Scanning and transmission electron microscopy of in situ bacterial colonization of intravenous and intraarterial catheters

Biosensor incorporating cell barrier architectures for detecting Staphylococcus aureus alpha toxin

Alpha toxin is a common virulent factor of Staphylococcus aureus and is believed to play crucial roles in pathogenicity induced by S. aureus. Alpha toxin is also known to induce permeability to endothelial cell monolayers in vitro due to the formation of interendothelial gaps. The present study is directed towards measuring alpha toxin using a whole-cell-based biosensor. The biosensor, consisting of a confluent monolayer of human umbilical vein endothelial cells (HUVECs) on a potassium ion-selective electrode, takes advantage of cell permeability dysfunction to detect the presence of small quantities of alpha toxin. When a confluent monolayer of cells was formed on the membrane surface, the response of the electrode toward the marker ion, potassium, was inhibited. Upon exposing this sensor to varying concentrations of alpha toxin for 20 min, an increase in sensor response to potassium was observed. The response thus obtained was indirectly related to the concentration of alpha toxin. The detection limit of this sensor for alpha toxin was found to be 0.1 ng/ml. Cell monolayers were stained with silver nitrate to quantify the formation of intercellular gaps as well as to study the effect of this toxin on HUVECs morphology. A strong positive correlation was observed between the response obtained from the biosensor and the area of the intercellular gaps. Silver staining also revealed the tendency of cells to round up upon being exposed to alpha toxin.

Use of Vancomycin-Containing Lock or Flush Solutions for Prevention of Bloodstream Infection Associated with Central Venous Access Devices: A Meta-Analysis of Prospective, Randomized Trials

BACKGROUND

Prolonged exposure to central venous access devices carries significant risk of device-associated bloodstream infection (BSI), which is associated with morbidity, added health care costs, and attributable mortality. We aimed to determine the efficacy of vancomycin-heparin lock or flush solution in preventing BSI in patients being treated with long-term central venous intravascular devices (IVDs).

METHODS

We collected data from January 1966 to January 2006 from multiple computerized databases and compiled reference lists of identified articles. We identified prospective, randomized controlled trials comparing a vancomycin-heparin lock or flush solution with heparin alone for prevention of BSI associated with long-term central venous IVDs. Using a standardized form, we abstracted data regarding study quality, patient characteristics, and incidence of BSI.

RESULTS

Seven randomized, controlled trials involving a total of 463 patients being treated with IVDs met the inclusion criteria; 5 studies were conducted among patients with cancer, 1 among a critically ill neonatal population, and 1 among patients with cancer or who required parenteral nutrition. We could not detect publication bias. The summary risk ratio with a vancomycin heparin-lock solution for IVD-associated BSI was 0.49 (95% confidence interval [CI], 0.26-0.95; P = .03). Results of the test for heterogeneity were statistically significant; however, when a single study was removed from the analysis, heterogeneity was no longer present. Use of vancomycin as a true lock solution--instilling it for a defined period, rather than simply flushing it directly through the device--conferred a much greater benefit, with a risk ratio of 0.34 (95% CI, 0.12-0.98; P = .04). The 2 studies that performed prospective surveillance cultures to identify colonization or infection by vancomycin-resistant organisms did not find an increased risk.

CONCLUSIONS

Use of a vancomycin lock solution in high-risk patient populations being treated with long-term central IVDs reduces the risk of BSI. The use of an anti-infective lock solution warrants consideration for patients who require central access but who are at high risk of BSI, such as patients with malignancy or low-birthweight neonates.

Fungal—bacterial interactions: a mixed bag of mingling microbes

Fungi and bacteria co-inhabit a wide variety of environments, from soils and food products to plants and mammals. Interactions between bacteria and fungi can have dramatic effects on the survival, colonization and pathogenesis of these organisms. There are instances where bacteria provide fungi with compounds that enhance the production of fungal virulence determinants. Other bacteria produce factors that are likely to inhibit pathogenesis by repressing fungal filamentation. Furthermore, mixed bacterial-fungal biofilms can have properties that are distinct from their single-species counterparts. Clinical studies, in combination with in vitro model systems, are necessary to understand how bacterial-fungal interactions impact human health.

Genetics and genomics of Candida albicans biofilm formation

Biofilm formation by the opportunistic fungal pathogen Candida albicans is a complex process with significant consequences for human health: it contributes to implanted medical device-associated infections. Recent advances in gene expression profiling and genetic analysis have begun to clarify the mechanisms that govern C. albicans biofilm development and acquisition of unique biofilm phenotypes. Such studies have identified candidate adhesin genes, and have revealed that biofilm drug resistance is multifactorial. Newly defined cell-cell communication pathways also have profound effects on biofilm formation. Future challenges include the elucidation of the structure and function of the extracellular exopolymeric substance that surrounds biofilm cells, and the extension of in vitro biofilm observations to newly developed in vivo biofilm models.

A vancomycin-heparin lock solution for prevention of nosocomial bloodstream infection in critically ill neonates with peripherally inserted central venous catheters: a prospective, randomized trial

OBJECTIVE

Critically ill neonates are at high risk for vascular catheter-related bloodstream infection (CRBSI), most often caused by coagulase-negative staphylococci. Most CRBSIs with long-term devices derive from intraluminal contaminants. The objective of this study was to ascertain the safety and the efficacy of a vancomycin-heparin lock solution for prevention of CRBSI.

METHODS

A prospective, randomized double-blind trial was conducted during 2000-2001 at a community hospital level III NICU. Very low birth weight and other critically ill neonates with a newly placed peripherally inserted central venous catheter were randomized to have the catheter locked 2 or 3 times daily for 20 or 60 minutes with heparinized normal saline (n = 43) or heparinized saline that contained vancomycin 25 microg/mL (n = 42). The origin of each nosocomial bloodstream infection (BSI) was studied by culturing skin, catheter hubs, and implanted catheter segments and blood cultures, demonstrating concordance by restriction-fragment DNA subtyping. Surveillance axillary and rectal cultures were performed to detect colonization by vancomycin-resistant organisms. The main outcome measures were (1) CRBSIs and (2) colonization or infection by vancomycin-resistant Gram-positive bacteria.

RESULTS

Two (5%) of 42 infants in the vancomycin-lock group developed a CRBSI as compared with 13 (30%) of 43 in the control group (2.3 vs 17.8 per 1000 catheter days; relative risk: 0.13; 95% confidence interval: 0.01-0.57). No vancomycin-resistant enterococci or staphylococci were recovered from any cultures. Vancomycin could not be detected in the blood of infants who did not receive systemic vancomycin therapy. Twenty-six neonates (8 vancomycin-lock group, 18 control group) had at the end of a catheter-lock period asymptomatic hypoglycemia that resolved promptly when glucose-containing intravenous fluids were restarted.

CONCLUSIONS

Prophylactic use of a vancomycin-heparin lock solution markedly reduced the incidence of CRBSI in high-risk neonates with long-term central catheters and did not promote vancomycin resistance but was associated with asymptomatic hypoglycemia. The use of an anti-infective lock solution for prevention of CRBSI with long-term intravascular devices has achieved proof of principle and warrants selective application in clinical practice.

Noninvasive biophotonic imaging for monitoring of catheter-associated urinary tract infections and therapy in mice

Urinary tract infections (UTIs) are among the most common bacterial infections acquired by humans, particularly in catheterized patients. A major problem with catheterization is the formation of bacterial biofilms on catheter material and the risk of developing persistent UTIs that are difficult to monitor and eradicate. To better understand the course of UTIs and allow more accurate studies of in vivo antibiotic efficacy, we developed a catheter-based biofilm infection model with mice, using bioluminescently engineered bacteria. Two important urinary tract pathogens, Pseudomonas aeruginosa and Proteus mirabilis, were made bioluminescent by stable insertion of a complete lux operon. Segments of catheter material (precolonized or postimplant infected) with either pathogen were placed transurethrally in the lumen of the bladder by using a metal stylet without surgical manipulation. The bioluminescent strains were sufficiently bright to be readily monitored from the outside of infected animals, using a low-light optical imaging system, including the ability to trace the ascending pattern of light-emitting bacteria through ureters to the kidneys. Placement of the catheter in the bladder not only resulted in the development of strong cystitis that persisted significantly longer than in mice challenged with bacterial suspensions alone but also required prolonged antibiotic treatment to reduce the level of infection. Treatment of infected mice for 4 days with ciprofloxacin at 30 mg/kg of body weight twice a day cured cystitis and renal infection in noncatheterized mice. Similarly, ciprofloxacin reduced the bacterial burden to undetectable levels in catheterized mice but did not inhibit rebound of the infection upon cessation of antibiotic therapy. This methodology easily allows spatial information to be monitored sequentially throughout the entire disease process, including ascending UTI, treatment efficacy, and relapse, all without exogenous sampling, which is not possible with conventional methods.

Alteplase as a Catheter Locking Solution: In Vitro Evaluation of Biochemical Stability and Antimicrobial Properties

PURPOSE

To reduce potential complications of fibrin deposition to catheter surfaces, there is increasing empiric use of alteplase as a catheter lock solution. The purpose is to evaluate the properties of alteplase when reconstituted in sterile water (SW) or bacteriostatic water (BW) for prolonged periods.

MATERIALS AND METHODS

Alteplase in glass vials was reconstituted (1 mg/mL) with SW or BW (0.9% benzyl alcohol) in duplicates and stored at 37 degrees C. Biochemical assays were performed at days 0 and 7 and included optical clarity, protein concentration, percent protein monomer, and in vitro clot lysis activity. Microbiologic assays were performed on days 7 through 28 with use of a standardized antimicrobial effectiveness test (pass/fail) and pour-plate methods incubated at 22.5 degrees C (fungus, 3-7 days) or 32.5 degrees C (bacteria, 3-5 days). Organisms tested included Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and Aspergillus niger.

RESULTS

Biochemical assay results were as follows: on day 0, all samples were clear/colorless; protein concentrations were 1.10 mg/mL +/- 0 in SW and 1.11 mg/mL +/- 0 in BW; percent protein monomer was 8.2% +/- 0.07 in SW and 98.6% +/- 0.07 in BW; and in vitro clot lysis activity (in percent of relative activity) was 100% in all samples. On day 7, all samples were clear/colorless, protein concentrations were 1.11 mg/mL +/- 0.07 in SW and 1.11 mg/mL +/- 0.07 in BW; percent protein monomer was 97.4% +/- 0.21 in SW and 96.1% +/- 0.21 in BW; and in vitro clot lysis activity (relative activity compared with day 0) was 91% +/- 2.8 in SW and 90% +/- 2.8 in BW. Microbiologic assays (US Pharmacopeia [USP] antimicrobial effectiveness test) yielded a failing result for alteplase reconstituted in SW and a passing result for alteplase reconstituted in BW.

CONCLUSIONS

Alteplase reconstituted with SW or BW remains relatively stable with retained bioactivity when stored at 37 degrees C for as long as 7 days. Despite the biochemical similarities of the two solutions, only alteplase in BW met USP criteria as an effective antimicrobial solution. Further clinical evaluation is warranted.

Bacterial colonization on different suture materials—A potential risk for intraoral dentoalveolar surgery

In this in vivo and in vitro study on resorbable (Monocryl and nonresorbable (Deknalon) monofilament sutures used in intraoral dentoalveolar surgery the bacterial colonization was compared. For the in vivo study the sutures were applied in 11 patients during dental surgery. Eight days postoperative the sutures were removed and the adhered bacteria were isolated and identified by biochemistry, morphology, antibiotic susceptibility, and gas chromatography. The colonization was studied by scanning electron microscopy. Aerobic and anaerobic bacteria were isolated in nearly equal colony-forming units (cfu) on each suture. In comparison with Monocryl about 15% more aerobic and anaerobic strains were isolated on Deknalon. Regarding the pathogens only, about three times more anaerobic strains were isolated on both sutures in total. Additionally, more pathogens were found on Deknalon than on Monocryl (aerobic >40%, anaerobic >25%). The variety of bacteria correspond with purulent infections, not with normal oral flora. Intraindividual comparisons of cfu showed differences in dependence of the patient as described for subgingivale plaques. For the in vitro study the sutures were incubated with Streptococcus intermedius and Prevotella intermedia for 0.5 h. Scanning electron microscopy was performed to examine qualitatively the level of bacterial adherence. After 0.5 h the bacteria adhered very well. The colonization rate of Streptococcus intermedius on both sutures was similar. Coccoid bacteria within biofilms were seen. The growth of Prevotella intermedia was much better on Deknalon than on Monocryl. The risk of bacteremia at the time of suture removal is discussed.

Punctal Plugs in the Management of Dry Eyes

Punctal plugs appear to be a relatively safe, effective, and reversible method of preserving aqueous and artificial tears on the ocular surface to reduce the signs and symptoms of dry eye. An absorbable plug may be used temporarily to assess the effectiveness of this therapy prior to insertion of a longterm nonabsorbable plug (Freeman-type, Herrick Lacrimal Plug, or SmartPlug) or cautery. Indications and contraindications for use of punctal plugs are discussed, as are features of various plugs, techniques of insertion and removal, complications, and outcomes.

Slime production by clinical isolates of Blastoschizomyces capitatus from patients with hematological malignancies and catheter-related fungemia

In order to expand the present knowledge of the pathogenic potential of Blastoschizomyces capitatus in central venous catheter (CVC)-related bloodstream infections, six strains of the organism recovered from three leukemic patients with CVC-related fungemia in different years were investigated. Isolates and control strains were tested for their genetic relatedness and for their ability to produce slime in glucose-containing solutions. DNA restriction enzyme analysis revealed that all strains of B. capitatus were identical, whereas slime production assays and examination of ex vivo material showed that they were able to produce large amounts of slime. Slime production may therefore play a relevant pathogenic role in cases of CVC-related fungemia caused by B. capitatus.

Interactions of Candida albicans with other Candida spp. and bacteria in the biofilms

AIMS

To study the interactions between Candida albicans and 12 other species of Candida and bacteria in biofilms.

METHODS AND RESULTS

The number of cells within growing biofilms in a polystyrene tube model was measured after adding C. albicans to preformed biofilms of other micro-organisms and vice versa. It was also measured after simultaneous biofilm formation of C. albicans and other micro-organisms. The number of cells of C. albicans within the growing biofilms decreased significantly (P < 0.05) when the fungus was added to preformed biofilms of Candida spp. and bacteria except, with C. parapsilosis, Torulopsis glabrata and the glycocalyx producer Pseudomonas aeruginosa. When C. parapsilosis, Staphylococcus epidermidis (nonglycocalyx producer) or Serratia marcescens was added to preformed biofilms of C. albicans, the number of cells of these micro-organisms increased in the growing biofilms.

CONCLUSIONS

Biofilms of C. albicans are capable of holding other micro-organisms and more likely to be heterogeneous with other bacteria and fungi in the environment and on medical devices.

SIGNIFICANCE AND IMPACT OF THE STUDY

Recognition of the heterogeneity of biofilm-associated organisms can influence treatment decisions, particularly in patients who do not respond to initial appropriate therapy.

Surface glycans of Candida albicans and other pathogenic fungi: physiological roles, clinical uses, and experimental challenges

Although fungi have always been with us as commensals and pathogens, fungal infections have been increasing in frequency over the past few decades. There is a growing body of literature describing the involvement of carbohydrate groups in various aspects of fungal disease. Carbohydrates comprising the cell wall or capsule, or as a component of glycoproteins, are the fungal cell surface entities most likely to be exposed to the surrounding environment. Thus, the fungus-host interaction is likely to involve carbohydrates before DNA, RNA, or even protein. The interaction between fungal and host cells is also complex, and early studies using whole cells or crude cell fractions often produced seemingly conflicting results. What was needed, and what has been developing, is the ability to identify specific glycan structures and determine how they interact with immune system components. Carbohydrate analysis is complicated by the complexity of glycan structures and by the challenges of separating and detecting carbohydrates experimentally. Advances in carbohydrate chemistry have enabled us to move from the foundation of composition analysis to more rapid characterization of specific structures. This, in turn, will lead to a greater understanding of how fungi coexist with their hosts as commensals or exist in conflict as pathogens.

Effect of ammonia on the methanogenic activity of methylaminotrophic methane producing Archaea enriched biofilm

Ammonia is a metabolic product in the decomposition of protein wastes, and has a recognized inhibitory effect on methanogenesis; this effect has been slightly quantified on methanogenic biofilms and particularly those populated by methanogenic Archaea which produce ammonia as a catabolic product from methylated amines. This paper presents studies on the effect of ammonia on maximum methanogenic activity of anaerobic biofilms enriched by methylaminotrophic methane producing Archaea (mMPA). The effect of unionized free ammonia on the specific maximum methanogenic activity of a mMPA enriched biofilm was studied, using 250 mL flasks containing ceramic rings colonized by 30 day-old experimental biofilm and adding 48.8 (control system), 73.8, 98.8, 148.8, 248.8, 448.8 and 848.8 mg NH(3)-N/L. The systems were maintained for ten days at a pH of 7.5 and temperature of 37 degrees C. The results showed that at 848.8 mg NH(3)-N/L, biofilm methane production required 36 h adaptation period, prior to entering into maximum production phase. The highest maximum methanogenic activity reached a value of 2.337+/-0.213 g COD methane/g VSS *day when 48.8 mg NH(3)-N/L was added, and inhibition was clearly observed in those systems above 148.8 mg NH(3)-N/L, producing under 1.658+/-0.185 g COD methane/g VSS *day. The lowest methanogenic activity reached was 0.639+/-0.162 g COD methane/g VSS *day at the system added with 848.8 mg NH(3)-N/L. When applying the Luong and non-competitive inhibition models, the best fit was obtained with the non-competitive model, which predicted 50% inhibition of methanogenic activity at 365.288 mg NH(3)-N/L.

The application of biofilm science to the study and control of chronic bacterial infections

Unequivocal direct observations have established that the bacteria that cause device-related and other chronic infections grow in matrix-enclosed biofilms. The diagnostic and therapeutic strategies that have served us so well in the partial eradication of acute epidemic bacterial diseases have not yielded accurate data or favorable outcomes when applied to these biofilm diseases. We discuss the potential benefits of the application of the new methods and concepts developed by biofilm science and engineering to the clinical management of infectious diseases.

The application of biofilm science to the study and control of chronic bacterial infections

Unequivocal direct observations have established that the bacteria that cause device-related and other chronic infections grow in matrix-enclosed biofilms. The diagnostic and therapeutic strategies that have served us so well in the partial eradication of acute epidemic bacterial diseases have not yielded accurate data or favorable outcomes when applied to these biofilm diseases. We discuss the potential benefits of the application of the new methods and concepts developed by biofilm science and engineering to the clinical management of infectious diseases.

The pathogenesis of catheter-related bloodstream infection with noncuffed short-term central venous catheters

OBJECTIVE

Short-term, noncuffed, percutaneously inserted central venous catheters (CVCs) are widely used and cause more than 250,000 bloodstream infections (BSIs) in hospitals each year in the United States. We report a prospective study undertaken to determine the pathogenesis of CVC-related BSI.

DESIGN AND SETTING

Prospective cohort study in a university hospital 24-bed medical-surgical intensive care unit.

PATIENTS AND PARTICIPANTS

Patients participating in two randomized trials during 1998-2000-one studying the efficacy of a 1% chlorhexidine-75% alcohol solution for cutaneous antisepsis and the other a novel chlorhexidine-impregnated sponge dressing-formed the study population; CVC-related BSIs were considered to be extraluminally acquired if concordance was identified solely between isolates from catheter segments, skin, and blood cultures and intraluminally acquired if concordance was demonstrated only between hub or infusate and blood culture isolates, as confirmed by DNA subtyping of isolates from blood and catheter sites or infusate.

RESULTS

Of 1,263 catheters (6075 CVC days) prospectively studied, 35 (2.7%) caused BSI (5.9 per 1000 CVC days); 27 were caused by coagulase-negative staphylococci. Overall, 45% of infections were extraluminally acquired, 26% were intraluminally derived, and the mechanism of infection was indeterminate in 29%. In the pooled control groups of the two trials, 25 CVC-related BSIs occurred (7.0 per 1000 CVC days), of which 60% of infections were extraluminally acquired, 12% were intraluminally derived and 28% were indeterminate. In contrast, CVC-related BSIs in the treatment groups were most often intraluminally derived (60%, p=0.006).

CONCLUSIONS

Most catheter-related BSIs with short-term percutaneously inserted, noncuffed CVCs were extraluminally acquired and derived from the cutaneous microflora. Strategies achieving successful suppression of cutaneous colonization can substantially reduce the risk of catheter-related BSI with short-term CVCs.

Alpha-toxin is required for biofilm formation by Staphylococcus aureus

Staphylococcus aureus is a common pathogen associated with nosocomial infections. It can persist in clinical settings and gain increased resistance to antimicrobial agents through biofilm formation. We have found that alpha-toxin, a secreted, multimeric, hemolytic toxin encoded by the hla gene, plays an integral role in biofilm formation. The hla mutant was unable to fully colonize plastic surfaces under both static and flow conditions. Based on microscopy studies, we propose that alpha-hemolysin is required for cell-to-cell interactions during biofilm formation.

Human leukocytes adhere to, penetrate, and respond to Staphylococcus aureus biofilms

Staphylococcus aureus is a common pathogen responsible for nosocomial and community infections. It readily colonizes indwelling catheters, forming microbiotic communities termed biofilms. S. aureus bacteria in biofilms are protected from killing by antibiotics and the body's immune system. For years, one mechanism behind biofilm resistance to attack from the immune system's sentinel leukocytes has been conceptualized as a deficiency in the ability of the leukocytes to penetrate the biofilm. We demonstrate here that under conditions mimicking physiological shear, leukocytes attach, penetrate, and produce cytokines in response to maturing and fully matured S. aureus biofilm.

Patterns of infection in patients maintained on long-term peritoneal dialysis therapy with multiple episodes of peritonitis

The causes of peritonitis in patients with end-stage renal disease maintained on long-term peritoneal dialysis (PD) are unclear. One possible explanation for peritonitis, particularly in patients with multiple episodes of infection, is the release of planktonic bacteria from biofilm on the walls of catheters. Bacteria form biofilm on the walls of catheters within 48 hours of their placement. If this explanation were correct, one would expect there to be reappearance of organisms causing infection in patients with multiple episodes of peritonitis. The charts of all patients starting long-term PD at New Haven CAPD from January 1, 1990, through July 31, 2000, were reviewed. Patients were included in the study if they had experienced more than one episode of culture-positive peritonitis and complete data were available concerning cultured organisms and antibiotic sensitivity patterns. Episodes of infection, organisms, and sensitivities and catheter changes were reviewed. Of 630 patients, 198 were identified as meeting these criteria. There were 114 men; 104 patients were white. Of 198 patients, 157 (80%) had at least one repeat infection with the same organism. In 124 (79%) patients, more than 50% of the peritonitis episodes were caused by the same organism. Of 90 patients who had more than four episodes of infection in their history, 59 (65%) had at least half or more of their episodes caused by the same organism. Sequential analyses for independence revealed that for Staphylococcus epidermidis and for Staphylococcus aureus, there was a significantly increased likelihood for these organisms to follow themselves as causative organisms of peritonitis. When the data were analyzed using the Spearman correlation test, the results indicated that the likelihood of repeat infections occurring was significantly greater than by chance alone. Of 67 patients with catheter changes and subsequent peritonitis, only 10 (15%) developed repeat infections with the same organism after the catheter change. Eight of these were due to yeast. These data support the hypothesis that bacterial biofilm on the walls of peritoneal catheters may be associated with peritonitis in patients maintained on long-term PD and may contribute to at least some of these episodes of infection.

The promise of novel technology for the prevention of intravascular device-related bloodstream infection. I. Pathogenesis and short-term devices

Intravascular devices (IVDs) are widely used for vascular access but are associated with substantial risk of development of IVD-related bloodstream infection (BSI). The development of novel technologies, which are based on an understanding of pathogenesis, promises a quantum reduction in IVD-related infections in an era of growing nursing shortages. Infections of short-term IVDs (that is, those in place <10 days), including peripheral venous catheters, noncuffed and nontunneled central venous catheters (CVCs), and arterial catheters, derive mainly from microorganisms colonizing the skin around the insertion site, which most often gain access extraluminally. More-effective cutaneous antiseptics, such as chlorhexidine, a chlorhexidine-impregnated sponge dressing, CVCs with an anti-infective coating, anti-infective CVC hubs, and novel needleless connectors, have all been shown to reduce the risk of IVD-related BSI in prospective randomized trials. The challenge for the future will be to identify new preventative technologies and to begin to adapt more widely those technologies already shown to be efficacious and cost-effective.

Biofilm bacteria: formation and comparative susceptibility to antibiotics

The Calgary Biofilm Device (CBD) was used to form bacterial biofilms of selected veterinary gram-negative and gram-positive pathogenic bacteria from cattle, sheep, pigs, chicken, and turkeys. The minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) of ampicillin, ceftiofur, cloxacillin, oxytetracycline, penicillin G, streptomycin, tetracycline, enrofloxacin, erythromycin, gentamicin, tilmicosin, and trimethoprim-sulfadoxine for gram-positive and -negative bacteria were determined. Bacterial biofilms were readily formed on the CBD under selected conditions. The biofilms consisted of micro-colonies encased in extracellular polysaccharide material. Biofilms composed of Arcanobacterium (Actinomyces) pyogenes, Staphylococcus aureus, Staphylococcus hyicus, Streptococcus agalactiae, Corynebacterium renale, or Corynebacterium pseudotuberculosis were not killed by the antibiotics tested but as planktonic bacteria they were sensitive at low concentrations. Biofilm and planktonic Streptococcus dysgalactiae and Streptococcus suis were sensitive to penicillin, ceftiofur, cloxacillin, ampicillin, and oxytetracycline. Planktonic Escherichia coli were sensitive to enrofloxacin, gentamicin, oxytetracycline and trimethoprim/ sulfadoxine. Enrofloxacin and gentamicin were the most effective antibiotics against E. coli growing as a biofilm. Salmonella spp. and Pseudomonas aeruginosa isolates growing as planktonic populations were sensitive to enrofloxacin, gentamicin, ampicillin, oxytetracycline, and trimethoprim/sulfadoxine, but as a biofilm, these bacteria were only sensitive to enrofloxacin. Planktonic and biofilm Pasteurella multocida and Mannheimia haemolytica had similar antibiotic sensitivity profiles and were sensitive to most of the antibiotics tested. The CBD provides a valuable new technology that can be used to select antibiotics that are able to kill bacteria growing as biofilms.

Rapid diagnosis of fungal infection of intravascular catheters in newborns by scanning electron microscopy

Intravascular catheters carry a significant risk of becoming colonized with bacteria and fungi and are important risk factors of septicemia in premature neonates. The study was undertaken to evaluate whether scanning electron microscopy (SEM) examination of removed catheters can be useful in early diagnosis of plastic infection by Candida, providing information useful for initiation of an eventual therapy. The evolution of biofilms in 28 catheters (umbilical or central) implanted in 24 newborns for prematurity was studied by SEM and transmission electron microscopy (TEM). In 4 of 24 patients, SEM examination revealed the presence of Candida in form of yeast or hyphae. In one of these patients, TEM confirmed the presence of organisms. In each case, hemoculture and culture of the catheter itself confirmed the diagnosis. The study demonstrates that SEM can identify fungi in the biomaterials covering the catheter surface in a few hours, allowing an early diagnosis of plastic infection.

Interaction between biofilms formed by Staphylococcus epidermidis and quinolones

The interaction between pefloxacin, ciprofloxacin, norfloxacin, and ofloxacin and biofilms formed by Staphylococcus epidermidis (20 clinical isolates) was studied. In the presence of 1/2-MIC and 1/8-MIC of quinolones, the optical density of the biofilms was reduced to 22-24% and 65-74% of the controls, respectively. Treatment of preformed biofilms with quinolones in concentrations ranging from 12.5 microg/ml to 400 microg/mL caused reduction in the optical density of the adherent biofilms to 45-77% of the control. In an in vitro model of vascular catheter colonization, subinhibitory concentrations (12, 14 and 1/8 MIC) of fluoroquinolones reduced the number of adherent bacteria to 24-28%, 48-55% and 58-76% of the controls, respectively. The vascular catheter segments precolonized with Staphylococcus epidermidis for 24 h and exposed to the fluoroquinolones in 8-16 times MIC (100 microg/mL) for 2 h showed no growth of adherent cells. The activity of pefloxacin in reducing the bacterial adhesion and eradicating the preformed biofilms was demonstrated by scanning electron microscope. These data show that subinhibitory concentrations of ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin inhibit the adhesion of Staphylococcus epidermidis to plastic surfaces and vascular catheters. Higher concentrations of fluoroquinolones were able to eradicate the preformed biofilms on vascular catheters.

The detection of bacteria and bacterial biofilms in punctal plug holes

PURPOSE

An investigation into bacterial biofilm formation on and in punctal plugs.

METHODS

The study involved 21 patients with severe dry eye whose puncta were occluded by the use of punctal plugs. Of these, 15 had Sjögren's syndrome, 3 had non-Sjögren's syndrome, 2 had Stevens-Johnson syndrome, and 1 had graft-versus-host disease. From 17 of the 21 subjects, 18 samples of material were extracted from the holes of the punctal plugs (16 unilateral and 1 bilateral) and were subjected to enrichment culture. Nineteen punctal plugs were removed and processed for electron microscopy: 15 by scanning electron microscopy, and 4 by transmission electron microscopy.

RESULTS

Positive cultures were found in 8 of 18 (44%) samples of the material extracted from the holes of punctal plugs. In six of these eight cases (75%) the cultured bacterial species was Staphylococcus epidermidis, whereas in the other two cases (25%) it was S. aureus. In 8 of the 15 punctal plugs examined by scanning electron microscopy and in the material extracted from 1 plug that was examined by transmission electron microscopy, there was clear evidence of bacterial colonization.

CONCLUSION

Careful observation of patients with punctal plugs is important. If material accumulates in or on a punctal plug, it may contain bacteria and may form a bacterial biofilm. In these cases, replacement of the plug, clearing of the hole, or an alternative treatment should be considered.

Bacterial colonization of functionalized polyurethanes

A protocol was developed for studying the growth of bacteria upon polyurethanes subsequent to the establishment of an adherent bacterial population. An inocula of approximately 10(5) cfu S. aureus were spread on functionalized polyurethanes which included Pellethane, sulfonated Pellethane, phosphonated Pellethane, quaternized amine polyurethanes, and a zwitterionic phosphonated polyurethane. After 24 h incubation, Pellethane, sulfonated Pellethane, and phosphonated Pellethane showed bacterial growth by at least a factor of 10. In contrast, the zwitterionic phosphonated polyurethane showed a factor of 10 decrease in bacteria after 24 h and the quaternized amine polyurethanes reduced the bacteria to only a few hundred after only 1 h. When treated with bovine serum albumin, Pellethane, sulfonated Pellethane, and phosphonated Pellethane again showed bacterial growth by as much as a factor of 10 over 24 h. The quaternized amine polyurethanes and the zwitterionic phosphonated polyurethane still exhibited bactericidal abilities even when coated with bovine serum albumin, with the zwitterionic material reducing bacteria by more than a factor of 10 over 24 h and the quaternized amine polyurethane reducing the bacteria to only a few hundred after only 1 h. A zone of inhibition study suggested that the bactericidal activity of the zwitterionic phosphonated polyurethane was due to the leaching of cadmium ions. A quaternized amine polyurethane which contained chloride instead of iodide as the counterion to the amine moiety was less bactericidal than the iodide-containing polymer when treated with albumin. Thus, bacteria were able to colonize Pellethane, phosphonated sulfonated Pellethane, and phosphonated Pellethane, but the iodide-containing quaternized amine polyurethane and the zwitterionic polyurethane prevented colonization.

Molecular mechanisms of Staphylococcus epidermidis biofilm formation

Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the predominant cause of implanted medical-device related infections. The formation of adherent multi-layered biofilms embedded into a glycocalyx composed of exopolysaccharides on implanted devices is believed to be essential for the pathogenesis of S. epidermidis infections. Biofilm formation may be separated into primary attachment of bacteria to native or modified polymer surfaces followed by proliferation of attached bacterial cells leading to accumulation of multi-layered cell-clusters and glycocalyx formation. Recent progress in the understanding of the molecular mechanisms cooperating in S. epidermidis biofilm formation is reviewed and current thinking on the relevance of these mechanisms for S. epidermidis device-related infections is discussed.

High and low pressure pulsatile lavage of contaminated tibial fractures: an in vitro study of bacterial adherence and bone damage

OBJECTIVE

This study was designed to examine the effect of pulsatile irrigation on microscopic bone architecture and its time-dependent efficacy in removing adherent slime-producing bacteria from cortical bone.

DESIGN

Using an in vitro model, ten-millimeter transverse cut sections from five human tibiae were contaminated with Staphylococcus aureus and subjected to either high pressure pulsatile lavage (HPPL; seventy pounds per square inch, normal saline) or low pressure pulsatile lavage (LPPL; fourteen pounds per square inch, normal saline) or served as controls. Alteration of bony architecture was quantified by using a previously described ordinal scale and histomorphometric analysis of each transverse cut section of tibia. To assess the time-dependent effectiveness of pulsatile lavage in removing adherent bacteria from bone, ten-millimeter transverse cut sections from ten canine tibiae were contaminated with S. aureus and subjected to high or low pressure pulsatile lavage immediately or after one, three, or six hours. Scanning electron microscopy and bacterial cultures were used to assess the removal of adherent bacteria.

RESULTS

HPPL resulted in significantly greater macroscopic damage than was seen with LPPL or in controls (ANOVA, p < 0.001). Histomorphometry revealed that HPPL was associated with significantly larger and more numerous fissures or defects in the cortical bone when compared with low pressure irrigation (p < 0.001). However, high and low pressure lavage were associated with similar degrees of periosteal separation from the cortical bone surface (p = 0.87). Both high and low pressure lavage were effective in removing adherent bacteria from bone at three hours irrigation delay, but only high pressure lavage removed adherent bacteria from bone at six hours delay.

CONCLUSION

In this in vitro study, compared with HPPL, LPPL led to less structural damage and was equally effective in removing bacteria within three hours debridement delay; however, the efficacy of LPPL at six hours debridement delay is questionable. This finding may have clinical significance in the development of infection following open tibial fractures.

The Calgary Biofilm Device: new technology for rapid determination of antibiotic susceptibilities of bacterial biofilms

Determination of the MIC, based on the activities of antibiotics against planktonic bacteria, is the standard assay for antibiotic susceptibility testing. Adherent bacterial populations (biofilms) present with an innate lack of antibiotic susceptibility not seen in the same bacteria grown as planktonic populations. The Calgary Biofilm Device (CBD) is described as a new technology for the rapid and reproducible assay of biofilm susceptibilities to antibiotics. The CBD produces 96 equivalent biofilms for the assay of antibiotic susceptibilities by the standard 96-well technology. Biofilm formation was followed by quantitative microbiology and scanning electron microscopy. Susceptibility to a standard group of antibiotics was determined for National Committee for Clinical Laboratory Standards (NCCLS) reference strains: Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 29213. Growth curves demonstrated that biofilms of a predetermined size could be formed on the CBD at specific time points and, furthermore, that no significant difference (P > 0.1) was seen between biofilms formed on each of the 96 pegs. The antibiotic susceptibilities for planktonic populations obtained by the NCCLS method or from the CBD were similar. Minimal biofilm eradication concentrations, derived by using the CBD, demonstrated that for biofilms of the same organisms, 100 to 1,000 times the concentration of a certain antibiotic were often required for the antibiotic to be effective, while other antibiotics were found to be effective at the MICs. The CBD offers a new technology for the rational selection of antibiotics effective against microbial biofilms and for the screening of new effective antibiotic compounds.

In vivo resistance to bacterial biofilm formation on tympanostomy tubes as a function of tube material

Adherent bacterial biofilms have been implicated in the irreversible contamination of implanted medical devices. We evaluated the resistance of various tympanostomy (pressure equalization [PE]) tube materials to biofilm formation using an in vivo model. PE tubes of silicone, silver oxide-impregnated silicone, fluoroplastic, silver oxide-impregnated fluoroplastic, and ion-bombarded silicone were inserted into the tympanic membranes of 18 Hartley guinea pigs. Staphylococcus aureus was then inoculated into the middle ears. An additional 8 guinea pigs were used as controls; the PE tubes were inserted without middle ear inoculation. All PE tubes were removed on day 10 and analyzed for bacterial contamination using culture, immunofluorescence, and scanning electron microscopy (SEM). All infected ears developed otitis media with otorrhea, but none of the animal control ears drained. Fluorescence imaging of the animal control tubes showed large cellular components consistent with inflammation. The infected tubes showed heavy DNA fluorescence consistent with bacteria and inflammatory cells. All animal control tubes except the ion-bombarded silicone tubes showed adherent inflammatory film on SEM. Also, all tubes placed in infected ears except the ion-bombarded silicone tubes showed adherent bacterial and inflammatory films on SEM. Nonadherent surface properties such as the ion-bombarded silicone may be helpful in preventing chronic PE tube contamination.

Chronic groin sepsis following tension-free inguinal hernioplasty

BACKGROUND

Chronic groin sepsis requiring mesh removal is said to be a rare complication of tension-free inguinal hernioplasty. The aim of this study was to determine the number of surgeons performing tension-free inguinal hernioplasty in the West of Scotland and assess the frequency with which chronic groin sepsis was encountered.

METHODS

A questionnaire was sent to all consultant surgeons performing inguinal hernia repair in the region and follow-up of patients with chronic groin sepsis following tension-free inguinal hernioplasty was undertaken.

RESULTS

Of 80 consultants who replied to the questionnaire, 79 were performing tension-free hernioplasty. Of these, 76 were performing only open repairs while three were also undertaking laparoscopic repairs. Sixteen consultants reported 20 patients with groin sepsis after mesh repair. Twelve patients were traced; eight had chronic sinuses and four had groin abscesses. The median interval between repair and presentation was 4 months (range from 2 weeks to 39 months). All have required complete (11 patients) or partial (one) removal of mesh to resolve the symptoms.

CONCLUSION

Tension-free inguinal hernioplasty has become the operation of choice for surgeons in the region. Chronic groin sepsis may be more frequent than reported previously. Complete removal of mesh is required to treat this condition.

Antifungal resistance in non- albicans Candida species

Non- Candida albicans species have emerged as important bloodstream pathogens. They tend to have decreased susceptibility to antifungal agents in vitro and cause infections associated with high morbidity and mortality. Fluconazole resistance can emerge in any Candida spp., but is most commonly seen with Candida krusei, for which resistance is universal, and with Candida glabrata. Amphotericin B resistance has also been increasingly reported, most notably in isolates of Candida lusitaniae and Candida guilliermondii. Efforts are underway to correlate in-vitro antifungal susceptibility of individual Candida isolates with response to therapy of patients with candidemia. Future advances in this field might allow physicians to identify Candida isolates resistant to specific antifungal agents and thereby tailor therapy of candidemia. Copyright 1999 Harcourt Publishers Ltd.

[Postoperative infections related to pacing wires, pulmonary arterial catheters, and drainage tubes temporarily inserted during open-heart surgery]

Bacterial examinations of temporary pacing wires (P-wires), pulmonary arterial (P-A) catheters, and drainage tubes temporarily inserted during open-heart surgery were performed in 213 patients. Bacteria were detected in 19 (2.8%) of 672 specimens gathered from the subject patients, with coagulase-negative Staphylococcus (CNS) being most frequently observed. P-wires accounted for 17 out of 19 of the culture-positive specimens, and 7 of the P-wires remained in place for more than two weeks. The frequency of infection with the P-wires was significantly higher than with the P-A catheters or drainage tubes. The period of time that the P-wire was left in place significantly longer than for P-A catheter or drainage tube. There was, however, no statistically significant difference between the culture-positive and negative groups in respect to age, detention periods, operation times, CPB times, or length of ICU stay. As a result of these findings, we have concluded that P-wires should be removed as soon as possible following surgery, and in any case, a meticulous care should be taken to prevent transcutaneous infection.

A 140-kilodalton extracellular protein is essential for the accumulation of Staphylococcus epidermidis strains on surfaces

Two distinct pathogenic mechanisms, adhesion to polymer surfaces and subsequent accumulation of sessile bacterial cells, are considered important pathogenic steps in foreign body infections caused by Staphylococcus epidermidis. By using mitomycin mutagenesis, we have recently generated a mutant, strain M7, from S. epidermidis RP62A which is unaffected in adhesion but deficient in accumulation on glass or polystyrene surfaces and lacks a 115-kDa extracellular protein (designated the 140-kDa antigen; F. Schumacher-Perdreau, C. Heilmann, G. Peters, F. Götz, and G. Pulverer, FEMS Microbiol. Lett. 117:71-78, 1994). To evaluate the role of this protein in accumulation, we harvested extracellular proteins from S. epidermidis RP62A grown on dialysis membranes placed over chemically defined medium, purified the protein by using ion-exchange chromatography, determined its N-terminal amino acid sequence, and raised antiserum in rabbits. The antibody recognized only a single band in a Western immunoblot of the crude extracellular extract. With the microtiter biofilm test, antiserum at a dilution of < or =1:1,000 blocked accumulation of RP62A up to 98% whereas preimmune serum did not. The 140-kDa antigen was found only in extracellular products from bacteria grown under sessile conditions. Of 58 coagulase-negative clinical isolates, 32 strains were 140-kDa antigen positive and produced significantly larger amounts of biofilm than the 26 strains that were 140-kDa antigen negative. The 140-kDa protein appears to be biochemically and functionally unrelated to any previously described factors associated with biofilm formation. Thus, the 140-kDa antigen, referred to as accumulation-associated protein, may be a factor essential in S. epidermidis accumulation and, due to its immunogenicity, may allow the development of novel immunotherapeutic strategies for prevention of foreign body infection.

Bacterial colonization of indwelling vascular catheters in newborn infants

OBJECTIVE

To determine the incidence of bacterial colonization of intravascular catheters, to compare the incidence of colonization of intra-arterial (IA), intravenous (IV) and central venous catheters (CVC), and to determine the association, if any, between catheter withdrawal and bacterial sepsis.

METHODOLOGY

A prospective observational study was carried out at the neonatal intensive care unit of a university-affiliated regional referral centre. A total of 155 catheters (45 IA, 54 IV and 56 CVC) were obtained from 96 infants admitted to the unit and the distal 0.75 cm studied under the scanning electron microscope. The adjoining 0.75 cm was cultured for bacteria.

RESULTS

Scanning electron microscopy revealed that 46% of catheters had bacteria on the internal surface and 13% had bacteria on the outer surface. Greater numbers of CVC were colonized with bacteria compared to IA and IV catheters (P < 0.01). Bacterial colonization of intravascular catheters was not significantly associated with the duration the catheter remained in situ or local reaction at the site of entry of the catheter. Colonization of the external surface of the catheter was significantly associated with bacterial septicaemia (P = 0.0466). Eighty-three per cent of 155 catheters studied had coagulum on the inner or outer surface. Only 53% of these were colonized with bacteria. Bacterial colonization occurred in the absence of a coagulum in only three instances. Catheter withdrawal was not associated with bacterial sepsis. Lack of coagulum on the internal surface of the catheter was strongly associated with septicaemia during the 7 days after catheter withdrawal.

CONCLUSIONS

Although significant numbers of intravascular catheters were colonized with bacteria, only colonization with the external surface was associated with catheter-related sepsis.

The intercellular adhesin involved in biofilm accumulation of Staphylococcus epidermidis is a linear beta-1,6-linked glucosaminoglycan: purification and structural analysis

The primary attachment to polymer surfaces followed by accumulation in multilayered cell clusters leads to biofilm production of Staphylococcus epidermidis, which is thought to contribute to virulence in biomaterial-related infections. We purified a specific polysaccharide antigen of biofilm-producing S. epidermidis 1457 and RP62A, which was recently shown to have a function in the accumulative phase of biofilm production by mediating intercellular adhesion (D. Mack, M. Nedelmann, A. Krokotsch, A. Schwarzkopf, J. Heesemann, and R. Laufs, Infect. Immun. 62:3244-3253, 1994). Following Sephadex G-200 gel filtration, this antigen was separated by Q-Sepharose chromatography into a major polysaccharide, polysaccharide I (> 80%), which did not bind to Q-Sepharose, and a minor polysaccharide, polysaccharide II (< 20%), which was moderately anionic. As shown by chemical analyses and nuclear magnetic resonance spectroscopy, polysaccharide I is a linear homoglycan of at least 130 beta-1,6-linked 2-deoxy-2-amino-D-glucopyranosyl residues. On average, 80 to 85% of them are N acetylated; the rest are non-N-acetylating and positively charged. Chain cleavage by deamination with HNO2 revealed a more or less random distribution of the non-N-acetylated glucosaminyl residues, with some prevalence of glucosaminyl-rich sequences. Cation-exchange chromatography separated molecular species whose content of non-N-acetylated glucosaminyl residues varied between 2 and 26%. Polysaccharide II is structurally related to polysaccharide I but has a lower content of non-N-acetylated D-glucosaminyl residues and contains phosphate and ester-linked succinate, rendering it anionic. Enzyme-linked immunosorbent assay inhibition with various monosaccharides revealed the beta-anomeric form and the acetylated amino group of the D-glucosaminyl residues as important for reactivity with the specific antiserum. The unbranched polysaccharide structure favors long-range contacts and interactions between polysaccharide strands and the cell wall and/or lectin-like proteins, leading to intercellular adhesion and biofilm accumulation. The structure of the polysaccharide is, so far, considered to be unique and, according to its function, is referred to as S. epidermidis polysaccharide intercellular adhesin (PIA).

Antimicrobial activity and biocompatibility of polyurethane and silicone catheters containing low concentrations of silver: a new perspective in prevention of polymer-associated foreign-body-infections

In modern medicine, infection is one of the most serious complications of implanted plastic devices. The host is not able to overcome this special type of opportunistic infection despite having a normal immune response and a low virulence of most of the bacteria involved. Antimicrobial therapy alone generally cannot cure the infection and the removal of catheters often remains the only choice of therapy. Bacterial adhesion to the polymer surface of the catheter, be it luminal or external, is an important step in the pathogenesis of catheter-associated infections. In this report, we describe new approaches to the prevention of infections by impregnation of polyurethane and silicone with silver by two different methods. The antimicrobial activity of these silver-impregnated catheters is more than 10 fold higher for coagulase-negative staphylococci (CNS) compared to catheters without silver. Similar results are obtained with other microbial organisms like Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. The new polymers show no cytotoxic or thrombogenic side effects in vitro.

Modulation of biofilms of Pseudomonas aeruginosa by quinolones

The interaction between four fluoroquinolones (ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin) and biofilms of Pseudomonas aeruginosa in wells of microtiter plates and on segments of vascular catheters were studied in an in vitro model of vascular catheter colonization. Subinhibitory concentrations (one-half, one-fourth, and one-eight of the MIC) of the fluoroquinolones reduced the adherence of P. aeruginosa to 30 to 33, 44 to 47, and 61 to 67% of that of controls, respectively. The addition of high concentrations of the fluoroquinolones (12.5 and 400 micrograms/ml) to preformed biofilms (grown for 48 h at 37 degrees C) decreased the adherence of P. aeruginosa to 69 to 77 and 39 to 60% of that of controls, respectively. In an in vitro model of vascular catheter colonization, subinhibitory concentrations (one-half, one-fourth, and one-eight of the MIC) of fluoroquinolones reduced the number of adherent bacteria to 21 to 23, 40 to 46, and 55 to 70% of that of the controls, respectively. Scanning electron microscopy demonstrated a significant reduction in glycocalyx formation and adherent bacteria in the presence of pefloxacin at one-half to one-eight of the MIC. Vascular catheter segments precolonized with P. aeruginosa for 24 h and exposed to the fluoroquinolones at 4 to 25 times the MIC (50 micrograms/ml) for 2 h showed <5% growth of adherent cells compared with controls. No adherent organisms were cultured in the presence of 8 to 50 times the MIC (100 micrograms/ml). Scanning electron microscopy studies of preformed biofilms exposed to pefloxacin verified the results obtained by culture. These data show that subinhibitory concentrations of ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin inhibit the adherence of P. aeruginosa to plastic surfaces and vascular catheters. Clinically achievable concentrations of fluoroquinolones (50 to 100 micrograms/ml) were able to eradicate preformed biofilms on vascular catheters.

The effect of electrical currents and tobramycin on Pseudomonas aeruginosa biofilms

The combined use of antibiotics with low levels of electrical current has been reported to be more effective in controlling biofilms (the bioelectric effect) than antibiotics alone. An electrical colonisation cell was designed to study the effect of antibiotics on biofilms formed on a dialysis membrane away from the electrode surface. To avoid the electrochemical generation of toxic products, Pseudomonas aeruginosa biofilms were formed in minimal salts medium that excluded chloride-containing compounds. Under these conditions, electrical currents of up to 20 mA cm-2 did not prevent biofilm formation or have any detrimental effect on an established biofilm. Tobramycin alone at concentrations of 10 micrograms ml-1 did not affect the biofilm, but were significantly enhanced by 9 mA cm-2. The effect of tobramycin concentrations of 25 micrograms ml-1 were enhanced by a 15 mA cm-2 electrical current. In both cases higher levels of electrical current, up to 20 mA cm-2, did not further enhance the effect of the antibiotic. The possible mechanisms of action of the bioelectric effect have been reported to involve electrophoresis, iontophoresis and electroporesis, thus overcoming the biofilm biomass and cell wall barriers. Our results suggest that other factors may also be important, such as the metabolic activity and growth rate of the bacteria. Such factors may be critical in maximising antibiotic efficacy.

Histopathological characteristics of explanted human prosthetic arterial grafts: implications for the prevention and management of graft infection

OBJECTIVE

to study the histopathological characteristics of prosthetic vascular graft infection.

DESIGN

prospective clinical study over 2 years.

SETTING

University Hospital.

MATERIALS

36 infected and 29 uninfected (control) chronically implanted vascular prostheses (half aortic) were removed and 352 sections prepared.

CHIEF OUTCOME MEASURES

light microscopy (multiple stains), scanning electron microscopy (SEM), and multiple culture techniques to identify characteristics of healing, infection, and microorganisms.

MAIN RESULTS

Acute inflammation (AI) (neurophils, granulocytes and necrosis) were seen in 75% of infected grafts, were most prominent in the perigraft tissue and rarely seen on the luminal surface. These were usually well localised, leaving the remainder of a graft well incorporated with no signs of infection. In 25% of clinically infected, culture-positive grafts there was no significant acute inflammation. Chronic inflammation (CI) (macrophages, lymphocytes, monocytes, giant cells) was seen in 70% of both control and infected grafts. In 50% of both groups a significant lymphocytic population was composed exclusively of T-lymphocytes suggesting a true host vs graft response. Unincorporated chronically implanted grafts (> 1 yr) were seen with equal frequency in the two groups although more diffusely unincorporated grafts were infected. Microorganisms were cultured from 23 infected grafts (64%) and were, at microscopy, mostly found outside the graft and nerves on the luminal side.

CONCLUSIONS

This data cast doubt on criteria commonly used to distinguish graft infections and host vs. graft reactions from normal graft healing. Acute and chronic inflammation are not predictive of infection.

Variations in DNA subtype, antifungal susceptibility, and slime production among clinical isolates of Candida parapsilosis

Candida parapsilosis is an important nosocomial pathogen that can proliferate in high concentrations of glucose and form biofilms on prosthetic materials. We investigated the genotypic diversity, slime production, and antifungal susceptibility among 60 isolates of C. parapsilosis from 44 patients and 10 patient care providers from five different medical centers. Molecular typing was performed using macrorestriction digest profiles with BssHII followed by pulsed-field gel electrophoresis (REAG) and by electrophoretic karyotyping (EK). Slime production was evaluated by growing the organisms in Sabouraud broth with 8% glucose and examining the walls of the tubes for the presence of an adherent slime layer. Antifungal susceptibility to amphotericin B, 5-fluorocytosine, fluconazole, and itraconazole was determined using National Committee for Clinical Laboratory Standards proposed standard methods. Overall 28 different DNA types were identified by REAG and EK methods. MIC90 values ranged from 0.12 microgram/ml for itraconazole to 1.0 microgram/ml for fluconazole and amphotericin B. Sixty-five percent of the isolates produced slime: 37% were moderately to strongly positive, 28% were weakly positive, and 35% were negative. Overall, 83% of blood and catheter isolates were slime positive versus 53% of isolates from all other sites (P < 0.05). These data underscore the genetic diversity and susceptibility of C. parapsilosis to antifungal agents. Slime production may be important in enabling C. parapsilosis to cause catheter-related bloodstream infections.

Characterization of transposon mutants of biofilm-producing Staphylococcus epidermidis impaired in the accumulative phase of biofilm production: genetic identification of a hexosamine-containing polysaccharide intercellular adhesin

The primary attachment to polymer surfaces followed by accumulation in multilayered cell clusters leads to production of Staphylococcus epidermidis biofilms, which are thought to contribute to virulence in biomaterial-related infections. We isolated Tn917 transposon mutants of biofilm-producing S. epidermidis 13-1, which were completely biofilm negative. In pulsed-field gel electrophoresis no obvious deletions of the mutants were noted. The Tn917 insertions of mutants M10 and M11 were located on different EcoRI fragments but on identical 60-kb SmaI and 17-kb BamHI chromosomal fragments. Linkage of transposon insertions of mutants M10 and M11 with the altered phenotype was demonstrated by phage transduction, whereas the several other mutants apparently represented spontaneous variants. In a primary attachment assay with polystyrene spheres, no significant difference between any of the mutants and the wild type could be detected. Cell clustering as an indication of intercellular adhesion, which is a prerequisite for accumulation in multilayered cell clusters, was not detected with any mutant. These results demonstrate that the mutants were impaired in the accumulative phase of biofilm production. Mutants M10 and M11 did not produce detectable amounts of a specific polysaccharide antigen (D. Mack, N. Siemssen, and R. Laufs, Infect. Immun. 60:2048-2057, 1992), whereas substantially reduced amounts of antigen were produced by the spontaneous variants. Hexosamine was determined as the major specific component of the antigen enriched by gel filtration of biofilm-producing S. epidermidis 1457 because almost no hexosamine was detected in material prepared from the isogenic biofilm-negative transductant 1457-M11, which differentiates the antigen from other S. epidermidis polysaccharide components. Our results provide direct genetic evidence for a function of the antigen in the accumulative phase of biofilm production by S. epidermidis by mediating intercellular adhesion.

A sandwich cup method for the penetration assay of antimicrobial agents through Pseudomonas exopolysaccharides

We developed new sandwich cup method to assay the penetration of various antimicrobial agents through Pseudomonas exopolysaccharides. Using alginate extracted from mucoid-type Pseudomonas aeruginosa and gellan gum from Pseudomonas elodea, the role of exopolysaccharides as a barrier against drug penetration was examined. The penetration of positively charged hydrophilic drugs such as aminoglycosides and polypeptides was markedly inhibited by the gels tested, but that of beta-lactams, quinolones, and macrolides was not inhibited. The penetration of gentamicin was strongly influenced by the gel concentration, the solution to be used, and the presence of Ca2+. These results suggest that the microenvironment at the infection site could greatly influence drug penetration through biofilms in vivo.

Agar-entrapped bacteria as an in vitro model of biofilms and their susceptibility to antibiotics

A simple in vitro system was developed as a model structure of biofilms and to evaluate their susceptibility to antibiotics. Viable Escherichia coli cells were entrapped in agar gel layers and incubated for 2 days in a minimal salt medium supplemented with glucose. After subsequent culture for 3 weeks under metal ion depletion, the biomass distribution inside the gel layer was highly heterogeneous. The cell concentration reached 10(11) cfu/g gel in the outer regions of the agar structure whereas the inner gel areas were less colonized (10(9) cfu/g gel). Immobilized cells displayed enhanced resistance to latamoxef as compared with free microorganisms. Moreover, a 3-week-old immobilized-cell membrane was less susceptible to the antibiotic than a younger (2 days old) one. The exposure for 11 h to 64 micrograms/cm3 latamoxef killed about 90% of the bacteria entrapped in the older agar layer, whereas the number of killed cells was 100-fold higher in the younger structure. Effective diffusivity measurements showed that the diffusion of latamoxef in the biofilm-like agar structures was moderately restricted as compared to that in water, and independent of the immobilized-cell content.

Genotypic variation and slime production among blood and catheter isolates of Candida parapsilosis

Candida parapsilosis is an important nosocomial pathogen that can proliferate in high concentrations of glucose and form biofilms on prosthetic materials. We investigated the genotypic diversity and slime production among 31 isolates of C. parapsilosis from individual patients with bloodstream or catheter infections. DNA subtyping was performed by using electrophoretic karyotyping plus restriction endonuclease analysis with BssHII followed by pulsed-field gel electrophoresis. Slime production was evaluated by growing organisms in Sabouraud broth with 8% glucose and examining the walls of the tubes for the presence of an adherent slime layer. Overall there were 14 DNA subtypes among the 31 isolates. Eighty percent of the isolates produced slime; 67% of the isolates were moderately to strongly positive, 13% were weakly positive, and 20% were not slime producers. The ability of isolates of a given DNA type to produce slime under these conditions was variable. The results of these studies indicate moderate genotypic variation among clinical isolates of C. parapsilosis. The propensity of these isolates to form slime in glucose-containing solutions suggests that this phenotypic characteristic may contribute to the ability of C. parapsilosis to adhere to plastic catheters and cause infections.

Pathogenesis of infections related to intravascular catheterization

Over the past few decades, there have been major technological improvements in the manufacture of intravenous solutions and the manufacture and design of catheter materials. However, the risk of infection in patients receiving infusion therapy remains substantial, in part because of host factors (for example, increased use of immunosuppressive therapy, more aggressive surgery and life support, and improved survival at the extremes of life) and in part because of the availability of catheters that can be left in place for very long periods. Microbial components of normal skin flora, particularly coagulase-negative staphylococci, have emerged as the predominant pathogens in catheter-associated infections. Therefore, efforts to prevent skin microorganisms from entering the catheter wound (such as tunnelling of catheters and use of catheter cuffs and local antimicrobial agents) are logical and relatively effective. The specific properties of microorganisms that transform normally harmless commensals such as coagulase-negative staphylococci into formidable pathogens in the presence of a plastic foreign body are being explored. For example, Staphylococcus epidermidis elaborates a polysaccharide adhesin that also functions as a capsule and is a target for opsonic killing. However, the interactions between microorganism and catheter that lead to adherence, persistence, infection, and dissemination appear to be multifactorial.