Biofilms on Central Venous Catheters: Is Eradication Possible?

Biofilm Matrix Formation in Human: Clinical Significance, Diagnostic Techniques, and Therapeutic Drugs

Context: Some recent reports have indicated that almost 80% of clinical infections in humans have biofilm origin and impose additional healthcare costs. This study was an updated review of extracellular polymeric substance matrix (Biofilm) formation in humans and elaborated on its clinical significance, diagnosis, and therapeutic approaches. Evidence Acquisition: This narrative study reviewed the most recent information on the significance of microbial biofilm formation in clinical settings, common biofilm-producing bacterial species, its diagnosis, antibiotic drug resistance, and new approaches to the treatment of infections associated with biofilm formation. Results: Evidence indicated a permanent increase in the frequency of microbial biofilm in the central venous catheter, mechanical heart valve, and urinary catheter, as well as persistent infections. However, antimicrobial resistance induced by biofilms formation and the antimicrobial treatment of biofilms were problematic. Moreover, several assays and lab devices were described to evaluate biofilm formation. Furthermore, new attitudes towards anti-biofilm treatments were introduced in this paper. Conclusions: The number of different mechanisms were in accordance with the recent knowledge on how biofilms play a critical role in the disease pathogenesis. Biofilm strikes the treatment and surveillance of patients bearing infectious diseases under different conditions. The use of new methods in anti-biofilm treatments is effective for the recovery of infected patients.

Tryptophol Coating Reduces Catheter-Related Cerebral and Pulmonary Infections by Scedosporium apiospermum

Introduction

Central venous catheter (CVC) is a medical device that is used to administer medication for a long duration. Colonization by an emerging opportunistic pathogen Scedosporium apiospermum in the CVC lumen is frequently reported to cause severe complications in patients. Here, we describe the effect of fungal quorum-sensing molecule (QSM) known as tryptophol (TOH) to control S. apiospermum colonization in catheter tube lumens in both in vitro and in vivo models.

Methods

Antifungal susceptibility of TOH against S. apiospermum was compared with voriconazole, and the colony diameter was determined on days 2, 4, and 6. Experimental catheterization rat model was conducted with pre-coating of TOH and voriconazole or an uncoated control and an infection with S. apiospermum. Biofilm formation on the catheter luminal surface was assessed using the scanning electron microscopy, crystal violet, and 2,3-bis(2-methoxy-4-ni-tro-5-sulfophenyl)-5-(phenylamino)-carbonyl-2H-tetra-zolium hydroxide (XTT) reduction assays. Brain and lung samples of catheterized rats were histopathologically assessed. Serum samples from catheterized rats were injected into Galleria mellonella larvae. Survival of catheterized rats and G. mellonella was determined.

Results

TOH impeded the growth of S. apiospermum by reducing the colony diameter in a dose-dependent manner. TOH coating remarkably lessened S. apiospermum biofilm formation and fungal cell viability on the catheter luminal surface. Additionally, TOH coating lessens cerebral edema that is associated with abscess and invasive pulmonary damages due to S. apiospermum catheter-related infection. Furthermore, TOH coating also lessened the virulence of S. apiospermum in sera of experimental catheterized rats and extended the survival rate of larvae Galleria mellonella infection model.

Conclusion

An alternative modification of catheter by coating with TOH is effective in preventing S. apiospermum colonization in vivo. Our study gives a new strategy to control catheter contamination and prevents nosocomial diseases due to S. apiospermum infection.

Salmonella Typhimurium biofilm disruption by a human antibody that binds a pan-amyloid epitope on curli

Bacterial biofilms, especially those associated with implanted medical devices, are difficult to eradicate. Curli amyloid fibers are important components of the biofilms formed by the Enterobacteriaceae family. Here, we show that a human monoclonal antibody with pan-amyloid-binding activity (mAb 3H3) can disrupt biofilms formed by Salmonella enterica serovar Typhimurium in vitro and in vivo. The antibody disrupts the biofilm structure, enhancing biofilm eradication by antibiotics and immune cells. In mice, 3H3 injections allow antibiotic-mediated clearance of catheter-associated S. Typhimurium biofilms. Thus, monoclonal antibodies that bind a pan-amyloid epitope have potential to prevent or eradicate bacterial biofilms.

Curli amyloid fibers are important components of bacterial biofilms formed by E. coli and Salmonella. Here, Tursi et al. show that a human monoclonal antibody with pan-amyloid binding activity can disrupt biofilms formed by Salmonella Typhimurium in vitro and in vivo.

Vitamin E for Prevention of Biofilm-caused Healthcare-associated Infections

The healthcare-associated infections (HCAIs) occur in patients both in nosocomial environments and in community. More often HCAIs are associated to the use of medical devices and bacterial biofilm development on these equipments. Due to the clinical and economic relevance of this topic, new strategies for the treatment of infections caused by biofilm proliferation are unceasingly searched by scientists.

The present study investigated the role of vitamin E to reduce the biofilm formation for a larger panel of human pathogens, including strains of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Acinetobacter baumannii, Pseudomonas aeruginosa and Pseudomonas putida.

This potential activity was tested by placing a preparation of vitamin E (α-Tocopheryl acetate) as interface between the bacterial culture and the polystyrene walls of a 96 well plate at different concentrations of glucose, used as a biofilm enhancer.

The Staphylococcus genus was further investigated by spreading the vitamin E on a silicone catheter lumen and evaluating its influence on the bacterial colonization.

From our results, vitamin E has been able to interfere with bacterial biofilm and prevent in vitro biofilm formation. Furthermore, the ability of Staphylococcus aureus and Staphylococcus epidermidis to colonize the catheter surface decreased as a result of vitamin E application.

RNA-Dependent Regulation of Virulence in Pathogenic Bacteria

During infection, bacterial pathogens successfully sense, respond and adapt to a myriad of harsh environments presented by the mammalian host. This exquisite level of adaptation requires a robust modulation of their physiological and metabolic features. Additionally, virulence determinants, which include host invasion, colonization and survival despite the host's immune responses and antimicrobial therapy, must be optimally orchestrated by the pathogen at all times during infection. This can only be achieved by tight coordination of gene expression. A large body of evidence implicate the prolific roles played by bacterial regulatory RNAs in mediating gene expression both at the transcriptional and post-transcriptional levels. This review describes mechanistic and regulatory aspects of bacterial regulatory RNAs and highlights how these molecules increase virulence efficiency in human pathogens. As illustrative examples, Staphylococcus aureus, Listeria monocytogenes, the uropathogenic strain of Escherichia coli, Helicobacter pylori, and Pseudomonas aeruginosa have been selected.

Resistance of L. monocytogenes and S. Typhimurium towards Cold Atmospheric Plasma as Function of Biofilm Age

The biofilm mode of growth protects bacterial cells against currently applied disinfection methods for abiotic (food) contact surfaces. Therefore, innovative methods, such as Cold Atmospheric Plasma (CAP), should be investigated for biofilm inactivation. However, more knowledge is required concerning the influence of the biofilm age on the inactivation efficacy in order to comment on a possible application of CAP in the (food) processing industry. L. monocytogenes and S. Typhimurium biofilms with five different ages (i.e., 1, 2, 3, 7, and 10 days) were developed. For the untreated biofilms, the total biofilm mass and the cell density were determined. To investigate the biofilm resistance towards CAP treatment, biofilms with different ages were treated for 10 min and the remaining cell density was determined. Finally, for the one-day old reference biofilms and the most resistant biofilm age, complete inactivation curves were developed to examine the influence of the biofilm age on the inactivation kinetics. For L. monocytogenes, an increased biofilm age resulted in (i) an increased biomass, (ii) a decreased cell density prior to CAP treatment, and (iii) an increased resistance towards CAP treatment. For S. Typhimurium, similar results were obtained, except for the biomass, which was here independent of the biofilm age.

Printing of Patterned, Engineered E. coli Biofilms with a Low-Cost 3D Printer

Biofilms can grow on virtually any surface available, with impacts ranging from endangering the lives of patients to degrading unwanted water contaminants. Biofilm research is challenging due to the high degree of biofilm heterogeneity. A method for the production of standardized, reproducible, and patterned biofilm-inspired materials could be a boon for biofilm research and allow for completely new engineering applications. Here, we present such a method, combining 3D printing with genetic engineering. We prototyped a low-cost 3D printer that prints bioink, a suspension of bacteria in a solution of alginate that solidifies on a calcium-containing substrate. We 3D-printed Escherichia coli in different shapes and in discrete layers, after which the cells survived in the printing matrix for at least 1 week. When printed bacteria were induced to form curli fibers, the major proteinaceous extracellular component of E. coli biofilms, they remained adherent to the printing substrate and stably spatially patterned even after treatment with a matrix-dissolving agent, indicating that a biofilm-mimicking structure had formed. This work is the first demonstration of patterned, biofilm-inspired living materials that are produced by genetic control over curli formation in combination with spatial control by 3D printing. These materials could be used as living, functional materials in applications such as water filtration, metal ion sequestration, or civil engineering, and potentially as standardizable models for certain curli-containing biofilms.

Colonization of Electrospun Polycaprolactone Fibers by Relevant Pathogenic Bacterial Strains

Electrospun biodegradable polymers have emerged as promising materials for their applications in several fields, including biomedicine and food industry. For this reason, the susceptibility of these materials to be colonized by different pathogens is a critical issue for public health, and their study can provide future knowledge to develop new strategies against bacterial infections. In this work, the ability of three pathogenic bacterial species ( Pseudomonas aeruginosa, Acinetobacter baumannii, and Listeria monocytogenes) to adhere and form biofilm in electrospun polycaprolactone (PCL) microfibrous meshes was investigated. Bacterial attachment was analyzed in meshes with different microstructure, and comparisons with other materials (borosilicate glass and electrospun polylactic acid (PLA)) fibers were assessed. Analysis included colony forming unit (CFU) counts, scanning electron microscopy (SEM), and crystal violet (CV) staining. All the obtained data suggest that PCL meshes, regardless of their microstructure, are highly susceptible to be colonized by the pathogenic relevant bacteria used in this study, so a pretreatment or a functionalization with compounds that present some antimicrobial activity or antibiofilm properties is highly recommended before their application. Moreover, an experiment designed to simulate a chronic wound environment was used to demonstrate the ability of these meshes to detach biofilms from the substratum where they have developed, thus making them promising candidates to be used in wound cleaning and disinfection.

Comparison of Microbiological Examination by Test Tube and Congo Red Agar Methods to Detect Biofilm Production on Clinical Isolates

Biofilm on medical devices can cause significant diseases and deaths and give a large effecton disease transmission among patients and health providers and potentially increasethe cost of patient treatment. By knowing the presence of biofilm on a patient, one can differentiate the treatment management for that particular patient from the patients without biofilm on their medical device. The purpose of this study was to obtain diagnostic method to detect biofilm formation on isolates from the medical devices by simple method that is easy to do and can be applied in resource-limited microbiology laboratory. 36 specimens obtained from IV Line, CVC, urinary catheter and ETT were grown on Muller Hinton agar and continued with 3 methods, i.e., Test Tube method, Congo Red Agar method and Microtiter Plate Assay method. Results of this study showed Test Tube (nephelometer), Test Tube (visual) and Congo Red Agar in order to have the same sensitivity of 100% but has higher specificity compared to Test Tube method (visual) and Congo Red Agar method in detecting biofilm production on isolates from medical devices that had been plugged into patients body. The biofilm formation inside devices depends on factors, i.e., host, device and the microorganism itself.

Nitric Oxide Releasing Polymeric Coatings for the Prevention of Biofilm Formation

The ability of nitric oxide (NO)-releasing polymer coatings to prevent biofilm formation is described. NO-releasing coatings on (poly(ethylene terephthalate) (PET) and silicone elastomer (SE)) were fabricated using aminosilane precursors. Pristine PET and SE were oxygen plasma treated, followed by immobilisation of two aminosilane molecules: N-(3-(trimethoxysilyl)propyl)diethylenetriamine (DET3) and N-(3-trimethoxysilyl)propyl)aniline (PTMSPA). N-diazeniumdiolate nitric oxide donors were formed at the secondary amine sites on the aminosilane molecules producing NO-releasing polymeric coatings. The NO payload and release were controlled by the aminosilane precursor, as DET3 has two secondary amine sites and PTMSPA only one. The antibacterial efficacy of these coatings was tested using a clinical isolate of Pseudomonas aeruginosa (PA14). All NO-releasing coatings in this study were shown to significantly reduce P. aeruginosa adhesion over 24 h with the efficacy being a function of the aminosilane modification and the underlying substrate. These NO-releasing polymers demonstrate the potential and utility of this facile coating technique for preventing biofilms for indwelling medical devices.

Preventing microbial biofilms on catheter tubes using ultrasonic guided waves

Biofilms on indwelling tubes and medical prosthetic devices are among the leading causes of antibiotic-resistant bacterial infections. In this work, a new anti-biofilm catheter prototype was proposed. By combining an endotracheal tube (ET) with a group of ultrasonic guided wave (UGW) transducers, the general idea was to prevent bacteria aggregation with UGW vibrations. Based on quantitative analysis of UGW propagation, detailed approach was achieved through (a) selection of ultrasonic frequency, wave modes and vibration amplitude; and (b) adoption of wave coupling and 45° wave incidence technique. Performance of the proposed UGW-ET prototype was demonstrated via in vitro experiments, during which it deterred deposition of Pseudomonas aeruginosa (P. aeruginosa) biofilms successfully. With current configuration, UGW amplitudes ranged from 0.05-5 nm could be optimal to achieve biofilm prevention. This work sheds a light in the underlying mechanism of ultrasound-mediated biofilm prevention, and will inspire the development of new catheters of better antibacterial capability.

Microbial biofilm in human health - an updated theoretical and practical insight

The term biofilm designates an aggregate of microorganisms belonging to one or more species which adhere to various surfaces but also to each another. These microbial communities are included and interconnected within an organic structure known as slime, composed of protein substances, polysaccharides, and DNA.

The Center for Disease prevention and control considers infections with bacteria in biofilms among the 7 most important challenges which must be overcome in order to improve the safety of health services. The risk of microbial biofilm development exists for a long list of medical devices and equipment, as well as in certain diseases such as cystic fibrosis. An aggravating aspect is represented by the almost 1,000 times higher antimicrobial resistance of bacteria growing and multiplying within biofilms. Thus, in case of biofilm-infected medical devices, the resistance to antimicrobial treatments requires the removal of the device which essentially means the failure of the exploratory or therapeutic intervention in question.

The role of microbial biofilms in medical pathology is a subject that raises interest for both researchers and clinicians in order to establish new methods for prevention and treatment of biofilms. This paper is intended as an overview in the management of microbial biofilms, presenting future insights, with technological progress in microscopy, molecular genetics, and genome analysis. Therefore the present paper will focus on describing the mechanisms involved in biofilm development, biofilm related infections, methods of detection and quantification of microbial communities and therapeutical approaches.

Assessment of antivirulence activity of several d-amino acids against Acinetobacter baumannii and Pseudomonas aeruginosa

OBJECTIVES

Biofilm formation and bacterial adherence are important requirements for persistence, multidrug resistance and infection. The d-amino acids play a role as modulators of bacterial growth and persistence, though their ability to inhibit biofilms is much debated. In this study, we analysed the effects of 18 different d-amino acids on the pathogens Acinetobacter baumannii and Pseudomonas aeruginosa.

METHODS

In vitro assays were carried out to analyse the effect of d-amino acids on bacterial growth, biofilm formation/disassembly, capacity to attach to eukaryotic cells and cellular death. In addition, in vivo assays were performed in mice, using experimental models of sepsis and pneumonia.

RESULTS

Biofilm formation was inhibited in A. baumannii by d-His, d-Cys and d-Trp (35%-86%) at 2 mM and in P. aeruginosa by d-Cys, d-Trp and d-Tyr (10%-30%) at 4 mM. Attachment to the A549 human alveolar cells was reduced in A. baumannii by d-Cys, d-His, d-Met, d-Val and d-Ser, and in P. aeruginosa by d-Arg and d-Trp. Growth was inhibited in A. baumannii by d-Cys and d-Trp, and in P. aeruginosa by d-Trp. In virulence assays, incubation of alveolar cells infected with P. aeruginosa with d-Cys, d-Trp and d-Arg reduced cell death (56%-45%). However, no significant effect of d-amino acids was observed in vivo.

CONCLUSIONS

Some d-amino acids can inhibit bacterial growth, biofilm formation and adherence to eukaryotic cells in A. baumannii and P. aeruginosa, and showed a protective effect against infection of alveolar cells with P. aeruginosa. Despite the fact that some considerable protection was observed in mice, survival differences between treated and control groups were not statistically significant.

Inhibition and Dispersal of Pseudomonas aeruginosa Biofilms by Combination Treatment with Escapin Intermediate Products and Hydrogen Peroxide

Escapin is an l-amino acid oxidase that acts on lysine to produce hydrogen peroxide (H2O2), ammonia, and equilibrium mixtures of several organic acids collectively called escapin intermediate products (EIP). Previous work showed that the combination of synthetic EIP and H2O2 functions synergistically as an antimicrobial toward diverse planktonic bacteria. We initiated the present study to investigate how the combination of EIP and H2O2 affected bacterial biofilms, using Pseudomonas aeruginosa as a model. Specifically, we examined concentrations of EIP and H2O2 that inhibited biofilm formation or fostered disruption of established biofilms. High-throughput assays of biofilm formation using microtiter plates and crystal violet staining showed a significant effect from pairing EIP and H2O2, resulting in inhibition of biofilm formation relative to biofilm formation in untreated controls or with EIP or H2O2 alone. Similarly, flow cell analysis and confocal laser scanning microscopy revealed that the EIP and H2O2 combination reduced the biomass of established biofilms relative to that of the controls. Area layer analysis of biofilms posttreatment indicated that disruption of biomass occurs down to the substratum. Only nanomolar to micromolar concentrations of EIP and H2O2 were required to impact biofilm formation or disruption, and these concentrations are significantly lower than those causing bactericidal effects on planktonic bacteria. Micromolar concentrations of EIP and H2O2 combined enhanced P. aeruginosa swimming motility compared to the effect of either EIP or H2O2 alone. Collectively, our results suggest that the combination of EIP and H2O2 may affect biofilms by interfering with bacterial attachment and destabilizing the biofilm matrix.

Elucidating the pH-Dependent Structural Transition of T7 Bacteriophage Endolysin

Bacteriophages are the most abundant and diverse biological entities on earth. Bacteriophage endolysins are unique peptidoglycan hydrolases and have huge potential as effective enzybiotics in various infectious models. T7 bacteriophage endolysin (T7L), also known as N-acetylmuramoyl-l-alanine amidase or T7 lysozyme, is a 17 kDa protein that lyses a range of Gram-negative bacteria by hydrolyzing the amide bond between N-acetylmuramoyl residues and the l-alanine of the peptidoglycan layer. Although the activity profiles of several of the T7 family members have been known for many years, the molecular basis for their pH-dependent differential activity is not clear. In this study, we explored the pH-induced structural, stability, and activity characteristics of T7L by applying a variety of biophysical techniques and protein nuclear magnetic resonance (NMR) spectroscopy. Our studies established a reversible structural transition of T7L below pH 6 and the formation of a partially denatured conformation at pH 3. This low-pH conformation is thermally stable and exposed its hydrophobic pockets. Further, NMR relaxation measurements and structural analysis unraveled that T7L is highly dynamic in its native state and a network of His residues are responsible for the observed pH-dependent conformational dynamics and transitions. As bacteriophage chimeric and engineered endolysins are being developed as novel therapeutics against multiple drug resistance pathogens, we believe that our results are of great help in designing these entities as broadband antimicrobial and/or antibacterial agents.

Antibacterial Action of Nitric Oxide-Releasing Chitosan Oligosaccharides against Pseudomonas aeruginosa under Aerobic and Anaerobic Conditions

Chitosan oligosaccharides were modified with N-diazeniumdiolates to yield biocompatible nitric oxide (NO) donor scaffolds. The minimum bactericidal concentrations and MICs of the NO donors against Pseudomonas aeruginosa were compared under aerobic and anaerobic conditions. Differential antibacterial activities were primarily the result of NO scavenging by oxygen under aerobic environments and not changes in bacterial physiology. Bacterial killing was also tested against nonmucoid and mucoid biofilms and compared to that of tobramycin. Smaller NO payloads were required to eradicate P. aeruginosa biofilms under anaerobic versus aerobic conditions. Under oxygen-free environments, the NO treatment was 10-fold more effective at killing biofilms than tobramycin. These results demonstrate the potential utility of NO-releasing chitosan oligosaccharides under both aerobic and anaerobic environments.

Disinfection of Needleless Connector Hubs: Clinical Evidence Systematic Review

Background. Needleless connectors (NC) are used on virtually all intravascular devices, providing an easy access point for infusion connection. Colonization of NC is considered the cause of 50% of postinsertion catheter-related infections. Breaks in aseptic technique, from failure to disinfect, result in contamination and subsequent biofilm formation within NC and catheters increasing the potential for infection of central and peripheral catheters. Methods. This systematic review evaluated 140 studies and 34 abstracts on NC disinfection practices, the impact of hub contamination on infection, and measures of education and compliance. Results. The greatest risk for contamination of the catheter after insertion is the NC with 33-45% contaminated, and compliance with disinfection as low as 10%. The optimal technique or disinfection time has not been identified, although scrubbing with 70% alcohol for 5-60 seconds is recommended. Studies have reported statistically significant results in infection reduction when passive alcohol disinfection caps are used (48-86% reduction). Clinical Implications. It is critical for healthcare facilities and clinicians to take responsibility for compliance with basic principles of asepsis compliance, to involve frontline staff in strategies, to facilitate education that promotes understanding of the consequences of failure, and to comply with the standard of care for hub disinfection.

Molecular mechanisms involved in Bacillus subtilis biofilm formation

Biofilms are the predominant lifestyle of bacteria in natural environments, and they severely impact our societies in many different fashions. Therefore, biofilm formation is a topic of growing interest in microbiology, and different bacterial models are currently studied to better understand the molecular strategies that bacteria undergo to build biofilms. Among those, biofilms of the soil-dwelling bacterium Bacillus subtilis are commonly used for this purpose. Bacillus subtilis biofilms show remarkable architectural features that are a consequence of sophisticated programmes of cellular specialization and cell-cell communication within the community. Many laboratories are trying to unravel the biological role of the morphological features of biofilms, as well as exploring the molecular basis underlying cellular differentiation. In this review, we present a general perspective of the current state of knowledge of biofilm formation in B. subtilis and thereby placing a special emphasis on summarizing the most recent discoveries in the field.

Combined use of bacteriophage K and a novel bacteriophage to reduce Staphylococcus aureus biofilm formation

Biofilms are major causes of impairment of wound healing and patient morbidity. One of the most common and aggressive wound pathogens is Staphylococcus aureus, displaying a large repertoire of virulence factors and commonly reduced susceptibility to antibiotics, such as the spread of methicillin-resistant S. aureus (MRSA). Bacteriophages are obligate parasites of bacteria. They multiply intracellularly and lyse their bacterial host, releasing their progeny. We isolated a novel phage, DRA88, which has a broad host range among S. aureus bacteria. Morphologically, the phage belongs to the Myoviridae family and comprises a large double-stranded DNA (dsDNA) genome of 141,907 bp. DRA88 was mixed with phage K to produce a high-titer mixture that showed strong lytic activity against a wide range of S. aureus isolates, including representatives of the major international MRSA clones and coagulase-negative Staphylococcus. Its efficacy was assessed both in planktonic cultures and when treating established biofilms produced by three different biofilm-producing S. aureus isolates. A significant reduction of biofilm biomass over 48 h of treatment was recorded in all cases. The phage mixture may form the basis of an effective treatment for infections caused by S. aureus biofilms.

Activity of imipenem against Klebsiella pneumoniae biofilms in vitro and in vivo

Encapsulated Klebsiella pneumoniae has emerged as one of the most clinically relevant and more frequently encountered opportunistic pathogens in combat wounds as the result of nosocomial infection. In this report, we show that imipenem displayed potent activity against established K. pneumoniae biofilms under both static and flow conditions in vitro. Using a rabbit ear model, we also demonstrated that imipenem was highly effective against preformed K. pneumoniae biofilms in wounds.

Endolysins as antimicrobials

Peptidoglycan (PG) is the major structural component of the bacterial cell wall. Bacteria have autolytic PG hydrolases that allow the cell to grow and divide. A well-studied group of PG hydrolase enzymes are the bacteriophage endolysins. Endolysins are PG-degrading proteins that allow the phage to escape from the bacterial cell during the phage lytic cycle. The endolysins, when purified and exposed to PG externally, can cause "lysis from without." Numerous publications have described how this phenomenon can be used therapeutically as an effective antimicrobial against certain pathogens. Endolysins have a characteristic modular structure, often with multiple lytic and/or cell wall-binding domains (CBDs). They degrade the PG with glycosidase, amidase, endopeptidase, or lytic transglycosylase activities and have been shown to be synergistic with fellow PG hydrolases or a range of other antimicrobials. Due to the coevolution of phage and host, it is thought they are much less likely to invoke resistance. Endolysin engineering has opened a range of new applications for these proteins from food safety to environmental decontamination to more effective antimicrobials that are believed refractory to resistance development. To put phage endolysin work in a broader context, this chapter includes relevant studies of other well-characterized PG hydrolase antimicrobials.

Antimicrobial Pressure of Ciprofloxacin and Gentamicin on Biofilm Development by an Endoscope-Isolated Pseudomonas aeruginosa

This work aims at characterizing endoscope biofilm-isolated (PAI) and reference strain P. aeruginosa (PA) adhesion, biofilm formation and sensitivity to antibiotics. The recovery ability of the biofilm-growing bacteria subjected to intermittent antibiotic pressure (ciprofloxacin (CIP) and gentamicin (GM)), as well as the development of resistance towards antibiotics and benzalkonium chloride (BC), were also determined. The capacity of both strains to develop biofilms was greatly impaired in the presence of CIP and GM. Sanitization was not complete allowing biofilm recovery after the intermittent cycles of antibiotic pressure. The environmental pressure exerted by CIP and GM did not develop P. aeruginosa resistance to antibiotics nor cross-resistance towards BC. However, data highlighted that none of the antimicrobials led to complete biofilm eradication, allowing the recovery of the remaining adhered population possibly due to the selection of persister cells. This feature may lead to biofilm recalcitrance, reinforcement of bacterial attachment, and recolonization of other sites.

Review article: biofilm formation by Helicobacter pylori as a target for eradication of resistant infection

BACKGROUND

Helicobacter pylori is one of the most common causes of bacterial infection in humans. Resistance of this infection to conventional therapies has suggested the role of a biofilm-growing bacterium, which is recalcitrant to many antimicrobial agents.

AIM

To review the current knowledge on biofilm formation by H. pylori and to discuss the implications of this behaviour in the context of human infections and their treatment.

RESULTS

Scanning electron microscopy analysis of gastric biopsies of infected patients demonstrated that H. pylori forms biofilm on the gastric mucosa epithelium. Adaptation to the biofilm environment may produce many persister cells, namely dormant cells, which are highly tolerant to antimicrobials that could account for the recalcitrance of H. pylori infections in vivo. Resistant H. pylori infection has become increasingly common with triple or quadruple therapy, even in the presence of H. pylori strains susceptible to all antibiotics. The mucolytic and thiol-containing antioxidant N-acetylcysteine, associated with antibiotics, was successfully used in clinic for therapy of patients with chronic respiratory tract infections. Consistently, N-acetylcysteine treatment prior to starting antibiotic therapy allowed the disappearance of gastric biofilm in all patients in whom H. pylori was eradicated.

CONCLUSION

Effective strategies targeting H. pylori biofilm infections are possible, through the use of substances degrading components of the biofilm.

Candida biofilms and the host: models and new concepts for eradication

Biofilms define mono- or multispecies communities embedded in a self-produced protective matrix, which is strongly attached to surfaces. They often are considered a general threat not only in industry but also in medicine. They constitute a permanent source of contamination, and they can disturb the proper usage of the material onto which they develop. This paper relates to some of the most recent approaches that have been elaborated to eradicate Candida biofilms, based on the vast effort put in ever-improving models of biofilm formation in vitro and in vivo, including novel flow systems, high-throughput techniques and mucosal models. Mixed biofilms, sustaining antagonist or beneficial cooperation between species, and their interplay with the host immune system are also prevalent topics. Alternative strategies against biofilms include the lock therapy and immunotherapy approaches, and material coating and improvements. The host-biofilm interactions are also discussed, together with their potential applications in Candida biofilm elimination.

Surface acoustic waves increase the susceptibility of Pseudomonas aeruginosa biofilms to antibiotic treatment

Bacterial urinary tract infections resulting from prolonged patient catheterization have become a major health problem. One of the major issues is bacterial resistance to antibiotic treatments due to biofilm formation inside the catheters, thus enhancing the search for alternative treatments. In the present study, a device containing a piezo element capable of transmitting low-frequency surface acoustic waves (SAW) onto the indwelling catheter was used. The SAW were able to eradicate biofilm-residing bacteria by >85% when applied simultaneously with an antibiotic in three clinically relevant species, viz. Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa. Moreover, transcriptome analysis revealed that SAW can alter the transcription pattern of P. aeruginosa, suggesting that this signal can be specifically sensed by the bacterium.

Randomized study of minocycline and edetic acid as a locking solution for central line (port-a-cath) in children with cancer

BACKGROUND

Contamination of central catheters is frequent, and biofilm perpetuates infections. Heparin does not protect against infections because it has no antibiotic action. Minocycline and edetic acid (M-EDTA), a potent calcium chelating agent that destroys bacterial and fungal cell membrane and disrupts biofilm, may be an alternative to allow the associated antibiotic to act locally at a high and safe concentration.

METHODS

Fifty children with cancer and a port-a-cath were followed up: 26 received heparin (group 1) and 24 M-EDTA (group 2). A total of 762 serial prospective blood cultures were obtained, 387 from group 1 and 375 from group 2.

RESULTS

In group 1 (heparin), 19 blood cultures were positive, and infection incidence was 73.1% (19/26 ports). In group 2 (M-EDTA), 5 blood cultures were positive, and the incidence rate was 20.8% (5/24 ports).

CONCLUSION

M-EDTA, compared with heparin, prevents and treats catheter infections, and is a promising alternative to decrease sepsis during chemotherapy.

Principles of source control in the early management of sepsis

Source control refers to the spectrum of physical measures that are undertaken to control a focus of infection, and to facilitate restoration of optimal anatomy and physiology. These measures are classified as drainage-the evacuation of infected liquid through the creation of a controlled sinus or fistula, debridement-the physical removal of necrotic infected tissue, device removal, and the definitive measures that comprise the process of reconstruction and rehabilitation. Effective and timely source control is critical to the successful management of life-threatening infection. This article reviews the principles of diagnosis and source-control management, and their application to common infections that result in severe sepsis and septic shock.

Mini-review: Antimicrobial central venous catheters--recent advances and strategies

Central venous catheters (CVCs) nowadays constitute critical devices used in medical care, namely in intensive care units. However, CVCs also represent one of the indwelling medical devices with enhanced risk of nosocomial device-related infection. Catheter-related infections (CRIs) are a major cause of patient morbidity and mortality, often justifying premature catheter removal and an increase in costs and use of resources. Adhesion and subsequent biofilm formation on the surfaces of indwelling catheters is elemental to the onset of pathogenesis. Seeking the prevention of CVC colonisation and CRI, a variety of approaches have been studied, tested and, in some cases, already applied in clinical practice. This review looks at the current preventive strategies often used to decrease the risk of CRIs due to colonization and biofilm formation on catheter surfaces, as well as at the more recent approaches under investigation.

Hacking into bacterial biofilms: a new therapeutic challenge

Microbiologists have extensively worked during the past decade on a particular phase of the bacterial cell cycle known as biofilm, in which single-celled individuals gather together to form a sedentary but dynamic community within a complex structure, displaying spatial and functional heterogeneity. In response to the perception of environmental signals by sensing systems, appropriate responses are triggered, leading to biofilm formation. This process involves various molecular systems that enable bacteria to identify appropriate surfaces on which to anchor themselves, to stick to those surfaces and to each other, to construct multicellular communities several hundreds of micrometers thick, and to detach from the community. The biofilm microbial community is a unique, highly competitive, and crowded environment facilitating microevolutionary processes and horizontal gene transfer between distantly related microorganisms. It is governed by social rules, based on the production and use of "public" goods, with actors and recipients. Biofilms constitute a unique shield against external aggressions, including drug treatment and immune reactions. Biofilm-associated infections in humans have therefore generated major problems for the diagnosis and treatment of diseases. Improvements in our understanding of biofilms have led to innovative research designed to interfere with this process.

Interaction of bacteria isolated from clinical biofilms with cardiovascular prosthetic devices and eukaryotic cells

PURPOSE

To identify the relationships between some infectious agents implicated in cardiovascular diseases with the cellular substrate and prosthetic devices in the presence of antibiotics.

SPECIFIC OBJECTIVES

Strains isolation and identification, comparative study of antibiotic resistance of planktonic (disk diffusion, E-test, automatic systems) and sessile (using original experimental models for in vitro development of monospecific biofilms) bacterial cells, virulence assays (adherence and invasion of HeLa cells, slime test, soluble virulence factors expression), dynamic study of biofilm development on inert substrata, under the influence of antibiotics, the influence of cellular and soluble bacterial fractions on HeLa cells (by flow cytometry and real-time PCR).

RESULTS

The identified strains were isolated from different sources, the etiology being dominated by Gram-negative non-fermentative bacilli, Gram-positive cocci and yeasts, harboring invasion enzymes responsible for development of systemic infections. The isolated strains exhibited a high level of antibiotic resistance to beta-lactams, aminoglycosides and quinolones, and an evident tendency of colonizing the cellular and inert substrate, the degree of colonization depending on the physico-chemical nature of the substrate. By comparison with planktonic ones, the sessile bacterial strains expressed a changed profile of antibiotic resistance, this aspect being very important for the readjustment of the treatment and prevention of infections associated with prosthetic devices. In vitro experiments suggested that different fractions of S. aureus cultures could trigger the release of proinflammatory (TNF-α, IL-1b, IL-6) and anti-inflammatory (IL-8) cytokines and induced apoptosis in HeLa cells.

In vitro evaluation of antibiotic lock technique for the treatment of Candida albicans, C. glabrata, and C. tropicalis biofilms

Candidaemia associated with intravascular catheter-associated infections is of great concern due to the resulting high morbidity and mortality. The antibiotic lock technique (ALT) was previously introduced to treat catheter-associated bacterial infections without removal of catheter. So far, the efficacy of ALT against Candida infections has not been rigorously evaluated. We investigated in vitro activity of ALT against Candida biofilms formed by C. albicans, C. glabrata, and C. tropicalis using five antifungal agents (caspofungin, amphotericin B, itraconazole, fluconazole, and voriconazole). The effectiveness of antifungal treatment was assayed by monitoring viable cell counts after exposure to 1 mg/mL solutions of each antibiotic. Fluconazole, itraconazole, and voriconazole eliminated detectable viability in the biofilms of all Candida species within 7, 10, and 14 days, respectively, while caspofungin and amphotericin B did not completely kill fungi in C. albicans and C. glabrata biofilms within 14 days. For C. tropicalis biofilm, caspofungin lock achieved eradication more rapidly than amphotericin B and three azoles. Our study suggests that azoles may be useful ALT agents in the treatment of catheter-related candidemia.

UVC fluencies for preventative treatment of Pseudomonas aeruginosa contaminated polymer tubes

Exposing Pseudomonas aeruginosa biofilm grown on the inner surface of Teflon and silicone tubes to UVC light (265 nm) from light emitting diodes (LED) has previously been shown to substantially reduce biofilm growth. Smaller UVC fluencies were required to disinfect Teflon tubes compared to silicone tubes. Light propagation enhancement in tubes can be obtained if the refractive index of the intra-luminal saline solution is higher than that of the polymer. This condition is achieved by using Teflon tubes with a low refractive index (1.34) instead of the polymers with a high refractive index (1.40-1.50) normally used for tubing in catheter production. Determining whether or not UVC light exposure can disinfect and maintain the intra-luminal number of colony forming units (CFUs) at an exceedingly low level and thus avoid the growth and establishment of biofilm is of interest. The use of UVC diodes is demonstrated to be a preventative disinfection treatment on tubes made of Teflon, which enhances the UVC light propagation, and on tubes made of a softer material, ethylene vinyl acetate (EVA), which is suitable for catheters but much less suitable for UVC light propagation. Simulating an aseptic breach (∼10(3)-10(4) CFU ml(-1)), the UVC disinfection set-up was demonstrated using tubes contaminated with planktonic P. aeruginosa. After the tubes (10-20 cm) were inoculated with the bacterial solution for 3 h, they were emptied and filled with saline solutions (0.9-20%). Next UVC fluencies (0-21 mJ cm(-2)) were applied to the tubes 3 h after inoculation. Colony counts were carried out on liquid samples drawn from the tubes the first day after UVC treatment and liquid and surface samples were collected and analyzed 3-4 days later. A fluence of approximately 1.0 mJ cm(-2) was noted as being sufficient for no growth for a period of 3-4 days for the Teflon tubes. Determining the fluence threshold for the EVA tubes was not possible. Almost all of the UVC-treated EVA tubes were disinfected simply by filling the tubes with a saline solution. Direct UVC treatment of the contaminated EVA tubes revealed, however, that a fluence of 21 mJ cm(-2) killed the bacteria present in the tubes and kept them disinfected for a period of 3-4 days.

Biofilms

The ability to form biofilms is a universal attribute of bacteria. Biofilms are multicellular communities held together by a self-produced extracellular matrix. The mechanisms that different bacteria employ to form biofilms vary, frequently depending on environmental conditions and specific strain attributes. In this review, we emphasize four well-studied model systems to give an overview of how several organisms form biofilms: Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus. Using these bacteria as examples, we discuss the key features of biofilms as well as mechanisms by which extracellular signals trigger biofilm formation.

Decreasing central line associated bloodstream infection in neonatal intensive care

Central Line Associated Bloodstream Infections (CLABSIs) have come to be recognized as preventable adverse events that result from lapses in technique at multiple levels of care. CLABSIs are associated with increased mortality and adverse outcomes that may have lifelong consequences. This review provides a summary of evidence-based strategies to reduce CLABSI in the newborn intensive care unit that have been described in the literature over the past decades. Implementation of these strategies in "bundles" is also discussed, citing examples of successful quality improvement collaboratives. The methods of implementation require an understanding of the scientific data and technical developments, as well as knowledge of how to influence change within the unique and complicated milieu of the newborn intensive care unit.

Principles of source control in the management of sepsis

The term "source control" encompasses all those physical measures used to control a focus of invasive infection and to restore the optimal function of the affected area. Source-control measures can be categorized into 3 broad modalities: drainage controls the liquid component of an infection by converting a closed space infection to a controlled sinus or fistula; debridement is the physical removal of solid necrotic tissue (removal of an infected device can be considered a form of debridement); definitive measures seek to restore optimal function to the involved area. This article discusses specific approaches to source control in the abdomen, chest, and skin and soft tissues.

Impact of sarA on daptomycin susceptibility of Staphylococcus aureus biofilms in vivo

We used a murine model of catheter-associated biofilm formation to determine whether the mutation of the staphylococcal accessory regulator (sarA) has an impact on the susceptibility of established Staphylococcus aureus biofilms to treatment with daptomycin in vivo. The experiments were done with two clinical isolates, one of which (UAMS-1) was obtained from the bone of a patient suffering from osteomyelitis, while the other (UAMS-1625) is an isolate of the USA300 clonal lineage of community-acquired methicillin (meticillin)-resistant S. aureus. UAMS-1625 had a reduced capacity to form a biofilm in vivo compared to that of UAMS-1 (P = 0.0015), but in both cases the mutation of sarA limited biofilm formation compared to that of the corresponding parent strain (P < or = 0.001). The mutation of sarA did not affect the daptomycin MIC for either strain, but it did result in increased susceptibility in vivo in the context of an established biofilm. Specifically, daptomycin treatment resulted in the clearance of detectable bacteria from <10% of the catheters colonized with the parent strains, while treatment with an equivalent daptomycin concentration resulted in the clearance of 46.4% of the catheters colonized with the UAMS-1 sarA mutant and 69.1% of the catheters colonized with the UAMS-1625 sarA mutant. In the absence of daptomycin treatment, mice with catheters colonized with the UAMS-1625 parent strain also developed skin lesions in the region adjacent to the implanted catheter. No such lesions were observed in any other experimental group, including untreated mice containing catheters colonized with the UAMS-1625 sarA mutant.

Effect of a solution containing citrate/Methylene Blue/parabens on Staphylococcus aureus bacteria and biofilm, and comparison with various heparin solutions

OBJECTIVES

Some antibiotic solutions increase bacterial resistance and may cause toxic side effects. Heparin, frequently used as an anticoagulant in catheter lock solutions, may cause bleeding and stimulate biofilm formation. The aim of this study was to investigate the effect of a new antibacterial/antithrombotic solution, citrate/Methylene Blue/parabens (C/MB/P), versus various heparin solutions on the viability and the structure of preformed mature biofilms of Staphylococcus aureus bacteria. The degree of eradication of both planktonic and sessile microorganisms was evaluated.

METHODS

The changes in the structure of biofilms after exposure to C/MB/P and several concentrations of heparin were analysed by means of confocal laser scanning microscopy. COMSTAT image analysis was utilized to compare biofilm biomass, average and maximum height, surface coverage and roughness coefficient. Viability studies were performed on both biofilms and supernatant solutions.

RESULTS

C/MB/P, in contrast to heparin solutions, significantly reduced biofilm biomass and thickness and reduced viability by 5 log when compared with saline treatment. No viable planktonic bacteria were detected and the few remaining biofilm cells appeared to be lysed. In contrast, most heparin solutions only reduced viability up to 1.0 log and failed to eradicate planktonic bacteria.

CONCLUSIONS

C/MB/P has a rapid bactericidal effect on the preformed, mature biofilm of S. aureus. The structural changes of biofilms treated with C/MB/P, together with the observed log reduction of viable biofilm cells, confirmed the high potential of this solution to eliminate sessile bacteria. Furthermore, the tested solution entirely eliminated planktonic bacteria detached from the biofilm.

Preventing biofilms of clinically relevant organisms using bacteriophage

Biofilms might result in healthcare-associated infections and substantially impact healthcare delivery. Bacteriophage (phage) has been used to treat infectious diseases in humans and there is interest in phage to control biofilms. Phages propagate in their bacterial host and many phages produce depolymerases that hydrolyze biofilm extracellular polymers. Drawbacks of phage to consider include narrow host range, bacterial resistance to phage and phage-encoded virulence genes that can incorporate into the host bacterial genome. The immune system might inactivate phage, and impure phage preparations could contain endotoxin. Phage mixtures or engineered phages could provide effective strategies to overcome these obstacles. Lytic bacteriophages could become a new class of anti-biofilm agents.