Infections associated with indwelling devices: concepts of pathogenesis; infections associated with intravascular devices

Delayed versus primary sternal closure for left ventricular assist device implantation: Impact on mechanical circulatory support infections

BACKGROUND

Delayed sternal closure may be required after left ventricular assist device (LVAD) implantation due to coagulopathy or hemodynamic instability. There is conflicting data regarding infection risk.

METHODS

We performed a single-center, retrospective analysis of patients who received their first LVAD between May 2012 and January 2021. Patients were divided into delayed sternal closure (DSC) and primary sternal closure (PSC) groups. We used chi-squared or Fisher Exact tests, as appropriate, to compare the incidence of postoperative LVAD-related infections (mediastinal/sternal wound) and LVAD-specific infections (driveline and pump pocket) after definitive chest closure between these two groups.

RESULTS

A total of 327 patients met eligibility criteria, including 127 (39%) patients that underwent DSC and 200 (61%) patients that had a PSC. Demographic and clinical characteristics were similar except for an overrepresentation of men (87% vs. 75%, p = .016), Interagency Registry of Mechanically Assisted Circulatory Support class I-II patients (89% vs 66%, p < .001), patients with a previous sternotomy (43% vs 13%, p < .001), and patients with chronic kidney disease (55% vs 43%, p = .030) in the DSC group. The median DSC time was 24 (IQR: 24-48) hours. The incidence of LVAD-related mediastinal/sternal wound infection was similar between the DSC and PSC groups (4.7% vs 3.0%, p = .419). There was no difference between DSC and PSC groups in the incidence of driveline infection (6.3% vs 9%, p = .411) and pump pocket infection (1.6% vs 1.5%, p =.901), respectively.

CONCLUSIONS

DSC does not seem to increase the incidence of LVAD-related or LVAD-specific infection rates in heart failure patients undergoing device implantation surgery.

Infections Associated with Prosthetic Devices: Clinical Considerations

The successful development of synthetic materials and introduction of artificial devices into nearly all body systems has been shadowed by the adaptation of microorganisms to the opportunities these devices afford for eluding defenses and invading the host. Clinicians are faced with the task of recognizing the manifestations of device-associated infection, predicting the likely pathogens involved, knowing the appropriate diagnostic methods, and initiating appropriate therapy. Infections associated with prosthetic heart valves are particularly challenging to successfully treat; surgical replacement may be necessary. Infection associated with an artificial joint usually requires removal of the device in addition to appropriate antibiotics. Intravascular associated infections are the leading cause of nosocomial bacteremias and, because of their intravascular location, these infections are often life catheter threatening if not promptly diagnosed and treated. Even contact lenses, external to epithelial surfaces, may give rise to serious sight-threatening infections. Although artificial devices play a paramount role in medicine today, infection is an ever present potential with which clinicians must be familiar.

Role of Klebsiella pneumoniae type 1 and type 3 fimbriae in colonizing silicone tubes implanted into the bladders of mice as a model of catheter-associated urinary tract infections

Catheter-associated urinary tract infections are biofilm-mediated infections that cause a significant economic and health burden in nosocomial environments. Using a newly developed murine model of this type of infection, we investigated the role of fimbriae in implant-associated urinary tract infections by the Gram-negative bacterium Klebsiella pneumoniae, which is a proficient biofilm former and a commonly isolated nosocomial pathogen. Studies have shown that type 1 and type 3 fimbriae are involved in attachment and biofilm formation in vitro, and these fimbrial types are suspected to be important virulence factors during infection. To test this hypothesis, the virulence of fimbrial mutants was assessed in independent challenges in which mouse bladders were inoculated with the wild type or a fimbrial mutant and in coinfection studies in which the wild type and fimbrial mutants were inoculated together to assess the results of a direct competition in the urinary tract. Using these experiments, we were able to show that both fimbrial types serve to enhance colonization and persistence. Additionally, a double mutant had an additive colonization defect under some conditions, indicating that both fimbrial types have unique roles in the attachment and persistence in the bladder and on the implant itself. All of these mutants were outcompeted by the wild type in coinfection experiments. Using these methods, we are able to show that type 1 and type 3 fimbriae are important colonization factors in the murine urinary tract when an implanted silicone tube is present.

Enterococcus faecalis overcomes foreign body-mediated inflammation to establish urinary tract infections

Urinary catheterization elicits major histological and immunological changes that render the bladder susceptible to microbial invasion, colonization, and dissemination. However, it is not understood how catheters induce these changes, how these changes act to promote infection, or whether they may have any protective benefit. In the present study, we examined how catheter-associated inflammation impacts infection by Enterococcus faecalis, a leading cause of catheter-associated urinary tract infection (CAUTI), a source of significant societal and clinical challenges. Using a recently optimized murine model of foreign body-associated UTI, we found that the implanted catheter itself was the primary inducer of inflammation. In the absence of the silicone tubing implant, E. faecalis induced only minimal inflammation and was rapidly cleared from the bladder. The catheter-induced inflammation was only minimally altered by subsequent enterococcal infection and was not suppressed by inhibitors of the neurogenic pathway and only partially by dexamethasone. Despite the robust inflammatory response induced by urinary implantation, E. faecalis produced biofilm and high bladder titers in these animals. Induction of inflammation in the absence of an implanted catheter failed to promote infection, suggesting that the presence of the catheter itself is essential for E. faecalis persistence in the bladder. Immunosuppression prior to urinary catheterization enhanced E. faecalis colonization, suggesting that implant-mediated inflammation contributes to the control of enterococcal infection. Thus, this study underscores the need for novel strategies against CAUTIs that seek to reduce the deleterious effects of implant-mediated inflammation on bladder homeostasis while maintaining an active immune response that effectively limits bacterial invaders.

Bacterial retention on superhydrophobic titanium surfaces fabricated by femtosecond laser ablation

Two-tier micro- and nanoscale quasi-periodic self-organized structures, mimicking the surface of a lotus Nelumbo nucifera leaf, were fabricated on titanium surfaces using femtosecond laser ablation. The first tier consisted of large grainlike convex features between 10 and 20 μm in size. The second tier existed on the surface of these grains, where 200 nm (or less) wide irregular undulations were present. The introduction of the biomimetic surface patterns significantly transformed the surface wettabilty of the titanium surface. The original surface possessed a water contact angle of θ(W) 73 ± 3°, whereas the laser-treated titanium surface became superhydrophobic, with a water contact angle of θ(W) 166 ± 4°. Investigations of the interaction of S. aureus and P. aeruginosa with these superhydrophobic surfaces at the surface-liquid interface revealed a highly selective retention pattern for two pathogenic bacteria. While S. aureus cells were able to successfully colonize the superhydrophobic titanium surfaces, no P. aeruginosa cells were able to attach to the surface (i.e., any attached bacterial cells were below the estimated lower detection limit).

The nature and role of microbial biofilm in infections associated with prosthetic devices

An understanding of the role of microbial biofilm in infections associated with prosthetic devices is essential for the implementation of successful treatment regimens.

The mode of biofilm formation on smooth surfaces by Campylobacter jejuni

Many microorganisms produce extracellular polymers referred to collectively as "slime" or glycocalyx, and form biofilms on solid surfaces in natural ecosystems. Campylobacter jejuni, one of the most important foodborne pathogens, also has the ability to form biofilm on stainless steel, glass, or polyvinyl chloride in vitro. However, the issue of biofilm formation by Campylobacter species has not been extensively examined. The present study was performed to examine the mode of adhesion of C. jejuni to a smooth surface. When bacterial suspensions in Brucella broth were incubated in microplate wells with a glass coverslip, microcolonies 0.5~2 mm in diameter were formed on the coverslip within 2 hr from the start of incubation. These microcolonies gradually grew and formed a biofilm of net-like connections within 6 hr. Transmission electron microscopy indicated that massive amounts of extracellular material masked the cell surface, and this material bound ruthenium red, suggesting the presence of a polysaccharide moiety. Scanning electron microscopy indicated that the flagella acted as bridges, forming net-like connections between the organisms. To determine the genes associated with biofilm formation, aflagellate (flaA(-)) and flagellate but non-motile (motA(-)) mutants were constructed from strain 81-176 by natural transformation-mediated allelic exchange. The flaA(-) and motA(-) mutants did not form the biofilm exhibited by the wild-type strain. These findings suggest that flagella-mediated motility as well as flagella is required for biofilm formation in vitro.

An appraisal of the strengths and weaknesses of newborn and juvenile rat models for researching gastrointestinal development

Research on the impact of bioactive compounds on the development and functional maturation of the gastrointestinal (GI) tract using newborn and juvenile rats has greatly contributed to the knowledge of GI physiology and to the improved clinical management of both premature and full-term newborns. Of the animal models available, two types have been described for use with young rats – maintenance models and substitution models. Maintenance models are those in which the young are reared with the dam and therefore benefit from continuation of natural nutrition and maternal care. Substitution models are those in which the young are reared in the absence of the dam using artificially formulated milk delivered by various means into specific GI sites. In this review, we describe these models and their operation, and discuss the strengths and weaknesses of each. Attention is also given to questions of scientific validity and some animal welfare issues raised by the use of these models.

Use of telechelic cis-1,4-polyisoprene cationomers in the synthesis of antibacterial ionic polyurethanes and copolyurethanes bearing ammonium groups

New crosslinked ionic polyurethanes and copolyurethanes were yielded by reaction of telechelic cis-1,4-oligoisoprenes, bearing a variable number of ammonium and hydroxy groups, with isocyanurate of isophorone diisocyanate (I-IPDI). Aiming for a comparative study, polyurethane elastomers based on non-ionic telechelic oligomers were also synthesized. Thermo-mechanical behavior and crosslinking density of these three families of materials were investigated by DMTA and swelling test, respectively. Surface properties were examined by static contact angle measurements and AFM imaging. The bactericidal activity of the polymers was investigated by enumerating living Pseudomonas aeruginosa on material surfaces and on water suspensions. The number of attached living bacteria was found to depend on the chemical structure of the material and on the contact time between the microorganisms and the surface. An exclusive bactericidal activity was obtained with the ionic copolyurethane family. Materials with weak crosslinking density were found to release bactericidal moieties. The abilities of the polymers to prevent bacterial growth were examined through zone of inhibition experiments against P. aeruginosa, which shown a bacteriostatical effect for each synthesized material. These experiments were not sufficiently sensitive to detect the leaching of bactericidal moieties from the materials with weak crosslinking density. When the zone of inhibition experiments was performed on more sensitive bacteria, namely Staphylococcus epidermidis, the leaching of bactericidal moieties as well as bacteriostatic effect was detected. This work demonstrates the potentiality for making functional biomaterials from natural rubber, a renewable resource.

Gallstones containing bacteria are biofilms: bacterial slime production and ability to form pigment solids determines infection severity and bacteremia

OBJECTIVE

Gallstone bacteria provide a reservoir for biliary infections. Slime production facilitates adherence, whereas beta-glucuronidase and phospholipase generate colonization surface. These factors facilitate gallstone formation, but their influence on infection severity is unknown.

METHODS

Two hundred ninety-two patients were studied. Gallstones, bile, and blood (as applicable) were cultured. Bacteria were tested for beta-glucuronidase/phospholipase production and quantitative slime production. Infection severity was correlated with bacterial factors.

RESULTS

Bacteria were present in 43% of cases, 13% with bacteremia. Severe infections correlated directly with beta-glucuronidase/phospholipase (55% with vs 13% without, P < 0.0001), but inversely with slime production (55 vs 8%, slime <75 or >75, P = 0.008). Low slime production and beta-glucuronidase/phospholipase production were additive: Severe infections were present in 76% with both, but 10% with either or none (P < 0.0001). beta-Glucuronidase/phospholipase production facilitated bactibilia (86% with vs 62% without, P = 0.03). Slime production was 19 (+/-8) vs 50 (+/-10) for bacteria that did or did not cause bacteremia (P = 0.004). No bacteria with slime >75 demonstrated bacteremia.

CONCLUSIONS

Bacteria-laden gallstones are biofilms whose characteristics influence illness severity. Factors creating colonization surface (beta-glucuronidase/phospholipase) facilitated bacteremia and severe infections; but abundant slime production, while facilitating colonization, inhibited detachment and cholangiovenous reflux. This shows how properties of the gallstone biofilm determine the severity of the associated illness.

SdrF, a Staphylococcus epidermidis Surface Protein, Binds Type I Collagen

Staphylococcus epidermidis is the leading cause of device-related infections. These infections require an initial colonization step in which S. epidermidis adheres to the implanted material. This process is usually mediated by specific bacterial surface proteins and host factors coating the foreign device. Some of these surface proteins belong to the serine-aspartate repeat (Sdr) family, which includes adhesins from Staphyloccus aureus and S. epidermidis. Using a heterologous expression system in Lactococcus lactis to overcome possible staphylococcal adherence redundancy we observed that one of these Sdr proteins, SdrF, mediates binding to type I collagen when present on the lactococcal cell surface. We used lactococcal recombinant strains, a protein-protein interaction assay and Western ligand blot analysis to demonstrate that this process occurs via the B domain of SdrF and both the alpha1 and alpha2 chains of type I collagen. It was also found that a single B domain repeat of S. epidermidis 9491 retains the capacity to bind to type I collagen. We demonstrated that the putative ligand binding N-terminal A domain does not bind to collagen which suggests that SdrF might be a multiligand adhesin. Antibodies directed against the B domain significantly reduce in vitro adherence of S. epidermidis to immobilized collagen.

Biliary bacterial factors determine the path of gallstone formation

BACKGROUND

Bacteria cause pigment gallstones and can act as a nidus for cholesterol gallstone formation. Bacterial factors that facilitate gallstone formation include beta-glucuronidase (bG), phospholipase (PhL), and slime. The current study sought to determine whether bacterial factors influence the path of gallstone formation.

METHODS

A total of 382 gallstones were cultured and/or examined using scanning electron microscopy (SEM). Bacteria were tested for bG and slime production. Gallstone composition was determined using infrared spectrography. Ca-palmitate presence documented bacterial PhL production. Groups were identified based upon bacterial factors present: slime and bGPhL (slime/bGPhL), bGPhL only, and slime only. Influence of bacterial stone-forming factors on gallstone composition and morphology was analyzed.

RESULTS

Bacteria were present in 75% of pigment, 76% of mixed, and 20% of cholesterol stones. Gallstones with bGPhL producing bacteria contained more pigment (71% vs. 26%, P < .0001). The slime/bGPhL group was associated (79%) with pigment stones, bGPhL was associated (56%) with mixed stones, while slime (or none) only was associated (67%) with cholesterol stones (P < .031, all comparisons).

CONCLUSIONS

Bacterial properties determined the path of gallstone formation. Bacteria that produced all stone-forming factors promoted pigment stone formation, while those that produced only bGPhL promoted mixed stone formation. Bacteria that only produced slime lacked the ability to generate pigment solids, and consequently were more common in the centers of cholesterol stones. This shows how bacterial characteristics may govern the process of gallstone formation.

Staphylococci and implant surfaces: a review

Surfaces of internal fracture fixation implants are generally designed to encourage soft- and/or hard-tissue adherence, eventually leading to tissue or osseo integration. Unfortunately, this feature may also encourage bacterial adhesion. About half of the two million cases of nosocomial infections per year in the US are associated with indwelling devices. In the UK, implant-associated infections are estimated to cost pound 7-11 million per year, and with the rise in antibiotic-resistant bacteria, are an important issue. Soft-tissue infections and osteomyelitis are serious complications associated with implants, particularly open fractures, external fixation devices, and intramedullary nailing. Consequences of implant-associated infections include prolonged hospitalization with systemic antibiotic therapy, several revision procedures, possible amputation, and even death. This review discusses the issue of implant-associated infections and some of the methods used to prevent bacterial adhesion to osteosynthesis implants.

Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions

Persistence of infection can occur when the host immune response is compromised because of the presence of a foreign implant. Surface modification of biomaterials with phospholipid polymers may enhance biocompatibility and reduce incidence of infection by impeding bacterial and leukocyte adhesion. A rotating disk model, which generates shear stress from 0 to 18 dynes/cm(2), was used to characterize adhesion of neutrophils, monocytes, and bacteria in phosphate-buffered saline (PBS) or 25% human serum on polyethylene terephthalate surfaces coated with a phospholipid polymer, poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate (BMA)]. The material designated PMB30 contains a methylene chain length, (CH(2))(n), of n = 2, whereas PMHB30 contains a chain length of n = 6. In PBS, bacterial adhesion was shear stress dependent with the lowest bacterial density observed on PMB30. However, the presence of serum proteins eliminated shear stress and surface chemistry effects in addition to bacterial adhesion reduced to <10% of adhesion in PBS. Trends for leukocyte adhesion in serum demonstrated shear dependence with PMB30 exhibiting the lowest cell density throughout the range of shear stresses. In conclusion, modification of the polyethylene terephthalate surfaces with phospholipid polymers resulted in reduced bacterial and leukocyte adhesion. Furthermore, shortening the methylene chain length of the MAPC copolymer most effectively reduced adhesion.

Infections associated with medical devices: pathogenesis, management and prophylaxis

The insertion or implantation of foreign bodies has become an indispensable part in almost all fields of medicine. However, medical devices are associated with a definitive risk of bacterial and fungal infections. Foreign body-related infections (FBRIs), particularly catheter-related infections, significantly contribute to the increasing problem of nosocomial infections. While a variety of micro-organisms may be involved as pathogens, staphylococci account for the majority of FBRIs. Their ability to adhere to materials and to promote formation of a biofilm is the most important feature of their pathogenicity. This biofilm on the surface of colonised foreign bodies is regarded as the biological correlative for the clinical experience with FBRI, that is, that the host defence mechanisms often seem to be unable to handle the infection and, in particular, to eliminate the micro-organisms from the infected device. Since antibacterial chemotherapy is also frequently not able to cure these infections despite the use of antibacterials with proven in vitro activity, removal of implanted devices is often inevitable and has been standard clinical practice. However, in specific circumstances, such as infections of implanted medical devices with coagulase-negative staphylococci, a trial of salvage of the device may be justified. All FBRIs should be treated with antibacterials to which the pathogens have been shown to be susceptible. In addition to systemic antibacterial therapy, an intraluminal application of antibacterial agents, referred to as the 'antibiotic-lock' technique, should be considered to circumvent the need for removal, especially in patients with implanted long-term catheters. To reduce the incidence of intravascular catheter-related bloodstream infections, specific guidelines comprising both technological and nontechnological strategies for prevention have been established. Quality assurance, continuing education, choice of the catheter insertion site, hand hygiene and aseptic techniques are aspects of particular interest. Furthermore, all steps in the pathogenesis of biofilm formation may represent targets against which prevention strategies may be directed. Alteration of the foreign body material surface may lead to a change in specific and nonspecific interactions with micro-organisms and, thus, to a reduced microbial adherence. Medical devices made out of a material that would be antiadhesive or at least colonisation resistant would be the most suitable candidates to avoid colonisation and subsequent infection. Another concept for the prevention of FBRIs involves the impregnation of devices with various substances such as antibacterials, antiseptics and/or metals. Finally, further studies are needed to translate the knowledge on the mechanisms of biofilm formation into applicable therapeutic and preventive strategies.

Local Delivery of Vancomycin for the Prophylaxis of Prosthetic Device-Related Infections

PURPOSE

To evaluate the in vivo efficacy and pharmacokinetics of vancomycin delivered from glycerylmonostearate (GMS) implants in a prosthetic-device based biofilm infection model.

METHODS

A biofilm infection model was developed in male Sprague-Dawley rats by implanting a vascular graft on the dorsal side of each rat and infecting it with 1.5 x 10(8) cfu/ml Staphylococcus epidermidis. The rats were divided into 3 groups of 6 rats each: 1) the control group that received no antibiotics, 2) the IM group that received multiple IM injections of vancomycin at a dose of 25 mg/kg every 6 h for a total of 12 doses, and 3) the implant group that received GMS implants designed to deliver vancomycin at a total dose of 300 mg/kg for a period of 4 days. The pharmacokinetics of vancomycin was determined from IM and implant groups by analyzing for vancomycin in blood using HPLC. In vivo efficacy was studied by evaluation of the wound site and the prosthetic device upon excision, for evidence of infection in the form of purulent discharge at the wound site and yellowish discoloration of the prosthetic device and inflammation as sign of biofilm formation. Microbiological evaluation on the wound site and the prosthetic device was performed by culturing the swabs at the wound site and the prosthetic device in sterile tryptic soy broth for 36-48 h at 37 degrees C.

RESULTS

Vancomycin was successfully delivered in a sustained manner for 100 h from GMS implants and the resulting plasma profile showed that the concentrations, after an initial burst, plateaued at about of 4.77 +/- 1.43 mug/ml with less fluctuations than the IM group in which the plasma concentrations fluctuated between 2.73 +/- 0.94 mug/ml and 19.26 +/- 3.67 mug/ml. Upon excision of the wound site, all the animals in the control group developed infection in the form of purulent discharge and yellowish discoloration of the prosthetic device. However, none of the rats in the implant group showed evidence of infection clearly demonstrating the efficacy of the local delivery system in preventing infection. Systemically delivered vancomycin by IM injections failed to prevent infection in four out of six rats. Microbiological evaluation of the wound site and prosthetic device resulted in isolation of biofilm-producing organisms such as Staphylococcus epidermidis, Enterococcus faecalis, and Staphylococcus aureus. These organisms were isolated in greater number of animals in the control group compared to the IM and implant groups.

CONCLUSIONS

The GMS implants as a delivery system for vancomycin were successful in preventing infection in all the animals compared to the IM and control groups demonstrating the efficacy of a local delivery system in a prosthetic device related biofilm infection model.

Surface-Imprinted Polyurethane Having Affinity Sites for Ampicillin

Affinity sites for an antibacterial drug, ampicillin, were created on the surface of polyurethane using the technique of non-covalent molecular imprinting. This was achieved by polymerizing aminophenylboronic acid in the presence of the ampicillin as a template. The extent of adsorption of the drug by the imprinted surface is nearly five times higher than the non-imprinted surface. The in vitro release studies have shown that the drug is retained for a prolonged period on the imprinted surface while it is rapidly released from the non-imprinted surface. These modified materials were subjected to interactions with two bacterial strains, E. Coli and S. aureus. These species could not adhere to the imprinted surface, further showing the ability of the surface to retain the drug for a prolonged period of time. The non-imprinted surface retained the bacterial strains, reflecting the lack of the drug on the surface. This novel approach seems to be useful for creating surfaces capable of retaining components of interest through non-covalent interactions to impart specific features, such as improved blood compatibility and antibacterial properties. [diagram in text].

Staphylococcus aureus adhesion to titanium oxide surfaces coated with non-functionalized and peptide-functionalized poly(L-lysine)-grafted-poly(ethylene glycol) copolymers

Implanted biomaterials are coated immediately with host plasma constituents, including extracellular matrix (ECM); this reaction may be undesirable in some cases. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) has been shown to spontaneously adsorb from aqueous solution onto metal oxide surfaces, effectively reducing the degree of non-specific adsorption of blood and ECM proteins, and decreasing the adhesion of fibroblastic and osteoblastic cells to the coated surfaces. Cell adhesion through specific peptide-integrin receptors could be restored on surfaces coated with PLL-g-PEG functionalized with peptides of the RGD (Arg-Asp-Gly) type. To date, no study has examined the effect of surface modifications by PLL-g-PEG-based polymers on bacterial adhesion. The ability of Staphylococcus aureus to adhere to the ECM and plasma proteins deposited on biomaterials is a significant factor in the pathogenesis of medical-device-related infections. This study describes methods for visualizing and quantifying the adhesion of S. aureus to smooth and rough (chemically etched) titanium surfaces without and with monomolecular coatings of PLL-g-PEG, PLL-g-PEG/PEG-RGD and PLL-g-PEG/PEG-RDG. The different surfaces were exposed to S. aureus cultures for 1-24h and bacteria surface density was evaluated using scanning electron microscopy and fluorescence microscopy. Coating titanium surfaces with any of the three types of copolymers significantly decreased the adhesion of S. aureus to the surfaces by 89-93% for PLL-g-PEG, and 69% for PLL-g-PEG/PEG-RGD. Therefore, surfaces coated with PLL-g-PEG/PEG-RGD have the ability to attach cells such as fibroblasts and osteoblasts while showing reduced S. aureus adhesion, resulting in a selective biointeraction pattern that may be useful for applications in the area of osteosynthesis, orthopaedic and dental implantology.

Poly(ethylene glycol)-polyacrylate copolymers modified to control adherent monocyte-macrophage physiology: Interactions with attachingStaphylococcus epidermidis orPseudomonas aeruginosa bacteria

The ability of various surface modifications of poly(ethylene glycol)-graft-polyacrylate (PEG-g-PA) copolymers (tethered adhesion peptides and fragments of monoclonal antibodies) to modulate monocyte-macrophage cell interactions with surface colonizing bacteria is reported. The PEG-g-PA copolymers were made to inhibit nonspecific protein and cellular adhesion. The copolymers were then covalently modified with either cell adhesion peptides (YRGDS, YEILDV, or YRGES) or fragments of antibodies to monocyte-macrophage integrin receptors (anti-VLA4, anti-beta(1), anti-beta(2), and anti-CD64), which are known to enhance macrophage adhesion and perhaps modulate their activation. Cytokine expression and phagocytosis response by surface adherent monocyte-macrophages to Staphylococcus epidermidis and Pseudomonas aeruginosa bacteria were quantified. The cytokine expression (interleukins 6 and 1 beta) of adherent macrophages in response to the modified polymers only and to bacterial challenges were quantified by dynamic ELISA assays. The adherent macrophage phagocytic response (oxidative burst) to various materials is compared to oxidative responses to both opsonized and nonopsonized S. epidermidis and P. aeruginosa bacteria. The efficiency of adherent macrophages to ingest and kill both species was determined using radiolabeled and fluorescent labeled bacterial cell ingestion studies as a function of the PEG-g-PA surface modification. Materials modified with adhesion peptides marginally enhanced (2x) macrophage attachment versus controls but, upon bacterial challenges, these materials predisposed adherent macrophages to overexpress proinflammatory cytokines and to exhibit a significant phagocytic response. Conversely, PEG-g-PA materials modified by fragments of monoclonal antibodies significantly enhanced (7x) macrophage adhesion but, upon bacterial challenge, "per cell" cytokine expression levels were reduced compared to peptide modified materials. Macrophages adhering to antibody fragment modified surfaces also exhibited sustained enhanced phagocytic response and higher bacterial killing efficiencies when compared with peptide modified materials.

Macroporous poly(ϵ-caprolactone) with antimicrobial activity obtained by iodine polymerization

The most serious problem usually encountered in the field of implanted biomedical devices is infectious morbidity as a primary source of mortality. In this work, the synthesis and characterization of a macroporous iodine-based sanitizer (iodophor), poly(caprolactone)-iodine (PCL-I(2)), are presented. Characterization methods include nuclear magnetic resonance spectroscopy, gel permeation chromatography, nitrogen adsorption-desorption, and scanning electron microscopy. The in vitro cytotoxicity to CHO cells based on cell viability with Chinese hamster ovary cells (CHO) and antimicrobial activities against Escherichia coli and Staphylococcus aureus were examined. The obtained macropore PCL-I(2) structures had a rather narrow size distribution. The PCL-I(2) iodophor was noncytotoxic to Chinese hamster ovary cells. The antimicrobial activities of the PCL-I(2) were assessed against E. coli and S. aureus. The tested PCL-I(2) showed better antimicrobial activity against E. coli than against S. aureus.

Identification and characterization of a novel autolysin (Aae) with adhesive properties from Staphylococcus epidermidis

Staphylococcus epidermidisbiofilm formation on polymer surfaces is considered a major pathogenicity factor in foreign-body-associated infections. Previously, the 148 kDa autolysin AtlE fromS.epidermidis, which is involved in the initial attachment of the cells to polymer surfaces and also binds to the extracellular matrix protein vitronectin, was characterized. Here, the characterization of a novel autolysin/adhesin (Aae) inS.epidermidis is described. Aae was identified as a 35 kDa surface-associated protein that has bacteriolytic activity and binds vitronectin. Its N-terminal amino acid sequence was determined and the respective gene,aae, was cloned. DNA-sequence analysis revealed thataaeencodes a deduced protein of 324 amino acids with a predicted molecular mass of 35 kDa. Aae contains three repetitive sequences in its N-terminal portion. These repeats comprise features of a putative peptidoglycan binding domain (LysM domain) found in a number of enzymes involved in cell-wall metabolism and also in some adhesins. Expression ofaaebyEscherichia coliand subsequent analysis revealed that Aae possesses bacteriolytic activity and adhesive properties. The interaction of Aae with fibrinogen, fibronectin and vitronectin was found to be dose-dependent and saturable and to occur with high affinity, by using the real-time Biomolecular Interaction Analysis (BIA). Aae binds to the Aα- and Bβ-chains of fibrinogen and to the 29 kDa N-terminal fragment of fibronectin. In conclusion, Aae is a surface-associated protein with bacteriolytic and adhesive properties representing a new member of the staphylococcal autolysin/adhesins potentially involved in colonization.

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.

Pathogenesis of infections due to coagulase-negative staphylococci

As a group, the coagulase-negative staphylococci (CoNS) are among the most frequently isolated bacteria in the clinical microbiology laboratory and are becoming increasingly important, especially as causes of hospital-acquired infections. These bacteria are normal inhabitants of human skin and mucous membranes and, therefore, one of the major challenges of daily diagnostic work is to distinguish clinically significant CoNS from contaminant strains. This overview addresses current knowledge of the pathogenesis of infections due to CoNS and particularly focuses on virulence factors of the species Staphylococcus epidermidis. S epidermidis has been identified as a major cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. Most important in the pathogenesis of foreign-body-associated infections is the ability of these bacteria to colonise the polymer surface by the formation of a thick, multilayered biofilm. Biofilm formation takes place in two phases. The first phase involves the attachment of the bacteria to polymer surfaces that may be either unmodified or coated with host extracellular matrix proteins. In the second phase, the bacteria proliferate and accumulate into multilayered cell clusters that are embedded in an extracellular material. The bacterial factors involved in both phases of biofilm formation are discussed in this review. In addition, the most important aspects of the pathogenic potential of S saprophyticus, S lugdunensis, and S schleiferi are described, although, compared with S epidermidis, much less is known in these species concerning their virulence factors.

Immunology of Staphylococcal biofilm infections in the eye: new tools to study biofilm endophthalmitis

Endophthalmitis is an important disease of the eye that is most frequently caused by postoperative and post-traumatic introduction of bacteria into the posterior segment of the eye. In the case of severe infections, visual acuity is greatly damaged or completely lost. Much work has focused on the ability of planktonic bacteria to cause infection and ocular damage while little work has focused on chronic infections in endophthalmitis mediated by the formation of bacterial biofilms on the surface of the lens. This review focuses on the interaction of Staphylococcus aureus and Staphylococcus epidermidis lens-associated biofilms in endophthalmitis. Additionally, this review highlights some relevant biofilm-immune system interactions and outlines a new in vivo mouse model to explore biofilm-related infections in endophthalmitis.

Fibrin sheath enhances central venous catheter infection

OBJECTIVE

To determine whether fibrin-coated central venous catheters have a higher infection rate, and spawn more septic emboli, than uncoated catheters after exposure to bacteremia.

DESIGN

Animal study comparing catheter infection and blood cultures of fibrin-coated and uncoated catheters exposed to bacteremia.

SETTING

Animal laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

A total of 210 rats had catheters placed with the proximal end buried subcutaneously. Rats were divided into three groups: tail vein bacterial injection on day 0 (no fibrin group) or on day 10 (fibrin group), or no injection/saline injection (control, n = 40). Bacterial injections were 1 x 108 colony forming units of either Staphylococcus epidermidis (n = 100) or Enterobacter cloacae (n = 60). Animals were killed 3 days after injection. Blood cultures were obtained via cardiac puncture, and catheters were removed via the chest. Half of the catheter was rolled onto agar and the other half was placed in trypticase soy broth. Plates and broth were incubated at 37 degrees C for 48 hrs. The presence of >15 colonies on roll plates, or growth in broth, was accepted as a positive sign of infection. Microscopy was performed on day 20-10 catheters. Thirty animals without catheters had bacterial injections and underwent blood culture 3 days after injection.

MEASUREMENTS AND MAIN RESULTS

Catheter infection with S. epidermidis occurred in 32% of roll plates and 80% of broth from the fibrin group vs. 4% and 20% from the no fibrin group (p <.01 for each). Catheter infection with E. cloacae occurred in 50% of roll plates and 80% of broth from the fibrin group vs. 0% and 12% from the no fibrin group (p <.01 for each). Positive blood cultures occurred in 47 of 68 animals from the fibrin group vs. 8 of 68 from the no fibrin group (p <.01). Microscopy showed a fibrin sheath on 20 of 20 catheters. Without catheters, 30 of 30 blood cultures were negative.

CONCLUSION

The fibrin sheath significantly enhanced catheter-related infection and persistent bacteremia.

[Catheter-related infection in intensive care. Physiopathology, diagnosis, treatment and prevention]

PURPOSE

To review the mechanisms, diagnosis, treatment and prophylaxis of catheter-related sepsis in intensive care unit patients.

DATA SOURCES

A Medline research of the English- or French-language reports published between 1966 and 2000 and a manual research of references of relevant papers.

STUDY SELECTION

Experimental, clinical and basic research studies related to catheter-related sepsis.

DATA EXTRACTION

Data in selected articles were reviewed, and relevant clinical information was extracted.

DATA SYNTHESIS

Infection remains the major complication related to catheter insertion. No bacteriological exam or systematic catheter change is required in the absence of infection suspicion. In the intensive care unit, and without septic shock, the surveillance of skin cultures at the catheter insertion site or the time to positivity of hub-blood versus peripheral-blood culture determination may reduce the number of unnecessary removed catheters. Catheter change over a guidewire is not recommended because of the risk of dissemination of infection. When the catheter is removed, a quantitative culture is warranted. The treatment of catheter-related sepsis is based on catheter removal. The use of antibiotics is limited to some organisms or when the infection is complicated. The persistence of fever and positive blood cultures 72 h after catheter removal require to look for dissemination of infection or septic thrombophlebitis, especially if S. aureus or Candida are incriminated. The treatment of infection without catheter removal is not recommended in the intensive care unit because of a high risk of treatment failure. Compliance with catheter care guidelines and continuing quality improvement programs are the two major procedures in reducing catheter infection.

CONCLUSIONS

Improved understanding of the pathophysiology of catheter-related sepsis has led to improved prevention. Compliance with catheter care guidelines and continuing quality improvement programs are majors procedures to reduce the risk of catheter infection.

Comparative in vitro activity of vancomycin and levofloxacin in combination with rifampin against planktonic versus sessile cells of Staphylococcus epidermidis

STUDY OBJECTIVE

To evaluate the activity of vancomycin and levofloxacin alone and combined with rifampin against planktonic and sessile cells.

INTERVENTION

Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of the three drugs were determined against a clinical isolate of methicillin-resistant Staphylococcus epidermidis (MRSE 23) and a reference strain of MRSE (ATCC 35984).

MEASUREMENTS AND MAIN RESULTS

The MICs/MBCs of vancomycin, levofloxacin, and rifampin against MRSE 23 were 0.78/0.78 microg/ml, 0.19/0.19 microg/ml or below, and 0.19/0.19 microg/ml or below, and against ATCC 35984 were 0.78/1.56 microg/ml, 0.19/0.19 microg/ml or below, and 0.19/0.19 microg/ml or below, respectively. A 99.9% killing activity was achieved with vancomycin, levofloxacin, and vancomycin-levofloxacin against planktonic cells of MRSE 23 (18.9, 21.3, and 17.5 hrs, respectively) and only with levofloxacin against ATCC 35984 (21.5 hrs). No regimen achieved 99.9% killing activity against sessile cells.

CONCLUSION

Adding rifampin was antagonistic against planktonic cells and had an additive effect against sessile cells. Activity typically reported using nutrient-rich, planktonic cells may not be applicable to sessile cells under environmental and growth restrictions.

Synthesis and characterization of a novel biodegradable antimicrobial polymer

Bacterial infection is a frequent complication associated with the use of medical devices. In an effort to address this problem, antibacterial agents have been incorporated or applied directly onto the surfaces of numerous types of medical devices. This study assessed the feasibility of using a novel biodegradable polymer to release antibiotic drugs in response to inflammatory related enzymes. A model drug polymer was synthesized using 1,6-hexane diisocyanate (HDI), polycaprolactone diol (PCL), and a fluoroquinolone antibiotic, ciprofloxacin. Polymers were characterized by size-exclusion chromatography (SEC), and elemental analysis. Biodegradation studies were carried out by incubating the polymers with solutions of cholesterol esterase (CE) or phosphate buffer (pH 7.0) for 30 days at 37 degrees C. The degradation was assessed by high-performance liquid chromatography (HPLC), mass spectrometry (MS) and 14C radiolabel release. Subsequently, the activity of the released antibiotic was assessed against a clinical isolate of Pseudomonas aeruginosa. HPLC analysis showed the release of multiple degradation products which were identified, by tandem MS, to include ciprofloxacin and derivatives of ciprofloxacin. The microbiological assessment showed that the released ciprofloxacin possessed antimicrobial activity; 1 microg/ml was measured after 10 days. The results of this study suggest that these novel bioresponsive antimicrobial polymers or similar analogs show promise for use in the control of medical device associated infections.

[The risk factors associated with colonization and bacteremia in non-tunnelled central venous catheters]

OBJECTIVE

To identify risk factors for colonization and bacteremia among patients with non-tunnelled central venous catheters.

MATERIALS AND METHODS

A prospective study was conducted of a cohort of patients carrying non-tunnelled central venous catheters. Different parameters were obtained and the degree of its association with colonization of the distal portion of the catheter or with bacteremia associated with colonization was estimated. The CDC (centers for Disease Control) diagnostic criteria of colonization and catheter-related bacteremia were used.

RESULTS

A total of 118 catheters were eventually analyzed, corresponding to 114 patients, with a catheterization mean time of 14 +/- 8 days (mean +/- SD); out of these 114 patients, 51 were colonized and in 22 the presence of associated bacteremia was confirmed. The parameters associated with a higher risk for catheter colonization included length of colonization, femoral location, number of lumina and a vital prognosis lower than one month. All these factors, with the exception of the increase in the number of lumina, showed an independent association with colonization on the multivariate analysis [catheterization length (in weeks): OR 1.46; 95% CI: 1.0-2.11; femoral location: OR 3.73; 95% CI: 1.16-11.9; vital prognosis lower than one month: OR 12.7; 95% CI: 1.4-112.7]. As for risk for catheter-related bacteremia, the univariate analysis showed an association with catheterization length and a vital prognosis lower than one month; the latter was the only factor that maintained an independent association in the multivariate analysis (OR 5.75; 95% CI: 1.17-28.27).

CONCLUSION

The present study documents the relevance of prolonged catheterization as a consistent risk for colonization of non-tunnelled central venous catheters. This risk increases independently in canalization at femoral site and particularly among severely ill patients. The presence of these factors allows the identification of a high risk population for the development of catheter related bacteremia.

Morbidity associated with central venous catheter-use in a cohort of 212 hospitalized subjects with HIV infection

Technical complications and nosocomial bloodstream infections associated with short-term central venous catheterization remain a heavy burden in terms of morbidity, mortality and cost in HIV-positive subjects. Between 1994 and 1997, 327 central venous catheters (CVCs) inserted in 212 patients for a total of 5005 catheter days were investigated. Forty-two technical complications (13%) occurred in 40 patients. Logistic regression analysis revealed that a high APACHE III score was associated with development of CVC-related complications (P = 0.01). One hundred and eight of 327 CVCs (33%) were suspected as being infected. However only 61 episodes (61/327, 19%) were finally diagnosed as CVC-related sepsis. Three variables affecting the rate of CVC-related sepsis were identified: 1) administration of TPN (P = 0.01); 2) low number of circulating CD4+ cells (P = 0.04); 3) high APACHE III score (P = 0. 04). Doctors responsible for AIDS patients should carefully consider the relative risks and benefits of CVC insertion in an individual patient.

The intercellular adhesion (ica) locus is present in Staphylococcus aureus and is required for biofilm formation

Nosocomial infections that result in the formation of biofilms on the surfaces of biomedical implants are a leading cause of sepsis and are often associated with colonization of the implants by Staphylococcus epidermidis. Biofilm formation is thought to require two sequential steps: adhesion of cells to a solid substrate followed by cell-cell adhesion, creating multiple layers of cells. Intercellular adhesion requires the polysaccharide intercellular adhesin (PIA), which is composed of linear beta-1,6-linked glucosaminylglycans and can be synthesized in vitro from UDP-N-acetylglucosamine by products of the intercellular adhesion (ica) locus. We have investigated a variety of Staphylococcus aureus strains and find that all strains tested contain the ica locus and that several can form biofilms in vitro. Sequence comparison with the S. epidermidis ica genes revealed 59 to 78% amino acid identity. Deletion of the ica locus results in a loss of the ability to form biofilms, produce PIA, or mediate N-acetylglucosaminyltransferase activity in vitro. Cross-species hybridization experiments revealed the presence of icaA in several other Staphylococcus species, suggesting that cell-cell adhesion and the potential to form biofilms is conserved within this genus.

Shear stress effects on bacterial adhesion, leukocyte adhesion, and leukocyte oxidative capacity on a polyetherurethane

Infection of implanted cardiovascular biomaterials still occurs despite inherent host defense mechanisms. Using a rotating disk system, we investigated Staphylococcus epidermidis and polymorphonuclear leukocyte (PMN) adhesion to a polyetherurethane urea (PEUU-A') under shear stress (0-17.5 dynes/cm2) for time periods up to 6 h. In addition, the superoxide (SO) release capacity of PMNs after transient exposure to PEUU-A' under shear stress was determined. Bacterial adhesion in phosphate-buffered saline (PBS) showed a linear shear dependence, decreasing with increasing shear stress. Overall adhesion in PBS decreased with time. However, bacterial adhesion in 25% human serum was similar for all time points up to 360 min. Adhesion was observed at all shear levels, displaying no shear dependence. In contrast, PMN adhesion demonstrated a strong shear dependence similarly for times up to 240 min, decreasing sharply with increasing shear stress. Although PMNs preexposed to shear stress showed a slightly diminished SO release response compared to fresh cells for all stimuli, it was not statistically significant regardless of the stimulus. We conclude that circulating leukocytes are unable to adhere in regions of high shear which may contain adherent bacteria. In addition, exposure to PEUU-A' and shear stress (in the range 0-18 dynes/cm2) is insufficient to cause a depression in the oxidative response of PMNs.

Prophylactic antibiotics with intracranial pressure monitors and external ventricular drains: a review of the evidence

BACKGROUND

The role of prophylactic antibiotics (PABs) in preventing infections associated with intracranial pressure (ICP) monitors and external ventricular drains (EVD) is not well defined.

METHODS

This study includes an analysis of published reports and a survey of current practices regarding the use of PABs with ICP monitors and EVDs. A computerized data search and a review of the abstracts from two major national neurosurgical meetings over the past decade yielded 85 related articles. Three independent investigators, blinded to the title, author(s), institution(s), results, and conclusions of the articles used predetermined inclusion criteria to select studies for meta-analysis. Thirty-six responses were returned from 98 questionnaires (37%) mailed to university neurosurgical programs.

RESULTS

Among the articles reviewed, only two studies met the predetermined inclusion criteria for the meta-analysis, and they were of insufficient size to produce statistically significant results. Among the 36 programs that responded to the survey, 26 (72%) used PABs, mainly cephalosporins (46%) and semisynthetic penicillins (38%), with ICP monitors and EVDs. Twenty-two (85%) used one drug, and 4 (15%) used two drugs. Twenty-two (61%) of the total group reported intra-institutional variation in practices among individual staff neurosurgeons. Nineteen (53%) expressed interest in a retrospective study, and 27 (75%) expressed interest in a prospective study on the role of PABs in minor neurosurgical procedures.

CONCLUSION

No consensus regarding the use of PABs with ICP monitors and EVDs is noted. Randomized controlled trials of sufficiently large size with appropriate blinding are needed to address this issue.

Binding of immobilized fibronectin by biliary drain isolates

Occlusion of biliary stents, as the result of bacterial adhesion and colonization onto biliary stents, still remains a major problem. Biliary proteins, such as fibronectin (Fn) and vitronectin (Vn), have been presumed to be involved in the process of bacterial adhesion to biliary biomaterial. In the present study, Fn binding by 5 strains of E. coli isolated from biliary drains or from bile was studied. All strains did not bind detectable amounts of soluble Fn but bound to immobilized plasma Fn. Adhesion of four strains of E. coli to ovalbumin was reduced by periodate treatment of ovalbumin, but adhesion to Fn was unaffected. Adhesion was inhibited by mannose-containing saccharides, trypsin treatment of the protein, and protease treatment of the bacterial cells. Autoradiography showed that components of cell extracts from three E. coli strains bind 125I-Fn but not a 150 kD Fn fragment. The findings indicate that the adhesion of these bacteria to Fn is a protein-protein interaction, inhibited by D-mannose, and possibly mediated by fimbrial components.

Catheter-related infections following axillary vein catheterization

BACKGROUND

The aim of this study was to determine the rate of infectious complications following axillary vein cannulation and to compare to that observed after internal jugular vein catheterization.

METHODS

A prospective comparative open study was carried out to determine the rate of infectious complications related to the use of catheters inserted via the axillary vein or the internal jugular vein. During the study period all patients submitted to central venous catheterization were evaluated. A total of 141 patients entered and completed the study. Catheter insertion sites were either the axillary vein punctured in the axilla, or the internal jugular vein punctured using an anterior approach. Catheter tips were cultured using a quantitative technique. Clinical information pertaining to the analysis was prospectively collected.

RESULTS

A total of 141 catheters from 141 patients entered was studied. Clinical characteristics and risk factors for catheter infection were similar in both groups. The incidence of catheter-related infection (including catheter-related sepsis, and bacteremia) was not different between the two groups (axillary vein: 8.1%; internal jugular vein: 7.6%). Catheter-related bacteremia were seen at a rate of 3.7% in the internal jugular vein group and a rate of 1.6% in the axillary vein group (NS). The incidence of catheter colonization was similar in both groups (axillary vein: 14.5%; internal jugular vein: 11.4%).

CONCLUSION

Catheter-related infection after axillary vein catheterization was similar to that observed after internal jugular vein catheterization. The chance of developing catheter-related sepsis was less than 10% with either route when catheters were used for the treatment of severely ill patients.

Increasing incidence of nosocomial Chryseobacterium indologenes infections in Taiwan

To understand the clinical features, antimicrobial therapy, and epidemiology of Chryseobacterium indologenes infections, the medical records of 36 patients with nosocomial Chryseobacterium indologenes infections seen over a three-year period at National Taiwan University Hospital were reviewed. The 36 isolates recovered from these patients were studied by molecular typing and determination of antimicrobial susceptibility patterns. Nine patients had underlying neoplastic diseases, seven had diabetes mellitus, five had burn wounds, and four had uremia. The clinical syndrome included ten patients with intraabdominal infections, nine with wound sepsis, six with intravascular catheter-related bacteremia, and four with ventilator-associated pneumonia. Thirteen patients had monomicrobial bacteremia, and four had polymicrobial bacteremia. Nineteen patients (53%) developed infections associated with various indwelling devices. The deaths of five patients (14%) were directly attributable to infection with Chryseobacterium indologenes. All isolates recovered showed a wide range of resistance to commonly used antimicrobial agents. The random amplified polymorphic DNA (RAPD) patterns of the isolates differed from each other, indicating the absence of epidemiological relatedness among these isolates. Nosocomial infection caused by multiresistant Chryseobacterium indologenes appears to be an emerging problem in Taiwan and should be studied further.

The effects of adherence to silicone surfaces on antibiotic susceptibility in Staphylococcus aureus

Sensitivity of Staphylococcus aureus to the antibiotics tetracycline, benzylpenicillin and vancomycin was found to decrease by 2-10 fold when cells were grown adherent to silicone catheter surfaces. Sensitivity to rifampicin and fusidic acid was not significantly altered in adherent cells. Susceptibility further decreased with increased adherence time prior to antibiotic challenge. The resistance observed was not genotypic, or due to the presence of a specialized subpopulation of bacteria, as it disappeared when the bacteria were removed from the catheter, subcultured and retested. Also, adherent bacteria were found to grow more slowly than bacteria growing planktonically. It is concluded that the decrease in antibiotic susceptibility of adherent bacteria is a function of the physiological status of the individual cells rather than a function of biofilm formation or slime production. The decrease in growth rate of the adherent bacteria is a result of the adherence process rather than a result of nutrient depletion. The decrease in growth rate is implicated, but is not the sole factor, in the decreased antibiotic susceptibility of adherent bacteria.

Leukocyte-biomaterial interactions in the presence of Staphylococcus epidermidis: flow cytometric evaluation of leukocyte activation

The adhesion of bacteria on a biomaterial surface is believed to be the first step in the development of biomaterial-related infection. The goal of this study was to investigate the mechanisms that permit adherent bacteria to persist on the surface of an implanted cardiovascular biomaterial. We hypothesized that circulating leukocytes are unable to adhere to the biomaterial surface under physiologic shear stress conditions, and this prevents them from interacting with adherent bacteria. To address this hypothesis, we investigated the adhesion profiles of Staphylococcus epidermidis and polymorphonuclear leukocytes (PMN), incubated under controlled shear stress conditions with the test biomaterial. We found that bacteria could adhere on the biomaterial surface, even when their concentration in the test medium was as low as 10(3) cfu/mL. At this concentration, the bacteria did not induce significant complement activation. PMN adhesion on the biomaterial surface was sensitive to shear stress and minimal at shear stress > 10 dynes/cm2. Low concentrations of bacteria could induce a significant increase in the expression of PMN adhesion molecules CD11b and CD11c. We conclude that the presence of bacteria induces PMN activation but does not increase PMN adhesion on biomaterial surfaces under physiologic shear stress conditions. This could be a major mechanism that protects adherent bacteria from PMN antibacterial activity.

Central venous catheter-related sepsis in a cohort of 366 hospitalised patients

Five hundred two central venous catheters inserted in 366 patients were evaluated prospectively over a one-year period to determine the frequency and risk factors associated with catheter-related sepsis. For study purposes, in cases in which catheter infection was suspected but the initial blood cultures were negative, the catheters were replaced by guidewire technique; otherwise, the catheters were routinely changed after 21 days by guidewire technique. A catheter-related infection was suspected in 190 cases (190/502, 38%). A diagnosis of catheter-related sepsis was established in 50 patients, which represents 10% of the total number of lines (502). Over a total of 6428 days of catheter use, the infection rate was 0.8 cases of sepsis per 100 catheter-days. Staphylococcus epidermidis, Staphylococcus aureus, and Candida spp. were the most frequently isolated aetiological agents of sepsis. On univariate analysis, six variables affecting the rate of catheter-related sepsis were identified: neutropenia for more than eight days (p < 0.001); AIDS (p < 0.001); haematological malignancy (p < 0.001); administration of total parenteral nutrition (p = 0.001); duration of site use (p = 0.04); and high APACHE II score (p = 0.04). The logistic regression analysis revealed that AIDS and haematological malignancies were independent risk factors of catheter-related sepsis. Catheter replacement over a guidewire was no more likely to be associated with sepsis than was percutaneous catheter insertion. In conclusion, although the incidence of established catheter infection is much lower than the incidence of suspected infection, in most cases of suspected infection it is wise to change the catheter with the guidewire technique and wait for culture of the tip, rather than to remove the catheter immediately. Such a policy may help reduce the number of unnecessary catheter removals.