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In vitro activity of tigecycline against Staphylococcus epidermidis growing in an adherent-cell biofilm model.

The activity of tigecycline against Staphylococcus epidermidis growing in an in vitro adherent-cell biofilm model was determined. Tigecycline minimum bactericidal concentrations (MBCs) ranged from 1 to 8 microg/ml for S. epidermidis growing in a biofilm of adherent cells, compared to MBCs of 0.12 to >32 microg/ml for freely growing cells. The killing activity of tigecycline against the adherent bacteria was at least fourfold better than that of vancomycin and daptomycin.

Bacterial Adhesion↗

Influence of optic and haptic materials on the adherence of Staphylococcus epidermidis to intraocular lenses: a pilot study.

To evaluate in vitro the adherence of Staphylococcus epidermidis to intraocular lenses (IOL) of different optic and haptic materials and design, we used a quantitative cultural method. Polymethylmethacrylate (PMMA), PMMA-prolene, polyHEMA, silicone and surface-modified PMMA (wet and dry) implants were tested. Adherence differed significantly in the various groups, with the best performance by all-PMMA IOL.

Bacterial Adhesion↗

Rifampin treatment of prosthetic valve endocarditis due to Staphylococcus epidermidis.

Twenty-three patients with prosthetic valve endocarditis caused by methicillin-resistant Staphylococcus epidermidis were studied retrospectively for assessment of the role of rifampin treatment. Rifampin (900-1,200 mg daily) was administered in combination with either vancomycin or a beta-lactam antibiotic for an average of 38 days. Eight patients also received an aminoglycoside. Infection was cured in 16 (70%) of these patients; i.e., in 13 (87%) of 15 receiving rifampin plus vancomycin and in three (38%) of eight receiving rifampin plus a beta-lactam antibiotic (P = .025). The addition of rifampin to vancomycin regimens resulted in an increase in serum bactericidal activity. The selection of rifampin-resistant strains of S. epidermidis during treatment with a combination of antibiotics was noted in two patients with persistent infection. The rates of cure obtained with rifampin-beta-lactam combinations were similar to those obtained with beta-lactam agents alone; however, the cure rates obtained with rifampin plus vancomycin (with or without an aminoglycoside) were encouraging and merit further study.

Anti-Bacterial Agents↗

Determinants of ICU mortality in necrotizing pancreatitis: the influence of Staphylococcus epidermidis.

BACKGROUND: The severity of acute necrotizing pancreatitis ranges from self-limited to rapidly progressive illness leading to multiple organ failure. Several scoring systems and clinical parameters have been used to predict the course of the disease. The aim of this study was to evaluate the clinical and microbiological determinants of poor outcome in necrotizing acute pancreatitis. METHODS: Medical records of 67 consecutive patients admitted to the intensive care unit (ICU) of Oulu University Hospital due to acute necrotizing pancreatitis were retrospectively analyzed. All patients received standard surgical intensive care. RESULTS: Patients who died (n=14) had significantly higher APACHE II, SAPS II and Ranson scores at admission to the ICU and maximum SOFA score achieved during ICU stay than did the survivors. The non-survivors were hospitalized later from the time the symptoms were first manifest (5.3 vs. 2.4 days, P=0.051). Mechanical ventilation (P=0.002), surgical management (P=0.028), open packing surgical management (P=0.03), renal replacement therapy (P<0.001), use of inotropic drugs (P=0.012) and Staphylococcus epidermidis growth (P=0.029) in infected pancreatic tissue were all associated with mortality. CONCLUSIONS: In this study the time to hospitalization, severity of illness, intensity of care, and surgical management were associated with poor outcome. In addition, Staphylococcus epidermidis in pancreatic necrosis was associated with increased mortality.

APACHE↗

Surgical biomaterials and differential colonization by Staphylococcus epidermidis.

The data presented in this communication demonstrate preferential colonization of certain biomaterials by Staphylococcus epidermidis. Using a laminar flow biomaterial colonization chamber and surgical-grade biomaterials (stainless steel, aluminium ceramic, methyl methacrylate and high-density polyethylene), the pattern of colonization was quantitated using plate count techniques and electron microscopy. Under comparable conditions, methyl methacrylate was colonized by S. epidermidis in greater numbers than the other biomaterials. Increased bacterial colonization and slime production on methyl methacrylate was time-dependent and 15 times higher than on stainless steel and aluminium and four times higher than on high-density polyethylene. The data reveal that certain biomaterials may promote infection by favouring colonization by potential pathogens. This variable should be explored extensively in an in vivo setting because of its implication in clinical infections.

Aluminum↗

Clinical behavior of implant infections due to Staphylococcus epidermidis.

UNLABELLED: Surgical implants and other foreign material are increasingly used in modern medicine to restore or to improve the function of the human body. Infection of an implant is associated with considerable morbidity due to frequent hospitalizations, surgery and antimicrobial treatment. The underlying mechanism is the formation of a bacterial biofilm on the surface of the implanted body. The recognition and diagnosis of implant infections is essential for further therapy and, above all, the decision to remove and exchange the implant. METHODS: We compared the data of 60 patients with implant infections with those of 60 patients with transient bacteremia caused by Staphylococcus epidermidis. The pathogens isolated from blood were characterized with regard to antimicrobial susceptibility and formation of biofilms using a static microtiter plate model. Wild type skin isolates from non-hospitalized healthy volunteers served as control with regard to antimicrobial susceptibility and biofilm formation. RESULTS: Clinical signs and symptoms, underlying diseases and outcome were not different in either group. However, patients with implant infection had fever over a longer time (mean 12 days versus 3 days, respectively, p < 0.05) and more often positive blood cultures than patients with transient bacteremia (3.1 versus 1.2, p < 0.05). Thrombocytopenia was observed in patients with implant infections but not in patients with transient bacteremia (p < 0.05). Biofilms were formed in 86.4 % of the isolates in implant infection, in 88.8 % in transient bacteremia and in 76.9 % of the isolates from healthy volunteers (not significant). Multi-resistance to penicillin, oxacillin, erythromycin, clindamycin, ciprofloxacin and trimethoprim was more common in the hospital strains than in the wild type strains (75.6 % versus 48.7 %, p < 0.05). CONCLUSIONS: The clinical features of implant infections are indistinguishable from those of transient bacteremia. Persisting fever and multiple blood culture yielding the growth of skin flora bacteria are strong indicators for infection of implanted material. Biofilm formation and antimicrobial multi-resistance, as common in implant infection as in transient bacteremia, seem to be accessory factors in infections due to Staphylococcus epidermidis.

Adult↗

Effect of subinhibitory concentrations of clindamycin and trospectomycin on the adherence of Staphylococcus epidermidis in an in vitro model of vascular catheter colonization.

Septicemia, often due to Staphylococcus epidermidis, is a life-threatening complication associated with indwelling vascular catheters. An important factor in the development of such infections is glycocalix, or slime. An in vitro model that mimics intravenous delivery systems in humans was developed. It consisted of a modified Robbins device containing slices of silicone catheters in the removable ports, through which S. epidermidis diluted in 5% dextrose-normal saline with 10% heat-inactivated normal human serum was run, with and without clindamycin and trospectomycin. S. epidermidis was recovered from all catheters in the absence of antibiotics; no growth was detected with antibiotics. Scanning electron microscopy demonstrated significant reduction in glycocalix and no visible organisms with all concentrations except 0.5 micrograms/ml trospectomycin and 1 microgram/ml clindamycin; for those, a moderate amount of glycocalix and a few bacteria were seen. Thus, subinhibitory levels of trospectomycin and clindamycin may have a role in the prevention of microbial adherence to vascular catheters.

Anti-Bacterial Agents↗

A novel plasmid from Staphylococcus epidermidis specifying resistance to kanamycin, neomycin and tetracycline.

The naturally occurring plasmid pSTS7 from Staphylococcus epidermidis mediated resistance to tetracycline via a tetL gene and to kanamycin and neomycin via an aadD gene. Plasmid pSTS7 showed partial restriction map and sequence homology to the previously described tetracycline resistance plasmid pNS1981 from Bacillus subtilis and to the kanamycin/neomycin/bleomycin resistance plasmid pUB110 from S. aureus. Sequence analysis of the regions flanking the two resistance genes in pSTS7 led to the identification of a novel site for interplasmid recombination which could explain the derivation of pSTS7 from the incompatible pNS1981- and pUB110-like parental plasmids under tetracycline-selective pressure.

Amino Acid Sequence↗

Search for the insertion element IS256 within the ica locus of Staphylococcus epidermidis clinical isolates collected from biomaterial-associated infections.

Staphylococcus epidermidis biofilm-forming strains produce a polysaccharide intercellular adhesin (PIA), which mediates bacterial cell aggregation and favours the colonisation on prosthetic implants. PIA synthesis is regulated by the icaADBC locus. In vitro, by repeated subcultures of a biofilm-producing strain, the loss of the ability to produce biofilm appears associated with the insertion of the IS256 element into the ica locus. This study was aimed (i) to investigate if the five genes of ica locus are always all present in different strains of S. epidermidis, and (ii) to search if IS256 insertion naturally occurs in ica locus without making recourse to the experimental procedure of repeated subcultures of strains. 120 S. epidermidis clinical isolates from peri-prosthesis infections were investigated both by an original multiplex PCR analysis of the ica genes and by PCR amplification of the IS256 element. Also two reference strains (the biofilm-negative S. epidermidis ATCC 12228 and the biofilm-forming ATCC 35984 [RP62A]) and two biofilm-negative RP62A-derived acriflavin mutants (D9 and HAM892) were analysed. D9 e HAM892 were for the first time shown to contain in ica locus, at the base 3319, a 1300-bp insertion with a DNA sequence corresponding to IS256. Among the 120 clinical isolates, 51 (43%) turned out completely ica-positive, 69 completely ica-negative (57%). The genes of the ica locus appear, in all cases of the present collection, strictly linked each other, so they are either all present or all absent. In this collection, IS256 was present in eight out of the 69 ica-negative strains and in 34 out of the 51 ica-positive strains. IS256, also when present in bacterial genomic DNA, was never found inside the ica locus, thus suggesting that insertion/excision of this element is not a natural occurring mechanism for off/on switching of biofilm production.

Biocompatible Materials↗

Therapy of methicillin-resistant Staphylococcus epidermidis experimental endocarditis.

Antibiotic therapy of methicillin-resistant Staphylococcus epidermidis endocarditis was investigated with the rabbit endocarditis model. Time-kill studies in vitro demonstrated that gentamicin and rifampin had the most rapid early bactericidal rates. With rifampin alone, rifampin-resistant subpopulations emerged. Combinations of antibiotics with gentamicin or rifampin in vitro did not significantly alter the killing rate but prevented emergence of subpopulations resistant to the latter. In the rabbit endocarditis model, gentamicin and vancomycin were the most effective single antibiotic regimens in terms of ability to reduce the bacterial densities on cardiac valve vegetations. Five treatment regimens were equally effective, including vancomycin, gentamicin, vancomycin plus rifampin or gentamicin, and rifampin plus gentamicin. The three-drug combination of vancomycin, rifampin, and gentamicin did not significantly improve the results. Cephalothin therapy was significantly less effective than any of the regimens noted above. It was no more effective than no treatment at 2 days and was only slightly more effective at 4 days. This result with cephalothin treatment was not predicted by routine types of in vitro antibiotic susceptibility testing. Treatment of rabbits with methicillin or cephalothin was associated with an increase in the subpopulation of bacteria resistant to the respective drugs. A number of regimens show potential for therapy of these infections, including vancomycin plus rifampin or gentamicin, rifampin plus gentamicin, and vancomycin alone.

Animals↗

A simple alternative method for rapid detection of slime produced by Staphylococcus epidermidis isolates in bacterial keratitis.

BACKGROUND & OBJECTIVES: Slime is a known virulence factor of Staphylococcus epidermidis. The conventional Christensen's method for detection of slime in the laboratory takes at least 48 h. We, therefore, tried to evaluate the efficacy of the Congo red agar method as a routine procedure for detecting slime among isolates from corneal ulcers. METHODS: A total of 244 isolates from corneal ulcers were identified as S. epidermidis by the standard procedures. Slime was detected both by the conventional Christensen's method as well as by the Congo red agar method. RESULTS: Ninety two (37.7%) isolates were positive and 86 (35.2%) were negative for slime by both the techniques. Fifty four (22.1%) isolates were positive in Congo red agar, but negative by Christensen's method; whereas only 12 (4.9%) were negative by Congo red but positive by Christensen's method. Detection of slime by Congo red agar method was rapid i.e., all the 146 strains were positive within 24 h of incubation. On the other hand, Christensen's method had a delayed response; 42.3 per cent (44/104) strains being negative during the first 24 h of incubation. INTERPRETATION & CONCLUSION: Our results suggested that culture on Congo red agar was a sensitive and rapid test for detecting slime. This might help in the quick identification in a routine laboratory of slime positive isolates in bacterial keratitis.

Bacteriological Techniques↗

Solid-phase radioimmunoassay for IgG antibodies to Staphylococcus epidermidis. Use in serious coagulase-negative staphylococcal infections.

A radioimmunoassay (RIA) for human IgG antibodies to Staphylococcus epidermidis was compared with an agar-gel-diffusion assay in patients with a variety of infections. The RIA was sensitive and reproducible and discriminated between endocarditis and uncomplicated bacteremias due to coagulase-negative staphylococci. Anti-S epidermidis antibodies by RIA were elevated in 16 (89%) of 18 patients with coagulase-negative staphylococcal endocarditis but in none of 28 patients with uncomplicated bacteremia (n = 18) or with blood culture contaminated with these organisms (n = 10). Cross-reacting IgG antibodies to S epidermidis antigens were also detected by RIA in 13 (76%) of 17 patients with Staphylococcus aureus endocarditis but in none of 17 patients with nonvalvular S aureus bacteremias and in none of 25 patients with endocarditis or bacteremia caused by other pathogens. Agar-gel-diffusion assay was less sensitive than RIA for detecting coagulase-negative staphylococcal endocarditis, being positive in nine (50%) of 18 such patients. This RIA may be useful in distinguishing patients with endocarditis from those with nonvalvular staphylococcemias or blood culture contamination.

Antibodies, Bacterial↗

Phenotypic expression of oxacillin resistance in Staphylococcus epidermidis: roles of mecA transcriptional regulation and resistant-subpopulation selection.

The MICs for many oxacillin-resistant (OR) Staphylococcus epidermidis (ORSE) strains are below the Staphylococcus aureus methicillin or oxacillin resistance breakpoint. The difficulty detecting the OR phenotype in S. epidermidis may be due to extreme heterotypy in resistance expression and/or transcriptional repression of mecA, the OR gene, by MecI. To determine the role of these factors in the phenotypic expression of ORSE, 17 geographically diverse mecI(+) ORSE isolates representing 14 distinct pulsed-field gel electrophoresis pulse types (>3 band differences) were investigated. Thirteen of the 14 types contained mecI and mecA promoter-operator sequences known to be associated with maximal mecA repression, and in all isolates, mecA transcription was repressed. All 17 were heterotypic in their resistance expression. Oxacillin MICs ranged from 1 to 128 microg/ml and increased for 16 of 17 isolates after beta-lactam induction. Allelic replacement inactivation of mecI in three isolates similarly resulted in a four- to sevenfold increase in MIC. In the two of these three isolates producing beta-lactamase, mecA transcription was regulated by both mecI and beta-lactamase regulatory sequences. Heterotypic expression of resistance in these three isolates was unaffected by either beta-lactam induction or mecI inactivation. However, prolonged incubation in concentrations of oxacillin just sufficient to produce a lag in growth (0.5 to 1.0 microg/ml) converted the population resistance expression from heterotypic to homotypic. Homotypic conversion could also be demonstrated in microtiter wells during MIC determinations in one isolate for which the MIC was high. We conclude that the phenotypic expression of S. epidermidis OR in broth can be affected both by mecA transcriptional regulation and by subpopulation resistance expression.

Bacterial Proteins↗

Phenotypic and genomic variation among Staphylococcus epidermidis strains infecting joint prostheses.

We studied the SmaI and SstII macrorestriction patterns of 54 Staphylococcus epidermidis strains isolated from 14 patients infected following the implantation of joint prostheses. Multiple strains from pus and infected tissue specimens of each patient were selected on the basis of different colony morphologies and drug resistance patterns. The same criteria were used to select 23 S. epidermidis strains from hand swabs of eight healthy individuals. For 10 of the 14 patients, all the intrapatient strains appeared to be closely or possibly related, whereas related strains were detected in the skin flora of only one of the eight healthy individuals. This observation suggests that, in most cases, the patients were infected by a single S. epidermidis clone which subsequently underwent rearrangements that yielded derivatives with divergent phenotypes and, occasionally, divergent macrorestriction patterns. The four patients whose specimens contained unrelated S. epidermidis strains were probably infected with several polyclonal strains.

Arthroplasty, Replacement↗

Simplified method for the isolation, identification, and characterization of Staphylococcus epidermidis in epidemiologic studies.

A simplified method for the isolation, identification, and characterization of Staphylococcus epidermidis from humans is described. Swabs of the nose and skin are cultured on mannitol salt agar. Isolated colonies not producing acid from mannitol (presumptive coagulase-negative staphylococci or micrococci) are then inoculated onto purple agar containing erythromycin and glycerol. All colonies growing on this medium are then replicated onto media that tests for the production of phosphatase, the production of acid from trehalose, and susceptibility to four antibiotics. All S. epidermidis sensu stricto are confirmed by the API Staph-Ident system. As a result, Staphylococcus aureus and all other coagulase-negative staphylococci are effectively identified and eliminated from further study and only strains of S. epidermidis are left for further characterization. Of the 252 isolates from 48 cultures of the nares and the fingers, 112 (44%) were eliminated during different stages of this isolation and identification procedure. The antibiotic susceptibility data further distinguished those isolates in the predominant API biochemical profile number. This scheme has applications in the early stages of either ecologic or epidemiologic studies of this important nosocomial pathogen.

Cephalothin↗

The fibrinogen binding protein of Staphylococcus epidermidis is a target for opsonic antibodies.

Antibodies against the fibrinogen binding protein (Fbe) of Staphylococcus epidermidis significantly increased macrophage phagocytosis. Antibodies against autolysin E were opsonic but to a lesser extent. Antibodies against a novel, putatively surface-located antigen were unable to enhance phagocytosis. The severity of systemic infection of mice with S. epidermidis was reduced if the bacteria were preopsonized with anti-Fbe prior to administration. Fbe is thus a strong candidate for protein vaccination against S. epidermidis infection, and antibodies against Fbe can be used to prevent or treat infections caused by S. epidermidis.

Animals↗

Prosthetic valve endocarditis caused by Staphylococcus epidermidis. Development of rifampin resistance during vancomycin and rifampin therapy.

Development of rifampin-resistant Staphylococcus epidermidis was documented in three patients receiving vancomycin and rifampin therapy for prosthetic valve endocarditis. The minimum inhibitory concentrations and minimum bactericidal concentrations of rifampin for the original three isolates were 0.4 micrograms/mL or less. Organisms cultured during relapse or prosthetic valve replacement had minimum inhibitory concentrations of rifampin that were 12.5, 50, and greater than 100 micrograms/mL, respectively. Surgical intervention was necessary in all patients. One died, and one required a second prosthetic valve placement. The patients were treated with vancomycin plus aminoglycoside following identification of rifampin resistance. These observations suggest that vancomycin and rifampin may not be adequate therapy for prosthetic valve endocarditis caused by S epidermidis.

Drug Resistance, Microbial↗

Parallel induction by glucose of adherence and a polysaccharide antigen specific for plastic-adherent Staphylococcus epidermidis: evidence for functional relation to intercellular adhesion.

The initial attachment and the accumulation of Staphylococcus epidermidis on polymer surfaces in multilayered cell clusters embedded in amorphous slime, which together lead to the plastic-adherent phenotype detected by the adherence assay used in this study, have been proposed to be major virulence factors of these bacteria. An antigen specific for plastic-adherent S. epidermidis strains was detected by an indirect immunofluorescence test using absorbed antiserum raised against the strongly plastic-adherent S. epidermidis 1457. A coagglutination assay was established, which allowed the quantitation of the antigen in bacterial extracts under different physiologic growth conditions. Expression of the antigen and of plastic adherence depended significantly on the presence of glucose in the growth medium. Parallel to increased plastic adherence, a 32- to 64-fold increase in the amount of the antigen was detected in bacterial extracts of cells grown in tryptone soya broth (TSB) compared with that in extracts of cells grown in TSB lacking glucose. A parallel time-dependent increase of plastic adherence and expression of the antigen was observed after stimulation by glucose of stationary-phase cultures of plastic-adherent S. epidermidis strains grown in TSB lacking glucose. The antigen consisted most probably of polysaccharide, because its immunologic reactivity was completely abolished by periodate oxidation but was resistant to protease digestion. A significant proportion of cells of plastic-adherent as compared with nonadherent S. epidermidis strains grown in TSB were located in large cell clusters exceeding 50 cells, which completely disintegrated after periodate oxidation of the cell preparations. Periodate oxidation of adherent bacterial films in situ led to release of the adherent cells from the plastic surface. These results strongly indicate a functional relation of the antigen to adherence of S. epidermidis to polymer surfaces, most probably by mediating intercellular adhesion of cells leading to accumulation in multilayered cell clusters.

Agglutination↗