Influence of carbon dioxide on the surface characteristics and adherence potential of coagulase-negative staphylococci

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

"Biofilmology": a multidisciplinary review of the study of microbial biofilms

The observation of biofilm formation is not a new phenomenon. The prevalence and significance of biofilm and aggregate formation in various processes have encouraged extensive research in this field for more than 40 years. In this review, we highlight techniques from different disciplines that have been used to successfully describe the extracellular, surface and intracellular elements that are predominant in understanding biofilm formation. To reduce the complexities involved in studying biofilms, researchers in the past have generally taken a parts-based, disciplinary specific approach to understand the different components of biofilms in isolation from one another. Recently, a few studies have looked into combining the different techniques to achieve a more holistic understanding of biofilms, yet this approach is still in its infancy. In order to attain a global understanding of the processes involved in the formation of biofilms and to formulate effective biofilm control strategies, researchers in the next decade should recognise that the study of biofilms, i.e. biofilmology, has evolved into a discipline in its own right and that mutual cooperation between the various disciplines towards a multidisciplinary research vision is vital in this field.

The resistance of polyvinylpyrrolidone–Iodine–poly(ε-caprolactone) blends to adherence of Escherichia coli

In this study, the resistance of biodegradable biomaterials, composed of blends of poly(-caprolactone) (PCL) and the polymeric antimicrobial complex, polyvinylpyrrolidone-iodine (PVP-I) to the adherence of a clinical isolate of Escherichia coli is described. Blends of PCL composed of a range of high (50,000 g mol(-1)) to low (5000 g mol(-1)) molecular weight ratios of polymer and either devoid of or containing PVP-I (1% w/w) were prepared by solvent evaporation. Following incubation (4 h), there was no relationship between m. wt. ratio of PCL in films devoid of PVP-I and adherence of E. coli. Conversely, microbial adherence to PCL containing PVP-I decreased as the ratio of high:low m. wt. polymer was decreased and was approximately 1000 fold lower than that to comparator films devoid of PVP-I. Following periods of immersion of PVP-I containing PCL films under sink conditions in phosphate buffered saline, subsequent adherence of E. coli was substantially reduced for 2 days (40:60 m. wt. ratio) and 6 days (100:0 m. wt. ratio). Concurrent exposure of PCL and E. coli to sub-minimum inhibitory concentrations (sub-MIC) of PVP-I significantly reduced microbial adherence to the biomaterial; however, the molecular weight ratio of PCL did not affect this outcome. Pretreatment of PCL with similar sub-MIC of PVP-I prior to inclusion within the microbial adherence assay significantly decreased the subsequent adherence of E. coli. Greatest reduction in adherence was observed following treatment of PCL (40:60 m. wt. ratio) with 0.0156% w/w PVP-I. In conclusion, this study has illustrated the utility of PVP-I as a suitable therapeutic agent for incorporation within PCL as a novel biomaterial. Due to the combined antimicrobial and biodegradable properties, these biomaterials offer a promising strategy for the reduction in medical device related infection.

Peritoneal fluid titer test for peritoneal dialysis-related peritonitis

Standard microbiological tests (i.e., MIC) do not account for the unique factors of peritoneal dialysis (PD)-related peritonitis which can significantly influence treatment response. Our goals were to develop a peritoneal fluid titer (PFT) test and to conduct a pilot study of its association with clinical outcome. The methodology was developed by using spent dialysate collected from patients with bacterial PD-related peritonitis prior to the initiation of antibiotics. Dialysate was processed and spiked with antibiotic to simulate two standard intraperitoneal regimens: cefazolin plus tobramycin and cefazolin alone. Thirty-six clinical isolates, including Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa, were tested. In the pilot study, dialysate was collected from 14 patients with bacterial PD-related peritonitis. Titers were determined by using each patient's dialysate and infecting pathogen. Titers were highly reproducible, with discrepancies in only 1% of cases. Overall, PFTs were notably higher against gram-positive bacteria (P < 0.0001). The addition of tobramycin increased titers significantly from zero to values of 1/16 to 1/64 against E. cloacae and P. aeruginosa (P < 0.0001). In the pilot study, peritoneal fluid inhibitory titers were significantly associated with clinical outcome, with a median value of 1/96 for patients who were cured compared to 1/32 for those who failed treatment (P = 0.036). In conclusion, this study provides preliminary support for the PFT as a pharmacodynamic index specific to the treatment of PD-related peritonitis. With further characterization and validation in patients, the PFT test may advance the study of antibiotic therapies for PD-related peritonitis.

Influence of the incubation atmosphere on the production of biofilm by staphylococci

Biofilm formation by Staphylococcus epidermidis, Staphylococcus hemolyticus, Staphylococcus sciuri and Staphylococcus aureus in aerobic, anaerobic and CO2 incubation atmospheres was quantified by the modified microtiter plate test. The S. epidermidis and S. aureus strains showed significantly lower biofilm production when grown in a CO2-rich environment compared to that exhibited in aerobic incubation. The amount of biofilm produced by these strains under anaerobic conditions did not differ significantly from the biofilm formation detected in the aerobic incubation. The incubation atmosphere did not affect S. sciuri biofilm formation. Biofilm production by S. hemolyticus isolates was very low regardless of the experimental conditions used.

Evaluation of a poly(vinyl pyrollidone)-coated biomaterial for urological use

The associated problems of bacterial biofilm formation and encrustation that may cause obstruction or blockage of urethral catheters and ureteral stents often hinders the effective use of biomaterials within the urinary tract. In this in vitro study, we have investigated the surface properties of a hydrophilic poly(vinyl pyrollidone) (PVP)-coating applied to polyurethane and determined its suitability for use as a urinary tract biomaterial by comparing its lubricity and ability to resist bacterial adherence and encrustation with that of uncoated polyurethane and silicone. The PVP-coated polyurethane was significantly more hydrophilic and more lubricious than either uncoated polyurethane or silicone. Adherence of a hydrophilic Escherichia coli isolate to PVP-coated polyurethane and uncoated polyurethane was similar but significantly less than adherence to silicone. Adherence of a hydrophobic Enterococcus faecalis isolate to PVP-coated polyurethane and silicone was similar but was significantly less than adherence to uncoated polyurethane. Struvite encrustation was similar on the PVP-coated polyurethane and silicone but significantly less than on uncoated polyurethane. Furthermore, hydroxyapatite encrustation was significantly less on the PVP-coated polyurethane than on either uncoated polyurethane or silicone. The results suggest that the PVP-coating could be useful in preventing complications caused by bacterial biofilm formation and the deposition of encrustation on biomaterials implanted in the urinary tract and, therefore, warrants further evaluation.

Regulation of Staphylococcus aureus type 5 and type 8 capsular polysaccharides by CO(2)

Staphylococcus aureus expression of capsular polysaccharide type 5 (CP5) has been shown to be downregulated by CO(2). Here we show that CO(2) reduces CP5 expression at the transcriptional level and that CO(2) regulates CP8 expression depending on the genetic background of the strains. Growth in the presence of air supplemented with 5% CO(2) caused a significant decrease in CP8 expression in four S. aureus strains, a marginal effect in four strains, and higher CP8 expression in strain Becker. Absolute CP8 expression in the nine S. aureus strains differed largely from strain to strain. Four groups of strains were established due to sequence variations in the promoter region of cap5 and cap8. To test whether these sequence variations are responsible for the different responses to CO(2), promoter regions from selected strains were fused to the reporter gene xylE in pLC4, and the plasmids were electrotransformed into strains Becker and Newman. XylE activity was negatively regulated by CO(2) in all derivatives of strain Newman and was always positively regulated by CO(2) in all derivatives of strain Becker. Differences in promoter sequences did not influence the pattern of CP8 expression. Therefore, the genetic background of the strains rather than differences in the promoter sequence determines the CO(2) response. trans-acting regulatory molecules may be differentially expressed in strain Becker versus strain Newman. The strain dependency of the CP8 expression established in vitro was also seen in lung tissue sections of patients with cystic fibrosis infected with CP8-positive S. aureus strains.

Conditioning film and environmental effects on the adherence of Candida spp. to silicone and poly(vinylchloride) biomaterials

The reported incidence of colonization of oropharyngeal medical devices with Candida spp. has increased in recent years, although few studies that have systematically examined the adherence of yeast cells to such biomaterials, the primary step in the process of colonization. This study, therefore, examined the effects of oropharyngeal atmospheric conditions (5% v/v carbon dioxide) and the presence of a salivary conditioning film on both the surface properties and adherence of Candida albicans, Candida krusei and Candida tropicalis to PVC and silicone. Furthermore, the effects of the salivary conditioning film on the surface properties of these biomaterials are reported. Growth of the three Candida spp. in an atmosphere containing 5% v/v CO2 significantly increased their cell surface hydrophobicity and reduced the zeta potential of C. albicans and C. krusei yet increased the zeta potential of C. tropicalis (p<0.05). Furthermore, growth in 5% v/v CO2 decreased the adherence of C. tropicalis and C. albicans to both PVC and silicone, however, increased adherence of C. krusei (p<0.05). Pre-treatment of the microorganisms with pooled human saliva significantly decreased their cell surface hydrophobicity and increased their adherence to either biomaterial in comparison to yeast cells that had been pre-treated with PBS (p<0.05). Saliva treatment of the microorganisms had no consistent effect on microbial zeta potential. Interestingly, adherence of the three, saliva-treated Candida spp. to saliva-treated silicone and PVC was significantly lower than whenever the microorganisms and biomaterials had been treated with PBS (p<0.05). Treatment of silicone and PVC with saliva significantly altered the surface properties, notably reducing both the advancing and receding contact angles and, additionally, the microrugosity. These effects may contribute to the decreased adherence of saliva-treated microorganisms to these biomaterials. In conclusion, this study has demonstrated the effects of physiological conditions within the oral cavity on the adherence of selected Candida spp. to biomaterials employed as oropharyngeal medical devices. In particular, this study has ominously shown that these materials act as substrates for yeast colonization, highlighting the need for advancements in biomaterial design. Furthermore, it is important that physiological conditions should be employed whenever biocompatibility of oropharyngeal biomaterials is under investigation.

A novel image-analysis technique for measurement of bacterial cell surface tension

Cell-surface hydrophobicity is different for Staphylococcus epidermidis cells grown under different environmental conditions; this might influence attachment and colonization of surfaces. Although a wide variety of techniques has been employed to measure bacterial surface hydrophobicity, including contact angle determinations, adherence to hydrocarbons, hydrophobic-interaction chromatography and salt aggregation, many of these either require large numbers of cells or do not yield comparable quantitative data. This study describes a novel, quantitative method for the determination of bacterial surface tension on the basis of image analysis of cell-cell interactions. S. epidermidis (strains 900 and 901) were suspended in different concentrations of propanol of known surface tension and examined by bright-field microscopy linked via a charge-couple device (CCD) camera to an image analyser. Frames were chosen randomly and the data recorded as a ratio of count/percentage coverage for each frame. The results showed that for strains 900 and 901 this ratio was maximum at surface tensions of 67 and 61 mN m(-1) respectively. At these values of minimal interaction the surface tension of the liquid was equal to the bacterial cell surface tension. The results were in close agreement with those obtained from contact angles. The advantage of surface tension measurements is that, irrespective of the method used, the results generated are quantitative values and are therefore directly comparable. The method reported is reliable, reproducible and is of particular value because the number of cells required is, typically, at least two orders of magnitude lower than is required for commonly used alternative methods.

Characterization and assessment of a novel poly(ethylene oxide)/polyurethane composite hydrogel (Aquavene) as a ureteral stent biomaterial

The effective long-term use of indwelling ureteral stents is often hindered by the formation of encrusting deposits which may cause obstruction and blockage of the stent. Development of improved ureteral stent biomaterials capable of preventing or reducing encrustation is therefore particularly desirable. In this study, the suitability as a ureteral stent biomaterial of Aquavene, a novel poly(ethylene oxide)/polyurethane composite hydrogel was compared with that of silicone and polyurethane, two materials widely employed in ureteral stent manufacture. Examination of Aquavene in dry and hydrated states by confocal laser scanning microscopy, scanning electron microscopy, and atomic force microscopy showed the presence of numerous channels within a cellular matrix structure. The channel size increased considerably to as much as 10 microm in diameter in the hydrated state. Aquavene provided superior resistance to encrustation and intraluminal blockage over a 24-week period in a simulated urine flow model. Unobstructed urine flow continued with Aquavene at 24 weeks, whereas silicone and polyurethane stents became blocked with encrustation at 8 and 10 weeks, respectively. Weight loss within Aquavene on the order of 9% (w/w) over the 24-week flow period indicates that extraction of the noncrosslinked poly(ethylene oxide) hydrogel may be responsible for the prevention of encrustation blockage of this biomaterial. In the dry state, Aquavene was significantly harder than either silicone or polyurethane, as shown by Young's modulus, and rapidly became soft on hydration. These additional properties of Aquavene would facilitate ease of stent insertion in the dry state past obstructions in the ureter and provide improved patient comfort on subsequent biomaterial hydration in situ. Aquavene is a promising candidate for use in the urinary tract, as it is probable that effective long-term urine drainage would be maintained in vivo. Further evaluation of this novel biomaterial is therefore warranted.

The use of X-ray photoelectron spectroscopy for the study of oral streptococcal cell surfaces

Physicochemical and structural properties of microbial cell surfaces play an important role in their adhesion to surfaces and are determined by the chemical composition of the outermost cell surface. Many traditional methods used to determine microbial cell wall composition require fractionation of the organisms and consequently do not yield information about the composition of the outermost cell surface. X-ray photoelectron spectroscopy (XPS) measures the elemental composition of the outermost cell surfaces of micro-organisms. The technique requires freeze-drying of the organisms, but, nevertheless, elemental surface concentration ratios of oral streptococcal cell surfaces with peritrichously arranged surface structures showed good relationships with physicochemical properties measured under physiological conditions, such as zeta potentials. Isoelectric points appeared to be governed by the relative abundance of oxygen- and nitrogen-containing groups on the cell surfaces. Also, the intrinsic microbial cell-surface hydrophobicity by water contact angles related to the cell-surface composition as by XPS and was highest for strains with an elevated isoelectric point. Inclusion of elemental surface compositions for tufted streptococcal strains caused deterioration of the relationships found. Interestingly, hierarchical cluster analysis on the basis of the elemental surface compositions revealed that, of 36 different streptococcal strains, only four S. rattus as well as nine S. mitis strains were located in distinct groups, well separated from the other streptococcal strains, which were all more or less mixed in one group.

Assessment of encrustation behaviour on urinary tract biomaterials

The effective clinical use of biomaterials within the urinary tract is often hindered by the associated problems of bacterial biofilm formation and encrustation which may cause obstruction or blockage of urethral catheters and ureteral stents. Methods for assessing encrustation formation on these devices are reviewed and novel urinary tract biomaterials which may be more effective at resisting encrustation are discussed.

Conditioning fluid influences on the surface properties of silicone and polyurethane peritoneal catheters: implications for infection

Catheter-related infection remains a considerable problem in continuous ambulatory peritoneal dialysis (CAPD). This study examined the adherence of clinical isolates of Staphylococcus epidermidis to commercially available polyurethane and silicone peritoneal catheters in the presence and absence of a proteinaceous conditioning film. In addition, the effects of the conditioning film on the surface properties (advancing and receding contact angles, and surface rugosity) of these biomaterials were investigated. Bacterial adherence to polyurethane and silicone catheters, pre-treated with phosphate-buffered saline (PBS) or artificial spent peritoneal dialysate (ASD) for 1 h at 37 degrees C, was examined using a radiometric (2-3H-adenine) adherence assay. The advancing and receding contact angles and the surface rugosity of ASD- and PBS-treated biomaterials were examined using a dynamic contact angle analyser and an atomic force microscope, respectively. The bacterial isolates were selected to represent high and low cell surface hydrophobicity. The hydrophobic isolate exhibited both a significantly greater rate and a significantly greater extent of adherence than the hydrophilic isolate to both catheter materials, independent of pre-treatment. In general, pre-treatment of the catheter materials with ASD significantly decreased the subsequent adherence of both isolates owing to the deposition of a conditioning film on the surface of the biomaterial. ASD treatment also decreased both the advancing and receding contact angles and the surface rugosity of both catheter materials. This study highlights the influence of both bacterial cell surface hydrophobicity and biomaterial surface conditioning films on bacterial adherence to CAPD catheters. In addition, it is recommended that the effects of proteinaceous conditioning films on biomaterial surface properties should be considered when assessing materials for medical devices and products.

Expression of slime interferes with in vitro detection of host protein receptors of Staphylococcus epidermidis

We hypothesized that slime may mask bacterial molecules important in the attachment of Staphylococcus epidermidis to inanimate surfaces. In support of this hypothesis, we found that slime-negative strains attached significantly better to fibrinogen or fibronectin than the parent strains and exhibited greater surface hydrophobicity. Comparable results were obtained with 53 clinical isolates.

Role of physiological conditions in the oropharynx on the adherence of respiratory bacterial isolates to endotracheal tube poly(vinyl chloride)

Pneumonia is a major problem in intensive care patients and can be induced by pathogenic bacteria adhering to poly(vinyl chloride) (PVC) endotracheal (ET) tubes. This study examines the influence of surface properties on the adherence of the respiratory isolates Staphylococcus aureus and Pseudomonas aeruginosa to PVC. In particular, the influence of respiratory tract physiological conditions, 5% CO2 and saliva, on adherence was investigated. In general, decreased adherence to PVC was observed when bacteria were grown in CO2. When these CO2-grown bacteria were treated with saliva their adherence to PVC significantly increased; however, their adherence was significantly reduced to saliva-treated PVC. Treatment of both bacterial isolates with saliva decreased their negative zeta potential, a factor which may directly contribute to the observed increased microbial (saliva pretreated) adherence to PVC. Cell surface hydrophobicity (CSH) was evaluated by measuring the initial rates of microbial removal from a buffered aqueous phase, to ensure the absence of electrostatic interactions, to an organic phase (xylene). Under physiological conditions, CSH did not appear to be a dominant factor in biomaterial adherence as the CSH of S. aureus was decreased by saliva treatment but was unchanged for Ps. aeruginosa. Additionally, CSH also differed for the two isolates when grown in CO2, significantly decreasing with S. aureus but remaining unaltered with Ps. aeruginosa. Saliva treatment of PVC also decreased the advancing and receding contact angles of the biomaterial and its surface roughness, which may be a factor in the decreased adherence of saliva-treated bacteria to this surface. Alternative biomaterials or surface modifications appear necessary for the desired improvements in ET tube effectiveness. This study highlights the influence of physiological conditions on biomaterial and bacterial surface characteristics and subsequent interactions. It is imperative that the physiological conditions predominating in the clinical area of biomaterial use be considered when investigating device biocompatibility.

Development of a model for assessment of biomaterial encrustation in the upper urinary tract

A need exists for ureteral stent materials capable of preventing or reducing encrustation. The aim of this study, therefore, was to develop an in vitro model producing biomaterial encrustation similar to that on stents in vivo. Three models were designed and evaluated. Polyurethane stent sections were immersed in human urine (37 degrees C, 5% CO2): (1) with and (2) without crushed human kidney stone and (3) in an artificial urine (37 degrees C, 5% CO2). Encrustation of similar composition, as determined by infrared spectroscopy, X-ray diffraction and energy dispersive X-ray analysis, formed on stent materials in vivo, in artificial urine and in human urine with crushed kidney stone. Magnesium ammonium phosphate (struvite) and calcium phosphate (hydroxyapatite) predominated in all encrustations. The reproducibility and ease of use of the artificial urine model provided optimum encrustation assessment of materials presently used in ureteral stents and evaluation of novel biomaterials.

Continuous ambulatory peritoneal dialysis-associated peritonitis as a model device-related infection: phenotypic adaptation, the staphylococcal cell envelope and infection

During the development of infection, pathogens are translocated from one body site to another and so must readily adapt to changing environmental conditions. The influence of host environment on bacterial behaviour and virulence gene expression is, however, often overlooked. Environmental signals such as temperature, pH and nutrient (especially iron) availability which inform pathogens of their living conditions thus contribute to both bacterial survival and virulence. In the context of medical device-associated infections such as peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients, the pathogenesis of infection is related to the ability of the infecting organism to multiply, to adhere to catheter polymers and host tissues and to evade host defences. Coagulase-negative staphylococci (CNS) such as Staphylococcus epidermidis are commonly responsible for CAPD-associated peritonitis. Although staphylococci cannot grow in commercial peritoneal dialysate solutions, these fluids are modified during dialysis and become enriched by a plasma ultrafiltrate which can support bacteria growth. Given that growth environment exerts considerable influence on bacterial behaviour, the physiology of CNS cultured in vitro in a model system employing pooled human peritoneal dialysate and in vivo in implanted peritoneal chambers in the rat has been investigated. Using such models marked variation in surface physicochemistry, antibiotic susceptibility and adherence to catheter polymers has been observed. This plasticity is clearly reflected in the cell envelope phenotype of CNS, the study of which has recently lead to the discovery of a staphylococcal receptor for the iron-binding serum glycoprotein, transferrin.

Influence of the incubation atmosphere on the production of slime by Staphylococcus epidermidis

The influence of various incubation atmospheres on the growth and slime production of 23 Staphylococcus epidermidis strains was studied. The atmospheres evaluated were aerobiosis (control), anaerobiosis, candle jar, 5% CO2 and 10% CO2. As compared to the aerobic control, growth was 55.7 +/- 19% (p < 0.01) in anaerobic incubation, 113.7 +/- 12% (p < 0.01) in 5% CO2, 112.8 +/- 13% (p < 0.01) in 10% CO2 and 106.4 +/- 7% (p > 0.1) in the candle jar. The slime production in relation to the aerobic control was 20.3 +/- 19% in anaerobiosis (p < 0.01), 22.3 +/- 27% (p < 0.01) in 5% CO2, 29.4 +/- 39% (p < 0.01) in 10% CO2 and 68.3 +/- 26% (p > 0.1) in the candle jar. The results of this study may explain the discrepancies which have been noted on occasion between slime formation data and pathogenicity.

Lack of evidence for increased adherent growth in broth or human serum of clinically significant coagulase-negative staphylococci

The relevance of adherent growth of coagulase-negative staphylococci (CNS) in vitro to their clinical significance is controversial. We have investigated the accumulation on polymer surfaces of clinically significant CNS strains, isolated from blood cultures and intravascular catheter tips, compared with controls. The adherent growth of significant CNS isolates in a microtitre tray assay was not greater than controls, and this finding was repeated when different combinations of target polymer surface, culture medium and incubation atmosphere type were investigated. The surface accumulation of CNS cultured in pooled human serum was poor compared with culture in broth. Whole cell and surface protein profiles of serum grown Staphylococcus epidermidis differed markedly from broth cultured cells. We recommend the use of human body fluids, such as serum, as useful culture media to assess whether potential virulence determinants are likely to be expressed in vivo. The microtitre tray assay of adherent growth is not helpful in determining the virulence of individual CNS isolates.

Update on clinical significance of coagulase-negative staphylococci

The clinical significance of coagulase-negative Staphylococcus species (CNS) continues to increase as strategies in medical practice lead to more invasive procedures. Hospitalized patients that are immunocompromised and/or suffering from chronic diseases are the most vulnerable to infection. Since CNS are widespread on the human body and are capable of producing very large populations, distinguishing the etiologic agent(s) from contaminating flora is a serious challenge. For this reason, culture identification should proceed to the species and strain levels. A much stronger case can be made for the identification of a CNS etiologic agent if the same strain is repeatedly isolated from a series of specimens as opposed to the isolation of different strains of one or more species. Strain identity initially can be based on colony morphology, and then one or more molecular approaches can be used to gain information on the genotype. Many of the CNS species are commonly resistant to antibiotics that are being indicated for staphylococcal infections, with the exception of vancomycin. The widespread use of antibiotics in hospitals has provided a reservoir of antibiotic-resistant genes. The main focus on mechanisms of pathogenesis has been with foreign body infections and the role of specific adhesins and slime produced by Staphylococcus epidermidis. Slime can reduce the immune response and opsonophagocytosis, thereby interfering with host defense mechanisms. As we become more aware of the various strategies used by CNS, we will be in a better position to compromise their defense mechanisms and improve treatment.

Variable fixation of staphylococcal slime by different histochemical fixatives

A variety of histochemical fixatives were used to compare the fixation of bacterial films produced by a standard slime-producing strain of Staphylococcus epidermidis on plastic tissue culture plates. Some reagents were completely ineffective in fixing the slime layer, whereas others gave variable results. The best alternative to the fixative of the reference method, the potentially explosive Bouin's reagent, was air drying.

Effect of growth conditions on expression and antigenicity of Staphylococcus epidermidis RP62A cell envelope proteins

Staphylococcus epidermidis RP62A (ATCC 35984) was grown in tryptic soy broth (TSB), iron-depleted TSB (TSB-Fe), iron-reconstituted TSB-Fe (TSB+Fe), a chemically defined medium, and fetal calf serum (FCS) and on silastic disks in chambers that were sutured to the pig peritoneal wall. Bacterial cell wall proteins were extracted by digestion with recombinant lysostaphin, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and detected by silver staining. Cell wall proteins from TSB-, chemically defined medium-, or FCS-grown cells had a complex profile of greater than 25 protein bands spanning the full molecular mass range. By contrast, a digest obtained from in vivo-grown cells had only five major proteins of 40 kDa or greater. Proteins of 130 and 106 kDa were present in the cell envelopes of TSB-Fe- and in vivo-grown cells but not in those grown in TSB or TSB+Fe. A 43-kDa protein expressed by in vitro-grown cells and 52- and 96-kDa proteins expressed by in vivo-grown cells reacted with antisera from pigs with the chamber implants and from catheterized, paracatheter-inoculated pigs but not with hyperimmune sera from pigs immunized with TSB-grown cells. The data indicate that S. epidermidis, growing under in vivo conditions, expresses antigens distinct from those that are grown in vitro.

The slime of coagulase-negative staphylococci: biochemistry and relation to adherence

In recent years, infections of implanted plastic devices by coagulase-negative staphylococci have become a major cause of septicaemia in human patients. The causal bacterial species is usually Staphylococcus epidermidis and these organisms grow as a biofilm adherent to a solid surface. Several methods have been introduced to assess the mass of adherent bacteria and the slimy matrix in which they are embedded. Some methods measure total biofilm, others measure the organisms or the slime alone. In vitro, the type of medium, the atmosphere during incubation, and the nature of the solid surface, affect the quantity of biofilm that is formed. In most studies on the chemistry of the slime, the material used was formed on complex media solidified with agar. Contamination by ingredients of the media or by agar may not always have been recognised. Recent work with chemically defined medium (liquid or solidified with silica gel) shows that the slime is a mixture of about 80% (w/w) teichoic acid and 20% protein. Growth as a biofilm may protect the staphylococci from antibiotics. At present, the greatest success in preventing infection has come from improved surgical techniques during the insertion of implants.

Importance of medium and atmosphere type to both slime production and adherence by coagulase-negative staphylococci

Marked differences in both the production of slime and adherence by Staphylococcus epidermidis were observed when comparing four culture media. Slime isolated from a strain cultured in a chemically defined medium (HHW) in air was chemically indistinguishable from that formed in both HHW and synthetic dialysis fluid (SDF) in air with 5% CO2. The presence of a physiological level of CO2 during culture in tryptone soya broth (TSB) prevented production of slime. It was not possible to separate the constituents of slime from those of the culture medium in bacteria grown in TSB in air using DEAE cellulose. Slime production was notably poor in used peritoneal dialysis fluid (PUD). Adherent growth was marked in HHW and SDF but was poor in TSB and PUD when air with 5% CO2 was used. These findings emphasize the advantages in using chemically defined and biological fluids when studying slime production and adherence by S. epidermidis.

Control of staphylococcal adhesion to polystyrene surfaces by polymer surface modification with surfactants

The adherence of three clinical isolates of Staphylococcus epidermidis to model polystyrene surfaces was studied in vitro using epifluorescent image analysis. A series of 16 Pluronic surfactants (A-B-A block copolymers where A is poly(ethylene oxide) (PEO) and B is poly(propylene oxide) (PPO)) were used as surface modifiers for the model polystyrene surfaces. Substantial reductions (up to 97%) in bacterial adhesion levels were achieved with all copolymers tested, irrespective of the PPO or PEO block lengths. It appears likely that such treatments create a sterically stabilized surface with adsorbed PEO chains, conferring nonspecific anti-adhesive properties which can limit bacterial attachment.

Influence of carbon dioxide on growth and antibiotic susceptibility of coagulase-negative staphylococci cultured in human peritoneal dialysate

Used peritoneal dialysis fluid was collected from patients undergoing continuous ambulatory peritoneal dialysis, and its pH and composition were assessed after incubation in either air or air with 5% CO2. Precipitation of calcium, magnesium, phosphate, and proteins occurred in the dialysis fluid incubated in air at 37 degrees C and was associated with a mean pH increase of 1.23 U. Incubation of dialysis fluid in air with 5% CO2 prevented precipitation and maintained pCO2 and pH levels at those found physiologically. Coagulase-negative staphylococcal strains isolated from patients with peritonitis tended to grow less well in dialysis fluid incubated in air than in dialysis fluid incubated in the carbon dioxide-enriched atmosphere. MICs of cefuroxime, ciprofloxacin, and vancomycin for seven strains of coagulase-negative staphylococci in dialysis fluid were markedly affected by atmosphere type (16 of 21 MICs). Of these 16 atmosphere-dependent MICs, 14 were at least fourfold higher in air than in air with 5% CO2.