Microbiology of indwelling central intravascular catheters

Limitations of Murine Models for Assessment of Antibody-Mediated Therapies or Vaccine Candidates against Staphylococcus epidermidis Bloodstream Infection

Staphylococcus epidermidis is normally a commensal colonizer of human skin and mucus membranes, but, due to its ability to form biofilms on indwelling medical devices, it has emerged as a leading cause of nosocomial infections. Bacteremia or bloodstream infection is a frequent and costly complication resulting from biofilm fouling of medical devices. Our goal was to develop a murine model of S. epidermidis infection to identify potential vaccine targets for the prevention of S. epidermidis bacteremia. However, assessing the contribution of adaptive immunity to protection against S. epidermidis challenge was complicated by a highly efficacious innate immune response in mice. Naive mice rapidly cleared S. epidermidis infections from blood and solid organs, even when the animals were immunocompromised. Cyclophosphamide-mediated leukopenia reduced the size of the bacterial challenge dose required to cause lethality but did not impair clearance after a nonlethal challenge. Nonspecific innate immune stimulation, such as treatment with a Toll-like receptor 4 (TLR4) agonist, enhanced bacterial clearance. TLR2 signaling was confirmed to accelerate the clearance of S. epidermidis bacteremia, but TLR2(-/-)mice could still resolve a bloodstream infection. Furthermore, TLR2 signaling played no role in the clearance of bacteria from the spleen. In conclusion, these data suggest that S. epidermidis bloodstream infection is cleared in a highly efficient manner that is mediated by both TLR2-dependent and -independent innate immune mechanisms. The inability to establish a persistent infection in mice, even in immunocompromised animals, rendered these murine models unsuitable for meaningful assessment of antibody-mediated therapies or vaccine candidates.

Antibodies to PhnD inhibit staphylococcal biofilms

Biofilm formation on central lines or peripheral catheters is a serious threat to patient well-being. Contaminated vascular devices can act as a nidus for bloodstream infection and systemic pathogen dissemination. Staphylococcal biofilms are the most common cause of central-line-associated bloodstream infections, and antibiotic resistance makes them difficult to treat. As an alternative to antibiotic intervention, we sought to identify anti-staphylococcal biofilm targets for the development of a vaccine or antibody prophylactic. A screening strategy was devised using a microfluidic system to test antibody-mediated biofilm inhibition under biologically relevant conditions of shear flow. Affinity-purified polyclonal antibodies to target antigen PhnD inhibited both Staphylococcus epidermidis and S. aureus biofilms. PhnD-specific antibodies blocked biofilm development at the initial attachment and aggregation stages, and deletion of phnD inhibited normal biofilm formation. We further adapted our microfluidic biofilm system to monitor the interaction of human neutrophils with staphylococcal biofilms and demonstrated that PhnD-specific antibodies also serve as opsonins to enhance neutrophil binding, motility, and biofilm engulfment. These data support the identification of PhnD as a lead target for biofilm intervention strategies performed either by vaccination or through passive administration of antibodies.

Central venous catheter-related bloodstream infections in the intensive care unit

CONTEXT

Central venous catheter-related bloodstream infection (CRBSI) is associated with high rates of morbidity and mortality in critically ill patients.

AIMS

This study was conducted to determine the incidence of central venous catheter-related infections (CRIs) and to identify the factors influencing it. So far, there are very few studies that have been conducted on CRBSI in the intensive care unit in India.

SETTINGS AND DESIGN

This was a prospective, observational study carried out in the medical intensive care unit (MICU) over a period of 1 year from January to December 2004.

MATERIALS AND METHODS

A total of 54 patients with indwelling central venous catheters of age group between 20 and 75 years were included. The catheters were cultured using the standard semiquantitative culture (SQC) method. Statistical analysis used SPSS-10 version statistical software.

RESULTS

A total of 54 CVC catheters with 319 catheter days were included in this study. Of 54 patients with CVCs studied for bacteriology, 39 (72.22%) catheters showed negative SQCs and also negative blood cultures. A total of 15 (27.77%) catheters were positive on SQC, of which 10 (18.52%) were with catheter-associated infection and four (7.41%) were with catheter-associated bacteremia; the remaining one was a probable catheter-associated bacteremia. CRIs were high among catheters that were kept in situ for more than 3 days and emergency procedures where two or more attempts were required for catheterization (P < 0.05). In multivariate analysis of covariance duration of catheter in situ for >3 days, inexperienced venupucturist, more number of attempts and emergency CVC were associated with more incidence of CVCBSIs, with P <0.02. The duration of catheter in situ was negatively correlated (-0.53) and number of attempts required to put CVC was positively correlated (+0.39) with incidence of CVCBSIs. Sixty-five percent of the isolates belonged to the CONS group (13/20). Staphylococcus epidermidis showed maximum susceptibility to amikacin, doxycycline and amoxycillin with clavulanic acid and was susceptible to vancomycin (100%). Klebsiella pneumoniae was 100% susceptible to amikacin and ciprofloxacin. Escherichia coli was susceptible to amikacin and cefotaxime.

CONCLUSIONS

The overall incidence of CRI was 27.77% (15/54). Catheter-associated BSIs were 47.31 per 1000 catheter-days. CRI was low in the catheters inserted by the experienced venipuncturists, elective procedure and CVC kept in situ for ≤3 days. S. epidermidis was the most common isolate.

Thoracic catheter-related infections

OBJECTIVE

To determine the incidence of local and systemic infection in a sample of patients catheterized with thoracic catheters (TCs) and to identify the prognostic factors for catheter-related infection.

METHODS

A retrospective study involving 48 patients (17 females and 31 males) catheterized with TCs between December of 2008 and March of 2009 in the Thoracic Surgery Department of the Adnan Menderes University Hospital, located in Aydin, Turkey. Blood samples for culture were collected from the distal end of each TC and from each of the 48 patients. We looked for correlations between positive culture and possible prognostic factors for catheter-related infection.

RESULTS

Culture results were positive in TC samples only for 3 patients, in blood samples only for 2, and in both types of samples for another 2. Advanced age correlated significantly with positive culture in TC samples and in blood samples (r = 0.512 and r = 0.312, respectively; p < 0.05 for both), as did prolonged catheterization (r = 0.347 and r = 0.372, respectively; p < 0.05). There was a significant correlation between having undergone surgery and positive culture in TC samples only (p < 0.05). However, having an inoperable malignancy correlated with bacterial growth in blood and in TC samples alike (p < 0.05 for both).

CONCLUSIONS

Risk factors, such as advanced age, prolonged catheterization, comorbidities, and inoperable malignancy, increase the risk of catheter-related infection. It is imperative that prophylaxis with broad-spectrum antibiotics be administered to patients who present with these risk factors and might be catheterized with a TC.

Central line sepsis

Since 1980, the placement of central venous access devices has become routine, and these catheters have been of great benefit in the treatment of patients with cancer. Unfortunately, central venous catheters have not been without complications. Central line sepsis has been reported to be one of the most frequently occurring complications, and although it is extremely costly to treat, more importantly, this condition is potentially life threatening to patients. Developing strategies that would prevent central line catheter infections has been a continual challenge for healthcare providers. Studies have been conducted on the use of catheters with antiseptic coatings, antimicrobial coatings, impregnated antimicrobial cuffs, prophylactic antibiotic therapy, antibiotic locks, use of antithrombolytics, different exit site dressings, and the use of various disinfectants for cleansing catheter exit sites. Healthcare providers, including oncology nurses, need to be knowledgeable concerning potential sources of infection and factors that may lead to central line sepsis (Chaiyakunapruk, Veenstra, Lipsky, & Saint, 2002; Darouiche et al., 1999; Little & Palmer, 1998; Veenstra, Saint, Saha, Lumley, & Sullivan, 1999). They need to advocate for the use of sterile technique during catheter insertion and aseptic technique when routine maintenance is provided and be aware of the standard treatments for and potential outcomes of central line catheter infections. In addition, oncology nurses should be encouraged to support and participate in controlled, randomized studies that may provide scientific-based practices that decrease the number of catheter-related infections in the future.

PEG site infections: a novel use for Actisorb Silver 220

Any breach in the integrity of the skin, such as occurs in wounds and incisions, and intravascular catheters, can act as a portal for the ingress of microorganisms and thereby predispose the patient to infection. The infection, if unchecked, can put the patient at risk of bacteraemia. We have reviewed the care of percutaneous enterostomal gastrostomy (PEG) sites in our trust hospital and in the local community and have implemented practice guidelines to reduce infection risks. These include protocols for skin care around PEG sites, and the use of an antibacterial dressing - Actisorb Silver 220 - to manage local colonization. The preliminary results of this exercise indicate that patient comfort can be improved, hypergranulation reduced, and methicillin-resistant Staphylococcus aureus colonization and infection eradicated.

Catheter-related infections: diagnosis and intravascular treatment

The diagnosis of catheter-related infections relies on the presence of clinical manifestations of infection and the evidence of colonization of the catheter tip by bacteria, mycobacteria, or fungi. The reference method to confirm the latter requires the withdrawal of the catheter for culturing, which frequently turns out to be inconvenient, unnecessary and costly. New methods try to avoid these drawbacks and to assess the presence of tip colonization without withdrawal. Comparative quantitative blood cultures with a marked increase (> or = 5) in colony counts between blood obtained from the catheter lumen and from a peripheral vein simultaneously is one of those methods. It has a high sensitivity (>80%) and specificity (94-100%) but it is cumbersome and requires both an easy backflow of blood in the catheter and the existence of bacteremia. Cytocentrifugation and acridine orange staining of blood withdrawn from an infected catheter lumen has a sensitivity and a specificity of over 90% for the diagnosis of tip colonization. 'Superficial cultures' comprise the semiquantitative culture of the hub, of the skin surrounding the catheter entrance and of the first subcutaneous portion (1 cm) of the catheter after swabbing. The sensitivity of this method is >90%, specificity is >80%, and positive and negative predictive values for catheters (considering together those with and without clinical data of infection) are 66 and 97%, respectively. Endoluminal brushing has proved to be an impractical and unreliable procedure, at least in our experience. New methods based on the speed of bacterial growth to detectable levels of micro-organisms in conventional blood cultures are a new and interesting way of assessing catheter-related infections. Moreover, as the use of antimicrobial-coated catheters becomes more prevalent, the existing definitions of catheter colonization and catheter-related infection may need to be modified, because such coatings may lead to false-negative culture results. Many catheter infections, diagnosed without catheter withdrawal, can be handled nowadays with the so-called 'antibiotic lock-in technique', which consists in 'locking' the infected catheter lumen with a solution containing antibiotics. A high proportion of infected catheters, mainly those with coagulase-negative staphylococci, can be maintained in place and sterilized with this technique, including catheters in patients with therapeutic failure after receiving conventional intravenous antibiotic therapy. New diagnostic and therapeutic techniques may avoid the unnecessary withdrawal of thousands of efficient, difficult to replace and expensive intravascular lines.

Catheter-related infections: diagnosis and intravascular treatment

The diagnosis of catheter-related infections relies on the presence of clinical manifestations of infection and the evidence of colonization of the catheter tip by bacteria, mycobacteria or fungi. The reference method to confirm the latter requires the withdrawal of the catheter for culturing, which frequently turns out to be inconvenient, unnecessary and costly. New methods try to avoid these inconveniences and to assess the presence of tip colonization without withdrawal. One of these methods uses quantitative blood cultures with a jump (> or = 5) in colony counts between blood obtained from the catheter lumen and simultaneously from a peripheral vein. It has a high sensitivity (>80%) and specificity (94%-100%) but is cumbersome and requires both an easy backflow of blood in the catheter and the existence of bacteremia. Cytocentrifugation and acridine orange staining of blood withdrawn from an infected catheter lumen has a sensitivity and a specificity of over 90% for the diagnosis of tip colonization. "Superficial cultures" consist in the semiquantitative culture of the hub, of the skin surrounding the catheter entrance and of the first (1 cm) subcutaneous portion of the catheter after swabbing. Sensitivity of this method is >90% and specificity is >80%, and positive and negative predictive values for catheters (considering together those with and without clinical data of infection) are 66% and 97%, respectively. Endoluminal brushing has turned out to be an impractical and unreliable procedure, at least in our experience. New methods based on the speed of bacterial growth to detectable levels of microorganisms in conventional blood cultures are a new and interesting way of assessing catheter-related infections. Besides, as use of antimicrobial-coated catheters becomes more prevalent, the existing definitions of catheter colonization and catheter-related infection may need to be modified, because such coatings may lead to false-negative culture results. Many catheter infections, diagnosed without catheter withdrawal, can be handled nowadays with the so-called "antibiotic lock-in technique", which consists in locking the infected catheter lumen with a solution containing antibiotics. A high proportion of infected catheters, mainly those with coagulase-negative staphylococci, can be maintained in place and sterilized with this technique, including catheters in patients with therapeutic failure after receiving conventional intravenous antibiotic therapy. New diagnostic and therapeutic techniques may avoid the unnecessary withdrawal of thousands of efficient, difficult to replace and expensive intravascular lines.

Cooperation of Toll-like receptor 2 and 6 for cellular activation by soluble tuberculosis factor and Borrelia burgdorferi outer surface protein A lipoprotein: role of Toll-interacting protein and IL-1 receptor signaling molecules in Toll-like receptor 2 signaling

Toll-like receptor 2 (TLR2) and TLR4 play important roles in innate immune responses to various microbial agents. We have previously shown that human dermal endothelial cells (HMEC) express TLR4, but very little TLR2, and respond to LPS, but not to Mycobacterium tuberculosis 19-kDa lipoprotein, unless transfected with TLR2. Here we report that HMEC are unresponsive to several additional biologically relevant TLR2 ligands, including, phenol-soluble modulin (PSM), a complex of three small secreted polypeptides from the skin commensal Staphylococcus epidermidis, soluble tuberculosis factor (STF), and Borrelia burgdorferi outer surface protein A lipoprotein (OspA-L). Expression of TLR2 renders HMEC responsive to all these ligands. We further characterized the signaling pathway in response to STF, OspA-L, and PSM in TLR2-transfected HMEC. The TLR2 signaling pathway for NF-kappaB trans-activation shares the IL-1R signaling molecules. Dominant negative constructs of TLR2 or TLR6 inhibit the responses of STF and OspA-L as well as PSM in TLR2-transfected HMEC, supporting the concept of functional cooperation between TLR2 and TLR6 for all these TLR2 ligands. Moreover, we show that Toll-interacting protein (Tollip) coimmunoprecipitates with TLR2 and TLR4 using HEK 293 cells, and overexpression of Tollip inhibits NF-kappaB activation in response to TLR2 and TLR4 signaling. Collectively, these findings suggest that there is functional interaction between TLR2 and TLR6 in the cellular response to STF and OspA-L in addition to S. epidermidis (PSM) Ags, and that engagement of TLR2 triggers a signaling cascade, which shares the IL-1R signaling molecules, similar to the TLR4-LPS signaling cascade. Our data also suggest that Tollip may be an important constituent of both the TLR2 and TLR4 signaling pathways.

Activities of bismuth thiols against staphylococci and staphylococcal biofilms

Indwelling medical devices are associated with infectious complications. Incorporating antimicrobials into indwelling materials may reduce bacterial colonization. Bismuth thiols are antibiofilm agents with up to 1,000-fold-greater antibacterial activity than other bismuth salts. Staphylococci are particularly sensitive, as determined by agar diffusion and broth dilution susceptibility testing. Bismuth-ethanedithiol inhibited 10 methicillin-resistant Staphylococcus epidermidis strains at 0.9 to 1.8, Staphylococcus aureus ATCC 25923 at 2.4, and S. epidermidis ATCC 12228 at 0.1 microM Bi(3+). Antiseptic-resistant S. aureus was sensitive to bismuth-2-3-dimercaptopropanol (BisBAL) at < or = 7 microM Bi(3+). Hydrogel-coated polyurethane rods soaked in BisBAL inhibited S. epidermidis for 39 days (inhibitory zone diameter in agar, > or = 30 mm for > 25 days). Slime from 16 slime-producing S. epidermidis strains was inhibited significantly by bismuth-3,4-dimercaptotoluene (BisTOL), but not by AgNO3, at subinhibitory concentrations. In conclusion, bismuth-thiols are bacteriostatic and bactericidal against staphylococci, including resistant organisms, but are also inhibitors of slime at subinhibitory concentrations. At subinhibitory concentrations, BisTOL may be useful in preventing the colonization and infection of indwelling intravascular lines, since staphylococci are important pathogens in this setting.

Novel methods for the prevention of infection of intravascular devices

Infections are often caused by bacteria that gain access either from the skin during insertion, or by migration from the skin to the surrounding subcutaneous tissue, once in situ. It is necessary to understand the pathogenesis with regard to sessile or planktonic forms of microorganisms and why they adhere to catheter surfaces, and the interactions between host, catheter and bug. To prevent colonization two general approaches have been adopted: the first concerns the site of insertion-prophylactic antibiotics, tunnelling, intraluminal antibiotic locks, topical application of antibiotics or antiseptics, cutaneous disinfection pre- and post-insertion with various antiseptics, catheter site care and frequency of dressing changes. The second approach considers the physical nature of catheter material-silver impregnated subcutaneous collagen cuffs, antiseptic hubs, antimicrobial coating of catheters with antibiotics e.g., rifampicin and minocycline, silver ions, chlorhexidine, chlorhexidine and silver sulphadiazine. Only by understanding the pathogenesis of catheter devices whereby micro-organisms are embedded in biofilms and are resistant to the action of antibiotics, will effective preventative measures be possible. In addition a proper risk-management review will be necessary to determine the cost-benefit of such modified catheters.

In vitro antimicrobial activity of a new antiseptic central venous catheter

A central venous catheter coated with a new antiseptic combination, silver chloride (AgCl) and benzalkonium chloride (BKC) in a polymer matrix, was developed. The antimicrobial efficacy and the ability to prevent surface colonization, after elution in both serum and saline, were evaluated and compared to catheters coated with silver sulfadiazine/chlorhexidine. The results of in vitro assays demonstrated that the AgCl-BKC coated catheters had a broad spectrum of activity against bacteria and C. albicans and prolonged antimicrobial activity for extraction periods of up to 30 days. These data suggest that AgCl-BKC coated catheters may provide another solution for reduction of catheter-related infections.

Diagnosis of vascular catheter-related bloodstream infection: a meta-analysis

Catheter-related bloodstream infections increased in incidence during the past decade, causing significant morbidity, mortality, and excess hospital costs. Absence of inflammation at the catheter site in most cases makes clinical diagnosis uncertain. The relative accuracy and cost-effectiveness of different microbiologic tests for confirming that bloodstream infection is catheter related have remained unclear. A meta-analysis of published studies was conducted regarding the accuracy of diagnostic test methods using pooled sensitivity and specificity and summary receiver operating characteristic (ROC) curve analysis. The cost for each test was estimated by methods published by the College of American Pathologists. Costs of catheter replacement and antibiotic therapy for false positive results were included in the cost per accurate test result. Twenty-two studies evaluating six test methods met inclusion criteria for the meta-analysis. Accuracy increased in ROC analysis for catheter segment cultures with increasing quantitation (P = 0.03) (i.e., quantitative > semiquantitative > qualitative) largely due to an increase in specificity. The highest Youden index (mean = 0.85) was observed with quantitative catheter segment culture, the only method with pooled sensitivity and specificity above 90%. For blood culture methods, there was no statistically significant trend toward increased accuracy. The unpaired quantitative catheter blood culture offered the lowest cost per accurate test result but was only 78% sensitive. In conclusion, quantitative culture was the most accurate method for catheter segment culture, and unpaired quantitative catheter blood culture was the single most cost-effective test, especially for long-term catheters.

Diagnosis of catheter-related infections

Catheter-related infections (CRI) are a major cause of febrile episodes in hospitalized patients. Additionally, approximately 40% of primary infections in intensive care patients are directly related to central venous catheters. Despite the clinical significance of CRI diagnostic procedures are still under debate. Clinical diagnosis which includes systemic signs of infection and suppuration at the catheter entry site is altogether a rare event. Therefore, most cases are still diagnosed by laboratory methods. Although the semiquantitative roll-plate technique is widely used and frequently regarded as gold standard, the disadvantages of a post-hoc diagnosis are obvious. In-situ techniques which leave the suspected catheter in place include differential blood cultures, skin and hub cultures and a new method of microscopic screening of blood drawn through the inflicted catheter. However, until now the true value of all these methods still lack unanimous acceptance. Further research is necessary to close the gap between clinical expectations and laboratory results.

Prevention of catheter-related infections by silver coated central venous catheters in oncological patients

Catheter-related infection (CRI) is a serious complication of central venous catheterization. We have investigated the efficacy of a silver-coated polyurethane catheter (Pellethane, Fresenius AG, Germany) in preventing CRI in oncological patients receiving chemotherapy in a phase II study. From November 1992 through April 1994, 266 patients were assigned to receive single lumen catheters, either standard uncoated catheters (UC, n = 113) or silver-coated ones (SC, n = 120). Catheters were inserted into the internal jugular vein after institutional approval and informed consent. Duration of catheterization (UC vs. SC = 13.3 vs. 12.7 days) and leukopenia (< 1.0 x 10(9) WBC/l; 4.3 vs. 3.6 days) were similar in both groups demonstrating a comparable risk for infections. Skin reactions at the catheter entry site were recorded daily. CRI and colonization rates were studied by semiquantitatively culturing intradermal and intravascular segments. CRI were confirmed by blood cultures obtained via catheter and from peripheral veins in cases of suspected sepsis or at the end of catheterization. No adverse effects from the silver-coated catheter could be observed. The bacteriological results showed that SC were colonized (> 15 CFU) in 45.1% and UC in 44.2%. CRI developed in 21.2% of the UC patients but only in 10.2% of the SC patients (p = 0.011). We conclude that this new silver-coated central venous catheter is biocompatible and effective in reducing the incidence of catheter-related infections in oncological patients.

Corynebacterium aquaticum septicaemia in a neutropenic patient

Corynebacteria are a well recognised cause of sepsis in the immunocompromised patient. Corynebacterium aquaticum, however, is rarely seen in the clinical setting, being an environmental organism associated with fresh water. A septicaemic episode caused by this organism in a 74 year old neutropenic woman with an indwelling central venous catheter is reported. It is postulated that the source of the organism was untreated stored rainwater which she used for showering.

The effect of electrical currents and tobramycin on Pseudomonas aeruginosa biofilms

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

Relevance of culturing Candida species from intravascular catheters

The significance of isolating Candida species from intravascular catheters was examined retrospectively. Our findings demonstrate that these organisms are encountered among patients with proven invasive candidiasis or as an isolated finding. Febrile patients with yeasts in two or more additional sites may be at risk for invasive cadidiasis and may benefit from treatment.

In vitro biocompatibility of a polyurethane catheter after deposition of fluorinated film

The in vitro biocompatibility of an experimental surface-treated polyurethane was compared with an untreated polyurethane already used for intravascular catheters. The experimental surface was coated with a fluorinated film using a glow discharge treatment. Neither of the catheters was cytotoxic for L929 murine fibroblasts, caused platelet adhesion or release reaction, or changed the mean platelet volume. The surface-treated polyurethane, however, caused a higher adhesion of Staphylococcus aureus than did the untreated one. Therefore, using in vitro testing, it has been ascertained that the examined material, though not being cytotoxic and not modifying platelet behaviour, could favour bacterial adherence.

Effect of treatment with methicillin and gentamicin in a new experimental mouse model of foreign body infection

A new mouse model of foreign body infection has been developed. Intraperitoneal placement of a silicone catheter followed by injection of 10(8) Staphylococcus aureus organisms resulted in a reproducible, localized foreign body infection. The infection persisted as an intra-abdominal abscess surrounding the catheter for at least 30 days. Treatment with up to nine doses of methicillin or gentamicin or both was started 3 days after infection. The treatment showed a significant effect (P < 0.05), measured as reduction of bacteria on the foreign body, for all three regimens with a reduction of up to 2 log units, but no synergism was observed. The result of the treatment was poor, despite the facts that the local concentrations of methicillin were greater than the MIC for at least 72 h and that nine peak concentrations of gentamicin of > 13 micrograms/ml were obtained. The poor result of the treatment was not caused by development of antibiotic resistance or influenced by protein concentration, pH, or local presence in the pus of inhibitors of antibiotics. Both antibiotics showed good effects in time-kill studies in vitro on bacteria on catheters taken out of infected mice and catheters infected in vitro. During treatment, the proportion of intracellular bacteria increased in all treated mice to 60 to 75% compared with 20 to 30% in nontreated mice (P < 0.05). This indicates that intracellular survival of staphylococci may influence the outcome of the treatment in foreign body infections.

Bronchopneumonia caused by Propionibacterium acnes

Propionibacterium acnes was identified as the pathogen in a case of subacute lung infection by examination of an open lung biopsy specimen. The patient was a 65-year-old male with exacerbation of chronic lung disease. The organism was isolated in pure culture and was present in large numbers on Gram stain. Histological examination demonstrated active interstitial fibrosis; macrophages laden with Propionibacterium acnes antigen were revealed using a peroxidase-antiperoxidase stain. This is the first report of subacute infection of pulmonary tissue due to this organism.

Catheter-related Staphylococcus aureus infections

Among 3394 patients with Staphylococcus aureus bacteraemia from the years 1986-89, 88 patients were found whose intravenous catheter and blood grew organisms of the same phage type. Strains of phage type 95 were more frequent among the patients with confirmed catheter-related bacteraemia than among other bacteraemia cases. Strains with particular phage-type patterns occurring with increasing frequency in Denmark during recent years also occurred with significantly higher frequencies among the confirmed catheter-related bacteraemias. No major differences in antibiotic resistance were observed. Patients with catheter-related bacteraemia had, in spite of a higher frequency of underlying diseases, a lower mortality compared with other bacteraemia patients, and endocarditis occurred less frequently (2% vs. 6%). Among 201 S. aureus isolates from catheters in 1988 only strains of group I occurred with increased frequency. The possible role of catheters as selection pressure on the S. aureus population is discussed.

Role of the Staphylococcus epidermidis slime layer in experimental tunnel tract infections

An experimental animal model was used to assess the slime layer of Staphylococcus epidermidis as a pathogenic factor in tunnel tract infections. Mice were inoculated with high-slime-producing or non-slime-producing strains of S. epidermidis, either along the length of a subcutaneous catheter or in the area where a catheter had been placed and immediately removed (controls). Among the catheter-bearing mice, the phenotypically distinct staphylococci produced similar, high frequencies of abscess formation (72% [44 of 61] versus 81% [31 of 38]; P = 0.29). In controls, the non-slime-producing organisms were significantly more pathogenic (87% [40 of 46] versus 57% [25 of 44] abscess formation; P = 0.001). No consistent difference was detected between blood isolates obtained from patients with central venous catheter bacteremia and those from neonates with bacteremia in the absence of a prosthetic medical device. Quantitative culture of removed catheters showed greater adherence by the slime-producing isolates (P = 0.014). In this mouse model, slime production by S. epidermidis did not increase the risk of catheter tunnel tract infection, despite the greater catheter adherence of the slime-producing organisms. These findings suggest that traumatized tissue may be a sufficient condition for the development of S. epidermidis catheter-associated infections.

Clinical significance of Staphylococcus warneri bacteremia

Twenty-seven episodes of bacteremia caused by Staphylococcus warneri were identified at Long Island Jewish Medical Center in New York between 1984 and 1989. Fourteen of these were thought to represent true bacteremias and 13 to represent contaminants. Of the 14 true bacteremias, 5 were in pediatric and 9 were in adult patients. Eight of 14 patients (57%) had catheter-related bacteremia and 5 of 14 had bacteremia of unknown source. There was one case of fulminant native valve S. warneri endocarditis. All cases of catheter-related bacteremia, except one, were nosocomially acquired, and 75% of these patients had an underlying immunosuppressive condition. Only 40% of patients with bacteremias of unknown source were immunocompromised, and S. warneri appeared to be noninvasive in this group. Interestingly, all five of the pediatric isolates were oxacillin susceptible, although four of five were resistant to penicillin, despite the fact these patients were hospitalized an average of 29 days. In contrast, seven of nine adult isolates were resistant to both oxacillin and penicillin. The only case of native valve S. warneri endocarditis occurred in a patient who had no known underlying valvular heart disease, but had an underlying immunosuppressive condition. Identification to species level of coagulase-negative staphylococci may lead to appreciation of the importance of bacteria such as S. warneri as human pathogens.

Defining Staphylococcus epidermidis cell wall proteins

Three Staphylococcus epidermidis isolates of differing bacteriophage types were studied to define proteins confined to the cell wall, which were surface exposed and thus available to interact with the host. Three major proteins of 37, 41, and 51 kDa were identified in all whole-cell lysates and cell wall extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Two additional proteins of 18 and 25 kDa became evident by using 125I labeling to delineate surface-exposed proteins. A classification scheme using P1 to P5 to delineate the 51-, 41-, 37-, 25- and 18-kDa proteins is proposed. Additionally, murine immune sera were used to identify two immunodominant proteins of 51 and 25 kDa (P1 and P4, respectively).

Effect of three plastic catheters on survival and growth of Pseudomonas aeruginosa

The effect of polyvinylchloride (PVC), polyurethane (PU) and siliconized latex (SL) catheters on the survival and growth of six non-mucoid and three mucoid strains of Pseudomonas aeruginosa was evaluated. Pseudomonas aeruginosa (1 x 10(8)) was incubated in PBS alone (control) or with 30 1-cm length segments of each catheter and the number of viable microorganisms was determined after 8 h, 1, 2, 5, 7 and 10 days. The presence of PVC catheters significantly favoured the survival and growth of non-mucoid strains in comparison to the control (P less than 0.05 at 5 days, P less than 0.01 at 7 days and thereafter); a similar result was observed with SL catheters (P less than 0.05 at 2 days, P less than 0.01 at 5 days and thereafter). No differences were observed with PU catheters. The number of mucoid microorganisms decreased with time in all controls and suspensions containing segments of catheter, but non-mucoid revertants appeared and quickly increased in the presence of PVC and SL (but not PU) catheters. Eluates of PBS previously containing PVC or SL segments induced a 100- to 500-fold increase in the growth of a non-mucoid strain in comparison with PBS alone. It is concluded that some plastic catheters can release substance(s) that favour the viability of P. aeruginosa.

Qualitative intravascular catheter tip cultures do not predict catheter-related bacteremia

During a 5-month period, we evaluated the sensitivity, specificity, and predictive value of qualitative cultures of intravenous catheters submitted to a university hospital microbiology laboratory. Of 36 catheters submitted for culture from nonseptic patients, 10 (28%) grew one or more microorganisms on qualitative culture. Of 44 catheters cultured from septic patients, 20 (45%) grew one or more microorganisms, but only 5 grew microorganisms that also were isolated from blood cultures. The sensitivity, specificity, and positive predictive values for catheter-related bacteremia were 71%, 96%, and 17%, values similar to those reported for quantitative methods. Although acceptable in terms of sensitivity and specificity, the very low positive predictive value suggests that catheter-related bacteremia cannot be predicted reliably by this test. We conclude, therefore, that nonstandardized qualitative IV catheter cultures have minimal value as predictors of bacteremia and recommend that they not be performed in clinical microbiology laboratories.

Laboratory diagnosis of intravascular catheter associated sepsis

Many different methods have been employed to aid in the laboratory diagnosis of intravascular catheter associated infection. However, because of differences in patient populations, the definition of catheter sepsis and types of catheters, comparison of these studies is difficult. Of even more fundamental importance, the question of the pathogenesis of intravascular catheter associated sepsis (i.e. whether the microorganisms migrate to the intravascular space via the internal or external surface of the catheter) has not been resolved and is the subject of ongoing controversy. Semiquantitative culture of catheter tips would appear the easiest and most labour-efficient method available at present to diagnose catheter related infection. With central vein catheter tips, however, a cut-off level below 15 CFU per plate should be adopted as indicating a positive test result, particularly in patient populations with a high prevalence of catheter associated infection. Methods for non-quantitative broth culture of catheter tips are likely to be more sensitive than the semiquantitative method, but are less specific. Quantitative broth methods improve the specificity, but because of the labour costs involved appear not to offer much advantage over the semiquantitative method in the routine clinical laboratory. Many studies have shown that organisms are more frequently seen on staining than recovered by culture of intravascular catheters. Further studies of intravascular cathether sepsis should include a catheter staining method in addition to culture. Aspiration and culture of blood through an intravascular catheter appears to be reasonably specific in diagnosing the presence of infection on the catheter tip, but is only of low sensitivity (20-40%) in the absence of associated bacteremia.

Mycobacterium chelonei infection of a Broviac catheter insertion site

Mycobacterium chelonei infection developed at the insertion site of an indwelling Broviac catheter in a child with erythroleukemia. Direct adherence to and colonization of the intra- and extra-luminal surfaces of the catheter, with extension to the adjacent subcutaneous tissue, by this rapidly growing mycobacterium may have been the primary factor underscoring the infection. Nontuberculous mycobacteria such as Mycobacterium chelonei grow readily on routine bacteriologic media and resemble Corynebacterium spp. (diphtheroids) in their Gram staining and microscopic characteristics. The persistence of the infectious process and a diphtheroid-like microorganism despite antimicrobial therapy should raise the suspicion for a mycobacterial species.