Adding α,α-disubstituted and β-linked monomers to the genetic code of an organism

The genetic code of living cells has been reprogrammed to enable the site-specific incorporation of hundreds of non-canonical amino acids into proteins, and the encoded synthesis of non-canonical polymers and macrocyclic peptides and depsipeptides1-3. Current methods for engineering orthogonal aminoacyl-tRNA synthetases to acylate new monomers, as required for the expansion and reprogramming of the genetic code, rely on translational readouts and therefore require the monomers to be ribosomal substrates4-6. Orthogonal synthetases cannot be evolved to acylate orthogonal tRNAs with non-canonical monomers (ncMs) that are poor ribosomal substrates, and ribosomes cannot be evolved to polymerize ncMs that cannot be acylated onto orthogonal tRNAs-this co-dependence creates an evolutionary deadlock that has essentially restricted the scope of translation in living cells to α-L-amino acids and closely related hydroxy acids. Here we break this deadlock by developing tRNA display, which enables direct, rapid and scalable selection for orthogonal synthetases that selectively acylate their cognate orthogonal tRNAs with ncMs in Escherichia coli, independent of whether the ncMs are ribosomal substrates. Using tRNA display, we directly select orthogonal synthetases that specifically acylate their cognate orthogonal tRNA with eight non-canonical amino acids and eight ncMs, including several β-amino acids, α,α-disubstituted-amino acids and β-hydroxy acids. We build on these advances to demonstrate the genetically encoded, site-specific cellular incorporation of β-amino acids and α,α-disubstituted amino acids into a protein, and thereby expand the chemical scope of the genetic code to new classes of monomers.

Cell-of-origin-specific proteomics of extracellular vesicles

The ability to assign cellular origin to low-abundance secreted factors in extracellular vesicles (EVs) would greatly facilitate the analysis of paracrine-mediated signaling. Here, we report a method, named selective isolation of extracellular vesicles (SIEVE), which uses cell type-specific proteome labeling via stochastic orthogonal recoding of translation (SORT) to install bioorthogonal reactive groups into the proteins derived from the cells targeted for labeling. We establish the native purification of intact EVs from a target cell, via a bioorthogonal tetrazine ligation, leading to copurification of the largely unlabeled EV proteome from the same cell. SIEVE enables capture of EV proteins at levels comparable with those obtained by antibody-based methods, which capture all EVs regardless of cellular origin, and at levels 20× higher than direct capture of SORT-labeled proteins. Using proteomic analysis, we analyze nonlabeled cargo proteins of EVs and show that the enhanced sensitivity of SIEVE allows for unbiased and comprehensive analysis of EV proteins from subpopulations of cells as well as for cell-specific EV proteomics in complex coculture systems. SIEVE can be applied with high efficiency in a diverse range of existing model systems for cell-cell communication and has direct applications for cell-of-origin EV analysis and for protein biomarker discovery.

Genetically programmed cell-based synthesis of non-natural peptide and depsipeptide macrocycles

The direct genetically encoded cell-based synthesis of non-natural peptide and depsipeptide macrocycles is an outstanding challenge. Here we programme the encoded synthesis of 25 diverse non-natural macrocyclic peptides, each containing two non-canonical amino acids, in Syn61Δ3-derived cells; these cells contain a synthetic Escherichia coli genome in which the annotated occurrences of two sense codons and a stop codon, and the cognate transfer RNAs (tRNAs) and release factor that normally decode these codons, have been removed. We further demonstrate that pyrrolysyl-tRNA synthetase/tRNA pairs from distinct classes can be engineered to direct the co-translational incorporation of diverse alpha hydroxy acids, with both aliphatic and aromatic side chains. We define 49 engineered mutually orthogonal pairs that recognize distinct non-canonical amino acids or alpha hydroxy acids and decode distinct codons. Finally, we combine our advances to programme Syn61Δ3-derived cells for the encoded synthesis of 12 diverse non-natural depsipeptide macrocycles, which contain two non-canonical side chains and either one or two ester bonds.

Refactored genetic codes enable bidirectional genetic isolation

The near-universal genetic code defines the correspondence between codons in genes and amino acids in proteins. We refactored the structure of the genetic code in Escherichia coli and created orthogonal genetic codes that restrict the escape of synthetic genetic information into natural life. We developed orthogonal and mutually orthogonal horizontal gene transfer systems, which permit the transfer of genetic information between organisms that use the same genetic code but restrict the transfer of genetic information between organisms that use different genetic codes. Moreover, we showed that locking refactored codes into synthetic organisms completely blocks invasion by mobile genetic elements, including viruses, which carry their own translation factors and successfully invade organisms with canonical and compressed genetic codes.

Sense codon reassignment enables viral resistance and encoded polymer synthesis

It is widely hypothesized that removing cellular transfer RNAs (tRNAs)-making their cognate codons unreadable-might create a genetic firewall to viral infection and enable sense codon reassignment. However, it has been impossible to test these hypotheses. In this work, following synonymous codon compression and laboratory evolution in Escherichia coli, we deleted the tRNAs and release factor 1, which normally decode two sense codons and a stop codon; the resulting cells could not read the canonical genetic code and were completely resistant to a cocktail of viruses. We reassigned these codons to enable the efficient synthesis of proteins containing three distinct noncanonical amino acids. Notably, we demonstrate the facile reprogramming of our cells for the encoded translation of diverse noncanonical heteropolymers and macrocycles.

Total synthesis of Escherichia coli with a recoded genome

Nature uses 64 codons to encode the synthesis of proteins from the genome, and chooses 1 sense codon-out of up to 6 synonyms-to encode each amino acid. Synonymous codon choice has diverse and important roles, and many synonymous substitutions are detrimental. Here we demonstrate that the number of codons used to encode the canonical amino acids can be reduced, through the genome-wide substitution of target codons by defined synonyms. We create a variant of Escherichia coli with a four-megabase synthetic genome through a high-fidelity convergent total synthesis. Our synthetic genome implements a defined recoding and refactoring scheme-with simple corrections at just seven positions-to replace every known occurrence of two sense codons and a stop codon in the genome. Thus, we recode 18,214 codons to create an organism with a 61-codon genome; this organism uses 59 codons to encode the 20 amino acids, and enables the deletion of a previously essential transfer RNA.

Labeling and identifying cell-specific proteomes in the mouse brain

We develop an approach to tag proteomes synthesized by specific cell types in dissociated cortex, brain slices, and the brains of live mice. By viral-mediated expression of an orthogonal pyrrolysyl-tRNA synthetase-tRNAXXX pair in a cell type of interest and providing a non-canonical amino acid with a chemical handle, we selectively label neuronal or glial proteomes. The method enables the identification of proteins from spatially and genetically defined regions of the brain.

Tagging and Enriching Proteins Enables Cell-Specific Proteomics

Cell-specific proteomics in multicellular systems and whole animals is a promising approach to understand the differentiated functions of cells and tissues. Here, we extend our stochastic orthogonal recoding of translation (SORT) approach for the co-translational tagging of proteomes with a cyclopropene-containing amino acid in response to diverse codons in genetically targeted cells, and create a tetrazine-biotin probe containing a cleavable linker that offers a way to enrich and identify tagged proteins. We demonstrate that SORT with enrichment, SORT-E, efficiently recovers and enriches SORT tagged proteins and enables specific identification of enriched proteins via mass spectrometry, including low-abundance proteins. We show that tagging at distinct codons enriches overlapping, but distinct sets of proteins, suggesting that tagging at more than one codon enhances proteome coverage. Using SORT-E, we accomplish cell-specific proteomics in the fly. These results suggest that SORT-E will enable the definition of cell-specific proteomes in animals during development, disease progression, and learning and memory.

•

A tetrazine-biotin probe containing a cleavable linker was created

•

Proteomes labeled with cyclopropene amino acids were enriched and identified

•

Proteome coverage is increased by targeting the amino acids to multiple codons

•

Cell-specific proteomics was accomplished in the fly

Genetic code expansion in the mouse brain

Site-specific incorporation of non-natural amino acids into proteins, via genetic code expansion with pyrrolysyl tRNA synthetase (PylRS) and tRNA(Pyl)CUA pairs (and their evolved derivatives) from Methanosarcina sp., forms the basis of powerful approaches to probe and control protein function in cells and invertebrate organisms. Here we demonstrate that adeno-associated viral delivery of these pairs enables efficient genetic code expansion in primary neuronal culture, organotypic brain slices and the brains of live mice.

Proteome labeling and protein identification in specific tissues and at specific developmental stages in an animal

Identifying the proteins synthesized at specific times in cells of interest in an animal will facilitate the study of cellular functions and dynamic processes. Here we introduce stochastic orthogonal recoding of translation with chemoselective modification (SORT-M) to address this challenge. SORT-M involves modifying cells to express an orthogonal aminoacyl-tRNA synthetase/tRNA pair to enable the incorporation of chemically modifiable analogs of amino acids at diverse sense codons in cells in rich media. We apply SORT-M to Drosophila melanogaster fed standard food to label and image proteins in specific tissues at precise developmental stages with diverse chemistries, including cyclopropene-tetrazine inverse electron demand Diels-Alder cycloaddition reactions. We also use SORT-M to identify proteins synthesized in germ cells of the fly ovary without dissection. SORT-M will facilitate the definition of proteins synthesized in specific sets of cells to study development, and learning and memory in flies, and may be extended to other animals.

The prevention of central venous catheter-related sepsis

Intravascular catheters continue to be a major source of sepsis which range from localised inflammation at the site of insertion to septicaemia. There are two main approaches which have been taken in an attempt to prevent these infections. These can be divided into the patient and the catheter. Approaches for prevention with patients include improved aseptic techniques, appropriate choice of antiseptic skin preparations, use of semi-occlusive dressings and cleaning schedules when using the devices. Catheters have also been developed to reduce the incidence of these infections. These include the production of polymers with smooth, anti-adhesive coatings, eg Hydromer, and more recently the introduction of devices which are either coated with antiseptics or antimicrobials. The antimicrobial coatings include antibiotics such as rifampicin and doxycycline or antiseptics, for example benzalkonium chloride or chlorhexidine. The efficacy of these approaches will be reviewed based on both laboratory and clinical studies. The treatment of intravascular catheter-related sepsis depends primarily on establishing the diagnosis. When the diagnosis has been made treatment ranges from the use of antimicrobials alone to removal of the device. More recent approaches have included the use of antibiotic locks within the catheters. Treatment schedules will also be reviewed.

Rapid serodiagnosis of gram-positive bacterial endocarditis

OBJECTIVES

To characterize a serological test for diagnosing endocarditis caused by Gram-positive cocci.

METHODS

We have developed an indirect enzyme-linked immunosorbent assay (ELISA) for the serological detection of Gram-positive infections. The test measures serum IgG directed towards lipid S, a recently identified exocellular glycolipid antigen which is related to lipoteichoic acid. We have previously shown the test to be of value in serodiagnosis of central venous catheter-associated sepsis and infection of orthopaedic prostheses caused by coagulase-negative staphylococci. We now describe the application of this test in endocarditis.

RESULTS

Serum IgG levels to lipid S were significantly elevated in 34 patients with Gram-positive bacterial endocarditis confirmed as 'definite' by the Duke criteria as compared to 50 control patients. The test had a sensitivity of 88% and a specificity of 88%.

CONCLUSIONS

The assay is independent of culture results or endocardial imaging, making it complementary to currently used investigations. It may therefore be possible to refine the current Duke criteria for diagnosing endocarditis. We describe an algorithm which incorporates lipid S serology into a positive diagnostic strategy.

A central venous catheter coated with benzalkonium chloride for the prevention of catheter-related microbial colonization

In an attempt to overcome infections associated with central venous catheters, a new antiseptic central venous catheter coated with benzalkonium chloride on the internal and external surfaces has been developed and evaluated in a clinical trial. Patients (235) randomly received either a triple-lumen central venous catheter coated with benzalkonium chloride (117) or a polyurethane non-antiseptic catheter (118). The incidence of microbial colonization of both catheters and retained antiseptic activity of the benzalkonium chloride device following removal were determined. The benzalkonium chloride resulted in a significant reduction of the incidence of microbial colonization on both the internal and external catheter surfaces. The reduction in colonization was detected at both the intradermal (21 benzalkonium chloride catheters vs. 38 controls, P = 0.0016) and distal segments of the antiseptic-coated catheters. Following catheter removal retained activity was demonstrated in benzalkonium chloride catheters which had been in place for up to 12 days. No patients developed adverse reactions to the benzalkonium chloride catheters. The findings demonstrate that the benzalkonium chloride catheter significantly reduced the incidence of catheter-associated colonization.

Identification of a novel antigen from Staphylococcus epidermidis

A genomic DNA library of Staphylococcus epidermidis NCTC 11047 was constructed, using the Lambda Zap Express cloning vector, and screened with serum collected from a patient with S. epidermidis endocarditis. Sequence analysis of a 30 kDa cloned protein, termed staphylococcal secretory antigen, SsaA, identified a novel protein not previously reported in S. epidermidis. SsaA showed strong homology with two other staphylococcal proteins: SceB from Staphylococcus carnosus and a staphyloxanthin biosynthesis protein from Staphylococcus aureus. Further investigation revealed SsaA to be a highly antigenic protein that was expressed in vivo and could be recovered from whole cells and from the culture supernatant. A combination of Western blot analysis and PCR screening identified SsaA or a homologue in 103/103 staphylococcal strains. SsaA-like genes were not detected in other Gram-positive bacteria of medical importance or a number of Gram-negative organisms. Elevated anti-SsaA IgG antibody levels were detected in sera of five patients with S. epidermidis endocarditis but not in patients with other S. epidermidis infections, endocarditis of other aetiologies or patients with no evidence of infection. The expression of SsaA during episodes of S. epidermidis endocarditis suggests a virulence role specific to the pathogenesis of this infectious disease.

Lipid S, a novel Staphylococcus epidermidis exocellular antigen with potential for the serodiagnosis of infections

We describe the characterisation of a novel glycerophosphoglycolipid (termed lipid S) produced by Staphylococcus epidermidis grown in a chemically defined medium. Lipid S is a short chain length form of the cellular lipoteichoic acid (LTA). It shares common antigenic determinants with LTA, but its chain length of six glycerophosphate units contrasts with 40-42 units in LTA. Lipid S is exocellular and can be recovered from liquid growth medium whereas LTA is associated with the cell wall and membrane. Healthy individuals have low serum levels of IgG against lipid S, but significantly higher titres have been detected in serum from patients with central venous catheter-related sepsis due to coagulase-negative staphylococci and infection of orthopaedic prostheses. An indirect enzyme-linked immunosorbent assay test based on lipid S allows the rapid diagnosis of Gram-positive infection and may have clinical applications in the management of patients with sepsis.

Serological detection of Gram-positive bacterial infection around prostheses

Coagulase-negative staphylococci produce an exocellular glycolipid antigen which has potential as a serological marker of infection in bone. The value of this newly detected antigen was investigated by enzyme-linked immunosorbent assay (ELISA) in 15 patients with culture-proven infection of prostheses caused by Gram-positive bacteria. The antigen was purified by gel-permeation chromatography from the culture supernatants of coagulase-negative staphylococci grown in a chemically defined medium. There were significant differences (p < 0.0001) between the serum IgG and IgM levels in patients with infection due to Gram-positive staphylococci and those of a control group of 32 patients with no infection. The ELISA test, which has potential for the diagnosis of infection, may be valuable in distinguishing between staphylococcal infection around prostheses and aseptic loosening.

Is hospital-acquired intravascular catheter-related sepsis associated with outbreak strains of coagulase-negative staphylococci?

Macrorestriction fragment profile analysis by pulsed field gel electrophoresis was used to type strains of coagulase-negative staphylococci (CNS) isolated from 30 patients with catheter-related sepsis at the University Hospital Birmingham NHS Trust, UK. Twenty-three infections were hospital-acquired. A total of 56 CNS were isolated from the patients and identified by API as Staphylococcus epidermidis (54), Staphylococcus lugdunensis (1) and Staphylococcus hominis (1). The micro-organisms were further characterized by antibiograms and restriction digestion using SmaI. Analysis of the macrorestriction fragment profiles demonstrated that the isolates from 24 patients were distinct, whereas a common genotype of S. epidermidis was isolated from the blood cultures of six patients, all of whom had acquired this infection in hospital. Three of these patients were located in a haematology ward, two on an intensive care unit and one on a dialysis unit. The data from this current study suggests that specific strains of S. epidermidis may be an important cause of nosocomial catheter-related sepsis resulting from cross-infection, and that this association would not be detected by conventional typing methods including biotyping and antibiograms.

Serological evidence of pertussis in patients presenting with cough in general practice in Birmingham

Three hundred and fifty-six patients in a large suburban practice (registered population 10,400), were diagnosed clinically with acute laryngitis/tracheitis or whooping cough (acute spasmodic cough of three weeks duration) between March 1996 and November 1997. Forty out of 145 who provided specimens for serological testing had evidence of recent infection with Bordetella pertussis. During the study a further 18 patients (mostly younger patients who presented early) had a diagnosis of pertussis confirmed by culture. Fifty-eight cases of pertussis in this population and time period was equivalent to an annual incidence of 330 per 100,000, whereas statutory notifications of pertussis in England and Wales suggested an incidence of less than 4 per 100,000 in the same period. Whooping cough remains an important cause of respiratory illness in all age groups. These results are a reminder for general practitioners to be alert to the diagnosis and a prompt to reconsider national vaccination policy.

A novel serological test for the diagnosis of central venous catheter-associated sepsis

OBJECTIVES

To determine the sensitivity and specificity of a novel antibody test for the diagnosis of intravascular catheter-related infections due to coagulase-negative staphylococci.

METHODS

Sixty-seven patients diagnosed as having central venous catheter (CVC)-associated sepsis based on strict clinical criteria, including positive blood cultures, were compared to 67 patients with a CVC in situ who exhibited no evidence of sepsis. An ELISA serological test based on a novel short-chain lipoteichoic acid antigen isolated from coagulase-negative staphylococci (CNS) was used to determine the patient's serological response (IgG and IgM) to CVC sepsis caused by CNS. The specificity and sensitivity of the test was determined.

RESULTS

There was a significant increase in the antibody levels (IgG and IgM) to the short-chain lipoteichoic acid in patients with CVC-associated staphylococcal sepsis as compared to the control patients.

CONCLUSIONS

This new serological method may offer a useful diagnostic test for intravascular catheter infections caused by staphylococci.

Plasmid-mediated vanB glycopeptide resistance in enterococci

Enterococcus faecium, which was highly resistant to vancomycin (MIC 256 mg/liter), but susceptible to teicoplanin (MIC 2 mg/liter), caused two distinct episodes of infection on a renal unit in the United Kingdom. Pulsed field gel electrophoresis (PFGE) indicated that a single strain caused the first episode, while the second episode, which occurred 1 year later, involved multiple strains, all of which were distinct from the original strain. Vancomycin resistance in all but one of these strains was mediated by transferable plasmids that carried the vanB glycopeptide resistance gene. Transfer either of resistance plasmids or the vanB resistance determinant itself to different strains occurred during the second episode. Plasmid-mediated vanB resistance has not been widely documented. A retrospective study of a reference collection revealed two other vanB-encoding plasmids from an E. faecalis and an E. faecium referred from two further UK centers. Although restriction analysis indicated no similarity between the plasmids from the three different centers, all contained a 2.1-kb EcoRV fragment that hybridized with a probe for the vanB gene. This suggests that there has been dissemination of a conserved glycopeptide resistance determinant, of which vanB is a part.

Interferential therapy machines as possible vehicles for cross-infection

Interferential therapy machines are used to apply alternating electric currents to patients for the treatment of various musculo-skeletal complaints. The potential for such machines to transfer skin microflora from one patient to another during treatment was investigated. The efficacy of the current disinfection procedure of the machines was also evaluated. In both the laboratory and clinical situation, interferential treatment, (which involves the direct application of electrodes to the skin surface) resulted in the transfer of micro-organisms from the skin of one subject to another. To decrease the likelihood of transmission of micro-organisms via interferential therapy machines, it is recommended that both the suction cups and sponges are disinfected with 70% isopropyl alcohol after the treatment of each patient. The use of disposable electrodes could also be considered.

The genomic diversity of coagulase-negative staphylococci associated with nosocomial infections

A total of 117 isolates of coagulase-negative staphylococci (CNS) were collected from patients in three medical centres. They were genotyped by pulsed-field gel electrophoresis (PFGE) following digestion with restriction enzymes SmaI and SstII. The isolates included Staphylococcus epidermidis, S. simulans, S. hominis, S. lugdunensis, S. capitis, S. saprophyticus, S. caprae and S. sciuri. They were collected at random from 82 patients and were associated with infected central venous lines, continuous ambulatory peritoneal dialysis (CAPD) catheters, endocarditis, osteomyelitis of prosthetic hips and internally fixed fractures. The genetic heterogeneity of the strains was demonstrated by PFGE profiles and two dendrograms. Though the strains were segregated into species, there was no clustering of the strains by type of infection, associated medical unit or geographical location of the patient. Numerous genotypes were identified, suggesting that no specific strains of CNS are associated with prosthetic related infection.

Antibacterial resistance in the intensive care unit: mechanisms and management

The incidence of multiple antimicrobial resistance of bacteria which cause infections in the intensive care unit is increasing. These include methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, penicillin-resistant Streptococcus pneumoniae and cephalosporin and quinolone resistant coliforms. More recently, pan antibiotic resistant coliforms, including carbapenems, have emerged. The rapidity of emergence of these multiple antibiotic-resistant organisms is not being reflected by the same rate of development of new antimicrobial agents. It is, therefore, conceivable that patients with serious infections will soon no longer be treatable with currently available antimicrobials. Strict management of antibiotic policies and surveillance programmes for multiple resistant organisms, together with infection control procedures, need to be implemented and continuously audited. As intensive care units provide a nidus of infection for other areas within hospitals, this is critically important for prevention of further spread and selection of these resistant bacteria.

Prevention of central venous catheter-related infection

Infections associated with central venous catheters continue to be a major source of sepsis, particularly in hospitalized patients. In developing a strategy for the prevention of these infections, the source and route of invasion of the causative micro-organisms need to be considered. The main source of micro-organisms is the patient's skin. They can gain access to a catheter at the time of insertion, as well as via the external or internal catheter surfaces. Attempts to reduce the incidence of infections range from the type of skin preparation selected, to care of the insertion site post-catheterization. Improvements in catheter design have also reduced the likelihood of infection and include the development of non-leachable smooth catheters with anti-adhesive coatings. More recently, catheters containing antimicrobial agents have become available and preliminary studies have demonstrated a reduction in microbial colonization and associated sepsis. Future preventative strategies may include the application of low voltage electric current in combination with antimicrobials.

Improved recovery of antibiotic-stressed microorganisms on inclusion of saponin in aerobic blood culture media

The recovery rates and times to detection of microorganisms isolated from two similar blood culture media, one containing saponin, were compared. A total of 2117 blood cultures were analysed in a prototype automated blood culture system. Significantly more gram-positive organisms (P<0.05) and gram-negative organisms (P<0.05), including Enterobacteriaceae (P<0.05) were recovered from the lytic medium. Average time to detection in the lytic medium was 15.8 h, compared to 22.7 h in the other medium (P<0.001). The improved recovery of microorganisms was most pronounced in blood samples obtained from patients being treated with antibiotics at the time of venesection. In vitro experiments on antibiotic affected bacteria confirmed the protective effect of saponin.

Role of antimicrobial-impregnated polymer and Teflon in the prevention of biliary stent blockage

Biliary stent blockage and microbial colonization is a common complication associated with polyurethane stents used for the relief of bile-duct obstruction caused by benign or malignant disease. In an attempt to overcome this problem the application of a 'Teflon' (polytetrafluoroethylene) stent and an antimicrobial benzalkonium chloride (BZC) impregnated polymer were investigated. The effects of these materials on microbial colonization were compared to a polyurethane stent in vitro in broth or bile. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of BZC for three commonly isolated biliary stent pathogens, Staphylococcus epidermidis, Enterococcus faecium and Enterobacter cloacae were also determined. All the isolates were sensitive to BZC. The growth kinetics of the three organisms in broth and in human pooled bile were similar. Adherence to the BZC impregnated polymer was significantly reduced as compared to the polyurethane and Teflon stents (P < 0.05) in nutrient broth. In bile, fewer organisms attached to the Teflon as compared with the polyurethane stent (P < 0.05) for all organisms. For two of the three test organisms there was less bacterial adherence to the Teflon than to the BZC impregnated polymer. The Teflon and antimicrobial stent materials studied may prevent biliary stent blockage resulting from microbial colonization.

Evaluation of the in-vitro activity of the glycopeptide antibiotic LY333328 in comparison with vancomycin and teicoplanin

The in-vitro activity of a new glycopeptide antibiotic, LY333328, was compared with vancomycin and teicoplanin against clinical isolates of Staphylococcus aureus, coagulase-negative staphylococci, vancomycin and teicoplanin resistant enterococci, and vancomycin sensitive and resistant enterococci. MIC, MBC, and time-kill kinetics were determined for each agent. LY333328 displayed similar or improved MIC/MBC values in comparison with vancomycin and teicoplanin. Time-kill kinetics for LY333328 demonstrated significantly improved bactericidal activity against the isolates. These findings suggest that LY333328 has improved in-vitro activity over vancomycin and teicoplanin against a range of gram-positive organisms.

Use of pulsed field gel electrophoresis to determine the source of microbial contamination of central venous catheters

Microorganisms detected in situ on the distal tip of central venous catheters (CVC) within 90 min of insertion were investigated using pulsed-field gel electrophoresis to analyse genomic fragments obtained with the SmaI restriction enzyme. Thirty patients received a triple lumen CVC, which was inserted directly through the skin using the Seldinger technique. In a further 30 patients a triple lumen CVC was inserted through a Swan sheath, thereby avoiding direct contact of the CVC with the skin. Staphylococci were isolated from the distal tips of the catheters in 6 patients (5 who had the CVC inserted directly through the skin and 1 who had the CVC inserted via a Swan sheath.) Twenty-three staphylococcal isolates were also isolated from the insertion equipment and the skin swabs surrounding the insertion site of these six patients. All the isolates were genotyped. In one of the patients the organisms isolated from the skin were identical to those on the CVC tip. In two further patients similar organisms were isolated from the insertion equipment and the patients' skin. These results, in addition to the reduced colonisation rates observed when catheters were introduced through a Swan sheath, support the hypothesis that microorganisms from the skin are impacted onto the CVC tip and the CVC insertion equipment at catheter insertion.

The potential for catheter microbial contamination from a needleless connector

Needleless connectors have been widely introduced into clinical practice to allow the connection of syringes and luers to peripheral and central vascular catheters. The potential for microbial contamination of catheters via these devices is currently unclear. A recently introduced connector, the 'Connecta Clave', was assessed by various in-vitro methods. The 'Connecta Clave' is specifically devised to separate external components from the fluid pathway. The compression seals of 50 devices were contaminated with 1 x 10(4) cfu Staphylococcus epidermidis, disinfected with isopropanol, and fluid passed through. Only one device allowed organisms to pass through, despite this challenge, representing a contamination rate of 2%. In comparison, when 50 connectors were challenged with 20 cfu of S. epidermidis, no organisms passed through the device during use. In the clinical situation, after manipulation, < 16 cfu of skin organisms were found associated with the compression seal of the devices. It is, therefore, likely that the contamination rates in clinical practice will be extremely low. Three methods of disinfecting the compression seals and associated rims were also evaluated. A combination of alcohol chlorhexidine spray, followed by a 70% isopropanol swab, resulted in the most efficacious disinfection. The isopropanol swabs produced an adequate disinfection rate. The overall results suggest that by use of specially designed connectors, not only are needlestick injuries reduced, but the likelihood of microbial contamination of catheters via the internal route may also be diminished.

Mechanisms of the bactericidal activity of low amperage electric current (DC)

The mechanisms whereby low amperage (10-100 microA) electric current (DC) is bactericidal were investigated with Staphylococcus epidermidis and Staphylococcus aureus. A zone of inhibition test involving the insertion of an anode and cathode into an agar plate inoculated with a lawn of bacteria was used to study the antimicrobial activity of electric current. A zone of inhibition was produced around the cathode when 10 microA (DC) was applied for 16 h. The diameter of the zone was greatly reduced in the presence of catalase. There was no zone around the cathode when the test was carried out under anaerobic conditions. H2O2 was produced at the cathode surface under aerobic conditions but not in the absence of oxygen. A salt-bridge apparatus was used to confirm that H2O2 was produced at the cathode and chlorine at the anode. The antimicrobial activity of low amperage electric current under anaerobic conditions and in the absence of chloride ions against bacteria attached to the surface of a current carrying electrode was also investigated. Antibacterial activity was reduced under anaerobic conditions, which is compatible with the role of H2O2 as a primary bactericidal agent of electricity associated with the cathode. A reduction in chloride ions did not significantly reduce the antibacterial activity suggesting that chlorine plays only a minor role in the bactericidal activity towards organisms attached to anodal electrode surfaces. The localized production of H2O2 and chlorine and the intrinsic activity due to electric current may offer a useful method for eradicating bacteria from catheter surfaces.

Comparison of serum, salivary, and rapid whole blood diagnostic tests for Helicobacter pylori and their validation against endoscopy based tests

BACKGROUND

A rapid, reliable, and accurate test for the diagnosis of infection with Helicobacter pylori is needed for screening dyspeptic patients before referral for endoscopy.

AIM

To compare a new rapid whole blood test (Helisal rapid blood, Cortecs), two serum enzyme linked immunosorbent assays (ELISAs; Helico-G, Shield and Helisal serum, Cortecs), and a salivary assay (Helisal saliva, Cortecs), with slide biopsy urease, 13C-urea breath test, and histology.

METHODS

Three hundred and three consecutive dyspeptic patients attending for gastroscopy underwent two antral biopsies for histology, and one for rapid slide biopsy urease test for assessment of H pylori status. Blood and saliva were also collected. One hundred of the patients also underwent a 13C-urea breath test. Gold standard positives were defined as those with at least two positive tests among slide urease, breath test, or histology, and gold standard negatives as those with all these (or two when the breath test was not done) negative.

RESULTS

Of 300 patients (median age 63, range 28-89) eligible for analysis, 137 (46%) were gold standard positives, of which Helisal rapid blood identified 116, Helico-G 129, Helisal serum 130, and Helisal saliva 120; 137 (46%) were gold standard negatives of which the number falsely identified as positive was 30 by Helisal rapid blood, 45 by Helico-G, 41 by Helisal serum, and 41 by Helisal saliva. Sensitivities and specificities were: for the whole blood test 85% and 78% respectively; for Helico-G 94% and 67%, for Helisal serum 95% and 70%, and for Helisal saliva 84% and 70%.

CONCLUSIONS

If endoscopy had been undertaken only on patients with positive tests two of 16 duodenal ulcers would have been missed if the Helisal rapid blood test was used, and one if any of the ELISA tests were used. None of the blood tests would have missed any of six gastric ulcers, but the salivary test would have missed one.

Microbial colonization of closed-system suction catheters used in liver transplant patients

The microbial colonization and the associated risk of respiratory infection during the application of a multiple-use closed-system suction catheter (CSSC) and a single-use open-system suction catheter (OSSC) on liver transplant patients was evaluated in this preliminary study. The cost differential for the two systems was also compared. Twenty post-orthotopic liver transplant (OLTx) patients who were mechanically ventilated via an endotracheal (ET) tube were studied. Ten subjects were randomly allocated ET suction by the CSSC and 10 with OSSC. Both groups were similar according to age, sex, clinical severity, presence of a naso-gastric tube, use of H2 antagonists and antibiotics used. Standard protocols were followed to intubate and suction the patients and to change ventilatory equipment. Suctioning performed with the CSSC did not significantly increase the risk of microbial colonization of the respiratory tract. Similarly there was no apparent difference in the incidence of nosocomial pneumonia between the two suction systems, based on the microbiological and clinical data. The mean daily cost of using the CSSC compared to the OSSC was 11.6 times higher. This may be balanced by a reduction in nursing time and reduced risk of spread of infection associated with the CSSC.

Novel approach to investigate a source of microbial contamination of central venous catheters

The potential route of contamination by skin microorganisms onto the distal tip of central venous catheters during insertion was investigated. Thirty patients undergoing cardiac surgery who required a central venous catheter (CVC) as part of their clinical management were studied. Following catheter placement, the device insertion equipment and the skin at the insertion site were sampled for microorganisms. The distal tips of the CVCs were also sampled in situ within 90 min post insertion. Bacteria were isolated from 20 of 30 (66%) CVC skin insertion sites, from 15 of 30 (50%) guidewires, and from five of 30 (16%) catheter distal tips in situ. These findings suggest that despite rigorous skin disinfection and strict aseptic technique, viable microorganisms are impacted during insertion onto the distal tip of the CVC, which may act as a subsequent nidus of infection.

Use of prototype automated blood culture system and gas-liquid chromatography for the analysis of continuous ambulatory peritoneal dialysis associated infection

AIMS

(1) To compare the recovery of organisms from continuous ambulatory peritoneal dialysis (CAPD) effluent fluid obtained from patients with clinical evidence of peritonitis, with an automated system (AS) and the Septichek blood culture system; (2) to evaluate the times to detection of organisms with the two systems; (3) to identify anaerobes from CAPD samples by extended anaerobic culture and gas-liquid chromatography (GLC).

METHODS

168 CAPD effluent fluid samples were studied, representing 157 episodes of peritonitis in 97 patients. CAPD samples were inoculated into two AS bottles-one anaerobic, one aerobic-and a Septichek bottle; samples were also examined for cell count, Gram stain, and direct culture. Culture bottles were then subcultured onto various media, and any organisms isolated were identified. After routine culture, GLC was performed on culture fluid in the anaerobic AS and Septichek bottles. When volatile fatty acids were detected, the broths were cultured anaerobically on specialised medium for a further five days.

RESULTS

147 organisms were isolated from the 168 samples: 96 (57%) yielded growth of significant organisms by direct culture, as compared to 129 (76.8%) by both AS and Septichek. There was no significant difference in isolation rates between AS and Septichek, but time to detection was more rapid with the AS system (p < 0.002). GLC showed volatile fatty acid in 15 specimens; of these, 14 subsequently grew anaerobic organisms.

CONCLUSIONS

AS was comparable to Septichek for numbers of isolations. Speed to detection was faster with the AS, which may be an advantage in management of patients with CAPD peritonitis. GLC showed anaerobes in several cases which would not have been detected without prolonged anaerobic culture; thus anaerobic cultures are recommended for patients who are unresponsive to antimicrobials or who have evidence of bowel perforation.

Do dressings with increased permeability reduce the incidence of central venous catheter related sepsis?

The incidence of catheter-related sepsis associated-with the use of Tegaderm or Opsite IV3000 dressings on 100 critically ill patients with liver disease was studied. All the patients had central venous catheters in situ and they were randomly assigned to one of the two dressings. In this study the sites of insertion were assessed at each dressing change, together with any fluid under the dressing. No statistically significant difference between the two dressings was found in accumulation of fluid, skin microbial colonization, local infection or systemic infection of patients in our sample. There was no apparent advantage to using the more permeable Opsite IV3000 dressing.

Intestinal permeability, gastric intramucosal pH, and systemic endotoxemia in patients undergoing cardiopulmonary bypass

OBJECTIVE

To examine the relationship between gastric intramucosal pH, intestinal permeability, endotoxemia, and oxygen delivery in patients undergoing cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Tertiary care center.

PATIENTS

Fifty patients undergoing elective cardiac surgery and 10 patients awaiting elective cardiac surgery.

INTERVENTIONS

Patients received chromium 51-labeled ethylenediaminetetraacetic acid (51Cr-EDTA) as a marker of intestinal permeability; insertion of a nasogastric tonometer to measure intramucosal pH (pHi); insertion of a pulmonary artery catheter to measure systemic oxygen delivery and consumption variables; arterial blood sampling for plasma endotoxin by the Limulus amebocyte lysate assay; and blood and urine sampling for measurement of 51Cr-EDTA.

MAIN OUTCOME MEASURES

Systemic oxygen delivery, duration of gastric mucosal acidosis, absorption of 51Cr-EDTA, appearance of systemic endotoxemia, renal dysfunction, and duration of hospital stay.

RESULTS

Median (range) 24-hour urinary recovery of 51Cr-EDTA in patients was 10.6% (2.1% to 40.2%) while that in controls was 1.2% (0.7% to 2.0%, P<.001). Intestinal permeability increased during CPB. The median (range) for the lowest pHi after bypass was 6.98 (6.74 to 7.17). The pHi did not decline until CPB was discontinued and the heart took over the load of the circulation. Endotoxin was detectable (>0.2 endotoxin unit per milliliter) in the plasma of 21 patients (42%) during the study, most of whom were endotoxemic by the end of CPB. There was no evident relationship between the degree of gut permeability, endotoxemia, gut ischemia, or systemic oxygen dynamics.

CONCLUSIONS

Cardiopulmonary bypass is associated with increases in gut permeability, which precede gut mucosal ischemia. In cardiac surgical patients, a low pHi is not necessarily indicative of an adverse clinical outcome. Endotoxemia as measured by the Limulus amebocyte lysate assay is common. The increased intestinal absorption of 51Cr-EDTA and gastric mucosal acidosis occur as independent phenomena and are not related in severity or time of onset.