An M protein with a single C repeat prevents phagocytosis of Streptococcus pyogenes: use of a temperature-sensitive shuttle vector to deliver homologous sequences to the chromosome of S. pyogenes

Expression of different group A streptococcal M proteins in an isogenic background demonstrates diversity in adherence to and invasion of eukaryotic cells

The M protein of group A streptococcus (GAS) is considered to be a major virulence factor because it renders GAS resistant to phagocytosis and allows bacterial growth in human blood. There are more than 80 known serotypes of M proteins, and protective opsonic antibodies produced during disease in humans are serotype specific. M proteins also mediate bacterial adherence to epithelial cells of skin and pharynx. GAS strains vary in the genomic organization of the mga regulon, which contains the genes encoding M and M-like proteins and other virulence factors. This diversity of organization makes it difficult to assess virulence of M proteins of different serotypes, unless they can be expressed in an isogenic background. Here, we express M proteins of different serotypes in the M protein- and protein F1-deficient GAS strain, SAM2, which also lacks M-like proteins. Genes encoding M proteins of different serotypes (emmXs) have been integrated into the SAM2 chromosome in frame with the emm6.1 promoter and its mga regulon, resulting in similar levels of emmX expression. Although SAM2 exhibits a very low level of adherence to and invasion of HEp-2 and HaCaT cells, a SAM2-derived strain expressing M6 protein adheres to and invades both cell types. In contrast, the isogenic strain expressing M18 protein adheres to both cell types, but invades with a very low efficiency. A strain expressing M3 protein adheres to both types of cells, but its invasion of HEp-2 cells is serum dependent. A GAS strain expressing M6 protein does not compete with the isogenic strain expressing M18 protein for adherence to or invasion of HaCaT cells. We conclude that M proteins of different serotypes recognize different repertoires of receptors on the surfaces of eukaryotic cells.

High-frequency intracellular invasion of epithelial cells by serotype M1 group A streptococci: M1 protein-mediated invasion and cytoskeletal rearrangements

A clonal variant of serotype M1 group A streptococcus (designated M1inv+) has been linked to severe and invasive infections, including sepsis, necrotizing fasciitis and toxic shock. High frequency internalization of cultured epithelial cells by the M1inv+ strain 90-226 is dependent upon the M1 protein. Invasion of HeLa cells was blocked by an anti-M1 antibody, invasion by an M1- strain (90-226 emm1::km) was greatly reduced, and latex beads bound to M1 protein were readily internalized by HeLa cells. Beads coated with a truncated M1 protein were internalized far less frequently. Scanning electron microscopy indicated that streptococci invade by a zipper-like mechanism, that may be mediated by interactions with host cell microvilli. Initially, internalized streptococci and streptococci undergoing endocytosis are associated with polymerized actin. Later in the internalization process, streptococcal-containing vacuoles are associated with the lysosomal membrane glycoprotein, LAMP-1.

Role of the Hypervariable Region in Streptococcal M Proteins: Binding of a Human Complement Inhibitor

Antigenic variation allows pathogenic microorganisms to evade the immune system of the infected host. The variable structure must play an important role in pathogenesis, but its function is in most cases unknown. Here, we identify a function for the surface-exposed hypervariable region of streptococcal M5 protein, a virulence factor that inhibits phagocytosis. The hypervariable region of M5 was found to bind the human complement inhibitor FHL-1 (factor H-like protein 1), a 42-kDa plasma protein. Plasma absorption experiments with M5-expressing bacteria showed that the interaction with FHL-1 occurs also under physiologic conditions. Studies of another extensively characterized M protein, M6, indicated that this protein also has a binding site for FHL-1 in the hypervariable region. The complement-inhibitory function of FHL-1 was retained after binding to streptococci, suggesting that bound FHL-1 protects bacteria against complement attack. All available data now indicate that FHL-1, or another human complement inhibitor, binds to the hypervariable region of M proteins. These findings provide insights into the forces that drive antigenic variation and may explain why the hypervariable region of M protein is essential for phagocytosis resistance. Moreover, these data add to a growing body of evidence that human complement inhibitors are major targets for pathogenic microorganisms.

Identification of csrR/csrS, a genetic locus that regulates hyaluronic acid capsule synthesis in group A Streptococcus

The hyaluronic acid capsule of group A Streptococcus (GAS) is an important virulence factor, but little is known about mechanisms that regulate capsule expression. Transposon Tn916 mutagenesis of the poorly encapsulated M-type 3 GAS strain DLS003 produced a transconjugant that exhibited a mucoid colony morphology, reflecting increased hyaluronic acid capsule production. Analysis of chromosomal DNA sequence immediately downstream of the transposon insertion identified two open reading frames, designated csrR and csrS, which exhibited sequence similarity to bacterial two-component regulatory systems. We constructed an in-frame deletion mutation within csrR, which encodes the putative response component. Replacement of the native csrR gene in the DLS003 chromosome with the mutant allele resulted in a sixfold increase in capsule production and a corresponding increase in transcription of the has operon, which contains the essential genes for hyaluronic acid synthesis. Increased capsule production by the csrR mutant strain was associated with enhanced resistance to complement-mediated opsonophagocytic killing in vitro and with a 500-fold increase in virulence in mice. These results establish CsrR as a negative regulator of hyaluronic acid capsule synthesis and suggest that it is part of a two-component regulatory system that influences capsule expression and virulence.

Molecular analysis of the capsule gene region of group A Streptococcus: the hasAB genes are sufficient for capsule expression

Enzymes directing the biosynthesis of the group A streptococcal hyaluronic acid capsule are encoded in the hasABC gene cluster. Inactivation of hasC, encoding UDP-glucose pyrophosphorylase in the heavily encapsulated group A streptococcal strain 87-282, had no effect on capsule production, indicating that hasC is not required for hyaluronic acid synthesis and that an alternative source of UDP-glucose is available for capsule production. Nucleotide sequence and deletion mutation analysis of the 5.5 kb of DNA upstream of hasA revealed that this region is not required for capsule expression. Many (10 of 23) group A streptococcal strains were found to contain insertion element IS1239' approximately 50 nucleotides upstream of the -35 site of the hasA promoter. The presence of IS1239' upstream of hasA did not prevent capsule expression. These results elucidate the molecular architecture of the group A streptococcal chromosomal region upstream of the has operon, indicate that hasABC are the sole components of the capsule gene cluster, and demonstrate that hasAB are sufficient to direct capsule synthesis in group A streptococci.

Molecular analysis of the role of the group A streptococcal cysteine protease, hyaluronic acid capsule, and M protein in a murine model of human invasive soft-tissue infection

Human invasive soft-tissue infections caused by group A Streptococcus are associated with significant morbidity and mortality. To investigate the pathogenesis of these serious infections, we characterized the host response to bacterial challenge with an M-type 3 isolate recovered from a patient with necrotizing fasciitis, or with isogenic gene replacement mutants deficient in cysteine protease, hyaluronic acid capsule, or M protein in a murine model of human invasive soft-tissue infection. Animals challenged with the wild-type or cysteine protease-deficient strain developed spreading tissue necrosis at the site of inoculation, became bacteremic, and subsequently died. Histopathologic examination of the necrotic lesion revealed bacteria throughout inflamed subcutaneous tissue. Arterioles and venules in the subcutaneous layer were thrombosed and the overlying tissue was infarcted. In contrast, animals challenged with either an acapsular or M protein-deficient mutant developed a focal area of tissue swelling at the site of inoculation without necrosis or subsequent systemic disease. Histopathologic examination of the soft-tissue lesion demonstrated bacteria confined within a well-formed subcutaneous abscess. We conclude that the group A streptococcal hyaluronic acid capsule and M protein, but not the cysteine protease, are critical for the development of tissue necrosis, secondary bacteremia, and lethal infection in a murine model of human necrotizing fasciitis.

Molecular characterization of a chromosomal determinant conferring resistance to zinc and cobalt ions in Staphylococcus aureus

A DNA fragment conferring resistance to zinc and cobalt ions was isolated from a genomic DNA library of Staphylococcus aureus RN450. The DNA sequence analysis revealed two consecutive open reading frames, designated zntR and zntA. The predicted ZntR and ZntA showed significant homology to members of ArsR and cation diffusion families, respectively. A mutant strain containing the null allele of zntA was more sensitive to zinc and cobalt ions than was the parent strain. The metal-sensitive phenotype of the mutant was complemented by a 2.9-kb DNA fragment containing zntR and zntA. An S. aureus strain harboring multiple copies of zntR and zntA showed an increased resistance to zinc. The resistance to zinc in the wild-type strain was inducible. Transcriptional analysis indicated that zntR and zntA genes were cotranscribed. The zinc uptake studies suggested that the zntA product was involved in the export of zinc ions out of cells.

Spo0A mutants of Bacillus subtilis with sigma factor-specific defects in transcription activation

The transcription factor Spo0A of Bacillus subtilis has the unique ability to activate transcription from promoters that require different forms of RNA polymerase holoenzyme. One class of Spo0A-activated promoter, which includes spoIIEp, is recognized by RNA polymerase associated with the primary sigma factor, sigma A (sigmaA); the second, which includes spoIIAp, is recognized by RNA polymerase associated with an early-sporulation sigma factor, sigma H (sigmaH). Evidence suggests that Spo0A probably interacts directly with RNA polymerase to activate transcription from these promoters. To identify residues of Spo0A that may be involved in transcriptional activation, we used PCR mutagenesis of the entire spo0A gene and designed a screen using two distinguishable reporter fusions, spoIIE-gus and spoIIA-lacZ. Here we report the identification and characterization of five mutants of Spo0A that are specifically defective in activation of sigmaA-dependent promoters while maintaining activation of sigmaH-dependent promoters. These five mutants identify a 14-amino-acid segment of Spo0A, from residue 227 to residue 240, that is required for transcriptional activation of sigmaA-dependent promoters. This region may define a surface or domain of Spo0A that makes direct contacts with sigmaA-associated holoenzyme.

Hyaluronic acid capsule modulates M protein-mediated adherence and acts as a ligand for attachment of group A Streptococcus to CD44 on human keratinocytes

We used wild-type and isogenic mutant strains of group A Streptococcus (GAS) that expressed M protein, capsule, or both to study the function of M protein and the hyaluronic acid capsular polysaccharide in attachment of GAS to human keratinocytes. Types 6 and 24, but not type 18, M protein were found to mediate attachment of GAS to soft palate or skin keratinocytes, but this interaction was prevented by the hyaluronic acid capsule on highly encapsulated, or mucoid, strains. Monoclonal antibody to CD44, the principal hyaluronic acid-binding receptor on keratinocytes, inhibited attachment of both highly encapsulated and poorly encapsulated wild type strains of GAS, but not the attachment of acapsular mutants. Transfection of K562 cells with cDNA encoding human CD44 conferred the capacity to bind each of six wild-type strains of GAS, but not to bind acapsular mutants. Because, in contrast to other potential adhesins, the group A streptococcal capsule is both highly conserved and surface-exposed, it may serve as a universal adhesin for attachment of diverse strains of GAS to keratinocytes of the pharyngeal mucosa and the skin.

Structure of the has operon promoter and regulation of hyaluronic acid capsule expression in group A Streptococcus

Group A streptococcal strains vary widely in the amount of hyaluronic acid capsule they produce, although the has operon, which encodes the enzymes required for hyaluronic acid synthesis, is highly conserved. The three genes making up the has operon are transcribed from a single promoter located upstream of the first gene in the operon, hasA. To investigate transcriptional regulation of capsule synthesis, we studied the structure and function of the has operon promoter sequences from two strains of group A Streptococcus: a highly encapsulated M-type 18 strain and a poorly encapsulated M-type 3 strain. Transcriptional fusions of the has operon promoter to a promoterless chloramphenicol acetyltransferase gene were constructed in a temperature-sensitive shuttle vector. The influence of promoter structure on has operon transcription was reflected by chloramphenicol acetyl transferase activity in cell lysates of Escherichia coli harbouring the recombinant plasmids and in group A Streptococcus after integration of the promoter fusions into the streptococcal chromosome. Fusions including as few as 12 nucleotides upstream from the -35 site of the has promoter exhibited full activity, indicating that sequences further upstream do not affect has gene transcription. A transcriptional fusion of the has promoter from the highly encapsulated M-type 18 strain was threefold more active than a similar construct from the poorly encapsulated M-type 3 strain. Analysis of the promoter sequences for the two strains revealed differences in three nucleotides in the -35, -10 spacer region of the promoter and in four nucleotides in the +2 to +8 positions relative to the start site of hasA transcription. To determine the relative importance of the two groups of nucleotide substitutions, chimeric promoter sequences were constructed in which either of the two clusters of variant nucleotides from the M18 has promoter was substituted for the corresponding positions in the M3 has promoter. Analysis of these chimeric promoter fusions showed that sequence changes in both regions influenced promoter strength. These results define the limits of cis-acting chromosomal sequences that influence transcription of the has operon and indicate that the fine structure of the promoter is an important determinant of capsule gene expression in group A Streptococcus.

Molecular co-operation between protein PAM and streptokinase for plasmin acquisition by Streptococcus pyogenes

Bacterial surface-associated plasmin formation is believed to contribute to invasion, although the underlying molecular mechanisms are poorly understood. To define the components necessary for plasmin generation on group A streptococci we used strain AP53 which exposes an M-like protein ("PAM") that contains a plasminogen-binding sequence with two 13-amino acid residues long tandem repeats (a1 and a2). Utilizing an Escherichia coli-streptococcal shuttle vector, we replaced a 29-residue long sequence segment of Arp4, an M-like protein that does not bind plasminogen, with a single (a1) or the combined a1a2 repeats of PAM. When expressed in E. coli, the purified chimeric Arp/PAM proteins both bound plasminogen, as well as plasmin, and when used to transform group A streptococcal strains lacking the plasminogen-binding ability, transformants with the Arp/PAM constructs efficiently bound plasminogen. Moreover, when grown in the presence of plasminogen, both Arp/PAM- and PAM-expressing streptococci acquired surface-bound plasmin. In contrast, plasminogen activation failed to occur on PAM- and Arp/PAM-expressing streptococci carrying an inactivated streptokinase gene: this block was overcome by exogenous streptokinase. Together, these results provide evidence for an unusual co-operation between a surface-bound protein, PAM, and a secreted protein, streptokinase, resulting in bacterial acquisition of a host protease that is likely to spur parasite invasion of host tissues.

Genetic inactivation of an extracellular cysteine protease (SpeB) expressed by Streptococcus pyogenes decreases resistance to phagocytosis and dissemination to organs

Streptococcal pyrogenic exotoxin B (SpeB), a conserved cysteine protease expressed by virtually all Streptococcus pyogenes strains, has recently been shown to be an important virulence factor (S. Lukomski, S. Sreevatsan, C. Amberg, W. Reichardt, M. Woischnik, A. Podbielski, and J. M. Musser, J. Clin. Invest. 99:2574-2580, 1997). Genetic inactivation of SpeB significantly decreased the lethality of a serotype M49 strain for mice and abolished the lethality of a serotype M3 strain after intraperitoneal (i.p.) injection. In the present study, a wild-type M3 isolate and an M3 speB mutant derivative were used to investigate the mechanism responsible for altered virulence. Following i.p. injection, the mutant and wild-type strains induced virtually identical cellular inflammatory responses, characterized largely by an influx of polymorphonuclear leukocytes (PMNs). In addition, the mutant and wild-type strains rapidly entered the blood and were recovered from all organs examined. However, significantly fewer (P < 0.05) CFUs of the isogenic mutant derivative than of the wild-type parent strain were recovered from blood and organs. PMNs effectively cleared the M3 speB mutant from the peritoneum by 22 h, thereby sparing the host. In contrast, the wild-type M3 strain continued to replicate intraperitoneally and had the ability to kill phagocytes. This process allowed the wild-type strain to continuously disseminate, resulting in host death. Our results indicate that genetic inactivation of the cysteine protease decreased the resistance of the mutant to phagocytosis and impaired its subsequent dissemination to organs. These results provide insight into the detrimental effect of SpeB inactivation on virulence.

Expression of Two Different Antiphagocytic M Proteins by Streptococcus pyogenes of the OF+ Lineage

All clinical isolates of Streptococcus pyogenes (group A streptococcus) share the ability to resist phagocytosis and grow in human blood. In many strains, this property is due to the expression of a single antiphagocytic M protein, while other strains express more than one M-like molecule, of which the role in phagocytosis resistance is unclear. In particular, all S. pyogenes strains of the OF+ lineage, representing approximately half of all isolates, express two M-like proteins, Mrp and Emm, which are immunologically unrelated. These two proteins bind different ligands that have been implicated in phagocytosis resistance: Mrp binds fibrinogen and Emm binds the complement inhibitor C4BP. Using a clinical isolate of the common serotype 22, we created mutants affected in the mrp and emm genes and characterized them in phagocytosis experiments and by electron microscopy. A double mutant mrp−emm− showed strongly decreased resistance to phagocytosis, while mrp− and emm− single mutants grew well in blood. However, optimal growth required the expression of both Mrp and Emm. Experiments in which coagulation was inhibited using the specific thrombin inhibitor, hirudin, rather than heparin, indicated that Emm is more important than Mrp for resistance to phagocytosis. Tuftlike surface structures typical for S. pyogenes were still present in the mrp−emm− double mutant, but not in a mutant affected in the regulatory gene mga, indicating that the presence of these surface structures is not directly correlated to phagocytosis resistance. Our data imply that OF+ strains of S. pyogenes express two antiphagocytic M proteins with different ligand-binding properties.

Improvement of Bacillus sphaericus toxicity against dipteran larvae by integration, via homologous recombination, of the Cry11A toxin gene from Bacillus thuringiensis subsp. israelensis

Integrative plasmids were constructed to enable integration of foreign DNA into the chromosome of Bacillus sphaericus 2297 by in vivo recombination. Integration of the aphA3 kanamycin resistance gene by a two-step procedure demonstrated that this strategy was applicable with antibiotic resistance selection. Hybridization experiments evidenced two copies of the operon encoding the binary toxin from B. sphaericus in the recipient strain. The Bacillus thuringiensis subsp. israelensis cry11Aal gene (referred to as cry11A), encoding a delta-endotoxin with toxicity against Culex, Aedes, and Anopheles larvae, was integrated either by a single crossover event [strain 2297 (::pHT5601), harboring the entire recombinant plasmid] or by two successive crossover events [strain 2297 (::cry11A)]. The level of the Cry11A production in B. sphaericus was high; two crystalline inclusions were produced in strain 2297 (::pHT5601). Synthesis of the Cry11A toxin conferred toxicity to the recombinant strains against Aedes aegypti larvae, for which the parental strain was not toxic. Interestingly, the level of larvicidal activity of strain 2297 (::pHT5601) against Anopheles stephensi was as high as that of B. thuringiensis subsp. israelensis and suggested synergy between the B. thuringiensis and B. sphaericus toxins. The toxicities of parental and recombinant B. sphaericus strains against Culex quinquefasciatus were similar, but the recombinant strains killed the larvae more rapidly. The production of the Cry11A toxin in B. sphaericus also partially restored toxicity for C. quinquefasciatus larvae from a population resistant to B. sphaericus 1593. In vivo recombination therefore appears to be a promising approach to the creation of new B. sphaericus strains for vector control.

New genetic techniques for group B streptococci: high-efficiency transformation, maintenance of temperature-sensitive pWV01 plasmids, and mutagenesis with Tn917

Three techniques were developed to improve the genetic manipulation of group B streptococci (GBS). We first optimized a protocol for transformation of GBS by electroporation, which provided transformation efficiencies of 10(5) CFU/microgram. Variables that influenced the transformation efficiency were the glycine content of the competent cell growth media, the electric field strength during electroporation, the electroporation buffer composition, the host origin of the transforming plasmid, and the concentration of selective antibiotic at the final plating. Our transformation protocol provides an efficiency sufficient for cloning from ligation reactions directly into GBS, obviating an intermediate host such as Escherichia coli. Second, temperature-sensitive plasmids of the pWV01 lineage were shown to transform GBS, and their temperature-sensitive replication was confirmed. Lastly, the temperature-sensitive pWV01 plasmid pTV1OK, which contains Tn917, was used as a transposon delivery vector for the construction of genomic Tn917 mutant libraries. We have shown, for the first time, that Tn917 transposes to the GBS chromosome and at a frequency of 10(-3)/CFU. Furthermore, representative clones from a Tn917 library contained single transposon insertions that were randomly located throughout the chromosome. These techniques should provide useful methods for cloning, mutagenesis, and characterization of genes from GBS.

Streptococcal protein H forms soluble complement-activating complexes with IgG, but inhibits complement activation by IgG-coated targets

Protein H, a surface protein of Streptococcus pyogenes interacting with the constant Fc region of IgG, is known to be released from the streptococcal surface by a cysteine proteinase produced by the bacteria. Poststreptococcal glomerulonephritis and rheumatic fever are conditions in which immune complexes and autoimmune mechanisms have been suggested to play pathogenetic roles. The present study demonstrates that addition of protein H to human serum produces complement activation with dose-dependent cleavage of C3. The activation was IgG-dependent and the result of complexes formed between IgG and protein H. These complexes were size heterogeneous with molecular masses of 400 kDa to 1.4 MDa. Using complement-depleted serum reconstituted with complement proteins, the activation by protein H was found to be dependent of the classical, but independent of the alternative pathway of complement. In contrast to results of experiments based on soluble protein H.IgG complexes, complement activation was inhibited by protein H when IgG was immobilized on a surface. The interaction between C1q and immunoglobulins represents the first step in the activation of the classical pathway, and protein H efficiently inhibited the binding of C1q to IgG immobilized on polyacrylamide beads. Protein H reduced C3 deposition on the IgG-coated beads and inhibited immune hemolysis of IgG-sensitized erythrocytes. Finally, significantly less C3 was deposited on the surface of protein H-expressing wild-type streptococci than on the surface of isogenic mutant bacteria devoid of protein H. The results demonstrate that protein H.IgG complexes released from the streptococcal surface can produce complement breakdown at the sites of infection, whereas complement activation on bacterial surfaces is inhibited. This should have important implications for host-parasite relationships. In addition, soluble protein H.IgG complexes might contribute to immunological complications of streptococcal infections.

Role of mga in growth phase regulation of virulence genes of the group A streptococcus

To determine whether growth phase affects the expression of mga and other virulence-associated genes in the group A streptococcus (GAS), total RNA was isolated from the serotype M6 GAS strain JRS4 at different phases of growth and transcript levels were quantitated by hybridization with radiolabeled DNA probes. Expression of mga (which encodes a multiple gene regulator) and the Mga-regulated genes emm (which encodes M protein) and scpA (which encodes a complement C5a peptidase) was found to be maximal in exponential phase and shut off as the bacteria entered stationary phase, while the housekeeping genes recA and rpsL showed constant transcript levels over the same period of growth. Expression of mga from a foreign phage promoter in a mga-deleted GAS strain (JRS519) altered the wild-type growth phase-dependent transcription profile seen for emm and scpA, as well as for mga. Therefore, the temporal control of mga expression requires its upstream promoter region, and the subsequent growth phase regulation of emm and scpA is Mga dependent. A number of putative virulence genes in JRS4 were shown not to require Mga for their expression, although several exhibited growth phase-dependent regulation that was similar to mga, i.e., slo (which encodes streptolysin O) and plr (encoding the plasmin receptor/glyceraldehyde-3-phosphate dehydrogenase). Still others showed a markedly different pattern of expression (the genes for the superantigen toxins MF and SpeC). These results suggest the existence of complex levels of global regulation sensitive to growth phase that directly control the expression of virulence genes and mga in GAS.

Keratinocyte proinflammatory responses to adherent and nonadherent group A streptococci

The gram-positive bacterium Streptococcus pyogenes (group A streptococcus) is the causative agent of a wide variety of suppurative infections of cutaneous tissues. Previous analyses have demonstrated that the M protein of S. pyogenes is an adhesin that directs the attachment of the streptococcus to keratinocytes in the skin. In this study, we have examined keratinocyte function in response to S. pyogenes and found that adherent versus nonadherent streptococci promote distinct patterns of expression of several proinflammatory molecules and keratinocyte cell fate. When analyzed by a quantitative reverse transcriptase PCR method, infection of cultured HaCaT keratinocytes with adherent, but not nonadherent, streptococci resulted in increased expression of mRNA for the cytokines interleukin-1alpha (IL-1alpha), IL-1beta, and IL-8 but neither infection induced expression of tumor necrosis factor alpha. In contrast, both adherent and nonadherent S. pyogenes induced expression of IL-6 and each promoted synthesis and release of prostaglandin E2 (PGE2). However, considerably greater levels of IL-6 expression were stimulated by adherent streptococci relative to nonadherent streptococci and the kinetics of PGE2 release in response to nonadherent streptococci was delayed compared to the response to adherent streptococci. Staining with the fluorescent probe ethidium homodimer-1 revealed that keratinocyte membranes were rapidly damaged upon infection with adherent streptococci but were not damaged by nonadherent streptococci. Finally, treatments which inhibited streptococcal metabolism completely blocked the ability of adherent streptococci to elicit responses. These data suggest that expression of an adhesin is a strategy used by S. pyogenes to modulate keratinocyte responses during infection of the skin and implicate additional streptococcal products in these signaling interactions.

Role of putative virulence factors of Streptococcus pyogenes in mouse models of long-term throat colonization and pneumonia

To investigate the role of putative virulence factors of Streptococcus pyogenes (group A streptococcus; GAS) in causing disease, we introduced specific mutations in GAS strain B514, a natural mouse pathogen, and tested the mutant strains in two models of infection. To study late stages of disease, we used our previously described mouse model (C3HeB/FeJ mice) in which pneumonia and systemic spread of the streptococcus follow intratracheal inoculation. To study the early stages of disease, we report here a model of long-term (at least 21 days) throat colonization following intranasal inoculation of C57BL/10SnJ mice. When the three emm family genes of GAS strain B514-Sm were deleted, the mutant showed no significant difference from the wild type in induction of long-term throat colonization or pneumonia. We inactivated the scpA gene, which encodes a complement C5a peptidase, by insertion of a nonreplicative plasmid and found no significant difference from the wild type in the incidence of throat colonization. However, there was a small but statistically significant decrease in the incidence of pneumonia caused by the scpA mutant. Finally, we demonstrated a very important effect of the hyaluronic acid capsule in both models. Following intranasal inoculation of mice with a mutant in which a nonreplicative plasmid was inserted into the hasA gene, which encodes hyaluronate synthase, we found that all bacteria recovered from the throats of the mice were encapsulated revertants. Following intratracheal inoculation with the hasA mutant, the incidence of pneumonia within 72 h was significantly reduced from that of the control strain (P = 0.006). These results indicate that the hyaluronic acid capsule of S. pyogenes B514 confers an important selective advantage for survival of the bacteria in the upper respiratory tract and is also an important determinant in induction of pneumonia in our model system.

Localization by site-directed mutagenesis of the site in human complement factor H that binds to Streptococcus pyogenes M protein

M-protein receptors located on Streptococcus pyogenes cells are known to bind human plasma protein factor H. Human factor H is composed of 20 short consensus repeat (SCR) domains containing approximately 60 amino acids each. Factor H controls the activation of the alternative pathway of complement in plasma. We have scanned the entire human factor H molecule by site-directed deletion mutagenesis, expressed the recombinant proteins in insect cells using the baculovirus system, and measured the binding of different purified mutant proteins to three strains of S. pyogenes. These studies have revealed that recombinant factor H lacking SCR domains 6 to 10 does not bind to wild-type M+ S. pyogenes JRS4. Experiments performed with S. pyogenes JRS251, in which both C-repeat domains of M protein were deleted, demonstrated that all of the factor H mutant proteins bound weakly to these cells except those lacking the SCR region from domains 6 to 10. Neither human factor H nor any of the recombinant proteins bound to the M- strain JRS145. Our results indicate that the only binding site on human factor H that interacts with streptococcus M protein is located in SCR domains 6 to 10 of factor H and that regions of M protein outside the C-repeat domains are involved in binding factor H.

Relative contributions of hyaluronic acid capsule and M protein to virulence in a mucoid strain of the group A Streptococcus

The antiphagocytic effect of M protein has been considered a critical element in virulence of the group A streptococcus. The hyaluronic acid capsule also appears to play an important role: studies of an acapsular mutant derived from the mucoid or highly encapsulated M protein type 18 group A streptococcal strain 282 indicated that loss of capsule expression was associated with decreased resistance to phagocytic killing and with reduced virulence in mice. To study directly the relative contributions to virulence of M protein and the hyaluronic acid capsule in strain 282, we inactivated the gene encoding the M protein (emm18) both in wild-type strain 282 and in its acapsular mutant, strain TX72. Inactivation of emm18 was accomplished by integrational plasmid mutagenesis, using the temperature-sensitive shuttle vector pJRS233 harboring a 5' DNA segment of emm18. As reported previously, wild-type strain 282 was resistant to phagocytic killing in vitro, both in whole human blood and in 10% serum. The capsule mutant TX72 was highly susceptible to phagocytic killing in 10% serum and moderately sensitive in whole blood. The M protein mutant 282KZ was highly susceptible to phagocytic killing in blood but only moderately sensitive in 10% serum. The double mutant TX74 was sensitive to killing in both conditions. In a mouse infection model, the 50% lethal dose was increased by 60- and 80-fold for the capsule and double mutants, respectively, compared with that of strain 282, but only by 6-fold for the M protein mutant. Integration of the strain 282 capsule genes into the chromosome of a nonmucoid M1 strain resulted in high-level capsule production and rendered the transformed strain resistant to phagocytic killing in 10% serum. These results provide further evidence that the hyaluronic acid capsule confers resistance to phagocytosis and enhances group A streptococcal virulence. The results suggest also that assessment of in vitro resistance to phagocytosis in 10% serum rather than in whole blood may be a more accurate reflection of virulence in vivo of group A streptococci.

Novel series of plasmid vectors for gene inactivation and expression analysis in group A streptococci (GAS)

Ten novel streptococcal shuttle vectors for genomic integration and allelic replacements have been constructed based on plasmid pSF152. These vectors can replicate in E. coli, but not in streptococci because of the absence of a streptococcal origin of replication. The basic vector pFW5 (2.8 kb, aad9 spectinomycin-resistance marker) carries two multiple cloning sites MCS-I and MCS-II (10 and 15 restrictions sites, respectively) to either side of the aad9 resistance gene. Each MCS is flanked by transcription termination sites for stabilization of recombinant plasmids. In vector pFW6 the transcription terminator between aad9 and MCS-II was deleted. Plasmids pFW7 through pFW10 carry resistance genes for kanamycin, chloramphenicol, erythromycin, and tetracyclin instead of aad9. Vectors pFW11 and pFW12 are pFW5/6 derivatives harboring an improved synthetic aad9 promoter. In pFW-phoA and pFW-gfp, promoterless alkaline phosphatase and green fluorescent protein boxes were integrated into MCS-I. If streptococcal DNA fragments are cloned into MCS-I and MSC-II, these vectors can be used for specific allelic replacements in streptococci via double-crossover recombinations. Depending on the vector used, this event will not lead to polar effects, facilitating mutagenesis within operons. The vectors containing reporter boxes allow in vivo studies of gene expression and promoter activity in pathogenic streptococci and potentially, also in other Gram-positive bacteria.

Insertional mutagenesis and recovery of interrupted genes of Streptococcus mutans by using transposon Tn917: preliminary characterization of mutants displaying acid sensitivity and nutritional requirements

New vectors were constructed for efficient transposon Tn917-mediated mutagenesis of poorly transformable strains of Streptococcus mutans(pTV1-OK) and subsequent recovery of interrupted genes in Escherichia coli (pT21delta2TetM). In this report, we demonstrate the utility of Tn917 mutagenesis of a poorly transformable strain of S. mutans (JH1005) by showing (i) the conditional replication of pTV1-OK, a repA(Ts) derivative of the broad-host-range plasmid pWVO1 harboring Tn9l7, in JH1005 at the permissive temperature (30 degrees C) versus that at the nonpermissive temperature (45 degrees C); (ii) transposition frequencies similar to those reported for Bacillus subtilis (10(-5) to 10(-4)) with efficient plasmid curing in 90 to 97% of the erythromycin-resistant survivors following a temperature shift to 42 to 45 degrees C; and (iii) the apparent randomness of Tn917 insertion as determined by Southern hybridization analysis and the ability to isolate nutritional mutants, mutants in acid tolerance, and mutants in bacteriocin production, at frequencies ranging from 0.1 to 0.7%. Recovery of transposon-interrupted genes was achieved by two methods: (i) marker rescue in E. coli with the recovery vector pTV21delta2TetM, a tetracycline-resistant and ampicillin-sensitive Tn9l7-pBR322 hybrid, and (ii) "shotgun" cloning of genomic libraries of Tn917 mutants into pUC19. Sequence analyses revealed insertions at five different genetic loci in sequences displaying homologies to Clostridium spp.fhs (66% identity), E. coli dfp (43% identity), and B. subtilis ylxM-ffh (58% identity), icd (citC [69% identity]), and argD (61% identity). Insertions in icd and argD caused nutritional requirements; the one in ylxM-ffh caused acid sensitivity, while those in fhs and dfp caused both acid sensitivity and nutritional requirements. This paper describes the construction of pTV1-OK and demonstrates that it can be efficiently employed to deliver Tn917 into S. mutans for genetic analyses with some degree of randomness and that insertions in the chromosome can be easily recovered for subsequent characterization. This represents the first published report of successful Tn9l7 mutagenesis in the genus Streptococcus.

Identification of isp, a locus encoding an immunogenic secreted protein conserved among group A streptococci

The protein Mga (mga), which is required for transcription of several virulence genes of group A streptococci (GAS), including the antiphagocytic M protein, was suggested to act as the response regulator element of a bacterial two-component pathway. To investigate whether a gene encoding a cognate sensor protein is located upstream of mga, 3.1 kb of DNA 5' of the mga translational start site was cloned from serotype M6 GAS strain JRS4. Sequence analysis of this region revealed two adjacent open reading frames, a previously described orf and a new locus, isp (immunogenic secreted protein), which could encode proteins of 9 and 59 kDa, respectively. Inactivation of either open reading frame had no significant effect on transcription of the gene encoding M protein (emm) under normal growth conditions, suggesting that neither isp nor orf is involved in the Mga regulatory circuit. A protein migrating at an apparent molecular weight of 65,000 was produced when isp was transcribed and translated in vitro. The predicted isp product (Isp) contains an amino-terminal signal sequence region homologous to that found in bacterial secreted proteins, and expression of isp in Escherichia coli resulted in the presence of Isp in the periplasmic fraction. Convalescent-phase serum from a patient with an active GAS infection recognized forms of Isp both from the periplasm of E. coli and the supernatant of a GAS strain. Both isp and orf are highly conserved among strains of GAS, as shown by hybridization analyses.

Differential expression of genes in the vir regulon of Streptococcus pyogenes is controlled by transcription termination

Streptococcal C5a peptidase (SCP), encoded by scpA in Streptococcus pyogenes, is a surface molecule which is able to cleave and inactivate the chemotactic factor C5a. The scpA gene is part of the vir regulon and subject to positive regulation by the Mga protein. It is down-regulated compared to another Mga-activated gene, emm. A chloramphenicol acetyltransferase (CAT) reporter gene was used to measure scpA promoter activity. Previous work had shown that when a large portion of the scpA promoter region was deleted, expression of CAT increased relative to the wild-type. This deleted region was found to contain an inverted repeat. In this study we show that the inverted repeat in the leader mRNA is the site of transcription termination, which down-regulates expression of scpA. This is a novel mechanism for regulation of gene expression in S. pyogenes. A specific deletion of the inverted repeat in the scpA promoter-CAT reporter construct was made using inverse PCR. Expression was measured from single-copy chromosomal integrants. When the inverted repeat was deleted, expression increased. Furthermore, Northern hybridization confirmed the existence of a truncated transcript, consistent with a transcription termination mechanism.

Biological properties of a Streptococcus pyogenes mutant generated by Tn916 insertion in mga

The mga regulon of Streptococcus pyogenes contains genes which contribute to the pathogenicity and virulence of this significant human pathogen. Transposon insertional inactivation of the regulatory mga gene in a S. pyogenes strain of the clinically important M1 serotype, blocked the expression of four genes located downstream of mga. These genes encode the M1 protein, the IgG-binding protein H, protein SIC which is an extracellular inhibitor of complement, and the C5a peptidase which interferes with granulocyte migration. The wild-type strain is resistant to phagocytosis and adheres to human skin tissue sections; properties that were lost in the transposon mutant. Moreover, the mutant was less virulent to mice but more cytolytic to human lymphocytes, the latter due to an increased activity of streptolysin S, whereas the production of streptolysin O, another toxin of S. pyogenes, was not affected. The mga mutation was complemented in trans with an intact mga gene which restored the phenotype of the wild-type strain.

Membrane cofactor protein (CD46) is a keratinocyte receptor for the M protein of the group A streptococcus

The pathogenic Gram-positive bacterium Streptococcus pyogenes (group A streptococcus) is the causative agent of numerous suppurative diseases of human skin. The M protein of S. pyogenes mediates the adherence of the bacterium to keratinocytes, the most numerous cell type in the epidermis. In this study, we have constructed and analyzed a series of mutant M proteins and have shown that the C repeat domain of the M molecule is responsible for cell recognition. The binding of factor H, a serum regulator of complement activation, to the C repeat region of M protein blocked bacterial adherence. Factor H is a member of a large family of complement regulatory proteins that share a homologous structural motif termed the short consensus repeat. Membrane cofactor protein (MCP), or CD46, is a short consensus repeat-containing protein found on the surface of keratinocytes, and purified MCP could competitively inhibit the adherence of S. pyogenes to these cells. Furthermore, the M protein was found to bind directly to MCP, whereas mutant M proteins that lacked the C repeat domain did not bind MCP, suggesting that recognition of MCP plays an important role in the ability of the streptococcus to adhere to keratinocytes.

Role of the conserved C-repeat region of the M protein of Streptococcus pyogenes

The surface-located M protein functions to protect Streptococcus pyogenes (the group A streptococcus) from phagocytosis by polymorphonuclear leukocytes. It has been suggested that this protection results from the ability of M protein to bind factor H, a serum protein that can inhibit the activation of complement. Among different serological variants of M protein, the C-repeat domain is highly conserved and is exposed on the bacterial surface. This domain has been implicated in binding to complement factor H and in M-protein-mediated adherence of streptococci to human keratinocytes in the cutaneous epithelium. In this study, we constructed an S. pyogenes mutant strain which expresses an M6 protein from which the entire C-repeat domain was deleted. As predicted, this mutant did not adhere well to human keratinocytes and was unable to bind to factor H. Unexpectedly, the mutant was able to survive and multiply in human blood. Therefore, while the binding of factor H and the facilitation of adherence to keratinocytes appear to involve recognition of the C-repeat domain, a region of the M-protein molecule distinct from the C-repeat domain confers upon S. pyogenes its ability to resist phagocytosis.

Expression of the Arp protein, a member of the M protein family, is not sufficient to inhibit phagocytosis of Streptococcus pyogenes

Many Streptococcus pyogenes immunoglobulin-binding proteins have structural similarities to the antiphagocytic M protein, including the well-known C repeats. One of these molecules is the immunoglobulin A-binding protein Arp, which is expressed by a serotype 4 strain for which no antiphagocytic M protein has yet been described. We expressed Arp4 in an S. pyogenes strain from which the structural gene for the M protein has been deleted and found that Arp4 is not sufficient to inhibit phagocytosis.

Location of the complement factor H binding site on streptococcal M6 protein

The surface M protein of group A streptococci binds factor H, a regulatory protein of the alternative complement pathway, which may contribute to the antiphagocytic activity of the M molecules. To locate the factor H binding domain in the alpha-helical coiled-coil structure of the M molecule, the M protein was cleaved with pepsin at pH 5.8, which separates the molecule approximately in half. Western blot (immunoblot), amino acid sequence, and mass spectrometric analyses revealed that factor H bound to a 14.6-kDa C-terminal fragment of the M molecule. Competitive inhibition of factor H binding to the 14.6-kDa fragment with M protein peptides localized the binding site to amino acids 256 to 292. This segment is located within the surface-exposed region of the M6 protein, identified as the C-repeat region, whose sequence is conserved among heterologous M and M-like molecules. These studies also identified a second pepsin-susceptible site with the sequence ELAK located within the cell wall-associated region of the M molecule.

Domain structure and conserved epitopes of Sfb protein, the fibronectin-binding adhesin of Streptococcus pyogenes

Streptococcus pyogenes expresses a fibronectin-binding surface protein (Sfb protein) which mediates adherence to human epithelial cells. The nucleotide sequence of the sfb gene was determined and the primary sequence of the Sfb protein was analysed. The protein consists of 638 amino acids and comprises five structurally distinct domains. The protein starts with an N-terminal signal peptide followed by an aromatic domain. The central part of the protein is formed by four proline-rich repeats which are flanked by non-repetitive spacer sequences. A second repeat region, consisting of four repeats that are distinct from the proline repeats and have been shown to form the fibronectin-binding domain, is located in the C-terminal part of the protein. The protein ends with a typical cell wall and membrane anchor region. Comparative sequence analysis of the N-terminal aromatic domain revealed similarities with carbohydrate-binding sites of other proteins. The proline repeat region of the Sfb protein shares characteristic features with proline-rich repeats of functionally distinct surface proteins from pathogenic Gram-positive cocci. Immunoelectron microscopy revealed an even distribution of the fibronectin-binding domain of Sfb protein on the surface of streptococcal cells. Analyses of 38 sfb genes originating from different S. pyogenes isolates revealed primary sequence variability in regions coding for the N-termini of mature Sfb proteins, whereas sequences coding for the central and C-terminal repeats were highly conserved. The repeat sequences are postulated to act as target sites for intragenic recombination events that result in variable numbers of repeats within the different sfb genes. A model of the Sfb protein is presented.

CooC and CooD are required for assembly of CS1 pili

Many strains of enterotoxigenic Escherichia coli (ETEC) isolated from patients with diarrhoeal disease exhibit CS1 pili on their surfaces. These appendages, which are thought to be important for colonization of the upper intestine, are composed largely of multiple identical protein subunits encoded by cooA. We have sequenced the DNA directly downstream of cooA and identified two open reading frames, cooC and cooD, transcribed in the same direction as cooB and cooA. Following cooD is DNA homologous to an insertion sequence, so cooB, A, C and D appear to encode all the information needed for E. coli K-12 to synthesize CS1 pili. Complementation analysis of mutants cloned in E. coli K-12 and constructed in an ETEC-derived strain indicates that cooC and cooD are not required for stability of the major CS1 pilin protein or for its transport to the periplasm, but, like cooB, both are needed for assembly of cooA into pili.

The identification of rofA, a positive-acting regulatory component of prtF expression: use of an m gamma delta-based shuttle mutagenesis strategy in Streptococcus pyogenes

Binding of the Gram-positive pathogenic bacterium Streptococcus pyogenes (group A streptococcus) to respiratory epithelium is mediated by the fibronectin-binding adhesin, protein F. Most strains of streptococci regulate the expression of protein F in response to oxygen levels and redox potential; however, JRS4 constitutively binds high levels of fibronectin under all environmental conditions. In this study, we have examined the regulation of protein F expression in JRS4 using a shuttle mutagenesis strategy novel to S. pyogenes. Cloned DNA representing the chromosomal loci adjacent to the gene which encodes protein F (prtF) was subjected to transposon mutagenesis in Escherichia coli using a derivative of transposon m gamma delta that was modified to contain a streptococcal antibiotic-resistance gene. mutagenized DNA was then returned to the streptococcal chromosome by allelic replacement. Analysis of the resulting fibronectin-binding phenotypes revealed that insertions in a region upstream of prtF abolished the constitutive phenotype. However, these mutants now demonstrated regulation in response to both oxygen levels and redox potential. Because these insertions define a locus responsible for the constitutive phenotype, it has been designated rofA (regulator of F). Chromosomal interruption studies using integrational plasmids together with complementation data from a previous study (VanHeyningen et al., 1993) suggested that rofA acts as a positive trans-acting regulator of prtF. Construction of prtF-lacZ fusions indicated that transcription of prtF is constitutive in JRS4 but is regulated in rofA mutants. Analysis of the DNA sequence defined by the rofA insertions revealed a 1495 bp open reading frame, whose predicted product (RofA) possessed both a putative helix-turn-helix motif and limited homology to two other transcriptional activators (Mry, PrgR) of Gram-positive surface proteins. Sequences homologous to rofA were found in regulated strains of S. pyogenes, which suggests that rofA may act as an activator of prtF in response to an unidentified environmental signal. We speculate that the allele reported here contains a mutation that renders it constitutively active.

Virulence of two Streptococcus pyogenes strains (types M1 and M3) associated with toxic-shock-like syndrome depends on an intact mry-like gene

The major virulence factor of Streptococcus pyogenes, the M protein, is positively regulated at the transcriptional level by mry in the M type 6 strain studied. We show here that in two S. pyogenes strains isolated from cases of toxic-shock-like syndrome, a type M1 strain and a type M3 strain, an mry-like gene is also required for resistance to phagocytosis.

Analysis of Streptococcus pyogenes promoters by using novel Tn916-based shuttle vectors for the construction of transcriptional fusions to chloramphenicol acetyltransferase

We have developed a series of shuttle vectors based on the conjugative transposon Tn916 that have been designed for the analysis of transcriptional regulation in Streptococcus pyogenes and other gram-positive bacteria. Designated the pVIT vectors (vectors for integration into Tn916), the vectors are small, stable plasmids in Escherichia coli to facilitate the fusion of promoters from cloned S. pyogenes genes to a promoterless gene which encodes chloramphenicol acetyltransferase. The vectors each contain one or more small regions of Tn916 to direct the integration of the transcriptional fusion into the transposon via homologous recombination following transformation of S. pyogenes or other suitable gram-positive hosts. Integration can be monitored by the inactivation or replacement of an antibiotic resistance determinant in modified derivatives of Tn916. Promoter activity can then be quantitated by the determination of chloramphenicol acetyltransferase-specific activity. In addition, since integration is into loci that do not disrupt the conjugative transpositional functions of Tn916, the vectors are useful for analysis of regulation in strains that are difficult or impossible to transform and can be introduced into these strains by conjugation following transformation of an intermediate host. The promoters for the genes which encode both the M protein and protein F of S. pyogenes were active in pVIT vectors, as was the region which controls transcription of mry, a trans-acting positive regulator of M protein expression. However, neither of the two characterized promoters for mry demonstrated activity when independently analyzed in pVIT-generated partial diploid strains, suggesting that regulation of mry is more complex than predicted by current models. The broad host range of Tn916 should make the pVIT vectors useful for analysis of regulation in numerous other bacterial species.

Adherence and fibronectin binding are environmentally regulated in the group A streptococci

The ability of the pathogenic Gram-positive bacterium Streptococcus pyogenes (group A streptococcus) to bind fibronectin and adhere to respiratory epithelial cells is dependent on a surface protein called protein F. In this study, we have examined the regulation of expression of protein F and have shown that it is environmentally regulated in response to alterations in atmosphere. In six recent clinical isolates expression of protein F was repressed during growth under reduced concentrations of O2. Expression in an anaerobic environment was induced by both superoxide-generating and redox-altering reagents. However, regulation did not involve mry, a gene that controls expression of several streptococcal surface proteins. Protein F was constitutively expressed in one of two laboratory-passaged strains analysed, and in a complementation analysis using an allele of the gene that encodes protein F (prtF) cloned from a regulated strain and expressed in a constitutive strain, the constitutive phenotype was shown to be dominant in trans. Regulation, as monitored by fusion of prtF to a promoterless chloramphenicol acetyltransferase gene, involved transcriptional control. Environmentally induced alterations in protein F expression affected the ability of the bacterium to adhere to epithelial cells, which suggests that the ability to regulate expression of protein F may be important during infection.