Persistence of group A streptococci in eukaryotic cells--a safe place?

Echinacea can help with Azithromycin in prevention of recurrent tonsillitis in children

PURPOSE

Recurrent tonsillitis in children is a common disease affecting children quality of life and extends to their families. The aim of this study was to assess the effect of combined use of oral Azithromycin (AZT) plus Echinacea compared to exclusive use of AZT in children with recurrent tonsillitis.

MATERIAL AND METHODS

A prospective comparative study including three groups of children with recurrent tonsillitis. Group 1: (100 patients) had no prophylactic treatment. Group 2 (100 patients) received [60 mg/kg] prophylactic dose of AZT divided as (10 mg/kg/day) over 6 consecutive days every month for 6 consecutive months. Group 3 (100 patients) received AZT as in group 2 plus commercially available Echinacea in a dose of 5 ml oral suspension; 3 times daily for 10 consecutive days every month for 6 consecutive months. Number of tonsillitis attacks and severity of tonsillitis symptoms were assessed and compared in different groups.

RESULTS

Group 2 and group 3 had significant less number of tonsillitis attacks and severity of assessed symptoms during 6 months of prophylactic treatment with significant better results in group 3 (i.e. AZT plus Echinacea) compared to group 2 (I.e. AZT alone). However; there was no significant difference in patients with any prophylaxis.

CONCLUSION

The combined use of Echinacea with Azithromycin produced favorable outcome than Azithromycin alone in pediatric patients with recurrent tonsillitis.

The Regulatory Small RNA MarS Supports Virulence of Streptococcus pyogenes

Small regulatory RNAs (sRNAs) play a role in the control of bacterial virulence gene expression. In this study, we investigated an sRNA that was identified in Streptococcus pyogenes (group A Streptococcus, GAS) but is conserved throughout various streptococci. In a deletion strain, expression of mga, the gene encoding the multiple virulence gene regulator, was reduced. Accordingly, transcript and proteome analyses revealed decreased expression of several Mga-activated genes. Therefore, and because the sRNA was shown to interact with the 5′ UTR of the mga transcript in a gel-shift assay, we designated it MarS for mga-activating regulatory sRNA. Down-regulation of important virulence factors, including the antiphagocytic M-protein, led to increased susceptibility of the deletion strain to phagocytosis and reduced adherence to human keratinocytes. In a mouse infection model, the marS deletion mutant showed reduced dissemination to the liver, kidney, and spleen. Additionally, deletion of marS led to increased tolerance towards oxidative stress. Our in vitro and in vivo results indicate a modulating effect of MarS on virulence gene expression and on the pathogenic potential of GAS.

Streptococcus pyogenes biofilms-formation, biology, and clinical relevance

Streptococcus pyogenes (group A streptococci, GAS) is an exclusive human bacterial pathogen. The virulence potential of this species is tremendous. Interactions with humans range from asymptomatic carriage over mild and superficial infections of skin and mucosal membranes up to systemic purulent toxic-invasive disease manifestations. Particularly the latter are a severe threat for predisposed patients and lead to significant death tolls worldwide. This places GAS among the most important Gram-positive bacterial pathogens. Many recent reviews have highlighted the GAS repertoire of virulence factors, regulators and regulatory circuits/networks that enable GAS to colonize the host and to deal with all levels of the host immune defense. This covers in vitro and in vivo studies, including animal infection studies based on mice and more relevant, macaque monkeys. It is now appreciated that GAS, like many other bacterial species, do not necessarily exclusively live in a planktonic lifestyle. GAS is capable of microcolony and biofilm formation on host cells and tissues. We are now beginning to understand that this feature significantly contributes to GAS pathogenesis. In this review we will discuss the current knowledge on GAS biofilm formation, the biofilm-phenotype associated virulence factors, regulatory aspects of biofilm formation, the clinical relevance, and finally contemporary treatment regimens and future treatment options.

Inhibition of Growth and Gene Expression by PNA-peptide Conjugates in Streptococcus pyogenes

While Streptococcus pyogenes is consistently susceptible toward penicillin, therapeutic failure of penicillin treatment has been reported repeatedly and a considerable number of patients exhibit allergic reactions to this substance. At the same time, streptococcal resistance to alternative antibiotics, e.g., macrolides, has increased. Taken together, these facts demand the development of novel therapeutic strategies. In this study, S. pyogenes growth was inhibited by application of peptide-conjugated antisense-peptide nucleic acids (PNAs) specific for the essential gyrase A gene (gyrA). Thereby, HIV-1 Tat peptide-coupled PNAs were more efficient inhibitors of streptococcal growth as compared with (KFF)3K-coupled PNAs. Peptide-anti-gyrA PNAs decreased the abundance of gyrA transcripts in S. pyogenes. Growth inhibition by antisense interference was enhanced by combination of peptide-coupled PNAs with protein-level inhibitors. Antimicrobial synergy could be detected with levofloxacin and novobiocin, targeting the gyrase enzyme, and with spectinomycin, impeding ribosomal function. The prospective application of carrier peptide-coupled antisense PNAs in S. pyogenes covers the use as an antimicrobial agent and the employment as a knock-down strategy for the investigation of virulence factor function.

Protective mechanisms of respiratory tract Streptococci against Streptococcus pyogenes biofilm formation and epithelial cell infection

Streptococcus pyogenes (group A streptococci [GAS]) encounter many streptococcal species of the physiological microbial biome when entering the upper respiratory tract of humans, leading to the question how GAS interact with these bacteria in order to establish themselves at this anatomic site and initiate infection. Here we show that S. oralis and S. salivarius in direct contact assays inhibit growth of GAS in a strain-specific manner and that S. salivarius, most likely via bacteriocin secretion, also exerts this effect in transwell experiments. Utilizing scanning electron microscopy documentation, we identified the tested strains as potent biofilm producers except for GAS M49. In mixed-species biofilms, S. salivarius dominated the GAS strains, while S. oralis acted as initial colonizer, building the bottom layer in mixed biofilms and thereby allowing even GAS M49 to form substantial biofilms on top. With the exception of S. oralis, artificial saliva reduced single-species biofilms and allowed GAS to dominate in mixed biofilms, although the overall two-layer structure was unchanged. When covered by S. oralis and S. salivarius biofilms, epithelial cells were protected from GAS adherence, internalization, and cytotoxic effects. Apparently, these species can have probiotic effects. The use of Affymetrix array technology to assess HEp-2 cell transcription levels revealed modest changes after exposure to S. oralis and S. salivarius biofilms which could explain some of the protective effects against GAS attack. In summary, our study revealed a protection effect of respiratory tract bacteria against an important airway pathogen and allowed a first in vitro insight into local environmental processes after GAS enter the respiratory tract.

The extracellular protein factor Epf from Streptococcus pyogenes is a cell surface adhesin that binds to cells through an N-terminal domain containing a carbohydrate-binding module

Streptococcus pyogenes is an exclusively human pathogen. Streptococcal attachment to and entry into epithelial cells is a prerequisite for a successful infection of the human host and requires adhesins. Here, we demonstrate that the multidomain protein Epf from S. pyogenes serotype M49 is a streptococcal adhesin. An epf-deficient mutant showed significantly decreased adhesion to and internalization into human keratinocytes. Cell adhesion is mediated by the N-terminal domain of Epf (EpfN) and increased by the human plasma protein plasminogen. The crystal structure of EpfN, solved at 1.6 Å resolution, shows that it consists of two subdomains: a carbohydrate-binding module and a fibronectin type III domain. Both fold types commonly participate in ligand receptor and protein-protein interactions. EpfN is followed by 18 repeats of a domain classified as DUF1542 (domain of unknown function 1542) and a C-terminal cell wall sorting signal. The DUF1542 repeats are not involved in adhesion, but biophysical studies show they are predominantly α-helical and form a fiber-like stalk of tandem DUF1542 domains. Epf thus conforms with the widespread family of adhesins known as MSCRAMMs (microbial surface components recognizing adhesive matrix molecules), in which a cell wall-attached stalk enables long range interactions via its adhesive N-terminal domain.

Once weekly azithromycin in secondary prevention of rheumatic fever

Rheumatic fever and rheumatic heart disease (RHD) are still important problems in developing countries. Secondary prophylaxis which is the most cost-effective method in preventing recurrences of rheumatic fever is fraught with problems of drug compliance. The utility of 500 mg once weekly azithromycin (AZT), an orally effective long-acting antibiotic was evaluated against oral penicillin (phenoxy methyl penicillin 250 mg twice daily) in this study. Forty-eight consecutive patients (44% males, mean age 29.4 years) with established RHD were randomised into two groups-26 patients received AZT and 22 received oral penicillin. Patients were evaluated at randomisation, at 1 month, 3 months, and 6 months, clinically, serologically and by throat swab culture. End points were absence of streptococcal colonisation, infection or fever at the end of 6 months. During the study, 4 patients (15.4%) in the AZT group developed sore throat and fever, had positive throat culture and positive serology indicating streptococcal infection. None satisfied the criteria for rheumatic fever reactivation. None in the oral penicillin group developed streptococcal infection. In conclusion, weekly 500 mg of AZT is not effective in the prevention of streptococcal throat infection compared to oral penicillin therapy in adult patients with established RHD.

Insights into Streptococcus pyogenes pathogenesis from transcriptome studies

Streptococcus pyogenes (group A Streptococcus [GAS]) is a major human pathogen, causing diseases ranging from mild superficial infections of the skin and pharyngeal mucosal membrane, up to severe systemic and invasive diseases and autoimmune sequelae. The capability of GAS to cause this wide variety of infections is due to the expression of a large set of virulence factors, their concerted transcriptional regulation, and bacterial adaptation mechanisms to various host niches, which we are now beginning to understand on a molecular level. The addition of -omics technologies for GAS pathogenesis investigation, on top of traditional molecular methods, led to fast progress in understanding GAS pathogenesis mechanisms. This article focuses on differential transcriptional analysis performed on the bacterial side as well as on the host cell side. The microarray studies discussed provide new insight into the following five topics: gene-expression patterns under infection-relevant conditions, gene-expression patterns in mutant strains compared with wild-type strains, emergence of exceptionally fit GAS clones, gene-expression patterns of eukaryotic target and immune cells in response to GAS infection, and mechanisms underlying shifts from a pharyngeal to invasive GAS lifestyle.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Eliminating biofilm from ureteral stents: the Holy Grail

PURPOSE OF REVIEW

Biofilms continue to be a major limiting factor in the long-term use of ureteral stents, promoting the development of chronic infections and antibiotic resistance and encrustation. Apart from stent removal in conjunction with antibiotic therapy, there is currently no treatment proven successful for completely eradicating a biofilm-related infection, highlighting the need for continued research in this area.

RECENT FINDINGS

Research continues to focus mainly on biofilm prevention, specifically the development of novel coatings comprising antibacterial, antifouling or bacterial signalling compounds. Notably, all three strategies have generated candidate coatings showing recent success both in vitro and in vivo.

SUMMARY

Despite the current lack of a completely biofilm-resistant device, coating or treatment strategy, continued research into the causation of bacterial biofilm formation and the continued development of novel antibacterial, antifouling and antibiofilm compounds is promising. Future work should be aimed at more rigorous testing of candidate coatings from both physical and bacterial challenge standpoints as well as increased in-vivo investigation via clinical trials.

Global epithelial cell transcriptional responses reveal Streptococcus pyogenes Fas regulator activity association with bacterial aggressiveness

The bacterial human pathogen Streptococcus pyogenes (group A streptococci, GAS) is able to adhere to, internalize into and cross-talk on multiple levels with its host cells. To gain insight into the Fas function in pathogenesis we used Affymetrix human genome DNA-arrays to measure temporal and global transcriptional responses of HEp-2 cells infected with M49 S. pyogenes wild-type bacteria and DeltafasX, an isogenic S. pyogenes two-component-signal-transduction system mutant. A modified stringent statistical analysis method identified a total of 86 HEp-2 cell genes as differentially transcribed upon infection over the investigated time course. Increased expression of genes encoding proteins involved in GAS host cell adherence and internalization (fibronectin, integrin-alpha5) was found as a common response. In contrast to earlier reports investigating other GAS serotype strains, Ras superfamily and RhoA pathways are exploited by M49 GAS, suggesting serotype specific interactions with the host cell cytoskeleton. Despite transcriptional induction, secreted IL-8 levels of deltafasX mutant infected cells were below those of non-infected cells, indicating an absence of Fas expression could be important for GAS tissue colonization and long-term intracellular persistence. Oppositely, activity of the S. pyogenes Fas-system apparently promotes high adherence and internalization rates, massive cytokine gene transcription and cytokine release, host cell apoptosis via a caspase-2 activation pathway, and cytotoxicity. Thus, the S. pyogenes Fas two-component signal transduction system could be involved in local tissue destruction and general bacterial aggressiveness towards host cells.

Prevalence of the internalization-associated gene prtF1 in a bacterial population of Streptococcus pyogenes isolated from children with acute pharyngotonsillitis before and after antibiotic therapy

The prevalence of the internalization-associated prtF1 gene was studied in 837 isolates of Streptococcus pyogenes obtained from 713 pediatric patients presenting with acute pharyngotonsillitis before and after antibiotic therapy. Its association with macrolide resistance and with bacteriological treatment failure was determined. The bacterial population isolated from baseline pharyngeal swabs showed an overall prtF1 positivity rate of 33%. A higher prtF1 positivity was found among erythromycin-resistant strains (45%) showing, however, marked differences between the inducible (iMLS), constitutive (cMLS), and efflux pump (M) resistance phenotypes. The prevalence was statistically higher (p < 0.001) in strains belonging to iMLS (84%) and cMLS (67%) phenotypes as compared to the M phenotype (15%). Interestingly, the prevalence of the prtF1 gene was significantly lower (p = 0.04) in strains belonging to M resistance phenotype as compared to erythromycin-susceptible strains (28%). Failed bacterial eradication was demonstrated in 124 patients. The prtF1 positivity rate remained unchanged in strains isolated before and after therapy in patients treated with macrolides (9/54). On the other hand, the positivity rate for the prtF1 gene was significantly higher (p = 0.015) in strains isolated after therapy with beta-lactams (21/70) as compared to baseline isolates (6/70), indicating a differential selection imposed on the organism by these agents. Finally, a high overall eradication rate (88%) of prtF1-positive isolates, belonging to both the erythromycin-susceptible and -resistant phenotypes, was demonstrated following macrolide treatment.

The intracellular status of Streptococcus pyogenes: role of extracellular matrix-binding proteins and their regulation

Streptococcus pyogenes (group A streptococci, GAS) is an important and exclusively human pathogen. Adherence to and internalization into host cells significantly contributes to the pathogenesis of GAS infections. The adherence mechanism is a two-step process in which host extracellular matrix (ECM) proteins act as prime targets. GAS may express more than a dozen different microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) that attach to fibronectin or collagen. One of them, protein F1/SfbI binds fibronectin and mediates adherence of GAS to host cells. Bound fibronectin acts as a bridging molecule towards host cell integrins, which in turn initialize the uptake process that leads to GAS internalization. In their safe intracellular niche GAS can persist protected from antibiotics and host defense, a scenario currently discussed in the context of treatment failure, asymptomatic GAS carriers and recurrent GAS infections. Patients with such low grade infections represent the main GAS reservoir from which the bacteria are spread in the general population. Due to their important function, expression of GAS MSCRAMMs is under control of several "stand alone" transcriptional regulators and two-component signal transduction systems. Several regulator genes are organized together with MSCRAMM genes on one of two potential pathogenicity islands, act together in a growth phase-dependent regulatory network and are expressed in a strain-specific manner. A detailed understanding of these mechanisms is crucial, since interference with MSCRAMM function alone or in conjunction with specific manipulations of regulators is an attractive goal for novel anti-infective strategies.

Recruitment of complement factor H-like protein 1 promotes intracellular invasion by group A streptococci

Numerous microbial pathogens exploit complement regulatory proteins such as factor H (FH) and factor H-like protein 1 (FHL-1) for immune evasion. Fba is an FHL-1 and FH binding protein expressed on the surface of the human pathogenic bacterium, Streptococcus pyogenes, a common agent of pharyngeal, skin, and soft-tissue infections. In the present study, we demonstrate that Fba and FHL-1 work in concert to promote invasion of epithelial cells by S. pyogenes. Fba fragments were expressed as recombinant proteins and assayed for binding of FHL-1 and FH by Western blotting, enzyme-linked immunosorbent assay, and surface plasmon resonance. A binding site for FHL-1 and FH was localized to the N-terminal half of Fba, a region predicted to contain a coiled-coil domain. Deletion of this coiled-coil domain greatly reduced FHL-1 and FH binding. PepSpot analyses identified a 16-amino-acid segment of Fba which overlaps the coiled-coil domain that binds both FHL-1 and FH. To localize the Fba binding site in FHL-1 and FH, surface plasmon resonance was used to assess the interactions between the streptococcal protein and a series of recombinant FH deletion constructs. The Fba binding site was localized to short consensus repeat 7 (SCR 7), a domain common to FHL-1 and FH. SCR 7 contains a heparin binding site, and heparin was found to inhibit FHL-1 binding to Fba. FHL-1 promoted entry of Fba(+) group A streptococci into epithelial cells in a dose-dependent manner but did not affect invasion by an isogenic fba mutant. To our knowledge, this is the first report of a bacterial pathogen exploiting a soluble complement regulatory protein for entry into host cells.

Epidemiology and virulence gene expression of intracellular group A streptococci in tonsils of recurrently infected adults

Intracellularly persistent group A streptococci (GAS, Streptococcus pyogenes) have been associated with recurrent tonsillopharyngitis and antibiotic treatment failure. As a supplementation of the published in vitro data, conventional bacteriology and molecular epidemiology was performed on material from 29 adult patients of a German army hospital with anamnestic signs of recurrent tonsillopharyngitis. Pre-surgery tonsil swabs and the surgically removed tonsils were examined with respect to growth of aerobic bacteria in absence and presence of antibiotics with exclusively extracellular activity. Under such antibiotic selection, Staphylococcus aureus and GAS were cultured from specimens of 13 and 3 patients, respectively. In every material GAS-positive by culture methods, the intracellular location of the penicillin-susceptible GAS isolates was confirmed by immunohistologic examination of tonsillar sections using a GAS-specific IgG antibody. The three intracellular GAS isolates were typed by emm gene sequencing and could be associated to types M6 and M49 (two isolates). The bacteria were serially passaged on sheep blood agar, and semiquantitative mRNA analysis from virulence genes was performed using bacteria of the 4th and 25th passage after isolation. An M-type-specific pattern of virulence gene expression and different gene expression levels in relation to the passage number were observed.

Virulence factor regulation and regulatory networks in Streptococcus pyogenes and their impact on pathogen-host interactions

Streptococcus pyogenes (group A streptococcus, GAS) is a very important human pathogen with remarkable adaptation capabilities. Survival within the harsh host surroundings requires sensing potential on the bacterial side, which leads in particular to coordinately regulated virulence factor expression. GAS 'stand-alone' response regulators (RRs) and two-component signal transduction systems (TCSs) link the signals from the host environment with adaptive responses of the bacterial cell. Numerous putative regulatory systems emerged from GAS genome sequences. Only three RRs [Mga, RofA-like protein (RALP) and Rgg/RopB] and three TCSs (CsrRS/CovRS, FasBCAX and Ihk/Irr) have been studied in some detail with respect to their growth-phase-dependent activity and their influence on GAS-host cell interaction. In particular, the Mga-, RALP- and Rgg/RopB-regulated pathways display interconnected activities that appear to influence GAS colonization, persistence and spreading mechanisms, in a growth-phase-related fashion. Here, we have summarized our current knowledge about these RRs and TCSs to highlight the questions that should be addressed in future research on GAS pathogenicity.