Co-immobilization of Ciprofloxacin and Chlorhexidine as a Broad-Spectrum Antimicrobial Dual-Drug Coating for Poly(vinyl chloride) (PVC)-Based Endotracheal Tubes

The endotracheal tube (ETT) affords support for intubated patients, but the increasing incidence of ventilator-associated pneumonia (VAP) is jeopardizing its application. ETT surfaces promote (poly)microbial colonization and biofilm formation, with a heavy burden for VAP. Devising safe, broad-spectrum antimicrobial materials to tackle the ETT bioburden is needful. Herein, we immobilized ciprofloxacin (CIP) and/or chlorhexidine (CHX), through polydopamine (pDA)-based functionalization, onto poly(vinyl chloride) (PVC) surfaces. These surfaces were characterized regarding physicochemical properties and challenged with single and polymicrobial cultures of VAP-relevant bacteria (Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis) and fungi (Candida albicans). The coatings imparted PVC surfaces with a homogeneous morphology, varied wettability, and low roughness. The antimicrobial immobilization via pDA chemistry was still evidenced by infrared spectroscopy. Coated surfaces exhibited sustained CIP/CHX release, retaining prolonged (10 days) activity. CIP/CHX-coated surfaces evidencing no A549 lung cell toxicity displayed better antibiofilm outcomes than CIP or CHX coatings, preventing bacterial attachment by 4.1-7.2 Log10 CFU/mL and modestly distressingC. albicans. Their antibiofilm effectiveness was endured toward polymicrobial consortia, substantially inhibiting the adhesion of the bacterial populations (up to 8 Log10 CFU/mL) within the consortia in dual- and even inP. aeruginosa/S. aureus/C. albicans triple-species biofilms while affecting fungal adhesion by 2.7 Log10 CFU/mL (dual consortia) and 1 Log10 CFU/mL (triple consortia). The potential of the dual-drug coating strategy in preventing triple-species adhesion and impairing bacterial viability was still strengthened by live/dead microscopy. The pDA-assisted CIP/CHX co-immobilization holds a safe and robust broad-spectrum antimicrobial coating strategy for PVC-ETTs, with the promise laying in reducing VAP incidence.

Aptamer-based therapy for fighting biofilm-associated infections

Biofilms are key players in the pathogenesis of most of chronic infections associated with host tissue or fluids and indwelling medical devices. These chronic infections are hard to be treated due to the increased biofilms tolerance towards antibiotics in comparison to planktonic (or free living) cells. Despite the advanced understanding of their formation and physiology, biofilms continue to be a challenge and there is no standardized therapeutic approach in clinical practice to eradicate them. Aptamers offer distinctive properties, including excellent affinity, selectivity, stability, making them valuable tools for therapeutic purposes. This review explores the flexibility and designability of aptamers as antibiofilm drugs but, importantly, as targeting tools for diverse drug and delivery systems. It highlights specific examples of application of aptamers in biofilms of diverse species according to different modes of action including inhibition of motility and adhesion, blocking of quorum sensing molecules, and dispersal of biofilm-cells to planktonic state. Moreover, it discusses the limitations and challenges that impaired an increased success of the use of aptamers on biofilm management, as well as the opportunities related to aptamers modifications that can significantly expand their applicability on the biofilm field.

Antimicrobial materials for endotracheal tubes: A review on the last two decades of technological progress

Ventilator-associated pneumonia (VAP) is an unresolved problem in nosocomial settings, remaining consistently associated with a lack of treatment, high mortality, and prolonged hospital stay. The endotracheal tube (ETT) is the major culprit for VAP development owing to its early surface microbial colonization and biofilm formation by multiple pathogens, both critical events for VAP pathogenesis and relapses. To combat this matter, gradual research on antimicrobial ETT surface coating/modification approaches has been made. This review provides an overview of the relevance and implications of the ETT bioburden for VAP pathogenesis and how technological research on antimicrobial materials for ETTs has evolved. Firstly, certain main VAP attributes (definition/categorization; outcomes; economic impact) were outlined, highlighting the issues in defining/diagnosing VAP that often difficult VAP early- and late-onset differentiation, and that generate misinterpretations in VAP surveillance and discrepant outcomes. The central role of the ETT microbial colonization and subsequent biofilm formation as fundamental contributors to VAP pathogenesis was then underscored, in parallel with the uncovering of the polymicrobial ecosystem of VAP-related infections. Secondly, the latest technological developments (reported since 2002) on materials able to endow the ETT surface with active antimicrobial and/or passive antifouling properties were annotated, being further subject to critical scrutiny concerning their potentialities and/or constraints in reducing ETT bioburden and the risk of VAP while retaining/improving the safety of use. Taking those gaps/challenges into consideration, we discussed potential avenues that may assist upcoming advances in the field to tackle VAP rampant rates and improve patient care. STATEMENT OF SIGNIFICANCE: The use of the endotracheal tube (ETT) in patients requiring mechanical ventilation is associated with the development of ventilator-associated pneumonia (VAP). Its rapid surface colonization and biofilm formation are critical events for VAP pathogenesis and relapses. This review provides a comprehensive overview on the relevance/implications of the ETT biofilm in VAP, and on how research on antimicrobial ETT surface coating/modification technology has evolved over the last two decades. Despite significant technological advances, the limited number of gathered reports (46), highlights difficulty in overcoming certain hurdles associated with VAP (e.g., persistent colonization/biofilm formation; mechanical ventilation duration; hospital length of stay; VAP occurrence), which makes this an evolving, complex, and challenging matter. Challenges and opportunities in the field are discussed.

Colistin conditioning surfaces combined with antimicrobial treatment to prevent ventilator-associated infections

Biofilm formation on endotracheal tubes (ETT) is an important factor in the development of ventilator-associated pneumonia (VAP). This work aimed to investigate the effectiveness of colistin (COL) against the early stages of biofilm formation by Pseudomonas aeruginosa. Two strategies were used: pre-conditioning the adhesion surfaces with COL before biofilm formation and growing biofilms in its presence. The combined effect of treating P. aeruginosa 24-hours old biofilms with Ciprofloxacin (CIP) or colistin (COL) on clean and COL-conditioned surfaces was also assessed. Random deposition of COL residues altered the physico-chemical properties of the adhesion surfaces and impaired biofilm formation. Moreover, as a consequence of the reduced amount of biofilms attached to COL conditioned surfaces, adhered cells became more exposed to the subsequent action of CIP or COL, suggesting a combined outcome of prophylactic and therapeutic COL-based strategies. Results highlighted the promising use of COL to prevent the establishment of biofilms on ETT.

Viable but non-cultivable state: a strategy for Staphylococcus aureus survivable in dual-species biofilms with Pseudomonas aeruginosa?

Pseudomonas aeruginosa and Staphylococcus aureus are two of the most prevalent respiratory pathogens in cystic fibrosis patients. Both organisms often cause chronic and recalcitrant infections, in large part due to their ability to form biofilms, being these mixed-species infections correlated with poor clinical outcomes. In this study, the hypothesis that S. aureus adopts phenotypes allowing its coexistence with P. aeruginosa during biofilm growth was put forward. We noticed that S. aureus undergoes a viable but non-cultivable (VBNC) state in the dominated P. aeruginosa dual-species consortia, whatsoever the strains used to form the biofilms. Moreover, an increased expression of genes associated with S. aureus virulence was detected suggesting that the phenotypic switching to VBNC state might account for S. aureus pathogenicity and, in turn, influence the clinical outcome of the mixed-species infection. Thus, P. aeruginosa seems to induce both phenotypic and transcriptomic changes in S. aureus, helping its survival and coexistence in the dual-species biofilms. Overall, our findings illustrate how interspecies interactions can modulate bacterial virulence in vitro, contributing to a better understanding of the behaviour of P. aeruginosa-S. aureus dual-species biofilms.

Chemical Characterization of Sambucus nigra L. Flowers Aqueous Extract and Its Biological Implications

The main goal of this study was to chemically characterize an aqueous S. nigra flower extract and validate it as a bioactive agent. The elderflower aqueous extraction was performed at different temperatures (50, 70 and 90 °C). The extract obtained at 90 °C exhibited the highest phenolic content and antiradical activity. Therefore, this extract was analyzed by GC-MS and HPLC-MS, which allowed the identification of 46 compounds, being quercetin and chlorogenic acid derivatives representative of 86% of the total of phenolic compounds identified in hydrophilic fraction of the aqueous extract. Naringenin (27.2%) was the major compound present in the lipophilic fraction. The antiproliferative effects of the S. nigra extract were evaluated using the colon cancer cell lines RKO, HCT-116, Caco-2 and the extract’s antigenotoxic potential was evaluated by the Comet assay in RKO cells. The RKO cells were the most susceptible to S. nigra flower extract (IC₅₀ = 1250 µg mL⁻¹). Moreover, the extract showed antimicrobial activity against Gram-positive bacteria, particularly Staphylococcus aureus and S. epidermidis. These results show that S. nigra-based extracts can be an important dietary source of bioactive phenolic compounds that contribute to health-span improving life quality, demonstrating their potential as nutraceutical, functional foods and/or cosmetic components for therapeutic purposes.

Tailoring the immobilization and release of chlorhexidine using dopamine chemistry to fight infections associated to orthopedic devices

A crucial factor in the pathogenesis of orthopedics associated infections is that bacteria do not only colonize the implant surface but also the surrounding tissues. This study aimed to engineer an antimicrobial release coating for stainless steel (SS) surfaces, to impart them with the ability to prevent Staphylococci colonization. Chlorhexidine (CHX) was immobilized using two polydopamine (pDA)-based approaches: a one-pot synthesis, where CHX is dissolved together with dopamine before its polymerization; and a two-step methodology, comprising the deposition of a pDA layer to which CHX is immobilized. To modulate CHX release, an additional layer of pDA was also added for both strategies. Immobilization of CHX using a one-step approach yielded surfaces with a more homogenous coating and less roughness than the other strategies. The amount of released CHX was lower for the one-step approach, as opposed to the two-step approach yielding the higher release, which could be decreased by applying an outward layer of pDA. Both one and two-step approaches provided the surfaces with the ability to prevent bacterial colonization of the surface itself and kill most of bacteria in the bulk phase up to 10 days. This long-term antimicrobial performance alluded a stable and enduring immobilization of CHX. In terms of biocompatibility, the amount of CHX released from the one-step approach did not compromise the growth of mammalian cells, contrary to the two-step strategy. Additionally, the few bacteria that managed to adhere to surfaces modified with one-step approach did not show evidence of resistance towards CHX. Overall data underline that one-step immobilization of CHX holds great potential to be further applied in the fight against orthopedic devices associated infections.

Discerning the role of polymicrobial biofilms in the ascent, prevalence, and extent of heteroresistance in clinical practice

Antimicrobial therapy is facing a worrisome and underappreciated challenge, the phenomenon of heteroresistance (HR). HR has been gradually documented in clinically relevant pathogens (e.g. Pseudomonas aeruginosa, Staphylococcus aureus, Burkholderia spp., Acinetobacter baumannii, Klebsiella pneumoniae, Candida spp.) towards several drugs and is believed to complicate the clinical picture of chronic infections. This type of infections are typically mediated by polymicrobial biofilms, wherein microorganisms inherently display a wide range of physiological states, distinct metabolic pathways, diverging refractory levels of stress responses, and a complex network of chemical signals exchange. This review aims to provide an overview on the relevance, prevalence, and implications of HR in clinical settings. Firstly, related terminologies (e.g. resistance, tolerance, persistence), sometimes misunderstood and overlapped, were clarified. Factors generating misleading HR definitions were also uncovered. Secondly, the recent HR incidences reported in clinically relevant pathogens towards different antimicrobials were annotated. The potential mechanisms underlying such occurrences were further elucidated. Finally, the link between HR and biofilms was discussed. The focus was to recognize the presence of heterogeneous levels of resistance within most biofilms, as well as the relevance of polymicrobial biofilms in chronic infectious diseases and their role in resistance spreading. These topics were subject of a critical appraisal, gaining insights into the ascending clinical implications of HR in antimicrobial resistance spreading, which could ultimately help designing effective therapeutic options.

Unraveling Pseudomonas aeruginosa and Candida albicans Communication in Coinfection Scenarios: Insights Through Network Analysis

Modern medicine is currently facing huge setbacks concerning infection therapeutics as microorganisms are consistently knocking down every antimicrobial wall set before them. The situation becomes more worrying when taking into account that, in both environmental and disease scenarios, microorganisms present themselves as biofilm communities that are often polymicrobial. This comprises a competitive advantage, with interactions between different species altering host responses, antimicrobial effectiveness, microbial pathogenesis and virulence, usually augmenting the severity of the infection and contributing for the recalcitrance towards conventional therapy. Pseudomonas aeruginosa and Candida albicans are two opportunistic pathogens often co-isolated from infections, mainly from mucosal tissues like the lung. Despite the billions of years of co-existence, this pair of microorganisms is a great example on how little is known about cross-kingdom interactions, particularly within the context of coinfections. Given the described scenario, this study aimed to collect, curate, and analyze all published experimental information on the molecular basis of P. aeruginosa and C. albicans interactions in biofilms, in order to shed light into key mechanisms that may affect infection prognosis, increasing this area of knowledge. Publications were optimally retrieved from PubMed and Web of Science and classified as to their relevance. Data was then systematically and manually curated, analyzed, and further reconstructed as networks. A total of 641 interactions between the two pathogens were annotated, outputting knowledge on important molecular players affecting key virulence mechanisms, such as hyphal growth, and related genes and proteins, constituting potential therapeutic targets for infections related to these bacterial-fungal consortia. Contrasting interactions were also analyzed, and quorum-sensing inhibition approaches were highlighted. All annotated data was made publicly available at www.ceb.uminho.pt/ISCTD, a database already containing similar data for P. aeruginosa and Staphylococcus aureus communication. This will allow researchers to cut on time and effort when studying this particular subject, facilitating the understanding of the basis of the inter-species and inter-kingdom interactions and how it can be modulated to help design alternative and more effective tailored therapies. Finally, data deposition will serve as base for future dataset integration, whose analysis will hopefully give insights into communications in more complex and varied biofilm communities.

Antimicrobial resistance three ways: healthcare crisis, major concepts and the relevance of biofilms

Worldwide, infections are resuming their role as highly effective killing diseases, as current treatments are failing to respond to the growing problem of antimicrobial resistance (AMR). The social and economic burden of AMR seems ever rising, with health- and research-related organizations rushing to collaborate on a worldwide scale to find effective solutions. Resistant bacteria are spreading even in first-world nations, being found not only in healthcare-related settings, but also in food and in the environment. In this minireview, the impact of AMR in healthcare systems and the major bacteria behind it are highlighted. Ecological aspects of AMR evolution and the complexity of its molecular mechanisms are explained. Major concepts, such as intrinsic, acquired and adaptive resistance, as well as tolerance and heteroresistance, are also clarified. More importantly, the problematic of biofilms and their role in AMR, namely their main resistance and tolerance mechanisms, are elucidated. Finally, some of the most promising anti-biofilm strategies being investigated are reviewed. Much is still to be done regarding the study of AMR and the discovery of new anti-biofilm strategies. Gladly, considerable research on this topic is generated every day and increasingly concerted actions are being engaged globally to try and tackle this problem.

Design of an Antifungal Surface Embedding Liposomal Amphotericin B Through a Mussel Adhesive-Inspired Coating Strategy

Microbial colonization of urinary catheters remains a serious problem for medicine as it often leads to biofilm formation and infection. Among the approaches reported to deal with this problem, surfaces functionalization to render them with antimicrobial characteristics, comprises the most promising one. Most of these strategies, however, are designed to target bacterial biofilms, while fungal biofilms are much less taken into account. In real-life settings, fungi will be inevitably found in consortium with bacteria, especially in the field of biomaterials. The development of antifungal coating strategies to be combined with antibacterial approaches will be pivotal for the fight of biomaterial-associated infections. The main goal of the present study was, therefore, to engineer an effective strategy for the immobilization of liposomal amphotericin B (LAmB) on polydimethylsiloxane (PDMS) surfaces to prevent Candida albicans colonization. Immobilization was performed using a two-step mussel-inspired coating strategy, in which PDMS is first immersed in dopamine solution. Its polymerization results in the deposition of a thin adherent film, called polydopamine (pDA), which allowed the incorporation of LAmB, afterwards. Different concentrations of LAmB were screened in order to obtain a contact-killing surface with no release of LAmB. Surface characterization confirmed the polymerization of dopamine and further functionalization with LAmB yielded surfaces with less roughness and more hydrophilic features. The proposed coating strategy rendered the surfaces of PDMS with the ability to prevent the attachment of C. albicans and kill the adherent cells, without toxicity toward mammalian cells. Overall results showed that LAmB immobilization on a surface retained its antifungal activity and reduced toxicity, holding therefore a great potential to be applied for the design of urinary catheters. Since the sessile communities commonly found associated to these devices exhibit a polymicrobial nature, the next challenge will be to co-immobilize LAmB with antibacterial agents to prevent the establishment of catheter-associated urinary tract infections (CAUTI).

Unveiling the early events of Pseudomonas aeruginosa adaptation in cystic fibrosis airway environment using a long-term in vitro maintenance

Pseudomonas aeruginosa chronic infections are the major cause of high morbidity and mortality in cystic fibrosis (CF) patients due to the use of sophisticated mechanisms of adaptation, including clonal diversification into specialized CF-adapted phenotypes. In contrast to chronic infections, very little is known about what occurs after CF lungs colonization and at early infection stages. This study aims to investigate the early events of P. aeruginosa adaptation to CF environment, in particular, to inspect the occurrence of clonal diversification at early stages of infection development and its impact on antibiotherapy effectiveness. To mimic CF early infections, three P. aeruginosa strains were long-term grown in artificial sputum (ASM) over 10 days and phenotypic diversity verified through colony morphology characterization. Biofilm sub- and inhibitory concentrations of ciprofloxacin were applied to non- and diversified populations to evaluate antibiotic effectiveness on P. aeruginosa eradication. Our results demonstrated that clonal diversification might occur after ASM colonization and growth. However, this phenotypic diversification did not compromise ciprofloxacin efficacy in P. aeruginosa eradication since a biofilm minimal inhibitory dosage would be applied. The expected absence of mutators in P. aeruginosa populations led us to speculate that clonal diversification in the absence of ciprofloxacin treatments could be driven by niche specialization. Yet, biofilm sub-inhibitory concentrations of ciprofloxacin seemed to overlap niche specialization as "fitter" variants emerged, such as mucoid, small colony and pinpoint variants, known to be highly resistant to antibiotics. The pathogenic potential of all emergent colony morphotypes-associated bacteria, distinct from the wild-morphotypes, revealed that P. aeruginosa evolved to a non-swimming phenotype. Impaired swimming motility seemed to be one of the first evolutionary steps of P. aeruginosa in CF lungs that could pave the way for further adaptation steps including biofilm formation and progress to chronic infection. Based on our findings, impaired swimming motility seemed to be a candidate to disease marker of P. aeruginosa infection development. Despite our in vitro CF model represents a step forward towards in vivo scenario simulation and provided valuable insights about the early events, more and distinct P. aeruginosa strains should be studied to strengthen our results.

Developing a model for cystic fibrosis sociomicrobiology based on antibiotic and environmental stress

Cystic fibrosis (CF) infections are invariably biofilm-mediated and polymicrobial, being safe to assume that a myriad of factors affects the sociomicrobiology within the CF infection site and modulate the CF community dynamics, by shaping their social activities, overall functions, virulence, ultimately affecting disease outcome. This work aimed to assess changes in the dynamics (particularly on the microbial composition) of dual-/three-species biofilms involving CF-classical (Pseudomonas aeruginosa) and unusual species (Inquilinus limosus and Dolosigranulum pigrum), according to variable oxygen conditions and antibiotic exposure. Low fluctuations in biofilm compositions were observed across distinct oxygen environments, with dual-species biofilms exhibiting similar relative proportions and P. aeruginosa and/or D. pigrum populations dominating three-species consortia. Once exposed to antibiotics, biofilms displayed high resistance profiles, and microbial compositions, distributions, and microbial interactions significantly challenged. The antibiotic/oxygen environment supported such fluctuations, which enhanced for three-species communities. In conclusion, antibiotic therapy hugely disturbed CF communities' dynamics, inducing significant compositional changes on multispecies consortia. Clearly, multiple perturbations may disturb this dynamic, giving rise to various microbiological scenarios in vivo, and affecting disease phenotype. Therefore, an appreciation of the ecological/evolutionary nature within CF communities will be useful for the optimal use of current therapies and for newer breakthroughs on CF antibiotherapy.

Quorum sensing inhibition in Pseudomonas aeruginosa biofilms: new insights through network mining

Quorum sensing plays a pivotal role in Pseudomonas aeruginosa's virulence. This paper reviews experimental results on antimicrobial strategies based on quorum sensing inhibition and discusses current targets in the regulatory network that determines P. aeruginosa biofilm formation and virulence. A bioinformatics framework combining literature mining with information from biomedical ontologies and curated databases was used to create a knowledge network of potential anti-quorum sensing agents for P. aeruginosa. A total of 110 scientific articles, corresponding to 1,004 annotations, were so far included in the network and are analysed in this work. Information on the most studied agents, QS targets and methods is detailed. This knowledge network offers a unique view of existing strategies for quorum sensing inhibition and their main regulatory targets and may be used to readily access otherwise scattered information and to help generate new testable hypotheses. This knowledge network is publicly available at http://pcquorum.org/ .

Construction of antimicrobial peptide-drug combination networks from scientific literature based on a semi-automated curation workflow

Considerable research efforts are being invested in the development of novel antimicrobial therapies effective against the growing number of multi-drug resistant pathogens. Notably, the combination of different agents is increasingly explored as means to exploit and improve individual agent actions while minimizing microorganism resistance. Although there are several databases on antimicrobial agents, scientific literature is the primary source of information on experimental antimicrobial combination testing. This work presents a semi-automated database curation workflow that supports the mining of scientific literature and enables the reconstruction of recently documented antimicrobial combinations. Currently, the database contains data on antimicrobial combinations that have been experimentally tested against Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes and Candida albicans, which are prominent pathogenic organisms and are well-known for their wide and growing resistance to conventional antimicrobials. Researchers are able to explore the experimental results for a single organism or across organisms. Likewise, researchers may look into indirect network associations and identify new potential combinations to be tested. The database is available without charges.

Database URL:http://sing.ei.uvigo.es/antimicrobialCombination/

Co-immobilization of Palm and DNase I for the development of an effective anti-infective coating for catheter surfaces

Biomaterial-associated infections, in particular, catheter-associated infections (CAI) are a major problem in clinical practice due to their ability to resist antimicrobial treatment and the host immune system. This study aimed to co-immobilize the antimicrobial lipopeptide Palm and the enzyme DNase I to introduce both antimicrobial and anti-adhesive functionalities to polydimethylsiloxane (PDMS) material, using dopamine chemistry. Surface characterization confirmed the immobilization of both compounds and no leaching of Palm from the surfaces for up to 5days. Co-immobilization of both agents resulted in a bifunctional coating with excellent surface antimicrobial and anti-biofilm properties against both Staphylococcus aureus and Pseudomonas aeruginosa. The modified surfaces demonstrated superior biocompatibility. To better discriminate co-adhesion of both species on modified surfaces, PNA FISH (Fluorescence in situ hybridization using peptide nucleic acid probes) was employed, and results showed that P. aeruginosa was the dominant organism, with S. aureus adhering afterwards on P. aeruginosa agglomerates. Furthermore, Palm immobilization exhibited no propensity to develop bacterial resistance, as opposite to the immobilization of an antibiotic. The overall results highlighted that co-immobilization of Palm and DNase I holds great potential to be applied in the development of catheters.

STATEMENT OF SIGNIFICANCE

Catheter-associated infections (CAI) are the most common hospital-acquired infections worldwide. Several coating strategies have been proposed to fight these infections but most of them present some important limitations, including the emergence of resistant bacteria and toxicity concerns. The present work describes a two-step polydopamine-based surface modification strategy to successfully co-immobilize an antimicrobial peptide (Palm) and an enzyme targeting an important component of biofilm matrix (DNase I). This immobilization approach imparted polydimethylsiloxane surfaces with both anti-adhesive and antimicrobial properties against the adhesion of relevant bacteria as single and dual-species, with excellent stability and biocompatible and anti-biofilm properties, holding, therefore, great potential in the development of catheters able to prevent CAI.

Bio-Inspired Coating Strategies for the Immobilization of Polymyxins to Generate Contact-Killing Surfaces

Microbial colonization of indwelling devices remains a major concern in modern healthcare. Developing approaches to prevent biomaterial-associated infections (BAI) is, therefore, in great demand. This study aimed to immobilize two antimicrobial peptides (polymyxins B and E) onto polydimethylsiloxane (PDMS) using two polydopamine (pDA)-based approaches: the conventional two-step method involving the deposition of a pDA layer to which biomolecules are immobilized, and a one-step method where peptides are dissolved together with dopamine before its polymerization. Surface characterization confirms the immobilization of polymyxins onto PDMS at a non-toxic concentration. Immobilization of polymyxins using a one-step pDA-based approach is able to prevent Pseudomonas aeruginosa adhesion and kill a significant fraction of the adherent ones. Living cells adhered to these modified surfaces exhibit the same susceptibility pattern as cells adhered to unmodified surfaces, highlighting no resistance development. Results suggest that polymyxins immobilization holds a great potential as an additional antimicrobial functionality in the design of biomaterials.

Polydopamine-Mediated Immobilization of Alginate Lyase to Prevent P. aeruginosa Adhesion

Given alginate's contribution to Pseudomonas aeruginosa virulence, it has long been considered a promising target for interventional therapies, which have been performed by using the enzyme alginate lyase. In this work, instead of treating pre-established mucoid biofilms, alginate lyase is immobilized onto a surface as a preventive measure against P. aeruginosa adhesion. A polydopamine dip-coating strategy is employed for functionalization of polycarbonate surfaces. Enzyme immobilization is confirmed by surface characterization. Surfaces functionalized with alginate lyase exhibit anti-adhesive properties, inhibiting the attachment of the mucoid strain. Moreover, surfaces modified with this enzyme also inhibit the adhesion of the tested non-mucoid strain. Unexpectedly, treatment with heat-inactivated enzyme also inhibits the attachment of mucoid and non-mucoid P. aeruginosa strains. These findings suggest that the antibacterial performance of alginate lyase functional coatings is catalysis-independent, highlighting the importance of further studies to better understand its mechanism of action against P. aeruginosa strains.

Heteroresistance to colistin in Klebsiella pneumoniae is triggered by small colony variants sub-populations within biofilms

The emergence of Klebsiella pneumoniae multidrug-resistant strains paves the way to the re-introduction of colistin as a salvage therapy. However, recent planktonic studies have reported several cases of heteroresistance to this antimicrobial agent. The aim of this present work was to gain better understanding about the response of K. pneumoniae biofilms to colistin antibiotherapy and inspect the occurrence of heteroresistance in biofilm-derived cells. Biofilm formation and its susceptibility to colistin were evaluated through the determination of biofilm-cells viability. The profiling of planktonic and biofilm cell populations was conducted to assess the occurrence of heteroresistance. Colony morphology was further characterized in order to inspect the potential role of colistin in K. pneumoniae phenotypic differentiation. Results show that K. pneumoniae was susceptible to colistin in its planktonic form, but biofilms presented enhanced resistance. Population analysis profiles pointed out that K. pneumoniae manifest heteroresistance to colistin only when grown in biofilm arrangements, and it was possible to identify a resistant sub-population presenting a small colony morphology (diameter around 5 mm). To the best of our knowledge, this is the first report linking heteroresistance to biofilm formation and a morphological distinctive sub-population. Moreover, this is the first evidence that biofilm formation can trigger the emergence of heteroresistance in an apparently susceptible strain.

Biofilm formation of Brazilian meticillin-resistant Staphylococcus aureus strains: prevalence of biofilm determinants and clonal profiles

Biofilms plays an important role in medical-device-related infections. This study aimed to determine the factors that influence adherence and biofilm production, as well as the relationship between strong biofilm production and genetic determinants in clinical isolates of meticillin-resistant Staphylococcus aureus (MRSA). Fifteen strains carrying different chromosomal cassettes recovered from hospitalized patients were selected; five SCCmecII, five SCCmecIII and five SCCmecIV. The SCCmec type, agr group and the presence of the virulence genes (bbp, clfA, icaA, icaD, fnbB, bap, sasC and IS256) were assessed by PCR. PFGE and multilocus sequence typing (MLST) techniques were also performed. The initial adhesion and biofilm formation were examined by quantitative assays. The surface tension and hydrophobicity of the strains were measured by the contact angle technique to evaluate the association between these parameters and adhesion ability. SCCmecIII and IV strains were less hydrophilic, with a high value for the electron acceptor parameter and higher adhesion in comparison with SCCmecII strains. Only SCCmecIII strains could be characterized as strong biofilm producers. The PFGE showed five major pulsotypes (A-E); however, biofilm production was related to the dissemination of one specific PFGE clone (C) belonging to MLST ST239 (Brazilian epidemic clonal complex). The genes agrI, fnbB and IS256 in SCCmecIII strains were considered as genetic determinants associated with strong biofilm-formation by an ica-independent biofilm pathway. This study contributes to the understanding of biofilm production as an aggravating factor potentially involved in the persistence and severity of infections caused by multidrug-resistant MRSA belonging to this genotype.

Enabling systematic, harmonised and large-scale biofilms data computation: the Biofilms Experiment Workbench

BACKGROUND AND OBJECTIVE

Biofilms are receiving increasing attention from the biomedical community. Biofilm-like growth within human body is considered one of the key microbial strategies to augment resistance and persistence during infectious processes. The Biofilms Experiment Workbench is a novel software workbench for the operation and analysis of biofilms experimental data. The goal is to promote the interchange and comparison of data among laboratories, providing systematic, harmonised and large-scale data computation.

METHODS

The workbench was developed with AIBench, an open-source Java desktop application framework for scientific software development in the domain of translational biomedicine. Implementation favours free and open-source third-parties, such as the R statistical package, and reaches for the Web services of the BiofOmics database to enable public experiment deposition.

RESULTS

First, we summarise the novel, free, open, XML-based interchange format for encoding biofilms experimental data. Then, we describe the execution of common scenarios of operation with the new workbench, such as the creation of new experiments, the importation of data from Excel spreadsheets, the computation of analytical results, the on-demand and highly customised construction of Web publishable reports, and the comparison of results between laboratories.

CONCLUSIONS

A considerable and varied amount of biofilms data is being generated, and there is a critical need to develop bioinformatics tools that expedite the interchange and comparison of microbiological and clinical results among laboratories. We propose a simple, open-source software infrastructure which is effective, extensible and easy to understand. The workbench is freely available for non-commercial use at http://sing.ei.uvigo.es/bew under LGPL license.

A harmonised vocabulary for communicating and interchanging Biofilms experimental results

Biofilm studies are at the crossroads of Biology, Chemistry, Medicine, Material Science and Engineering, among other fields. Data harmonisation in Biofilms is therefore crucial to allow for researchers to collaborate, interchange, understand, and replicate studies at an inter-laboratory and inter-domain scale. The international Minimum Information About a Biofilms Experiment initiative has prepared a set of guidelines for documenting biofilms experiments and data, namely the minimum information checklist. This paper goes a step forward and describes a new ontology for the broad description of biofilm experiments and data. In such an interdisciplinary context we chose to rely on a common integration framework provided by a foundational ontology that facilitates the addition and extension of various sub-domain modules, and the consistent integration of terminology extracted from several existing ontologies, e.g. EXPO and ChEBI. The community is participating actively in the production of this resource, and it is already used by public biofilms-centred databases, such as BiofOmics, and bioinformatics tools, such as the Biofilms Experiment Workbench. This practical validation serves the purpose of disseminating the controlled vocabulary among researchers and identifying current limitations, glitches, and inconsistencies. Information branches will be added, extended or refactored according to user feedback and group discussions.

Pseudomonas aeruginosa Diversification during Infection Development in Cystic Fibrosis Lungs-A Review

Pseudomonas aeruginosa is the most prevalent pathogen of cystic fibrosis (CF) lung disease. Its long persistence in CF airways is associated with sophisticated mechanisms of adaptation, including biofilm formation, resistance to antibiotics, hypermutability and customized pathogenicity in which virulence factors are expressed according the infection stage. CF adaptation is triggered by high selective pressure of inflamed CF lungs and by antibiotic treatments. Bacteria undergo genetic, phenotypic, and physiological variations that are fastened by the repeating interplay of mutation and selection. During CF infection development, P. aeruginosa gradually shifts from an acute virulent pathogen of early infection to a host-adapted pathogen of chronic infection. This paper reviews the most common changes undergone by P. aeruginosa at each stage of infection development in CF lungs. The comprehensive understanding of the adaptation process of P. aeruginosa may help to design more effective antimicrobial treatments and to identify new targets for future drugs to prevent the progression of infection to chronic stages.

Use of an aerobic selector to overcome filamentous bulking in an activated sludge wastewater treatment plant

An urban wastewater treatment plant (WWTP) with two different parallel lines of treatment and located in the north of Portugal was studied during four months, following recurrent episodes of filamentous bulking caused by Sphaerotilus natans and eventual occurrences of Nocardioforms and Type 1863. An aerobic selector was introduced in both lines in the beginning of the studied period, suppressed in one of the lines during six weeks, and then put into operation again until the end of the study. A total of 14 filamentous bacteria morphotypes were identified. The results showed that the presence of an aerobic biological selector in continuous operation prevented the overgrowth of the filamentous Type 1863, of Nocardioforms and, in particular, of S. natans. Simultaneously, it allowed lowering the oxygen levels in the aeration tanks without negative consequences in the overall performance of the WWTP, namely bulking occurrence. Dissolved oxygen (DO) in the aeration tank varied initially between 2 and 3 mg/L, but the introduction of the selector enabled to lower it to 1-1.5 mg/L in the aeration tank and around 0.5 mg/L in the selector. A significant energy save was allowed, even considering the aeration of the selector. The results are more relevant if one considers the fact that the main cause of the bulking problems in this WWTP was the overgrowth of S. natans, a filamentous bacterium known to be stimulated by low DO levels.

Mini-review: Antimicrobial peptides and enzymes as promising candidates to functionalize biomaterial surfaces

Biomaterial-associated infections remain a serious concern in modern healthcare. The development of materials that can resist or prevent bacterial attachment constitutes a promising approach to dealing with this problem. Antimicrobial peptides (AMPs) and enzymes have been recognized as promising candidates for the new generation of antimicrobial surfaces. AMPs have been the focus of great interest in recent years owing to a low propensity for developing bacterial resistance, broad-spectrum activity, high efficacy at very low concentrations, target specificity, and synergistic action with classical antibiotics. Biofilm-dispersing enzymes have been shown to inhibit biofilm formation, detach established biofilm, and increase biofilm susceptibility to other antimicrobials. This review critically examines the potential of these protein-like compounds for developing antibacterial coatings by reporting their immobilization into different substrata using different immobilization strategies.

Antimicrobial synergism against different lineages of methicillin-resistant Staphylococcus aureus carrying SCCmec IV

AIM

To evaluate the synergistic activity of antimicrobial drugs against lineages of methicillin-resistant Staphylococcus aureus (MRSA) carrying SCCmec IV. The biofilm production and related genes were also detected.

METHODS AND RESULTS

Forty two MRSA isolates were tested for biofilm production and related genes. Biofilm/biomass susceptibility to gentamicin (G), linezolid (L), rifampicin (R) and vancomycin (V) was determined for six isolates from three lineages prevalent in Rio de Janeiro hospitals in concentrations ranging from 0·25 to 64 μg ml(-1). Biomass was evaluated by microtitre plate test and number of viable cells (CFU cm(-2)) and inspected by epifluorescence microscopy. All isolates presented the icaA and sasG genes, but only 38% were biofilm producers. There were 50 and 45% biomass reductions when concentrations ≥4 μg ml(-1) of R or L and ≥16 μg ml(-1) of G or V, respectively, were used. Synergism tests produced a 55% biomass reduction with R(2μgml-1) + G(16μgml-1), R(2μgml-1) + L(2μgml-1), R(2μgml-1) + V(4μgml-1), and L(2μgml-1) + V(4μgml-1). Number of viable cells was reduced from 2 to 3 logs with R(2μgml-1) + L(2μgml-1) and R(2μgml-1) + V(4μgml-1).

CONCLUSIONS

Synergisms involving R plus L and R plus V caused important reductions in biofilm/biomass and the number of viable cells. Drug combinations should be considered in the chemotherapies of MRSA-SCCmec IV infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biofilms in MRSA infections restrict the clinical choice of antimicrobials. Thus, knowledge of the best options for monotherapy and drug synergisms could improve clinical results.

Pathogenicity phenomena in three model systems: from network mining to emerging system-level properties

Understanding the interconnections of microbial pathogenicity phenomena, such as biofilm formation, quorum sensing and antimicrobial resistance, is a tremendous open challenge for biomedical research. Progress made by wet-lab researchers and bioinformaticians in understanding the underlying regulatory phenomena has been significant, with converging evidence from multiple high-throughput technologies. Notably, network reconstructions are already of considerable size and quality, tackling both intracellular regulation and signal mediation in microbial infection. Therefore, it stands to reason that in silico investigations would play a more active part in this research. Drug target identification and drug repurposing could take much advantage of the ability to simulate pathogen regulatory systems, host-pathogen interactions and pathogen cross-talking. Here, we review the bioinformatics resources and tools available for the study of the gram-negative bacterium Pseudomonas aeruginosa, the gram-positive bacterium Staphylococcus aureus and the fungal species Candida albicans. The choice of these three microorganisms fits the rationale of the review converging into pathogens of great clinical importance, which thrive in biofilm consortia and manifest growing antimicrobial resistance.

New trends in peptide-based anti-biofilm strategies: a review of recent achievements and bioinformatic approaches

Antimicrobial peptides (AMPs) have a broad spectrum of activity and unspecific mechanisms of action. Therefore, they are seen as valid alternatives to overcome clinically relevant biofilms and reduce the chance of acquired resistance. This paper reviews AMPs and anti-biofilm AMP-based strategies and discusses ongoing and future work. Recent studies report successful AMP-based prophylactic and therapeutic strategies, several databases catalogue AMP information and analysis tools, and novel bioinformatics tools are supporting AMP discovery and design. However, most AMP studies are performed with planktonic cultures, and most studies on sessile cells test AMPs on growing rather than mature biofilms. Promising preliminary synergistic studies have to be consubstantiated and the study of functionalized coatings with AMPs must be further explored. Standardized operating protocols, to enforce the repeatability and reproducibility of AMP anti-biofilm tests, and automated means of screening and processing the ever-expanding literature are still missing.

Effect of antimicrobial residues on early adhesion and biofilm formation by wild-type and benzalkonium chloride-adapted Pseudomonas aeruginosa

Antimicrobial residue deposition can change the physico-chemical properties of bacteria and surfaces and thus promote or impair bacterial adhesion. This study focuses on benzalkonium chloride (BC) deposition on polystyrene (PS) surfaces and the influence of this conditioning film on the physico-chemical properties of PS and on early adhesion and biofilm formation by Pseudomonas aeruginosa wild-type and its laboratory BC-adapted strain. The latter readily acquired the ability to grow in BC, and also exhibited physico-chemical surface changes. The existence of residues on PS surfaces altered their hydrophobicity and favoured adhesion as determined by the free energy and early adhesion characterization. Adapted bacteria revealed a higher ability to adhere to surfaces and to develop biofilms, especially on BC-conditioned surfaces, which thereby could enhance resistance to sanitation attempts. These findings highlight the importance of investigations concerning the antimicrobial deposition effect after cleaning procedures, which may encourage bacterial adhesion, especially of bacteria that have been previously exposed to chemical stresses.

Cinnamomum zeylanicum extract on the radiolabelling of blood constituents and the morphometry of red blood cells: in vitro assay

Effects of Cinnamomum zeylanicum (cinnamon) on the labelling of blood constituents with technetium-99m(99mTc) and on the morphology of red blood cells were studied. Blood samples from Wistar rats were incubated with cinnamon extract for 1 hour or with 0.9% NaCl, as control. Labelling of blood constituents with 99mTc was performed. Plasma (P) and blood cells (BC), soluble (SF-P and SF-BC) and insoluble (IF-P and IF-BC) fractions were separated. The radioactivity in each fraction was counted and the percentage of radioactivity incorporated (%ATI) was calculated. Blood smears were prepared, fixed, stained and the qualitative and quantitative morphological analysis of the red blood cells was evaluated. The data showed that the cinnamon extract decreased significantly (p<0.05) the %ATI on BC, IF-P and IF-BC. No modifications were verified on shape of red blood cells. Cinnamon extracts could alter the labelling of blood constituents with 99mTc, and although our results were obtained with animals, precaution is suggested in interpretations of nuclear medicine examinations involving the labelling of blood constituents in patients who are using cinnamon.

Influence of biofilm composition on the resistance to detachment

Bacillus cereus and Pseudomonas fluorescens were used to develop monoculture biofilms in a bioreactor rotating system using a stainless steel cylinder for biofilm formation. The biofilms were allowed to grow for 7 days, exposed continuously to a Reynolds number of agitation (ReA) of 2,400. Afterwards, the biofilms were characterised in terms of respiratory activity, amount of biomass, cellular density, cellular size and total and extracellular proteins and polysaccharides. The biofilm mechanical stability was assessed by sequential submission of the biofilms to increasing ReA, respectively, 4,000, 8,100, 12,100 and 16,100. The results showed that P. fluorescens biofilms were five times more active, had a higher amount of biomass, cellular density, a reduced cellular size and a four-fold higher amount of extracellular proteins and polysaccharides than B. cereus biofilms. The application of shear stress forces higher than the one under which the biofilm was formed (ReA = 2,400) caused biomass removal. The high percentage of removal occurred with the implementation of a ReA of 8,100 for both B. cereus and P. fluorescens biofilms. The total series of ReA did not give rise to total biofilm removal, as only about 76% of P. fluorescens biofilm mass and 53% of B. cereus biofilm mass were detached from the cylinders. This latter result evidences that B. cereus had a higher mechanical stability than P. fluorescens biofilms. The overall results demonstrate that P. fluorescens and B. cereus formed physiologically distinct biofilms, B. cereus biofilms mainly being constituted by cells and P. fluorescens biofilms largely constituted by extracellular proteins and polysaccharides. B. cereus biofilms had a substantially higher mechanical stability than P. fluorescens biofilms.

The role of hydrodynamic stress on the phenotypic characteristics of single and binary biofilms of Pseudomonas fluorescens

This study investigates the phenotype of turbulent (Re = 5,200) and laminar (Re = 2,000) flow-generated Pseudomonas fluorescens biofilms. Three P. fluorescens strains, the type strain ATCC 13525 and two strains isolated from an industrial processing plant, D3-348 and D3-350, were used throughout this study. The isolated strains were used to form single and binary biofilms. The biofilm physiology (metabolic activity, cellular density, mass, extracellular polymeric substances, structural characteristics and outer membrane proteins [OMP] expression) was compared. The results indicate that, for every situation, turbulent flow-generated biofilms were more active (p < 0.05), had more mass per cm(2) (p < 0.05), a higher cellular density (p < 0.05), distinct morphology, similar matrix proteins (p > 0.1) and identical (isolated strains -single and binary biofilms) and higher (type strain) matrix polysaccharides contents (p < 0.05) than laminar flow-generated biofilms. Flow-generated biofilms formed by the type strain revealed a considerably higher cellular density and amount of matrix polysaccharides than single and binary biofilms formed by the isolated strains (p < 0.05). Similar OMP expression was detected for the several single strains and for the binary situation, not dependent on the hydrodynamic conditions. Binary biofilms revealed an equal coexistence of the isolated strains with apparent neutral interactions. In summary, the biofilms formed by the type strain represent, apparently, the worst situation in a context of control. The results obtained clearly illustrate the importance of considering strain variation and hydrodynamics in biofilm development, and complement previous studies which have focused on physical aspects of structural and density differences.

Comparative antibacterial potential of selected aldehyde-based biocides and surfactants against planktonic Pseudomonas fluorescens

The antimicrobial efficacy of two aldehyde-based biocides (glutaraldehyde, GTA, and ortho-phthalaldehyde, OPA) and two surfactants (cetyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulphate, SDS) was tested against planktonic Pseudomonas fluorescens. The antimicrobial effects were evaluated by respiratory activity as a measure of the oxygen uptake rate, adenosine triphosphate (ATP) release, outer membrane proteins (OMP) expression and cellular colour changes. The results were compared with the bacterial characteristics without chemical treatment. Tests in the presence of bovine serum albumin (BSA), in order to mimic a disinfection process in the real situation under dirty conditions, were performed according to the European Standard EN-1276. P. fluorescens was completely inactivated with OPA (minimum bactericidal concentration, MBC = 0.5 mM) and CTAB (MBC = 5 mM) and was resistant to GTA and SDS. Only CTAB promoted cellular disruption and consequent ATP release. The antimicrobial action of the chemicals tested was significantly reduced when BSA was introduced into the bacterial cultures, increasing markedly the MBC values. Additionally, the presence of BSA acted as a disruption protective agent when CTAB was applied and stimulated the bacterial respiratory activity when lower concentrations of SDS were tested. The OMP of the bacterial cells was affected by the application of both surfactants. OMP expression remained unaltered after biocide treatment. Bacterial colour change was noticed after treatment with biocides and surfactants. In summary, P. fluorescens was extremely resistant to GTA and SDS, with antimicrobial action being quenched markedly by the reaction with BSA.

Validation of respirometry as a short-term method to assess the efficacy of biocides

This study shows that a short-term respirometric measurement based on the rate of oxygen uptake needed to oxidize glucose is a reliable and fast method to assess biocide efficacy against P. fluorescens cells. Respiratory activity using oxygen consumption rate, the determination of viable and nonviable cells using Live/Dead BacLight kit and colony formation units (CFU), were compared as indicators of the biocidal efficacy of ortho-phthalaldehyde (OPA). The results showed that determining the effect of OPA against P. fluorescens using the different methods leads to different conclusions. The minimum bactericidal concentration (MBC) was 80 mgl(-1), 100 mgl(-1) and 65 mgl(-1) respectively, using respiratory activity, viability using BacLight counts and culturability. The plate count method was shown to underestimate the biocidal action of OPA, whilst data from respirometry and viability using Live/Dead BacLight kit correlated strongly and were not statistically different when yellow cells were considered nonviable. Respirometry therefore represents an expeditious, non-destructive and accurate method to determine the antimicrobial action of biocides against aerobic heterotrophic bacteria.

Monitoring the effects of biocide treatment of Pseudomonas fluorescens biofilms formed under different flow regimes

The effectiveness of glutaraldehyde (GTA), a very common biocide for controlling biofilms formed by Pseudomonas fluorescens on stainless steel slides, in laminar and turbulent flow, was investigated. Tests were performed using a concentration of biocide of 200 mg L(-1) and a range of exposure times. The GTA action was assessed by means of activity tests and dry weight of the biofilms. The physical stability of the biofilm without biocide application and after exposure to GTA for different periods of time was also studied and evaluated through the variation of the mass of the deposit after submission to different rotation velocities. The results showed that, in all the situations studied, biofilms were not controlled after the treatment with biocide, since they remained on the metal surface and were still active. The results also demonstrated that the physical stability of the biofilms increased with biocide application.

A versatile reactor for continuous monitoring of biofilm properties in laboratory and industrial conditions

AIMS

The understanding of the dynamics of surface microbial colonization with concomitant monitoring of biofilm formation requires the development of biofilm reactors that enable direct and real-time evaluation under different hydrodynamic conditions.

METHODS AND RESULTS

This work proposes and discusses a simple flow cell reactor that provides a means to monitoring biofilm growth by periodical removing biofilm-attached slides for off-line, both non-destructive and destructive biofilm analyses. This is managed without the stoppage of the flow, thus reducing the contamination and the disturbance of the biofilm development. With this flow cell, biofilm growth and respiratory activity can be easily followed, either in well-defined laboratory conditions or in an industrial environment.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

The reproducible and typical biofilm development curves obtained, validated this flow cell and confirmed its potential for different biofilm-related studies, which can include biocidal treatment.

Comparison of two biocides--carbamate and glutaraldehyde--in the control of fouling in pulp and paper industry

Formation of fouling deposits is a serious problem facing paper mills. Despite the search for alternative methods, chemical biocides still represent the chief countermeasure to control microbial growth and general fouling buid-up in pulp and paper mills. The purpose of this work was to determine the effect of two biocides (carbamate and glutaraldehyde) on both planktonic cells and fouling layers of a paper machine system. A flow system was used for the study of fouling accumulation in an industrial white water circuit. Both biocides proved to be more effective in reducing the microbial loading of the white water circuit than the deposit accumulated on the stainless steel surfaces. Carbamate, in contrast to glutaraldehyde, had the ability of promoting cell agglomeration since the microbial loading decreased much more when the white water, treated with carbamate, was filtered through a filter-linen. The retention of suspended cells in the cellulose fibres acquires major importance since it is obtained by using an already existing physical process (filtration), which strongly enhances the overall microbial reduction obtained with the addition of the carbamate, without increasing the economic costs. These results also suggest that the use of conventional retention agents in pulp and paper processes can be efficient in controlling unwanted microbial effects.