoding dihydropteroate synthase that play a role in conferring resistance to sulfamethoxazole. The presence of the suld mutation, found previously only in a laboratory mutant, was shown to occur in three of the wild-type clinical isolates. The duplication of Ser(61), the other previously defined mutation in the dihydropteroate synthase gene of S. pneumoniae, was observed in only one of the isolates characterized. We report two previously unidentified amino acid alterations, namely, a duplication of Arg(58) and Pro(59) and an insertion of an arginine residue between Gly(60) and Ser(61) in trimethoprim-sulfamethoxazole-resistant strains. The significance of these mutations was confirmed by site-directed mutagenesis and by the transformation of a susceptible strain of S. pneumoniae to sulfamethoxazole resistance. Two resistant isolates did not contain any mutations within the gene encoding dihydropteroate synthase. The results presented suggest the independent generation of resistant mutations among South African clinical isolates. It is also proposed that the mechanism of sulfonamide resistance in S. pneumoniae involves the expansion of a specific region within dihydropteroate synthase, which probably forms part of the sulfonamide binding site.

Pneumolysin: a multifunctional pneumococcal virulence factor

Pneumolysin (PLY) is a multifunctional pneumococcal virulence factor that appears to augment intrapulmonary growth and dissemination during the early pathogenesis of Streptococcus pneumoniae infection. Through its cytotoxicity to respiratory epithelium and endothelium, PLY disrupts pulmonary tissue barriers that serve as mechanical pulmonary defenses, thus facilitating S. pneumoniae growth and dissemination. Through direct inhibitory effects on immune and inflammatory cells and by activating complement, PLY inhibits bacterial clearance from the pulmonary interstitium and the blood. Because PLY stimulates local and systemic immune responses and enhances the immunogenicity of S. pneumoniae polysaccharide (PS), PLY-PS conjugates may form the basis for vaccines that not only induce protective and durable immune responses to pneumococcal PS but also generate neutralizing anti-PLY antibodies that can protect the respiratory mucosa from toxin-induced injury.

Emergence of the M phenotype of erythromycin-resistant pneumococci in South Africa

Erythromycin-resistant pneumococci have been isolated in South Africa since 1978; however, from 1987 to 1996, resistance to macrolides was only detected in 270 (2.7%) of 9,868 blood or cerebrospinal fluid (CSF) pneumococcal isolates, most of which were obtained from the public sector. In South Africa, macrolide use in the public sector is estimated at 56% of that in the private sector. Most erythromycin-resistant strains (89%) exhibited resistance to erythromycin and clindamycin (macrolide-lincosamide-streptogramin B phenotype). In the United States, most erythromycin-resistant pneumococci exhibit the newly described M phenotype (resistance to erythromycin alone), associated with the mefE gene. The M phenotype in South Africa increased significantly in the last 10 years, from 1 of 5,115 to 28 of 4,735 of blood and CSF isolates received from 1987 to 1991 compared with 1992 to 1996 (p = 5 x 10(-7)). These data suggest that, although macrolide resistance in pneumococci remains low in the public sector, the mefE gene is rapidly emerging in South Africa.

Molecular and genetic characterization of the capsule biosynthesis locus of Streptococcus pneumoniae type 19B

We have previously reported the nucleotide sequence of the Streptococcus pneumoniae type 19F capsular polysaccharide synthesis locus (cps19f), which consists of 15 open reading frames (ORFs) designated cps19fA to -O. Hybridization analysis indicated that close homologs for cps19fA to -H and cps19fK to -O were found in type 19B, but there were no homologs for cps19fI and -J. In this study we used long-range PCR to amplify and clone a 10.5-kb section of the S. pneumoniae type 19B capsule locus (cps19b) between cps19bH and cps19bK. This region of the cps19b locus is 4 kb larger than that in the cps19f locus and replaces cps19fI and cps19fJ with five new ORFs, designated cps19bP, -I, -Q, -R, and -J. We have proposed functions for four of the protein products, including functional homologs of Cps19fI and Cps19fJ. Transformation of a S. pneumoniae mutant containing an interrupted type 19F capsule locus with the 10.5-kb cps19b PCR product converted the recipient strain to type 19B. Southern hybridization analysis indicated that cps19bP, -I, -Q, -R, and -J are unique to type 19B and the closely related type 19C.

Identification of the tetracycline resistance gene, tet(O), in Streptococcus pneumoniae

Five isolates of Streptococcus pneumoniae resistant to tetracycline but lacking tet(M) were studied. The tetracycline resistance gene, tet(O), was detected for the first time in the pneumococcus. The gene was amplified and sequenced and found to share 99% nucleotide sequence identity and 99, 99, and 98% deduced amino acid sequence identity with the tet(O) resistance genes of Streptococcus mutans, Campylobacter coli, and Campylobacter jejuni, respectively.

Sequence heterogeneity of PsaA, a 37-kilodalton putative adhesin essential for virulence of Streptococcus pneumoniae

psaA encodes a 37-kDa putative pneumococcal surface adhesin. Although its complete nucleotide sequence has been determined, its contribution to the pathogenicity of Streptococcus pneumoniae has not previously been assessed. In this study, we used a PCR-amplified internal fragment of the psaA gene from S. pneumoniae type 2 strain D39 cloned in pVA891, to direct the construction of D39 derivatives in which the psaA gene had been specifically interrupted, by insertion-duplication mutagenesis. Two independent D39 psaA mutants (PsaA-(1) and PsaA-(2)) were significantly less virulent (as judged by intranasal or intraperitoneal challenge of mice) than either the wild-type D39 strain or a derivative of PsaA-(1) in which the psaA gene had been reconstituted by back-transformation with an intact copy of the cloned gene. pVA891-directed mutagenesis of an open reading frame (designated ORF3) immediately 3' to psaA or insertion of pVA891 between psaA and ORF3 had no impact on intranasal virulence. However, a small but significant difference in virulence was observed between these two derivatives and the parental D39 strain in a low-dose intraperitoneal challenge model, suggesting that the ORF3 product may also contribute to pathogenesis. Adherence of PsaA-(1) to A549 cells (type II pneumocytes) was only 9% of that for D39, while the ORF3-negative strain exhibited intermediate adherence (23%). This is the first functional evidence that PsaA is an adhesin. Sequence analysis of the psaA gene from D39 indicated significant deviation from that previously published for the homolog from S. pneumoniae R36A. The deduced amino acid sequences of mature PsaA from the two strains had only 81% homology, with the bulk of the variation occurring in the amino-terminal portion.

Cloning and characterization of nanB, a second Streptococcus pneumoniae neuraminidase gene, and purification of the NanB enzyme from recombinant Escherichia coli

Streptococcus pneumoniae is believed to produce more than one form of neuraminidase, but there has been uncertainty as to whether this is due to posttranslational modification of a single gene product or the existence of more than one neuraminidase-encoding gene. Only one stable pneumococcal neuraminidase gene (designated nanA) has been described. In the present study, we isolated and characterized a second neuraminidase gene (designated nanB), which is located close to nanA on the pneumococcal chromosome (approximately 4.5kb downstream). nanB was located on an operon separate from that of nanA, which includes at least five other open reading frames. NanB has a predicted size of 74.5 kDa after cleavage of a 29-amino-acid signal peptide. There was negligible amino acid homology between NanA and NanB, but NanB did exhibit limited homology with the sialidase of Clostridium septicum. NanB was purified from recombinant Escherichia coli and found to have a pH optimum of 4.5, compared with 6.5 to 7.0 for NanA. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis suggested that NanB has a molecular size of approximately 65 kDa. The discrepancy between this estimate and the size predicted from the nucleotide sequence is most likely a consequence of C-terminal processing or anomalous electrophoretic behavior.

Comparison of serum antibodies to pneumolysin with those to pneumococcal capsular polysaccharides in children with acute otitis media

BACKGROUND

Streptococcus pneumoniae is a major bacterial pathogens in acute otitis media. Pneumolysin is a species-specific protein toxin produced intracellularly by all clinically relevant pneumococcal strains, and antibodies to pneumolysin should therefore represent pneumococcal involvement in the disease, regardless of the serotype.

METHODS

Antibodies to pneumococcal pneumolysin and capsular polysaccharides were measured by enzyme immunoassay in acute and convalescent sera of 121 children with acute otitis media. A pneumococcal otitis episode was defined by a positive middle ear fluid culture and/or pneumolysin PCR.

RESULTS

Median age of the 10 children who developed a seroconversion response to pneumolysin was 1 year 8 months, and of the 21 children responding to polysaccharides it was 2 years 9 months. Eight of the 10 seroconversion responses to pneumolysin were of IgA class alone, whereas 17 of the 21 polysaccharide responses were of IgG class alone or IgG together with IgM and/or IgA. Of the 41 children with a pneumococcal otitis episode, 13 (39%) showed a seroconversion response, 3 (7%) to pneumolysin and 11 (27%) to capsular polysaccharides. The children with a pneumococcal otitis episode had lower titers of acute phase IgG to the capsular polysaccharide pool of S. pneumoniae (containing types 6B, 14, 19F and 23F), as compared with the titers in children with otitis caused by other pathogens and pneumococci only in the nasopharynx or not found at all (P = 0.04).

CONCLUSIONS

Serum antibodies to pneumolysin can be detected at an earlier age than those to the capsular polysaccharides. However, a seroconversion is rare and therefore of no diagnostic value. The presence of serum IgG to the pneumococcal capsular polysaccharides seems beneficial in the prevention of pneumococcal otitis.

Antibodies to pneumolysin and pneumococcal capsular polysaccharides in middle ear fluid of children with acute otitis media

Antibodies to pneumococcal pneumolysin and capsular polysaccharides were measured by enzyme immunoassay in 169 acute phase middle ear fluid samples of 116 children with acute otitis media. Antibodies to pneumococcal pneumolysin were detected in 84% and to capsular polysaccharides in 50% of the MEF samples. The Ig class detected most often was IgA to both types of pneumococcal antigens, and it was present in MEF even with non-detectable levels of serum IgA of the same specificity. 59% of the MEF samples positive for IgA to pneumolysin were also positive for secretory component of the same specificity, and 53% of IgA to capsular polysaccharide pool (containing serotypes 6B, 14, 19F, and 23F), respectively. This suggests both leakage of specific IgA from serum to the middle ear and local production of it. In contrast, specific IgG was detected in MEF only with concomitant IgG in serum. Antibodies to pneumolysin occurred in no relation to bacterial findings in MEF. On the contrary, IgG class antibodies to capsular polysaccharides, most likely serum-derived, were detected less often in MEF samples positive for pneumococcus than for other bacteria.

Characterization of a recombinant pneumolysin and its use as a protein carrier for pneumococcal type 18C conjugate vaccines

Pneumolysin from Streptococcus pneumoniae was expressed in Escherichia coli as a glutathione S-transferase fusion protein and purified by affinity and hydroxylapatite chromatography. The purified recombinant pneumolysin (rPL), with a molecular mass of 53 kDa, had a specific activity of 3 x 10(5) hemolytic units per mg of protein on rabbit erythrocytes and reacted identically in immunodiffusion with the antisera against native pneumolysin. The rPL was used as a protein carrier to prepare conjugate vaccine with pneumococcal type 18C polysaccharide (PS18C). The PS18C was directly coupled to rPL by reductive animation or was indirectly coupled to rPL via a spacer molecule, adipic acid dihydrazide. The conjugates were nontoxic for mice and guinea pigs at 100 micrograms per dose. The immunogenicity and protective efficacy of both conjugates were tested in mice. A single dose of either of the vaccines elicited a rise in immunoglobulin G antibody production; after two booster injections of the vaccines, statistically significant booster responses (P < 0.001) to both rPL and PS18C were produced. The sera containing the antibodies to rPL were capable of neutralizing the hemolytic activity of rPL to rabbit erythrocytes and the cytotoxicity of rPL to bovine pulmonary endothelial cells. Immunization with the conjugate vaccines conferred statistically significant protection in mice against lethal challenge with type 18C pneumococci.

Effect of defined point mutations in the pneumolysin gene on the virulence of Streptococcus pneumoniae

The thiol-activated toxin pneumolysin is a known pneumococcal virulence factor, with both cytotoxic (hemolytic) and complement activation properties. Copies of the pneumolysin gene carrying defined point mutations affecting either or both of these properties were introduced into the chromosome of Streptococcus pneumoniae D39 by insertion-duplication mutagenesis. The virulences of these otherwise isogenic strains were then compared. There was no significant difference in either the median survival time or overall survival rate between mice challenged with D39 derivatives producing the wild-type toxin and those expressing a pneumolysin gene with an Asp-385-->Asn mutation, which abolishes the complement activation property. However, mice challenged with strains carrying either His-367-->Arg or Trp-433-->Phe plus Cys-428-->Gly mutations, which reduce hemolytic activity to approximately 0.02 and 0.0001% of the wild-type level, respectively, had significantly greater median survival times and overall survival rates than mice challenged with D39 derivatives expressing a wild-type pneumolysin gene. No additional reduction in virulence was observed when mice were challenged with a D39 derivative carrying Trp-433-->Phe, Cys-428-->Gly, and Asp-385-->Asn, rather than Trp-433-->Phe and Cys-428-->Gly, mutations in the pneumolysin gene. Thus, it appears that in the intraperitoneal challenge model, the contribution of pneumolysin to virulence is largely attributable to its hemolytic (cytotoxic) properties rather than to its capacity to activate complement. Interestingly, however, the amount of pneumolysin required for full virulence may be very small, as D39 derivatives carrying the Trp-433-->Phe mutation (which reduces hemolytic activity to 0.1% of the wild-type level) had intermediate virulence.

Nucleotide sequence analysis of genes essential for capsular polysaccharide biosynthesis in Streptococcus pneumoniae type 19F

Previous studies have shown that the capsular polysaccharide synthesis (cps) locus of the type 19F Streptococcus pneumoniae strain SSZ was closely linked to a copy of the insertion sequence IS1202 (J.K. Morona, A. Guidolin, R. Morona, D. Hansman, and J.C. Paton, J. Bacteriol. 176:4437-4443, 1994). In the present study, we used plasmid insertion and rescue and inverse PCR to clone 6,322 bp of flanking DNA upstream of IS1202. Sequence analysis indicated that this region contains six complete open reading frames (ORFs) and one partial ORF that are arranged as a single transcriptional unit. Chromosomal disruption of any of these ORFs in a smooth-type 19F strain leads to a rough (unencapsulated) phenotype, indicating that this operon is essential for capsule production. The ORFs have therefore been designated cps19fA to cps19fG, where cps19fA is the first gene of the type 19F cps locus. Furthermore, many of the gene products from this incomplete operon exhibit strong similarities to proteins known to be involved in the production of capsular polysaccharide, exopolysaccharide, teichoic acid, enterobacterial common antigen, and lipopolysaccharide from numerous other bacterial species. This has allowed us to propose functions for many of the type 19F cps gene products. Southern hybridization studies reveal that cps19fA and cps19fB are conserved among all 12 pneumococcal serotypes tested, whereas genes downstream of cps19fB are conserved among some, but not all, of the serotypes tested.

Isolation, characterization, and nucleotide sequence of IS1202, an insertion sequence of Streptococcus pneumoniae

A comparative hybridization protocol was used to isolate a small segment of DNA present in the Streptococcus pneumoniae type 19F strain SSZ but absent from strain Rx1, a nonencapsulated derivative of the type 2 strain D39. This segment of DNA is a 1,747-bp insertion sequence, designated IS1202, flanked by 23-bp imperfect inverted repeats and containing a single open reading frame sufficient to encode a 54.4-kDa polypeptide. A 27-bp target sequence is duplicated at either end of the element. IS1202 is not related to any of the currently known insertion elements and is the first reported for S. pneumoniae. Although found predominantly in type 19F strains in up to five copies, it has also been shown to be present in the chromosomes of pneumococci belonging to other serotypes. One of the four IS1202 copies in the encapsulated strain SSZ is located 1,009 bp downstream of the dexB gene, and transformation studies reveal that it is also closely linked to the type 19F capsular polysaccharide synthesis (cps) locus.

Cloning and nucleotide sequence of the Streptococcus pneumoniae hyaluronidase gene and purification of the enzyme from recombinant Escherichia coli

A gene bank of Sau3A1-generated Streptococcus pneumoniae type 23 DNA fragments was constructed in Escherichia coli K-12 with the low-copy-number cosmid vector pOU61cos. Clone lysates were screened by immunoblotting using a mouse antiserum raised against a crude pneumococcal hyaluronidase preparation. One immunoreactive clone was isolated, and it produced high level of hyaluronidase activity. This clone contained a recombinant cosmid (designated pJCP800) with an approximately 35-kb DNA insert, and the putative hyaluronidase coding sequence was subcloned into pBluescript SK as a 3.8-kb PstI-ClaI fragment (designated pJCP802). The complete nucleotide sequence of this insert was determined. The region included an open reading frame sufficient to encode a polypeptide with an M(r) of 107,751. An active hyaluronidase with an M(r) of approximately 89,000 was purified to homogeneity from E. coli DH5 alpha(pJCP802). N-terminal amino acid sequence analysis of the purified protein suggested that translation initiation was occurring primarily at a TTG codon within the major open reading frame. However, immunoblot analysis using antiserum raised against the purified 89-kDa hyaluronidase indicated that E. coli DH5 alpha(pJCP802) also expressed the 107-kDa form of the enzyme. This antiserum labelled a 107-kDa protein in partially purified hyaluronidase preparations from S. pneumoniae. The hyaluronidase activity in this pneumococcal extract was also neutralized by the antiserum.

Clostridium perfringens invasiveness is enhanced by effects of theta toxin upon PMNL structure and function: the roles of leukocytotoxicity and expression of CD11/CD18 adherence glycoprotein

Clostridium perfringens infections are characterized by the lack of an inflammatory response at the site of infection and rapidly progressive margins of tissue necrosis. Studies presented here investigated the role of theta toxin from C. perfringens in the pathophysiology of these events. Mice passively immunized with neutralizing monoclonal antibody against theta toxin and challenged with an LD100 of log phase C. perfringens had significantly less mortality than untreated controls. Intramuscular injection of killed, washed C. perfringens in mice induced a massive time-dependent influx of polymorphonuclear leukocytes (PMNL) into tissue; injection of either viable, washed C. perfringens or killed organisms plus theta toxin dramatically attenuated PMNL influx although PMNL accumulated in adjacent vessels. The anti-inflammatory effects could not be attributed to an absence of chemoattractants since C. perfringens proteins had chemotactic factor activity, and killed bacilli generated serum-derived chemotactic factors. Scanning and transmission electron microscopy demonstrated the dramatic leukocidal effects of high doses of theta toxin on PMNL. In contrast, sublethal concentrations of theta toxin primed PMNL chemiluminescence, disrupted PMNL cytoskeletal actin polymerization/disassembly, and stimulated functional upregulation of CD11b/CD18 adherence glycoprotein. In summary, these results demonstrate that theta toxin is an important virulence factor in C. perfringens infection. In a concentration-dependent fashion, theta toxin contributes to the pathogenesis of clostridial gangrene by direct destruction of host inflammatory cells and tissues, and by promoting dysregulated PMNL/endothelial cell adhesive interactions.

Mapping of immunoreactive sites of pneumococcal pneumolysin by use of synthetic peptides

In the search for better diagnostic tools and improved vaccines against pneumococcal diseases, continuous antigenic sites of the pneumococcal pneumolysin molecule were identified with partially overlapping synthetic peptides. Peptides were derived from the predicted amino acid sequence according to the known DNA sequence of pneumolysin. The immunoreactivities of the peptides were studied by enzyme immunoassay with seven human serum samples and three rabbit hyperimmune serum samples. Two immunoreactive sites in the overlapping peptides at the amino-terminal end of the pneumolysin molecule were identified in this study. Two common immunoreactive sites for both human and rabbit sera were demonstrated.

Characterization of hemolytic bacteria in subgingival plaque

Three-quarters of the patients with periodontal diseases surveyed in this study had one or more distinct types of hemolytic bacteria in their subgingival plaque. Twelve different species of bacteria were identified, belonging to five genera (Actinomyces, Streptococcus, Staphylococcus, Prevotella, and Actinobacillus). Nine hemolytic isolates, consisting of four Prevotella denticola strains, two Actinomyces naeslundii genospecies 2 strains, and one each of P. melaninogenica, Streptococcus constellatus, and A. naeslundii genospecies 1 strains were characterized. Incorporation of pronase into blood agar medium inhibited hemolysis by all of the isolates, suggesting a proteinaceous component for each of their hemolysins. With one exception, hemolysin production appeared to be regulated by the concentration of environmental iron: exogenous hemin was found to inhibit hemolysin production, and the iron scavenging compound, 2,2'- dipyridyl, was found to promote hemolysin production by all of the strains except for the S. constellatus isolate. Genomic libraries of each of the hemolytic plaque isolates were prepared in Escherichia coli using pBR322. Hemolytic clones were isolated on blood agar medium containing ampicillin at frequencies ranging from 1-6.7 x 10(-4). Extensive restriction mapping revealed regions of homology in the case of clones derived from three P. denticola strains isolated from the same subjects. Two of the P. denticola-derived clones were virtually identical throughout the entrety of their > 5 Kb inserts. The clone derived from the third strain showed good homology to the other two within a 1.3 Kb region, but the flanking DNA showed no homology even though all three P. denticola isolates were shown to be clonally related by ribotyping.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of insertional inactivation of the genes encoding pneumolysin and autolysin on the virulence of Streptococcus pneumoniae type 3

Derivatives of Streptococcus pneumoniae type 3 deficient in production of either pneumolysin or autolysin were constructed. This was achieved by transformation of type 3 pneumococci with DNA from derivatives of a rough strain (Rx1), in which the respective genes had been interrupted by insertion-duplication mutagenesis using internal fragments of the cloned genes in the vector pVA891. Southern blot analysis confirmed that the pneumolysin or autolysin genes in the respective transformants had been interrupted by insertion of the plasmid-derived sequences. Both the pneumolysin-negative and the autolysin-negative strains had significantly reduced (P less than 0.0001) virulence in mice, as judged by survival time after intraperitoneal challenge. The median survival time of mice challenged with type 3 pneumococci in which either pneumolysin or autolysin production had been reconstituted by back-transformation of the mutants with an intact copy of the respective cloned gene (with concomitant elimination of plasmid-derived sequences), was indistinguishable from that of mice challenged with the wild-type strain. These results establish the importance of both pneumolysin and autolysin to the virulence of type 3 pneumococci.

Purification and immunogenicity of genetically obtained pneumolysin toxoids and their conjugation to Streptococcus pneumoniae type 19F polysaccharide

As part of an ongoing study concerned with improving human vaccines against Streptococcus pneumoniae, the genes for two defined pneumolysin (PL) toxoids (pneumolysoids), Pd-A (PL with a Cys----Gly substitution at amino acid 428) and Pd-B (PL with a Trp----Phe substitution at position 433), were inserted into the high-expression vector pKK233-2 in Escherichia coli and the pneumolysoids were purified. Groups of mice which had been immunized with either Pd-A, Pd-B, or native PL purified from S. pneumoniae were then challenged either intranasally or intraperitoneally with virulent pneumococci. Mice in all immunized groups survived significantly longer than sham-immunized controls. Both pneumolysoids were more effective than PL as protective immunogens. Pneumolysoid Pd-B was conjugated covalently with pneumococcal type 19F capsular polysaccharide (19F PS), and the immunogenicities of both the protein and the PS moieties of the conjugate in mice were determined. Significant anti-PL titers were obtained, and the immunogenicity of the 19F PS moiety was markedly enhanced compared with that of unconjugated PS. Conjugation also appears to have converted the 19F PS into an antigen capable of inducing a booster effect. These results support the notion that the efficacy of human, PS-based antipneumococcal vaccines might be improved by supplementation with pneumolysoid in the form of a covalent pneumolysoid-PS conjugate.

Virulence, immunity, and vaccine related to Streptococcus pneumoniae

The pathogenesis of bacterial infection involves a series of interactions between the virulence determinants of the microorganisms and the immunity of the host. Studies on the molecular structure and immunological properties of pneumococcal virulence factors have provided general knowledge for the chemical basis of immunogenicity and prevention of bacterial infection. Antibody responses to PS and protein antigens can be greatly affected by their physicochemical properties, e.g., molecular size, specific determinants, conformation, etc. Characterization of group 19 pneumolysins and cloning of their ply genes were studied to examine the relationship of ply to virulence. Group 19 pneumococci all contained ply; the disease-isolated types of 19F and 19A appeared to show a higher specific hemolytic activity and yield than the nonpathogenic types, 19B and 19C. Genomic DNA that contained the ply gene from group 19 strains were analyzed by the polymerase chain reaction (PCR). Type 2 oligonucleotide primers recognized and initiated synthesis of an identical 1.5 kb DNA fragment in types 2, 19F, 19A, 19B, and 19C. Their sizes of restriction DNA fragments were also found to be homologous. Thus, group 19 ply genes showed remarkably similar characteristics. A difficult problem in the development of vaccines against bacterial diseases is the poor immune response of young children to purified PSs. The efficacy of pneumococcal vaccine might be improved by supplementation with inactivated pneumolysin in the form of a PS-protein conjugate.

Measurement of antibody responses to pneumolysin--a promising method for the presumptive aetiological diagnosis of pneumococcal pneumonia

An enzymeimmunoassay (EIA) for measuring antibodies to pneumococcal pneumolysin has been developed. The method was used to study the possible pneumococcal aetiology of pneumonia in 159 mostly elderly patients admitted to hospital because of a positive chest X-ray. The results obtained with the assay were compared to those obtained by other diagnostic methods, namely blood culture, detection of pneumococcal antigen in urine and demonstration of an antibody response to pneumococcal C-polysaccharide and capsular polysaccharides. Antibody response to pneumolysin was found in 32 of 39 (82%) patients with pneumococcal pneumonia aetiologically diagnosed presumptively by other methods. In addition, the EIA for pneumolysin antibodies was positive in 31 patients without evidence of pneumococcal aetiology by other methods. The clinical and laboratory investigations of these patients supported the presumption of bacterial infection. We conclude that the EIA we have developed for measuring pneumolysin antibodies is a promising, sensitive method for the presumptive aetiological diagnosis of pneumococcal pneumonia. The assay is simple to perform because only one antigen is needed and measurement of IgG antibodies alone seems to be enough for aetiological diagnosis.

Contribution of autolysin to virulence of Streptococcus pneumoniae

Insertion-duplication mutagenesis was used to construct an autolysin-negative derivative of Streptococcus pneumoniae. This derivative was obtained by first transforming the nonencapsulated strain Rx1 with a derivative of the vector pVA891 carrying a 375-base-pair TaqI DNA fragment from the middle of the autolysin structural gene. DNA was extracted from the resultant erythromycin-resistant, autolysin-negative rough pneumococcus and used to transform S. pneumoniae D39, a virulent type 2 strain. Several erythromycin-resistant transformants were obtained from two independent experiments, and none of these transformants produced autolysin. Southern blot analysis confirmed that the autolysin gene in these transformants had been interrupted by the plasmid-derived sequences. The autolysin-negative mutants showed markedly reduced virulence for mice compared with that of strain D39; intranasal and intraperitoneal 50% lethal doses were increased 10(2)- and 10(5)-fold, respectively. Autolysin production was reinstated in one of the mutants by back-transformation with the cloned autolysin gene, with the concomitant loss of erythromycin resistance; the virulence of this isolate for mice was indistinguishable from that of D39. The importance of autolysin in pathogenesis was confirmed by immunization-challenge studies. Mice immunized with purified autolysin survived significantly longer than did control mice after intranasal challenge with strain D39. This study provides direct evidence that the pneumococcal autolysin contributes to virulence and identifies it as a potential vaccine antigen.

Production of pneumolysin, a pneumococcal toxin, in Bacillus subtilis

We have expressed the pneumolysin gene of Streptococcus pneumoniae in Bacillus subtilis, both from its own promoter and as a fusion protein. The level of expression of pneumolysin from its own promoter was low. The protein produced was hemolytically active. A higher level of expression (about 10 micrograms/ml of culture) was achieved when either one of two C-terminal fragments (corresponding to amino acids 265-471 and 55-471, respectively) or the entire coding part of the pneumolysin gene were fused to the promoter and signal sequence-coding region of the alpha-amylase gene of Bacillus amyloliquefaciens. The C-terminal fusion peptides reacted with anti-pneumolysin serum, but were not hemolytically active. In both cases most of the peptide remained cell-associated. When the entire pneumolysin gene was fused to the signal sequence, a hemolytically active form of pneumolysin could be detected, and most of the product was found in a processed form in the culture supernatant. The full-length pneumolysin secreted from B. subtilis was partially purified and used as antigen in an enzyme immunoassay with rabbit anti-pneumolysin serum.

Nucleotide sequence of the gene for perfringolysin O (theta-toxin) from Clostridium perfringens: significant homology with the genes for streptolysin O and pneumolysin

The nucleotide sequence was determined for the gene encoding the thiol-activated cytolysin, perfringolysin O (theta-toxin), from Clostridium perfringens. The nucleotide-sequence-derived primary structure of perfringolysin O is 499 residues long and exhibits a 27-amino-acid signal peptide. The calculated molecular weight of the secreted (mature) form of perfringolysin O is 52,469. The deduced amino-terminal sequence of perfringolysin O is identical to that determined for purified perfringolysin O. Hydropathy analysis indicated that, except for the signal peptide, no major stretches of hydrophobic residues are present. Extensive amino acid sequence homology (65%) was detected with the low-molecular-weight form of streptolysin O, and a lesser amount (42%) was detected with pneumolysin. The nucleotide sequence of the perfringolysin O gene (pfo) exhibits approximately 60% homology with the streptolysin O gene (slo) and 48% homology with the pneumolysin gene (ply). All three toxins contain an identical region of 12 amino acids, which includes the essential cysteine of all three toxins. The location of these 12 residues was conserved in all three toxins when the primary sequences were aligned for maximum homology.

Cloning and expression in Escherichia coli of the perfringolysin O (theta-toxin) gene from Clostridium perfringens and characterization of the gene product

The gene encoding perfringolysin O, the thiol-activated hemolysin from Clostridium perfringens (ATCC 13124), was cloned and expressed in Escherichia coli. A gene library of C. perfringens chromosomal DNA was constructed in bacteriophage lambda EMBL3. A recombinant was identified that produced a hemolysin that was inhibited by cholesterol and was tentatively identified as perfringolysin O. Subcloning experiments localized the perfringolysin O gene (pfo) to a 1.8-kilobase region on the cloned chromosomal fragment. E. coli which carried a plasmid subclone of pfo (pRT1B) expressed perfringolysin O and secreted it into the periplasm. The amino-terminal sequence of the pfo gene product was identical with that determined for perfringolysin O purified from C. perfringens, indicating that E. coli correctly removed the signal peptide during secretion. Purification of the pfo product was accomplished by high-resolution gel filtration and anion-exchange chromatography. Analysis of the pfo product by sodium dodecyl sulfate gel electrophoresis showed that it comigrated with authentic perfringolysin O; both had an estimated molecular weight of 54,000. Two-dimensional tryptic peptide maps of the pfo product and of authentic perfringolysin O purified from C. perfringens were identical. The hemolytic activity of the pfo product was similar to that of authentic perfringolysin O; one hemolytic unit (HU) of the cloned gene product or authentic perfringolysin O corresponded to approximately 1 ng or a hemolytic activity of 10(6) HU per mg.

Cloning and expression of the pneumococcal neuraminidase gene in Escherichia coli

A gene bank of Sau3AI-generated Streptococcus pneumoniae DNA fragments was constructed in Escherichia coli K-12 by cloning into the BamHI site of the cosmid vector pHC79. One clone capable of cleaving the fluorogenic neuraminidase substrate 2'-(4-methylumbelliferyl)-alpha-D-N-acetyl-neuraminic acid was isolated. This activity was inhibited by treatment with a mouse antiserum raised against purified pneumococcal neuraminidase. The recombinant plasmid purified from this clone (designated pJCP301) contained approximately 3.0 kb of pneumococcal DNA. Western-blot analysis indicated that E. coli K-12[pJCP301] produced a 98-kDa polypeptide which reacted with antineuraminidase serum.

Molecular cloning, characterization, and complete nucleotide sequence of the gene for pneumolysin, the sulfhydryl-activated toxin of Streptococcus pneumoniae

A recombinant lambda bacteriophage has been isolated that carries DNA from Streptococcus pneumoniae and expresses a potent hemolysin that has been shown to be pneumolysin, the sulfhydryl-activated toxin of the pneumococcus. Hemolytic activity is inhibited by cholesterol and neutralized by serum against streptolysin O. The cloned gene expresses two polypeptides (Mrs, 56,000 and 53,000) in an Escherichia coli in vitro transcription-translation system, and both are precipitated by the addition of anti-alveolysin serum and anti-streptolysin O serum in the presence of Staphylococcus aureus cells. Expression of pneumolysin occurs when the gene is cloned in both possible orientations in pUC8. The DNA sequence of a 5-kilobase ClaI fragment that carries the pneumolysin gene has been determined. An open reading frame was identified that encodes a polypeptide of 471 amino acids that is hydrophobic in character and has an N-terminal amino acid sequence which is identical to that deduced from amino acid sequencing of the purified protein. The predicted amino acid sequence of the polypeptide reveals a single cysteine residue located 44 residues from the C terminus. Putative promoter and ribosome binding sites have been identified 5' to the pneumolysin coding sequence.