Colin G. Adair

The concomitant development of poly(vinyl chloride)-related biofilm and antimicrobial resistance in relation to ventilator-associated pneumonia.

Ventilator-associated pneumonia is a major cause of death in intensive care patients and the endotracheal tube, commonly fabricated from poly(vinyl chloride) (PVC), is acknowledged as a significant factor in this. Bacteria colonise the biomaterial, thereby adopting a sessile mode of growth that progresses to the establishment of an antibiotic-resistant biofilm by the accretion of a protective glycocalyx. This study examined the sequential steps involved in the formation of biofilm on PVC by atomic force microscopy and the concomitant development of resistance to an antibiotic (ceftazidime) and to a non-antibiotic antimicrobial agent (hexetidine). Staphylococcus aureus and Pseudomonas aeruginosa isolated from ET tube biofilm were employed. The surface microrugosity of bacteria growing in sessile mode on PVC decreased significantly (p < 0.05) over the period 4, 24, 48 h and 5 d. The progressive accretion of bacterial glycocalyx was readily visualised in micrographs leading to a smoother surface topography with time. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) for ceftazidime and hexetidine against planktonic (suspension) S. aureus were lower than for Ps. aeruginosa. Furthermore, sessile populations of S. aureus and Ps. aeruginosa on PVC exhibited greater resistance to both ceftazidime and hexetidine when compared to planktonic bacterial growth. The efficacy of the agents, determined by kill kinetics, against sessile bacteria was dependent on age, with established biofilms (> or = 24 h) significantly more resistant (p < 0.05) than early sessile populations (< or = 4 h). Importantly, for practice, even newly colonised bacteria (1 h) were significantly more resistant to antibiotic than planktonic bacteria. Hexetidine was significantly more active (p < 0.05) than ceftazidime on biofilms of both isolates, irrespective of age, with total kill within 24 h treatment. Hexetidine may offer promise in the resolution of infection associated with PVC endotracheal tubes.

Incidence and nature of peritoneal catheter biofilm determined by electron and confocal laser scanning microscopy.

Thirty-two Tenckhoff catheters retrieved from continuous ambulatory peritoneal dialysis patients with a history of peritonitis were examined for microbial biofilm. Confocal laser scanning microscopy was successfully employed to visualize bacteria in biofilm occluded from view by scanning electron microscopy. Occluded but viable microbial biofilm was associated with 17 (81%) catheters from patients free from infection following renal transplant. Mixed isolate biofilm with two or more isolates of coagulase-negative staphylococci or Staphylococcus aureus was found on 41% of these catheters. Clearly visible viable biofilm consisting exclusively of Pseudomonas aeruginosa occurred on all four catheters removed due to recurrent peritonitis. Five (71%) catheters retrieved from patients transferred to haemodialysis had viable biofilm. Antibiotic sensitivities of the biofilm isolates were similar in profile to those reported for non-biofilm isolates from infected dialysate. Persistence of catheter biofilm despite direct contact with therapeutic levels of antibiotics in peritoneal dialysate requires that attention be directed towards improving antibiotic efficacy against peritonitis-causing bacteria in biofilm form.

Characterisation and evaluation of novel surfactant bacterial anti‐adherent coatings for endotracheal tubes designed for the prevention of ventilator‐associated pneumonia

It is accepted that ventilator‐associated pneumonia is a frequent cause of morbidity and mortality in intensive care patients. This study describes the physicochemical properties of novel surfactant coatings of the endotracheal tube and the resistance to microbial adherence of surfactant coated endotracheal tube polyvinylchloride (PVC). Organic solutions of surfactants containing a range of ratios of cholesterol and lecithin (0:100, 25:75, 50:50, 75:25, dissolved in dichloromethane) were prepared and coated onto endotracheal tube PVC using a multiple dip‐coating process. Using modulated temperature differential scanning calorimetry it was confirmed that the binary surfactant systems existed as physical mixtures. The surface properties of both surfactant‐coated and uncoated PVC., following treatment with either pooled human saliva or phosphate‐buffered saline (PBS), were characterised using dynamic contact angle analysis. Following treatment with saliva, the contact angles of PVC decreased; however, those of the coated biomaterials were unaffected, indicating different rates and extents of macromolecular adsorption from saliva onto the coated and uncoated PVC. The advancing and receding contact angles of the surfactant‐coated PVC were unaffected by sonication, thereby providing evidence of the durability of the coatings. The cell surface hydrophobicity and zeta potentials of isolates of Staphylococcus aureus and Pseudomonas aeruginosa, following treatment with either saliva or PBS, and their adherence to uncoated and surfactant‐coated PVC (that had been pre‐treated with saliva) were examined. Adherence of S. aureus and Ps. aeruginosa to surfactant‐coated PVC at each successive time period (0.5, 1, 2, 4, 8 h) was significantly lower than to uncoated PVC., the extent of the reduction frequently exceeding 90 %. Interestingly, the microbial anti‐adherent properties of the coatings were dependent on the lecithin content. Based on the impressive microbial anti‐adherence properties and durability of the surfactant coating on PVC following dip coatings, it is proposed that these systems may usefully reduce the incidence of ventilator‐associated pneumonia when employed as luminal coatings of the endotracheal tube.

Standardisation and comparison of methods employed for microbial cell surface hydrophobicity and charge determination

Abstract Whilst there area number of methods available to characterise the cell surface hydrophobicity (CSH) and cell surface charge (CSC) of microorganisms, there is still debate concerning the correlation of results between individual methods. In this study, the techniques of bacterial adherence to hydrocarbons (BATH) and hydrophobic interaction chromatography (HIC) were used to measure CSH. Electrostatic interaction chromatography (ESIC) and zeta potential (ZP) measurements were used to determine CSC. To allow meaningful comparisons between the BATH and HIC tests, between ESIC and ZP and also between CSH and CSC, the buffer systems employed in each test were standardised (phosphate buffered saline, pH 7.3, 0.01 mM). Isolates of Staphylococcus epidermidis derived from microbial biofilm were used as the test organism in this study. The isolates examined exhibited primarily medium to high CSH and a highly negative CSC. Good correlation of CSH measurement was observed between the BATH and HIC tests ( r = 0.89). Good correlation was observed between ESIC (anionic exchange column) and ZP measurements. No correlations were observed between isolate CSC and either increased or decreased CSH. It is recommended that whenever comparisons of various methods to determine either CSC or CSH (by partitioning methods), the buffer systems should remain constant throughout to achieve consistency of results.

Influence of selective decontamination of the digestive tract on microbial biofilm formation on endotracheal tubes from artificially ventilated patients

The effect of selective decontamination of the digestive tract on the nature and incidence of microbial biofilm formation on endotracheal tubes was assessed. Thirty endotracheal tubes were obtained post-extubation from patients in the intensive care unit who had been ventilated for a 1 to 15 day period and who did or did not receive the antibiotic regimen. Extensive biofilm formation was identified by scanning electron microscopy on 97 % of tubes examined. Endotracheal tube biofilm in tubes obtained from patients who received selective decontamination of the digestive tract showed a high prevalence of colonization with yeast (4 of 15 tubes) and gram-positive bacteria (streptococci, staphylococci and diphtheroids) (14 of 15 tubes).Staphylococcus aureus was isolated only from this group.Pseudomonas spp. were isolated from 2 of 15 tubes in both patient groups. Enteric gram-negative organisms (coliforms,Klebsiella andProteus spp.) were isolated only from tubes of patients who did not receive the antibiotic regimen (4 of 15 tubes). Yeasts, however, were not isolated from these tubes. Group D streptococcal isolates were resistant to tobramycin as were half of theStaphylococcus aureus isolates. For gram-negative bacteria, the MIC of tobramycin was in the range 1–64 µg/ml and the MIC of polymyxin in the range 0.5–16 µg/ml. Although a reduction was observed in the incidence of gram-negative microorganisms, this antibiotic regimen does not inhibit biofilm formation on the endotracheal tube by other pathogens associated with pneumonia in ventilated patients. This persistent nidus may be a factor in the pathogenesis of nosocomial pneumonia.

An exploration of work-related stress in Northern Ireland community pharmacy: a qualitative study

Objectives The aim of this study was, through qualitative methodology, to explore the factors which contribute to job‐related stress in community pharmacy in Northern Ireland.

Pharmaceutical strategies to prevent ventilator‐associated pneumonia

The increasing incidence of hospital‐acquired (nosocomial) infection is a disturbing phenomenon resulting in significant patient mortality and putting considerable strain on healthcare budgets and personnel. One particularly serious aspect of nosocomial infection is that of ventilator‐associated pneumonia (VAP). This arises in patients who receive mechanical ventilation within the intensive care unit. The quoted incidence of VAP varies widely (5–67%) and the reported mortality of patients with VAP is in the range of 24–71%. This review will examine the many factors that account for these wide ranges reported, including the patient population under investigation, the causative organism, the method of diagnosis, interventions employed and preventative strategies. The use of bioactive and drug‐impregnated biomaterials for endotracheal tube construction is discussed as novel approaches to the prevention of VAP.

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.

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°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.

Development and treatment of peritonitis in continuous ambulatory peritoneal dialysis

The main complication of continuous ambulatory peritoneal dialysis is peritonitis. This paper reviews its causes and treatment.