Intermedilysin Is Essential for the Invasion of Hepatoma HepG2 Cells byStreptococcus intermedius

Streptococcus intermedius causes endogenous infections leading to abscesses. This species produces intermedilysin (ILY), a human-specific cytolysin. Because of the significant correlation between higher ILY production levels by S. intermedius and deep-seated abscesses, we constructed ily knockout mutant UNS38 B3 and complementation strain UNS38 B3R1 in order to investigate the role of ILY in deep-seated infections. Strain UNS38 reduced the viability of human liver cell line HepG2 at infection but not of rat liver cell line BRL3A. Isogenic mutant strain UNS38 B3 was not cytotoxic in either cell line. Quantification of S. intermedius revealed that in infected HepG2 cells UNS38 but not UNS38 B3 increased intracellularly concomitantly with increasing cell damage. This difference between UNS38 and UNS38 B3 was not observed with UNS38 B3R1. Invasion and proliferation in BRL3A cells was not observed. Masking UNS38 or UNS38 B3R1 with ILY antibody drastically decreased adherence and invasion of HepG2. Moreover, coating strain UNS38 B3 with ILY partially restored adherence to HepG2 but without subsequent bacterial growth. At 1 day post-infection, many intact UNS38 were detected in the damaged phagosomes of HepG2 with bacterial proliferation observed in the cytoplasm of dead HepG2 after an additional 2 day incubation. These results indicate that surface-bound ILY on S. intermedius is an important factor for invasion of human cells by this bacterium and that secretion of ILY within host cells is essential for subsequent host cell death. These data strongly implicate ILY as an important factor in the pathogenesis of abscesses in vivo by this streptococcus.

HIV1 Vpr arrests the cell cycle by recruiting DCAF1/VprBP, a receptor of the Cul4-DDB1 ubiquitin ligase

How the HIV1 Vpr protein initiates the host cell response leading to cell cycle arrest in G(2) has remained unknown. Here, we show that recruitment of DCAF1/VprBP by Vpr is essential for its cytostatic activity, which can be abolished either by single mutations of Vpr that impair DCAF1 binding, or by siRNA-mediated silencing of DCAF1. Furthermore, DCAF1 bridges Vpr to DDB1, a core subunit of Cul4 ubiquitin ligases. Altogether these results point to a mechanism where Vpr triggers G(2) arrest by hijacking the Cul4/DDB1(DCAF1) ubiquitin ligase. We further show that, Vpx, a non-cytostatic Vpr-related protein acquired by HIV2 and SIV, also binds DCAF1 through a conserved motif. Thus, Vpr from HIV1 and Vpx from SIV recruit DCAF1 with different physiological outcomes for the host cell. This in turn suggests that both proteins have evolved to preserve interaction with the same Cul4 ubiquitin ligase while diverging in the recognition of host substrates targeted for proteasomal degradation.

[Pathogenicity factors of opportunistic enterobacteria and its role in development of diarrhea]

The data of pathogenicity factors of opportunistic enterobacteria, including Klebsiella, Enterobacter, Citrobacter, Proteus, Providencia and Hafnia species are submitted. The genetic control and a role of pathogenicity factors of opportunistic enterobacteria in development of diarrhea syndrome are presented. Data about adhesins, hemolysins, cytotoxic necrotizing factors and bacterial modulins are described. The characteristic of cytotonic and cytotoxic enterotoxins, including LT, ST, Shiga-like and cytolethal toxins, and mechanisms of diarrheagenic action are analysed. The role of bacterial lipopolysaccharide (endotoxin) and induction of locally synthesized proinflammatory cytokins in pathogenisis of diarrhea are discussed.

Pseudolipasin A is a specific inhibitor for phospholipase A2 activity of Pseudomonas aeruginosa cytotoxin ExoU

A number of bacterial pathogens utilize the type III secretion pathway to deliver effector proteins directly into the host cell cytoplasm. Certain strains of Pseudomonas aeruginosa associated with acute infections express a potent cytotoxin, exoenzyme U (ExoU), that is delivered via the type III secretion pathway directly into contacting host cells. Once inside the mammalian cell, ExoU rapidly lyses the intoxicated cells via its phospholipase A(2) (PLA(2)) activity. A high-throughput cell-based assay was developed to screen libraries of compounds for those capable of protecting cells against the cytotoxic effects of ExoU. A number of compounds were identified in this screen, including one group that blocks the intracellular activity of ExoU. In addition, these compounds specifically inhibited the PLA(2) activity of ExoU in vitro, whereas eukaryotic secreted PLA(2) and cytosolic PLA(2) were not inhibited. This novel inhibitor of ExoU-specific PLA(2) activity, named pseudolipasin A, may provide a new lead for virulence factor-based therapeutic design.

Escherichia coli cytotoxic necrotizing factor 1 blocks cell cycle G2/M transition in uroepithelial cells

Evidence is accumulating that a growing number of bacterial toxins act by modulating the eukaryotic cell cycle machinery. In this context, we provide evidence that a protein toxin named cytotoxic necrotizing factor 1 (CNF1) from uropathogenic Escherichia coli is able to block cell cycle G(2)/M transition in the uroepithelial cell line T24. CNF1 permanently activates the small GTP-binding proteins of the Rho family that, beside controlling the actin cytoskeleton organization, also play a pivotal role in a large number of other cellular processes, including cell cycle regulation. The results reported here show that CNF1 is able to induce the accumulation of cells in the G(2)/M phase by sequestering cyclin B1 in the cytoplasm and down-regulating its expression. The possible role played by the Rho GTPases in the toxin-induced cell cycle deregulation has been investigated and discussed. The activity of CNF1 on cell cycle progression can offer a novel view of E. coli pathogenicity.

Mapping of a domain required for protein-protein interactions and inhibitory activity of a Helicobacter pylori dominant-negative VacA mutant protein

The Helicobacter pylori VacA toxin is an 88-kDa secreted protein that causes multiple alterations in mammalian cells and is considered an important virulence factor in the pathogenesis of peptic ulcer disease and gastric cancer. We have shown previously that a VacA mutant protein lacking amino acids 6 to 27 (Delta6-27p88 VacA) is able to inhibit many activities of wild-type VacA in a dominant-negative manner. Analysis of a panel of C-terminally truncated Delta6-27p88 VacA proteins indicated that a fragment containing amino acids 1 to 478 (Delta6-27p48) exhibited a dominant-negative phenotype similar to that of the full-length Delta6-27p88 VacA protein. In contrast, a shorter VacA fragment lacking amino acids 6 to 27 (Delta6-27p33) did not exhibit detectable inhibitory activity. The Delta6-27p48 protein physically interacted with wild-type p88 VacA, whereas the Delta6-27p33 protein did not. Mutational analysis indicated that amino acids 351 to 360 are required for VacA protein-protein interactions and for dominant-negative inhibitory activity. The C-terminal portion (p55 domain) of wild-type p88 VacA could complement either Delta6-27p33 or Delta(6-27/351-360)p48, reconstituting dominant-negative inhibitory activity. Collectively, our data provide strong evidence that the inhibitory properties of dominant-negative VacA mutant proteins are dependent on interactions between the mutant VacA proteins and wild-type VacA, and they allow mapping of a domain involved in the formation of oligomeric VacA complexes.

The mechanism of pore formation by bacterial toxins

A remarkable group of proteins challenge the notions that protein sequence determines a unique three-dimensional structure, and that membrane and soluble proteins are very distinct. The pore-forming toxins typically transform from soluble, monomeric proteins to oligomers that form transmembrane channels. Recent structural studies provide ideas about how these changes take place. The recently solved structures of the beta-pore-forming toxins LukS, epsilon-toxin and intermedilysin confirm that the pore-forming regions are initially folded up on the surfaces of the soluble precursors. To create the transmembrane pores, these regions must extend and refold into membrane-inserted beta-barrels.

Modulation of host cell signal transduction pathways by Helicobacter pylori infection

Bacterial pathogens modulate host cell signal transduction responses to establish infection and cause disease. The purpose of the present summary, first presented at the Canadian Helicobacter Study Group meeting, is to discuss current knowledge of specific Helicobacter pylori factors, including the vacuolating cytotoxin, cytotoxin-associated gene A and the type four secretion system encoded by the cytotoxin-associated gene pathogenicity island and review the host cell signal transduction cascades that they modulate.

Mannheimia haemolytica leukotoxin induces apoptosis of bovine lymphoblastoid cells (BL-3) via a caspase-9-dependent mitochondrial pathway

Mannheimia haemolytica is a key pathogen in the bovine respiratory disease complex. It produces a leukotoxin (LKT) that is an important virulence factor, causing cell death in bovine leukocytes. The LKT binds to the beta(2) integrin CD11a/CD18, which usually activates signaling pathways that facilitate cell survival. In this study, we investigated mechanisms by which LKT induces death in bovine lymphoblastoid cells (BL-3). Incubation of BL-3 cells with a low concentration of LKT results in the activation of caspase-3 and caspase-9 but not caspase-8. Similarly, the proapoptotic proteins Bax and BAD were significantly elevated, while the antiapoptotic proteins Bcl-2, Bcl(XL) and Akt-1 were downregulated. Following exposure to LKT, we also observed a reduction in mitochondrial cytochrome c and corresponding elevation of cytosolic cytochrome c, suggesting translocation from the mitochondrial compartment to the cytosol. Consistent with this observation, tetramethylrhodamine ethyl ester perchlorate staining revealed that mitochondrial membrane potential was significantly reduced. These data suggest that LKT induces apoptosis of BL-3 cells via a caspase-9-dependent mitochondrial pathway. Furthermore, scanning electron micrographs of mitochondria from LKT-treated BL-3 cells revealed lesions in the outer mitochondrial membrane, which are larger than previous reports of the permeability transition pore through which cytochrome c is usually released.

Inactivation and Activity of Cholesterol-Dependent Cytolysins: What Structural Studies Tell Us

The homologous bacterially expressed cholesterol-dependent cytolysins (CDCs) form pores via oligomerization; this must occur preferentially once the target membrane has been engaged. Conformational changes in CDCs then drive partition from an aqueous environment to a lipidic one. This review addresses how premature oligomerization is prevented, how conformational changes are triggered, and how cooperativity between subunits brings about new functionality absent from isolated protomers. Variations are found in the answers provided by the CDCs to these issues. Some toxins use pH as a trigger of activity, but recent results have shown that dimerization in solution is an alternative way of preventing premature oligomerization, in particular for the CDC from Clostridium perfringens, perfringolysin. More controversially, there is still no resolution to the debate as to whether incomplete (arciform) oligomers form pores: recent results again suggest that they do.

Interaction of three-finger toxins with phospholipid membranes: comparison of S- and P-type cytotoxins

The CTs (cytotoxins) I and II are positively charged three-finger folded proteins from venom of Naja oxiana (the Central Asian cobra). They belong to S- and P-type respectively based on Ser-28 and Pro-30 residues within a putative phospholipid bilayer binding site. Previously, we investigated the interaction of CTII with multilamellar liposomes of dipalmitoylphosphatidylglycerol by wide-line (31)P-NMR spectroscopy. To compare interactions of these proteins with phospholipids, we investigated the interaction of CTI with the multilamellar liposomes of dipalmitoylphosphatidylglycerol analogously. The effect of CTI on the chemical shielding anisotropy and deformation of the liposomes in the magnetic field was determined at different temperatures and lipid/protein ratios. It was found that both the proteins do not affect lipid organization in the gel state. In the liquid crystalline state of the bilayer they disturb lipid packing. To get insight into the interactions of the toxins with membranes, Monte Carlo simulations of CTI and CTII in the presence of the bilayer membrane were performed. It was found that both the toxins penetrate into the bilayer with the tips of all the three loops. However, the free-energy gain on membrane insertion of CTI is smaller (by approximately 7 kcal/mol; 1 kcal identical with 4.184 kJ) when compared with CTII, because of the lower hydrophobicity of the membrane-binding site of CTI. These results clearly demonstrate that the P-type cytotoxins interact with membranes stronger than those of the S-type, although the mode of the membrane insertion is similar for both the types.

Enterococcal cytolysin: activities and association with other virulence traits in a pathogenicity island

Enterococcal cytolysin is a structurally novel bacterial toxin expressed by some strains of E. faecalis and is distantly related to the class of bacteriocins known as lantibiotics. The cytolysin can be encoded by large pheromone-responsive plasmids, or on the chromosome within pathogenicity island. It is produced by a complex process that involves the products of eight genes, designated cylR1, cylR2, cylLL, cylLS, cylM, cylB, cylA, and cylI. The cytolysin toxin, maturation and regulatory genes are organized into two divergent transcripts: a structural transcript cylLLLSMBAI, and a regulatory transcript cylR1R2. The active cytolysin subunits, CylLL" and CylLS", are synthesized ribosomally as non-identical peptides, post-translationally modified, then secreted and activated. The cytolysin operon is repressed by the activities of two proteins, CylR1 and CylR2, and derepressed by a quorum-sensing process involving secreted autoinducer CylLS". The cytolysin operon within the E. faecalis pathogenicity island is associated with other virulence determinants, including aggregation substance and enterococcal surface protein, Esp.

Pathogenic enterococci: new developments in the 21st century

Enterococci, traditionally viewed as Gram-positive commensal bacteria inhabiting the alimentary canals of humans and animals, are now acknowledged to be organisms capable of causing life-threatening infections in humans, especially in the nosocomial environment. The existence of enterococci in such a dual role is facilitated, at least in part, by its intrinsic and acquired resistance to virtually all antibiotics currently in use. Beginning with the initial identification of a 'streptococci of fecal origin' in the late 19th century, enterococci have been studied for over a century now. A number of comprehensive reviews during this time have addressed various aspects of enterococci, including classification, biology, virulence, antibiotic resistance and so on. This review specifically addresses the important advances in the field of enterococcal research that have occurred since the beginning of the 21st century. Most notable among these developments have been the insights into enterococcal genomes and pathogenicity.

The Rac-activating toxin cytotoxic necrotizing factor 1 oversees NK cell-mediated activity by regulating the actin/microtubule interplay

The cell cytoskeleton is widely acknowledged as a master for NK cell function. Specifically, actin filaments guide the NK cell binding to target cells, engendering the formation of the so-called immunological synapse, while microtubules direct the killer behavior. All these cytoskeleton-dependent activities are competently governed by the Rho GTPases, a family of regulatory molecules encompassing the three different subfamilies, Rho, Rac, and Cdc42. By using a Rac GTPase-activating bacterial protein toxin from Escherichia coli named cytotoxic necrotizing factor 1 (CNF1), we obtained results supporting the activation of Rac GTPase as a booster for effector cell-binding efficiency, recruitment ability, and, consequently, cytotoxicity. In particular, the augmented killer capacity of CNF1-treated NK cells was associated with the increased expression of certain cell adhesion or activation-associated molecules and the reshaping of the actin and microtubule networks. Importantly, CNF1 counteracted the activity exerted by toxins disrupting the cytoskeletal architecture. Hence, the activation of Rho GTPases, particularly Rac, induced by CNF1, appears to orchestrate a dynamic cross talk between microtubules and actin filaments, leading to a fruitful NK cell activity and polarization state. Our findings suggest that protein toxins might be viewed as modulators of NK cell cytotoxic activity and could possibly be regarded as useful pharmacological tools for certain Rho-linked immune diseases in the near future.

Antimicrobial and cytolytic peptides of venomous arthropods

As a response to invading microorganisms, the innate immune system of arthropods has evolved a complex arrangement of constitutive and inducible antimicrobial peptides that immediately destroy a large variety of pathogens. At the same time, venomous arthropods have developed an additional offensive system in their venom glands to subdue their prey items. In this complex venom system, several enzymes, low-molecular-mass compounds, neurotoxins, antimicrobial and cytolytic peptides interact together, resulting in extremely rapid immobilization and/or killing of prey or aggressors. This review provides an overview of antimicrobial peptides identified in the hemolymph of venomous arthropods, and especially of cytolytic peptides in their venom. For these peptides a dual role is proposed: acting as antimicrobials as well as increasing the potency of the venom by influencing excitable cells.

Redefining cholesterol's role in the mechanism of the cholesterol-dependent cytolysins

The cholesterol-dependent cytolysins (CDCs) constitute a large family of pore-forming toxins that function exclusively on cholesterol-containing membranes. A detailed analysis of the various stages in the cytolytic mechanism of three members of the CDC family revealed that significant depletion of cholesterol from the erythrocyte membrane stalls these toxins in the prepore complex. Therefore, the depletion of membrane cholesterol prevents the insertion of the transmembrane beta-barrel and pore formation. These unprecedented findings provide a paradigm for the involvement of cholesterol in the CDC cytolytic mechanism and that of other pore-forming toxins whose activity is enhanced by the presence of membrane cholesterol.

Different vulnerability to cytotoxicity and susceptibility to protection of progenitors versus mature oligodendrocytes

Oligodendrocytes are known to be particularly vulnerable to the cytotoxic effect evoked by different neurodegenerative processes, such as ischemic insult, hypoxia, hypoglycemia or autoaggressive immunological attack like SM. They are the neural cells that undergo sophisticated process of maturation characterized by huge changes in cell metabolism and morphology. Small bipolar cells differentiate into multiprocessed mature oligodendrocytes capable of myelinating CNS. A question arises whether there are any differences in their sensitivity to excitotoxic events? To address this problem, the cells of two distinct stages of differentiation, i.e. progenitors (O-2A) and mature, myelinating oligodendrocytes (MBP+) were selected for investigation of the effects of such apoptogenic factors as H(2)O(2) or serum-withdrawal in vitro. Primary cultures obtained from the brain hemispheres of 18 days old Wistar rat embryos served after 10 days for the establishing pure oligodendrocyte culture (the "shake-off" method by McCarthy and de Vellis, 1980). Oligodendrocytes were cultured in DMEM with addition of insulin, transferrin and sodium selenite. Cytotoxic influence of selected apoptotic factors as well as neuroprotective effects of CsA were estimated by immunochemical detection. The obtained data suggest that progenitors and mature cells respond to apoptogenic conditions by activation of different molecular pathways and specific cytoprotective conditions should be worked out for each type of the cells.

The C terminus of YopT is crucial for activity and the N terminus is crucial for substrate binding

Recently, it was shown that Yersinia outer protein T (YopT) belongs to a new family of cysteine proteases containing invariant C, H, and D residues that are crucial for its activity. YopT cleaves RhoA, Rac, and Cdc42 at their C termini, thereby releasing them from the membrane. Moreover, YopT inhibits the Rho-rhotekin and Rho-guanine nucleotide dissociation inhibitor interactions. To characterize the active domain of YopT, we constructed N- and C-terminal truncations and expressed them as glutathione S-transferase fusion proteins in Escherichia coli. The toxin fragments were tested for stability by trypsin digestion. The activity of the proteins was studied by membrane release assay, rhotekin pulldown experiments, and microinjection. Whereas deletion of the first 74 N-terminal amino acids did not influence the activity of YopT, deletion of 8 amino acids from the C terminus led to complete loss of activity. N-terminal deletion of 100 amino acids led to an inactive protein, although it still contained the amino acids C139, H258, and D274, which are essential for catalysis. Loss of activity of the N-terminal deletions corresponded to the block of interaction with RhoA, indicating that residues 75 to 100 of YopT are essential for binding to the GTPase. By contrast, when up to 15 amino acids of the C terminus were deleted, the protein had no activity but was still able to interact with RhoA, suggesting a role for the C terminus in the enzyme activity of YopT.

Outer membrane protein A and cytotoxic necrotizing factor-1 use diverse signaling mechanisms for Escherichia coli K1 invasion of human brain microvascular endothelial cells

Escherichia coli K1 invasion of brain microvascular endothelial cells (BMEC) is a prerequisite for penetration into the central nervous system. We previously have shown that outer membrane protein A (OmpA) and cytotoxic necrotizing factor-1 (CNF1) contribute to E. coli K1 invasion of BMEC. In this study we constructed a double-knockout mutant by deleting ompA and cnf1. We demonstrated that the double-knockout mutant was significantly less invasive in human BMEC as compared with its individual Delta ompA and Delta cnf1 mutants, suggesting that the contributions of OmpA and CNF1 to BMEC invasion are independent of each other. In addition, we showed that OmpA treatment of human BMEC resulted in phosphatidylinositol 3-kinase (PI3K) activation with no effect on RhoA, while CNF1 treatment resulted in RhoA activation with no effect on PI3K, supporting the concept that OmpA and CNF1 contribute to E. coli K1 invasion of BMEC using different mechanisms. This concept was further confirmed by using both PI3K inhibitor (LY294002) and Rho kinase inhibitor (Y27632), which exhibited additive effects on inhibiting E. coli K1 invasion of BMEC. We isolated a 96KD OmpA interacting human BMEC protein by affinity chromatography using purified OmpA, which was identified as gp96 protein, a member of the HSP90 family. This receptor differed from the CNF1 receptor (37LRP) identified from human BMEC. Taken together, these data indicate that OmpA and CNF1 contribute to E. coli K1 invasion of BMEC in an additive manner by interacting with different BMEC receptors and using diverse host cell signaling mechanisms.

Vibrio vulnificus infection: clinical manifestations, pathogenesis, and antimicrobial therapy

There has been a dramatic increase in the number of reported cases of infection due to Vibrio vulnificus in Taiwan. Although the organism has been etiologically implicated in a variety of clinical syndromes, most cases of V. vulnificus infection are categorized as primary bacteremia, skin and soft tissue infection. The mortality was up to 50% in septic patients, most of them dying within 48 h of admission. In most of the cases involving V. vulnificus infection have underlying disease, particularly liver cirrhosis. The pathogenesis may attribute to several virulent factors, such as lipopolysaccharide, capsular lipopolysaccharide, cytolysin, metalloprotease and siderophore. Tetracycline was suggested as the drug of choice based on an animal study. Our previous in vitro data showed that cefotaxime and minocycline acted synergistically in inhibiting V. vulnificus. Furthermore, another in vivo animal study indicated that therapy using combined with cefotaxime and minocycline was distinctly more advantageous than therapy with the single antibiotic regimen for the treatment of severe experimental murine V. vulnificus infection. Recently, we also demonstrated that the newer fluoroquinolones, as single agents were as effective as the combination therapy both in vitro and in vivo.

37-kDa laminin receptor precursor modulates cytotoxic necrotizing factor 1-mediated RhoA activation and bacterial uptake

Cytotoxic necrotizing factor 1 (CNF1) is a bacterial toxin known to activate Rho GTPases and induce host cell cytoskeleton rearrangements. The constitutive activation of Rho GTPases by CNF1 is shown to enhance bacterial uptake in epithelial cells and human brain microvascular endothelial cells. However, it is unknown how exogenous CNF1 exhibits such phenotypes in eukaryotic cells. Here, we identified 37-kDa laminin receptor precursor (LRP) as the receptor for CNF1 from screening the cDNA library of human brain microvascular endothelial cells by the yeast two-hybrid system using the N-terminal domain of CNF1 as bait. CNF1-mediated RhoA activation and bacterial uptake were inhibited by exogenous LRP or LRP antisense oligodeoxynucleotides, whereas they were increased in LRP-overexpressing cells. These findings indicate that the CNF1 interaction with LRP is the initial step required for CNF1-mediated RhoA activation and bacterial uptake in eukaryotic cells.

Functional convergence of invertebrate and vertebrate cytokine-like molecules based on a similar lectin-like activity

It is generally accepted that the action of cytokines results from their binding to specific receptors. However, many cytokines possess lectin-like activity that may be essential for the expression of their full biological activities. This review focuses on the physiological relevance of the lectin-like activity of cytokines during the innate immune response in mammals, using TNF as an illustrative example. Moreover, we will show that TNF displays functional analogies with a defense molecule from the earthworm Eisenia foetida termed CCF. These analogies are not reflected by primary sequence homology between CCF and TNF but are particularly based on a similar lectin-like activity/domain. Hence, from a phylogenetic point of view, the lectin-like activity/domain of CCF and TNF may represent an essential recognition mechanism that has been functionally conserved during the innate immune response of invertebrates and vertebrates as a result of convergent evolution.

How does Legionella pneumophila exit the host cell?

In recent years, tremendous progress has been made in unraveling the elegant mechanisms by which intracellular pathogens invade host cells and establish intracellular infections. By contrast, our knowledge of the mechanisms of host cell cytolysis and the egress of intracellular pathogens is still in its infancy. Temporal pore-formation-mediated lysis of the host and exit by Legionella pneumophila and Leishmania could provide a new model of egress for other intracellular pathogens, many of which exhibit pore-forming or cytolysin activity

Upper and lower respiratory tract infection by Streptococcus pneumoniae is affected by pneumolysin deficiency and differences in capsule type

Pneumococci frequently colonize the upper respiratory tract, and these pneumococci are believed to act as a reservoir for infection of the lower respiratory tract and bacteremia. We investigated how the pneumococcal toxin pneumolysin affects the capacity of pneumococci to infect the upper and lower respiratory tract of the mouse. Wild-type Streptococcus pneumoniae serotype 2 and 3 strains, a serotype 2 pneumolysin-deficient mutant, and a serotype 2 mutant with the pneumolysin gene reinserted were used to study differences in colonization and disease. In addition, we also examined a pneumococcal chimeric mutant (capsule type switched from serotype 2 to serotype 3) to gain further insight into the role that capsule plays in nasopharyngeal infection. Absence of pneumolysin was found to be associated with significantly lower numbers of pneumococci in the nasopharynx, trachea, and lungs. Differences in pneumococcal capsule type were found to have significant effects on pneumococcal infection of the nasopharynx, trachea, and lungs. However, it was the combination of capsule type and genetic background that was important, and the influence of this combination varied with the site of infection. For example, in the nasopharynx the wild-type serotype 3 strain and the capsule-switched mutant behaved similarly, whereas in the lungs the mutant that was switched to serotype 3 survived less well than the wild-type serotype 3 strain. The combination of capsule type and genetic background also determined virulence. Thus, the wild-type serotype 3 strain was virulent, whereas the capsule-switched mutant was avirulent.

Oro-facial gangrene (noma/cancrum oris): pathogenetic mechanisms

Cancrum oris (Noma) is a devastating infectious disease which destroys the soft and hard tissues of the oral and para-oral structures. The dehumanizing oro-facial gangrenous lesion affects predominantly children ages 2 to 16 years, particularly in sub-Saharan Africa, where the estimated frequency in some communities varies from 1 to 7 cases per 1000 population. The risk factors are poverty, malnutrition, poor oral hygiene, residential proximity to livestock in unsanitary environments, and infectious diseases, particularly measles and those due to the herpesviridae. Infections and malnutrition impair the immune system, and this is the common denominator for the occurrence of noma. Acute necrotizing gingivitis (ANG) and oral herpetic ulcers are considered the antecedent lesions, and ongoing studies suggest that the rapid progression of these precursor lesions to noma requires infection by a consortium of micro-organisms, with Fusobacterium necrophorum (Fn) and Prevotella intermedia (Pi) as the suspected key players. Additional to production of a growth-stimulating factor for Pi, Fn displays a classic endotoxin, a dermonecrotic toxin, a cytoplasmic toxin, and a hemolysin. Without appropriate treatment, the mortality rate from noma is 70-90%. Survivors suffer the two-fold afflictions of oro-facial mutilation and functional impairment, which require a time-consuming, financially prohibitive surgical reconstruction.

Cytotoxic necrotizing factor-1 contributes to Escherichia coli K1 invasion of the central nervous system

Escherichia coli K1 invasion of brain microvascular endothelial cells (BMECs) is a prerequisite for penetration into the central nervous system and requires actin cytoskeletal rearrangements. Here, we demonstrate that E. coli K1 invasion of BMECs requires RhoA activation. In addition, we show that cytotoxic necrotizing factor-1 (CNF1) contributes to E. coli K1 invasion of brain endothelial cells in vitro and traversal of the blood-brain barrier in the experimental hematogenous meningitis animal model. These in vitro and in vivo effects of CNF1 were dependent upon RhoA activation as shown by (a) decreased invasion and RhoA activation with the Delta cnf1 mutant of E. coli K1 and (b) restoration of invasion frequency of the Delta cnf1 mutant to the level of the parent E. coli K1 strain in BMECs with constitutively active RhoA. In addition, CNF1-enhanced E. coli invasion of brain endothelial cells and stress fiber formation were independent of focal adhesion kinase and phosphatidylinositol 3-kinase activation. This is the first demonstration that CNF1 contributes to E. coli K1 invasion of BMECs.

Type 1, P and S fimbriae, and afimbrial adhesin I are not essential for uropathogenic Escherichia coli to adhere to and invade bladder epithelial cells

Fimbrial (type 1, P, and S) and afimbrial adhesins, the unique virulence traits of uropathogenic Escherichia coli (UPEC), are well recognized for their role in the initial step of uropathogenesis. In this study, we investigated whether these adhesins are dispensable for UPEC in adherence and invasion of uroepithelial cells by using E. coli isolates (n=40) from cystitis patients and T-24 cells, the bladder carcinoma cell line. We found all isolates adherent to T-24 cells within 15 min of infection. In invasion assay, all isolates could invade T-24 cells to a variable degree; 22.5% of them were found highly invasive. About 33% of isolates that do not have any recognized adhesins were as invasive as other isolates. The amplitude of invasiveness was also independent of the adhesins. In conclusion, this study demonstrates that type 1 fimbriae, P fimbriae, S fimbriae, and afimbrial adhesin I are not required for UPEC to adhere to and invade uroepithelial cells.

Helicobacter: a paradigm shift in peptic ulcer disease and more?

There are many diseases where the cause is unknown and this makes a specific treatment difficult. In many cases all that can be achieved is amelioration of the illness. Peptic ulcer disease was one such condition no more that 20 years ago. The management was drastic--either an operation or life-long medication in order to reduce the acid secreted by the stomach. However, the cause of this condition was discovered in 1983. Although initially sceptical, the medical fraternity now almost universally endorse Helicobacter pylori as the cause of the majority of stomach ulcers. Peptic ulcers can now be cured by antibiotics. This is a major shift in medical practice. Continued investigations on Helicobacter pylori are bringing to light other possible associations with disease as well as delineating plausible biological mechanisms for disease pathogenesis.

Cytotoxic necrotizing factor type 1-positive Escherichia coli causes increased inflammation and tissue damage to the prostate in a rat prostatitis model

Infection of rat prostates with cytotoxic necrotizing factor type 1 (CNF1)-positive uropathogenic Escherichia coli caused more inflammation-mediated morphological and histological tissue damage than did infection with isogenic CNF1-negative mutants. These striking differences occurred despite the finding that bacterial counts for the strain pairs were indistinguishable. We conclude that CNF1 contributes to E. coli virulence in a model of acute prostatitis. To our knowledge, the results of this study provide the first demonstration of a role for any uropathogenic E. coli virulence factor in acute prostatitis.

A simple model host for identifying Gram-positive virulence factors

We demonstrate the use of the nematode Caenorhabditis elegans as a facile and inexpensive model host for several Gram-positive human bacterial pathogens. Enterococcus faecalis, Streptococcus pneumoniae, and Staphylococcus aureus, but not Bacillus subtilis, Enterococcus faecium, or Streptococcus pyogenes, kill adult C. elegans. Focusing our studies on the enterococcal species, we found that both E. faecalis and E. faecium kill C. elegans eggs and hatchlings, although only E. faecalis kills the adults. In the case of adults, a low inoculum of E. faecalis grows to a high titer in the C. elegans intestine, resulting in a persistent infection that cannot be eradicated by prolonged feeding on E. faecium. Interestingly, a high titer of E. faecium also accumulates in the nematode gut, but does not affect the longevity of the worms. Two E. faecalis virulence-related factors that play an important role in mammalian models of infection, fsr, a putative quorum-sensing system, and cytolysin, are also important for nematode killing. We exploit the apparent parallels between Gram-positive infection in simple and more complex organisms by using the nematode to identify an E. faecalis virulence factor, ScrB, which is relevant to mammalian pathogenesis.

Vacuolating cytotoxin of Helicobacter pylori induces apoptosis in the human gastric epithelial cell line AGS

Helicobacter pylori induces cell death by apoptosis. However, the apoptosis-inducing factor is still unknown. The virulence factor vacuolating cytotoxin A (VacA) is a potential candidate, and thus its role in apoptosis induction was investigated in the human gastric epithelial cell line AGS. The supernatant from the vacA wild-type strain P12 was able to induce apoptotic cell death, whereas the supernatant from its isogenic mutant strain P14 could not. That VacA was indeed the apoptosis-inducing factor was demonstrated further by substantial reduction of apoptosis upon treatment of AGS cells with a supernatant specifically depleted of native VacA. Furthermore, a recombinant VacA produced in Escherichia coli was also able to induce apoptosis in AGS cells but failed to induce cellular vacuolation. These findings demonstrate that the vacuolating cytototoxin of H. pylori is a bacterial factor capable of inducing apoptosis in gastric epithelial cells.

Virulence factors of Helicobacter pylori responsible for gastric diseases in Mongolian gerbil

Helicobacter pylori infection induces various gastroduodenal diseases. We examined the role of two genes, vacA and cagE, in the gastric pathogenesis induced by H. pylori using a long-term (62 wk) animal model. Reportedly, both genes are associated with the virulence of H. pylori: vacA encodes vacuolating cytotoxin, and cagE, with other genes in the cag pathogenicity islands, encodes a type IV secretion system. Mongolian gerbils were challenged in this study by a wild-type TN2 strain and its isogenic mutants of cagE or vacA. The wild-type and vacA mutants induced severe gastritis, whereas cagE mutants induced far milder changes. Gastric ulcer was induced at the highest rate (22/23) by the wild-type TN2, followed by the vacA mutant (19/28). No ulcer was found in the gerbils infected with the cagE mutant (0/27) or in controls (0/27). Intestinal metaplasia was also found in the gerbils infected with the wild-type (14/23) or vacA mutant (15/28). Gastric cancer developed in one gerbil with wild-type infection and in one with vacA mutant infection. In conclusion, the knocking out of the cagE gene deprived wild-type H. pylori of the pathogenicity for gastritis and gastric ulcer, suggesting that the secretion system encoded by cag pathogenicity island genes plays an essential role.

Fatty acid cytotoxicity to bovine lens epithelial cells: investigations on cell viability, ecto-ATPase, Na(+), K(+)-ATPase and intracellular sodium concentrations

Unsaturated non-esterified fatty acids have been shown to be cytotoxic in micromolar concentrations to bovine lens epithelial cells, in the following order: arachidonic acid > linoleic acid > oleic acid = linolenic acid. As unsaturated free fatty acids are known to be Na(+), K(+)-ATPase inhibitors, the aim of the study was to investigate whether or not the fatty acid cytotoxicity is correlated with effects on Na(+), K(+)-ATPase activity and function in bovine lens epithelial cells. Furthermore, we also examined the effects of linoleic acid on an ecto-ATPase activity which could be demonstrated on the outside of primarily cultured bovine lens epithelial cells. It has already been shown that 10 micro mol l(-1)linoleic acid was cytotoxic but did not impair the ecto-ATPase activity of intact cells nor the Na(+), K(+)-ATPase in enriched membrane fractions. Na(+), K(+)-ATPase activity was slightly activated with 10 micro mol l(-1)linoleic acid and inhibited by about 50% with 100 micro mol l(-1). Using the sodium-binding benzofuran isophthalate, measurements of intracellular sodium concentrations were carried out. In serum-starved bovine lens epithelial cells the basal [Na(+)](in)was clearly lower than 5 mmol l(-1). When the function of the Na(+), K(+)-ATPase was interrupted by omitting K(+)-ions from the medium, [Na(+)](in)increased at a rate of 0.318 mmol l(-1)min(-1). Linoleic acid intensified that increase strongly in a concentration dependent manner. However, in K(+)-containing medium the linoleic acid-induced increase of [Na(+)](in)was completely prevented. Therefore, the high linoleioc acid cytotoxicity cannot be mediated by linoleic acid effects on Na(+), K(+)-ATPase activity and function in bovine lens epithelial cells.

Molecular mechanisms of apoptosis induced by cytotoxic chemicals

The purpose of this review article is to discuss established molecular mechanisms of apoptosis and their relevance to cell death induced by environmental toxicants. Apoptosis is a highly regulated form of cell death distinguished by the activation of a family of cysteine-aspartate proteases (caspases) that cleave various proteins resulting in morphological and biochemical changes characteristic of this form of cell death. Abundant evidence supports a role for mitochondria in regulating apoptosis. Specifically, it seems that a number of death stimuli target these organelles and stimulate, by an unknown mechanism, the release of several proteins, including cytochrome c. Once released into the cytosol, cytochrome c binds to its adaptor molecule, Apaf-1, which oligomerizes and then activates pro-caspase-9. Caspase-9 can signal downstream and activate pro-caspase-3 and -7. The release of cytochrome c can be influenced by different Bcl-2 family member proteins, including, but not limited to, Bax, Bid, Bcl-2, and Bcl-X(L). Bax and Bid potentiate cytochrome c release, whereas Bcl-2 and Bcl-X(L) antagonize this event. Although toxicologists have traditionally associated cell death with necrosis, emerging evidence suggests that different types of environmental contaminants exert their toxicity, at least in part, by triggering apoptosis. The mechanism responsible for eliciting the pro-apoptotic effect of a given chemical is often unknown, although in many instances mitochondria appear to be key participants. This review describes our current understanding of the role of apoptosis in environmental toxicant-induced cell death, using dioxin, metals (cadmium and methylmercury), organotin compounds, dithiocarbamates, and benzene as specific examples. Finally, we conclude with a critical discussion of the current knowledge in this area and provide recommendations for future directions.

Biological properties of pneumolysin

Pneumolysin is a thiol-activated membrane-damaging toxin produced by Streptococcus pneumoniae. The toxin plays a role in virulence of the pneumococcus in animal models of infection. Pneumolysin has a range of biological activity including the ability to lyse eukaryotic cells and to interfere with the function of cells and soluble molecules of the immune system. The use of purified native and mutant toxin and of isogenic mutants of the pneumococcus expressing altered versions of the toxin has allowed the contribution of the various activities of this multifunctional toxin to virulence to be defined.

Infection of primary human gingival fibroblasts by Porphyromonas gingivalis and Prevotella intermedia

Adhesion and penetration of clinical isolates of Porphyromonas gingivalis and Prevotella intermedia in human gingival fibroblast monolayers were studied by transmission electron microscopy (TEM). Fibroblasts were cultured from biopsies of human healthy gingiva. Porphyromonas gingivalis and Prevotella intermedia were isolated from patients with periodontitis. Fibroblasts were incubated with microorganisms in an antibiotic-free medium for 24 h. Then cultures were washed to remove nonadherent bacteria. Consecutively, infected cultures were grown for another 24 h. Thereafter, the treated monolayers were prepared for TEM investigations. Internalized Porphyromonas gingivalis and Prevotella intermedia were visible after 24 h of incubation. Prevotella intermedia showed only division in cytoplasm of fibroblasts after 24 h and 48 h incubations. Infected fibroblasts revealed various morphological alterations such as extensive vacuolization and breakdown of mitochondria. These findings demonstrate that Porphyromonas gingivalis and Prevotella intermedia may invade human gingival fibroblasts and thus may damage these cells directly or due to the release of microbial cytotoxic components.

Lack of a role of cytotoxic necrotizing factor 1 toxin from Escherichia coli in bacterial pathogenicity and host cytokine response in infected germfree piglets

Some Escherichia coli strains isolated from intestinal or extraintestinal infections in pigs produce cytotoxic necrotizing factor 1 (CNF1). In order to analyze the role of CNF1 in the pathogenesis of porcine colibacillosis, newborn colostrum-deprived germfree piglets were orally inoculated with a wild-type CNF1-producing strain (M623) or with an isogenic cnf1 mutant (M623DeltaCNF1). The two isogenic strains induced a high mortality with similar lung and serosal inflammatory lesions, indicating that both strains were pathogenic in these piglets. Bacterial counts in various organs of inoculated piglets revealed an intestinal predisposition of M623 and M623DeltaCNF1 strains for the cecum and colon. Extraintestinal organs (lungs, liver, spleen, and kidney) were also colonized by both strains. Similar colonization of intestinal and extraintestinal tissues in animals inoculated with either strain was observed, except in the ileum, where M623 showed a higher colonization than M623DeltaCNF1. Intestinal (ileum and colon), extraintestinal (lung and kidney), and immune (mesenteric lymph nodes and spleen) tissues were sampled at 1 day postinoculation and analyzed for cytokine expression by a reverse transcriptase PCR technique. Inoculation with E. coli M623 induced an enhanced expression of inflammatory cytokines (interleukin-1alpha [IL-1alpha], tumor necrosis factor alpha, and IL-12p40) in the intestinal organs compared to uninoculated piglets or piglets inoculated with nonpathogenic intestinal E. coli 862B, which is also able to colonize the intestinal tract. There was little difference in cytokine transcript levels in the intestinal and extraintestinal organs in piglets inoculated with E. coli strains M623 or M623DeltaCNF1, except in the ileum, where IL-1alpha and IL-8 mRNA levels correlated with bacterial colonization. Expression of regulatory cytokines (gamma interferon and IL-4) was weak in immune tissues from piglets inoculated with M623 or M623DeltaCNF1. Taken together, our data indicate that the CNF1-producing strain, M623, is pathogenic and induces inflammatory cytokine expression in germfree, colostrum-deprived piglets. Nevertheless, in this model, the CNF1 toxin does not appear to be a major factor for pathogenicity or cytokine response, as demonstrated by the use of an isogenic cnf1 mutant.

Molecular pathogenesis of the cell surface proteins and lipids from Treponema denticola

Treponema denticola, frequently isolated from the human oral cavity, is thought to be a major pathogen of human periodontal disease. Recent developments in molecular analysis have clarified the surface structure of this microorganism and the characteristics of its pathogenic factors. Structural analysis of the outer sheath showed T. denticola to have a new type of outer membrane lipid. Limited exposure of the major outer sheath protein is suggested by electron-microscopic analysis. A protease-deficient mutant has revealed the roles of the protease in the organization of the outer sheath material and in T. denticola pathogenicity. The surface features that contribute to the pathogenicity of T. denticola in periodontal disease are gradually being elucidated, and are reviewed.

Cytopathogenicity of Acanthamoeba isolates on rat glial C6 cell line

The pathogenicity of Acanthamoeba isolates from keratitis patients (the Hamburg isolate from Germany, H-1 and a Philippine isolate, IB-1-7) as well as an environmental isolate, W4 was assayed in vitro using rat glial C6 cell line. Results indicate that both live amebae and cell-free supenatants from H-1 and IB-1-7 clones produced cytopathic effects (CPE) on rat glial C6 cells in a dose-and-time-dependent fashion. A dose of 10(5) cells/ml induced death and moderate areas of destruction of individual cells after 48 hours of incubation. Results of both free zone capillary electrophoresis and sodium dodecyl sulphate polyacrylamide gel electrophoresis suggest the release of amebic products to the culture medium that could at least partially explain the observed cytopathogenicity after 48 hours. Furthermore, results of SDS-PAGE indicate differences between the secretions of the isolates, with bands produced by the two ocular isolates that were not seen with the environmental isolates. That the secretions can produce a cytopathic effect (CPE) has been shown by the cytotoxicity assays using protein concentrations of the secretory products. Protein concentration of 0.30 microg/microl of culture supenatants from H-1 and IB-1-7 clones produced similar effects on the cell monolayers after 2 hours of incubation. This concentration caused the highest % cell death as measured by both trypan blue exclusion (TBE) and 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl-tetrazolium bromide (MTT) assays. In contrast, using W4 clone, corresponding concentrations of both trophozoites and culture supernatant did not cause significant cell death and cellular disintegration.

Heat shock protein 70 (Hsp70) stimulates proliferation and cytolytic activity of natural killer cells

We previously demonstrated that lysis of tumor cells that express Hsp70, the highly stress-inducible member of the HSP70 family, on their plasma membrane is mediated by natural killer (NK) cells. Here, we studied the effects of different proteins of the HSP70 family in combination with interleukin 2 (IL-2) on the proliferation and cytotoxic activity of human NK cells in vitro. Proliferation of NK cells was significantly enhanced by human recombinant Hsp70 (rHsp70) and to a lesser extent by rHsp70homC, the recombinant C-terminal peptide-binding domain derived from Hsp70hom, but not by the constitutive Hsc70 or DnaK, the Escherichia coli analogue of human Hsp70. Even rHsp70 protein alone moderately enhances proliferation and cytolytic activity of NK cells, thus indicating that the stimulatory effect is not strictly dependent on IL-2. NK cells stimulated with rHsp70 protein also exhibit an increased secretion of interferon gamma (IFN-gamma). The phenotypic characterization of NK cells with specificity for Hsp70-expressing tumor cells revealed a CD16dim/CD56bright and increased CD57 and CD94 expression. The cytolytic activity of NK cells also was significantly reduced when a CD94-specific antibody or rHsp70 was added directly before the cytotoxicity assay, whereas other antibodies directed against CD57 and major histocompatibility complex class I molecules or Hsp70 proteins, including Hsc70 and DnaK, did not affect the NK-mediated killing. However, long-term incubation of NK cells with rHsp70 protein enhances not only the proliferative but also the cytolytic response against Hsp70-expressing tumor cells. Our results indicate that the C-terminal domain of Hsp70 protein affects not only the proliferative but also the cytolytic activity of a phenotypically distinct NK cell population with specificity for Hsp70-expressing tumor cells. 1999 International Society for Experimental Hematology.

Helicobacter pylori VacA cytotoxin associated with the bacteria increases epithelial permeability independently of its vacuolating activity

Polarized epithelial monolayers of Madin-Darby canine kidney (MDCK) cells were used to study the pathogenicity of Helicobater pylori, with an emphasis on the effect of VacA. The adherence of H. pylori to MDCK monolayers resulted in a decrease in trans-epithelial resistance (TER) across the cell monolayer. Isogenic vacA mutants did not lower the TER, demonstrating that the effect is strictly linked to the action of the toxin. A similar effect was observed with all VacA-producing strains, including those producing m2 toxins that are inactive in the vacuolating assay. In contrast to that seen with purified toxin, TER decrease was not enhanced by acid pH, which may indicate that the toxin associated to the bacterial surface is possibly in a monomeric state and therefore does not require a pH-induced conformation to be active. These data raise the possibility that one role of VacA in ulcerogenesis may consist of increasing the paracellular permeability of the gastric epithelium.

A commentary on the pathogenesis of pertussis

In recent years a great deal of information has been generated on the virulence factors produced by Bordetella pertussis, the regulation of their expression, and their molecular mechanisms of action. There are numerous studies of Bordetella virulence factors and strains of B. pertussis in which the genes for some of these components have been mutated or deleted. In addition, several acellular vaccines composed of these virulence factors have been developed, tested, and licensed for use in the prevention of pertussis. Nevertheless, there exists little information specifically on the pathogenesis of the disease process caused by B. pertussis in humans, and such data are necessary for adequate understanding and treatment of this novel infectious disease.

Ulcerogenic and healing impairing actions of monochloramine in rat stomachs: effects of zinc L-carnosine, polaprezinc

Effects of a novel zinc compound (polaprezinc), N-(3-aminopropionyl)-L-histidinato zinc, on the mucosal ulcerogenic and healing impairing responses induced by monochloramine (NH2Cl) were examined in rat stomach. Oral administration of NH2Cl (> 60 mM) produced severe hemorrhagic lesions in unanesthetized rat stomachs with a marked increase of thiobarbituric acid reactants (TBAR). Pretreatment of the animals with polaprezinc (3 approximately 30 mg/kg, p.o.) showed a dose-dependent inhibition against gastric ulcerogenic and TBAR responses induced by NH2Cl (120 mM). Likewise, mucosal exposure to NH4OH (60 mM) in urethane anesthetized stomachs made ischemic by bleeding from the carotid artery (1 ml per 100 g body w.t.) resulted in severe gastric lesions. This ulcerogenic response caused NH4OH plus ischemia was also attenuated by prior application of polaprezinc as well as taurine (25 mg/ml, 1 ml). On the other hand, the healing of gastric mucosal lesions induced by NH2Cl occurred more slowly than of ethanol-induced lesions, and the latter was significantly delayed by the repeated administration of NH2Cl. Polaprezinc (> 10 mg/kg, p.o.) given twice daily for 7 days not only accelerated the healing of NH2Cl-induced gastric lesions but also antagonized the delayed healing of ethanol-induced lesions in the presence of NH2Cl as well. Polaprezinc showed a scavenging action against NH2Cl in vitro. These results suggest that NH2Cl caused deleterious action on the healing of pre-existing acute lesions as well as irritating action to the mucosa in the rat stomach. Polaprezinc not only protects the stomach against injury caused by NH2Cl but also promotes healing of NH2Cl-induced gastric lesions as well as the delayed healing of ethanol-induced lesions caused by NH2Cl. Although the detailed mechanisms underlying these actions of polaprezinc remain unknown, they may be partly attributable to a scavenging action of this agent against NH2Cl.