Nontypeable Haemophilus influenzae clearance by alveolar macrophages is impaired by exposure to cigarette smoke

Nontypeable Haemophilus influenzae (NTHI) is an opportunistic gram-negative pathogen that causes respiratory infections and is associated with progression of respiratory diseases. Cigarette smoke is a main risk factor for development of respiratory infections and chronic respiratory diseases. Glucocorticoids, which are anti-inflammatory drugs, are still the most common therapy for these diseases. Alveolar macrophages are professional phagocytes that reside in the lung and are responsible for clearing infections by the action of their phagolysosomal machinery and promotion of local inflammation. In this study, we dissected the interaction between NTHI and alveolar macrophages and the effect of cigarette smoke on this interaction. We showed that alveolar macrophages clear NTHI infections by adhesion, phagocytosis, and phagolysosomal processing of the pathogen. Bacterial uptake requires host actin polymerization, the integrity of plasma membrane lipid rafts, and activation of the phosphatidylinositol 3-kinase (PI3K) signaling cascade. Parallel to bacterial clearance, macrophages secrete tumor necrosis factor alpha (TNF-alpha) upon NTHI infection. In contrast, exposure to cigarette smoke extract (CSE) impaired alveolar macrophage phagocytosis, although NTHI-induced TNF-alpha secretion was not abrogated. Mechanistically, our data showed that CSE reduced PI3K signaling activation triggered by NTHI. Treatment of CSE-exposed cells with the glucocorticoid dexamethasone reduced the amount of TNF-alpha secreted upon NTHI infection but did not compensate for CSE-dependent phagocytic impairment. The deleterious effect of cigarette smoke was observed in macrophage cell lines and in human alveolar macrophages obtained from smokers and from patients with chronic obstructive pulmonary disease.

Klebsiella pneumoniae triggers a cytotoxic effect on airway epithelial cells

Klebsiella pneumoniae is a capsulated Gram negative bacterial pathogen and a frequent cause of nosocomial infections. Despite its clinical relevance, little is known about the features of the interaction between K. pneumoniae and lung epithelial cells on a cellular level, neither about the role of capsule polysaccharide, one of its best characterised virulence factors, in this interaction.

Characterization and biological role of the O-polysaccharide gene cluster of Yersinia enterocolitica serotype O:9

Yersinia enterocolitica serotype O:9 is a gram-negative enteropathogen that infects animals and humans. The role of lipopolysaccharide (LPS) in Y. enterocolitica O:9 pathogenesis, however, remains unclear. The O:9 LPS consists of lipid A to which is linked the inner core oligosaccharide, serving as an attachment site for both the outer core (OC) hexasaccharide and the O-polysaccharide (OPS; a homopolymer of N-formylperosamine). In this work, we cloned the OPS gene cluster of O:9 and identified 12 genes organized into four operons upstream of the gnd gene. Ten genes were predicted to encode glycosyltransferases, the ATP-binding cassette polysaccharide translocators, or enzymes required for the biosynthesis of GDP-N-formylperosamine. The two remaining genes within the OPS gene cluster, galF and galU, were not ascribed a clear function in OPS biosynthesis; however, the latter gene appeared to be essential for O:9. The biological functions of O:9 OPS and OC were studied using isogenic mutants lacking one or both of these LPS parts. We showed that OPS and OC confer resistance to human complement and polymyxin B; the OPS effect on polymyxin B resistance could be observed only in the absence of OC.

The pmrF polymyxin-resistance operon of Yersinia pseudotuberculosis is upregulated by the PhoP-PhoQ two-component system but not by PmrA-PmrB, and is not required for virulence

The Yersinia pseudotuberculosis chromosome contains a seven-gene polycistronic unit (the pmrF operon) whose products share extensive homologies with their pmrF counterparts in Salmonella enterica serovar Typhimurium (S. typhimurium), another Gram-negative bacterial enteropathogen. This gene cluster is essential for addition of 4-aminoarabinose to the lipid moiety of LPS, as demonstrated by MALDI-TOF mass spectrometry of lipid A from both wild-type and pmrF-mutated strains. As in S. typhimurium, 4-aminoarabinose substitution of lipid A contributes to in vitro resistance of Y. pseudotuberculosis to the antimicrobial peptide polymyxin B. Whereas pmrF expression in S. typhimurium is mediated by both the PhoP-PhoQ and PmrA-PmrB two-component regulatory systems, it appears to be PmrA-PmrB-independent in Y. pseudotuberculosis, with the response regulator PhoP interacting directly with the pmrF operon promoter region. This result reveals that the ubiquitous PmrA-PmrB regulatory system controls different regulons in distinct bacterial species. In addition, pmrF inactivation in Y. pseudotuberculosis has no effect on bacterial virulence in the mouse, again in contrast to the situation in S. typhimurium. The marked differences in pmrF operon regulation in these two phylogenetically close bacterial species may be related to their dissimilar lifestyles.

Lipopolysaccharide O antigen status of Yersinia enterocolitica O:8 is essential for virulence and absence of O antigen affects the expression of other Yersinia virulence factors

Lipopolysaccharide (LPS) is the major component of the outer membrane of Gram-negative bacteria. Although much attention has been given to the biological effects of its lipid A portion, a great body of evidence indicates that its O chain polysaccharide (O antigen) portion plays an important role in the bacterium-host interplay. In this work we have studied in-depth the role of the O antigen in Yersinia enterocolitica serotype O:8 pathogenesis. We made a detailed virulence analysis of three mutants having different O antigen phenotypes: (i) LPS with no O antigen (rough mutant); (ii) LPS with one O unit (semirough mutant) and (iii) LPS with random distribution of O antigen chain lengths. We demonstrated that these LPS O antigen mutants were attenuated in virulence regardless of the infection route used. Co-infection experiments revealed that the rough and semirough mutants were severely impaired in their ability to colonize the Peyer's patches and in contrast to the wild-type strain they did not colonize spleen and liver. The mutant with random distribution of O antigen chain lengths, however, survived better but started to be cleared from mouse organs after 8 days. As an explanation to this attenuation we present here evidence that other Yersinia virulence factors depend on the presence of O antigen for their proper function and/or expression. We demonstrated that in the rough mutant: (i) the YadA function but not its expression was altered; (ii) Ail was not expressed and (iii) inv expression was downregulated. On the other hand, expression of flhDC, the flagellar master regulatory operon, was upregulated in this mutant with a concomitant increase in the production of flagellins. Finally, expression of yplA, encoding for the Yersinia phospholipase A, was also upregulated accompanied by an increased flagellar type III secretion system mediated secretion of YplA to culture medium. Together these findings suggest that the absence of O antigen in the outer membrane of Yersinia either directly or indirectly, for example through a cellular or membrane stress, could act as a regulatory signal.

The biosynthesis and biological role of lipopolysaccharide O-antigens of pathogenic Yersiniae

Lipopolysaccharide (LPS) is the major component of the outer leaflet of the outer membrane of Gram-negative bacteria. The LPS molecule is composed of two biosynthetic entities: the lipid A--core and the O-polysaccharide (O-antigen). Most biological effects of LPS are due to the lipid A part, however, there is an increasing body of evidence indicating that O-antigen (O-ag) plays an important role in effective colonization of host tissues, resistance to complement-mediated killing and in the resistance to cationic antimicrobial peptides that are key elements of the innate immune system. In this review, we will discuss: (i) the work done on the genetics and biosynthesis of the O-ags in the genus Yersinia; (ii) the role of O-ag in virulence of these bacteria; (iii) the work done on regulation of the O-ag gene cluster expression and; (iv) the impact that the O-ag expression has on other bacterial surface and membrane components.

Regulatory network of lipopolysaccharide O-antigen biosynthesis in Yersinia enterocolitica includes cell envelope-dependent signals

Lipopolysaccharide (LPS) is a glycolipid present in the outer membrane of all Gram-negative bacteria, and it is one of the signature molecules recognized by the receptors of the innate immune system. In addition to its lipid A portion (the endotoxin), its O-chain polysaccharide (the O-antigen) plays a critical role in the bacterium-host interplay and, in a number of bacterial pathogens, it is a virulence factor. We present evidence that, in Yersinia enterocolitica serotype O:8, a complex signalling network regulates O-antigen expression in response to temperature. Northern blotting and reporter fusion analyses indicated that temperature regulates the O-antigen expression at the transcriptional level. Promoter cloning showed that the O-antigen gene cluster contains two transcriptional units under the control of promoters P(wb1) and P(wb2). The activity of both promoters is under temperature regulation and is repressed in bacteria grown at 37 degrees C. We demonstrate that the RosA/RosB efflux pump/potassium antiporter system and Wzz, the O-antigen chain length determinant, are indirectly involved in the regulation mainly affecting the activity of promoter P(wb2). The rosAB transcription, under the control of P(ros), is activated at 37 degrees C, and P(wb2) is repressed through the signals generated by the RosAB system activation, i.e. decreased [K+] and increased [H+]. The wzz transcription is under the control of P(wb2), and we show that, at 37 degrees C, overexpression of Wzz downregulates slightly the P(wb1) and P(wb2) activities and more strongly the P(ros) activity, with the net result that more O-antigen is produced. Finally, we demonstrate that overexpression of Wzz causes membrane stress that activates the CpxAR two-component signal transduction system.

Temperature-regulated efflux pump/potassium antiporter system mediates resistance to cationic antimicrobial peptides in Yersinia

Most bacterial pathogens are resistant to cationic antimicrobial peptides (CAMPs) that are key components of the innate immunity of both vertebrates and invertebrates. In Gram-negative bacteria, the known CAMPs resistance mechanisms involve outer membrane (OM) modifications and specifically those in the lipopolysaccharide (LPS) molecule. Here we report, the characterization of a novel CAMPs resistance mechanism present in Yersinia that is dependent on an efflux pump/potassium antiporter system formed by the RosA and RosB proteins. The RosA/RosB system is activated by a temperature shift to 37 degrees C, but is also induced by the presence of the CAMPs, such as polymyxin B. This is the first report of a CAMPs resistance system that is induced by the presence of CAMPs. It is proposed that the RosA/RosB system protects the bacteria by both acidifying the cytoplasm to prevent the CAMPs action and pumping the CAMPs out of the cell.

NO-loaded Zn2+-exchanged zeolite materials: A potential bifunctional anti-bacterial strategy

Nitric oxide (NO) is important for the regulation of a number of diverse biological processes, including vascular tone, neurotransmission, inflammatory cell responsiveness, defence against invading pathogens and wound healing. Transition metal exchanged zeolites are nanoporous materials with high-capacity storage properties for gases such as NO. The NO stores are liberated upon contact with aqueous environments, thereby making them ideal candidates for use in biological and clinical settings. Here, we demonstrate the NO release capacity and powerful bactericidal properties of a novel NO-storing Zn2+-exchanged zeolite material at a 50 wt.% composition in a polytetrafluoroethylene polymer. Further to our published data showing the anti-thrombotic effects of a similar NO-loaded zeolite, this study demonstrates the antibacterial properties of NO-releasing zeolites against clinically relevant strains of bacteria, namely Gram-negative Pseudomonas aeruginosa and Gram-positive methicillin-sensitive and methicillin-resistant Staphylococcus aureus and Clostridium difficile. Thus our study highlights the potential of NO-loaded zeolites as biocompatible medical device coatings with anti-infective properties. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Efficacy of Biocides Used in the Modern Food Industry To Control Salmonella enterica, and Links between Biocide Tolerance and Resistance to Clinically Relevant Antimicrobial Compounds

Biocides play an essential role in limiting the spread of infectious disease. The food industry is dependent on these agents, and their increasing use is a matter for concern. Specifically, the emergence of bacteria demonstrating increased tolerance to biocides, coupled with the potential for the development of a phenotype of cross-resistance to clinically important antimicrobial compounds, needs to be assessed. In this study, we investigated the tolerance of a collection of susceptible and multidrug-resistant (MDR) Salmonella enterica strains to a panel of seven commercially available food-grade biocide formulations. We explored their abilities to adapt to these formulations and their active biocidal agents, i.e., triclosan, chlorhexidine, hydrogen peroxide, and benzalkonium chloride, after sequential rounds of in vitro selection. Finally, cross-tolerance of different categories of biocidal formulations, their active agents, and the potential for coselection of resistance to clinically important antibiotics were investigated. Six of seven food-grade biocide formulations were bactericidal at their recommended working concentrations. All showed a reduced activity against both surface-dried and biofilm cultures. A stable phenotype of tolerance to biocide formulations could not be selected. Upon exposure of Salmonella strains to an active biocidal compound, a high-level of tolerance was selected for a number of Salmonella serotypes. No cross-tolerance to the different biocidal agents or food-grade biocide formulations was observed. Most tolerant isolates displayed changes in their patterns of susceptibility to antimicrobial compounds. Food industry biocides are effective against planktonic Salmonella. When exposed to sublethal concentrations of individual active biocidal agents, tolerant isolates may emerge. This emergence was associated with changes in antimicrobial susceptibilities.

Structural-Functional Studies of Burkholderia cenocepacia D-Glycero-beta-D-manno-heptose 7-Phosphate Kinase (HldA) and Characterization of Inhibitors with Antibiotic Adjuvant and Antivirulence Properties

As an essential constituent of the outer membrane of Gram-negative bacteria, lipopolysaccharide contributes significantly to virulence and antibiotic resistance. The lipopolysaccharide biosynthetic pathway therefore serves as a promising therapeutic target for antivirulence drugs and antibiotic adjuvants. Here we report the structural-functional studies of D-glycero-beta-D-manno-heptose 7-phosphate kinase (HldA), an absolutely conserved enzyme in this pathway, from Burkholderia cenocepacia. HldA is structurally similar to members of the PfkB carbohydrate kinase family and appears to catalyze heptose phosphorylation via an in-line mechanism mediated mainly by a conserved aspartate, Asp270. Moreover, we report the structures of HldA in complex with two potent inhibitors in which both inhibitors adopt a folded conformation and occupy the nucleotide-binding sites. Together, these results provide important insight into the mechanism of HldA-catalyzed heptose phosphorylation and necessary information for further development of HldA inhibitors.

Chemical Communication of Antibiotic Resistance by a Highly Resistant Subpopulation of Bacterial Cells

The overall antibiotic resistance of a bacterial population results from the combination of a wide range of susceptibilities displayed by subsets of bacterial cells. Bacterial heteroresistance to antibiotics has been documented for several opportunistic Gram-negative bacteria, but the mechanism of heteroresistance is unclear. We use Burkholderia cenocepacia as a model opportunistic bacterium to investigate the implications of heterogeneity in the response to the antimicrobial peptide polymyxin B (PmB) and also other bactericidal antibiotics. Here, we report that B. cenocepacia is heteroresistant to PmB. Population analysis profiling also identified B. cenocepacia subpopulations arising from a seemingly homogenous culture that are resistant to higher levels of polymyxin B than the rest of the cells in the culture, and can protect the more sensitive cells from killing, as well as sensitive bacteria from other species, such as Pseudomonas aeruginosa and Escherichia coli. Communication of resistance depended on upregulation of putrescine synthesis and YceI, a widely conserved low-molecular weight secreted protein. Deletion of genes for the synthesis of putrescine and YceI abrogate protection, while pharmacologic inhibition of putrescine synthesis reduced resistance to polymyxin B. Polyamines and YceI were also required for heteroresistance of B. cenocepacia to various bactericidal antibiotics. We propose that putrescine and YceI resemble "danger" infochemicals whose increased production by a bacterial subpopulation, becoming more resistant to bactericidal antibiotics, communicates higher level of resistance to more sensitive members of the population of the same or different species.

Mal (MyD88-adapter-like) is required for Toll-like receptor-4 signal transduction

The recognition of microbial pathogens by the innate immune system involves Toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns. Different TLRs recognize different pathogen-associated molecular patterns, with TLR-4 mediating the response to lipopolysaccharide from Gram-negative bacteria. All TLRs have a Toll/IL-1 receptor (TIR) domain, which is responsible for signal transduction. MyD88 is one such protein that contains a TIR domain. It acts as an adapter, being involved in TLR-2, TLR-4 and TLR-9 signalling; however, our understanding of how TLR-4 signals is incomplete. Here we describe a protein, Mal (MyD88-adapter-like), which joins MyD88 as a cytoplasmic TIR-domain-containing protein in the human genome. Mal activates NF-kappaB, Jun amino-terminal kinase and extracellular signal-regulated kinase-1 and -2. Mal can form homodimers and can also form heterodimers with MyD88. Activation of NF-kappaB by Mal requires IRAK-2, but not IRAK, whereas MyD88 requires both IRAKs. Mal associates with IRAK-2 by means of its TIR domain. A dominant negative form of Mal inhibits NF-kappaB, which is activated by TLR-4 or lipopolysaccharide, but it does not inhibit NF-kappaB activation by IL-1RI or IL-18R. Mal associates with TLR-4. Mal is therefore an adapter in TLR-4 signal transduction.

Hylaranins: prototypes of a new class of amphibian antimicrobial peptide from the skin secretion of the oriental broad-folded frog, Hylarana latouchii

Amphibian skin secretions contain a broad spectrum of biologically active compounds, particularly antimicrobial peptides, which are considered to constitute a first line of defence against bacterial infection. Here we describe the identification of two prototype peptides representing a novel structural class of antimicrobial peptide from the skin secretion of the oriental broad-folded frog, Hylarana latouchii. Named hylaranin-L1 (GVLSAFKNALPGIMKIIVamide) and hylaranin-L2 (GVLSVIKNALPGIMRFIAamide), both peptides consist of 18 amino acid residues, are C-terminally amidated and are of unique primary structures. Their primary structures were initially deduced by MS/MS fragmentation sequencing from reverse-phase HPLC fractions of skin secretion that demonstrated antimicrobial activity. Subsequently, their precursor-encoding cDNAs were cloned from a skin secretion-derived cDNA library and their primary structures were confirmed unequivocally. Synthetic replicates of both peptides exhibited broad-spectrum antimicrobial activity with mean inhibitory concentrations (MICs) of 34 µM against Gram-negative Escherichia coli, 4.3 µM against Gram-positive Staphylococcus aureus and 4–9 µM against the yeast, Candida albicans. Both peptides exhibited little haemolytic activity (<6 %) at the MICs for S. aureus and C. albicans. Amphibian skin secretions thus continue to provide novel antimicrobial peptide structures that may prove to be lead compounds in the design of new classes of anti-infection therapeutics.

Lactobacillus strains isolated from infant faeces possess potent inhibitory activity against intestinal alpha- and beta-glucosidases suggesting anti-diabetic potential

Purpose: Inhibitors of intestinal alpha-glucosidases are used therapeutically to treat type 2 diabetes mellitus. Bacteria such as Actinoplanes sp. naturally produce potent alpha-glucosidase inhibitor compounds, including the most widely available drug acarbose. It is not known whether lactic acid bacteria (LAB) colonising the human gut possess inhibitory potential against glucosidases. Hence, the study was undertaken to screen LABs having inherent alpha- and beta-glucosidase inhibitory potential. Methods: This study isolated, screened, identified and extracted Lactobacillus strains (Lb1–15) from human infant faecal samples determining their inhibitory activity against intestinal maltase, sucrase, lactase and amylase. Lactobacillus reference strains (Ref1–7), a Gram positive control (Ctrl1) and two Gram negative controls (Ctrl2–3), were also analysed to compare activity. Results: Faecal isolates were identified by DNA sequencing, with the majority identified as unique strains of Lactobacillus plantarum. Some strains (L. plantarum, L. fermentum, L. casei and L. rhamnosus) had potent and broad spectrum inhibitory activities (up to 89 %; p < 0.001; 500 mg/ml wet weight) comparable to acarbose (up to 88 %; p < 0.001; 30 mg/ml). Inhibitory activity was concentration-dependent and was freely available in the supernatant, and was not present in other bacterial genera (Bifidobacterium bifidum and Escherichia coli or Salmonella typhimurium). Interestingly, the potency and spectrum of inhibitory activity across strains of a single species (L. plantarum) differed substantially. Some Lactobacillus extracts had broader spectrum activities than acarbose, effectively inhibiting beta-glucosidase activity (lactase) as well as alpha-glucosidase activities (maltase, sucrase and amylase). Anti-diabetic potential was indicated by the fact that oral gavage with a L. rhamnosus extract (1 g/kg) was able to reduce glucose excursions (Area under curve; 22 %; p < 0.05) in rats during a carbohydrate challenge (starch; 2 g/kg). Conclusion: These results definitively demonstrate that Lactobacillus strains present in the human gut have alpha- and beta-glucosidase inhibitory activities and can reduce blood glucose responses in vivo. Although the potential use of LAB such as Lactobacillus as a dietary supplement, medicinal food or biotherapeutic for diabetes is uncertain, such an approach might offer advantages over drug therapies in terms of broader spectrum activities and fewer unpleasant side effects. Further characterisation of this bioactivity is warranted, and chronic studies should be undertaken in appropriate animal models or diabetic subjects.