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.

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.

An audit of peripheral catheter care in a teaching hospital.

Post-insertion care of peripheral venous catheters (PVCs) in 100 patients on general medical and surgical wards of a teaching hospital was audited. A variety of methods were used to attach the PVC to the patients' skin including 'Vecafix' dressings, bandages and adhesive tape. Sixty-eight PVC were incorrectly attached, and of these 49 (71%) were associated with two or more symptoms or signs of inflammation at the insertion site. Of those PVC that were correctly attached only five out of 32 (16%) were associated with inflammation. There was a significant association between incorrect dressing application and inflammation (P < 0 center dot 01). Similarly, there was a direct relationship between inflammation and PVCs that had been in situ for greater than 48 h (P < 0 center dot 01). The results suggest that a significant reduction in the incidence of inflammation associated with PVC use may be achieved by correct application of dressings and replacing the catheters after 48 h in situ.

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.

A prospective clinical study to investigate the microbial contamination ofa needleless connector.

Needleless connectors, which allow direct access to intravascular catheters, are widely used in clinical practice. The benefits of these devices to healthcare workers are well documented; however, the potential risk of microbial contamination and associated infection is unclear. This clinical study evaluated microbial contamination rates for a needleless connector, Connecta Clave(R) (CC(R)), as compared to a conventional three-way tap, which was connected to the hubs of central venous catheters (CVC) immediately following insertion. Patients in the study group had CC(R) attached to the three-way taps, whereas the control group had standard entry port caps. On removal (up to 72 h) the connectors were studied for microbial contamination. There was no significant difference between the number of three-way taps contaminated on the internal surface with micro-organisms in the control group with entry port caps (19/132, 14%) compared to the group with CC(R) (18/105, 17%). Sixteen percent (27/173) of the CC(R) were contaminated with micro-organisms on the internal surfaces. The external surface of 33% (27/82) of the CC(R) silicone seals were contaminated after clinical use. Micro-organisms were also isolated from 9% (8/91) of the silicone seals after disinfection. The use of this needleless connector, compared to standard caps therefore does not appear to increase the risk of infection via the internal lumen of three-way taps.

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.

An audit programme for central venous catheter-associated infections.

Central venous catheters (CVC) are commonly associated with both localized and systemic infection. This paper describes an audit programme which was designed to review clinical practice associated with the insertion and subsequent care of CVC and their possible relationship to the development of infection. The programme was produced by a joint working group of the Hospital Infection Society and the Research Unit of the Royal College of Physicians and is subdivided into an audit of hospital practices and patient management associated with the use of CVC. It consists of a number of questions designed to evaluate all areas of CVC use, including the assessment of the incidence of associated local and systemic infection. Use of the questionnaire should allow policies for CVC insertion and care to be reviewed thereby, facilitating improvements, which may in turn reduce the incidence of infection associated with CVC.

Genotypic and phenotypic properties of coagulase-negative staphylococci causing dialysis catheter-related sepsis.

Sixty coagulase-negative staphylococcus (CNS) isolates were recovered from the blood cultures or peritoneal dialysate effluent of 43 patients on renal dialysis. The patients had either renal dialysis catheter-related sepsis (CRS) or continuous ambulatory peritoneal dialysis (CAPD)-associated peritonitis. Isolates were characterized by biotyping, and genotyped by pulsed-field gel electrophoresis (PFGE). Phenotypic properties of the strains were also investigated. Several genotypes were identified with no one specific strain of CNS being associated with CRS. However, closely related strains were isolated from several patients within the units studied, suggesting horizontal transfer of micro-organisms. Genotypic macro-restriction profiles did not concur with phenotypic profiles or biotypes, confirming that genotyping is required for epidemiological studies. All staphylococcal strains were investigated for the production of phenotypic characteristics. Significant differences were predominantly seen in the production of lipase, esterase and elastase in strains isolated from the renal patients with CRS and CAPD-associated peritonitis, compared with a non-septic control group. These phenotypic characteristics may therefore have a role in the maintenance of CRS in renal patients.

The influence of aldose reductase on the oxidative burst in diabetic neutrophils.

Lucigenin-enhanced chemiluminescence was examined as an index of neutrophil superoxide production in four groups of 20 subjects: controls with/without infection and type 1 diabetics with/without infection. At 5 mM glucose there was no significant difference in chemiluminescence output between neutrophils from the four groups (P greater than 0.01). Increasing the in vitro glucose concentration from 5 to 20 mM produced an 8.75% reduction in superoxide in the combined control groups, compared with a 21.45% reduction in the diabetic subjects (P less than 0.01). With the addition of an aldose reductase inhibitor (Statil, ICI) to neutrophils from diabetic subjects, the suppression caused by an increase in glucose concentration to 20 mM was reduced to 4.5%. This value was similar to the controls (P greater than 0.01). Neutrophil aldose reductase activity, measured in 28 diabetic subjects was 0.024 +/- 0.003 U/10(8) cells (mean +/- SE). There was a significant correlation between aldose reductase activity and superoxide suppression (P less than 0.01, r = 0.64). These results suggest that aldose reductase is responsible for reduced superoxide production in diabetic patients and the addition of an aldose reductase inhibitor to the diabetic neutrophil restores superoxide output to control values.

The potential reduction of microbial contamination of central venous catheters.

The microbial contamination of stopcock entry ports attached to central venous catheters (CVC) was determined using a specially designed swab. The swab was made of a highly porous material, Porex, and was designed to fit exactly into the entry port of stopcocks. The swab was used to determine the frequency of microbial contamination of entry ports attached to CVC in patients located on an Intensive Care Unit. Of the 200 swabs obtained 44 (22%) contained microorganisms. Coagulase-negative staphylococci were recovered from 43 of the swabs and diphtheroid bacilli from 1 swab. In vitro studies were carried out to investigate the efficiency of the swab in removing excess residual fluid and organisms from entry ports. The swab absorbed relatively large numbers of bacteria within seconds. When entry ports were inoculated with between 10(3) and 10(5) cfu of either Staphylococcus epidermidis or Klebsiella pneumoniae greater than 99% of the organisms were absorbed by the swab (P < 0.01). The absorbent swab was more efficient at removing S. epidermidis from the entry port when compared to a standard cotton swab (P < 0.01). In vitro this absorbent swab reduced the potential for catheter contamination resulting from migration of organisms from the entry port via the intraluminal route. The use of the swab in the clinical situation may reduce the incidence of CVC-related infections.

The effects of electric current on bacteria colonising intravenous catheters.

The effect of a direct electric current (10 microA) on the growth of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis was investigated. When the ends of negatively-charged intravascular catheters were placed in nutrient agar seeded with bacteria, circular zones of inhibition of bacterial growth were observed around the catheters. The zones ranged from 6 to 16 mm in diameter according to the organism under test. Zones of inhibition were not produced around positively-charged catheters. Bacteria colonising the surfaces of catheters were similarly affected by the application of a 10 microA electric current. A negative electric current applied to colonised catheters for 4 to 24 h significantly reduced the number of adherent viable organisms as compared to controls. The results demonstrated that a constant electric current of low amperage might be used to reduce bacterial colonisation of intravascular catheters. This may offer a novel means of protecting catheters and other prosthetic devices from associated sepsis in vivo.

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 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.

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.

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.

Modification of central venous catheter polymers to prevent in vitro microbial colonisation.

The efficacy of an antimicrobial catheter for the prevention of bacterial colonisation was investigated. The catheter was hydrophilic coated (Hydrocath) and impregnated with the quaternary ammonium antimicrobial agent, benzalkonium chloride (BZC). Microbial colonisation of this central venous catheter was compared to that of polyurethane catheters with or without a hydrophilic coating. Adherence of five strains of Staphylococcus epidermidis to the three catheter types was determined with a microbial colonisation model. Adherence of three strains of Staphylococcus epidermidis to Hydrocath catheters was significantly reduced in comparison to polyurethane catheters (p < 0.01). BZC-impregnated Hydrocath catheters prevented bacterial colonisation of both the internal and external catheter surfaces (p < 0.01). These results were confirmed by scanning electron microscopy. The findings demonstrate that hydrophilic-coated Hydrocath catheters can inhibit bacterial adherence in vitro. Bacterial colonisation was further restricted by the addition of BZC to these coated catheters.

A novel antimicrobial central venous catheter impregnated with benzalkonium chloride.

Catheter-related sepsis is a common complication associated with the use of central venous catheters (CVC). In an attempt to overcome this problem benzalkonium chloride was incorporated into a CVC polymer. The effect of the presence of benzalkonium chloride on microbial colonization of the CVC was then assessed in vitro. MICs and MBCs of benzalkonium chloride for a range of organisms were performed and good activity against Gram-positive organisms was confirmed. In order to assess the antimicrobial activity of the benzalkonium-chloride-impregnated catheter, 2 cm lengths were placed on to nutrient agar plates inoculated with various micro-organisms. Zones of inhibition against five strains of Staphylococcus epidermidis and two strains of Staphylococcus aureus were demonstrated. Smaller zones of inhibition was also produced with Gram-negative species and Candida albicans. The zone sizes correlated with the MICs. Bacterial adherence to the benzalkonium-chloride-impregnated catheters was determined in both static and dynamic models and was significantly reduced compared with control catheters, containing no antimicrobial agent (P < 0.01). Inhibition of microbial adherence to benzalkonium-chloride-impregnated catheters placed in 25% human blood in phosphate-buffered saline (PBS), for up to seven days or PBS alone for 14 days was detected. The findings indicate that benzalkonium-chloride-impregnated catheters exhibit reduced microbial colonization by a range of organisms in vitro. The incorporation of benzalkonium chloride into a CVC may thus offer an effective method for the prevention of catheter related sepsis.

The role of aldose reductase inhibition in diabetic neutrophil phagocytosis and killing.

This study examines whether an aldose reductase inhibitor (statil, ICI) can enhance neutrophil oxidative killing by diabetic neutrophils. We have examined a radiometric assay of phagocytosis and killing of Candida albicans by neutrophils from 20 controls and 20 subjects with insulin-dependent diabetes under various in vitro glucose concentrations. Glucose was present at 5, 10 and 20 mM in the presence and absence of statil (11 microM). Phagocytosis was unaffected by raised glucose levels in controls and in diabetic subjects. Killing by the diabetic cells was inhibited by increasing concentrations of glucose, killing was 18.9 +/- 2.0, 16.9 +/- 2.4 and 14.8 +/- 2.0% (mean +/- s.e.m.) at 5, 10 and 20 mM glucose, respectively (P less than 0.05). With the addition of statil under the same conditions killing improved to 19.3 +/- 2.0, 23.2 +/- 2.2 and 23.6 +/- 2.4 (P less than 0.01), these values were similar to the controls (P greater than 0.01). We conclude therefore that aldose reductase inhibition restores oxidative killing to normal.