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.     

micF RNA is a substrate for RNase E

Abstract The speA gene encoding streptococcal erythrogenic toxin A (SPE A) from Streptococcus pyogenes bacteriophage T12 was overexpressed in Escherichia coli under the control of the T7 promoter. Since most of the expressed protein was found in the periplasmic space, an osmotic shock extraction with 0.5 M sucrose resulted in a highly enriched preparation of SPE A. An additional two-step purification employing high pressure liquid chromatography resulted in a purified SPE A protein.     

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.     

Genome sequence of a nephritogenic and highly transformable M49 strain of Streptococcus pyogenes

The 1,815,783-bp genome of a serotype M49 strain of Streptococcus pyogenes (group A streptococcus [GAS]), strain NZ131, has been determined. This GAS strain (FCT type 3; emm pattern E), originally isolated from a case of acute post-streptococcal glomerulonephritis, is unusually competent for electrotransformation and has been used extensively as a model organism for both basic genetic and pathogenesis investigations. As with the previously sequenced S. pyogenes genomes, three unique prophages are a major source of genetic diversity. Two clustered regularly interspaced short palindromic repeat (CRISPR) regions were present in the genome, providing genetic information on previous prophage encounters. A unique cluster of genes was found in the pathogenicity island-like emm region that included a novel Nudix hydrolase, and, further, this cluster appears to be specific for serotype M49 and M82 strains. Nudix hydrolases eliminate potentially hazardous materials or prevent the unbalanced accumulation of normal metabolites; in bacteria, these enzymes may play a role in host cell invasion. Since M49 S. pyogenes strains have been known to be associated with skin infections, the Nudix hydrolase and its associated genes may have a role in facilitating survival in an environment that is more variable and unpredictable than the uniform warmth and moisture of the throat. The genome of NZ131 continues to shed light upon the evolutionary history of this human pathogen. Apparent horizontal transfer of genetic material has led to the existence of highly variable virulence-associated regions that are marked by multiple rearrangements and genetic diversification while other regions, even those associated with virulence, vary little between genomes. The genome regions that encode surface gene products that will interact with host targets or aid in immune avoidance are the ones that display the most sequence diversity. Thus, while natural selection favors stability in much of the genome, it favors diversity in these regions.     

Erythrogenic toxins A, B and C: Occurrence of the genes and exotoxin formation from clinical Streptococcus pyogenes strains associated with streptococcal toxic shock-like syndrome

We report the study of 53 clinical isolates of group A streptococci, all from patients with streptococcal toxic shock-like syndrome. The strains were analysed for the occurrence of the genes of erythrogenic toxins (pyrogenic exotoxins) types A, B and C and in vitro production of these toxins. In contrast to reports indicating that 85% of the toxic shock-like syndrome-associated isolates contained the erythrogenic toxin A gene, only 58.5% of our strains harboured this gene. The erythrogenic toxin C gene was detected in 22.6% of the isolates. Erythrogenic toxin A and erythrogenic toxin B were produced by 68.7% and 58.3% of the strains containing either gene. For all group A streptococci, irrespective of clinical association, the erythrogenic toxin B gene was detected in all the isolates tested. Thus, it is difficult to define a specific role for erythrogenic toxin B in toxic shock-like syndrome as there was no clear correlation between this disease and the presence of toxin genes. Our results suggest the existence of other pathogenic factor(s) produced by group A streptococci which may stimulate human peripheral T lymphocytes in a manner similar to that of erythrogenic toxins, thus explaining different observations in previous epidemiological genetic studies.     

Genetic diversity in temperate bacteriophages of Streptococcus pyogenes: identification of a second attachment site for phages carrying the erythrogenic toxin A gene.

Bacteriophage T12, the prototypic bacteriophage of Streptococcus pyogenes carrying the erythrogenic toxin A gene (speA), integrates into the bacterial chromosome at a gene for a serine tRNA (W. M. McShan, Y.-F. Tang, and J. J. Ferretti, Mol. Microbiol. 23:719-728, 1997). This phage is a member of a group of related temperate phages, and we show here that not all speA-carrying phages in this group use the same attachment site for integration into the bacterial chromosome. Additionally, other phages in the group use the same serine tRNA gene attachment site as phage T12 and yet do not carry speA. The evidence suggests that recombination between phage genomes has been an important means of generating diversity and disseminating virulence-associated genes like speA.     

Frequency of genes speA,speB, and speC in Streptococcus pyogenes strains and the identification of the infective agent by polymerase chain reaction

In cultures of S. pyogenes isolated from patients and carriers in different territories of the Russian Federation the genes of erythorogenic toxins A, B and C (speA, speB and specC) were detected. The possibility of the identification of S. pyogenes by means of PCR on the basis of primers to erythrogenic toxin B was determined. Gene speB was detected in all S. pyogenes cultures under study and proved to be species specific. Genes speA and speC were detected, respectively, in 29.4% and 9.35% of the S. pyogenes cultures under study. A test system for the identification of S. pyogenes on the basis of primers to gene speB was developed. The prospects for the detection of genes speA and speC for intraspecific typing of this infective agent were evaluated.     

Bacterial toxins induce heat shock proteins in human neutrophils

We studied the influence of different bacterial toxins (alveolysin; toxic shock syndrome toxin 1, TSST-1 and erythrogenic toxin A, ETA) on the expression of heat shock proteins (hsps) in isolated human polymorphonuclear granulocytes (PMNs). As was shown by Western blotting (anti-hsp72) ETA and TSST-1 were potent inducers of hsps at low toxin concentrations (10 ng/ml). Alveolysin led to the expression of hsps at hemolytic concentrations (1 HU; 700 ng/ml) whereas at subhemolytic concentrations (7 ng/ml) no heat shock response was observed. The induction of heat shock proteins was also accompanied by increased mRNA levels for hsp70 as was determined by PCR-analysis.     

D-alanylation of teichoic acids promotes group a streptococcus antimicrobial peptide resistance, neutrophil survival, and epithelial cell invasion

Group A streptococcus (GAS) is a leading cause of severe, invasive human infections, including necrotizing fasciitis and toxic shock syndrome. An important element of the mammalian innate defense system against invasive bacterial infections such as GAS is the production of antimicrobial peptides (AMPs) such as cathelicidins. In this study, we identify a specific GAS phenotype that confers resistance to host AMPs. Allelic replacement of the dltA gene encoding d-alanine-d-alanyl carrier protein ligase in an invasive serotype M1 GAS isolate led to loss of teichoic acid d-alanylation and an increase in net negative charge on the bacterial surface. Compared to the wild-type (WT) parent strain, the GAS DeltadltA mutant exhibited increased susceptibility to AMP and lysozyme killing and to acidic pH. While phagocytic uptake of WT and DeltadltA mutants by human neutrophils was equivalent, neutrophil-mediated killing of the DeltadltA strain was greatly accelerated. Furthermore, we observed the DeltadltA mutant to be diminished in its ability to adhere to and invade cultured human pharyngeal epithelial cells, a likely proximal step in the pathogenesis of invasive infection. Thus, teichoic acid d-alanylation may contribute in multiple ways to the propensity of invasive GAS to bypass mucosal defenses and produce systemic infection.     

Antibody inhibition of HeLa cell invasion by Yersinia enterocolitica

Antisera were prepared in rabbits against formalized and heat-killed bacteria of Yersinia enterocolitica serotype O:5,27 and against formalized bacteria of serotype O:8. Both strains used for immunization demonstrated adhesion to and invasion of HeLa cells. Coating of the bacteria with antibody did not greatly alter adhesion (i.e., extracellular attachment) to HeLa cells; however, antibody against formalized bacteria of both serotypes inhibited HeLa cell invasion by the homologous and heterologous strains. The Fab fragments from purified immunoglobulins also demonstrated cross-reacting inhibition of HeLa cell invasion. Antibody against heat-killed bacteria of serotype O:5,27 had no inhibitory activity. Adsorption of the antiserum against formalized bacteria of serotype O:5,27 with lipopolysaccharide from the homologous strain removed anti-lipopolysaccharide antibody but did not remove the inhibitory activity. The antiserum against formalized bacteria of serotype O:8 showed no antibody against lipopolysaccharide from serotype O:5,27 and no agglutinins against heat-killed bacteria of this strain. From these results, it is tentatively suggested that protein structures are important in mediating epithelial cell invasion by Y. enterocolitica.     

Translocation of botulinum neurotoxin serotype A and associated proteins across the intestinal epithelia

Botulinum neurotoxins (BoNTs) are some of the most poisonous natural toxins. Botulinum neurotoxins associate with neurotoxin‐associated proteins (NAPs) forming large complexes that are protected from the harsh environment of the gastrointestinal tract. However, it is still unclear how BoNT complexes as large as 900 kDa traverse the epithelial barrier and what role NAPs play in toxin translocation. In this study, we examined the transit of BoNT serotype A (BoNT/A) holotoxin, complex and recombinantly purified NAP complex through cultured and polarized Caco‐2 cells and, for the first time, in the small mouse intestine. Botulinum neurotoxin serotype A and NAPs in the toxin complex were detectable inside intestinal cells beginning at 2 h post intoxication. Appearance of the BoNT/A holotoxin signal was slower, with detection starting at 4–6 h. This indicated that the holotoxin alone was sufficient for entry but the presence of NAPs enhanced the rate of entry. Botulinum neurotoxin serotype A detection peaked at approximately 6 and 8 h for complex and holotoxin, respectively, and thereafter began to disperse with some toxin remaining in the epithelia after 24 h. Purified HA complexes alone were also internalized and followed a similar time course to that of BoNT/A complex internalization. However, recombinant HA complexes did not enhance BoNT/A holotoxin entry in the absence of a physical link with BoNT/A. We propose a model for BoNT/A toxin complex translocation whereby toxin complex entry is facilitated by NAPs in a receptor‐mediated mechanism. Understanding the intestinal uptake of BoNT complexes will aid the development of new measures to prevent or treat oral intoxications.     

An evolutionary conserved mechanism of T cell activation by microbial toxins. Evidence for different affinities of T cell receptor-toxin interaction.

The enterotoxins produced by Staphylococcus aureus are the most potent mitogens known. They belong to a group of distantly related mitogenic toxins that differ in other biologic activities. In this study we have compared the molecular mechanisms by which these mitogens activate human T lymphocytes. We used the staphylococcal enterotoxins A to E, the staphylococcal toxic shock syndrome toxin, the streptococcal erythrogenic toxins A and C (scarlet fever toxins, erythrogenic toxins (ET)A, ETC), and the soluble mitogen produced by Mycoplasma arthritidis. We found that all these toxins can activate both CD4+ and CD8+ T cells and require MHC class II expression on accessory and target cells. However, T cells could be activated in the absence of class II molecules if the toxins ETA or SEB were co-cross-linked on beads together with anti-CD8 or anti-CD2 antibodies. Enterotoxins, toxic shock syndrome toxin and scarlet toxins stimulate a major fraction of human T cells, and show preferential, but not exclusive, stimulation of T cells carrying certain TCR V beta. In contrast, the mitogen of M. arthritidis, a pathogen for rodents stimulates only a minority of human T cells but activates a major fraction of murine T cells. Analysis of human T cell clones expressing V beta 5 or V beta 8 TCR showed that these clones responded also to those toxins that did not stimulate V beta 5+ and V beta 8+ T cells in bulk cultures. These results indicate that different TCR bind to these toxins with different affinities and that the specificity of the TCR-V beta-toxin interaction is quantitative rather than qualitative in nature. Taken together our findings suggest that these toxins use a common mechanism of T cell activation. They are functionally bivalent proteins crosslinking MHC class II molecules with variable parts of the TCR. Besides V beta, other parts of the TCR must be involved in this binding. The finding that murine T cells responded more weakly to the toxins produced by the human-pathogenic bacteria than to the Mycoplasma mitogen could indicate that the toxins have been adapted to the host's immune system in evolution.     

The probiotic Escherichia coli strain Nissle 1917 interferes with invasion of human intestinal epithelial cells by different enteroinvasive bacterial pathogens

The probiotic Escherichia coli strain Nissle 1917 (Mutaflor) of serotype O6:K5:H1 was reported to protect gnotobiotic piglets from infection with Salmonella enterica serovar Typhimurium. An important virulence property of Salmonella is invasion of host epithelial cells. Therefore, we tested for interference of E. coli strain Nissle 1917 with Salmonella invasion of INT407 cells. Simultaneous administration of E. coli strain Nissle 1917 and Salmonella resulted in up to 70% reduction of Salmonella invasion efficiency. Furthermore, invasion of Yersinia enterocolitica, Shigella flexneri, Legionella pneumophila and even of Listeria monocytogenes were inhibited by the probiotic E. coli strain Nissle 1917 without affecting the viability of the invasive bacteria. The observed inhibition of invasion was not due to the production of microcins by the Nissle 1917 strain because its isogenic microcin-negative mutant SK22D was as effective as the parent strain. Reduced invasion rates were also achieved if strain Nissle 1917 was separated from the invasive bacteria as well as from the INT407 monolayer by a membrane non-permeable for bacteria. We conclude E. coli Nissle 1917 to interfere with bacterial invasion of INT407 cells via a secreted component and not relying on direct physical contact with either the invasive bacteria or the epithelial cells.     

Influence of capsular neuraminic acid on properties of streptococci of serological group B.

Neuraminic acid is thought to be a critical virulence factor of group B streptococci. The present study was designed to further characterize a previously described type III group B streptococcus and its transposon-mutagenized asialo capsular mutant. The wild-type group B streptococcus grew as short chains with a uniform turbidity and had diffuse colonies in soft agar media. In contrast, the asialo mutant grew in fluid media as a granular sediment, formed significantly longer chains and had compact colonies in soft agar. These differences, possibly related to the surface charge of the bacteria, could also be demonstrated in salt aggregation tests and hexadecane adherence studies. The wild-type group B streptococcus showed hydrophilic, and the asialo mutant hydrophobic surface properties. Removal of neuraminic acid from the wild-type strain changed the surface properties from hydrophilic to hydrophobic. A similar masking effect of capsular neuraminic acid could be observed in adherence and phagocytosis experiments. In contrast to the wild-type strain, the asialo mutant adhered significantly more to buccal epithelial cells and was phagocytosed more by polymorphonuclear leucocytes. These altered properties might possibly be of importance for group B streptococcal pathogenicity.