The Potential of Antimicrobial Peptides as Biocides

Antimicrobial peptides constitute a diverse class of naturally occurring antimicrobial molecules which have activity against a wide range of pathogenic microorganisms. Antimicrobial peptides are exciting leads in the development of novel biocidal agents at a time when classical antibiotics are under intense pressure from emerging resistance, and the global industry in antibiotic research and development stagnates. This review will examine the potential of antimicrobial peptides, both natural and synthetic, as novel biocidal agents in the battle against multi-drug resistant pathogen infections.

Research strategies to improve honeybee health in Europe

Understanding the fundaments of colony losses and improving the status of colony health will require cross-cutting research initiatives including honeybee pathology, chemistry, genetics and apicultural extension. The 7th framework of the European Union requested research to empirically and experimentally fill knowledge gaps on honeybee pests and diseases, including 'Colony Collapse Disorder' and the impact of parasites, pathogens and pesticides on honeybee mortality. The interactions among these drivers of colony loss will be studied in different European regions, using experimental model systems including selected parasites (e. g. Nosema and Varroa mites), viruses (Deformed Wing Virus, Black Queen Cell Virus, Israeli Acute Paralysis Virus) and model pesticides (thiacloprid, tau-fluvalinate). Transcriptome analyses will be used to explore host-pathogen-pesticide interactions and identify novel genes for disease resistance. Special attention will be given to sublethal and chronic exposure to pesticides and will screen how apicultural practices affect colony health. Novel diagnostic screening methods and sustainable concepts for disease prevention will be developed resulting in new treatments and selection tools for resistant stock. Research initiatives will be linked to various national and international ongoing European, North-and South-American colony health monitoring and research programs, to ensure a global transfer of results to apicultural practice in the world community of beekeepers.

Does infection by Nosema ceranae cause "Colony Collapse Disorder" in honey bees (Apis mellifera)?

Nosema ceranae is an emergent and potentially virulent pathogen of the honey bee (Apis mellifera) that has spread across the world in the last 10 or so years. Its precise origin and timing of spread are currently unclear because of a lack of appropriate genetic markers and inadequate sampling in putative Asian source populations. Though it has been dismissed as a cause of CCD in the USA based on correlational analyses of snapshot sampling of diseased hives, observations of naturally infected colonies suggest that it leads to colony collapse in Spain. Experiments are sorely needed to investigate its impact on individuals and colonies, and to pin down a causal relationship between N. ceranae and colony collapse. Whether N. ceranae is displacing N. apis is uncertain. For temperate zone apiculturalists, global climate change may mean that N. ceranae presents more of a challenge than has hitherto been considered the case.

A Family of Helminth Molecules that Modulate Innate Cell Responses via Molecular Mimicry of Host Antimicrobial Peptides

Over the last decade a significant number of studies have highlighted the central role of host antimicrobial (or defence) peptides in modulating the response of innate immune cells to pathogen-associated ligands. In humans, the most widely studied antimicrobial peptide is LL-37, a 37-residue peptide containing an amphipathic helix that is released via proteolytic cleavage of the precursor protein CAP18. Owing to its ability to protect against lethal endotoxaemia and clinically-relevant bacterial infections, LL-37 and its derivatives are seen as attractive candidates for anti-sepsis therapies. We have identified a novel family of molecules secreted by parasitic helminths (helminth defence molecules; HDMs) that exhibit similar biochemical and functional characteristics to human defence peptides, particularly CAP18. The HDM secreted by Fasciola hepatica (FhHDM-1) adopts a predominantly alpha-helical structure in solution. Processing of FhHDM-1 by F. hepatica cathepsin L1 releases a 34-residue C-terminal fragment containing a conserved amphipathic helix. This is analogous to the proteolytic processing of CAP18 to release LL-37, which modulates innate cell activation by classical toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS). We show that full-length recombinant FhHDM-1 and a peptide analogue of the amphipathic C-terminus bind directly to LPS in a concentration-dependent manner, reducing its interaction with both LPS-binding protein (LBP) and the surface of macrophages. Furthermore, FhHDM-1 and the amphipathic C-terminal peptide protect mice against LPS-induced inflammation by significantly reducing the release of inflammatory mediators from macrophages. We propose that HDMs, by mimicking the function of host defence peptides, represent a novel family of innate cell modulators with therapeutic potential in anti-sepsis treatments and prevention of inflammation.

Characteristics and Treatment of Medical Device Related Infections

Medical device related infections are becoming an increasing prevalent area of infectious disease. They can be attributed to a multitude of factors from an increasing elderly population with reduced immunological status to increasing microbial resistance and evolution. Of greatest significance is the failure of standard antimicrobial regimens to eradicate biomaterial-related infections due to the formation of microbial biofilms consisting of extracellular polymeric substances. Biofilms form and thrive at the abiotic device surface where nutrients are more concentrated and symbiotic colonies can be formed. The formation of a biofilm matrix occurs in a series of steps beginning with reversible attachment of bacteria to the surface of the substrate and terminating in dispersion of mature biofilm microcolonies that aim to colonise fresh surfaces high in nutrients. Mature biofilms can resist 10-1000 times the concentrations of standard antibiotic regimens that are required to kill genetically equivalent planktonic forms. The extent of the infection and the pathogen(s) present can be attributed to both the form and location of the device. It is important that preventative measures and treatment strategies relate to combating the causative microorganisms. Preventative measures include: the use of anti-infective biomaterials that can be coated or incorporated with standard or innovative antimicrobials; modified anti-adhesive medical devices; environmental sterilisation protocols and prophylactic drug therapy. Treatment of established infection may require removal of the device or if deemed possible the device may be salvageable through the initiation of antimicrobial therapy. The increasing spectre of antibiotic resistance and medical device related infections are a large and increasing burden on health care systems and the patient’s quality of life and long term prognosis. As an infectious disease it represents one of the most difficult challenges facing modern science and healthcare.

Secreted cysteine proteases of the carcinogenic liver fluke, Opisthorchis viverrini: Regulation of cathepsin F activation by autocatalysis and trans-processing by cathepsin B

Opisthorchis viverrini is an important helminth pathogen of humans that is endemic in Thailand and Laos. Adult flukes reside within host bile ducts and feed on epithelial tissue and blood cells. Chronic opisthorchiasis is associated with severe hepatobiliary diseases such as cholangiocarcinoma. Here we report that adult O. viverrini secrete two major cysteine proteases: cathepsin F (Ov-CF-1) and cathepsin B1 (Ov-CB-1). Ov-CF-1 is secreted as an inactive zymogen that autocatalytically processes and activates to a mature enzyme at pH 4.5 via an intermolecular cleavage at the prosegment-mature domain junction. Ov-CB-1 is also secreted as a zymogen but, in contrast to Ov-CF-1, is fully active against peptide and macromolecular substrates despite retaining the N-terminal prosegment. The active Ov-CB-1 zymogen was capable of trans-activating Ov-CF-1 by proteolytic removal of its prosegment at pH 5.5, a pH at which the Ov-CF-1 zymogen cannot autocatalytically activate. Both cathepsins hydrolyse human haemoglobin but their combined action more efficiently degrades haemoglobin to smaller peptides than each enzyme alone. Ov-CF-1 degraded extracellular matrix proteins more effectively than Ov-CB-1 at physiological pH. We propose that Ov-CB-1 regulates Ov-CF-1 activity and that both enzymes work together to degrade host tissue contributing to the development of liver fluke-associated cholangiocarcinoma.

Investigating the persistence of tick-borne pathogens via the R-0 model

In the epidemiology of infectious diseases, the basic reproduction number, R-0, has a number of important applications, most notably it can be used to predict whether a pathogen is likely to become established, or persist, in a given area. We used the R-0 model to investigate the persistence of 3 tick-borne pathogens; Babesia microti, Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in an Apodemus sylvaticus-Ixodes ricinus system. The persistence of these pathogens was also determined empirically by screening questing ticks and wood mice by PCR. All 3 pathogens behaved differently in response to changes in the proportion of transmission hosts on which I. ricinus fed, the efficiency of transmission between the host and ticks and the abundance of larval and nymphal ticks found on small mammals. Empirical data supported theoretical predictions of the R-0 model. The transmission pathway employed and the duration of systemic infection were also identified as important factors responsible for establishment or persistence of tick-borne pathogens in a given tick-host system. The current study demonstrates how the R-0 model can be put to practical use to investigate factors affecting tick-borne pathogen persistence, which has important implications for animal and human health worldwide.

Survival of pathogenic bacteria during mesophilic anaerobic-digestion of animal waste

The survival of pathogenic bacteria was investigated during the operation of a full-scale anaerobic digester which was fed daily and operated at 28-degrees-C. The digester had a mean hydraulic retention time of 24 d. The viable numbers of Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes and Campylobacter jejuni were reduced during mesophilic anaerobic digestion. Escherichia coli had the smallest mean viable numbers at each stage of the digestion process. Its mean T90 value was 76-9 d. Yersinia enterocolitica was the least resistant to the anaerobic digester environment; its mean T90 value was 18.2 d. Campylobacter jejuni was the most resistant bacterium; its mean T90 value was 438.6 d. Regression analysis showed that there were no direct relationships between the slurry input and performance of the digester and the decline of pathogen numbers during the 140 d experimental period.

Discovery and evolving history of two genetically related but phenotypically different viruses, porcine circoviruses 1 and 2

Porcine circoviruses (PCVs) belong to the genus Circovirus, family Circoviridae. and are the smallest non-enveloped, single stranded, negative sense, circular DNA viruses that replicate autonomously in mammalian cells. Two types of PCV have been characterised, PCV1 and PCV2 and these two viruses show 83% sequence identity at open reading frame (ORF) 1 and 67% identity at ORF2. PCV1 is a nonpathogenic virus of pigs. In contrast, PCV2 has emerged as a major pathogen of swine around the world. The discovery of PCV1 and how the subsequent studies on this virus eventually led to the recognition and characterisation of PCV2, and the disease scenarios associated with PCV2, serve as a model of how multidisciplinary collaboration among field veterinarians, diagnosticians and researchers can lead to the rapid characterisation and control of a globally important emerging disease. (C) 2011 Elsevier B.V. All rights reserved.

Temporal distribution of porcine circovirus 2 genogroups recovered from postweaning multisystemic wasting syndrome-affected and -nonaffected farms in Ireland and Northern Ireland

Porcine circovirus type 2 (PCV2) is now recognized as the essential infectious component of porcine postweaning multisystemic wasting syndrome (PMWS). PMWS was first recognized in high-status, specific pathogen-free pigs in Canada in 1991 and is now an economically important disease that affects the swine industry around the world. Recently, reports of genomic studies on PCV2 viruses indicated that 2 distinctive genogroups of PCV2 exist.(4,10) This report involves the results of a study on the distribution of predominant PCV2 genogroups recovered from samples taken from PMWS-affected and PMWS-nonaffected farms on the island of Ireland over a 9-year period and the results of a study on PCV2 genogroup recovery from fecal samples taken from a farm in Northern Ireland from 2003 to 2005 that was first diagnosed as PMWS positive in August 2005. The results indicate that, although at least 2 distinct genogroups of PCV2 have been circulating on pig farms on the island of Ireland, there does not appear to be a direct relationship between infection with these different genogroups of PCV2 and the development of PMWS.

Comparison of the binding specificity of two bacterial metalloproteases, LasB of Pseudomonas aeruginosa and ZapA of Proteus mirabilis, using N-alpha mercaptoamide template-based inhibitor analogues

The metalloproteases ZapA of Proteus mirabilis and LasB of Pseudomonas aeruginosa are known to be virulence factors their respective opportunistic bacterial pathogens, and are members of the structurally related serralysin and thermolysin families of bacterial metalloproteases respectively. Secreted at the site of infection, these proteases play a key role in the infection process, contributing to tissue destruction and processing of components of the host immune system. Inhibition of these virulence factors may therefore represent an antimicrobial strategy, attenuating the virulence of the infecting pathogen. Previously we have screened a library of N-alpha mercaptoamide dipeptide inhibitors against both ZapA and LasB, with the aim of mapping the S1' binding site of the enzymes, revealing both striking similarities and important differences in their binding preferences. Here we report the design, synthesis, and screening of several inhibitor analogues, based on two parent inhibitors from the original library. The results have allowed for further characterization of the ZapA and LasB active site binding pockets, and have highlighted the possibility for development of broad-spectrum bacterial protease inhibitors, effective against enzymes of the thermolysin and serralysin metalloprotease families.

Burkholderia cenocepacia disrupts host cell actin cytoskeleton by inactivating Rac and Cdc42

Burkholderia cenocepacia, a member of the Burkholderia cepacia complex, is an opportunistic pathogen that causes devastating infections in patients with cystic fibrosis. The ability of B. cenocepacia to survive within host cells could contribute significantly to its virulence in immunocompromised patients. In this study, we explored the mechanisms that enable B. cenocepacia to survive inside macrophages. We found that B. cenocepacia disrupts the actin cytoskeleton of infected macrophages, drastically altering their morphology. Submembranous actin undergoes depolymerization, leading to cell retraction. The bacteria perturb actin architecture by inactivating Rho family GTPases, particularly Rac1 and Cdc42. GTPase inactivation follows internalization of viable B. cenocepacia and compromises phagocyte function: macropinocytosis and phagocytosis are markedly inhibited, likely impairing the microbicidal and antigen-presenting capability of infected macrophages. The type VI secretion system is essential for the bacteria to elicit these changes. This is the first report demonstrating inactivation of Rho family GTPases by a member of the B. cepacia complex.

The Type VI secretion system of Burkholderia cenocepacia affects multiple Rho family GTPases disrupting the actin cytoskeleton and the assembly of NADPH oxidase complex in macrophages

Burkholderia cenocepacia is a Gram-negative opportunistic pathogen of patients with cystic fibrosis and chronic granulomatous disease. The bacterium survives intracellularly in macrophages within a membrane-bound vacuole (BcCV) that precludes the fusion with lysosomes. The underlying cellular mechanisms and bacterial molecules mediating these phenotypes are unknown. Here, we show that intracellular B. cenocepacia expressing a type VI secretion system (T6SS) affects the activation of the Rac1 and Cdc42 RhoGTPase by reducing the cellular pool of GTP-bound Rac1 and Cdc42. The T6SS also increases the cellular pool of GTP-bound RhoA and decreases cofilin activity. These effects lead to abnormal actin polymerization causing collapse of lamellipodia and failure to retract the uropod. The T6SS also prevents the recruitment of soluble subunits of the NADPH oxidase complex including Rac1 to the BcCV membrane, but is not involved in the BcCV maturation arrest. Therefore, T6SS-mediated deregulation of Rho family GTPases is a common mechanism linking disruption of the actin cytoskeleton and delayed NADPH oxidase activation in macrophages infected with B. cenocepacia.

Burkholderia cenocepacia BC2L-C Is a Super Lectin with Dual Specificity and Proinflammatory Activity

Lectins and adhesins are involved in bacterial adhesion to host tissues and mucus during early steps of infection. We report the characterization of BC2L-C, a soluble lectin from the opportunistic pathogen Burkholderia cenocepacia, which has two distinct domains with unique specificities and biological activities. The N-terminal domain is a novel TNF-alpha-like fucose-binding lectin, while the C-terminal part is similar to a superfamily of calcium-dependent bacterial lectins. The C-terminal domain displays specificity for mannose and L-glycero-D-manno-heptose. BC2L-C is therefore a superlectin that binds independently to mannose/heptose glycoconjugates and fucosylated human histo-blood group epitopes. The apo form of the C-terminal domain crystallized as a dimer, and calcium and mannose could be docked in the binding site. The whole lectin is hexameric and the overall structure, determined by electron microscopy and small angle X-ray scattering, reveals a flexible arrangement of three mannose/heptose-specific dimers flanked by two fucose-specific TNF-alpha-like trimers. We propose that BC2L-C binds to the bacterial surface in a mannose/heptose-dependent manner via the C-terminal domain. The TNF-alpha-like domain triggers IL-8 production in cultured airway epithelial cells in a carbohydrate-independent manner, and is therefore proposed to play a role in the dysregulated proinflammatory response observed in B. cenocepacia lung infections. The unique architecture of this newly recognized superlectin correlates with multiple functions including bacterial cell cross-linking, adhesion to human epithelia, and stimulation of inflammation.

Transcriptional responses of Burkholderia cenocepacia to polymyxin B in isogenic strains with diverse polymyxin B resistance phenotypes

Background: Burkholderia cenocepacia is a Gram-negative opportunistic pathogen displaying high resistance to antimicrobial peptides and polymyxins. We identified mechanisms of resistance by analyzing transcriptional changes to polymyxin B treatment in three isogenic B. cenocepacia strains with diverse polymyxin B resistance phenotypes: the polymyxin B-resistant parental strain K56-2, a polymyxin B-sensitive K56-2 mutant strain with heptoseless lipopolysaccharide (LPS) (RSF34), and a derivative of RSF34 (RSF34 4000B) isolated through multiple rounds of selection in polymyxin B that despite having a heptoseless LPS is highly polymyxin B-resistant.