Bacterial biofilms within the clinical setting: what healthcare professionals should know

Detection of Actinobacillus pleuropneumoniae in drinking water from pig farms

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia and is normally transmitted by aerosols and direct contact between animals. A. pleuropneumoniae has traditionally been considered an obligate pathogen of pigs and its presence in the environment has yet to be investigated. Here, the presence of A. pleuropneumoniae was detected in drinking water of pig farms in Mexico using a PCR specific for the RTX toxin gene, apxIV. The presence of A. pleuropneumoniae in farm drinking water was confirmed by indirect immunofluorescence using an A. pleuropneumoniae-specific polyclonal antibody and by fluorescent in situ hybridization. Viable bacteria from the farm drinking water were detected using the Live/Dead BacLight stain. Additionally, viable A. pleuropneumoniae was selected and isolated using the cAMP test and the identity of the isolated bacteria were confirmed by Gram staining, a specific polyclonal antibody and an A. pleuropneumoniae-specific PCR. Furthermore, biofilms were observed by scanning electron microscopy in A. pleuropneumoniae-positive samples. In conclusion, our data suggest that viable A. pleuropneumoniae is present in the drinking water of swine farms and may use biofilm as a strategy to survive in the environment.

Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions

Staphylococcus comprises up to two-thirds of all pathogens in orthopedic implant infections and they are the principal causative agents of two major types of infection affecting bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone. Bacterial adhesion is the first and most important step in implant infection. It is a complex process influenced by environmental factors, bacterial properties, material surface properties and by the presence of serum or tissue proteins. Properties of the substrate, such as chemical composition of the material, surface charge, hydrophobicity, surface roughness and the presence of specific proteins at the surface, are all thought to be important in the initial cell attachment process. The biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. This work will provide an overview of the mechanisms and factors involved in bacterial adhesion, the techniques that are currently being used studying bacterial-material interactions as well as provide insight into future directions in the field.

Evidence for the involvement of the anthranilate degradation pathway in Pseudomonas aeruginosa biofilm formation

Bacterial biofilms are complex cell communities found attached to surfaces and surrounded by an extracellular matrix composed of exopolysaccharides, DNA, and proteins. We investigated the whole-genome expression profile of Pseudomonas aeruginosa sessile cells (SCs) present in biofilms developed on a glass wool substratum. The transcriptome and proteome of SCs were compared with those of planktonic cell cultures. Principal component analysis revealed a biofilm-specific gene expression profile. Our study highlighted the overexpression of genes controlling the anthranilate degradation pathway in the SCs grown on glass wool for 24 h. In this condition, the metabolic pathway that uses anthranilate for Pseudomonas quinolone signal production was not activated, which suggested that anthranilate was primarily being consumed for energy metabolism. Transposon mutants defective for anthranilate degradation were analyzed in a simple assay of biofilm formation. The phenotypic analyses confirmed that P. aeruginosa biofilm formation partially depended on the activity of the anthranilate degradation pathway. This work points to a new feature concerning anthranilate metabolism in P. aeruginosa SCs.

Comparative analysis of single-species and polybacterial wound biofilms using a quantitative, in vivo, rabbit ear model

INTRODUCTION

The recent literature suggests that chronic wound biofilms often consist of multiple bacterial species. However, without appropriate in vivo, polybacterial biofilm models, our understanding of these complex infections remains limited. We evaluate and compare the effect of single- and mixed-species biofilm infections on host wound healing dynamics using a quantitative, in vivo, rabbit ear model.

METHODS

Six-mm dermal punch wounds in New Zealand rabbit ears were inoculated with Staphylococcus aureus strain UAMS-1, Pseudomonas aeruginosa strain PAO1, or both, totaling 10/6 colony-forming units/wound. Bacterial proliferation and maintenance in vivo were done using procedures from our previously published model. Wounds were harvested for histological measurement of wound healing, viable bacterial counts using selective media, or inflammatory cytokine (IL-1β, TNF-α) expression via quantitative reverse-transcription PCR. Biofilm structure was studied using scanning electron microscopy (SEM). For comparison, biofilm deficient mutant UAMS-929 replaced strain UAMS-1 in some mixed-species infections.

RESULTS

Bacterial counts verified the presence of both strains UAMS-1 and PAO1 in polybacterial wounds. Over time, strain PAO1 became predominant (p<0.001). SEM showed colocalization of both species within an extracellular matrix at multiple time-points. Compared to each monospecies infection, polybacterial biofilms impaired all wound healing parameters (p<0.01), and increased expression of IL-1β and TNF-α (p<0.05). In contrast, mixed-species infections using biofilm-deficient mutant UAMS-929 instead of wild-type strain UAMS-1 showed less wound impairment (p<0.01) with decreased host cytokine expression (p<0.01), despite a bacterial burden and distribution comparable to that of mixed-wild-type wounds.

CONCLUSIONS

This study reveals that mixed-species biofilms have a greater impact on wound healing dynamics than their monospecies counterparts. The increased virulence of polybacterial biofilm appears dependent on the combined pathogenicity of each species, verified using a mutant strain. These data suggest that individual bacterial species can interact synergistically within a single biofilm structure.

Efficacy of end-only-functionalized oligo(arylene-ethynylene)s in killing bacterial biofilms

Cationic end-only-functionalized oligo(arylene-ethynylene)s (EO-OPEs) have recently been found to be broad-spectrum and effective antimicrobial agents because of their unique structure and optical properties. In this study, we investigated their potential use for preventing and reducing Escherichia coli (E. coli) biofilms. The Calgary biofilm device (CBD) was used to form bacterial biofilms of E. coli; in these studies, the minimum inhibitory concentration (MIC) and the minimum biofilm eradication concentration (MBEC) were determined. E. coli biofilms uniformly grow on pegs of the CBD device lid. The MIC values determined for EO-OPEs are comparable to those found for standard antibiotics such as kanamycin (MIC = 11.2 μg/mL). About 10-30 times the concentration of EO-OPEs was required to eradicate E. coli biofilms and prevent regrowth in the dark. Near-UV irradiation of EO-OPEs enhanced their efficacy in killing biofilms.

Applications of small molecule activators and inhibitors of quorum sensing in Gram-negative bacteria

Quorum sensing is a form of intercellular communication used by many species of bacteria that facilitates concerted interactions between the cells comprising a population. The phenotypes regulated by quorum sensing are extremely diverse, with many having a significant impact upon healthcare, agriculture, and the environment. Consequently there has been significant interest in developing methods to manipulate this signalling process and recent years have witnessed significant theoretical and practical developments. A wide range of small molecule modulators of quorum sensing systems has been discovered, providing an expansive chemical toolbox for the study and modulation of this signalling mechanism. In this review, a selection of recent case studies which illustrate the value of both activators and inhibitors of quorum sensing in Gram-negative bacteria are discussed.

Quantitative comparison and analysis of species-specific wound biofilm virulence using an in vivo, rabbit-ear model

BACKGROUND

Although bacterial biofilm is recognized as an important contributor to chronic wound pathogenesis, differences in biofilm virulence between species have never been studied in vivo.

STUDY DESIGN

Dermal punch wounds in New Zealand white rabbit ears were inoculated with Klebsiella pneumoniae, Staphylococcus aureus, or Pseudomonas aeruginosa, or left uninfected as controls. In vivo biofilm was established and maintained using procedures from our previously published wound biofilm model. Virulence was assessed by measurement of histologic wound healing and host inflammatory mediators. Scanning electron microscopy (SEM) and bacterial counts verified biofilm viability. Extracellular polymeric substance (EPS)-deficient P aeruginosa was used for comparison.

RESULTS

SEM confirmed the presence of wound biofilm for each species. P aeruginosa biofilm-infected wounds showed significantly more healing impairment than uninfected, K pneumoniae, and S aureus (p < 0.05), while also triggering the largest host inflammatory response (p < 0.05). Extracellular polymeric substance-deficient P aeruginosa demonstrated a reduced impact on the same quantitative endpoints relative to its wild-type strain (p < 0.05).

CONCLUSIONS

Our novel analysis demonstrates that individual bacterial species possess distinct levels of biofilm virulence. Biofilm EPS may represent an integral part of their distinct pathogenicity. Rigorous examination of species-dependent differences in biofilm virulence is critical to developing specific therapeutics, while lending insight to the interactions within clinically relevant, polybacterial biofilms.

Understanding the host inflammatory response to wound infection: an in vivo study of Klebsiella pneumoniae in a rabbit ear wound model

Wound infection development is critically dependent on the complex interactions between bacteria and host. Klebsiella pneumoniae has become an increasingly common wound pathogen, but its natural history within wounds has never been studied. Using a validated, in vivo rabbit ear model, wounds were inoculated with K. pneumoniae at different concentrations (10²-10⁷ colony-forming units) with measurement of viable and nonviable bacterial counts, histological wound-healing parameters, and host inflammatory gene expression at multiple time points postinoculation (48, 96, and 240 hours). Bacteria and wound morphologies were evaluated with scanning electron microscopy. Comparable experiments were performed in ischemic ears to model immune response impairment. All wounds, despite different inoculants, equilibrated to similar bacterial concentrations by 96 hours. With a 10⁶ colony-forming units inoculant, wounds at 240 hours showed decreased bacterial counts (p < 0.01), with a corresponding improvement in healing (p < 0.01) and a decrease in inflammatory response (p < 0.05). In contrast, ischemic wounds revealed impaired inflammatory gene expression (p < 0.05) resulting in higher steady-state bacterial concentrations (p < 0.01), impaired healing (p < 0.05), and biofilm formation on scanning electron microscopy. We conclude that a normal inflammatory response can effectively stabilize and overcome a K. pneumoniae wound infection. An impaired host cannot control this bacterial burden, preventing adequate healing while allowing bacteria to establish a chronic presence. Our novel study quantitatively validates the host immune response as integral to wound infection dynamics.

TOF-SIMS imaging of adsorbed proteins on topographically complex surfaces with Bi(3) (+) primary ions

Although previous studies have demonstrated that TOF-SIMS is a powerful method for the characterization of adsorbed proteins due to its specificity and surface sensitivity, it was unclear from earlier work whether the differences between proteins observed on uniform flat surfaces were large enough to facilitate clear image contrast between similar proteins in small areas on topographically complex samples that are more typical of biological tissues. The goal of this study was to determine whether Bi(3) (+) could provide sufficiently high sensitivity to provide clear identification of the different proteins in an image. In this study, 10 μm polystyrene microspheres were adsorbed with one of three different proteins, human serum albumin (HSA), bovine serum albumin (BSA), and hemoglobin. Spheres coated with HSA were then mixed with spheres coated with either BSA (a very similar protein) or hemoglobin (a dramatically different protein), and deposited on silicon substrates. Fluorescent labeling was used to verify the SIMS results. With maximum autocorrelation factors (MAF) processing, images showed clear contrast between both the very different proteins (HSA and hemoglobin) and the very similar proteins (HSA and BSA). Similar results were obtained with and without the fluorescent labels. MAF images were calculated using both the full spectrum and only characteristic amino acid fragments. Although better image contrast was obtained using the full spectrum, differences between the spheres were still evident when only the amino acid fragments were included in the analysis, suggesting that we are truly observing differences between the proteins themselves. These results demonstrate that TOF-SIMS, with a Bi(3) (+) primary ion, is a powerful technique for characterizing interfacial proteins not only on large uniform surfaces, but also with high spatial resolution on the topographically complex samples typical in biological analysis.

The Effect of Bacterial Adhesion on Grafted Chains Revealed by the Non-Invasive Sum Frequency Generation Spectroscopy

In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm formation, a microbial consortia more resistant to antibiotics than planktonic bacteria. In order to design materials able to limit the biofilm formation, the effect of bacteria on materials has to be well characterized. In this work, a well-defined surface composed of a self-assembled monolayer (SAM) of octadecanethiol (ODT) onto a gold surface is probedin situ. The SAM conformation is obtained using the femtosecond vibrational sum frequency generation (SFG) spectroscopy. This technique provides selectively the molecular vibrational signature of the interface. The behaviour of the ODT SAM is studied in different environments: in air, in water, and upon exposure to hydrophilic or hydrophobicLactococcus lactisbacteria. Modelling the experimental SFG spectra reveals a measurable change of the SAM conformation which depends on the environment, especially on the hydrophilic-hydrophobic character.

The effect of topical negative pressure on wound biofilms using an in vitro wound model

Chronic non-healing wounds affect a significant number of patients worldwide. Although the etiologies of these wounds are varied, bacterial infection has been suggested as a major factor responsible for the perpetual inflammation and tissue destruction observed in such wounds. Recent evidence has emerged suggesting that bacterial biofilms in particular may have a significant role in this process. At the same time, topical negative pressure dressing is gaining acceptance as a therapy which promotes healing in recalcitrant wounds. In this study an in vitro Pseudomonas aeruginosa biofilm model was developed to mimic potential surface wound biofilms. Topical negative pressure dressing was applied to the model and the effects of topical negative pressure dressing on the in vitro wound biofilms were examined using both quantitative microbiological counting technique and imaging studies. The results demonstrated a small but statistically significant reduction in biofilm bacteria at 2 weeks when exposed to topical negative pressure. When this was combined with silver impregnated foam, the reduction was far more significant and was observable within 24 hours. Microscopically, it was also noted that topical negative pressure compressed the biofilm architecture with a reduction in thickness and diffusion distance.

Deletion of σ(54) (rpoN) alters the rate of autolysis and biofilm formation in Enterococcus faecalis

Transcription initiation is a critical step in bacterial gene regulation and is often controlled by transcription regulators. The alternate sigma factor (σ(54)) is one such regulator that facilitates activator-dependent transcription initiation and thus modulates the expression of a variety of genes involved in metabolism and pathogenesis in bacteria. This study describes the role of σ(54) in the nosocomial pathogen Enterococcus faecalis. Biofilm formation is one of the important pathogenic mechanisms of E. faecalis, as it elevates the organism's potential to cause surgical site and urinary tract infections. Lysis of bacterial cells within the population contributes to biofilm formation by providing extracellular DNA (eDNA) as a key component of the biofilm matrix. Deletion of rpoN rendered E. faecalis resistant to autolysis, which in turn impaired eDNA release. Despite the significant reduction in eDNA levels compared to the parental strain, the rpoN mutant formed more robust biofilms as observed using laser scanning confocal microscopy and Comstat analysis, indicating and emphasizing the presence of other matrix components. Initial adherence to a polystyrene surface was also enhanced in the mutant. Proteinase K treatment at early stages of biofilm development significantly reduced the accumulation of biofilm by the rpoN mutant. In conclusion, our data indicate that other factors in addition to eDNA might contribute to the overall composition of the enterococcal biofilm and that the regulatory role of σ(54) governs the nature and composition of the biofilm matrix.

Intravenous drug preparation: the infection risks

The preparation of intravenous drugs is a common yet inherently dangerous nursing procedure. Potential errors associated with this procedure include incorrect drugs, doses and routes of administration. As a consequence of these recognized risks, a variety of checks are used to optimize safety. This paper explores the literature around infusate contamination, which can cause infusate-related bloodstream infection (IR-BSI). In addition, this paper will discuss the mechanisms of infusate contamination, as well as details of the types of microorganisms that cause contamination and the types of drugs that enable proliferation of microorganisms. Deficits within current guidance are revealed. The paper concludes that IR-BSI is a significant but under-recognized risk to patients. As microbial contamination sufficient to cause IR-BSI is not detectable to the naked eye, those who prepare intravenous drugs must be more aware of contamination risks and how to reduce them.

Horizontal gene exchange in environmental microbiota

Horizontal gene transfer (HGT) plays an important role in the evolution of life on the Earth. This view is supported by numerous occasions of HGT that are recorded in the genomes of all three domains of living organisms. HGT-mediated rapid evolution is especially noticeable among the Bacteria, which demonstrate formidable adaptability in the face of recent environmental changes imposed by human activities, such as the use of antibiotics, industrial contamination, and intensive agriculture. At the heart of the HGT-driven bacterial evolution and adaptation are highly sophisticated natural genetic engineering tools in the form of a variety of mobile genetic elements (MGEs). The main aim of this review is to give a brief account of the occurrence and diversity of MGEs in natural ecosystems and of the environmental factors that may affect MGE-mediated HGT.

Sterilization of biological pathogens using supercritical fluid carbon dioxide containing water and hydrogen peroxide

Novel noninvasive techniques for the removal of biological contaminants to generate clean or sterile materials are in demand by the medical, pharmaceutical and food industries. The sterilization method described here uses supercritical fluid carbon dioxide (SF-CO(2)) containing 3.3% water and 0.1% hydrogen peroxide (v/v/v) to achieve from four to eight log viability reduction of all tested microbial species, including vegetative cells, spores and biofilms. The sterilization method employs moderate pressure and temperature (80 atm, 50°C) and a short (30-minute) treatment time. The procedure kills various opportunistic pathogens that often persist in biofilm structures, fungal spores commonly associated with nosocomial infections, and Bacillus pumilus SAFR-032 endospores that are notoriously hard to eradicate by conventional sterilization techniques.

Non-invasive vibrational SFG spectroscopy reveals that bacterial adhesion can alter the conformation of grafted "brush" chains on SAM

Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.

Differences in the in vitro susceptibility of planktonic and biofilm-associated Escherichia coli strains to antimicrobial agents

The in vitro susceptibility of seven Escherichia coli biofilm-producing strains in their planktonic and biofilm-associated forms to amoxicillin, amoxicillin/clavulanic acid, cefotaxime, gentamicin, and ciprofloxacin was studied. Minimum inhibitory concentrations (MICs) were determined by the standard microdilution method and by the Alamar blue assay (providing the AB-MIC) at two levels of metabolic suppression and using standard and large inocula. Minimal biofilm inhibitory concentrations (AB-MBICs) on preformed biofilms on polystyrene plates were higher than the MICs and AB-MICs. Differences in magnitude depended on the antibiotic, strain, inoculum size, and the level of suppression of metabolism. Ciprofloxacin and gentamicin showed the greatest differences in the AB-MBIC as compared to AB-MIC. the possibility of antibiotic-resistant mutant selection within the biofilms was ruled out since bacteria recovered from the biofilm maintained the same MICs as before exposure to the antimicrobial agents. E. coli biofilms were much less sensitive than their planktonic counterparts.

Synthesis and biological activity of 2-aminoimidazole triazoles accessed by Suzuki-Miyaura cross-coupling

A pilot library of 2-aminoimidazole triazoles (2-AITs) was synthesized and assayed against Acinetobacter baumannii and methicillin-resistant Staphylococus aureus (MRSA). Results from these studies show that these new derivatives have improved biofilm dispersal activities as well as antibacterial properties against A. baumannii. With MRSA biofilms they are found to possess biofilm inhibition capabilities at low micromolar concentrations.

Novel biocatalytic polymer-based antimicrobial coatings as potential ureteral biomaterial: preparation and in vitro performance evaluation

Catheters and other indwelling devices placed inside human body are prone to bacterial infection, causing serious risk to patients. Infections associated with implants are difficult to resolve, and hence the prevention of bacterial colonization of such surfaces is quite appropriate. In this context, the development of novel antimicrobial biomaterials is currently gaining momentum. We describe here the preparation and antibacterial properties of an enzyme-embedded polycaprolactone (PCL)-based coating, coimpregnated with the antibiotic gentamicin sulfate (GS). The enzyme uses PCL itself as substrate; as a result, the antibiotic gets released at a rate controlled by the degradation of the PCL base. In vitro drug release studies demonstrated sustained release of GS from the PCL film throughout its lifetime. By modulating the enzyme concentration in the PCL film, we were able to vary the lifetime of the coating from 33 h to 16 days. In the end, the polymer is completely degraded, delivering the entire load of the antibiotic. The polymer exhibited antibacterial properties against three test isolates: Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Foley urinary catheters coated with the modified polymer exhibited sustained in vitro release of GS over a 60-h period. The results suggest that the antibiotic-plus-enzyme-loaded polymer can be used as tunable self-degrading antimicrobial biomaterial coating on catheters.

Attachment and colonization by Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Typhimurium, and Staphylococcus aureus on stone fruit surfaces and Survival through a simulated commercial export chain

The ability of the foodborne pathogens Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Typhimurium, and Staphylococcus aureus to attach, colonize, and survive on stone fruit surfaces was investigated. Fifty microliters of bacterial suspension was spot inoculated onto the sterile intact fructoplane of whole peaches and plums. Minimum time required for initial adhesion and attachment was recorded for different surface contact times. Surface colonization patterns of the four pathogens and survival under simulated commercial export conditions also were evaluated. L. monocytogenes and Salmonella Typhimurium attached immediately to stone fruit surfaces. E. coli O157:H7 and S. aureus were visibly attached after 30 s and 1 h, respectively, of direct exposure. Holding freshly harvested stone fruit at 0.5 degrees C to simulate cold storage conditions significantly lowered the titer of E. coli O157:H7 on plums and the titers of L. monocytogenes and Salmonella Typhimurium on stone fruit. E. coli O157:H7 and L. monocytogenes at a low inoculum level and S. aureus and Salmonella Typhimurium at high and low levels did not survive the simulated export chain conditions at titers that exceeded the minimum infectious dose. However, E. coli O157:H7 and L. monocytogenes were able to survive on stone fruit surfaces when inoculated at an artificially high level. In this case, the final titer at the end of the supply chain was higher than the infectious dose. In this laboratory experiment, E. coli O157:H7, L. monocytogenes, Salmonella Typhimurium, and S. aureus at potential natural contamination levels were unable to survive simulated export conditions.

Effect of cyclic bis(3'-5')diguanylic acid and its analogs on bacterial biofilm formation

Cyclic bis(3'-5')diguanylic acid (cyclic-di-GMP) functions as a second messenger in diverse species of bacteria to trigger wide-ranging physiological changes. We measured cyclic-di-GMP and its structural analogs such as cyclic bis(3'-5')guanylic/adenylic acid (cyclic-GpAp), cyclic bis(3'-5')guanylic/inosinic acid (cyclic-GpIp) and monophosphorothioic acid of cyclic-di-GMP (cyclic-GpGps) for effects on the biofilm formation of Staphylococcus aureus and Pseudomonas aeruginosa. We constructed a knockout mutant of SA0701, which is a GGDEF motif protein relevant to diguanylate cyclase from S. aureus 2507. We confirmed that the biofilm formation of this mutant (MS2507 Delta SA0701) was reduced. Cyclic-di-GMP corresponding to physiological intracellular levels given in the culture recovered the biofilm formation of MS2507 Delta SA0701, whereas its analogs did not, indicating that unlike a previous suggestion, cyclic-di-GMP was involved in the positive regulation of the biofilm formation of S. aureus and its action was structurally specific. At a high concentration (200 microM), cyclic-di-GMP and its analogs showed suppression effects on the biofilm formation of S. aureus and P. aeruginosa, and according to the quantification study using costat analysis, the suppression potential was in the order of cyclic-di-GMP, cyclic-GpGps, cyclic-GpAp and cyclic-GpIp, suggesting that the suppression effect was not strictly specific and the change of base structure quantitatively affected the suppression activity.

Preventive efficacy and cost-effectiveness of point-of-use water filtration in a subacute care unit

Infections with Pseudomonas aeruginosa and other waterborne pathogens (WBPs) are major contributors to serious morbidity and mortality in hospitals. We sought to determine whether point-of-use (POU) water filtration might result in decreased risk of infection in the subacute care unit (SACU) of a 208-bed medical center. Our findings indicate that POU water filtration can significantly and cost-effectively reduce colonization of and infection with WBPs, including ventilator-associated pneumonia, in an SACU.

Biofilm characteristics of Staphylococcus epidermidis isolates associated with device-related meningitis

Staphylococcus epidermidis biofilm causes device-related meningitis in neurosurgical patients. This study assessed the contribution of polysaccharide and protein to the development of a strong biofilm-positive phenotype in four S. epidermidis isolates associated with probable device-related meningitis, under varying environmental conditions. RT-PCR analysis of the intercellular adhesion operon (icaADBC) and assessment of polysaccharide intercellular adhesin (PIA) production indicated a correlation between increased icaA transcription and PIA production in ica(+) isolates grown in medium with 4 % ethanol and 4 % NaCl. Treatment of biofilm with sodium metaperiodate caused dispersion of adhered cells (P <0.0001), indicating involvement of PIA. Transcriptional levels of protein factors revealed that atlE transcription levels were similar in all isolates, whilst aap levels were variable, with induction being seen in two isolates following growth in the presence of alcohol or salt. Transcription of agr did not influence protein expression and RNAIII transcription varied among the strains. Although aap transcription was induced, the treatment of biofilm with proteinase K did not always disperse the biofilm. Our data suggest that, among the three ica(+) S. epidermidis isolates clinically associated with meningitis that were studied, PIA contributed to the strong biofilm-positive phenotype, whereas protein factors appeared to have a secondary role.

Modeling microbial survival in buildup biofilm for complex medical devices

Background

Flexible endoscopes undergo repeated rounds of patient-use and reprocessing. Some evidence indicates that there is an accumulation or build-up of organic material that occurs over time in endoscope channels. This "buildup biofilm" (BBF) develops as a result of cyclical exposure to wet and dry phases during usage and reprocessing. This study investigated whether the BBF matrix represents a greater challenge to disinfectant efficacy and microbial eradication than traditional biofilm (TBF), which forms when a surface is constantly bathed in fluid.

Methods

Using the MBEC (Minimum Biofilm Eradication Concentration) system, a unique modelling approach was developed to evaluate microbial survival in BBF formed by repetitive cycles of drying, disinfectant exposure and re-exposure to the test organism. This model mimics the cumulative effect of the reprocessing protocol on flexible endoscopes. Glutaraldehyde (GLUT) and accelerated hydrogen peroxide (AHP) were evaluated to assess the killing of microbes in TBF and BBF.

Results

The data showed that the combination of an organic matrix and aldehyde disinfection quickly produced a protective BBF that facilitated high levels of organism survival. In cross-linked BBF formed under high nutrient conditions the maximum colony forming units (CFU) reached ~6 Log₁₀ CFU/peg. However, if an oxidizing agent was used for disinfection and if organic levels were kept low, organism survival did not occur. A key finding was that once established, the microbial load of BBF formed by GLUT exposure had a faster rate of accumulation than in TBF. The rate of biofilm survival post high-level disinfection (HLD) determined by the maximum Log₁₀CFU/initial Log₁₀CFU for E. faecalis and P. aeruginosa in BBF was 10 and 8.6 respectively; significantly different compared to a survival rate in TBF of ~2 for each organism. Data from indirect outgrowth testing demonstrated for the first time that there is organism survival in the matrix. Both TBF and BBF had surviving organisms when GLUT was used. For AHP survival was seen less frequently in BBF than in TBF.

Conclusion

This BBF model demonstrated for the first time that survival of a wide range of microorganisms does occur in BBF, with significantly more rapid outgrowth compared to TBF. This is most pronounced when GLUT is used compared to AHP. The data supports the need for meticulous cleaning of reprocessed endoscopes since the presence of organic material and microorganisms prevents effective disinfection when GLUT and AHP are used. However, cross-linking agents like GLUT are not as effective when there is BBF. The data from the MBEC model of BBF suggest that for flexible endoscopes that are repeatedly used and reprocessed, the assurance of effective high-level disinfection may decrease if BBF develops within the channels.

Material wear of polymeric tracheostomy tubes: a six-month study

OBJECTIVES

The objectives were to study long-term material wear of tracheostomy tubes made of silicone (Si), polyvinyl chloride (PVC), and polyurethane (PU) after 3 and 6 months of clinical use.

STUDY DESIGN

The study has a prospective and comparative design.

METHODS

Nineteen patients with long-term tracheostomy, attending the National Respiratory Center in Sweden, were included, n = 6 with Si tubes, n = 8 with PVC tubes, and n = 5 with PU tubes. The tubes were exposed to the local environment in the trachea for 3 and 6 months and analyzed by scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and differential scanning calorimetry.

RESULTS

All tubes revealed severe surface changes. No significant differences were established after 3 or 6 months of exposure between the various materials. The changes had progressed significantly after this period, compared to previously reported changes after 30 days of exposure. The results from all analyzing techniques correlated well.

CONCLUSIONS

All tubes, exposed in the trachea for 3-6 months, revealed major degradation and changes in the surface of the material. Polymeric tracheostomy tubes should be changed before the end of 3 months of clinical use.

Effects of combined treatment with sansanmycin and macrolides on Pseudomonas aeruginosa and formation of biofilm

OBJECTIVE

To observe the effects of combined treatment with sansanmycin and macrolides on Pseudomonas aeruginosa and formation of biofilm.

METHODS

Micro-dilution method was used to determine the minimal inhibitory concentrations (MICs) of sansanmycin, gentamycin, carbenicillin, polymyxin B, roxithromycin, piperacillin, and tazobactam. PA1 and PA27853 biofilms were observed under optical microscope after staining and under SEM after treatment with sansanmycin at different dosages and combined treatment with sansanmycin and roxithromycin. Viable bacteria in PA1 and PA27853 biofilms were counted after treatment with sansanmycin at different dosages or combined treatment with sansanmycin and roxithromycin.

RESULTS

The MIC of sansanmycin was lower than that of gentamycin and polymyxin B, but was higher than that of carbenicillin. Roxithromycin enhanced the penetration of sansanmycin to PA1 and PA27853 strains through biofilms. PA1 and PA27853 biofilms were gradually cleared with the increased dosages of sansanmycin or with the combined sansanmycin and roxithromycin.

CONCLUSION

Sub-MIC levels of roxithromycin and sansanmycin substantially inhibit the generation of biofilms and proliferation of bacteria. Therefore, combined antibiotics can be used in treatment of intractable bacterial infection.

Biofilms in wounds: management strategies

Biofilms probably induce a chronic and/or 'quiet' inflammation in the chronic wound and so delay healing. This paper reviews current strategies that can be used to suppress biofilms in chronic wounds until better options are available.

Biofilms in nephrology

BACKGROUND

Biofilms are bacterial communities ubiquitous to moist environments. Biofilm formation is a factor in the development and persistence of infectious diseases. In clinical nephrology, biofilms influence the development of kidney stones and affect dialysis systems, including peritoneal and central venous catheters. Biofilms also play critical roles in persistent and resistant renal and urinary tract infections.

OBJECTIVE

To describe the physiology of biofilms and potential effects of biofilms upon infectious diseases, focusing on the role of biofilms in kidney stones, indwelling catheters and dialysis equipment.

METHODS

A literature search with Medline to identify pertinent English language articles published up to early 2008 using the keywords biofilm, nephrology, renal, calculi and infection.

RESULTS/CONCLUSION

Biofilms are ubiquitous in clinical nephrology and play a role in the pathogenesis of resistant infections. Strategies for reducing the effects of biofilms in nephrology are described.

Impact of water quality and dialysis fluid composition on dialysis practice

An essential but frequently neglected aspect of dialysis treatment is the dialysis fluid produced by blending treated tap water with concentrated solutions containing electrolytes and buffer. Chemical and microbiological contaminants as well as the electrolyte and buffer composition of the dialysis fluid play major roles in the induction or modulation of morbidity associated with regular dialysis therapy.

A new colorimetric microtitre model for the detection of Staphylococcus aureus biofilms

AIMS

Research on biofilms requires validated quantitative models that focus both on matrix and viable bacterial mass. In this study, a new microplate model for the detection of Staphylococcus aureus biofilms was developed.

METHODS AND RESULTS

Dimethyl methylene blue (DMMB) dye was used to quantify biofilm matrix colorimetrically. Initially developed for the detection of glycosaminoglycans, the DMMB protocol was optimized for S. aureus biofilm research. In addition, the redox indicator resazurin was used to determine the viable bacterial biofilm burden.

CONCLUSION

A new, simple and reproducible microplate test system based on DMMB and resazurin, offering a reliable differentiation between biofilm matrix and cellular activity, was developed and validated for the detection of S. aureus biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The DMMB-resazurin microtitre plate model is a valuable tool for high capacity screening of biocides and for the development of synergistic mixtures of biocides, destroying both biofilm matrix and bacteria.

Influence of quorum sensing and iron on twitching motility and biofilm formation in Pseudomonas aeruginosa

Reducing iron (Fe) levels in a defined minimal medium reduced the growth yields of planktonic and biofilm Pseudomonas aeruginosa, though biofilm biomass was affected to the greatest extent and at FeCl3 concentrations where planktonic cell growth was not compromised. Highlighting this apparently greater need for Fe, biofilm growth yields were markedly reduced in a mutant unable to produce pyoverdine (and, so, deficient in pyoverdine-mediated Fe acquisition) at concentrations of FeCl3 that did not adversely affect biofilm yields of a pyoverdine-producing wild-type strain. Concomitant with the reduced biofilm yields at low Fe concentrations, P. aeruginosa showed enhanced twitching motility in Fe-deficient versus Fe-replete minimal media. A mutant deficient in low-Fe-stimulated twitching motility but normal as regards twitching motility on Fe-rich medium was isolated and shown to be disrupted in rhlI, whose product is responsible for synthesis of the N-butanoyl homoserine lactone (C4-HSL) quorum-sensing signal. In contrast to wild-type cells, which formed thin, flat, undeveloped biofilms in Fe-limited medium, the rhlI mutant formed substantially developed though not fully mature biofilms under Fe limitation. C4-HSL production increased markedly in Fe-limited versus Fe-rich P. aeruginosa cultures, and cell-free low-Fe culture supernatants restored the twitching motility of the rhlI mutant on Fe-limited minimal medium and stimulated the twitching motility of rhlI and wild-type P. aeruginosa on Fe-rich minimal medium. Still, addition of exogenous C4-HSL did not stimulate the twitching motility of either strain on Fe-replete medium, indicating that some Fe-regulated and RhlI/C4-HSL-dependent extracellular product(s) was responsible for the enhanced twitching motility (and reduced biofilm formation) seen in response to Fe limitation.

Full activation of Enterococcus faecalis gelatinase by a C-terminal proteolytic cleavage

Enterococci account for nearly 10% of all nosocomial infections and constitute a significant treatment challenge due to their multidrug resistance properties. One of the well-studied virulence factors of Enterococcus faecalis is a secreted bacterial protease, termed gelatinase, which has been shown to contribute to the process of biofilm formation. Gelatinase belongs to the M4 family of bacterial zinc metalloendopeptidases, typified by thermolysin. Gelatinase is synthesized as a preproenzyme consisting of a signal sequence, a putative propeptide, and then the mature enzyme. We determined that the molecular mass of the mature protein isolated from culture supernatant was 33,030 Da, which differed from the predicted molecular mass, 34,570 Da, by over 1,500 Da. Using N-terminal sequencing, we confirmed that the mature protein begins at the previously identified sequence VGSEV, thus suggesting that the 1,500-Da molecular mass difference resulted from a C-terminal processing event. By using mutants with site-directed mutations within a predicted C-terminal processing site and mutants with C-terminal deletions fused to a hexahistidine tag, we determined that the processing site is likely to be between residues D304 and I305 and that it requires the Q306 residue. The results suggest that the E. faecalis gelatinase requires C-terminal processing for full activation of protease activity, making it a unique enzyme among the members of the M4 family of proteases of gram-positive bacteria.