Effect of hydrophilic coating on microorganism colonization in silicone tubing

Summary Background. Shunt infections are one of the major causes of mortality and morbidity of patients with hydrocephalus. The aim of this research is to compare the bacterial colonization characteristics of a regular silicone elastomer shunt material coated with polyvinylpyrrolidone and dimethylpolysiloxane (silicone).Method. Regular coated shunt materials were compared by in-vivo and in-vitro methods. In the in-vitro experiment, silicone and coated material immersed and not immersed in vancomycin solution was treated with a certain concentration of Staphylococcus epidermidis. In the in-vivo study, silicone and coated material specimens were treated with Staphylococcus epidermidis and they were stereotactically placed in the lateral ventricles of the rats. One week after the inoculation, shunt pieces were removed and the colonies were counted by using a scanning electron microscope.Findings. There was a statistically significant difference of colonization in the in-vitro groups in coated material vs. silicone, coated material vs. vancomycin treated silicone, vancomycin treated coated material vs. silicone, vancomycin treated coated material vs. vancomycin treated silicone. There was no statistically significant difference for colonization in in-vitro groups of coated material and vancomycin treated coated material. With in-vivo experiments we can say that, coated material catheters are superior than the silicone catheters in respect to colonization but after the bacterial colonization has occurred, the amount of colonization did not differ.Interpretation. Coated material catheters are superior to silicone catheters and they prevent bacterial colonization in some respect.     

Bacterial adhesion to surfactant-modified silicone surfaces

OBJECTIVE: Ventricular shunt infections are a major contributor to morbidity in patients being treated for hydrocephalus. The majority of these infections are from Staphylococcus epidermidis. Prevention of bacterial adhesion to the silicone surface of a ventricular catheter could decrease shunt infections. We studied the effectiveness of a surfactant and/or 2% iodine prewash on preventing bacterial adhesion to Silastic catheter material. METHODS: In a laboratory setting, various concentrations of a surfactant, Poloxamer-188 (P188), and a bactericidal agent, iodine, were compared against a control solution in their ability to prevent bacterial adhesion of S. epidermidis to a silicone surface. Silicone wafers were soaked for 1 hour in the test solution, then inoculated and incubated with S. epidermidis for 24 hours. Bacterial counts were then obtained and compared. RESULTS: The most effective method tested in this study was 20% P188, which allowed only 3.02% bacterial adhesion compared with 22.2% bacterial adhesion in the control (P < 0.001). P188 at a 10% concentration or 20% mixed with iodine had the next most effective inhibition. Of the germicidal solutions, a 5-ppm solution of iodine was the most effective. The most ineffective method tested was 2 ppm iodine, which allowed 13.2% bacterial adhesion. CONCLUSION: Use of a surfactant and/or a germicidal will provide some protection against bacteria attaching to silicone surfaces before they are surgically implanted. The use of a surfactant soak of 20% P188 or iodine at a concentration of 5 ppm before inoculation with S. epidermidis significantly decreased the bacterial adhesion to silicone wafers. This finding has relevance to clinical practice because it highlights a simple step undertaken before implanting a ventricular catheter that could reduce the adhesion rate of the most common contaminant of these catheters. This step may become an important factor in decreasing infection rates in shunt-dependent patients.     

A flexible metal ventricular catheter for treatment of complicated and protracted infections of the cerebrospinal fluid spaces: Preliminary experiences

Summary In the management of shunt infection, the use of ventricular catheters made of silicone rubber for the temporary external drainage of cerebrospinal fluid (CSF) is general practice. However, the eradication of the primary source of infection may be hindered by the affinity of bacteria to silicone-based material. Compared to silicone catheters, a metal drainage device for temporary ventriculostomy appears to offer more favourable conditions for successful eradication of the infection. Since metal needles cannot be implanted permanently and since their screw-type fixation precludes attachment to the skulls of infants or small children, we developed a flexible metal catheter. This catheter was used exclusively for the treatment of particularly serious or chronic infections of the CSF spaces. The catheter is made of implantation steel and consists of a corrugated tube that renders it flexible. Cerebrospinal fluid drains into a receptable bulb at the tip of the tube. Tubing of other materials may be connected to the end of the metal catheter for either external or internal drainage. It was implanted as a temporary and later permanent CSF drainage in 7 male patients aged from 4 to 60 years, who suffered from chronic, recurrent ventriculitis (n = 5) with an average of 7 previous surgical revisions, as well as from complex infections (n = 2; basal tuberculous meningitis, brain abscess). The infections were successfully eliminated in 6 patients. In the remaining patient, the metal catheter for external ventriculostomy had to be removed after 4 days due a leakage of CSF; it was replaced by a silicone catheter and later on by a needle drainage. Other complications, such as secondary infection or intracerebral haemorrhage, did not occur. The average duration of external CSF drainage via the flexible metal catheter was 27 days (range 4–50 days). In 4 patients, the CSF drainage was converted to a permanent ventriculoperitoneal shunt using a new flexible metal catheter. At the time of post-operative follow-up examination (average = 34 weeks), all shunts were functioning and there was no evidence of infection. In cases of especially complicated and protracted CSF infections, the flexible metal ventricular catheter is a promising device for treatment.     

Bacterial Colonization in Hemodialysis Temporary Dual Lumen Catheters: A Prospective Study

Aims. The use of hemodialysis temporary dual-lumen catheters is often complicated by infections, which may be a significant cause of death among patients with end stage renal disease (ESRD). The aim of this study was to assess the incidence of bacteremia and bacterial colonization related to non-tunneled, non-cuffed, dual-lumen temporary catheters in patients with ESRD submitted to hemodialysis. Methods. This study included 29 patients with ESRD. After catheter implantation, patients were monitored throughout the period of catheter permanence by means of blood samples collected weekly from a peripheral vein. Bacteria were isolated and identified according to CLSI recommendations. When catheters were removed for any reason, their tips were evaluated microbiologically. Results. A total of 194 blood samples from the 29 patients implanted with 55 catheters were analyzed. Of these, 15.5% (30 samples) demonstrated bacterial growth, principally Staphylococcus epidermidis (64.5%). Twenty patients (68.9%) presented at least one positive blood culture during follow-up. The median time for catheter colonization was 18.5 days (95% CI: 16.8–30.3). Of the 55 catheters implanted, 28 (50.9%) showed bacterial colonization, corresponding to 23.4 episodes/1000 catheter/days and 9.2 episodes of bacteremia /1000 catheter/days. Fifteen of 28 catheter tips analyzed showed bacterial growth (53.5%). In 14 of these (93.3%), there was agreement between the isolates from the catheter tip and blood cultures. Of 24 episodes of positive blood cultures from 20 different patients in 17 episodes (70.8%), the patients showed no clinical signs or symptoms of bacteremia. Conclusions. The high incidence of catheter colonization, the correlation between blood and catheter tip cultures, and the occurrence of frequent cases of asymptomatic bacteremia justify the proposal of routine peripheral blood collections to monitor patients undergoing hemodialysis with temporary dual-lumen catheters.     

Infection-resistant continuous peritoneal dialysis catheters

The techniques of bonding of anionic antibiotics by treatment with cationic surfactants were applied to continuous ambulatory peritoneal dialysis (CAPD) catheters. The elution of 14C-penicillin from tridodecylmethylammonium chloride (TDMAC) treated silicone elastomer catheters in dialysis solution was biphasic, with 95% dissociated from the catheter by 48 h. Forty percent of the TDMAC left the catheter surface during the initial 2 days. The ability of the surfactant TDMAC to bind antibiotics after incubation in dialysis solution correlated directly with the amount of surfactant remaining. Rats with intraperitoneal dialysis catheters were inoculated with exit site and intraluminal bacterial challenges. Intraperitoneal catheter tips treated with TDMAC-penicillin were rendered more resistant to colonization after exit site and intraluminal bacterial challenges.     

Peritonitis in peritoneal dialysis: bacterial colonization by biofilm spread along the catheter surface

We have used modern techniques of direct microscopic examination and quantitative bacterial recovery to show the existence of a route of bacterial colonization along the external and internal surfaces of Tenckhoff catheters implanted in experimental animals. The external route of progressive bacterial colonization extends from the cutaneous exit site through the dacron cuff and into the peritoneum. Bacterial growth along this route consists primarily of glycocalyx enclosed bacterial biofilms adherent to catheter and tissue surfaces, and this surface colonization may or may not give rise to peritoneal infection in which free-living bacteria are found in the peritoneal fluid. The rate of this progressive bacterial colonization depends on the degree of bacterial contamination of the exit site at the time of implantation. Exit site sterilization (hibitane) delays the process while inoculation with rabbit skin strains of Staphylococcus epidermidis accelerates it. Even with optimal implantation techniques, bacterial colonization proceeds via this subcutaneous route so that most Tenckhoff catheter surfaces are covered with a bacterial biofilm, consisting predominantly of gram positive cocci, within three weeks after the implantation of these devices. The rate of bacterial biofilm development on both surfaces of these Tenckhoff catheters, the bacterial colonization of peritoneal tissues, and the dissemination of bacteria into the peritoneal fluid are all significantly accelerated by dialysis in this experimental animal model of continuous ambulatory peritoneal dialysis (CAPD).     

Large bore catheters with surface treatments versus untreated catheters for vascular access in hemodialysis

Infection, thrombosis, and stenosis are among the most frequent complications associated with blood-contacting catheters. Complications resulting from infection remain a major problem for hemodialysis catheters, with significant numbers of catheters being removed due to catheter-related sepsis. Numerous strategies have been employed to reduce the occurrence of infection and im-prove long-term outcomes, with varying degrees of success. The most important is the careful and sterile handling by the attending staff of the catheters during hemodialysis treatments to minimize or stop a microbial colonization of the skin and the catheter. Another approach is coating the external surface of the catheters with substances which are antibacterial like silver and/or substances with low thrombogenicity like silicone. This investigation reviews results of animal and clinical experiments conducted to assess the efficacy and biocompatibility of silver and silicone coated dialysis catheters. It is concluded that silver coatings can reduce bacterial colonization and occurrence of infection associated with these devices. The catheters employing ion implantation of silicone rubber showed low thrombogenicity. Results of the studies indicate that ion beam based processes can be used to improve thrombus and infection resistance of blood contacting catheters. A new development is the microdomain structured surface (PUR-SMA coated catheters). Preliminary results with these catheters are very encouraging.     

A model of catheter-associated urinary tract infection initiated by bacterial contamination of the catheter tip

OBJECTIVE

To examine the microbial colonization of urinary catheters that have been used by patients, to model catheter colonization in vitro and thus provide information about the way bacteria gain access to the bladder during catheterization.

MATERIALS AND METHODS

Microbial growth patterns from patients’ indwelling catheters and from catheters used in an in vitro model of the catheterized urinary tract were compared. Catheters were cut into short segments, microorganisms from the inside and outside of each segment of the catheters were removed by sonication, and viable bacteria counted. DNA was extracted from selected patient catheter isolates and the DNA fragment of 16S ribosomal RNA was amplified by polymerase chain reaction and confirmed by DNA sequencing. The DNA sequences from the isolates obtained from different catheter sections and from urine in the same patient were compared.

RESULTS

After 1 day of catheterization there was significant bacterial growth on the outside of all the segments of patient catheters; there was significant growth on the inside of all segments by 4 days. Higher viable counts and a wider spectrum of genera were found on the outside than on the inside of these catheters. The same strains of bacteria, as determined by ≥98% similarity of the 16S ribosomal DNA sequence, were found on the outside and inside of catheters and in the urine. In the in vitro model, when the distal urethra was inoculated before inserting the catheter, the viable counts after incubation were variable along the outside of the catheter and the inside counts were uniformly high. By contrast, there was a different pattern after inoculating the inside of the distal end of the catheter, leading to an ascending biofilm on the inside. A smaller inoculum delayed but did not prevent infection in the model.

CONCLUSION

The present results are consistent with the hypothesis that contamination of the tip of the catheter while it is being inserted is a possible means by which bacteria gain access to the bladder.     

External Ventricular Drainage Catheters: Effect of Surface Heparinization on Bacterial Colonization and Infection

Summary  Surface heparinization of central venous catheters has earlier been shown to reduce the frequency of bacterial colonization and septicaemia. The present study was undertaken to investigate the benefit of surface heparinization of external ventricular drainage (EVD) catheters in relation to bacterial colonization, as measured by bacterial growth and examination by a 16S-rRNA PCR assay, of catheters and of samples of cerebrospinal fluid (CSF). Ninety-eight heparinized and one hundred unheparinized EVD catheters from the same batch of catheters were used. Twenty point five percent of the heparinized and 22.8% (p=0.63) of the unheparinized EVD catheters were colonized with bacteria. Culture of CSF, which is the definition of clinical infection in this study, yielded growth in 10.3% of patients with heparinized and in 6.3% (p=0.18) of those with unheparinized catheters. PCR examination yielded positive signal in 31.3% of patients with heparinized catheters and in 37.7% (p=0.061) of patients without (CSF and catheters). In the subgroup of patients with subarachnoid haemorrhages, there was a tendency, though not statistically significant, towards a lowered frequency of colonization with 23.1% for heparinized and 33.3% (p=0.31) for unheparinized catheters. PCR examination did not contribute any further to the diagnostic procedure in the patients concerned. The EVD catheters are skin-penetrating devices and contamination from the skin flora is common. Skin cultures, obtained after skin disinfection and insertion of catheters, showed growth of bacteria in 62% of the patients.     

DEVELOPMENT OF A STAPHYLOCOCCUS EPIDERMIDIS VASCULAR GRAFT INFECTION MODEL IN SHEEP

Staphylococcus epidermidis is an increasingly recognized causative organism of vascular graft infections. To increase our understanding of this problem we have tried to establish Staph. epidermidis vascular graft infection in sheep by direct inoculation. A 2 cm long, 5 mm diameter polytetrafluoroethylene (PTFE) or a gelatin sealed Dacron vascular graft was inserted into the left carotid artery, At the completion of the operation 1 mL of normal saline containing either 10⁴, 10⁶, or 10⁸ colony forming units (cfu) of a slime producing Staph. epidermidis was inoculated directly onto the graft. After 3 weeks the grafts were harvested in a sterile fashion. Swabs were taken of the perigraft tissues and the external and internal aspects of the grafts; a 3–5 mm segment of the graft was incubated in broth medium and a second segment was ground for 5 min and then incubated in broth medium. Note was made of the presence of abscess formation, anastomotic failure or thrombosis. Thirteen sheep received a PTFE graft and 14 received a gelatin sealed Dacron graft. Three sheep died immediately postoperatively. The rate of infection was 40% at 10⁴. 67% at 10⁶ and 80% at 10⁸ cfu Staph. epidermidis. In only four cases were all five cultures positive. In nine cases two or less cultures were positive, the majority of these being the broth cultures. Nine other organisms were isolated from nine mixed infections. Nine out of 13 PTFE and seven out of 11 Dacron grafts were infected. The rate of graft infection grew with increasing concentration of inoculum. Retrieval of bacteria was greatest when the graft was cultured directly, especially with physical disruption. Infection with additional organisms was common. There was no difference in the infection rate between gelatin sealed Dacron and PTFE.     

Subcutaneous tunneling of caudal catheters reduces the rate of bacterial colonization to that of lumbar epidural catheters

Bacterial colonization is regarded as a causative factor for septic complications of caudal catheters in children. To determine whether tunneling caudal catheters reduces the bacterial colonization rate effectively, we evaluated 506 children being treated with tunneled or untunneled caudal or untunneled lumbar epidural catheters. Four-hundred-nine children completed the study. After aseptic removal, the catheters were cultured and sent for microbiological assessment. We found a bacterial colonization rate of 29% in untunneled caudal catheters, 11% in tunneled caudal catheters, and 9% in untunneled lumbar catheters. No severe infectious complications were reported. There was no correlation between catheter retention time and bacterial colonization except for the first 24 h, during which no bacterial colonization was detected. The overall colonization rate remained constant at approximately 13%. We found a positive correlation between bacterial colonization and redness at the catheter entry site. We conclude that tunneled caudal epidural catheters can be used in children for postoperative analgesia without an increased risk of epidural infection.     

Bacterial colonization in hemodialysis temporary dual lumen catheters: a prospective study

AIMS: The use of hemodialysis temporary dual-lumen catheters is often complicated by infections, which may be a significant cause of death among patients with end stage renal disease (ESRD). The aim of this study was to assess the incidence of bacteremia and bacterial colonization related to non-tunneled, non-cuffed, dual-lumen temporary catheters in patients with ESRD submitted to hemodialysis. METHODS: This study included 29 patients with ESRD. After catheter implantation, patients were monitored throughout the period of catheter permanence by means of blood samples collected weekly from a peripheral vein. Bacteria were isolated and identified according to CLSI recommendations. When catheters were removed for any reason, their tips were evaluated microbiologically. RESULTS: A total of 194 blood samples from the 29 patients implanted with 55 catheters were analyzed. Of these, 15.5% (30 samples) demonstrated bacterial growth, principally Staphylococcus epidermidis (64.5%). Twenty patients (68.9%) presented at least one positive blood culture during follow-up. The median time for catheter colonization was 18.5 days (95% CI: 16.8-30.3). Of the 55 catheters implanted, 28 (50.9%) showed bacterial colonization, corresponding to 23.4 episodes/1000 catheter/days and 9.2 episodes of bacteremia /1000 catheter/days. Fifteen of 28 catheter tips analyzed showed bacterial growth (53.5%). In 14 of these (93.3%), there was agreement between the isolates from the catheter tip and blood cultures. Of 24 episodes of positive blood cultures from 20 different patients in 17 episodes (70.8%), the patients showed no clinical signs or symptoms of bacteremia. CONCLUSIONS: The high incidence of catheter colonization, the correlation between blood and catheter tip cultures, and the occurrence of frequent cases of asymptomatic bacteremia justify the proposal of routine peripheral blood collections to monitor patients undergoing hemodialysis with temporary dual-lumen catheters.     

The continuous femoral nerve block catheter for postoperative analgesia: bacterial colonization, infectious rate and adverse effects

We investigated the incidence of bacterial and vascular or neurological complications resulting from femoral nerve catheters used for postoperative analgesia. Patients requiring continuous femoral blockade were consecutively included. Using surgical aseptic procedure, 211 femoral nerve catheters were placed (short-beveled insulated needle, peripheral nerve stimulator). After 48 h, each catheter was removed and semiquantitative bacteriological cultures were performed on each distal catheter tip. Postoperative analgesia and antibiotics were standardized. All complications during the insertion of the catheters and postoperatively (after 48 h and 6 wk) were noted. Few initial complications with no immediate or delayed complications were noted (20 difficult insertions, 3 impossible injections, 3 ineffective catheters, and 12 vascular punctures). After 48 h, 208 catheters were analyzed; 57% had positive bacterial colonization (with a single organism in 53%). The most frequent organisms were Staphylococcus epidermidis (71%), Enterococcus (10%), and Klebsiella (4%). Neither cellulitis nor abscess occurred. Three transitory bacteremias likely related to the catheter occurred. After 6 wk, no septic complications were noted. One femoral paresthesia, partially recovered 1 yr later, was noted. We conclude that the risk of bacterial complications is small with femoral nerve catheters, although the rate of colonization is frequent. IMPLICATIONS: In this prospective study, continuous femoral nerve catheters were effective for postoperative analgesia but had a frequent rate of bacterial catheter colonization. We found no serious infections after short-term (2-day) infusion. Side effects were few, but one nerve injury occurred.     

Closed continuous drainage of cerebrospinal fluid via a lumbar subarachnoid catheter for treatment or prevention of cranial/spinal cerebrospinal fluid fistula.

One hundred and seven patients who had a lumbar subarachnoid catheter (teflon or silicone) placed for closed continuous cerebrospinal fluid (CSF) drainage between 1983-1991 are presented. Overall, the drain was successful in achieving the desired goal in 101 of 107 (94%) cases. There were no deaths. Five of 107 (5%) patients developed infections including two cases (2%) of meningitis. There were three cases (3%) of overdrainage with temporary neurologic decline, but all recovered. Five of fifteen (33%) teflon catheters required replacement because of occlusion, but only 5 of 92 (5%) silicone catheters required replacement. Transient lumbar nerve root irritation was seen in 15 of 107 (14%) patients treated for a CSF fistula, and all symptoms resolved after drain removal. CSF fistula/pseudomeningocele after spine surgery was cured by CSF drainage in 36 of 39 (92%) cases; there was a 10% incidence of infection (1 wound, 2 discitis, 1 meningitis). CSF fistula after cranial surgery was cured in 22 of 25 (87%) cases; there was 1 case of (4%) infection and 1 case (4%) of overdrainage. A drain was used to augment a tenuous dural closure in 38 patients with 100% success; no infection occurred and there were 2 cases (5%) of overdrainage. Five patients were successfully treated for traumatic CSF rhinorrhea/otorrhea without complications. The silicone catheter appears superior to the teflon catheter; however, both are simple, safe, and efficacious for the treatment or prevention of CSF fistulas.     

Presence of vitronectin and activated complement factor C9 on ventriculoperitoneal shunts and temporary ventricular drainage catheters.

OBJECT: The pathogenesis of cerebrospinal fluid (CSF) shunt infection is characterized by staphylococcal adhesion to the polymeric surface of the shunt catheter. Proteins from the CSF--fibronectin, vitronectin, and fibrinogen--are adsorbed to the surface of the catheter immediately after insertion. These proteins can interfere with the biological systems of the host and mediate staphylococcal adhesion to the surface of the catheter. In the present study, the presence of fibronectin, vitronectin, and fibrinogen on CSF shunts and temporary ventricular drainage catheters is shown. The presence of fragments of fibrinogen is also examined. METHODS: The authors used the following methods: binding radiolabeled antibodies to the catheter surface, immunoblotting of catheter eluates, and scanning force microscopy of immunogold bound to the catheter surface. The immunoblot showed that vitronectin was adsorbed in its native form and that fibronectin was degraded into small fragments. Furthermore, the study demonstrated that the level of vitronectin in CSF increased in patients with an impaired CSF-blood barrier. To study complement activation, an antibody that recognizes the neoepitope of activated complement factor C9 was used. The presence of activated complement factor C9 was shown on both temporary catheters and shunts. CONCLUSIONS: Activation of complement close to the surface of an inserted catheter could contribute to the pathogenesis of CSF shunt infection.     

Prevention of catheter sepsis by antibiotic bonding

The techniques of antibiotic bonding were applied to the problem of hyperalimentation catheter sepsis. Pretreatment with tridodecylmethylammonium chloride (TDMAC) increased the bonding of 14C-penicillin to polyethylene catheter segments from 3.1 to 212 micrograms/cm and to silicone elastomer catheter segments from 0.09 to 181 micrograms/cm. The elution of the bound ligands from silicone elastomer catheter segments in the presence of plasma was studied. At 2 weeks more than 60% of the bound TDMAC remained adherent to the catheter. The elution of the bonded penicillin from the silicone elastomer catheters was biphasic, initially 95% dissociated after 48 hours of incubation. A bioassay revealed that the dissociated penicillin was bacteriocidal. Polyethylene catheters were placed in the jugular vein of rats and positioned in the right atrium. The catheters were tunneled posteriorly, exited between the forelimb shoulder girdles, and connected to a swivel mechanism. The exit site was inoculated before closure with 1 X 10(8) Staphylococcus aureus. Five days after insertion the catheters were removed via sterile thoracotomy and the tips cultured. Untreated control catheters, catheters treated by antibiotic soaking, and catheters pretreated with TDMAC all had high rates of catheter colonization (60% to 80)%. TDMAC-penicillin-bonded catheters did not become colonized. This difference was significant (p less than 0.005). Antibiotic bonding may prove effective in preventing hyperalimentation catheter sepsis.     

Bacterial adhesion to cerebrospinal fluid shunts

Bacterial adherence to cerebrospinal fluid (CSF) shunts was analyzed in vivo and in vitro. Scanning electron micrographs (SEM's) of catheters removed from pediatric patients with shunts infected by Staphylococcus aureus or Klebsiella pneumoniae revealed numerous bacterial cells and microcolonies, leukocytes, and erythrocytes attached to the CSF catheters' inner walls, as well as the existence of surface irregularities, such as fissures, rugosities, and holes. Permeability analyses and SEM's demonstrated that catheters develop physical alterations over the period of implantation. Different bacterial strains presented a different in vitro adherence to CSF shunts, suggesting that this attachment may be affected by specific properties of the outer structures of each strain. The attachment of microbial pathogens to CSF shunts seems to contribute to the persistence of bacterial cells within a catheter and the onset of recurrent shunt infection. This study demonstrated that some bacteria can remain attached within shunts in vitro despite a CSF flow at rates up to 200 times higher than those normally demonstrated in vivo. Furthermore, surface irregularities found throughout this study may help to anchor and hide bacterial microcolonies. Based on these findings, it seems advisable to remove an infected shunt and to replace it with a new one after proper antimicrobial therapy, in order to prevent recurrent infections.     

Persistence of bacterial growth on antibiotic-loaded beads: Is it actually a problem?

Background and purpose?Implantation of antibiotic-loaded beads is used for orthopedic infections. However, recent in vitro reports have emphasized that bacteria can persist on—or even colonize—antibiotic-impregnated bone cement. We therefore assessed whether bacterial adherence and growth could be determined on gentami-cin- and gentamicin-vancomycin-loaded beads that had been removed after eradication of infection.

Material and methods?We bacteriologically examined 18 chains of antibiotic-loaded beads (11 gentami-cin-loaded, 7 gentamicin-vancomycin-loaded) that had been implanted because of orthopedic infections. Among the causative agents, Staphylococcus epidermidis, Staph-ylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) were the most frequent organisms identified.

Results?In 4 cases (3 with S. epidermidis and one with MRSA), we found that there was persistence of bacterial growth on the beads. S. epidermidis strains persisted only on gentamicin-loaded beads, while MRSA could grow on gentamicin-vancomycin-impregnated cement. In one case, the emergence of a gentamicin-resistant S. epidermidis strain was observed despite the fact that preoperative samples of S. epidermidis from this patient had been susceptible to the antibiotic.

Interpretation?Persistence of bacterial growth on bone cement remains a hazardous problem in orthopedic surgery. Adherence of bacteria to cement can lead to emergence of bacterial resistance to antibiotics and might result in clinical recurrence of infection.     

Analysis of retained ventricular shunt catheters.

To identify the causes of ventricular shunt catheter retention, 42 shunt removals in 28 patients in our neurosurgical clinic from 1982 to 1991 were analyzed. The mean patient age was 13.8 years (2 mos-78 yrs), and mean shunt duration was 20.1 months (0.5-94 mos). There were nine retained ventricular catheters, including five with obstruction of the ventricular catheter. Shunt duration was significantly longer compared with the unretained group. Three retained ventricular catheters were stained by HE for histological examination. Light microscopy showed the inner lumen of catheters filled with granulomatous connective tissue and reactive glial tissue, and giant cell reaction to silicone material. Scanning electron microscopy of two catheters found peeling on the inner surface of the catheter, evidence of aging of the material. Granulomatous connective tissue and glial tissue reaction to aged silicone are suggested as the cause of catheter retention.     

Cuff-shaving procedure. A rescue treatment for exit-site infection unresponsive to medical therapy

We performed 41 cuff-shaving procedures in 38 patients on continuousambulatory peritoneal dialysis (CAPD) with exit-site infectionunresponsive to medical treatment. Cuff shaving was performedon three patients with two catheters each. This procedure waseffective in eliminating 50% of S. aureus exit-site infectionand all S. epidermidis exit-site infection, but was ineffectivein Gram-negative exit-site infection. After cuff-shaving procedure,20 catheters (49%) were removed; 11 for persistent tunnel infectionand nine because of development of secondary peritonitis. Theprobability of catheter survival at 1 year was 50% and remainedstable thereafter. Cuff-shaving procedure may be a valuablemode of therapy for treating patients with S. aureus and/orS. epidermidis exit-site infection unresponsive to medical treatment.