Role of oxidants in microbial pathophysiology

Transcriptome analysis of the response of Pseudomonas aeruginosa to hydrogen peroxide

Pseudomonas aeruginosa must often overcome a high concentration of oxidants to successfully infect the human host. We report here the results of a transcriptome profiling comparing cells treated with H(2)O(2) and untreated controls. The data indicate that the early response of P. aeruginosa to H(2)O(2) consists of an upregulation of protective mechanisms and a downregulation of primary metabolism.

Role and regulation of the superoxide dismutases of Staphylococcus aureus

Staphylococcus aureus has two superoxide dismutases (SODs), encoded by the sodA and sodM genes, which inactivate harmful superoxide radicals () encountered during host infection or generated from aerobic metabolism. The transcriptional start sites have been mapped and expression analysis on reporter fusions in both genes has been carried out. Under standard growth conditions, manganese (Mn), a mineral superoxide scavenger, elevated total SOD activity but had no effect on the transcription of either gene. Transcription of sodA and sodM was most strongly induced by either internally or externally generated, respectively. Sensitivity to internally generated was linked with SodA deficiency. Mn supplementation completely rescued a sodA mutant when challenged by internally generated, and this was growth-phase-dependent. Sensitivity to externally generated stress was only observed in a sodA sodM mutant and was Mn-independent. In a mouse abscess model of infection, isogenic sodA, sodM and sodA sodM mutants had reduced virulence compared to the parental strain, showing the importance of the enzymic scavenging system for the survival of the pathogen.

Localized reactive oxygen and nitrogen intermediates inhibit escape of Listeria monocytogenes from vacuoles in activated macrophages

Listeria monocytogenes (Lm) evades being killed after phagocytosis by macrophages by escaping from vacuoles into cytoplasm. Activated macrophages are listericidal, in part because they can retain Lm in vacuoles. This study examined the contribution of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) to the inhibition of Lm escape from vacuoles. Lm escaped from vacuoles of nonactivated macrophages within 30 min of infection. Macrophages activated with IFN-gamma, LPS, IL-6, and a neutralizing Ab against IL-10 retained Lm within the vacuoles, and inhibitors of ROI and RNI blocked inhibition of vacuolar escape to varying degrees. Measurements of Lm escape in macrophages from gp91(phox-/-) and NO synthase 2(-/-) mice showed that vacuolar retention required ROI and was augmented by RNI. Live cell imaging with the fluorogenic probe dihydro-2',4,5,6,7,7'-hexafluorofluorescein coupled to BSA (DHFF-BSA) indicated that oxidative chemistries were generated rapidly and were localized to Lm vacuoles. Chemistries that oxidized DHFF-BSA were similar to those that retained Lm in phagosomes. Fluorescent conversion of DHFF-BSA occurred more efficiently in smaller vacuoles, indicating that higher concentrations of ROI or RNI were generated in more confining volumes. Thus, activated macrophages retained Lm within phagosomes by the localization of ROI and RNI to vacuoles, and by their combined actions in a small space

Phagocytosis of Treponema pallidum and reactive oxygen species production by isolated rat Kupffer cells

The in vitro phagocytosis of viable Treponema pallidum subsp. pallidum by isolated rat Kupffer cells, studied by immunofluorescence staining of Kupffer cells-associated bacteria, showed that ingestion of live, unopsonized treponemes was slow: in fact, Kupffer cells started to be positive 1 h after infection, when only 4% of the cells presented small round fluorescent inclusion-like bodies. Thereafter, the number of positive cells progressively increased with time: 7%, 17%, 36%, and 69% of Kupffer cells were positive, respectively, 2, 4, 6 and 8 h after infection. Opsonization of T. pallidum with human immune serum did not substantially modify the percentage (8%) of Kupffer cells ingesting T. pallidum 1 h after infection, whereas opsonization significantly ( P<0.01) increased phagocytosis after 2, 4 and 6 h of incubation, when 44%, 58%, and 68% of Kupffer cells were positive, respectively. At 8 h after infection of Kupffer cells by opsonized T. pallidum, 75% of the cells were positive by immunofluorescence. Heat-inactivation of T. pallidum slightly enhanced phagocytosis. In contrast, opsonization of heat-inactivated spirochetes with specific antibodies significantly ( P<0.01) increased the phagocytosis of bacteria by Kupffer cells, beginning as early as 30 min after infection, when 65% of the cells were positive by immunofluorescence. The reactive oxygen species (ROS) production by Kupffer cells following incubation with spirochetes was also determined by chemiluminescence. Treponemes induced an oxidative burst in Kupffer cells in a dose-dependent manner and the generation of ROS was already detectable 20 min after the exposure of the Kupffer cells to treponemes and peaked at 35 min of incubation. Live, as well as live and opsonized, and heat-inactivated treponemes, induced an O(2)(-) production lower than that induced by heat-inactivated and opsonized spirochetes.

Iron deficiency leads to inhibition of oxygen transfer and enhanced formation of virulence factors in cultures of Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa PAO1 was recently found to exhibit two remarkable physiological responses to oxidative stress: (1) a strong reduction in the efficiency of oxygen transfer from the gas phase into the liquid phase, thus causing oxygen limitation in the culture and (2) formation of a clear polysaccharide capsule on the cell surface. In this work, it has been shown that the iron concentration in the culture plays a crucial role in evoking these phenomena. The physiological responses of two P. aeruginosa PAO1 isolates (NCCB 2452 and ATCC 15692) were examined in growth media with varied iron concentrations. In a computer-controlled bioreactor cultivation system for controlled dissolved oxygen tension (pO2), a strong correlation between the exhaustion of iron and the onset of oxygen limitation was observed. The oxygen transfer rate of the culture, characterized by the volumetric oxygen transfer coefficient, kLa, significantly decreased under iron-limited conditions. The formation of alginate and capsule was more strongly affected by iron concentration than by oxygen concentration. The reduction of the oxygen transfer rate and the subsequent oxygen limitation triggered by iron deficiency may represent a new and efficient way for P. aeruginosa PAO1 to adapt to growth conditions of iron limitation. Furthermore, the secretion of proteins into the culture medium was strongly enhanced by iron limitation. The formation of the virulence factor elastase and the iron chelators pyoverdine and pyochelin also significantly increased under iron-limited conditions. These results have implications for lung infection of cystic fibrosis patients by P. aeruginosa in view of the prevalence of iron limitation at the site of infection and the respiratory failure leading to death.

Molecular characterization and quantitative analysis of superoxide dismutases in virulent and avirulent strains of Aeromonas salmonicida subsp. salmonicida

Aeromonas salmonicida subsp. salmonicida is a facultatively intracellular gram-negative bacterium that is the etiological agent of furunculosis, a bacterial septicemia of salmonids that causes significant economic loss to the salmon farming industry. The mechanisms by which A. salmonicida evades intracellular killing may be relevant in understanding virulence and the eventual design of appropriate treatment strategies for furunculosis. We have identified two open reading frames (ORFs) and related upstream sequences that code for two putative superoxide dismutases (SODs), sodA and sodB. The sodA gene encoded a protein of 204 amino acids with a molecular mass of approximately 23.0 kDa (SodA) that had high similarity to other prokaryotic Mn-SODs. The sodB gene encoded a protein of 194 amino acids with a molecular mass of approximately 22.3 kDa that had high similarity to other prokaryotic Fe-SODs. Two enzymes with activities consistent with both these ORFs were identified by inhibition of O(2)(-)-catalyzed tetrazolium salt reduction in both gels and microtiter plate assays. The two enzymes differed in their expression patterns in in vivo- and in vitro-cultured bacteria. The regulatory sequences upstream of putative sodA were consistent with these differences. We could not identify other SOD isozymes such as sodC either functionally or through data mining. Levels of SOD were significantly higher in virulent than in avirulent strains of A. salmonicida subsp. salmonicida strain A449 when cultured in vitro and in vivo.

Not every disulfide lasts forever: disulfide bond formation as a redox switch

Cellular compartments differ dramatically in their redox potentials. This translates directly into variations in the extent of disulfide bond formation within proteins, depending on their cellular localization. It has long been assumed that proteins that are present in the reducing environment of the cytosol do not possess disulfide bonds. The recent discovery of a number of cytosolic proteins that use specific and reversible disulfide bond formation as a functional switch suggests that this view needs to be revised. Oxidative stress-induced disulfide bond formation appears to be the main strategy to adjust the protein activity of the oxidative stress transcription factors Yap1 and OxyR, the molecular chaperone Hsp33, and the anti-sigma factor RsrA. This elegant and rapid regulation allows the cells to respond quickly to environmental changes that manifest themselves in the accumulation of reactive oxygen species.

MtsABC is important for manganese and iron transport, oxidative stress resistance, and virulence of Streptococcus pyogenes

MtsABC is a Streptococcus pyogenes ABC transporter which was previously shown to be involved in iron and zinc accumulation. In this study, we showed that an mtsABC mutant has impaired growth, particularly in a metal-depleted medium and an aerobic environment. In metal-depleted medium, growth was restored by the addition of 10 microM MnCl(2), whereas other metals had modest or no effect. A characterization of metal radioisotope accumulation showed that manganese competes with iron accumulation in a dose-dependent manner. Conversely, iron competes with manganese accumulation but to a lesser extent. The mutant showed a pronounced reduction (>90%) of (54)Mn accumulation, showing that MtsABC is also involved in Mn transport. Using paraquat and hydrogen peroxide to induce oxidative stress, we show that the mutant has an increased susceptibility to reactive oxygen species. Moreover, activity of the manganese-cofactored superoxide dismutase in the mutant is reduced, probably as a consequence of reduced intracellular availability of manganese. The enzyme functionality was restored by manganese supplementation during growth. The mutant was also attenuated in virulence, as shown in animal experiments. These results emphasize the role of MtsABC and trace metals, especially manganese, for S. pyogenes growth, susceptibility to oxidative stress, and virulence.

Rabbit chronic ileitis leads to up-regulation of adenosine A1/A3 gene products, oxidative stress, and immune modulation

A rabbit model of chronic ileitis has helped decipher the mechanism of alteration of multiple electrolyte and nutrient malabsorptions in inflammatory bowel disease (IBD). This study examined alterations in the adenosine A1/A3 receptor, oxidant, antioxidant, and immune-inflammatory pathways in chronic ileitis. Chronic ileal inflammation was induced 13-15 days after infection with 10,000 Eimeria magna oocytes. Quantitative analysis in 16 rabbits was done for oxidants, antioxidants, A1 and A3 transcripts, transport, injury, and inflammatory mediators. Inflamed gut had villus blunting, crypt hyperplasia and fusion, and immune cell infiltration. Alkaline phosphatase and Na-glucose co-transport were reduced by 78% (P=0.001) and 89% (P=0.001), respectively. Real-time fluorescence monitoring (TaqMan)-polymerase chain reaction revealed a transcriptional up-regulation of 1.34-fold for A1 and 5.40-fold for A3 receptors in inflamed gut. Lipid peroxidation increased in the mucosa (78%, P=0.012), longitudinal muscle-myenteric plexus (118%, P=0.042), and plasma (104%, P=0.001). Mucosal antioxidants were altered by inflammation: reductions occurred in superoxide dismutase (32%, P=0.001) and catalase (43%, P=0.001), whereas increases occurred in glutathione (75%, P=0.0271) and glutathione reductase (86%, P=0.0007). Oxidant enzyme activities were elevated by 21% for xanthine oxidase (P=0.004), 172% for chloramine (P=0.022), 47% for gelatinase (P=0.041), and 190% for myeloperoxidase (P=0.002). Mast cell tryptase increased by 79% (P=0.006). Increases occurred in the plasma concentration of leukotriene B(4) (13-fold, P=0.003), thromboxane B(2) (61-fold, P=0.018), and tumor necrosis factor-alpha (9-fold, P=0.002). In conclusion, chronic ileitis and tissue injury are associated with discrete alterations in complex multi-level oxidant, antioxidant, and immune inflammatory components. The rabbit ileitis model is a suitable model to gain further insight into chronic inflammation and IBD. We hypothesize that adenosine A3 and A1 receptors may provide a novel target for therapy in chronic ileitis and perhaps IBD.

Involvement of nitric oxide donor compounds in the bactericidal activity of human neutrophils in vitro

The bactericidal activity of human neutrophils against extracellular and facultatively intracellular bacteria was studied in the presence of the nitric oxide (NO) donors sodium nitroprusside (SNP) and 3-morpholinosydnonimine (SIN-1), a molsidomine metabolite. SNP and molsidomine are drugs commonly used as nitrovasodilators in coronary heart disease. It is demonstrated here that the NO donor compounds themselves did not affect the viability and survival of the bacterial strains tested. Neither SNP nor SIN-1 had any effect on the process of bacteria ingestion. In contrast, NO donors enhanced the ability of neutrophils to kill Escherichia coli, Proteus vulgaris and Salmonella Anatum. However, strains differed in their susceptibility to SNP- and SIN-1-mediated killing by neutrophils. Removal of the superoxide anion reduced the bactericidal activity of SNP- and SIN-1-treated neutrophils against E. coli and S. Anatum. This suggests that the NO derivatives formed in the reaction of NO generated from donors with the reactive oxygen species released by phagocytosed neutrophils potentiate the bactericidal activity of human neutrophils in vitro. The above original observation discussed here suggests clinical significance for the treatment of patients with nitrovasodilators in the course of coronary heart disease therapy.

Functional genomics approach to the identification of virulence genes involved in Edwardsiella tarda pathogenesis

Edwardsiella tarda is an important cause of hemorrhagic septicemia in fish and also of gastro- and extraintestinal infections in humans. Here, we report the identification of 14 virulence genes of pathogenic E. tarda that are essential for disseminated infection, via a genome-wide analysis. We screened 490 alkaline phosphatase fusion mutants from a library of 450,000 TnphoA transconjugants derived from strain PPD130/91, using fish as an infection model. Compared to the wild type, 15 mutants showed significant decreases in virulence. Six mutants had insertions in the known virulence-related genes, namely, fimA, gadB, katB, pstS, pstC, and ssrB. Some mutants corresponded to known genes (astA, isor, and ompS2) that had not been previously shown to be involved in pathogenesis, and three had insertions in two novel genes. In vivo infection kinetics experiments confirmed the inability of these attenuated mutants to proliferate and cause fatal infection in fish. Screening for the presence of the above-described virulence genes in six virulent and seven avirulent strains of E. tarda indicated that seven of the genes were specific to pathogenic E. tarda. The genes identified here may be used to develop vaccines and diagnostic kits as well as for further studying the pathogenesis of E. tarda and other pathogenic bacteria.

Purification, gene cloning, gene expression, and mutants of Dps from the obligate anaerobe Porphyromonas gingivalis

The periodontopathogen Porphyromonas gingivalis is an obligate anaerobe that is devoid of catalase but exhibits a relatively high degree of resistance to peroxide stress. In the present study, we demonstrate that P. gingivalis contains a Dps homologue that plays an important role in the protection of cells from peroxide stress. The Dps protein isolated from P. gingivalis displayed a ferritin-like spherical polymer consisting of 19-kDa subunits. Molecular cloning and sequencing of the gene encoding this protein revealed that it had a high similarity in nucleotide and amino acid sequences to Dps proteins from other species. The expression of Dps was significantly increased by exposure of P. gingivalis to atmospheric oxygen in an OxyR-dependent manner, indicating that it is regulated by the reactive oxygen species-regulating gene oxyR. The Dps-deficient mutants, including the dps single mutant and the ftn dps double mutant, showed no viability loss upon exposure to atmospheric oxygen for 6 h. In contrast to the wild type, however, these mutants exhibited the high susceptibility to hydrogen peroxide, thereby disrupting the viability. On the other hand, no significant difference in sensitivity to mitomycin C and metronidazole was observed between the wild type and the mutants. Furthermore, the dps single mutant, compared with the wild type, showed a lower viability in infected human umbilical vein endothelial cells.

Characterization of Cu,Zn superoxide dismutase (SOD1) gene knock-out mutant of Cryptococcus neoformans var. gattii: role in biology and virulence

The pathogenic yeast Cryptococcus neoformans (Cn) var. gattii causes meningoencephalitis in healthy individuals, unlike the better known Cn varieties grubii and neoformans, which are common in immunocompromised individuals. The virulence determinants and mechanisms of host predilection are poorly defined for var. gattii. The present study focused on the characterization of a Cu,Zn superoxide dismutase (SOD1) gene knock-out mutant constructed by developing a DNA transformation system. The sod1 mutant was highly sensitive to the redox cycling agent menadione, and showed fragmentation of the large vacuole in the cytoplasm, but no other defects were seen in growth, capsule synthesis, mating, sporulation, stationary phase survival or auxotrophies for sulphur-containing amino acids. The sod1 mutant was markedly attenuated in virulence in a mouse model, and it was significantly susceptible to in vitro killing by human neutrophils (PMNs). The deletion of SOD1 also resulted in defects in the expression of a number of virulence factors, i.e. laccase, urease and phospholipase. Complementation of the sod1 mutant with SOD1 resulted in recovery of virulence factor expression and menadione resistance, and in restoration of virulence. Overall, these results suggest that the antioxidant function of Cu,Zn SOD is critical for the pathogenesis of the fungus, but is dispensable in its saprobic life. This report constitutes the first instance in which superoxide dismutase has been directly implicated in the virulence of a fungal pathogen.

The iron-binding protein Dps confers hydrogen peroxide stress resistance to Campylobacter jejuni

We identified and characterized the iron-binding protein Dps from Campylobacter jejuni. Electron microscopic analysis of this protein revealed a spherical structure of 8.5 nm in diameter, with an electron-dense core similar to those of other proteins of the Dps (DNA-binding protein from starved cells) family. Cloning and sequencing of the Dps-encoding gene (dps) revealed that a 450-bp open reading frame (ORF) encoded a protein of 150 amino acids with a calculated molecular mass of 17,332 Da. Amino acid sequence comparison indicated a high similarity between C. jejuni Dps and other Dps family proteins. In C. jejuni Dps, there are iron-binding motifs, as reported in other Dps family proteins. C. jejuni Dps bound up to 40 atoms of iron per monomer, whereas it did not appear to bind DNA. An isogenic dps-deficient mutant was more vulnerable to hydrogen peroxide than its parental strain, as judged by growth inhibition tests. The iron chelator Desferal restored the resistance of the Dps-deficient mutant to hydrogen peroxide, suggesting that this iron-binding protein prevented generation of hydroxyl radicals via the Fenton reaction. Dps was constitutively expressed during both exponential and stationary phase, and no induction was observed when the cells were exposed to H(2)O(2) or grown under iron-supplemented or iron-restricted conditions. On the basis of these data, we propose that this iron-binding protein in C. jejuni plays an important role in protection against hydrogen peroxide stress by sequestering intracellular free iron and is expressed constitutively to cope with the harmful effect of hydrogen peroxide stress on this microaerophilic organism without delay.

Leptospires are killed in vitro by both oxygen-dependent and -independent reactions

This study reports for the first time that leptospires are killed by H(2)O(2) and by low-molecular-weight primary granule components, which are agents normally released by neutrophils upon stimulation. Although both pathogenic and nonpathogenic strains were sensitive to H(2)O(2)-mediated killing, nonpathogenic organisms were found to be more susceptible. In addition, the killing of leptospires by H(2)O(2) was found to be independent of the presence of the neutrophil primary granule component myeloperoxidase and therefore not a consequence of halogenation reactions. We have also determined that leptospires are significantly sensitive only to primary granule components and, among those, to proteins and/or peptides of less than 30 kDa.

Identification by RNA profiling and mutational analysis of the novel copper resistance determinants CrdA (HP1326), CrdB (HP1327), and CzcB (HP1328) in Helicobacter pylori

Mechanisms involved in maintaining cytoplasmic metal ion homeostasis play a central role in the adaptation of Helicobacter pylori to the changing gastric environment. An investigation of the global regulatory responses to copper ions by using RNA profiling with a threshold factor of 4.0 revealed that copper induces transcription of 19 H. pylori genes and that only the ferritin gene pfr is repressed. The 57-fold copper induction identified the HP1326 gene encoding an H. pylori-specific protein as a candidate for a novel copper resistance determinant. The HP1326 gene is expressed as a monocistronic unit, and two small HP1326 mRNAs are copper induced. The HP1326 protein is secreted and is required for copper resistance maintained by cytoplasmic copper homeostasis, as H. pylori HP1326 mutants were copper sensitive and displayed increased copper induction of HP1326 transcription as well as elevated copper repression of ferritin synthesis. The clear copper-sensitive phenotype displayed by H. pylori HP1327 and HP1328 mutants provides strong evidence that the HP1326 protein, together with the signal peptide site of the H. pylori-specific protein HP1327, whose gene is located downstream from that encoding HP1326, and the CzcB and CzcA metal efflux system component homologs HP1328 and HP1329, constitutes a novel type of copper efflux pump, as discussed below. The HP1329 gene could not be inactivated, but the 14-fold transcriptional copper induction determined by RNA profiling points towards a function of the encoded CzcA homolog in copper resistance. In summary, results from RNA profiling identified the novel H. pylori-specific copper resistance determinants CrdA (HP1326) and CrdB (HP1327), which are required for adaptation to copper-rich environmental conditions.

In vivo inhibition of inducible nitric oxide synthase decreases lung injury induced by Toxocara canis in experimentally infected rats

The direct effect of nitric oxide (NO) on the viability of Toxocara canis larvae was studied. We observed that the nitric oxide donors, SIN-1 and SNOG, exert no cytotoxic effect on the in vitro viability of T. canis larvae. In addition, we developed a model in rats to elucidate the role of NO during T. canis infection. We evaluated different indicators in four experimental groups: morphological parameters, the total number cells and cell types recovered, nitrite and protein concentration, lactate dehydrogenase and alkaline phosphatase enzymatic activity in the bronchoalveolar lavage fluid, lung index and detection of anti-T. canis specific antibodies. We observed significant differences between non-infected and infected groups. The infected animals treated with the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine were less damaged than infected, non-treated animals. Our results suggest that the in vivo inhibition of the synthesis of NO triggered by iNOS diminishes the deleterious effects of the parasite upon the host, especially the vascular alterations in the lungs. We could show that in vivo production of NO induced by infection with T. canis results in direct host damage. Thus, this induction may constitute an evasion/adaptation mechanism of the parasite.

Human peripheral blood polymorphonuclear leukocytes at the ovulatory period are in an activated state

The ovulatory process has been compared with inflammation. We investigated the state of female peripheral polymorphonuclear leukocytes (PMN) during menstrual cycles, and found that PMN contained high levels of superoxide, hydrogen peroxide and nitric oxide (NO) during at the peri-ovulatory period. Assuming the cause of this elevation to be a luteinizing hormone (LH), the surge of which preceded the ovulation, we examined the responsiveness of PMN to pituitary LH. The results revealed that this hormone elevated dose-dependently the production of reactive oxygen intermediates (ROI). Furthermore, we demonstrated the mRNA expression of LH receptors and their presence on PMN. The data indicated that the LH surge before on the ovulatory day resulted in general activation of PMN, suggesting that this state of PMN may be a necessary step for initiation of ovulation, rather than a defensive role against infection.

Physiological responses of Pseudomonas aeruginosa PAO1 to oxidative stress in controlled microaerobic and aerobic cultures

Pseudomonas aeruginosa PAO1 was found to exhibit several remarkable physiological responses to oxidative stress upon its growth in a computer-controlled suspension culture. First, it strongly reduced the transfer rate of oxygen from the gas into the liquid phase, causing oxygen-limited or microaerophilic conditions in the culture after a short period of cultivation, even at high aeration rates with pure oxygen. Second, PAO1 that was previously classified as 'non-mucoid' formed a clear polysaccharide capsule on the cell surface (mucoid phenotype) under oxidative-stress conditions. Third, the strain showed a reduced growth rate and a longer lag phase under high oxygen tension. Finally, P. aeruginosa PAO1 released a high amount of proteins into the culture broth. The release of some virulence factors by PAO1, such as elastase, was significantly enhanced or only occurred under microaerobic conditions (i.e. dissolved oxygen tension value around 1% of air saturation). Hence, it is concluded that P. aeruginosa PAO1 prefers microaerobic conditions for growth and for the formation of some of its virulence factors. PAO1 can create such growth conditions by at least two mechanisms: (i) blockage of the transfer of oxygen and (ii) formation of a polysaccharide capsule on the cell surface. It is postulated that the blockage of oxygen transfer may play an important role in the defence of this pathogen against reactive oxygen intermediates.

Oxidative stress tolerance is manganese (Mn(2+)) regulated in Streptococcus gordonii

The Sca permease in the oral bacterium Streptococcus gordonii is a member of a family of ATP-binding cassette (ABC)-type transporters for manganese (Mn(2+)) and related cations that are associated with streptococcal virulence in a number of infection models. Since Mn(2+) has a protective function against oxidative damage in a variety of bacteria, we have investigated the role of Sca permease in oxidative stress tolerance in Streptococcus gordonii. A single Mn(2+)-dependent superoxide dismutase (SOD), encoded by sodA, is expressed by S. gordonii and was >10-fold up-regulated under oxidative stress conditions. Inactivation of sodA resulted in increased susceptibility of S. gordonii cells to growth inhibition by dioxygen (O(2)), and to killing by paraquat (a superoxide anion generator) and by hydrogen peroxide (H(2)O(2)). Expression of thiol peroxidase, encoded by the tpx gene located immediately downstream of the scaCBA operon, was also up-regulated under oxidative conditions. Inactivation of tpx led to increased susceptibility of cells to H(2)O(2), but not to O(2) or paraquat. In low-Mn(2+) medium (0.01 micro M Mn(2+)) sodA and tpx genes were transcriptionally down-regulated, SOD activity was reduced and cells were more sensitive to growth inhibition by O(2). A Sca permease-deficient (scaC) mutant showed further reduced SOD activity and hypersensitivity to O(2) in medium containing <0.1 micro M Mn(2+). These results demonstrate that the Sca (Mn(2+)) permease in S. gordonii is essential for protection against oxidative stress.

Comparative proteome analysis of Brucella melitensis vaccine strain Rev 1 and a virulent strain, 16M

The genus Brucella consists of bacterial pathogens that cause brucellosis, a major zoonotic disease characterized by undulant fever and neurological disorders in humans. Among the different Brucella species, Brucella melitensis is considered the most virulent. Despite successful use in animals, the vaccine strains remain infectious for humans. To understand the mechanism of virulence in B. melitensis, the proteome of vaccine strain Rev 1 was analyzed by two-dimensional gel electrophoresis and compared to that of virulent strain 16M. The two strains were grown under identical laboratory conditions. Computer-assisted analysis of the two B. melitensis proteomes revealed proteins expressed in either 16M or Rev 1, as well as up- or down-regulation of proteins specific for each of these strains. These proteins were identified by peptide mass fingerprinting. It was found that certain metabolic pathways may be deregulated in Rev 1. Expression of an immunogenic 31-kDa outer membrane protein, proteins utilized for iron acquisition, and those that play a role in sugar binding, lipid degradation, and amino acid binding was altered in Rev 1.

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.

The regulator PerR is involved in oxidative stress response and iron homeostasis and is necessary for full virulence of Streptococcus pyogenes

Ferric uptake regulator (Fur) and Fur-like proteins form an important family of transcriptional regulators in many bacterial species. In this work we have characterized a Fur-like protein, the peroxide regulator PerR, in an M1 serotype of Streptococcus pyogenes. To determine the role of PerR in S. pyogenes, we inactivated the gene by allelic replacement. PerR-deficient bacteria showed 48% reduction of (55)Fe incorporation from the culture medium. Transcriptional analysis revealed that mtsA, encoding a metal-binding protein of an ABC transporter in S. pyogenes, was transcribed at lower levels than were wild-type cells. Although total iron accumulation was reduced, the growth of the mutant strain was not significantly hampered. The mutant showed hyperresistance to hydrogen peroxide, and this response was induced in wild-type cells by growth in aerobiosis, suggesting that PerR acts as an oxidative stress-responsive repressor. PerR may also participate in the response to superoxide stress, as the perR mutant was more sensitive to the superoxide anion and had a reduced transcription of sodA, which encodes the sole superoxide dismutase of S. pyogenes. Complementation of the mutation with a functional perR gene restored (55)Fe incorporation, response to peroxide stress, and transcription of both mtsA and sodA to levels comparable to those of wild-type bacteria. Finally, the perR mutant was attenuated in virulence in a murine air sac model of infection (P < 0.05). These results demonstrate that PerR is involved in the regulation of iron homeostasis and oxidative stress responses and that it contributes to the virulence of S. pyogenes.

Essential role of ferritin Pfr in Helicobacter pylori iron metabolism and gastric colonization

The reactivity of the essential element iron necessitates a concerted expression of ferritins, which mediate iron storage in a nonreactive state. Here we have further established the role of the Helicobacter pylori ferritin Pfr in iron metabolism and gastric colonization. Iron stored in Pfr enabled H. pylori to multiply under severe iron starvation and protected the bacteria from acid-amplified iron toxicity, as inactivation of the pfr gene restricted growth of H. pylori under these conditions. The lowered total iron content in the pfr mutant, which is probably caused by decreased iron uptake rates, was also reflected by an increased resistance to superoxide stress. Iron induction of Pfr synthesis was clearly diminished in an H. pylori feoB mutant, which lacked high-affinity ferrous iron transport, confirming that Pfr expression is mediated by changes in the cytoplasmic iron pool and not by extracellular iron. This is well in agreement with the recent discovery that iron induces Pfr synthesis by abolishing Fur-mediated repression of pfr transcription, which was further confirmed here by the observation that iron inhibited the in vitro binding of recombinant H. pylori Fur to the pfr promoter region. The functions of H. pylori Pfr in iron metabolism are essential for survival in the gastric mucosa, as the pfr mutant was unable to colonize in a Mongolian gerbil-based animal model. In summary, the pfr phenotypes observed give new insights into prokaryotic ferritin functions and indicate that iron storage and homeostasis are of extraordinary importance for H. pylori to survive in its hostile natural environment.

Secreted aspartic proteases as virulence factors of Candida species

Candida infections have emerged as a significant medical problem during the last few decades. Among the different virulence traits of C. albicans, secreted proteolytic activity has been intensively investigated. Pathogenesis of the various forms of candidiasis was shown to be associated with the differential and temporal regulation of the expression of genes coding for secreted aspartic proteases (Sap). These enzymes act as cytolysins in macrophages after phagocytosis of Candida, are present in tissue penetration and are also involved in adherence to epithelial cells. Since the introduction of new antiretroviral therapeutics such as HIV protease inhibitors, oropharyngeal candidiasis is less often observed in AIDS patients. Different HIV aspartic protease inhibitors were able to inhibit the C. albicans Saps involved in adherence. The lower rates of oropharyngeal candidiasis observed in individuals receiving antiretroviral combination therapy could reflect not only an improvement in the immune system but also direct inhibition of Candida Saps by HIV protease inhibitors. Therefore, the development of specific aspartic protease inhibitors might be of interest for the inhibition of candidiasis.

Oxidative stress in phagocytes--"the enemy within"

Phagocytes represent a powerful defense system against invading microorganisms that threaten the life or functional integrity of the host. The capacity to generate and release substantial amounts of reactive oxygen species is a unique property of activated polymorphonuclear and mononuclear phagocytes. The crucial role of these molecules in killing microorganisms and their consecutive contribution to tissue damage during injury and inflammation is widely known. Although much research has been done to explore the molecular events involved in the interaction of oxygen intermediates with microbes or host tissue, surprisingly little attention has been paid to the effect of reactive metabolites on the phagocyte itself. This fact is especially surprising, since it is apparent that the activated phagocyte is directly exposed to its own toxic metabolites. The potential damage occurring during excessive radical formation might notably alter the vital functions of these primarily immunocompetent cells. Moreover, the critical role of oxygen radicals in apoptosis of leukocytes has been recently revealed. Apoptosis is now supposed to represent a key mechanism in neutrophil deactivation and resolution of inflammation. Therefore, this review will focus on the delicate balance between released oxidants and antioxidative protection within the phagocytes themselves. General and phagocyte-specific antioxidative mechanisms, which have co-evolved with the radical generating machinery of phagocytes, are discussed, since the outcome of local inflammation can directly depend on this antioxidative capacity and might range from adequate elimination of the pathogen with minimal acute tissue damage to progression towards a systemic inflammatory response syndrome.

Effect of progressive cachectic parasitism and growth hormone treatment on hepatic 5'-deiodinase activity in calves

Thyroid status is compromised in a variety of acute and chronic infections. Conversion of thyroxine (T(4)) into the metabolically active hormone, triiodothyronine (T(3)), is catalyzed by 5'-deiodinase (5'D) mainly in extrathyroidal tissues. The objective of this study was to examine the effect of protozoan parasitic infection (Sarcocystis cruzi) on hepatic 5'D (type I) activity and plasma concentrations of T(3) and T(4) in placebo- or bovine GH (bGH)-injected calves. Holstein bull calves (127.5+/-2.0 kg BW) were assigned to control (C, ad libitum fed), infected (I, 250,000 S. cruzi sporocysts per os, ad libitum fed), and pair-fed (PF, non-infected, fed to intake of I treatment) groups placebo-injected, and three similar groups injected daily with pituitary-derived bGH (USDA-B-1, 0.1mg/kg, i.m.) designated as C(GH), I(GH) and PF(GH). GH injections were initiated on day 20 post-infection (PI), 3-4 days prior to the onset of clinical signs of the acute phase response (APR), and were continued to day 56 PI at which time calves were euthanized for liver collection. Blood samples were collected on day 0, 28, and 55 PI. Alterations in nutritional intake did not affect type I 5'D in liver. Treatment with bGH increased (P<0.05) 5'D activity in C (24.6%) and PF (25.5%) but not in I calves. Compared to PF calves, infection with S. cruzi reduced 5'D activity 25% (P<0.05) and 47.8% (P<0.01) in placebo- and bGH-injected calves, respectively. Neither nutrition nor bGH treatment significantly affected plasma concentrations of T(4) and T(3) on day 28 and 55 PI. However, plasma thyroid hormones were reduced by infection. On day 28 PI, the average plasma concentrations of T(3) and T(4) were reduced in infected calves (I and I(GH)) 36.4% (P<0.01) and 29.4% (P<0.05), respectively, compared to pair-fed calves (PF and PF(GH)). On day 55 PI, plasma T(3) still remained lower (23.7%, P<0.01 versus PF) in infected calves while plasma T(4) returned to control values. The data suggest that parasitic infection in growing calves inhibits both thyroidal secretion and extrathyroidal T(4) to T(3) conversion during the APR. After recovery from the APR, thyroidal secretion returns to normal but basal and bGH-stimulated generation of T(3) in liver remains impaired.

A superoxide-hypersusceptible Salmonella enterica serovar Typhimurium mutant is attenuated but regains virulence in p47(phox-/-) mice

Salmonella enterica serovar Typhimurium is a gram-negative, facultative intracellular pathogen that predominantly invades mononuclear phagocytes and is able to establish persistent infections. One of the innate defense mechanisms of phagocytic cells is the production of reactive oxygen species, including superoxide. S. enterica serovar Typhimurium has evolved mechanisms to resist such radicals, and these mechanisms could be decisive in its ability to survive and replicate within macrophages. Recently, we described a superoxide-hypersusceptible S. enterica serovar Typhimurium mutant strain, DLG294, that carries a transposon in sspJ, resulting in the lack of expression of SspJ, which is necessary for resistance against superoxide and replication within macrophages. Here we show that DLG294, which is a 14028s derivative, hardly induced any granulomatous lesions in the livers upon subcutaneous infection of C3H/HeN (Ity(r)) mice with 3 x 10(4) bacteria and that its bacterial counts were reduced by 3 log units compared to those of wild-type S. enterica serovar Typhimurium 14028s on day 5 after infection. In contrast, DLG294 replicated like wild-type S. enterica serovar Typhimurium 14028s and induced a phenotypically similar liver pathology in p47(phox-/-) mice, which are deficient in the p47(phox) subunit of the NADPH oxidase complex and which do not produce superoxide. Consistent with these results, DLG294 reached bacterial counts identical to those of wild-type S. enterica serovar Typhimurium 14028s in bone marrow-derived macrophages from p47(phox-/-) mice and in X-CGD PLB-985 cells at 24 h after challenge. These results indicate that SspJ plays a role in the bacterium's resistance to oxidative stress and in the survival and replication of S. enterica serovar Typhimurium both in vitro and in vivo.

Determinants of the phagosomal pH in neutrophils

Phagosomes formed by neutrophils are much less acidic than those of other phagocytic cells. The defective acidification seen in neutrophils has been attributed to consumption of protons during the dismutation of superoxide, because a large, sustained acidification is unmasked when the cells are treated with inhibitors of the NADPH oxidase. Consumption of protons transported into the phagosome by dismutation would tightly couple the activities of the NADPH oxidase and the vacuolar type H(+)-pump (or V-ATPase). We tested the existence of the predicted coupling using microfluorimetry and digital imaging and found that the rate of superoxide generation was independent of the activity of the H(+)-pump. Moreover, we failed to detect the alkalinization predicted to develop through dismutation when the pump was inhibited. Instead, two other mechanisms were found to contribute to the inability of neutrophil phagosomes to acidify. First, the insertion of V-ATPases into the phagosomal membrane was found to be reduced when the oxidase is active. Second, the passive proton (equivalent) permeability of the phagosomal membrane increased when the oxidase was activated. The increased permeability cannot be entirely attributed to the conductive H(+) channels associated with the oxidase, since it is not eliminated by Zn(2+). We conclude that the NADPH oxidase controls the phagosomal pH by multiple mechanisms that include reduced proton delivery to the lumen, increased luminal proton consumption, and enhanced backflux (leak) into the cytosol.

Two antioxidative lactobacilli strains as promising probiotics

Two antioxidative strains tentatively identified as Lactobacillus fermentum, E-3 and E-18, were isolated from intestinal microflora of a healthy child. Survival time of these strains in the presence of reactive oxygen species (ROS), like hydrogen peroxide, superoxide anions and hydroxyl radicals, was significantly increased compared with a non-antioxidative strain, and also was quite similar to a highly ROS resistant strain of Salmonella typhimurium. E-3 and E-8 contain a remarkable level of glutathione, express Mn-SOD, which is important for the prevention of lipid peroxidation, and secrete hydrogen peroxide. Their significant antimicrobial activity combined with antioxidative properties may serve as defensive principles in the intestinal microbial ecosystem and overcome exo- and endogenous oxidative stress.

ohr, Encoding an organic hydroperoxide reductase, is an in vivo-induced gene in Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia, a disease characterized by pulmonary necrosis and hemorrhage caused in part by neutrophil degranulation. In an effort to understand the pathogenesis of this disease, we have developed an in vivo expression technology (IVET) system to identify genes that are specifically up-regulated during infection. One of the genes that we have identified as being induced in vivo is ohr, encoding organic hydroperoxide reductase, an enzyme that could play a role in detoxification of organic hydroperoxides generated during infection. Among the 12 serotypes of A. pleuropneumoniae, ohr was found in only serotypes 1, 9, and 11. This distribution correlated with increased resistance to cumene hydroperoxide, an organic hydroperoxide, but not to hydrogen peroxide or to paraquat, a superoxide generator. Functional assays of Ohr activity demonstrated that A. pleuropneumoniae serotype 1 cultures, but not serotype 5 cultures, were able to degrade cumene hydroperoxide. In A. pleuropneumoniae serotype 1, expression of ohr was induced by cumene hydroperoxide, but not by either hydrogen peroxide or paraquat. In contrast, an ohr gene from serotype 1 cloned into A. pleuropneumoniae serotype 5 was not induced by cumene hydroperoxide or by other forms of oxidative stress, suggesting the presence of a serotype-specific positive regulator of ohr in A. pleuropneumoniae serotype 1.

Chemiluminescence of superoxide generated by Candida albicans: differential effects of the superoxide generator paraquat on a wild-type strain and a respiratory mutant

We previously reported that a respiration-competent parent strain (K) of Candida albicans was more susceptible to the intracellular superoxide radical (O2-) generator paraquat (PQ) than was a respiration-deficient mutant (KRD-19), although both showed a similar sensitivity to extracellularly generated O2-. To clarify the cause of the differential PQ lethality, we developed a chemiluminescence method for measuring O2- generated by C. albicans cells by using the probe methyl-Cypridina-luciferin analogue (MCLA), and examined the effects of PQ on O2- generation in both parent and mutant strains. Endogenous O2- generation without stimulation by PQ was unexpectedly low in both strains. PQ-induced O2- generation in the parent strain was maximal in logarithmic phase cells and lowered in stationary phase cells. In contrast, O2- generation in the mutant remained low throughout the growth phase, even when stimulated by PQ. The extent of PQ-induced O2- generation in the parent strain depended on the carbon source added to the assay mixture; in decreasing order, glucose, glycerol, no carbon source. The inhibitor of the cytochrome respiratory chain, antimycin A, suppressed almost completely the PQ-induced O2- generation in the parent strain. It has been established that PQ is converted to its radical form (PQ+) by receiving a single electron in cells. PQ+ then reduces molecular oxygen to O2- by redox cycling. Thus, the high tolerance to PQ of the respiration-deficient mutant can be explained by minimal PQ+/O2- production due to the limited supply of electrons from the impaired respiratory system.

Modulation of the cytosolic and phagosomal pH by the NADPH oxidase

Proton (equivalents) are primary participants in the control and potency of the NADPH oxidase. Both the cytosolic and intraphagosomal pH are influenced during oxidase activation, and maintenance of the optimal environment requires the coordinated action of a series of sophisticated, highly regulated H(+) transporters, including the Na(+)/H(+) exchange, vacuolar H(+)-ATPase, and H(+)-conductive pathway(s). In addition, protons that are produced during some of the NADPH oxidase reactions then are substrates for the dismutation of superoxide, which precedes production of additional bactericidal agents. In this review, pH homeostasis is shown in conjunction with the NADPH oxidase to present an integrated picture of leukocyte physiology during the phagocytic response.

Peroxidase- and nitrite-dependent metabolism of the anthracycline anticancer agents daunorubicin and doxorubicin

Oxidation of the anticancer anthracyclines doxorubicin (DXR) and daunorubicin (DNR) by lactoperoxidase(LPO)/H(2)O(2) and horseradish peroxidase(HRP)/H(2)O(2) systems in the presence and absence of nitrite (NO(2)(-)) has been investigated using spectrophotometric and EPR techniques. We report that LPO/H(2)O(2)/NO(2)(-) causes rapid and irreversible loss of anthracyclines' absorption bands, suggesting oxidative degradation of their chromophores. Both the initial rate and the extent of oxidation are dependent on both NO(2)(-) concentration and pH. The initial rate decreases when the pH is changed from 7 to 5, and the reaction virtually stops at pH 5. Oxidation of a model hydroquinone compound, 2,5-di-tert-butylhydroquinone, by LPO/H(2)O(2) is also dependent on NO(2)(-); however, in contrast to DNR and DXR, this oxidation is most efficient at pH 5, indicating that LPO/H(2)O(2)/NO(2)(-) is capable of efficiently oxidizing simple hydroquinones even in the neutral form. Oxidation of anthracyclines by HRP/H(2)O(2)/NO(2)(-) is substantially less efficient relative to that by LPO/H(2)O(2)/NO(2)(-) at either pH 5 or pH 7, most likely due to the lower rate of NO(2)(-) metabolism by HRP/H(2)O(2). EPR measurements show that interaction of anthracyclines and 2,5-di-tert-butylhydroquinone with LPO/H(2)O(2)/NO(2)(-) generates the corresponding semiquinone radicals presumably via one-electron oxidation of their hydroquinone moieties. The possible role of the (*)NO(2) radical, a putative LPO metabolite of NO(2)(-), in oxidation of these compounds is discussed. Because in vivo the anthracyclines may co-localize with peroxidases, H(2)O(2), and NO(2)(-) in tissues, their oxidation via the proposed mechanism is likely. These observations reveal a novel, peroxidase- and nitrite-dependent mechanism for the oxidative transformation of the anticancer anthracyclines, which may be pertinent to their biological activities in vivo.

Novel Salmonella enterica serovar Typhimurium protein that is indispensable for virulence and intracellular replication

Upon contact with host cells, the intracellular pathogen Salmonella enterica serovar Typhimurium promotes its uptake, targeting, and survival in intracellular niches. In this process, the bacterium evades the microbicidal effector mechanisms of the macrophage, including oxygen intermediates. This study reports the phenotypic and genotypic characterization of an S. enterica serovar Typhimurium mutant that is hypersusceptible to superoxide. The susceptible phenotype is due to a MudJ insertion-inactivation of a previously undescribed Salmonella gene designated sspJ that is located between 54.4 and 64 min of the Salmonella chromosome and encodes a 392-amino-acid protein. In vivo, upon intraperitoneal injection of 10(4) to 10(7) bacteria in C3H/HeN and 10(1) to 10(4) bacteria in BALB/c mice, the mutant strain was less virulent than the wild type. Consistent with this finding, during the first hour after ingestion by macrophage-like J774 and RAW264.7 cells in vitro, the intracellular killing of the strain carrying sspJ::MudJ is enhanced fivefold over that of wild-type microorganisms. Wild-type salmonellae displayed significant intracellular replication during the first 24 h after uptake, but sspJ::MudJ mutants failed to do so. This phenotype could be restored to that of the wild type by sspJ complementation. The SspJ protein is found in the cytoplasmic membrane and periplasmic space. Amino acid sequence homology analysis did reveal a leader sequence and putative pyrroloquinoline quinone-binding domains, but no putative protein function. We excluded the possibility that SspJ is a scavenger of superoxide or has superoxide dismutase activity.

Role for inducible nitric oxide synthase in protection from chronic Chlamydia trachomatis urogenital disease in mice and its regulation by oxygen free radicals

It has been previously reported that although inducible nitric oxide synthase (iNOS) gene knockout (NOS2(-/-)) mice resolve Chlamydia trachomatis genital infection, the production of reactive nitrogen species (RNS) via iNOS protects a significant proportion of mice from hydrosalpinx formation and infertility. We now report that higher in vivo RNS production correlates with mouse strain-related innate resistance to hydrosalpinx formation. We also show that mice with a deletion of a key component of phagocyte NADPH oxidase (p47(phox-/-)) resolve infection, produce greater amounts of RNS in vivo, and sustain lower rates of hydrosalpinx formation than both wild-type (WT) NOS2(+/+) and NOS2(-/-) controls. When we induced an in vivo chemical block in iNOS activity in p47(phox-/-) mice using N(G)-monomethyl-L-arginine (L-NMMA), a large proportion of these mice eventually succumbed to opportunistic infections, but not before they resolved their chlamydial infections. Interestingly, when compared to WT and untreated p47(phox-/-) controls, L-NMMA-treated p47(phox-/-) mice resolved their infections more rapidly. However, L-NMMA-treated p47(phox-/-) mice lost resistance to chronic chlamydial disease, as evidenced by an increased rate of hydrosalpinx formation that was comparable to that for NOS2(-/-) mice. We conclude that phagocyte oxidase-derived reactive oxygen species (ROS) regulate RNS during chlamydial urogenital infection in the mouse. We further conclude that while neither phagocyte oxidase-derived ROS nor iNOS-derived RNS are essential for resolution of infection, RNS protect from chronic chlamydial disease in this model.

Extracellular superoxide production by Enterococcus faecalis requires demethylmenaquinone and is attenuated by functional terminal quinol oxidases

The intestinal commensal bacterium, Enterococcus faecalis, is unusual among prokaryotic organisms in its ability to produce substantial extracellular superoxide. Transposon mutagenesis, allelic replacement, and electron spin resonance (ESR)-spin trapping showed that superoxide production and generation of derivative hydroxyl radical were dependent on membrane-associated demethylmenaquinone. Extracellular superoxide was generated through univalent reduction of oxygen by reduced demethylmenaquinone. Moreover, extracellular superoxide production was inhibited by exogenous haematin, an essential cofactor for cytochrome bd, and by fumarate, a substrate for fumarate reductase. As integral membrane quinol oxidases, cytochrome bd and fumarate reductase redox cycle demethylmenaquinone, and are necessary for aerobic and anaerobic respiration respectively. A rat model of intestinal colonization demonstrated that conditions exist in the mammalian intestinal tract that permit a mode of respiration for E. faecalis that results in the formation of hydroxyl radical. These results identify and characterize the mechanism by which E. faecalis generates extracellular free radicals.

Infection with Mycobacterium avium differentially regulates the expression of iron transport protein mRNA in murine peritoneal macrophages

Iron is an important element for the growth of microorganisms as well as in the defense of the host by serving as a catalyst for the generation of free radicals via the Fenton/Haber-Weiss reactions. The iron transporter natural resistance-associated macrophage protein 1 (Nramp1) confers resistance to the growth of a variety of intracellular pathogens including Mycobacterium avium. Recently several other proteins that are involved in iron transport, including the highly homologous iron transporter Nramp2 and the transferrin receptor-associated protein HFE (hereditary hemochromatosis protein), have been described. The relationship of these proteins to host defense and to the growth of intracellular pathogens is not known. Here, we report that infection with M. avium differentially regulates mRNA expression of the proteins associated with iron transport in murine peritoneal macrophages. Both Nramp1 and Nramp2 mRNA levels increase following infection, while the expression of transferrin receptor mRNA decreases. The level of expression of HFE mRNA remains unchanged. The difference in the expression of the mRNA of these proteins following infection or cytokine stimulation suggests that they may play an important role in host defense by maintaining a delicate balance between iron availability for host defense and at the same time limiting iron availability for microbial growth.

Enhancement of innate immunity against Mycobacterium avium infection by immunostimulatory DNA is mediated by indoleamine 2,3-dioxygenase

Bacterial DNA and its synthetic immunostimulatory oligodeoxynucleotide analogs (ISS-ODN) activate innate immunity and promote Th1 and cytotoxic T-lymphocyte immune responses. Based on these activities, we investigated whether ISS-ODN could modify the course of Mycobacterium avium infection. M. avium growth in vitro was significantly inhibited by ISS-ODN treatment of human and mouse macrophages, and M. avium growth in vivo was similarly inhibited in C57BL/6 mice treated with ISS-ODN. This protective effect of ISS-ODN was largely independent of tumor necrosis factor alpha (TNF-alpha), interleukin 12 (IL-12), nitric oxide, NADPH oxidase, alpha/beta interferon (IFN-alpha/beta), and IFN-gamma. In contrast, we found that the induction of indoleamine 2,3-dioxygenase (IDO) was required for the antimycobacterial effect of ISS-ODN. To evaluate the potential for synergism between ISS-ODN and other antimycobacterial agents, treatment with a combination of ISS-ODN and clarithromycin (CLA) was tested in vitro and in vivo. ISS-ODN significantly enhanced the therapeutic effect of CLA in both human and mouse macrophages and in C57BL/6 mice. This study newly identifies IDO as being involved in the antimicrobial activity of ISS-ODN and suggests the usefulness of ISS-ODN when used in combination with conventional chemotherapy for microbial infections.

Opsonized virulent Edwardsiella tarda strains are able to adhere to and survive and replicate within fish phagocytes but fail to stimulate reactive oxygen intermediates

Edwardsiella tarda is responsible for hemorrhagic septicemia (edwardsiellosis) in fish and also causes diseases in higher vertebrates such as birds, reptiles, and mammals, including humans. Interactions of E. tarda with blue gourami phagocytes were studied by light microscopy as well as by adherence, intracellular replication, and superoxide anion assays. Both nonopsonized virulent (PPD130/91 and AL9379) and avirulent (PPD125/87 and PPD76/87) bacteria could adhere to and survive and replicate within phagocytes, while only opsonized virulent strains replicated within the phagocytes. Furthermore, only avirulent E. tarda elicited a higher rate of production of reactive oxygen intermediates (ROIs) by phagocytes, indicating that they were unable to avoid and/or resist reactive oxygen radical-based killing by the fish phagocytes. TnphoA transposon mutagenesis was used to construct a library of 200 alkaline phosphatase (PhoA+) fusion mutants from a total of 182,000 transconjugants derived from E. tarda PPD130/91. Five of these mutants induced more ROI production in phagocytes than the wild-type strain. Two mutants had lower replication ability inside phagocytes and moderately higher 50% lethal dose values than the wild-type strain. Sequence analysis revealed that three of these mutants had insertions at sequences having homology to PhoS, dipeptidase, and a surface polymer ligase of lipid A core proteins of other pathogens. These three independent mutations might have changed the cell surface characteristics of the bacteria, which in turn induced phagocytes to produce increased ROIs. Sequences from two other mutants had no homology to known genes, indicating that they may be novel genes for antiphagocytic killing. The present study showed that there are differences in the interactions of virulent and avirulent E. tarda organisms with fish phagocytes and PhoA+ fusion mutants that could be used successfully to identify virulence genes. The information elucidated here would help in the development of suitable strategies to combat the disease caused by E. tarda.

Contribution of Mn-cofactored superoxide dismutase (SodA) to the virulence of Streptococcus agalactiae

Superoxide dismutases convert superoxide anions to molecular oxygen and hydrogen peroxide, which, in turn, is metabolized by catalases and/or peroxidases. These enzymes constitute one of the major defense mechanisms of cells against oxidative stress and hence play a role in the pathogenesis of certain bacteria. We previously demonstrated that group B streptococci (GBS) possess a single Mn-cofactored superoxide dismutase (SodA). To analyze the role of this enzyme in the pathogenicity of GBS, we constructed a sodA-disrupted mutant of Streptococcus agalactiae NEM316 by allelic exchange. This mutant was subsequently cis complemented by integration into the chromosome of pAT113/Sp harboring the wild-type sodA gene. The SOD specific activity detected by gel analysis in cell extracts confirmed that active SODs were present in the parental and complemented strains but absent in the sodA mutant. The growth rates of these strains in standing cultures were comparable, but the sodA mutant was extremely susceptible to the oxidative stress generated by addition of paraquat or hydrogen peroxide to the culture medium and exhibited a higher mutation frequency in the presence of rifampin. In mouse bone marrow-derived macrophages, the sodA mutant showed an increased susceptibility to bacterial killing by macrophages. In a mouse infection model, after intravenous injection the survival of the sodA mutant in the blood and the brain was markedly reduced in comparison to that of the parental and complemented strains whereas only minor effects on survival in the liver and the spleen were observed. These results suggest that SodA plays a role in GBS pathogenesis.

Cu,Zn superoxide dismutase of Mycobacterium tuberculosis contributes to survival in activated macrophages that are generating an oxidative burst

Macrophages produce reactive oxygen species and reactive nitrogen species that have potent antimicrobial activity. Resistance to killing by macrophages is critical to the virulence of Mycobacterium tuberculosis. M. tuberculosis has two genes encoding superoxide dismutase proteins, sodA and sodC. SodC is a Cu,Zn superoxide dismutase responsible for only a minor portion of the superoxide dismutase activity of M. tuberculosis. However, SodC has a lipoprotein binding motif, which suggests that it may be anchored in the membrane to protect M. tuberculosis from reactive oxygen intermediates at the bacterial surface. To examine the role of the Cu,Zn superoxide dismutase in protecting M. tuberculosis from the toxic effects of exogenously generated reactive oxygen species, we constructed a null mutation in the sodC gene. In this report, we show that the M. tuberculosis sodC mutant is readily killed by superoxide generated externally, while the isogenic parental M. tuberculosis is unaffected under these conditions. Furthermore, the sodC mutant has enhanced susceptibility to killing by gamma interferon (IFN-gamma)-activated murine peritoneal macrophages producing oxidative burst products but is unaffected by macrophages not activated by IFN-gamma or by macrophages from respiratory burst-deficient mice. These observations establish that the Cu,Zn superoxide dismutase contributes to the resistance of M. tuberculosis against oxidative burst products generated by activated macrophages.

Induction of nitric oxide synthase during Japanese encephalitis virus infection: evidence of protective role

The ability of Japanese encephalitis virus (JEV) and JEV-induced macrophage-derived factor (MDF) to modulate nitric oxide synthase (NOS) activity in brain and tumor necrosis factor-alpha (TNF-alpha) and the possible antiviral role of NOS during JEV infection were investigated. NOS activity and particularly that of the inducible form of NOS (iNOS) was significantly enhanced in JEV or JEV-induced MDF-treated mice. Following JEV infection, total NOS activity in brain was gradually increased from Day 3 and reached a peak on Day 6. MDF-induced NOS activity and iNOS activity were dose dependent and maximum activity was observed at 1 h after treatment. The response was sensitive to anti-MDF antibody treatment and N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NOS. Pretreatment of JEV-infected mice with L-NMMA increased the mortality as evident from reduced mean survival time (MST, 11.8 days) compared to placebo treated JEV-infected mice (MST, 17 days). The enhanced level of TNF-alpha observed in the early phase of JEV infection correlated well with the enhanced activity of iNOS. These observations thus provide evidence of the protective role of iNOS during JEV infection and indicate that iNOS may be a key mediator in host innate immune response to infection.

Listeria pathogenesis and molecular virulence determinants

The gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal individuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research.

Two-dimensional electrophoresis and characterization of antigens from Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a fungal pathogen of humans. To identify antigens from P. brasiliensis we fractionated a crude preparation of proteins from the fungus and detected the IgG reactive proteins by immunoblot assays of yeast cellular extracts with sera of patients with paracoccidioidomycosis (PCM). We identified and characterized six new antigens by amino acid sequencing and homology search analyses with other proteins deposited in a database. The newly characterized antigens were highly homologous to catalase, fructose-1,6-biphosphate aldolase (aldolase), glyceraldehyde-3-phosphate dehydrogenase, malate dehydrogenase and triosephosphate isomerase from several sources. The characterized antigens presented preferential synthesis in yeast cells, the host fungus phase.

Effect of iron deficiency on Trichuris suis and Ascaris suum infections in pigs

The objective of this experiment was to detect a possible interaction between iron deficiency and intestinal nematode infections. We report on a 2 x 2 study where thirty-one 10-week-old pigs fed a low or a normal iron diet were infected with both Trichuris suis (4500 eggs) and Ascaris suum (1200 eggs). No significant difference was detected between diet groups with respect to parasitological parameters for A. suum or the total number of adult T. suis recovered at necropsy 10 weeks p.i. However, in the low iron group T. suis were located more proximally and the worms were increased in length. A higher proportion of pigs with initial faecal egg excretion at 6 weeks p.i. was observed in the low iron group, indicating a shortened pre-patency period. Worm fecundity and total faecal egg excretion were also highest in the low iron group. A significant correlation was found between female worm length and fecundity. The peripheral eosinophil counts were diminished in the low iron host groups. The infected low iron group experienced more severe pathophysiological changes in terms of hypoalbuminaemia and decreases in erythrocyte volumes. A significant inverse correlation existed between iron content in the bone-marrow and liver (body) store. In conclusion, iron deficiency increased the severity of T. suis infection in pigs.

A critical role for inducible nitric oxide synthase in host survival following coxsackievirus B4 infection

Coxsackieviral infections have been linked etiologically to multiple diseases. The serotype CB4 is associated with acute pancreatitis and autoimmune type 1 diabetes. To delineate the mechanisms of host survival after an acute infection with CB4 (strain E2), we have investigated the role of nitric oxide (NO), generated by the inducible form of nitric oxide synthase (NOS2), in viral clearance and pancreatic beta-cell maintenance. Mice deficient in NOS2 (NOS2-/- mice) and their wild-type (wt) counterparts were injected with CB4, after which both groups developed severe pancreatitis, hepatitis, and hypoglycemia within 3 days. Within 4 to 7 days postinfection (p.i.), most of the NOS2-/- mice died and at a strikingly higher mortality rate than wt mice. Histological examination of pancreata from both infected NOS2-/- and infected wt mice revealed early and complete destruction of the pancreatic acinar tissue, but intact, insulin-stained islets. When examined up to 8 weeks p.i., neither surviving NOS2-/-mice nor surviving wt mice developed hyperglycemia. However, the clearance of infectious CB4 was different between the mice. The spleens of NOS2-/- survivors were cleared of infectious virus with kinetics similar to that of wt mice, but the livers, pancreata, kidneys, and hearts of the NOS2-/- groups cleared virus more slowly than those of the wt group. This delayed clearance was particularly prominent in the livers of infected NOS2-/- mice, which also showed prolonged histopathological features of viral hepatitis. Taken together, this outcome suggests that NOS2 (and NO) is not required for the prevention of pancreatic beta-cell depletion after CB4 infection. Instead the critical actions of NOS2 apparently occur early in the host immune response, allowing mice to survive and clear virus. Moreover, the data support the existence of an organ-specific dependency on NO for a rapid clearance of CB4.

Iron metabolism in pathogenic bacteria

The ability of pathogens to obtain iron from transferrins, ferritin, hemoglobin, and other iron-containing proteins of their host is central to whether they live or die. To combat invading bacteria, animals go into an iron-withholding mode and also use a protein (Nramp1) to generate reactive oxygen species in an attempt to kill the pathogens. Some invading bacteria respond by producing specific iron chelators-siderophores-that remove the iron from the host sources. Other bacteria rely on direct contact with host iron proteins, either abstracting the iron at their surface or, as with heme, taking it up into the cytoplasm. The expression of a large number of genes (>40 in some cases) is directly controlled by the prevailing intracellular concentration of Fe(II) via its complexing to a regulatory protein (the Fur protein or equivalent). In this way, the biochemistry of the bacterial cell can accommodate the challenges from the host. Agents that interfere with bacterial iron metabolism may prove extremely valuable for chemotherapy of diseases.