Immunization with Recombinant Pneumolysin Induces the Production of Antibodies and Protects Mice in a Model of Systemic Infection Caused by Streptococcus pneumoniae

Immunogenic and protective activity of recombinant pneumolysin was studied in experiments on male BALB/c mice. The mice were immunized intraperitoneally with recombinant pneumolysin sorbed on Al(OH)₃ (200 μg per mouse). In 2 weeks after immunization, the isotypes of antibodies to recombinant pneumolysin in the serum of immunized mice were determined by ELISA. The animals were infected with Streptococcus pneumoniae serotype 3. Immunization with recombinant pneumolysin induced the production of anti-pneumolysin antibodies, mainly of IgG1 subisotype. On day 21 after intraperitoneal infection with S. pneumoniae serotype 3 in a dose of 10⁶ microbial cells, the survival rate of animals immunized with recombinant pneumolysin in a dose of 25 μg/mouse was 67% vs. 0% in the control (p<0.001). Recombinant pneumolysin could be considered as a promising protective antigen for inclusion in the serotype-independent vaccine against S. pneumoniae.

[Construction and characterization of hemolysin S gene mutant strain producing hyaluronic acid]

OBJECTIVE

Streptococcus equi subsp. zooepidemicus (GCS) is mainly used to produce hyaluronic acid (HA) in the industry. GCS secretes the hemolysis toxin (streptolysin S, SLS) that causes hemolysis in the host cells. Therefore, the safety of HA produced by GCS is concerned. We constructed an engineering strain, to produce commercial HA without SLS by knocking out saga.

METHOD

The sagA of GCS was knocked out by the thermosensitive delivery vector system pJR700. The sagA mutant was identified through PCR with primers homologous to the flanking regions and SLS analysis. The yield of HA, HA molecular weight and virulence factors such as streptolysin Hylc, hyaluronate lyase, glyceraldehyde-3-phosphate dehydrogenase and cell surface proteins were determined by spectrophotometer and SDS-PAGE.

RESULT

We constructed successfully the in-frame deletion sagA mutant strain of GCS. In the sagA mutant, HA titer increased more than 30% than that of the wild type strain and no SLS hemolytic activity was detected. Compared to the wild type strain the sagA mutant decreased the quality of surface proteins, hemolytic Hylc activity and glyceraldehyde-3-phosphate dehydrogenase activity. The activities of hyaluronidase and cell were increased in the sagA mutant.

CONCLUSION

The sagA not only expressed hemolysis S but also regulated production of HA, the quality of surface proteins and activities of hyaluronidase, hemolysis Hylc and glyceraldehydes-3-phosphate dehydrogenase in Streptococcus equi subsp. zooepidemicus.

Streptococcus pneumoniae in biofilms are unable to cause invasive disease due to altered virulence determinant production

It is unclear whether Streptococcus pneumoniae in biofilms are virulent and contribute to development of invasive pneumococcal disease (IPD). Using electron microscopy we confirmed the development of mature pneumococcal biofilms in a continuous-flow-through line model and determined that biofilm formation occurred in discrete stages with mature biofilms composed primarily of dead pneumococci. Challenge of mice with equal colony forming units of biofilm and planktonic pneumococci determined that biofilm bacteria were highly attenuated for invasive disease but not nasopharyngeal colonization. Biofilm pneumococci of numerous serotypes were hyper-adhesive and bound to A549 type II pneumocytes and Detroit 562 pharyngeal epithelial cells at levels 2 to 11-fold greater than planktonic counterparts. Using genomic microarrays we examined the pneumococcal transcriptome and determined that during biofilm formation S. pneumoniae down-regulated genes involved in protein synthesis, energy production, metabolism, capsular polysaccharide (CPS) production, and virulence. We confirmed these changes by measuring CPS by ELISA and immunoblotting for the toxin pneumolysin and the bacterial adhesins phosphorylcholine (ChoP), choline-binding protein A (CbpA), and Pneumococcal serine-rich repeat protein (PsrP). We conclude that biofilm pneumococci were avirulent due to reduced CPS and pneumolysin production along with increased ChoP, which is known to bind C-reactive protein and is opsonizing. Likewise, biofilm pneumococci were hyper-adhesive due to selection for the transparent phase variant, reduced CPS, and enhanced production of PsrP, CbpA, and ChoP. These studies suggest that biofilms do not directly contribute to development of IPD and may instead confer a quiescent mode of growth during colonization.

Incompetence of neutrophils to invasive group A streptococcus is attributed to induction of plural virulence factors by dysfunction of a regulator

Group A streptococcus (GAS) causes variety of diseases ranging from common pharyngitis to life-threatening severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock-like syndrome. The characteristic of invasive GAS infections has been thought to attribute to genetic changes in bacteria, however, no clear evidence has shown due to lack of an intriguingly study using serotype-matched isolates from clinical severe invasive GAS infections. In addition, rare outbreaks of invasive infections and their distinctive pathology in which infectious foci without neutrophil infiltration hypothesized us invasive GAS could evade host defense, especially neutrophil functions. Herein we report that a panel of serotype-matched GAS, which were clinically isolated from severe invasive but not from non-invaive infections, could abrogate functions of human polymorphnuclear neutrophils (PMN) in at least two independent ways; due to inducing necrosis to PMN by enhanced production of a pore-forming toxin streptolysin O (SLO) and due to impairment of PMN migration via digesting interleukin-8, a PMN attracting chemokine, by increased production of a serine protease ScpC. Expression of genes was upregulated by a loss of repressive function with the mutation of csrS gene in the all emm49 severe invasive GAS isolates. The csrS mutants from clinical severe invasive GAS isolates exhibited high mortality and disseminated infection with paucity of neutrophils, a characteristic pathology seen in human invasive GAS infection, in a mouse model. However, GAS which lack either SLO or ScpC exhibit much less mortality than the csrS-mutated parent invasive GAS isolate to the infected mice. These results suggest that the abilities of GAS to abrogate PMN functions can determine the onset and severity of invasive GAS infection.

[Structural homology between streptolysin O (SLO) produced by streptococcus pyogenes and SLO-like protein produced by non-pathogenic streptococci and cross-reactivity of antibody against SLO-like protein to SLO]

Nine clones of non-pathogenic streptococci were isolated from the pharynges of seven healthy subjects, and grown on sheep blood agar plates with a hemolysis or gamma hemolysis, then cultured in LB broth for 16 hrs. Purified streptolysin O (SLO) purchased from Sigma Chemical Co. (Sigma-SLO), SLO antigen as a latex agglutination reagent from A company (A-SLO) and supernatants from four culture media were electrophoresed on 12% SDS-polyacrylamide gel and transferred to PVDF membranes. Immunological analyses of antibodies against SLO in healthy sera and proteins in culture medium demonstrated that healthy sera contained an antibody recognizing Sigma-SLO, A-SLO and a protein of the same size as SLO (SLO-like protein) in culture medium. These findings suggest that healthy subjects develop an antibody directed against SLO-like protein produced by non-pathogenic streptococci, and that this antibody cross-reacts with Sigma-SLO and A-SLO. Using DNA from Streptococcus pyogenes and non-pathogenic streptococci, the SLO gene and SLO-like protein gene were analyzed by direct sequencing with oligonucleotide primers designed to cover no. 74 to approximately 1900 of the SLO gene. There were three different bases resulting in amino acid substitution between the SLO gene and SLO-like protein gene, namely 101Lys (AAA) of SLO to Asn (AAT), 175Met (ATG) to Arg (AGG) and 185Asp (GAT) to Asn (AAT). Remaining 560 residues of 563 amino acids constituting SLO-like protein were homologous to SLO. Non-pathogenic streptococci on the pharynges of healthy subjects produce an SLO-like protein composed of amino acids similar to those of SLO, which induces an antibody against this SLO-like protein in serum. It is likely that an antibody against SLO-like protein in healthy sera cross-reacts with SLO and causes a pseudo-positive reaction on ASO measurement by the latex agglutination method using SLO antigen.

Comparison of the effects of macrolides, amoxicillin, ceftriaxone, doxycycline, tobramycin and fluoroquinolones, on the production of pneumolysin by Streptococcus pneumoniae in vitro

OBJECTIVES

To compare the effects of subinhibitory concentrations of amoxicillin, ceftriaxone, azithromycin, clarithromycin, erythromycin, telithromycin, clindamycin, ciprofloxacin, moxifloxacin, tobramycin and doxycycline on pneumolysin production by a macrolide-susceptible strain and two macrolide-resistant strains [erm(B) or mef(A)] of Streptococcus pneumoniae.

METHODS

Pneumolysin was assayed using a functional procedure based on the influx of Ca(2+) into human neutrophils.

RESULTS

Only the macrolides/macrolide-like agents caused significant attenuation of the production of pneumolysin, which was evident with all three strains of the pneumococcus.

CONCLUSIONS

Macrolides, at sub-MICs, but not other classes of antibiotic, subvert the production of pneumolysin, even in the presence of (and irrespective of the mechanism of) macrolide resistance in S. pneumoniae.

Presence of nonhemolytic pneumolysin in serotypes of Streptococcus pneumoniae associated with disease outbreaks

Pneumolysin is an important virulence factor of the human pathogen Streptococcus pneumoniae. Sequence analysis of the ply gene from 121 clinical isolates of S. pneumoniae uncovered a number of alleles. Twenty-two strains were chosen for further analysis, and 14 protein alleles were discovered. Five of these had been reported previously, and the remaining 9 were novel. Cell lysates were used to determine the specific hemolytic activities of the pneumolysin proteins. Six strains showed no hemolytic activity, and the remaining 16 were hemolytic, to varying degrees. We report that the nonhemolytic allele reported previously in serotype 1, sequence type (ST) 306 isolates is also present in a number of pneumococcal isolates of serotype 8 that belong to the ST53 lineage. Serotype 1 and 8 pneumococci are known to be associated with outbreaks of invasive disease. The nonhemolytic pneumolysin allele is therefore associated with the dominant clones of outbreak-associated serotypes of S. pneumoniae.

Streptococcus iniae beta-hemolysin streptolysin S is a virulence factor in fish infection

Streptococcus iniae is a leading pathogen of intensive aquaculture operations worldwide, although understanding of virulence mechanisms of this pathogen in fish is lacking. S. iniae possesses a homolog of streptolysin S (SLS), a secreted, pore-forming cytotoxin that is a proven virulence factor in the human pathogen S. pyogenes. Here we used allelic exchange mutagenesis of the structural gene for the S. iniae SLS precursor (sagA) to examine the role of SLS in S. iniae pathogenicity using in vitro and in vivo models. The isogenic Delta sagA mutant was less cytotoxic to fish blood cells and cultured epithelial cells, but comparable to wild-type (WT) S. iniae in adherence/invasion of epithelial cell monolayers and resisting phagocytic killing by fish whole blood or macrophages. In a hybrid striped bass infection model, loss of SLS production led to marked virulence attenuation, as injection of the Delta sagA mutant at 1000x the WT lethal dose (LD80) produced only 10% mortality. The neutralization of SLS could represent a novel strategy for control of S. iniae infection in aquaculture.

Roxithromycin favorably modifies the initial phase of resistance against infection with macrolide-resistant Streptococcus pneumoniae in a murine pneumonia model

Sub-MIC levels of macrolides down-regulate bacterial virulence factors and suppress inflammatory processes. The ability of macrolides to reduce the production of pneumolysin has been shown to explain the discrepancy between in vitro resistance and outcomes with macrolides against macrolide-resistant Streptococcus pneumoniae. In this study, we determined whether the ability of macrolides to regulate inflammatory processes is beneficial for innate resistance to macrolide-resistant pneumococci in a murine pneumonia model. Among the macrolides tested, only roxithromycin did not affect in vitro pneumococcal virulence factors at sub-MIC levels. Roxithromycin (1.25 to 10 mg/kg of body weight/day) was administered to mice by oral gavage for 3 days before infection with a resistant strain of S. pneumoniae. We evaluated the efficacy of the treatment by determining mouse survival curves and by measuring bacterial burdens and several inflammatory parameters in the airways. Pneumolysin and PspA in infected lungs were examined by Western blot assay. Roxithromycin at doses of > or =5 mg/kg/day increased the median survival time and retarded bacteremia without suppressing the production of pneumolysin and PspA in infected lungs. This treatment reduced matrix metalloproteinase-7 expression and activation and keratinocyte-derived chemokine production in the lungs, while it increased mononuclear cell responses in the lungs, with enhanced bacterial clearance. Concentrations of roxithromycin in plasma and tissues were below the MICs for the inoculated strain during infection. The treatment also reduced inflammatory responses to killed pneumococci in the lungs. These results suggest that the modification by roxithromycin of airway inflammatory responses, including those of matrix metalloproteinase-7 and phagocytes, is beneficial for initial resistance to macrolide-resistant pneumococci.

Clarithromycin alone and in combination with ceftriaxone inhibits the production of pneumolysin by both macrolide-susceptible and macrolide-resistant strains of Streptococcus pneumoniae

OBJECTIVES

To investigate the effects of clarithromycin (0.01-0.5 mg/L) alone or in combination with ceftriaxone (0.1 and 0.25 mg/L) on pneumolysin production by both macrolide-susceptible and -resistant [2 erm(B) positive and 2 mef(A) positive] strains of Streptococcus pneumoniae.

METHODS

The bacteria were cultured for 6 h at 37 degrees C/5% CO(2) in tryptone soy broth, washed, enumerated and resuspended to 0.5-3 x 10(8) cfu/mL in tissue culture medium, RPMI 1640. After 16 h of incubation at 37 degrees C / 5% CO(2), pneumolysin was assayed in the bacteria-free supernatants, as well as in lysates, using a functional assay based on the influx of calcium into human neutrophils.

RESULTS

Exposure of not only macrolide-susceptible strains, but also the macrolide-resistant strains, of S. pneumoniae to sub-MICs of clarithromycin resulted in dose-related inhibition of the pneumolysin production, whereas production of the toxin was unaffected by ceftriaxone.

CONCLUSIONS

These observations demonstrate that even in the setting of macrolide resistance the production of pneumolysin, a key virulence factor of the pneumococcus, is attenuated by exposure of this microbial pathogen to clarithromycin.

Growth phase-dependent effect of clindamycin on production of exoproteins by Streptococcus pyogenes

The administration of high-dose clindamycin plus benzylpenicillin has been recommended for the treatment of streptococcal toxic shock-like syndrome caused by Streptococcus pyogenes, and clindamycin has been found to be more effective than beta-lactams in retrospective analyses of human cases. Although therapeutic doses of clindamycin have also been shown to be effective against experimental infections and clindamycin has great efficacy against the production of bacterial exoproteins, we recently reported that the level of production of some exoproteins was unchanged or even increased by a subinhibitory dose of clindamycin when it is added upon the initiation of bacterial culture and the treated cultures were analyzed by two-dimensional gel electrophoresis. In this study we further examined the effect of clindamycin on the production of exoproteins by adding it to Streptococcus pyogenes cultures during various growth phases. We found that the levels of production of some proteins, NAD+ glycohydrolase, streptolysin O, and streptococcal inhibitor of complement, were increased when clindamycin was added at early-log-phase growth, which was the result that was seen when clindamycin was added at the beginning of culture. However, clindamycin inhibited the production of most types of proteins when it was administered to Streptococcus pyogenes cultures at mid-log-phase growth. In csrS- or mga-knockout bacterial strains, the increase in exoproteins seen in parental strains was considerably inhibited. Our study indicates that the in vitro effect of clindamycin on the production of exoproteins greatly depends on the growth phase of bacteria and some regulatory factors of Streptococcus pyogenes that are involved in this phenomenon.

Tex, a putative transcriptional accessory factor, is involved in pathogen fitness in Streptococcus pneumoniae

We have identified a pneumococcal gene, tex, which has the potential to regulate gene expression. The tex gene is named for its role in toxin expression in Bordetella pertussis, where it was characterized as an essential gene. Homologous sequences have been found in both Gram-positive and Gram-negative bacteria and are highly conserved at the protein level. Tex family proteins contain a S1 RNA-binding domain at the C-terminus. Members of this family are putative transcriptional accessory factors. Although tex in Streptococcus pneumoniae is homologous to that in B. pertussis, there are distinct differences. Since the tex gene in S. pneumoniae is not an essential gene, we were able to delete tex in strain D39. The tex knockout mutant, DeltaTex, did not affect production of the pneumococcal toxin pneumolysin. However, we observed decreased growth of DeltaTex in the presence of the wild-type strain both in vitro and in vivo as determined by generation numbers and competitive index (CI). The interaction between recombinant Tex and nucleic acids was confirmed by southwestern and northwestern analysis, supporting its role as a transcriptional accessory factor.

[Preparation of new protein carrier of vaccine against pneumococcal otitis media with genetic engineering technology]

OBJECTIVE

To prepare pneumolysin as a new protein carrier of vaccine against otitis media with genetic engineering technology and establish the base of the study on pneumococcal conjugative vaccines.

METHODS

Genomic DNA was isolated from streptococcus pneumoniae. A pair of primers which included two restriction sites was designed based on the published pneumolysin gene sequence. The pneumolysin gene was amplified from pneumococcal DNA with PCR technology. The restriction enzyme digested fragment was linked into the cloning vector PET-28a and the recombinant plasmid DNA containing pneumolysin was then transfected into host cell E. coli JM109 (DE3).

RESULTS

DNA fragments were subcloned to construct the complete pneumolysin gene by a conventional coning and PCR. The inserted pneumolysin gene sequence was confirmed by DNA sequencing and the pneumolysin protein was successfully expressed. The relative molecular mass of the expressed product was 52 000. The expressed product amounted to 8% of the total host cell protein.

CONCLUSIONS

The pneumolysin gene was successfully cloned into host cell using genetic engineering technology. The recombinant pneumolysin was expressed and purified for preparation. This work laid a foundation of the preparation of pneumococcal conjugative vaccines.

Genetic and biochemical properties of streptococcal NAD-glycohydrolase inhibitor

The gene encoding streptolysin O (slo), a cytolysin of hemolytic streptococci, is transcribed polycistronically from the promoter of the preceding NAD-glycohydrolase (NADase) gene (nga). Between nga and slo, a putative open reading frame (orf1) is located whose function has been totally unknown. Present investigation demonstrated that the orf1 encodes a protein designated as streptococcal NADase inhibitor (SNI). From its nucleotide sequence, SNI was inferred to comprise 161 amino acid residues and the deduced molecular weight was 18,800. This protein was detectable only within cells. Coexpression of SNI was essential for production of streptococcal NADase, and NADase precursor existed as an inactive complex with SNI, in recombinant Escherichia coli. Monomeric NADase and SNI rapidly formed in vitro a stable heterodimer complex in the ratio 1:1, resulting in complete suppression of the hydrolase activity. Unlike other bacterial NADase inhibitors, SNI was thermostable. This protein, coexpressed and complexed with NADase, may protect the producer cocci from exhaustion of NAD.

Differences in clinical manifestation of Streptococcus pneumoniae infection are not correlated with in vitro production and release of the virulence factors pneumolysin and lipoteichoic and teichoic acids

Production and release of the pneumococcal virulence factors pneumolysin and lipoteichoic and teichoic acid in 75 clinical isolates were investigated. No difference was found between strains causing systemic infection or localized respiratory infection and isolates from asymptomatic carriers. This suggests that the presence of pneumolysin and lipoteichoic and teichoic acid is a necessary but not a sufficient condition for pneumococcal infection and development of invasive disease.

Role for serine protease HtrA (DegP) of Streptococcus pyogenes in the biogenesis of virulence factors SpeB and the hemolysin streptolysin S

The serine protease HtrA is involved in the folding and maturation of secreted proteins, as well as in the degradation of proteins that misfold during secretion. Depletion of HtrA has been shown to affect the sensitivity of many organisms to thermal and environmental stresses, as well as being essential for virulence in many pathogens. In the present study, we compared the behaviors of several different HtrA mutants of the gram-positive pathogen Streptococcus pyogenes (group A streptococcus). Consistent with prior reports, insertional inactivation of htrA, the gene that encodes HtrA, resulted in a mutant that grew poorly at 37 degrees C. However, an identical phenotype was observed when a similar polar insertion was placed immediately downstream of htrA in the streptococcal chromosome, suggesting that the growth defect of the insertion mutant was not a direct result of insertional inactivation of htrA. This conclusion was supported by the observation that a nonpolar deletion mutation of htrA did not produce the growth defect. However, this mutation did affect the production of several secreted virulence factors whose biogenesis requires extensive processing. For the SpeB cysteine protease, the loss of HtrA was associated with a failure to proteolytically process the zymogen to an active protease. For the streptolysin S hemolysin, a dramatic increase in hemolytic activity resulted from the depletion of HtrA. Interestingly, HtrA-deficient mutants were not attenuated in a murine model of subcutaneous infection. These data add to the growing body of information that implies an important role for HtrA in the biogenesis of secreted proteins in gram-positive bacteria.

Immunizations with pneumococcal surface protein A and pneumolysin are protective against pneumonia in a murine model of pulmonary infection with Streptococcus pneumoniae

Intranasal infection of mice with certain strains of capsular group 19 Streptococcus pneumoniae can result in focal pneumonia in the absence of bacteremia. Using this model of murine pneumonia, we demonstrated that immunization with recombinant forms of either pneumococcal surface protein A (PspA) or PdB (a genetically detoxified derivative of pneumolysin) elicited significant protection against focal pulmonary infection. This may be the first demonstration that a proposed vaccine antigen can protect against pneumococcal pneumonia. The best protection was obtained by immunizing mice with a mixture of PspA and PdB, indicating that the protection elicited by these antigens can complement each other. This result is in agreement with previous studies that used pneumococcal sepsis and nasal colonization models and demonstrate that the best protein vaccines for prevention of infection may be those that include more than one protection-eliciting pneumococcal protein.

Effect of date extract on growth and hemolytic activity of Streptococcus pyogenes

The effect of date extract on growth and hemolytic activity of S. pyogenes was examined. It was found that 5% DE caused 78 % growth inhibition. However, 20% DE inhibited the growth by 86%. 5% DE inhibited hemolysin and streptolysin O activities by 43% and 24% respectively,while 20% caused 95 and 91 %inhibition.

Evaluation of gene-technological and conventional methods in the identification of Streptococcus pneumoniae

To find reliable methods able to identify the "difficult" Streptococcus pneumoniae isolates, an in-house polymerase chain reaction (PCR) for pneumolysin gene (Ply-PCR) and a commercial RNA hybridisation test (AccuProbe) were evaluated. Selected isolates of suspected pneumococci, sent for confirmation of identification and for serotyping, were classified into four groups based on their optochin sensitivity and capsule reaction. All isolates in Group 1, which consisted of 24 typical, optochin-sensitive, encapsulated pneumococcal strains, were positive in the Ply-PCR and AccuProbe tests. In Group 2, which consisted of 25 optochin-sensitive, but unencapsulated pneumococcal strains, all the isolates were positive in the Ply-PCR test, and 23 were positive in the AccuProbe test. In Group 3, which consisted of 15 atypical, optochin-resistant but encapsulated pneumococci, 12 of the isolates were positive in the Ply-PCR and 12 in the AccuProbe test, and 11 of these 12 strains were positive in both tests. In Group 4, which consisted of 36 equivocal optochin-resistant, unencapsulated isolates, 15 strains were positive in the Ply-PCR test and 8 strains in the AccuProbe test. As a conclusion, the Ply-PCR and AccuProbe tests identified similarly typical optochin-sensitive pneumococci, but gave partly controversial results about atypical pneumococci. Thus, they did not reliably help in the identification of suspected pneumococcal isolates lacking the conventional characteristics of pneumococcus.

Dual control of streptokinase and streptolysin S production by the covRS and fasCAX two-component regulators in Streptococcus dysgalactiae subsp. equisimilis

Synthesis of the plasminogen activator streptokinase (SK) by group A streptococci (GAS) has recently been shown to be subject to control by two two-component regulators, covRS (or csrRS) and fasBCA. In independent studies, response regulator CovR proved to act as the repressor, whereas FasA was found to act indirectly as the activator by controlling the expression of a stimulatory RNA, fasX. In an attempt at understanding the regulation of SK production in the human group C streptococcal (GCS) strain H46A, the strongest SK producer known yet, we provide here physical and functional evidence for the presence of the cov and fas systems in GCS as well and, using a mutational approach, compare the balance between their opposing actions in H46A and GAS strain NZ131. Sequence analysis combined with Southern hybridization revealed that the covRS and fasCAX operons are preserved at high levels of primary structure identity between the corresponding GAS and GCS genes, with the exception of fasB, encoding a second sensor kinase that is not a member of the GCS fas operon. This analysis also showed that wild-type H46A is actually a derepressed mutant for SK and streptolysin S (SLS) synthesis, carrying a K102 amber mutation in covR. Using cov and fas mutations in various combinations together with strain constructs allowing complementation in trans, we found that, in H46A, cov and fas contribute to approximately equal negative and positive extents, respectively, to constitutive SK and SLS activity. The amounts of SK paralleled the level of skc(H46A) transcription. The most profound difference between H46A and NZ131 regarding the relative activities of the cov and fas systems consisted in significantly higher activity of a functional CovR repressor in NZ131 than in H46A. In NZ131, CovR decreased SK activity in a Fas(+) background about sevenfold, compared to a 1.9-fold reduction of SK activity in H46A. Combined with the very short-lived nature of covR mRNA (decay rate, 1.39/min), such differences may contribute to strain-specific peculiarities of the expression of two prominent streptococcal virulence factors in response to environmental changes.

New gene cluster for lantibiotic streptin possibly involved in streptolysin S formation

Streptolysin S (SLS) is a serum-extractable and oxygen-stable hemolysin produced by Group A Streptococcus. A SLS-deficient mutant in which transposon Tn 916 was inserted in a locus distinct from the sag gene cluster [Nizet et al. (2000) Infect. Immun. 68, 4245-4254] was obtained by filter mating of the transposon-harbouring Enterococcus faecalis strain and Streptococcus pyogenes BL(T). This mutant, N22, had completely lost the hemolytic activity, in consequence of insertion of a single Tn 916 into a hitherto-unknown lantibiotic gene cluster composed of 10 open reading frames. The arrangement and sequence of this lantibiotic gene cluster were similar to those of nisin and subtilin, and so we designated this new lantibiotic as streptin. The bactericidal activity of streptin was abolished on treatment with trypsin or proteinase K. The different host range and nucleotide sequence clearly distinguished streptin from streptococcins. Streptin was not hemolytic and its bacteriocin activity was independent of carrier oligonucleotides effective for SLS. The fact that N22 also lost the anti-bacterial activity against indicator streptococci reveals that the factor(s) required for lantibiotic formation plays an important role in SLS formation as well.

Genetic locus for streptolysin S production by group A streptococcus

Group A streptococcus (GAS) is an important human pathogen that causes pharyngitis and invasive infections, including necrotizing fasciitis. Streptolysin S (SLS) is the cytolytic factor that creates the zone of beta-hemolysis surrounding GAS colonies grown on blood agar. We recently reported the discovery of a potential genetic determinant involved in SLS production, sagA, encoding a small peptide of 53 amino acids (S. D. Betschel, S. M. Borgia, N. L. Barg, D. E. Low, and J. C. De Azavedo, Infect. Immun. 66:1671-1679, 1998). Using transposon mutagenesis, chromosomal walking steps, and data from the GAS genome sequencing project (www.genome.ou.edu/strep. html), we have now identified a contiguous nine-gene locus (sagA to sagI) involved in SLS production. The sag locus is conserved among GAS strains regardless of M protein type. Targeted plasmid integrational mutagenesis of each gene in the sag operon resulted in an SLS-negative phenotype. Targeted integrations (i) upstream of the sagA promoter and (ii) downstream of a terminator sequence after sagI did not affect SLS production, establishing the functional boundaries of the operon. A rho-independent terminator sequence between sagA and sagB appears to regulate the amount of sagA transcript produced versus transcript for the entire operon. Reintroduction of the nine-gene sag locus on a plasmid vector restored SLS activity to the nonhemolytic sagA knockout mutant. Finally, heterologous expression of the intact sag operon conferred the SLS beta-hemolytic phenotype to the nonhemolytic Lactococcus lactis. We conclude that gene products of the GAS sag operon are both necessary and sufficient for SLS production. Sequence homologies of sag operon gene products suggest that SLS is related to the bacteriocin family of microbial toxins.

A two-component regulatory system, CsrR-CsrS, represses expression of three Streptococcus pyogenes virulence factors, hyaluronic acid capsule, streptolysin S, and pyrogenic exotoxin B

Certain Tn916 insertions in the chromosome of an M1-type, nonmucoid Streptococcus pyogenes isolate (MGAS166) were previously shown to result in stable mucoidy with increased expression of the capsular synthetic genes. The transposon insertions in these strains are directly upstream of an apparent operon encoding a two-component regulatory system, designated csrR-csrS. Compared with MGAS166, these mucoid mutants are more hemolytic and cause significantly more tissue damage in a murine model of skin infection. To extend these observations, we constructed an in-frame deletion in the gene encoding the response regulator, csrR, and we evaluated the expression of other known S. pyogenes virulence factors. We discovered that csrR mutants have enhanced transcription of sagA, a gene associated with streptolysin S (SLS) and speB, the gene encoding pyrogenic exotoxin B (SpeB). The mutants also express substantially higher SLS activity and SpeB antigen in late-exponential-phase cultures. There is no change in expression of emm, scpA, sic, or cpa (genes encoding other S. pyogenes virulence factors). CsrR- strains but not the wild-type parental strain produce necrotizing lesions in a mouse model of subcutaneous infection. A double mutant with deletions in both csrR and the capsular synthesis genes caused fewer and smaller necrotic skin lesions than the csrR mutants. However, this nonmucoid csrR strain was more likely than the wild type to yield necrotic lesions, suggesting that mucoidy contributes to virulence in this model of infection but that there are other csrR-regulated factors involved in the production of necrotic lesions.

[Production and partial purification of the main hemolysin (pneumolysin) of Streptococcus pneumoniae]

The capacity of 36 Cuban strains of Streptococcus pneumoniae to produce pneumolysin was studied, and 94.4% of them were determined to be producers of that enzyme. One of the best producers was cultured at a great scale and the pneumolysin found in the supernatan was partially purified through an ion-exchange chromatography in mono-Q column. This method made it possible to recover the enzyme whose purity level increased by 4.39 with 100% output.

A comparison of the early inflammatory effects of an agr-/sar- versus a wild type strain of Staphylococcus aureus in a rat model of endophthalmitis

PURPOSE

We examined the ability of a wild type and an isogenic mutant strain of Staphylococcus aureus, deficient in the production of hemolysins and lipase (agr (-)/sar (-)), to induce endophthalmitis and inflammatory cell infiltration into the eye at 6, 24 and 48 hours after injection in a rat model of endophthalmitis.

METHODS

Rat eyes were injected with 25 microl of viable S. aureus or sterile saline. Eyes were graded for clinical signs of inflammation daily, removed and processed for standard histologic analysis 6, 24 and 48 hours after injections. Comparisons of clinical scores and mean inflammatory cell numbers were made between S. aureus and control injected eyes.

RESULTS

Both experimental groups developed clinical signs of endophthalmitis and demonstrated infiltration of inflammatory cells at 24 and 48 hours. Clinical inflammation in the Mutant I group was less than the wild type group at these times and significantly less at 48 hours (p<0.05). No statistically significant difference in the number of inflammatory cells was detected between the wild type and Mutant I injected eyes at 24 hours. At 48 hours, inflammatory cells increased by 75.0% in the wild type group and decreased by 19.0% in the Mutant I group and a statistically significant difference was seen between these two groups (p<0.05). At all times, the majority of inflammatory cells were neutrophils. By 48 hours, an increase in monocytes-macrophages was noted.

CONCLUSION

Both strains of S. aureus induced clinical signs of inflammation and inflammatory cell infiltration. Clinical inflammation and inflammatory cell numbers were less in rats injected with the Mutant I strain. These results suggest that hemolysins and lipase may be important in the early induction phase of the inflammatory response.

Unique synthetic peptides stimulating streptolysin S production in streptococci

A peptide has been isolated from pronase digest of bovine serum albumin as the stimulatory factor of streptolysin S (SLS) production by Streptococcus pyogenes, and its primary structure has been deduced [Akao et al. (1992) Infect. Immun. 60, 4777-4780]. To determine the essential structure for the stimulation, a peptide (P-1) having the deduced structure, in which three peptide fragments are linked by two disulfide bonds, and shorter analogs (P-2 to P-4) of peptide P-1 were chemically synthesized. Another peptide (P-5), in which Ala is inserted between the two Cys residues in the middle peptide chain of P-1, was also synthesized. These synthetic peptides were identified by mass spectrometry and analysis of amino acid compositions. The synthetic P-1 stimulated SLS production in a dose-dependent manner. Other peptide analogs also showed remarkable stimulation of SLS production. Treatment of P-1 with performic acid resulted in loss of its stimulatory activity, indicating that disulfide bridges of the peptides are necessary for their activity on SLS production. These results suggest that the unique primary structure of three peptide chains linked by two disulfide bridges is requisite for the stimulatory effect on SLS production.

Characterization of the haemolytic activity of Streptococcus equi

The haemolytic activity of Streptococcus equi, the cause of equine strangles, was characterized. Production of haemolysin in Todd Hewitt broth was dependent on an equine serum supplement and the logarithmic phase of growth after which activity declined sharply. RNA core also induced haemolysin production from cells harvested at the end of the logarithmic phase of growth. Haemolysis was not affected by cholesterol, was only slightly increased in reducing conditions and was completely inactivated by trypan blue, identifying the haemolytic activity as streptolysin S-like (SLS-like). Purification by hydroxyapatite and Sephacryl column chromatography yielded proteins of molecular weights of approximately 6000 and 17 000-22 000 Da with a 64-fold increase in specific activity. Low molecular weight proteins from the RNA core were still present in the purified toxin. Two non-haemolytic mutants were derived by conjugation with an Enterococcus faecalis-carrying transposon Tn916. Southern blots of HindIII digests of DNA revealed that one of the mutants contained three transposon insertions and the other just one. A lambda phage library of S. equi contained plaques whose haemolytic activity was enhanced by reducing conditions and inhibited by cholesterol, suggesting a streptolysin O-like (SLO-like) activity. However, haemolysin in culture sonicates of host E. coli in which the lambda phage insert was subcloned into plasmid (pUC18), was not affected by these conditions. Seven isolates of S. equi in medium without SLS-like inducers showed no SLO-like activity and no evidence for an SLO-like toxin could be found by immunoblotting with pneumolysin antiserum and monoclonal antibodies or by polymerase chain reaction with primers derived from sequences conserved between the SLO genes of Lancefield group A, C and G streptococci. S. equi does not appear to possess a streptolysin O but does make a streptolysin S-like toxin whose production can be interrupted at just one genetic locus.

Effects of synthetic hydroxy isothiocyanates on microbial systems

Hydroxy isothiocyanates (ITCs), including some new derivatives of naturally occurring compounds, were synthesized and their minimum inhibitory, minimum fungicidal, and minimum bactericidal concentrations for Aspergillus niger, Aspergillus fumigatus, Staphylococcus aureus, and Escherichia coli were estimated. These compounds were strongly antimicrobial; for example, 2-(4-hydroxyphenyl) ethyl ITC inhibited growth of all strains examined at concentrations of 7.8 to 15.6 micrograms/ml. The ATP concentration in E. coli was markedly reduced when cells were treated with 2-(4-hydroxyphenyl)ethyl ITC. Inhibition of the growth of E. coli by 2-(4-hydroxyphenyl)ethyl ITC was decreased in the presence of cysteine. Streptolysin S production in washed cells of Streptococcus equisimilis was extremely sensitive to this ITC derivative and this inhibition also was counteracted by cysteine. The results showed that the ITC compounds had antimicrobial effects by blocking sulfhydryl groups.

Temporal production of streptococcal erythrogenic toxin B (streptococcal cysteine proteinase) in response to nutrient depletion

The effects of various growth conditions on the production of streptococcal erythrogenic toxin B (streptococcal pyrogenic exotoxin B [SPE B]) by Streptococcus pyogenes were analyzed. SPE B was detected in broth culture supernatant fluid only during the stationary phase of growth when glucose and other potential carbon sources were depleted from the medium. Additionally, SPE B production was inhibited when the concentration of glucose in the medium was maintained. These results suggest that SPE B is secreted under conditions of starvation and may be involved in nutrient acquisition.

Differences in virulence for mice among Streptococcus pneumoniae strains of capsular types 2, 3, 4, 5, and 6 are not attributable to differences in pneumolysin production

We observed that differences in the in vivo growth kinetics of pneumococcal strains of capsular types 3, 4, 5, and 6 were reminiscent of differences that we had previously reported for type 2 strain D39 and its pneumolysin-deficient mutant, PLN. Capsular type 2 Streptococcus pneumoniae D39 exhibits exponential growth in the blood of XID mice until the death of the mice at 24 to 36 h. In contrast, PLN reaches a plateau in growth that is maintained for several days. Capsular type 3 and 5 strains exhibited exponential growth and caused rapid death of XID mice following intravenous challenge, similar to the observation with D39. Strains of capsular types 4 and 6 exhibited growth kinetics reminiscent of PLN. Since the observed differences in the pathogenesis of types 3 and 5 compared to 4 and 6 were reminiscent of the effects of pneumolysin deficiency in type 2, we examined the levels of in vitro pneumolysin production for the entire panel of strains. The onset of pneumolysin production in most strains was rapid and occurred near the end of log-phase growth. Differences in in vivo growth patterns of capsular type 2, 3, 4, 5, and 6 strains were not found to be associated with differences in the levels of pneumolysin.

Expression of active streptolysin O in Escherichia coli as a maltose-binding-protein--streptolysin-O fusion protein. The N-terminal 70 amino acids are not required for hemolytic activity

Streptolysin 0 (SLO) is the prototype of a family of cytolysins that consists of proteins which bind to cholesterol and form very large transmembrane pores. Structure/function studies on the pore-forming cytolysin SLO have been complicated by the proteolytic inactivation of a substantial portion of recombinant SLO (rSLO) expressed in Escherichia coli. To overcome this problem, translational fusions between the E. coli maltose-binding protein (MBP) gene and SLO were constructed, using the vectors pMAL-p2 and pMAL-c2. MBP-SLO fusion proteins were degraded if secreted into the E. coli periplasm, but intact, soluble MBP-SLO fusion proteins were produced at high levels in the cytoplasm. Active SLO with the expected N-terminus was separated from the MBP carrier by cleavage with factor Xa. Cleavage with plasmin or trypsin also yielded active, but slightly smaller forms of SLO. Surprisingly, uncleaved MBP-SLO was also hemolytic and cytotoxic to human fibroblasts and keratinocytes. The MBP-SLO fusion protein displayed equal activities to SLO. Sucrose density gradient analyses showed that the fusion protein assembled into polymers, and no difference in structure was discerned compared with polymers formed by native SLO. These studies show that the N-terminal 70 residues of mature (secreted) SLO are not required for pore formation and that the N-terminus of the molecule is probably not inserted into the bilayer. In addition, they provide a simple means for producing mutants for structure/function studies and highly purified SLO for use as a permeabilising reagent in cell biology research.

The role of pneumolysin and autolysin in the pathology of pneumonia and septicemia in mice infected with a type 2 pneumococcus

Mice were infected intranasally with a serotype 2 pneumococcus, a pneumolysin-negative derivative (PLN-A), or an autolysin-negative derivative (AL-2). Numbers of wild type pneumococci were seen in the lung from approximately 12 h after infection and were first detected in the blood around this time. Immunofluorescent staining of lung sections showed that pneumolysin was produced in vivo. Pneumococcal infection resulted in alteration of the composition of the blood but not the bone marrow. Some of the hematologic changes did not occur after PLN-A. PLN-A had a slower growth rate in the lung and bacteremia was delayed. AL-2 was rapidly cleared from the lungs and was not detected in the blood. These events paralleled the pattern of histology in the lung, with the severity of inflammation reduced with PLN-A and no inflammation or hematologic changes with AL-2.

Expression of streptolysin O gene in Bacillus subtilis

Streptolysin O (SLO) is a hemolytic, extracellular protein produced by Streptococcus pyogenes. A hybrid gene consisting of the promoter and signal sequence fused to the region encoding the mature sequence of the slo gene was constructed to secrete SLO in Bacillus subtilis. To increase secretion of SLO into the culture supernatant, several SLO expression vectors containing various combinations of promoters and pre-pro sequences were constructed. B. subtilis harboring pPA consisting of the P-43 promoter and the coding sequence of the pre region of the alkaline protease gene that was fused to the pro-mature region of the slo gene secreted SLO into media. The degree of hemolytic activity was found to be about 40-fold higher in the geneticaly engineered B. subtilis strain than that of S. pyogenes. Recombinant SLO was reacted with patients' sera infected by group A streptococci.

Postantibiotic effect of roxithromycin on streptolysin O production, hydrophobicity, and bactericidal activity of PMNL by Streptococcus pyogenes

Exposure of Streptococcus pyogenes to 5 x minimum inhibitory concentration of roxithromycin for 1 h produced a significant postantibiotic effect. More than 2.5 h was necessary for roxithromycin-treated bacteria to increase by 1 log10 in colony-forming units after drug removal, compared with the unexposed cells. After exposure to and removal of the drug, treated cells failed to exhibit normal hemolytic activity for at least 4 h. The inhibitory effect persisted for 20 h after drug removal, although the extent of growth for treated and untreated cells was almost the same. Hydrophobicity of treated cells, studied throughout the logarithmic growth phase with a water-hexadecan two-phase system, was markedly decreased by 40%, compared with untreated cells 4 h after drug removal. Cells that had been treated with roxithromycin became more susceptible to the bactericidal activity of human PMNL than untreated bacteria. The data indicate that some of the metabolic activity that contributes to the virulence of S. pyogenes is affected by postexposure to roxithromycin, and its minimum inhibitory concentration and serum level might not be the best indicators of efficacy in this class of drugs.

Purification and characterization of a peptide essential for formation of streptolysin S by Streptococcus pyogenes

Peptides in a pronase digest of bovine serum albumin were required for streptolysin S formation by Streptococcus pyogenes besides maltose and a carrier (the oligonucleotide fraction obtained by treatment of Saccharomyces cerevisiae RNA with RNase A). A peptide essential for streptolysin S formation was purified to homogeneity from a pronase digest of bovine serum albumin by Sephadex G-25 column chromatography, and anion-exchange, reverse-phase, and gel filtration high-performance liquid chromatography. The purified peptide was divided into more than two peptides by HCOOOH oxidation and was composed of four residues of cysteine, three of leucine, and one each of aspartic acid and glutamic acid. Leucine and cysteine were detected as amino-terminal residues, and leucine and glutamic acid were detected as carboxyl-terminal residues, suggesting that two or three peptides are linked by a disulfide bond(s). A disulfide bond structure in the peptide seemed to be required for streptolysin S formation.

The effect of roxithromycin on the virulence of gram-positive cocci

Antibiotics whose recognized mode of action comprises inhibition of bacterial protein biosynthesis are also recognized to modulate the expression of bacterial virulence factors when incorporated into culture media at sub-MIC levels. In this respect, one of the new macrolides, roxithromycin, has been examined for its effect on toxin/enzyme production by strains of Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus pneumoniae. Biosynthesis of staphylococcal coagulase and DNase could be potentiated, whereas that of staphylococcal alpha-hemolysin, streptolysins O and S, and pneumolysin were unaltered. Expression of one structural virulence factor, pneumococcal polysaccharide, was repressed in the drug's presence, resulting in potentiation of phagocytic ingestion of the drug-exposed bacteria. The drug failed to have any effect on ingestion of Staph. aureus or Strep. pyogenes. These studies provide evidence that roxithromycin may exhibit "added value" as an antibiotic in its ability to potentiate the susceptibility of Strep. pneumoniae to host defenses such as phagocytosis.

The effect of Streptococcus pneumoniae pneumolysin on human respiratory epithelium in vitro

Streptococcus pneumoniae culture filtrates and pneumolysin both slow human ciliary beating and damage respiratory epithelium in vitro. A polyclonal pneumolysin antibody bound to sepharose beads removed pneumolysin from culture filtrates and showed that pneumolysin alone was responsible for the effects on epithelium. In a 48-h organ culture pneumolysin caused ciliary slowing and epithelial disruption in a dose-dependent manner down to 5 ng/ml. Comparison of the ciliary slowing activity and pneumolysin concentration in filtrates in a continuous broth culture showed a maximal effect at 16 h (pneumolysin 7.5 micrograms/ml). Later the activity decreased while the pneumolysin concentration increased (8.8 micrograms/ml). This loss of activity was prevented by neutralisation of the acid pH of the culture medium. Eight different culture filtrates produced significant (P less than 0.05) ciliary slowing which correlated (r = 0.95) with simultaneously measured haemolytic (pneumolysin) activity. Substitution of tryptophan (position 433) by phenylalanine reduced the haemolytic and ciliary slowing activity of pneumolysin, but did not affect its ability to activate complement. There was no correlation between the ciliary slowing produced by the culture filtrate and that produced by the autolysate of a particular strain, nor between ciliary slowing and the extent of autolysis or the serotype of the strain.

Effect of Streptococcus pneumoniae on human respiratory epithelium in vitro

A total of 11 of 15 Streptococcus pneumoniae culture filtrates and all five bacterial autolysates produced by cell death in the stationary phase caused slowed ciliary beating and disruption of the surface integrity of human respiratory epithelium in organ culture. This effect was inhibited by cholesterol and was heat labile and reduced by standing at room temperature but was stable at -40 degrees C. The activity was detected at the late stationary phase of culture and was associated with the presence of hemolytic activity. Gel filtration of a concentrated culture filtrate and autolysate both yielded a single fraction of approximately 50 kilodaltons which slowed ciliary beating and were the only fractions with hemolytic activity. Rabbit antiserum to pneumolysin, a sulfhydryl-activated hemolytic cytotoxin released by S. pneumoniae during autolysis, neutralized the effect of the culture filtrate on respiratory epithelium. Both native and recombinant pneumolysin caused ciliary slowing and epithelial disruption. Electron microscopy showed a toxic effect of pneumolysin on epithelial cells: cytoplasmic blebs, mitochondrial swelling, cellular extrusion, and cell death, but no change in ciliary ultrastructure. Recombinant pneumolysin (10 micrograms/ml) caused ciliary slowing in the absence of changes in cell ultrastructure. Release of pneumolysin in the respiratory tract during infection may perturb host defenses, allowing bacterial proliferation and spread.

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.

The role of iron in the growth and hemolysin (Streptolysin S) production in Streptococcus pyogenes

Four strains of Streptococcus pyogenes were propagated at 37 degrees C in a reduced iron medium supplemented with Fe3+-citrate to give concentrations of 1 through 11 micrograms per milliliter, in order to observe the effects of iron on growth and on the vitro production of Streptolysin S. Both growth and hemolysin production were observed to be influenced by medium iron concentration of which 1.2 micrograms per ml of iron was critical. Hemolysin was produced during the exponential phase of the growth cycle with maximum yield as the organism entered the stationary phase. Hemolytic activity (which was accepted as the ability of the hemolysin to lyse sheep erythrocytes) fell below detectable levels as the organisms entered fully into the stationary phase (9-10 hours post incubation). Serum (bovine, human, chicken) was observed to have a high stabilizing effect on the hemolysin.