Signal transduction by a death signal peptide: uncovering the mechanism of bacterial killing by penicillin

Structure, Function, and Regulation of LytA: The N-Acetylmuramoyl-l-alanine Amidase Driving the "Suicidal Tendencies" of Streptococcus pneumoniae-A Review

Streptococcus pneumoniae (pneumococcus) is a significant human pathogen responsible for a range of diseases from mild infections to invasive pneumococcal diseases, particularly affecting children, the elderly, and immunocompromised individuals. Despite pneumococcal conjugate vaccines having reduced disease incidence, challenges persist due to serotype diversity, vaccine coverage gaps, and antibiotic resistance. This review highlights the role of LytA, a key autolysin (N-acetylmuramoyl-l-alanine amidase), in pneumococcal biology. LytA regulates autolysis, contributes to inflammation, and biofilm formation, and impairs bacterial clearance. It also modulates complement activation, aiding immune evasion. LytA expression is influenced by environmental signals and genetic regulation and is tied to competence for genetic transformation, which is an important virulence trait, particularly in meningitis. With the increase in antibiotic resistance, LytA has emerged as a potential therapeutic target. Current research explores its use in bacteriolytic therapies, vaccine development, and synergistic antibiotic strategies. Various compounds, including synthetic peptides, plant extracts, and small molecules, have been investigated for their ability to trigger LytA-mediated bacterial lysis. Future directions include the development of novel anti-pneumococcal interventions leveraging LytA's properties while overcoming vaccine efficacy and resistance-related challenges. Human challenge models and animal studies continue to deepen our understanding of pneumococcal pathogenesis and potential treatment strategies.

Antibiotic adjuvants against multidrug-resistant Gram-negative bacteria: important component of future antimicrobial therapy

The swift emergence and propagation of multidrug-resistant (MDR) bacterial pathogens constitute a tremendous global health crisis. Among these pathogens, the challenge of antibiotic resistance in Gram-negative bacteria is particularly pressing due to their distinctive structure, such as highly impermeable outer membrane, overexpressed efflux pumps, and mutations. Several strategies have been documented to combat MDR Gram-negative bacteria, including the structural modification of existing antibiotics, the development of antimicrobial adjuvants, and research on novel targets that MDR bacteria are sensitive to. Drugs functioning as adjuvants to mitigate resistance to existing antibiotics may play a pivotal role in future antibacterial therapy strategies. In this review, we provide a brief overview of potential antibacterial adjuvants against Gram-negative bacteria and their mechanisms of action, and discuss the application prospects and potential for bacterial resistance to these adjuvants, along with strategies to reduce this risk.

Structural basis of peptidoglycan synthesis by E. coli RodA-PBP2 complex

Peptidoglycan (PG) is an essential structural component of the bacterial cell wall that is synthetized during cell division and elongation. PG forms an extracellular polymer crucial for cellular viability, the synthesis of which is the target of many antibiotics. PG assembly requires a glycosyltransferase (GT) to generate a glycan polymer using a Lipid II substrate, which is then crosslinked to the existing PG via a transpeptidase (TP) reaction. A Shape, Elongation, Division and Sporulation (SEDS) GT enzyme and a Class B Penicillin Binding Protein (PBP) form the core of the multi-protein complex required for PG assembly. Here we used single particle cryo-electron microscopy to determine the structure of a cell elongation-specific E. coli RodA-PBP2 complex. We combine this information with biochemical, genetic, spectroscopic, and computational analyses to identify the Lipid II binding sites and propose a mechanism for Lipid II polymerization. Our data suggest a hypothesis for the movement of the glycan strand from the Lipid II polymerization site of RodA towards the TP site of PBP2, functionally linking these two central enzymatic activities required for cell wall peptidoglycan biosynthesis.

Streptococcal bacterial components in cancer therapy

The incidence rate of cancer is steadily increasing all around the world, and there is an urgent need to develop novel and more effective treatment strategies. Recently, bacterial therapy has been investigated as a new approach to target cancer, and is becoming a serious option. Streptococcus strains are among the most common and well-studied virulent bacteria that cause a variety of human infections. Everyone has experienced a sore throat during their lifetime, or has been asymptomatically colonized by streptococci. The ability of Streptococcus bacteria to fight cancer was discovered more than 100 years ago, and over the years has undergone clinical trials, but the mechanism is not yet completely understood. Recently, several animal models and human clinical trials have been reported. Streptococcal strains can have an intrinsic anti-tumor activity, or can activate the host immune system to fight the tumor. Bacteria can selectively accumulate and proliferate in the hypoxic regions of solid tumors. Moreover, the bacteria can be genetically engineered to secrete toxins or enzymes that can specifically attack the tumors.

PEP27-2, a Potent Antimicrobial Cell-Penetrating Peptide, Reduces Skin Abscess Formation during Staphylococcus aureus Infections in Mouse When Used in Combination with Antibiotics

PEP27, a 27-amino acid (aa) peptide secreted by Streptococcus pneumoniae, is an autolytic peptide that functions as a major virulence factor. To develop a clinically applicable antimicrobial peptide (AMP), we designed PEP27 analogs with Trp substitutions to enhance its antimicrobial activity compared to that of PEP27. Particularly, PEP27-2 showed strong antimicrobial activity against a wide variety of bacteria, including multidrug-resistant (MDR) bacteria. It was found that the antimicrobial activity of PEP27-2 was increased by substituting Trp for the aa at the middle position of PEP27. We found that PEP27-2 acts as an effective cell-penetrating peptide in bacterial and mammalian cells. Here, we proved that subcutaneous infection with MDR Staphylococcus aureus induced skin lesions such as skeletal muscle damage, deep inflammation, and necrosis of the overlaying dermis in mice. Combination treatment with antibiotics revealed synergistic effects, remarkably reducing abscess size and improving the bacteria removal rate from the infection site. Moreover, PEP27-2-antibiotic combination treatment reduced inflammation, lowering levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, inducible NO synthase (iNOS), and cyclooxygenase (COX-2) in skin abscess tissue. The results suggest that the PEP27-2 peptide is a promising therapeutic option for combating MDR bacterial strains by enhancing antibiotic penetration and protecting against MDR bacteria.

12/111phiA Prophage Domestication Is Associated with Autoaggregation and Increased Ability to Produce Biofilm in Streptococcus agalactiae

CC17 Streptococcus agalactiae carrying group-A prophages is increasingly responsible for neonatal infections. To investigate the impact of the genetic features of a group-A prophage, we first conducted an in silico analysis of the genome of 12/111phiA, a group-A prophage carried by a strain responsible for a bloodstream infection in a parturient. This revealed a Restriction Modification system, suggesting a prophage maintenance strategy and five ORFs of interest for the host and encoding a type II toxin antitoxin system RelB/YafQ, an endonuclease, an S-adenosylmethionine synthetase MetK, and an StrP-like adhesin. Using the WT strain cured from 12/111phiA and constructing deleted mutants for the ORFs of interest, and their complemented mutants, we demonstrated an impact of prophage features on growth characteristics, cell morphology and biofilm formation. Our findings argue in favor of 12/111phiA domestication by the host and a role of prophage features in cell autoaggregation, glycocalyx and biofilm formation. We suggest that lysogeny may promote GBS adaptation to the acid environment of the vagina, consequently colonizing and infecting neonates.

Crystal Structure of the Pneumococcal Vancomycin-Resistance Response Regulator DNA-Binding Domain

Vancomycin response regulator (VncR) is a pneumococcal response regulator of the VncRS two-component signal transduction system (TCS) of Streptococcus pneumoniae. VncRS regulates bacterial autolysis and vancomycin resistance. VncR contains two different functional domains, the N-terminal receiver domain and C-terminal effector domain. Here, we investigated VncR C-terminal DNA binding domain (VncRc) structure using a crystallization approach. Crystallization was performed using the micro-batch method. The crystals diffracted to a 1.964 Å resolution and belonged to space group P212121. The crystal unit-cell parameters were a = 25.71 Å, b = 52.97 Å, and c = 60.61 Å. The structure of VncRc had a helix-turn-helix motif highly similar to the response regulator PhoB of Escherichia coli. In isothermal titration calorimetry and size exclusion chromatography results, VncR formed a complex with VncS, a sensor histidine kinase of pneumococcal TCS. Determination of VncR structure will provide insight into the mechanism by how VncR binds to target genes.

Pneumococcal pep27 mutant immunization suppresses allergic asthma in mice

Asthma is an allergic airway disease (AAD) characterized by eosinophilic inflammation, mucus hypersecretion, and airway hyper responsiveness, and it is caused by dysregulated immune responses. Conversely, regulatory T cells (Tregs) control aberrant immune responses and maintain homeostasis. Recent evidence suggests that Streptococcus pneumoniae, including its components as well as a live attenuated mutant, and pneumococcal infection induce Tregs and can thus potentially be harnessed therapeutically for asthma treatment. Previously, a pep27 deletion mutant (Δpep27) demonstrated a significantly attenuated virulence in a sepsis model, and Δpep27 immunization induced serotype-nonspecific protection against S. pneumoniae infection, as well as influenza virus, possibly via an immune tolerance mechanism. Here, the potential of Δpep27 immunization for asthma protection was studied. Mice were immunized intranasally with Δpep27 before or after ovalbumin sensitization and subsequent challenge. Δpep27 immunization suppressed hallmark features of AAD, including antigen-specific type 2 helper T cell cytokine and antibody responses, peripheral and pulmonary eosinophil accumulation, and goblet cell hyperplasia. Thus, a Δpep27 vaccine may be highly feasible as a preventive or therapeutic agent for asthma.

Nanoparticles: Antimicrobial Applications and Its Prospects

Nowadays, nanomaterials [NPs; size, 1–100 nm] have emerged as unique antimicrobial agents. Specially, several classes of antimicrobial NPs and nanosized carriers for antibiotic delivery have proven their efficacy for handling infectious diseases, including antibiotic-resistant ones, in vitro as well as in animal models, which can offer better therapy than classical drugs due to their high surface area-to-volume ratio, resulting in appearance of new mechanical, chemical, electrical, optical, magnetic, electro-optical, and magneto-optical properties, unlike from their bulk properties. Thus, scientifically NPs have been validated to be fascinating in fighting bacteria. In this chapter, we will discuss precise properties of microorganisms and their modifications among each strain specifically. The toxicity mechanisms vary from one stain to another. Even the NP’s efficacy to treat against bacteria and drug-resistant bacteria and their defense mechanisms change according to strains in particular composition of cell walls, the enzymic composition, and so on. Thus, we provide an outlook on NPs in the microbial world and mechanism to overcome the drug resistance by tagging antibiotics in NPs and its future prospects for the scientific world.

The Understanding and Management of Organism Toxicity in Septic Shock

The toxicity caused by different organisms in septic shock is substantially complex and characterized by an intricate pathogenicity that involves several systems and pathways. Immune cells' pattern recognition receptors initiate the host response to pathogens after the recognition of pathogen-associated molecular patterns. In essence, the subsequent activation of downstream pathways may progress to infection resolution or to a dysregulated host response that represents the hallmark of organ injury in septic shock. Likewise, the management of organism toxicity in septic shock is complicated and comprises a multiplicity of suitable targets. In this review, the classic immune responses to pathogens are discussed as well as other factors that are relevant in the pathogenicity of septic shock, including sepsis-induced immune suppression, inflammasome activation, intestinal permeability, and the role of lipids and proprotein convertase subtilisin/kexin type 9. Current therapies aiming to eliminate the organisms causing septic shock, recent and ongoing trials in septic shock treatment, and potential new therapeutic strategies are also explored.

Induction of the pneumococcal vncRS operon by lactoferrin is essential for pneumonia

Streptococcus pneumoniae (pneumococcus), the major pathogen for pneumonia, commonly colonizes the lung, but the mechanism underlying the coordination of virulence factors during invasion via the host protein remains poorly understood. Bacterial lysis releases the components of the cell wall, and triggers innate immunity and the subsequent secretion of pro-inflammatory cytokines. Previously, the virulence of the pep27 mutant was shown to be attenuated as a feasible candidate for vaccine development. However, the role of pep27 gene, belonging to the vancomycin-resistance locus (vncRS operon), in virulence, is largely unknown. This study demonstrates that transferrin in the host serum reduces the survival of the host during S. pneumoniae infections in mice. The exposure of the pneumococcal D39 strain to lactoferrin induced the vncRS operon, lysis, and subsequent in vivo cytokine production, resulting in lung inflammation. However, these responses were significantly attenuated in pneumococci harboring a mutation in pep27. Mechanistically, the VncS ligand, identified as lactoferrin, induced the vncRS operon and increased the in vivo mortality rates. Thus, serum-induced activation of vncRS plays an essential role in inducing pneumonia.

Bacillus anthracis Peptidoglycan Integrity Is Disrupted by the Chemokine CXCL10 through the FtsE/X Complex

The antimicrobial activity of the chemokine CXCL10 against vegetative cells of Bacillus anthracis occurs via both bacterial FtsE/X-dependent and-independent pathways. Previous studies established that the FtsE/X-dependent pathway was mediated through interaction of the N-terminal region(s) of CXCL10 with a functional FtsE/X complex, while the FtsE/X-independent pathway was mediated through the C-terminal α-helix of CXCL10. Both pathways result in cell lysis and death of B. anthracis. In other bacterial species, it has been shown that FtsE/X is involved in cellular elongation though activation of complex-associated peptidoglycan hydrolases. Thus, we hypothesized that the CXCL10-mediated killing of vegetative cells of B. anthracis through the FtsE/X-dependent pathway resulted from the disruption of peptidoglycan processing. Immunofluorescence microscopy studies using fluorescent peptidoglycan probes revealed that incubation of B. anthracis Sterne (parent) strain with CXCL10 or a C-terminal truncated CXCL10 (CTTC) affected peptidoglycan processing and/or incorporation of precursors into the cell wall. B. anthracis ΔftsX or ftsE(K123A/D481N) mutant strains, which lacked a functional FtsE/X complex, exhibited little to no evidence of disruption in peptidoglycan processing by either CXCL10 or CTTC. Additional studies demonstrated that the B. anthracis parent strain exhibited a statistically significant increase in peptidoglycan release in the presence of either CXCL10 or CTTC. While B. anthracis ΔftsX strain showed increased peptidoglycan release in the presence of CXCL10, no increase was observed with CTTC, suggesting that the FtsE/X-independent pathway was responsible for the activity observed with CXCL10. These results indicate that FtsE/X-dependent killing of vegetative cells of B. anthracis results from a loss of cell wall integrity due to disruption of peptidoglycan processing and suggest that FtsE/X may be an important antimicrobial target to study in the search for alternative microbial therapeutics.

Intrinsic, adaptive and acquired antimicrobial resistance in Gram-negative bacteria

Gram-negative bacteria are responsible for a large proportion of antimicrobial-resistant infections in humans and animals. Among this class of bacteria are also some of the most successful environmental organisms. Part of this success is their adaptability to a variety of different niches, their intrinsic resistance to antimicrobial drugs and their ability to rapidly acquire resistance mechanisms. These mechanisms of resistance are not exclusive and the interplay of several mechanisms causes high levels of resistance. In this review, we explore the molecular mechanisms underlying resistance in Gram-negative organisms and how these different mechanisms enable them to survive many different stress conditions.

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

Streptococcus pneumoniae inflicts a huge disease burden as the leading cause of community-acquired pneumonia and meningitis. Soon after mainstream antibiotic usage, multiresistant pneumococcal clones emerged and disseminated worldwide. Resistant clones are generated through adaptation to antibiotic pressures imposed while naturally residing within the human upper respiratory tract. Here, a huge array of related commensal streptococcal strains transfers core genomic and accessory resistance determinants to the highly transformable pneumococcus. β-Lactam resistance is the hallmark of pneumococcal adaptability, requiring multiple independent recombination events that are traceable to nonpneumococcal origins and stably perpetuated in multiresistant clonal complexes. Pneumococcal strains with elevated MICs of β-lactams are most often resistant to additional antibiotics. Basic underlying mechanisms of most pneumococcal resistances have been identified, although new insights that increase our understanding are continually provided. Although all pneumococcal infections can be successfully treated with antibiotics, the available choices are limited for some strains. Invasive pneumococcal disease data compiled during 1998 to 2013 through the population-based Active Bacterial Core surveillance program (U.S. population base of 30,600,000) demonstrate that targeting prevalent capsular serotypes with conjugate vaccines (7-valent and 13-valent vaccines implemented in 2000 and 2010, respectively) is extremely effective in reducing resistant infections. Nonetheless, resistant non-vaccine-serotype clones continue to emerge and expand.

CXCL10 Acts as a Bifunctional Antimicrobial Molecule against Bacillus anthracis

Bacillus anthracis is killed by the interferon-inducible, ELR(−) CXC chemokine CXCL10. Previous studies showed that disruption of the gene encoding FtsX, a conserved membrane component of the ATP-binding cassette transporter-like complex FtsE/X, resulted in resistance to CXCL10. FtsX exhibits some sequence similarity to the mammalian CXCL10 receptor, CXCR3, suggesting that the CXCL10 N-terminal region that interacts with CXCR3 may also interact with FtsX. A C-terminal truncated CXCL10 was tested to determine if the FtsX-dependent antimicrobial activity is associated with the CXCR3-interacting N terminus. The truncated CXCL10 exhibited antimicrobial activity against the B. anthracis parent strain but not the ΔftsX mutant, which supports a key role for the CXCL10 N terminus. Mutations in FtsE, the conserved ATP-binding protein of the FtsE/X complex, resulted in resistance to both CXCL10 and truncated CXCL10, indicating that both FtsX and FtsE are important. Higher concentrations of CXCL10 overcame the resistance of the ΔftsX mutant to CXCL10, suggesting an FtsX-independent killing mechanism, likely involving its C-terminal α-helix, which resembles a cationic antimicrobial peptide. Membrane depolarization studies revealed that CXCL10 disrupted membranes of the B. anthracis parent strain and the ΔftsX mutant, but only the parent strain underwent depolarization with truncated CXCL10. These findings suggest that CXCL10 is a bifunctional molecule that kills B. anthracis by two mechanisms. FtsE/X-dependent killing is mediated through an N-terminal portion of CXCL10 and is not reliant upon the C-terminal α-helix. The FtsE/X-independent mechanism involves membrane depolarization by CXCL10, likely because of its α-helix. These findings present a new paradigm for understanding mechanisms by which CXCL10 and related chemokines kill bacteria.

Chemokines are a class of molecules known for their chemoattractant properties but more recently have been shown to possess antimicrobial activity against a wide range of Gram-positive and Gram-negative bacterial pathogens. The mechanism(s) by which these chemokines kill bacteria is not well understood, but it is generally thought to be due to the conserved amphipathic C-terminal α-helix that resembles cationic antimicrobial peptides in charge and secondary structure. Our present study indicates that the interferon-inducible, ELR(−) chemokine CXCL10 kills the Gram-positive pathogen Bacillus anthracis through multiple molecular mechanisms. One mechanism is mediated by interaction of CXCL10 with the bacterial FtsE/X complex and does not require the presence of the CXCL10 C-terminal α-helix. The second mechanism is FtsE/X receptor independent and kills through membrane disruption due to the C-terminal α-helix. This study represents a new paradigm for understanding how chemokines exert an antimicrobial effect that may prove applicable to other bacterial species.

Dynamic capsule restructuring by the main pneumococcal autolysin LytA in response to the epithelium

Bacterial pathogens produce complex carbohydrate capsules to protect against bactericidal immune molecules. Paradoxically, the pneumococcal capsule sensitizes the bacterium to antimicrobial peptides found on epithelial surfaces. Here we show that upon interaction with antimicrobial peptides, encapsulated pneumococci survive by removing capsule from the cell surface within minutes in a process dependent on the suicidal amidase autolysin LytA. In contrast to classical bacterial autolysis, during capsule shedding, LytA promotes bacterial survival and is dispersed circumferentially around the cell. However, both autolysis and capsule shedding depend on the cell wall hydrolytic activity of LytA. Capsule shedding drastically increases invasion of epithelial cells and is the main pathway by which pneumococci reduce surface bound capsule during early acute lung infection of mice. The previously unrecognized role of LytA in removing capsule to combat antimicrobial peptides may explain why nearly all clinical isolates of pneumococci conserve this enzyme despite the lethal selective pressure of antibiotics.

Pneumococci produce a carbohydrate capsule that protects them against components of the host immune system but sensitizes them to host antimicrobial peptides. Here, Kietzman et al. show that pneumococci respond to antimicrobial peptides by capsule shedding, which requires the main autolysin LytA.

Polymeric nanoarchitectures on Ti-based implants for antibacterial applications

Because of the excellent mechanical properties and good biocompatibility, titanium-based metals are widely used in hard tissue repair, especially load-bearing orthopedic applications. However, bacterial infection and complication during and after surgery often causes failure of the metallic implants. To endow titanium-based implants with antibacterial properties, surface modification is one of the effective strategies. Possessing the unique organic structure composed of molecular and functional groups resembling those of natural organisms, functionalized polymeric nanoarchitectures enhance not only the antibacterial performance but also other biological functions that are difficult to accomplish on many conventional bioinert metallic implants. In this review, recent advance in functionalized polymeric nanoarchitectures and the associated antimicrobial mechanisms are reviewed.

Strategies for the empirical management of infection in cancer patients with emphasis on the emergence of resistant gram-negative bacteria

Combinations of antibiotics (namely penicillins and aminoglycosides) have been advocated in the 1970s for the empirical therapy of FN in cancer patients in order to take advantage of the possible synergism between these agents and to extend the potential antimicrobial spectrum of empirical therapy. Later, with the development of potent broad spectrum antibiotics, the need for combinations became less obvious as monotherapy with these new agents appeared as effective and less toxic than previously used combinations. However, today we are facing a major challenge through the emergence of multi-resistant microrganisms. With such bacteria, we might be coming back to the pre-antibiotic era when no active agents were available. This situation is due, in part, by the excessive use of antibiotics, namely as a prophylaxis for infection, and is complicated by the fact that very few new effective antibiotics are being developed by the pharmaceutical industry. Under these circumstances, it is likely that we will have to resort to "old timers" such as the polymyxins. It is also possible that combination therapy will come back in favor to take advantage of the synergism and extend the spectrum of coverage, just as it has been the case for the management of resistant tuberculosis. At the same time, the development of multidisciplinary antimicrobial stewardship is mandatory for efficient infection control and minimizing emergence of antimicrobial resistance.

Vancomycin tolerance in Gram-positive cocci

Vancomycin, a glycopeptide antimicrobial agent, represents the last line of defence against a wide range of multi-resistant Gram-positive pathogens such as enterococci, staphylococci and streptococci. However, vancomycin-resistant enterococci and staphylococci, along with vancomycin-tolerant clinical isolates, are compromising the therapeutic efficacy of vancomycin. It is conceivable that tolerance may emerge during prolonged vancomycin use. It has not been until recently, however, that the molecular basis of this tolerance began to be understood. Superoxide anions might be involved in the bactericidal activity of vancomycin in enterococci, and recent evidence suggests that the stringent response is partly responsible for vancomycin tolerance in Enterococcus faecalis. The mechanism of vancomycin tolerance in Staphylococcus aureus and Streptococcus pneumoniae is sometimes associated with a reduction of autolysin activity. Vancomycin tolerance in S. aureus and S. pneumoniae also appears to be somehow related with the two-component regulatory systems linked to cell envelope stress, although the precise molecular regulatory pathways remain poorly defined.

Sequencing and comparative genome analysis of two pathogenic Streptococcus gallolyticus subspecies: genome plasticity, adaptation and virulence

Streptococcus gallolyticus infections in humans are often associated with bacteremia, infective endocarditis and colon cancers. The disease manifestations are different depending on the subspecies of S. gallolyticus causing the infection. Here, we present the complete genomes of S. gallolyticus ATCC 43143 (biotype I) and S. pasteurianus ATCC 43144 (biotype II.2). The genomic differences between the two biotypes were characterized with comparative genomic analyses. The chromosome of ATCC 43143 and ATCC 43144 are 2,36 and 2,10 Mb in length and encode 2246 and 1869 CDS respectively. The organization and genomic contents of both genomes were most similar to the recently published S. gallolyticus UCN34, where 2073 (92%) and 1607 (86%) of the ATCC 43143 and ATCC 43144 CDS were conserved in UCN34 respectively. There are around 600 CDS conserved in all Streptococcus genomes, indicating the Streptococcus genus has a small core-genome (constitute around 30% of total CDS) and substantial evolutionary plasticity. We identified eight and five regions of genome plasticity in ATCC 43143 and ATCC 43144 respectively. Within these regions, several proteins were recognized to contribute to the fitness and virulence of each of the two subspecies. We have also predicted putative cell-surface associated proteins that could play a role in adherence to host tissues, leading to persistent infections causing sub-acute and chronic diseases in humans. This study showed evidence that the S. gallolyticus still possesses genes making it suitable in a rumen environment, whereas the ability for S. pasteurianus to live in rumen is reduced. The genome heterogeneity and genetic diversity among the two biotypes, especially membrane and lipoproteins, most likely contribute to the differences in the pathogenesis of the two S. gallolyticus biotypes and the type of disease an infected patient eventually develops.

Vancomycin tolerance in clinical and laboratory Streptococcus pneumoniae isolates depends on reduced enzyme activity of the major LytA autolysin or cooperation between CiaH histidine kinase and capsular polysaccharide

Vancomycin is frequently added to standard therapy for pneumococcal meningitis. Although vancomycin-resistant Streptococcus pneumoniae strains have not been isolated, reports on the emergence of vancomycin-tolerant pneumococci are a cause of concern. To date, the molecular basis of vancomycin tolerance in S. pneumoniae is essentially unknown. We examined two vancomycin-tolerant clinical isolates, i.e. a purported autolysin negative (LytA(-)), serotype 23F isolate (strain S3) and the serotype 14 strain 'Tupelo', which is considered a paradigm of vancomycin tolerance. S3 was characterized here as carrying a frameshift mutation in the lytA gene encoding the main pneumococcal autolysin. The vancomycin tolerance of strain S3 was abolished by transformation to the autolysin-proficient phenotype. The original Tupelo strain was discovered to be a mixture: a strain showing a vancomycin-tolerant phenotype (Tupelo_VT) and a vancomycin-nontolerant strain (Tupelo_VNT). The two strains differed only in terms of a single mutation in the ciaH gene present in the VT strain. Most interestingly, although the vancomycin tolerance of Tupelo_VT could be overcome by increasing the LytA dosage upon transformation by a multicopy plasmid or by externally adding the autolysin, we show that vancomycin tolerance in S. pneumoniae requires the simultaneous presence of a mutated CiaH histidine kinase and capsular polysaccharide.

How antibiotics kill bacteria: from targets to networks

Antibiotic drug-target interactions, and their respective direct effects, are generally well characterized. By contrast, the bacterial responses to antibiotic drug treatments that contribute to cell death are not as well understood and have proven to be complex as they involve many genetic and biochemical pathways. In this Review, we discuss the multilayered effects of drug-target interactions, including the essential cellular processes that are inhibited by bactericidal antibiotics and the associated cellular response mechanisms that contribute to killing. We also discuss new insights into these mechanisms that have been revealed through the study of biological networks, and describe how these insights, together with related developments in synthetic biology, could be exploited to create new antibacterial therapies.

Shaping a bacterial genome by large chromosomal replacements, the evolutionary history of Streptococcus agalactiae

Bacterial populations are subject to complex processes of diversification that involve mutation and horizontal DNA transfer mediated by transformation, transduction, or conjugation. Tracing the evolutionary events leading to genetic changes allows us to infer the history of a microbe. Here, we combine experimental and in silico approaches to explore the forces that drive the genome dynamics of Streptococcus agalactiae, the leading cause of neonatal infections. We demonstrate that large DNA segments of up to 334 kb of the chromosome of S. agalactiae can be transferred through conjugation from multiple initiation sites. Consistently, a genome-wide map analysis of nucleotide polymorphisms among eight human isolates demonstrated that each chromosome is a mosaic of large chromosomal fragments from different ancestors suggesting that large DNA exchanges have contributed to the genome dynamics in the natural population. The analysis of the resulting genetic flux led us to propose a model for the evolutionary history of this species in which clonal complexes of clinical importance derived from a single clone that evolved by exchanging large chromosomal regions with more distantly related strains. The emergence of this clone could be linked to selective sweeps associated with the reduction of genetic diversity in three regions within a large panel of human isolates. Up to now sex in bacteria has been assumed to involve mainly small regions; our results define S. agalactiae as an alternative paradigm in the study of bacterial evolution.

The pseudomonas quinolone signal (PQS) balances life and death in Pseudomonas aeruginosa populations

When environmental conditions deteriorate and become inhospitable, generic survival strategies for populations of bacteria may be to enter a dormant state that slows down metabolism, to develop a general tolerance to hostile parameters that characterize the habitat, and to impose a regime to eliminate damaged members. Here, we provide evidence that the pseudomonas quinolone signal (PQS) mediates induction of all of these phenotypes. For individual cells, PQS, an interbacterial signaling molecule of Pseudomonas aeruginosa, has both deleterious and beneficial activities: on the one hand, it acts as a pro-oxidant and sensitizes the bacteria towards oxidative and other stresses and, on the other, it efficiently induces a protective anti-oxidative stress response. We propose that this dual function fragments populations into less and more stress tolerant members which respond differentially to developing stresses in deteriorating habitats. This suggests that a little poison may be generically beneficial to populations, in promoting survival of the fittest, and in contributing to bacterial multi-cellular behavior. It further identifies PQS as an essential mediator of the shaping of the population structure of Pseudomonas and of its response to and survival in hostile environmental conditions.

Mode of antibacterial action of a signal peptide, Pep27 from Streptococcus pneumoniae

The aim of this study was to assess the in vitro antimicrobial activity of Pep27 and its mode of action. The results indicated Pep27 exhibited antibacterial activities against pathogenic Gram-positive and Gram-negative bacteria without hemolytic effect on human erythrocytes, but it did not exhibit antifungal activity. To understand the mode of action of Pep27, the cellular distribution of the peptide was investigated. Flow cytometry analysis exhibited Pep27 penetrated the bacterial membrane by an energy-independent pathway without any damage to the membrane when examined using liposome and membrane probe. After penetration into the bacterial cells, Pep27 was not affected by macromolecular synthesis, but activated protein phosphatase activity in dose ranges of 10-15 microM and time range of 5-10 min in case of Staphylococcus epidermidis and Pseudomonas aeruginosa, respectively. These results demonstrated the antibacterial activities of Pep27 are fundamentally attributable to a physiological change by activated phosphatase activity.

SpxB is a suicide gene of Streptococcus pneumoniae and confers a selective advantage in an in vivo competitive colonization model

The human bacterial pathogen Streptococcus pneumoniae dies spontaneously upon reaching stationary phase. The extent of S. pneumoniae death at stationary phase is unusual in bacteria and has been conventionally attributed to autolysis by the LytA amidase. In this study, we show that spontaneous pneumococcal death is due to hydrogen peroxide (H(2)O(2)), not LytA, and that the gene responsible for H(2)O(2) production (spxB) also confers a survival advantage in colonization. Survival of S. pneumoniae in stationary phase was significantly prolonged by eliminating H(2)O(2) in any of three ways: chemically by supplementing the media with catalase, metabolically by growing the bacteria under anaerobic conditions, or genetically by constructing DeltaspxB mutants that do not produce H(2)O(2). Likewise, addition of H(2)O(2) to exponentially growing S. pneumoniae resulted in a death rate similar to that of cells in stationary phase. While DeltalytA mutants did not lyse at stationary phase, they died at a rate similar to that of the wild-type strain. Furthermore, we show that the death process induced by H(2)O(2) has features of apoptosis, as evidenced by increased annexin V staining, decreased DNA content, and appearance as assessed by transmission electron microscopy. Finally, in an in vivo rat model of competitive colonization, the presence of spxB conferred a selective advantage over the DeltaspxB mutant, suggesting an explanation for the persistence of this gene. We conclude that a suicide gene of pneumococcus is spxB, which induces an apoptosis-like death in pneumococci and confers a selective advantage in nasopharyngeal cocolonization.

Loss of penicillin tolerance by inactivating the carbon catabolite repression determinant CcpA in Streptococcus gordonii

OBJECTIVES

Antibiotic tolerance is a phenomenon allowing bacteria to withstand drug-induced killing. Here, we studied a penicillin-tolerant mutant of Streptococcus gordonii (Tol1), which was shown to be deregulated in the expression of the arginine deiminase operon (arc). arc was not directly responsible for tolerance, but is controlled by the global regulator CcpA. Therefore, we sought whether CcpA might be implicated in tolerance.

METHODS

The ccpA gene was characterized and subsequently inactivated by PCR ligation mutagenesis in both the susceptible wild-type (WT) and Tol1. The minimal inhibitory concentration and time-kill curves for the strains were determined and the outcome of penicillin treatment in experimental endocarditis assessed.

RESULTS

ccpA sequence and expression were similar between the WT and Tol1 strains. In killing assays, the WT lost 3.5 +/- 0.6 and 5.3 +/- 0.6 log(10) cfu/mL and Tol1 lost 0.4 +/- 0.2 and 1.4 +/- 0.9 log(10) cfu/mL after 24 and 48 h of penicillin exposure, respectively. Deletion of ccpA almost totally restored Tol1 kill susceptibility (loss of 2.5 +/- 0.7 and 4.9 +/- 0.7 log(10) cfu/mL at the same endpoints). In experimental endocarditis, penicillin treatment induced a significant reduction in vegetation bacterial densities between Tol1 (4.1 log(10) cfu/g) and Tol1DeltaccpA (2.4 log(10) cfu/g). Restitution of ccpA re-established the tolerant phenotype both in vitro and in vivo.

CONCLUSIONS

CcpA, a global regulator of the carbon catabolite repression system, is implicated in penicillin tolerance both in vitro and in vivo. This links antibiotic survival to bacterial sugar metabolism. However, since ccpA sequence and expression were similar between the WT and Tol1 strains, other factors are probably involved in tolerance.

Vancomycin-tolerant Streptococcus pneumoniae in Korea

A nationwide surveillance study was undertaken to monitor antimicrobial resistance among clinical isolates of Streptococcus pneumoniae in Korea, with a special focus on vancomycin tolerance. For the 6-month period from March to August 2002, clinical isolates of S. pneumoniae were collected from 11 university hospitals and 1 reference laboratory. One-hundred eighty-eight isolates were measured for lysis rates after exposure to vancomycin for 4 h. Two vancomycin-tolerant S. pneumoniae (VTSP) strains, S3 and H8, were isolated from sputum cultures of two patients, who had stayed in intensive-care units of different hospitals with long-term antibiotic therapy and were not treated for pneumococcal pneumonia. The penicillin, cefotaxime, and vancomycin MICs for S3 were 8 microg/ml, >16 microg/ml, and 0.5 microg/ml, and those for H8 were 2 microg/ml, 2 microg/ml, and 0.5 microg/ml, respectively. While S3 belonged to serotype 23F and was autolysin defective, H8 belonged to serotype 13F and had intact autolysin. These strains were not clonally related as determined by pulsed-field gel electrophoresis of chromosomal DNA. In agreement with previous reports, both isolates showed pairing of TIGR4 vex2 with R6 pep27 and had two identical amino acid substitutions, Q441K in vncS and N25D in vex2. These findings indicate that two VTSP strains have emerged independently in Korea, suggesting a prevalence rate of 1.1%. The emergence of VTSP would be a serious threat in Korea, where there are significant rates of penicillin resistance in S. pneumoniae. Monitoring of the prevalence of VTSP and further investigation of the clinical relevance of VTSP are warranted.

Synergistic effect of interleukin 1 alpha on nontypeable Haemophilus influenzae-induced up-regulation of human beta-defensin 2 in middle ear epithelial cells

Background

We recently showed that beta-defensins have antimicrobial activity against nontypeable Haemophilus influenzae (NTHi) and that interleukin 1 alpha (IL-1 alpha) up-regulates the transcription of beta-defensin 2 (DEFB4 according to new nomenclature of the Human Genome Organization) in human middle ear epithelial cells via a Src-dependent Raf-MEK1/2-ERK signaling pathway. Based on these observations, we investigated if human middle ear epithelial cells could release IL-1 alpha upon exposure to a lysate of NTHi and if this cytokine could have a synergistic effect on beta-defensin 2 up-regulation by the bacterial components.

Methods

The studies described herein were carried out using epithelial cell lines as well as a murine model of acute otitis media (OM). Human cytokine macroarray analysis was performed to detect the released cytokines in response to NTHi exposure. Real time quantitative PCR was done to compare the induction of IL-1 alpha or beta-defensin 2 mRNAs and to identify the signaling pathways involved. Direct activation of the beta-defensin 2 promoter was monitored using a beta-defensin 2 promoter-Luciferase construct. An IL-1 alpha blocking antibody was used to demonstrate the direct involvement of this cytokine on DEFB4 induction.

Results

Middle ear epithelial cells released IL-1 alpha when stimulated by NTHi components and this cytokine acted in an autocrine/paracrine synergistic manner with NTHi to up-regulate beta-defensin 2. This synergistic effect of IL-1 alpha on NTHi-induced beta-defensin 2 up-regulation appeared to be mediated by the p38 MAP kinase pathway.

Conclusion

We demonstrate that IL-1 alpha is secreted by middle ear epithelial cells upon exposure to NTHi components and that it can synergistically act with certain of these molecules to up-regulate beta-defensin 2 via the p38 MAP kinase pathway.

Vancomycin tolerance, a potential mechanism for refractory gram-positive bacteremia observational study in patients with cancer

BACKGROUND

The clinical significance of infections caused by vancomycin-tolerant (Vt) gram-positive organisms in patients with cancer remains unclear.

METHODS

Twenty-five patients with nonenterococcal gram-positive bloodstream infection, which was refractory to vancomycin therapy, were identified by reviewing the Infectious Diseases consultation database at the tertiary care cancer center. Among these, 8 patients in whom vancomycin-tolerance was documented are described. Antibiotic tolerance was defined as a > 32 times increase in minimum bactericidal concentration compared with minimum inhibitory concentration.

RESULTS

Eight patients with persistent fever and bacteremia of > 72 hours' duration after the initiation of vancomycin therapy were treated. The median age of these patients, which included 3 men and 5 women, was 44 years +/- 11 years. Solid tumors were more common (6 patients) and 2 patients had acute leukemia. Six patients (75%) were neutropenic (absolute neutrophil count < 500/mm3), including 2 breast cancer patients who had undergone autologous stem cell transplantation. The causative organisms were Staphylococcus aureus (n = 3 patients), group G streptococci (n = 2 patients), and Staphylococcus epidermidis, Streptococcus mitis, and Streptococcus sanguis (1 patient each). All isolates demonstrated a minimum bactericidal concentration for vancomycin that was at least 32 times greater than the minimum inhibitory concentration. Rapid defervescence (< or = 24 h) and resolution of bacteremia occurred with the addition of gentamicin (4 patients) or gentamicin plus rifampin (4 patients). None of these infections recurred after discontinuation of therapy.

CONCLUSIONS

Lack of clinical and/or microbiologic response to vancomycin should raise the suspicion of possible infection due to Vt gram-positive bacteria, and alternative bactericidal therapy should be instituted early, especially in patients with underlying immune suppression.

Functional and structural characteristics of anticancer peptide Pep27 analogues

BACKGROUND

A secreted peptide Pep27 initiates the cell death program in S. pneumoniae through signal transduction. This study was undertaken to evaluate the relation between the structure and cytotoxic activity of Pep27 and its analogues on cancer cells.

RESULTS

Pep27anal2 characterized substituting (2R-->W), (4E-->W), (11S-->W) and (13Q-->W) in native Pep27, exhibited greater hydrophobicity and anticancer activity than Pep27 and other analogues. The IC50 values of Pep27anal2 were approximately 10 - 30 microM in a number of cell lines (AML-2, HL-60, Jurkat, MCF-7 and SNU-601). Confocal microscopy showed that Pep27anal2-FITC was localized in the plasma membrane, and then moving from the membrane to subcellular compartments with the initiation of membrane blebbing. Flow cytometric analysis using propidium iodide and Annexin V also revealed that Pep27anal2 induced apoptosis with minor membrane damage. Electron microscopy revealed that Pep27 induced apoptosis in Jurkat cells. The anticancer activity of Pep27anal2 was neither abrogated by pan-caspase inhibitor (Z-VAD-fmk) nor related to cytochrome c release from mitochondria. The 3D solution structures of these two Pep27 peptides revealed that both form a random coil conformation in water; however, they adopted stable alpha-helical conformations in solutions.

CONCLUSION

The results indicate that Pep27anal2 can penetrate the plasma membrane, and then induce apoptosis in both caspase-and cytochrome c-independent manner. The hydrophobicity of Pep27anal2 appears to play an important role in membrane permeabilization and/or anticancer properties. The structure-functional relationships of these peptides are also discussed. It is proposed that Pep27anal2 is a potential candidate for anticancer therapeutic agents.

Revising the role of the pneumococcal vex-vncRS locus in vancomycin tolerance

Vancomycin is used increasingly to treat invasive infections caused by multidrug-resistant Streptococcus pneumoniae. Although no vancomycin-resistant strains have been isolated to date, tolerant strains that fail to die rapidly and that cause relapsing disease have been described. The vex123-pep27-vncRS locus, consisting of an ABC transporter, a presumed signaling peptide, and a two-component system, respectively, has been implicated in vancomycin tolerance. Recent findings, however, challenged this model. The data presented here indicate that erythromycin in the growth medium induces a vancomycin-tolerant phenotype and that loss of function of Pep27 or VncRS does not alter autolysis. However, a role for the ABC transporter encoded by the vex123 genes in tolerance was confirmed. A vex3 mutant was considerably more tolerant to vancomycin treatment than the wild-type strain T4, and the strength of the phenotype depended on the orientation of the resistance cassette used to construct the mutant. Microarray results suggested a number of genes that might be involved in tolerance in the vex3 mutant. Although the exact function and regulation of the vex123-pep27-vncRS locus remains to be determined, several factors influence the autolysis behavior of S. pneumoniae, including the bacterial capsule, erythromycin, and the lytA and vex3 gene products.

Bacterial virulence factors in neonatal sepsis: group B streptococcus

PURPOSE OF REVIEW

Group B streptococcus is a leading cause of neonatal pneumonia, septicaemia and meningitis. Up to one quarter of women in labour are now given intravenous antibiotics to prevent early-onset disease by the organism, a situation that will remain constant until a successful vaccine is available. From a molecular understanding of the pathogenicity of group B streptococcus we may be able to devise novel means for controlling disease, such as identifying inhibitors of key metabolic pathways or regulatory networks. This review summarizes our post-genomic knowledge of the regulation, metabolism and virulence of group B streptococcus.

RECENT FINDINGS

Although advances have been made in the understanding of classic group B streptococcus virulence traits, such as capsular polysaccharide, beta-haemolysin, C5a peptidase, adhesins and immunogenic surface proteins, the major recent contribution to group B streptococcus pathogenesis has been the whole genome sequencing of three group B streptococcus strains, representing serotypes Ia, III and V. From these genomes, we not only see where the classic virulence genes map, but we can also gain insights into the metabolism and regulation of the organism and how these affect its virulence.

SUMMARY

Knowledge of virulence factors and the organism's metabolism and gene regulation offers opportunities to find novel means of preventing group B streptococcus infection in babies.

Constitutive expression of PcsB suppresses the requirement for the essential VicR (YycF) response regulator in Streptococcus pneumoniae R6

We report several new findings about the function of the essential VicRK two-component regulatory system (TCS) in the human pathogen Streptococcus pneumoniae. The vicR-encoded response regulator, vicK-encoded histidine kinase and the protein encoded by the downstream vicX gene are the homologues of the YycF, YycG and YycJ proteins, respectively, studied previously in Bacillus subtilis and Staphylococcus aureus. Using a regulatable promoter, we demonstrated that the VicK histidine kinase is conditionally required for growth of S. pneumoniae. Likewise, we found that the VicX protein is also conditionally required for growth and probably plays a role in the essential signal transduction pathway mediated by VicR and VicK. Recovery of limited substitutions in the conserved aspartate 52 residue (D52) of VicR was consistent with a requirement for phosphorylation of VicR for growth under some conditions. We applied microarrays to characterize the changes in transcription patterns in bacteria depleted for vicRKX operon expression. Our results suggest that the pcsB gene is a target of the VicRK TCS. We present evidence that downregulation of pcsB could account for many of the defects in cell growth, shape, size and morphology observed in bacteria depleted for vicRKX expression. Furthermore, constitutive expression of pcsB+ suppressed the essential requirement for the VicRK TCS and allowed the isolation of vicR null mutants.

Death's toolbox: examining the molecular components of bacterial programmed cell death

Programmed cell death (PCD) is a genetically determined process of cellular suicide that is activated in response to cellular stress or damage, as well as in response to the developmental signals in multicellular organisms. Although historically studied in eukaryotes, it has been proposed that PCD also functions in prokaryotes, either during the developmental life cycle of certain bacteria or to remove damaged cells from a population in response to a wide variety of stresses. This review will examine several putative examples of bacterial PCD and summarize what is known about the molecular components of these systems.

Vancomycin tolerance induced by erythromycin but not by loss of vncRS, vex3, or pep27 function in Streptococcus pneumoniae

Vancomycin-tolerant Streptococcus pneumoniae is a growing problem among drug-resistant human pathogens. Some vancomycin-tolerant pneumococci have been reported to carry mutations in loci encoding a two-component regulatory system designated VncRS or in a proximal ABC transporter, Vex. A model was advanced proposing that the tolerance phenotype resulted from the inability of a vncS mutant to respond to the Vex-transported Pep27 "death peptide" signal and dephosphorylate VncR, thereby preventing relief of repression of autolytic and other cell death functions in response to antibiotics. To explore this hypothesis, we constructed mutations in vncS, vncR, vex3, and pep27 in S. pneumoniae strain R6 and two additional genetic backgrounds. The lytic responses of the isogenic DeltavncS, Deltavex3, DeltavncR, and Deltapep27 mutants, but not a DeltalytA strain, to vancomycin were indistinguishable from that of the parent strain. DeltavncS strains also failed to exhibit tolerance to vancomycin at various doses in multiple media and showed wild-type sensitivity to other classes of autolysis-inducing antibiotics. In contrast, addition of subinhibitory levels of the antibiotic erythromycin led to tolerance to vancomycin during late, but not early, exponential-phase growth in a DeltavncS strain, in the parent strain R6, and in two other strains bearing erythromycin resistance markers, namely, a DeltavncR strain and an unrelated DeltacomD strain that is defective in competence-quorum sensing. Thus, this tolerance effect resulted from changes in cell growth or other erythromycin-dependent phenomena and not inactivation of vncS per se. Consistent with these results, and in contrast to a previous report, we found that a synthetic form of Pep27 did not elicit lytic or nonlytic killing of pneumococci. Finally, microarray transcriptional analysis and beta-galactosidase reporter assays revealed VncS-dependent regulation of the vex123 gene cluster but did not support a role for VncRS in the regulation of autolytic or other putative cell death loci. Based on these findings, we propose that vancomycin tolerance in S. pneumoniae does not result from loss of vncS function alone.

Antibiotic tolerance in pneumococci

When bacteria such as Staphylococcus aureus and Streptococcus pneumoniae are exposed to lytic antibiotics such as penicillin and vancomycin, a self-induced killing process is initiated in the organism. This killing occurs via both non-lytic and lytic processes. Recent data suggest that the non-lytic killing system, which might affect the cytoplasmic membrane, secondarily activates murein hydrolases that eventually lyse the cell. Disturbances in this suicide pathway can lead to antibiotic tolerance, a process whereby the antibiotic still exerts its bacteriostatic effects but the self-induced killing system is impaired. In mutants obtained in vitro, signaling pathways have been affected that show either increased or decreased antibiotic-induced killing. Among clinical isolates of S. pneumoniae that are tolerant to penicillin and/or vancomycin, we do not yet know whether these signaling pathways are affected. We could, however, demonstrate that the activity of murein hydrolases is negatively controlled by the production of capsular polysaccharides in one vancomycin-tolerant isolate. Hence, type and level of capsular expression might constitute one factor that determines the degree of lysis, once the killing signal has been elicited by the antibiotic.

Genome sequence of Streptococcus agalactiae, a pathogen causing invasive neonatal disease

Streptococcus agalactiae is a commensal bacterium colonizing the intestinal tract of a significant proportion of the human population. However, it is also a pathogen which is the leading cause of invasive infections in neonates and causes septicaemia, meningitis and pneumonia. We sequenced the genome of the serogroup III strain NEM316, responsible for a fatal case of septicaemia. The genome is 2 211 485 base pairs long and contains 2118 protein coding genes. Fifty-five per cent of the predicted genes have an ortholog in the Streptococcus pyogenes genome, representing a conserved backbone between these two streptococci. Among the genes in S. agalactiae that lack an ortholog in S. pyogenes, 50% are clustered within 14 islands. These islands contain known and putative virulence genes, mostly encoding surface proteins as well as a number of genes related to mobile elements. Some of these islands could therefore be considered as pathogenicity islands. Compared with other pathogenic streptococci, S. agalactiae shows the unique feature that pathogenicity islands may have an important role in virulence acquisition and in genetic diversity.

Microarray-based identification of htrA, a Streptococcus pneumoniae gene that is regulated by the CiaRH two-component system and contributes to nasopharyngeal colonization

Nasopharyngeal carriage is the reservoir from which most disease with Streptococcus pneumoniae arises. Survival as a commensal in this environment is likely to require a set of adaptations distinct from those needed to cause disease, some of which may be mediated by two-component signal transduction systems (TCSTS). We examined the contributions of nine pneumococcal TCSTS to the process of nasopharyngeal colonization by using an infant rat model. Whereas deletions in all but one of these systems have been associated previously with a high degree of attenuation in a murine model of pneumonia, only the CiaRH system was necessary for efficient carriage. Transcriptional analysis by using microarray hybridization identified a locus consisting of two adjacent genes, htrA and spoJ, that was specifically and strongly downregulated in a DeltaciaRH-null mutant. A S. pneumoniae strain lacking the htrA gene encoding a putative serine protease, but not one lacking spoJ, showed decreased fitness in a competitive model of colonization, a finding consistent with this gene mediating a portion of the carriage deficit observed with the DeltaciaRH strain.

Evolution and spread of antibiotic resistance

Antibiotic resistance is a clinical and socioeconomical problem that is here to stay. Resistance can be natural or acquired. Some bacterial species, such as Pseudomonas aeruginosa, show a high intrinsic resistance to a number of antibiotics whereas others are normally highly antibiotic susceptible such as group A streptococci. Acquired resistance evolve via genetic alterations in the microbes own genome or by horizontal transfer of resistance genes located on various types of mobile DNA elements. Mutation frequencies to resistance can vary dramatically depending on the mechanism of resistance and whether or not the organism exhibits a mutator phenotype. Resistance usually has a biological cost for the microorganism, but compensatory mutations accumulate rapidly that abolish this fitness cost, explaining why many types of resistances may never disappear in a bacterial population. Resistance frequently occurs stepwise making it important to identify organisms with low level resistance that otherwise may constitute the genetic platform for development of higher resistance levels. Self-replicating plasmids, prophages, transposons, integrons and resistance islands all represent DNA elements that frequently carry resistance genes into sensitive organisms. These elements add DNA to the microbe and utilize site-specific recombinases/integrases for their integration into the genome. However, resistance may also be created by homologous recombination events creating mosaic genes where each piece of the gene may come from a different microbe. The selection with antibiotics have informed us much about the various genetic mechanisms that are responsible for microbial evolution.

A multitarget assay for inhibitors of membrane-associated steps of peptidoglycan biosynthesis

Peptidoglycan synthesis begins in the cytoplasm with the condensation of UDP-N-acetyl glucosamine (UDP-GlcNAc) and phosphoenolpyruvate catalyzed by UDP-N-acetylglucosamine enolpyruvoyl transferase. UDP-GlcNAc is also utilized as substrate for the glycosyltransferase MurG, a membrane-bound enzyme that catalyzes the production of lipid II. Membranes from Escherichia coli cells overproducing MurG support peptidoglycan formation at a rate approximately fivefold faster than membranes containing wild-type levels of MurG. Conditions have been optimized for the production of large amounts of membranes with increased levels of MurG, allowing the development of an assay suitable for high-throughput screening of large compound libraries. The quality of the purified membranes was assessed by electron microscopy and also by testing cross-linked peptidoglycan production. Moreover, kinetic studies allowed the determination of optimal concentrations of the substrates and membranes to be utilized for maximum sensitivity of the assay. Using a 96-well assay format, the IC50 values for vancomycin, tunicamycin, flavomycin, and bacitracin were 1.1 microM, 0.01 microg/ml, 0.03 microg/ml, and 0.7 microg/ml, respectively.

Molecular analysis of antibiotic tolerance in pneumococci

Widespread pneumococcal resistance and the emergence of tolerance underscores the need to develop new antimicrobials. Uncovering the mechanisms of autolysin activation could yield not only new antibacterial targets but also ways to eradicate a pool of bacteria facilitating the spread of resistance. Although several genes contributing to antibiotic tolerance among pneumococci have been identified, those important in the clinical arena thus far are in a single gene cluster, vex/pep27/vncS/vncR. Mutations within this signal transduction system represent at least one mechanism, which explains tolerance to both penicillin and vancomycin. Since mutations in this locus do not result in tolerance to penicillin alone, there must be other, yet unknown, mutations which account for tolerance to a single antibiotic. In the case of pneumococci, there exist two more autolysins other than LytA suggesting our understanding of how bacteria die is currently only at the beginning.

Resistance mechanisms of gram-positive bacteria

The introduction and increasing use of antibiotics for antibacterial therapy has initiated a rapid development and expansion of antibiotic resistance in microorganisms, particularly in human pathogens. Additionally, a shift to an increase in number and severity of Gram-positive infections has been observed the last decades. Common to these pathogens is their tendency to accumulate multiple resistances under antibiotic pressure and selection. Methicillin-resistant Staphylococcus aureus (MRSA), that have acquired multiresistance to all classes of antibiotics, have become a serious nosocomial problem. Recently, the emergence of the first MRSA with reduced vancomycin susceptibility evoked the specter of a totally resistant S. aureus. Problems with multiresistance expand also to penicillin-resistant Streptococcus pneumoniae that are partially or totally resistant to multiple antibiotics, and to vancomycin-resistant Enterococcus ssp., completely resistant to all commonly used antibiotics. The rapid development of resistance is due to mutational events and/or gene transfer and acquisition of resistance determinants, allowing strains to survive antibiotic treatment.

Glycopeptide antibiotic resistance

Glycopeptide antibiotics are integral components of the current antibiotic arsenal that is under strong pressures as a result of the emergence of a variety of resistance mechanisms over the past 15 years. Resistance has manifested itself largely through the expression of genes that encode proteins that reprogram cell wall biosynthesis and thus evade the action of the antibiotic in the enterococci, though recently new mechanisms have appeared that afford resistance and tolerance in the more virulent staphylococci and streptococci. Overcoming glycopeptide resistance will require innovative approaches to generate new antibiotics or otherwise to inhibit the action of resistance elements in various bacteria. The chemical complexity of the glycopeptides, the challenges of discovering and successfully exploiting new targets, and the growing number of distinct resistance types all increase the difficulty of the current problem we face as a result of the emergence of glycopeptide resistance.