Identification of a broadly active phage lytic enzyme with lethal activity against antibiotic-resistant Enterococcus faecalis and Enterococcus faecium

Enterococcus faecalis and Enterococcus faecium infections are increasingly difficult to treat due to high levels of resistance to antibiotics. PlyV12, a bacteriophage lytic enzyme, was isolated and shown to effectively kill both E. faecalis and E. faecium (including vancomycin-resistant strains), as well as other human pathogens. We propose its development and use as an alternative therapeutic tool.

Evolution of a molecular switch: universal bacterial GTPases regulate ribosome function

The GTPases comprise a protein superfamily of highly conserved molecular switches adapted to many diverse functions. These proteins are found in all domains of life and often perform essential roles in fundamental cellular processes. Analysis of data from genome sequencing projects demonstrates that bacteria possess a core of 11 universally conserved GTPases (elongation factor G and Tu, initiation factor 2, LepA, Era, Obg, ThdF/TrmE, Ffh, FtsY, EngA and YchF). Investigations aimed at understanding the function of GTPases indicate that a second conserved feature of these proteins is that they elicit their function through interaction with RNA and/or ribosomes. An emerging concept suggests that the 11 universal GTPases are either necessary for ribosome function or transmitting information from the ribosome to downstream targets for the purpose of generating specific cellular responses. Furthermore, it is suggested that progenitor GTPases were early regulators of RNA function and may have existed in precursors of cellular systems driven by catalytic RNA. If this is the case, then a corollary of this hypothesis is that GTPases that do not bind RNA arose at a later time from an RNA-binding progenitor that lost the capability to bind RNA.

Staphylococcus aureus Targets the Duffy Antigen Receptor for Chemokines (DARC) to Lyse Erythrocytes

In order for Staphylococcus aureus to thrive inside the mammalian host, the bacterium has to overcome iron scarcity. S. aureus is thought to produce toxins that lyse erythrocytes, releasing hemoglobin, the most abundant iron source in mammals. Here we identify the Duffy antigen receptor for chemokines (DARC) as the receptor for the S. aureus hemolytic leukocidins LukED and HlgAB. By assessing human erythrocytes with DARC polymorphisms, we determined that HlgAB- and LukED-mediated lysis directly relates to DARC expression. DARC is required for S. aureus-mediated lysis of human erythrocytes, and DARC overexpression is sufficient to render cells susceptible to toxin-mediated lysis. HlgA and LukE bind directly to DARC through different regions, and by targeting DARC, HlgAB and LukED support S. aureus growth in a hemoglobin-acquisition-dependent manner. These findings elucidate how S. aureus targets and lyses erythrocytes to release one of the scarcest nutrients within the mammalian host.

The effects of Staphylococcus aureus leukotoxins on the host: cell lysis and beyond

The success of Staphylococcus aureus as a leading cause of deadly hospital-acquired and community-acquired infections is attributed to its high-level resistance to most antibiotics, and the multitude of virulence factors it elaborates. Most clinical isolates produce up to four bi-component pore-forming toxins capable of lysing cells of the immune system. Subtle differences in activity and target range of each leukotoxin suggest that these toxins are not redundant, but instead may have specialized functions in attacking and/or evading host defenses. In turn, the host has developed countermeasures recognizing sublytic levels of leukotoxins as signals to activate protective immune defenses. The opposing cytotoxic and immune-activating effects of leukotoxins on host cells make for a complex dynamic between S. aureus and the host.

PlyPH, a bacteriolytic enzyme with a broad pH range of activity and lytic action against Bacillus anthracis

We have cloned a lytic enzyme, PlyPH, with a specific lytic effect on Bacillus anthracis strains. PlyPH remains active between pH 4 and 10.5, and a single dose rescued a significant percentage of mice infected intraperitoneally with an attenuated B. anthracis strain. We propose PlyPH as a novel therapeutic agent.

High levels of antibody to panton-valentine leukocidin are not associated with resistance to Staphylococcus aureus-associated skin and soft-tissue infection

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) expressing Panton-Valentine leukocidin (PVL) causes severe skin and soft-tissue infection (SSTI), necrotizing pneumonia, and other invasive infections. The PVL toxin has been implicated as a virulence factor, and antibody to a component of this toxin is under investigation as a vaccine candidate. The role of PVL in pathogenesis remains controversial, and it is unknown whether human serum antibody to PVL modulates infection.

METHODS

We determined antibody levels to PVL in serum samples from children aged 0-18 years presenting with polymerase chain reaction-confirmed, PVL-positive MRSA-associated SSTI (with or without prior MRSA infection or SSTI), PVL-positive MRSA invasive infection, and PVL-negative MRSA infection, as well as uninfected control subjects. We also measured antibody-mediated neutralization of PVL-induced lysis of human polymorphonuclear cells.

RESULTS

Antibody to PVL was present in healthy children reaching adult levels by 4-6 years, with a nadir at 3-11 months likely due to loss of maternal antibody. Children with a primary PVL-positive MRSA infection had moderate levels of antibody to PVL that increased after infection. Children with prior MRSA infection or SSTI had high levels of antibody to PVL after the onset of PVL-positive MRSA infection. There was no increase in antibody to PVL in this population's serum samples after the onset of infection. Serum samples from children with PVL-positive MRSA-associated SSTIs, particularly those with prior MRSA infection or SSTI, and convalescent-phase serum samples from children with invasive PVL-positive MRSA infection potently inhibited PVL-induced lysis of polymorphonuclear cells.

CONCLUSIONS

Neutralizing antibody to PVL does not protect children against primary or recurrent CA-MRSA-associated SSTI.

Single-copy vectors for integration at the SaPI1 attachment site for Staphylococcus aureus

We have previously reported the construction of Staphylococcus aureus integration vectors based on the staphylococcal pathogenicity island 1 (SaPI1) site-specific recombination system. These are shuttle vectors that can be propagated in Escherichia coli, which allows for standard DNA manipulations. In S. aureus, these vectors are temperature-sensitive and can only be maintained at non-permissive (42 °C) temperatures by integrating into the chromosome. However, most S. aureus strains are sensitive to prolonged incubations at higher temperatures and will rapidly accumulate mutations, making the use of temperature-sensitive integration vectors impractical for single-copy applications. Here we describe improved versions of these vectors, which are maintained only in single-copy at the SaPI1 attachment site. In addition, we introduce several additional cassettes containing resistance markers, expanding the versatility of integrant selection, especially in strains that are resistant to multiple antibiotics.

Counter inhibition between leukotoxins attenuates Staphylococcus aureus virulence

Staphylococcus aureus subverts host defences by producing a collection of virulence factors including bi-component pore-forming leukotoxins. Despite extensive sequence conservation, each leukotoxin has unique properties, including disparate cellular receptors and species specificities. How these toxins collectively influence S. aureus pathogenesis is unknown. Here we demonstrate that the leukotoxins LukSF-PV and LukED antagonize each other's cytolytic activities on leukocytes and erythrocytes by forming inactive hybrid complexes. Remarkably, LukSF-PV inhibition of LukED haemolytic activity on both human and murine erythrocytes prevents the release of nutrients required for in vitro bacterial growth. Using in vivo murine models of infection, we show that LukSF-PV negatively influences S. aureus virulence and colonization by inhibiting LukED. Thus, while S. aureus leukotoxins can certainly injure immune cells, the discovery of leukotoxin antagonism suggests that they may also play a role in reducing S. aureus virulence and maintaining infection without killing the host.

Staphylococcus aureus strains produce a family of highly related toxins that puncture the cytoplasmic membrane of susceptible cells. Here, Yoong and Torres show that the toxins can counteract each other in a cell type-dependent manner by forming inactive hybrid complexes, thus modulating S. aureus virulence.

Staphylococcus aureus corneal infections: effect of the Panton-Valentine leukocidin (PVL) and antibody to PVL on virulence and pathology

PURPOSE

Community-associated methicillin-resistant Staphylococcus aureus strains expressing Panton-Valentine leukocidin (PVL) are associated with severe skin and soft tissue infections, necrotizing pneumonia, and eye infections. We determined PVL's toxicity on infected mouse and cultured human corneal epithelial cells and the role of PVL and antibody to PVL in pathogenesis of murine keratitis.

METHODS

Cytotoxicity on corneas and corneal epithelial cells was evaluated by LDH assays. Scratched corneas of female A/J mice were inoculated with approximately 10⁷ CFU/eye of either WT S. aureus, isogenic ΔPVL, or strains overproducing PVL. Antibodies to PVL or control sera were topically applied to infected corneas 0, 24, and 32 hours postinfection, corneas scored for pathology and tissue levels of S. aureus were determined.

RESULTS

PVL expression augmented the cytotoxicity of S. aureus on infected mouse corneas and human cultured corneal epithelial cells. Variable effects on leukocyte recruitment, pathogenesis, and immunity were obtained in the in vivo studies. Inactivation of PVL in USA300 strains caused reduced pathology and bacterial counts. Results were variable when comparing WT and ΔPVL USA400 strains, while USA400 strains overproducing PVL caused increased bacterial burdens. Topical treatment with polyclonal antibody to PVL yielded significant reductions in corneal pathology and bacterial CFU in corneas infected with USA300 strains, whereas effects were inconsistent in eyes infected with USA400 strains.

CONCLUSIONS

PVL enhanced the virulence of a subset of MRSA strains in a keratitis model. Coupled with a variable effect of antibody treatment, it appears that PVL plays an inconsistent role in pathogenesis and immunity to S. aureus corneal infection.

An rpsL-based allelic exchange vector for Staphylococcus aureus

Staphylococcus aureus is one of the most successful bacterial pathogens, harboring a vast repertoire of virulence factors in its arsenal. As such, the genetic manipulation of S. aureus chromosomal DNA is an important tool for the study of genes involved in virulence and survival in the host. Previously reported allelic exchange vectors for S. aureus are shuttle vectors that can be propagated in Escherichia coli, so that standard genetic manipulations can be carried out. Most of the vectors currently in use carry the temperature-sensitive replicon (pE194ts) that was originally developed for use in Bacillus subtilis. Here we show that in S. aureus, the thermosensitivity of a pE194ts vector is incomplete at standard non-permissive temperatures (42 °C), and replication of the plasmid is impaired but not abolished. We report rpsL-based counterselection vectors, with an improved temperature-sensitive replicon (pT181 repC3) that is completely blocked for replication in S. aureus at non-permissive and standard growth temperature (37 °C). We also describe a set of temperature-sensitive vectors that can be cured at standard growth temperature. These vectors provide highly effective tools for rapidly generating allelic replacement mutations and curing expression plasmids, and expand the genetic tool set available for the study of S. aureus.

Regional inequality in radiology research output in the UK: a 5-year bibliometric study

The objective of this study was to describe the patterns of peer-reviewed general radiology publication rates with reference to deaneries in the UK. This was a retrospective bibliometric analysis of publications in the six highest cited general radiology journals. Publications were identified using a manual search in PubMed between 2005 and 2009. Publications originating from UK radiology departments were identified and subcategorised into primary institution of origin, deanery and publication type. The total number of radiology trainees in each deanery was obtained from the General Medical Council. 913 publications were included in the study. Original papers constituted 48.7% (n=445), review articles 30.3% (n=277) and case reports 17.4% (n=159). The median number of publications in each deanery was 27 [interquartile range (IQR) 11-60], and the median number of publications per trainee was 0.49 (IQR 0.31-0.88). The largest proportion of publications came from the London deanery (n=354, 38.8%), followed by Eastern 86 (9.4%), Oxford and Yorkshire 70 (7.7% each). Relative to the number of trainees within each deanery, Oxford had the highest number of publications per trainee (1.78), followed by East Midlands (1.5), London (1.25) and Eastern (0.99). There was a significantly higher publication rate for those deaneries with academic radiologists (p<0.0001). There is a marked difference in the volume of published work in the general radiology literature among UK deaneries, even accounting for differences in the number of trainees. This probably means that opportunities for training in research are similarly non-uniform.

Enhancement of bacterial virulence by antibody neutralization of immune-activating toxins

Bacterial pathogens release a number of toxins that are able to form pores in target host cells, which can result in their destruction. Due to this property of this subgroup of toxins, they are considered virulence factors. A lesser known ability of these toxins when present at lower concentrations that are insufficient for host cell lysis to occur, is their activation of host immune cells. The Panton-Valentine Leukocidin (PVL) secreted by an alarming percentage of Staphylococcus aureus causing community-acquired infections, is one such: toxin. Due to the low inoculum of S. aureus we used to establish skin abscesses in a murine model of infection, lower amounts of PVL are likely to be present early in infection, hence, the proinflammatory properties of PVL may be more evident. Our data not only suggested that this was indeed the case, but we also showed that antibodies directed to PVL neutralized immune activation by this toxin resulting in a less robust host innate immune response. Thus, given the high levels of antibodies to PVL present in healthy individuals, these antibodies may directly enhance the virulence of PVL-producing S. aureus by dampening the innate immune response to infection. Since many pore-forming toxins share this dual property of concentration-dependent host cell lysis and immune activation, it is interesting to speculate that antibodies raised to some bacterial toxins may have the opposite intended outcome of directly enhancing bacterial virulence instead of controlling infection.

Ulnar nerve palsy after open carpal tunnel decompression: Case report and review of the literature

Open carpal tunnel release is the commonest surgical treatment of median nerve compression at the wrist. Although successful in most cases, there are well described complications. We report a case of laceration of the deep motor branch of the ulnar nerve at the level of the hook of hamate following a complicated carpal tunnel decompression. Good surgical technique and knowledge of wrist anatomy are essential for performing this apparently simple procedure safely.

Normal anatomical variants of the menisci and cruciate ligaments that may mimic disease

There are many normal anatomical variants of the knee joint. Some are common and others are rare. With continuing improvements in the spatial resolution of MRI, smaller variants are more clearly demonstrated and can be mistaken for disease. They can all be differentiated from pathological conditions by understanding their anatomy and key differentiating features. This review compares normal variants of the menisci and cruciate ligaments with the pathological disorders that can mimic them.

Ulnar nerve palsy after open carpal tunnel decompression: Case report and review of the literature

open carpal tunnel release is the commonest surgical treatment of median nerve compression at the wrist. although successful in most cases, there are well described complications. we report a case of laceration of the deep motor branch of the ulnar nerve at the level of the hook of hamate following a complicated carpal tunnel decompression. good surgical technique and knowledge of wrist anatomy are essential for performing this apparently simple procedure safely.

Thymic carcinoma - an unusual cause for unilateral breast oedema

An 83-year-old lady presented with oedema of the right breast with no focal masses and was found to have a tumour of thymic origin in the anterior mediastinum. We describe this interesting case along with a review of the causes of unilateral breast oedema.

Genicular Artery embolisation in Patients with Osteoarthritis of the Knee (GENESIS) Using Permanent Microspheres: Long-Term Results

PURPOSE

To report the 2-year follow-up of patients with mild-to-moderate knee osteoarthritis (OA) treated with genicular artery embolisation (GAE) as part of the GENESIS study.

MATERIALS AND METHODS

Forty-six patients, median age = 60 (45-83) underwent GAE using permanent microspheres (100-300 μm). Technical success was defined as embolisation of the targeted genicular arteries. Knee Injury and Osteoarthritis Outcome Score (KOOS) and Visual Analogue Scale (VAS) (0-100 mm) were recorded at baseline, 6 weeks, 3 months, 1, 2 years. Contrast-enhanced MRI knee scans were acquired at baseline and 1 year, and evaluated with the Whole-Organ Magnetic Resonance Imaging Score (WORMS). Functional MRI brain imaging and psychometric assessments were undertaken to investigate correlation between neuropsychological phenotypes and clinical outcome. Adverse events were recorded prospectively.

RESULTS

Technical success was achieved in forty patients (87%). Mean VAS improved from 58.63 (SD = 20.57, 95% CI 52.7-65.5) at baselines to 37.7 at 2-years (SD = 26.3, 95% CI 27.0-47.5). Whole and subgroup KOOS were significantly improved at each timepoint with associated reductions in analgesia usage. WORMS analysis demonstrated significant reduction in synovitis (p < 0.05) with no cases of osteonecrosis. Self-limiting skin discolouration occurred in four patients. A self-limiting groin haematoma and single case of deep-vein thrombosis due to immobilisation were also recorded. Nine patients subsequently underwent knee arthroplasty with no additional operational complexities identified. Neuropsychometric assessment elucidated a correlation between baseline catastrophising and greater reduction in pain post GAE.

CONCLUSION

GAE is a safe intervention for mild-moderate knee osteoarthritis, with sustained efficacy at 2 years. These results are promising and justify ongoing controlled trials.