Efficacy of silver-coating central venous catheters in reducing bacterial colonization

OBJECTIVE: To compare silver-coated and uncoated central venous catheters regarding bacterial colonization. To assess the relative contribution of catheter hub and skin colonization to catheter tip colonization. DESIGN: Prospective, randomized clinical trial. SETTING: Intensive care unit in a university hospital. PATIENTS: Patients after cardiac surgery who required a central venous double-lumen catheter (DLC). INTERVENTIONS: Sixty-seven adult patients were prospectively randomized to receive either a silver-coated (S group, n = 34) or an uncoated control (C group, n = 33) DLC. Blood cultures were drawn at catheter removal, and removed catheters were analyzed with quantitative cultures. Typing of microorganisms included DNA fingerprinting. MEASUREMENTS AND MAIN RESULTS: Catheters were removed if no longer necessary and aseptically divided into three segments: segment A, the catheter tip; segment B, an intermediate section; and segment C, the subcutaneous portion. Bacterial catheter colonization was quantitatively measured using sonication to detach adherent bacteria from the catheter segments in the broth and subsequent culture of an aliquot. Selected isolates of coagulase-negative staphylococci and other bacteria from catheter segments were examined by means of pulsed-field gel electrophoresis (PFGE) after macrorestriction digestion of bacterial DNA to study colonization pathogenesis. Quantitatively lower bacterial colonization could be demonstrated on the silver-coated catheters (200 +/- 550 colony forming units [CFUs]/cm catheter segment; mean +/- SD). The difference in the control catheters (1120 +/- 5350 CFUs/cm catheter segment; mean +/- SD) was not, however, significant (p = .25). The frequency of colonization of at least one catheter segment was 52.9% for the silver-coated catheters and 57.6% for the control catheters (p= .44), without any significant differences in the colonization of corresponding catheter segments. The rate of significant catheter colonization (i.e., > or = 10(3) CFUs/cm catheter by quantitative catheter culture or > or = 10(3) CFUs/mL by luminal flush) was nine in the silver group and seven in the control group, a difference that failed to reach significance (p = .41). Two patients in both groups developed catheter-related bacteremia. Pattern analysis after PFGE demonstrated that about 70% of the isolates found on the catheter tip were identical with those on the skin at the insertion site, whereas about 75% were identical with those recovered from the hub. In 29% of colonized catheters, identical bacteria were found on the hub and the skin at the insertion site. CONCLUSIONS: Silver-coating of DLCs did not significantly reduce bacterial catheter colonization compared with the control catheters. PFGE analysis of coagulase-negative staphylococci and other bacteria demonstrated various pathogenic routes of catheter-related colonization, whereby the microorganisms of the skin flora around the insertion site must be regarded as the main source of catheter-related infections.     

Effective prevention of microbial biofilm formation on medical devices by low-energy surface acoustic waves

Low-energy surface acoustic waves generated from electrically activated piezo elements are shown to effectively prevent microbial biofilm formation on indwelling medical devices. The development of biofilms by four different bacteria and Candida species is prevented when such elastic waves with amplitudes in the nanometer range are applied. Acoustic-wave-activated Foley catheters have all their surfaces vibrating with longitudinal and transversal dispersion vectors homogeneously surrounding the catheter surfaces. The acoustic waves at the surface are repulsive to bacteria and interfere with the docking and attachment of planktonic microorganisms to solid surfaces that constitute the initial phases of microbial biofilm development. FimH-mediated adhesion of uropathogenic Escherichia coli to guinea pig erythrocytes was prevented at power densities below thresholds that activate bacterial force sensor mechanisms. Elevated power densities dramatically enhanced red blood cell aggregation. We inserted Foley urinary catheters attached with elastic-wave-generating actuators into the urinary tracts of male rabbits. The treatment with the elastic acoustic waves maintained urine sterility for up to 9 days compared to 2 days in control catheterized animals. Scanning electron microscopy and bioburden analyses revealed diminished biofilm development on these catheters. The ability to prevent biofilm formation on indwelling devices and catheters can benefit the implanted medical device industry.     

Efficacy of preoperative antimicrobial skin preparation solutions on biofilm bacteria

RESEARCH ON THE MEDICAL EFFICACY of topical antimicrobials and antibiotics against infections has focused largely on the effect on free-floating, planktonic bacteria. IN THE PRESENCE OF nonbiological surfaces (eg, catheters, prosthetic devices, biomaterials), however, bacteria form highly complex biofilm systems that resist traditional medical treatment. BACTERIAL PATHOGENS commonly found in chronic infections in both the planktonic and biofilm state were challenged with a variety of commonly used topical antimicrobial formulations. BIOFILM BACTERIA were shown to be more resistant to killing than planktonic bacteria. Antimicrobial skin preparation times were adequate to significantly reduce bacterial populations protected in biofilms.     

Daptomycin antibiotic lock therapy in a rat model of staphylococcal central venous catheter biofilm infections

Antibiotic lock therapy (ALT) is an adjunctive procedure to prevent or treat central venous catheter infections, ensuing catheter-related bacteremia, and catheter-related metastatic infections. Daptomycin is a cyclic lipopeptide that is rapidly bactericidal against methicillin-susceptible and -resistant Staphylococcus aureus. The efficacies of daptomycin against central venous catheter biofilms, catheter-related bacteremia, and catheter-related metastatic infections were evaluated by adapting a previously reported central venous catheter biofilm model in rats. Combined daptomycin ALT and systemic dosing resulted in the clearance of an established in vivo S. aureus central venous catheter biofilm after just two daily ALT treatments (30 min with daptomycin at 5 mg/ml) with concurrent systemic daptomycin dosing (40 mg/kg of body weight/day subcutaneously [s.c.]; equivalent exposure of 6 mg/kg/day in people). Daptomycin ALT solutions formulated in either saline or lactated Ringer's solution were equally fast in eradicating established in vivo methicillin-resistant Staphylococcus epidermidis (MRSE) central venous catheter biofilms. However, the lactated Ringer's formulation was superior to that of saline in sustaining the bacterial clearance of treated central venous catheters (83% versus 50%). In MRSE-infected central venous catheter studies, 3 days of daptomycin or vancomycin ALT (18 h at 5 mg/ml) with systemic s.c. dosing (40 mg/kg/day daptomycin or 100 mg/kg/day vancomycin) was equally effective 1 week posttherapy in maintaining cleared central venous catheters (90% [n = 10] versus 100% [n = 8]). These results suggest that daptomycin ALT, along with systemic dosing, could be an effective treatment option for the prevention or eradication of staphylococcal central venous catheter biofilm infections, thereby reducing the occurrence of catheter-related bacteremia or catheter-related metastatic infections.     

Evaluation of strategies for central venous catheter replacement.

OBJECTIVES: To assess the consequences of leaving a bacterially colonized central venous catheter in place and to compare the effects of three catheter replacement strategies for catheter repair control in an animal model. DESIGN: Prospective study. SETTING: Laboratory and animal facility of a large university. SUBJECTS: Eighteen healthy, female, adult sheep. INTERVENTIONS: Radiopaque-siliconized elastomer central venous catheters were inserted into the jugular veins and colonized with either Escherichia coli or Staphylococcus epidermidis. After 7 days of infection, the catheters were either: a) exchanged using a guidewire; b) removed and replaced with a new catheter in a new jugular vein site after a 48-hr interval; or c) exchanged using a guidewire and antibiotics (tobramycin, cephaloridine) injected into the catheter. Animals were euthanized 7 days after insertion of the new catheter. Quantitative microbiology was performed on blood samples collected daily from the catheters and a peripheral vein, as well as from catheters and tissue recovered from the sheep at the time of autopsy. MEASUREMENTS AND MAIN RESULT: When catheters were changed using a guidewire, they became colonized by bacteria within 48 hrs, and the sheep had embolic pneumonia and vegetative endocarditis at autopsy. Similar consequences were observed when antibiotics were administered into the catheter lumen. If colonized catheters were removed and a new catheter was inserted after a 48-hr interval, recolonization, pneumonia, and endocarditis were not observed. CONCLUSIONS: Replacement of a biofilm-colonized central venous catheter over a guidewire is associated with rapid colonization of the replacement catheter and production of detached, slime-enclosed, antibiotic-resistant aggregates that colonize other catheters or initiate endocarditis or pneumonia by dissemination in the bloodstream.     

Quantitative tip culture methods and the diagnosis of central venous catheter-related infections.

The diagnostic usefulness of two quantitative catheter culture methods was compared in a prospective study of central venous arterial catheters. The roll-plate method followed by sonication was used to culture 177 catheters from 85 patients, and the sonication method was used to culture 136 catheters from 68 patients. All patients were evaluated for catheter-related infections. Catheter-related infections were associated with greater than or equal to 100 colony-forming units (CFU) isolated from catheter tips by either roll plate (p = 0.01) or sonication (p less than 0.001). The sensitivity, specificity, and positive and negative predictive values of greater than or equal to 10(3) CFU by roll plate for catheter-related septicemia were 56%, 97%, 63%, and 96% compared with 93%, 95%, 76%, and 99%, respectively, for the same level by sonication. For central venous and arterial catheters, the sonication method can distinguish infection from contamination and is superior to the roll-plate method in that it may offer a more sensitive and predictive alternative in the diagnosis of catheter-related septicemia.     

Positive tip cultures and related risk factors associated with intravascular catheterization in pediatric cardiac patients

The incidence and risk factors of positive catheter tip cultures were studied prospectively in 392 consecutive children undergoing cardiac surgery under cover of cephalothin prophylaxis. A total of 1649 catheter tips were cultured and 58 (3.5%) yielded positive cultures. Specifically, the incidence of positive catheter tip cultures for iv, central venous, arterial and pulmonary arterial (PA) catheters was 0.9%, 5.9%, 3.9% and 10.6%, respectively, whereas one of the six surgically placed venous and arterial catheters had a positive tip culture and none of the 279 transthoracic catheters. Staphylococcus epidermidis was isolated from 79% of the positive tip cultures. Ten percent of the children had one or more positive tip cultures but none developed catheter-related septicemia or endocarditis. Stepwise logistic regression analysis revealed that longer in situ time (p less than .001), younger age (p less than .001), and inotropic support (p = .003) were significant independent predictors of risk for children developing positive catheter tip cultures. The safe in situ period for arterial, central venous, and PA catheters is 3 days in infants under 1 yr and 4 and 6 days for arterial and central venous catheters, respectively, in older children, if 0.95 cumulative probability of remaining free of a positive tip culture is accepted. The data generally support the bacteriologic safety of invasive hemodynamic monitoring in infants and children undergoing cardiac surgery.     

Antibiofilm Activity of Electrical Current in a Catheter Model

Catheter-associated infections are difficult to treat with available antimicrobial agents because of their biofilm etiology. We examined the effect of low-amperage direct electrical current (DC) exposure on established bacterial and fungal biofilms in a novel experimental in vitro catheter model. Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida parapsilosis biofilms were grown on the inside surfaces of polyvinyl chloride (PVC) catheters, after which 0, 100, 200, or 500 μA of DC was delivered via intraluminally placed platinum electrodes. Catheter biofilms and intraluminal fluid were quantitatively cultured after 24 h and 4 days of DC exposure. Time- and dose-dependent biofilm killing was observed with all amperages and durations of DC administration. Twenty-four hours of 500 μA of DC sterilized the intraluminal fluid for all bacterial species studied; no viable bacteria were detected after treatment of S. epidermidis and S. aureus biofilms with 500 μA of DC for 4 days.     

导尿管伴随性尿路感染生物被膜阳性菌分布及耐药性分析

目的了解导尿管伴随性尿路感染中生物被膜阳性菌的类型及其对常用抗菌药物的耐药情况,指导临床合理用药。以便于采取易行实用的预防对策,降低医院感染的发生率。方法收集2007年1月至2008年12月在祁阳县人民医院给以尿道插管的住院病人导尿管标本进行无菌采集,对其行一系列处理筛查生物被膜阳性菌,用全自动微生物鉴定系统V1TEK-32进行细菌鉴定及用纸片（K—B）法对其进行药敏试验分析。结果共收集导尿管标本220例,其中确诊为尿路感染的标本为132倒,感染率为60．0％,生物被膜阳性菌78株,阳性率达35．5％。分别是：7株铜绿假单胞菌;24株粪肠球菌;29株表皮葡萄球菌;18株溶血葡萄球菌。结论导尿管伴随性尿路感染中表皮葡萄球菌、粪肠球菌易形成生物被膜,且耐药情况严重。生物被膜菌组与浮游菌组比较,药敏分析有差异,生物被膜组细菌耐药性更强。     

Effect of triclosan on the development of bacterial biofilms by urinary tract pathogens on urinary catheters

OBJECTIVES: To examine (i) the effect of triclosan on the formation of catheter biofilms by urinary tract pathogens and (ii) the diffusion of triclosan through the retention balloons of urinary catheters. METHODS: Models of the catheterized bladder were infected with eight different urinary tract pathogens and the effect of triclosan on biofilm formation was assessed by determining the numbers of viable cells colonizing the catheters and by scanning electron microscopy. HPLC was used to determine the triclosan concentration in urine draining from models that had been fitted with triclosan-inflated silicone catheters. RESULTS: When catheters were inflated with triclosan (10 g/L) the formation of catheter biofilm by Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Proteus mirabilis was prevented. The numbers of Enterococcus faecalis and Providencia stuartii cells colonizing catheters were also significantly reduced (P<0.05). Serratia marcescens, Morganella morganii and Pseudomonas aeruginosa, however, were able to produce extensive catheter biofilms in the presence of triclosan. Only P. mirabilis produced alkaline urine and encrusted the catheters. Concentrations of 0.02-0.16 mg/L of the biocide were detected in urine draining from the model over the 48 h experimental period. CONCLUSIONS: Triclosan diffused through silicone catheter balloons and produced urinary concentrations that prevented catheter encrustation by P. mirabilis and biofilm formation by several other common pathogens of the catheterized urinary tract. It had little effect on urease-producing P. aeruginosa, S. marcescens or M. morganii but these species did not produce alkaline urine or crystalline biofilms.     

The microbiological risk of invasive hemodynamic monitoring in adults undergoing cardiac valve replacement

The microbiological risk of invasive hemodynamic monitoring was studied prospectively in 230 consecutive patients undergoing cardiac valve replacement during prophylactic therapy with cephalothin. A total of 923 catheter tips were cultured, and 1.6% yielded positive cultures. The rate of positive cultures did not differ significantly between catheters inserted percutaneously (1.9% positive) and those inserted surgically (0.5% positive).The incidence of positive catheter tip cultures for intravenous, central venous, arterial, and pulmonary arterial catheters was 0, 1.5, 2.6, and 2.9%, respectively, whereas the surgically inserted right and left atrial catheters yielded 0.6 and 0% positive tip cultures, respectively. One patient developed septicemia related to a right atrial catheter. There was no correlation between the incidence of positive catheter tip cultures and the length of time that the catheters remained in situ. No patient developed early or late endocarditis. Invasive hemodynamic monitoring seems to be microbiologically safe, even in patients undergoing cardiac valve replacement.     

Prospective study of catheter-related infection during prolonged arterial catheterization

Ninety-six arterial catheters from 75 different anatomical sites in 56 surgical ICU patients were studied prospectively to determine the rate of catheter-related infection associated with prolonged arterial catheterization (defined as greater than 96 h). Every 96 h, all catheters were semiquantitatively (SQ) cultured and the percutaneous entry site was swab cultured. Sites were used indefinitely by exchanging the catheters over a guide-wire every 96 h as long as arterial monitoring was necessary and SQ cultures remained negative (less than or equal to 15 colonies). No sites used less than 96 h developed skin colonization, while 14/51 (27%) sites used greater than 96 h developed positive swab cultures. No SQ cultures were positive in sites with negative swab cultures (p less than .001). Catheter-related infection (a positive SQ culture) developed in 4/42 (9.5%) radial or femoral sites compared to 4/9 (44%) axillary sites used greater than 96 h (p less than .01). It is concluded that arterial catheter-related infection develops in less than 10% of radial or femoral sites used greater than 96 h, and 90% of radial and femoral sites may be used safely for prolonged periods if skin colonization at the percutaneous sites is controlled and SQ catheter cultures remain negative. Skin site swab cultures may be useful for determining when arterial catheters should be removed and SQ cultured.     

A prospective, randomized trial of rifampicin-minocycline-coated and silver-platinum-carbon-impregnated central venous catheters

OBJECTIVE: Central venous catheters are the predominant cause of nosocomial bacteremia; however, the effectiveness of different antimicrobial central venous catheters remains uncertain. We compared the infection rate of silver-platinum-carbon (SPC)-impregnated catheters with rifampicin-minocycline (RM)-coated catheters. DESIGN: A large, single-center, prospective randomized study. SETTING: Twenty-two-bed adult general intensive care unit in a large tertiary metropolitan hospital in Brisbane, Australia (2000-2001). PATIENTS: Consecutive series of all central venous catheterizations in intensive care unit patients. INTERVENTIONS: Randomization, concealment, and blinding were carefully performed. Catheter insertion and care were performed according to published guidelines. Blood cultures were taken at central venous catheter removal, and catheter-tip cultures were performed by both roll-plate and sonication techniques. Pulsed field gel electrophoresis was used to establish shared clonal origin for matched isolates. MEASUREMENTS AND MAIN RESULTS: Central venous catheter colonization and catheter-related bloodstream infection were determined with a blinded technique using the evaluation of the extensive microbiological and clinical data collected and a rigorous classification system. Six hundred forty-six central venous catheters (RM 319, SPC 327) were inserted, and 574 (89%) were microbiologically evaluable. Colonization rates were lower for the RM catheters than SPC catheters (25 of 280, 8.9%; 43 of 294, 14.6%; p=.039). A Kaplan-Meier analysis that included catheter time in situ did not quite achieve statistical significance (p=.055). Catheter-related bloodstream infection was infrequent for both catheter-types (RM 4, 1.4%; SPC 5, 1.7%). CONCLUSIONS: The SPC catheter is a clinically effective antimicrobial catheter; however, the RM catheter had a lower colonization rate. Both catheter types had low rates of catheter-related bloodstream infection. These results indicate that future studies will require similar rigorous methodology and thousands of central venous catheters to demonstrate differences in catheter-related bloodstream infection rates.     

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.     

Detection of viable but non-culturable staphylococci in biofilms from central venous catheters negative on standard microbiological assays

Viable bacteria were sought in 44 Maki-negative biofilms from central venous catheters (CVCs) using epifluorescence microscopy after live/dead staining. Thirty (77%) samples contained viable but non-culturable (VBNC) cells; the majority were positive on real-time PCR specific for Staphylococcus epidermidis (one also for Staphylococcus aureus). Viable cells were significantly (p<0.01) associated with CVCs from febrile patients, three of whom showed S. epidermidis-positive blood cultures, suggesting that CVC-associated biofilms can be reservoirs for staphylococci in the VBNC state. The possible role of VBNC staphylococci in persistent infections related to medical devices requires further investigation.     

The challenge of anticipating catheter tip colonization in major heart surgery patients in the intensive care unit: are surface cultures useful?

OBJECTIVE: Patients undergoing heart surgery show a high risk of catheter colonization and catheter-related bloodstream infections. We evaluated whether skin insertion site and catheter hub surveillance cultures ("surface cultures") could predict catheter colonization and help establish the origin of bloodstream infections. DESIGN:: Prospective cohort study. SETTING: An 11-bed heart surgery intensive care unit in a tertiary university hospital. PATIENTS: Heart surgery patients spending >4 days in intensive care over an 11-month period. INTERVENTIONS: All catheters were surveyed. Cultures were obtained from the skin insertion site and all hubs on day 5 after surgery, every 72 hrs thereafter, and on catheter removal. Swabs were processed semiquantitatively by streaking the surface of a Columbia agar plate. Catheters were processed using Maki's method. The observation of > or = 15 colonies/plate was taken to indicate a positive skin or catheter colonization culture result. MEASUREMENTS AND MAIN RESULTS: Over the study period, 561 catheters were inserted in 130 patients. The median time a catheter was in place was 6 days (interquartile range 3-11), and 3,712 surface cultures were obtained (median four per patient). Catheter colonization occurred in 133 catheters, and there were 15 episodes of catheter-related bloodstream infection (incidence density of colonization 29.3 and of catheter-related bloodstream infection 8.8 per 1,000 catheter-days). Validity indexes for the capacity of surface cultures to predict catheter colonization and catheter-related bloodstream infection, respectively, were as follows: accuracy, 71.4, 65.6; sensitivity, 83.5%, 100%; specificity, 67.1%, 64.7%; positive predictive value, 47.6%, 7.2%; negative predictive value, 91.9%, 100%; positive likelihood ratio, 2.5, 2.83; and negative likelihood ratio, 0.2, 0. Surface cultures correctly predicted 77.4% of all bacteremia episodes (catheter-related and non-catheter-related). CONCLUSIONS: Systematic surveillance cultures of catheter hub and skin insertion sites in patients admitted to a heart surgery intensive care unit could help identify patients who would benefit from decontamination and preventive measures and establish whether catheters are the portal of entry of bloodstream infection.     

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.     

Randomized, Double-Blind Trial of an Antibiotic-Lock Technique for Prevention of Gram-Positive Central Venous Catheter-Related Infection in Neutropenic Patients with Cancer

The aim of the present study was to determine the efficacy of an antibiotic-lock technique in preventing endoluminal catheter-related infection with gram-positive bacteria in neutropenic patients with hematologic malignancies. Patients with nontunneled, multilumen central venous catheters were assigned in a randomized, double-blinded manner to receive either 10 U of heparin per ml (57 patients) or 10 U of heparin per ml and 25 microg of vancomycin per ml (60 patients), which were instilled in the catheter lumen and which were allowed to dwell in the catheter lumen for 1 h every 2 days. Insertion-site and hub swabs were taken twice weekly. The primary and secondary end points of the trial were significant colonization of the catheter hub and catheter-related bacteremia, respectively. Significant colonization of the catheter hub occurred in nine (15.8%) patients receiving heparin (seven patients were colonized with Staphylococcus epidermidis, one patient was colonized with Staphylococcus capitis, and one patient was colonized with Corynebacterium sp.), whereas the catheter hubs of none of the patients receiving heparin and vancomycin were colonized (P = 0.001). Catheter-related bacteremia developed in four (7%) patients receiving heparin (three patients had S. epidermidis bacteremia and one patient had S. capitis bacteremia), whereas none of the patients in the heparin and vancomycin group had catheter-related bacteremia (P = 0.05). The times to catheter hub colonization and to catheter-related bacteremia by the Kaplan-Meier method were longer in patients receiving heparin and vancomycin than in patients receiving heparin alone (P = 0.004 and P = 0.06, respectively). Our study shows that a solution containing heparin and vancomycin administered by using an antibiotic-lock technique effectively prevents catheter hub colonization with gram-positive bacteria and subsequent bacteremia during chemotherapy-induced neutropenia in patients with hematologic malignancy.     

Activity of antibacterial impregnated central venous catheters against Klebsiella pneumoniae

OBJECTIVE: Antibiotically coated or impregnated catheters are effective in eliminating gram-positive bacteria from their surfaces. However, their activity against gram-negative bacteria is not well known. The aim of this study was to evaluate and compare the adherence, persistence and colonization of Klebsiella pneumoniae on catheter surfaces and also to assess bacteriostatic and bactericidal levels. DESIGN: Randomized, controlled, laboratory study. SETTING: University surgical microbiology laboratory. SUBJECTIVE: Silver sulfadiazine-chlorhexidine impregnated (SSC), minocycline and rifampin bonded (M+R), silver, platinum and carbon incorporated (SP+C) and non-antiseptic central venous catheter segments. INTERVENTIONS: Catheter segments were immersed in 1 ml of phosphate buffered saline (0.01 mol/l) with 0.25% dextrose (PBSD) and incubated at 37 degrees C. The PBSD was replaced daily. Effluents were frozen at -70 degrees C for subsequent determination of bacteriostatic and bactericidal activity. On days 1,3,7,14 and 21 after initial immersion, 1 ml standardized inoculum of Klebsiella pneumoniae was added to 90 tubes for a period of 30 min. The inoculum was then replaced with PBSD. One third of the samples were immediately sonicated and plated for the determination of bacterial adherence. The remaining segments were incubated for 4 and 24 h, followed by the same procedure to determine bacterial persistence and colonization with time. All plates were read after 24 h of incubation. MEASUREMENTS AND RESULTS: There was a significant reduction in initial bacterial adherence for SP+C catheters on all days ( p<0.05). SSC catheters prevented initial bacterial adherence for the first 7 days only ( p<0.05). SSC and SP+C catheters prevented bacterial persistence and further colonization on all days. However M+R catheters prevented bacterial colonization for 3 days only. Effluent studies indicated that the impregnated agents in catheter SSC were bactericidal compared to catheter M+R, which were bacteriostatic to K. pneumoniae. No antibacterial activity was detected in the effluents from catheter SP+C. CONCLUSIONS: SSC and SP+C catheters are effective in eliminating K. pneumoniae from their surfaces for at least 21 days. M+R catheters are less effective in eliminating bacterial adherence and colonization may be due to their bacteriostatic property.     

Role of Mutation in Pseudomonas aeruginosa Biofilm Development

The survival of bacteria in nature is greatly enhanced by their ability to grow within surface-associated communities called biofilms. Commonly, biofilms generate proliferations of bacterial cells, called microcolonies, which are highly recalcitrant, 3-dimensional foci of bacterial growth. Microcolony growth is initiated by only a subpopulation of bacteria within biofilms, but processes responsible for this differentiation remain poorly understood. Under conditions of crowding and intense competition between bacteria within biofilms, microevolutionary processes such as mutation selection may be important for growth; however their influence on microcolony-based biofilm growth and architecture have not previously been explored. To study mutation in-situ within biofilms, we transformed Pseudomonas aeruginosa cells with a green fluorescent protein gene containing a +1 frameshift mutation. Transformed P. aeruginosa cells were non-fluorescent until a mutation causing reversion to the wildtype sequence occurs. Fluorescence-inducing mutations were observed in microcolony structures, but not in other biofilm cells, or in planktonic cultures of P. aeruginosa cells. Thus microcolonies may represent important foci for mutation and evolution within biofilms. We calculated that microcolony-specific increases in mutation frequency were at least 100-fold compared with planktonically grown cultures. We also observed that mutator phenotypes can enhance microcolony-based growth of P. aeruginosa cells. For P. aeruginosa strains defective in DNA fidelity and error repair, we found that microcolony initiation and growth was enhanced with increased mutation frequency of the organism. We suggest that microcolony-based growth can involve mutation and subsequent selection of mutants better adapted to grow on surfaces within crowded-cell environments. This model for biofilm growth is analogous to mutation selection that occurs during neoplastic progression and tumor development, and may help to explain why structural and genetic heterogeneity are characteristic features of bacterial biofilm populations.