Role of biofilms in neurosurgical device-related infections

Prospective Comparative Study of External Ventricular Drain Catheter Colonization: Antibiotic-Impregnated versus Conventional Drains

OBJECTIVE

Our aim was to compare the prevalence of biofilm formation on antibiotic-impregnated (AIC) versus standard (SC) external ventricular drain (EVD) catheters.

METHODS

From March 2018 to November 2020, all consecutive EVD catheters inserted in adult patients were included. After removal, EVD catheters were analyzed under scanning electronic microscopy, on both extraluminal and intraluminal faces. Standard culture of catheter tips was also performed.

RESULTS

Overall, 114 catheters were included in 101 patients. There were 48 AICs and 66 SCs. Standard culture showed that ventriculostomy-related colonization was more frequent in SC than in AIC (26 vs. 10%; P = 0.06). Gram-negative rods accounted for 25% of ventriculostomy-related colonization in AICs, and none was documented in SCs. Scanning electronic microscopy observation showed mature biofilm on more than 80% of catheters, without significant difference between catheter type. Also, there was no difference between extraluminal and intraluminal colonization rate. There were 2 ventriculostomy-related infections in each group (5% and 3% among AICs and SCs respectively; P = 1).

CONCLUSIONS

Mature biofilm presence on the intraluminal and the extraluminal faces is similar on AICs and SCs. Accordingly, AICs do not seem to efficiently prevent biofilm formation on EVD catheters. The impact of AICs on the microbiological epidemiology of colonizing biofilm should be further evaluated.

Characteristics and outcomes of cerebrospinal fluid shunt and drain-associated infections

INTRODUCTION

Data on infections associated with cerebrospinal fluid shunt (CSF-S) or device-associated infection (CSF-SDI) are limited in adults. We performed a retrospective study to describe characteristics, management, and outcome of CSF-SDI.

METHODS

All patients with CSF-SDI and admitted to our institution from January 2013 to December 2019 were included.

RESULTS

Among 50 patients, fifty-six episodes of CSF-SDI (41 external ventricular device-associated infections (CSF-D) and 15 other shunt infections (CSF-S) were included. The incidence of CSF-SDI was 11.9 %. Fever was the most common symptom (81 %). Enterobacterales were more prevalent in CSF-S than in CSF-D (20 % vs 53 %, p = 0.02). As regards CSF-D, deceased patients (11/41, 27 %) more frequently had a Glasgow coma scale score decreasing from baseline (p < 0.01), lower glycorrhachia (p < 0.01), a higher protein level in CSF (p = 0.001) and a positive control CSF culture (p = 0.031).

CONCLUSIONS

CSF-SDIs are rare but with a high mortality rate. Mortality was more closely related to the infection than to comorbidities or underlying neurosurgical disease. A second CSF analysis significantly helped to detect patients with CSF-D with a poor prognosis.

Utilizing Immunoinformatics to Target Brain Tumors; An Aid to Current Neurosurgical Practice

Context: Despite major advancements in the field, the current neurosurgical practice requires an interdisciplinary approach. It is known that surgical practice and other cancer-eliminating treatments can be combined for optimal results. However, recent attempts have failed to address many debilitating conditions, indicating an emergent need for novel interdisciplinary therapeutic approaches. Evidence Acquisition: We searched PubMed and Google Scholar for the keywords “immunoinformatics,” “in silico,” “neurology,” and “neurosurgery.” Without time restriction. Results: The immune system is versatile because it is involved in physiological brain function and affects the course of central nervous system (CNS) disease and infection. A novel approach combines neurosurgery and immunoinformatics for optimal results. For instance, brain tumors, such as glioblastoma multiforme (GBM), are still associated with a severely reduced survival of patients, and resection of tumors may provide little help. In silico approaches could help to identify molecular pathways and design immunotherapies for such conditions at a significantly increased speed compared to traditional vaccinology approaches. Conclusions: The neurosurgical practice could be affected by different infectious organisms. These organisms can be targeted by in silico vaccinology techniques. Here, we provide a brief overview of bioinformatics/immunoinformatics and discuss the possible role of immunoinformatics in neurosurgery. In light of the current Coronavirus disease-2019 (COVID-19) epidemic, projections for future studies are also included.

Outcome of Patients with Surgical Site Infection after Craniotomy

Background: The management of surgical site infection (SSI) after craniotomy remains challenging with few existing recommendations. Patients and Methods: We reviewed the medical files of patients who underwent surgery between 2009 and 2018 to manage infection after craniotomy at our tertiary hospital. The Cox proportional hazards model and the Renyi test were used to investigate the association between relapse or all-cause mortality and selected variables. We compared infections with and without intra-cranial involvement using the Fisher test and the Wilcoxon rank sum test. Results: Seventy-seven episodes of infection were identified in 58 patients. The proportion of relapse was estimated to be 32.2% (± standard deviation [SD] 6.9) at five years. Intra-cranial infection was present in 15.6% of the cases (n = 12). Bone flap was removed in the majority of cases (93.5%) and the overall median duration of antibiotic therapy was six weeks (interquartile range [IQR] 6-12 weeks). Staphylococcus aureus was associated with a higher risk of relapse (p = 0.037). The administration of parenteral antibiotic agents (p = 0.012) and bone flap removal (p = 0.0051) were correlated with less relapse. In contrast, immunosuppressive drug use and radiotherapy were correlated with a higher risk of relapse (p = 0.014 and p = 0.031, respectively) and a higher all-cause mortality (p = 0.0093 and p < 0.0001, respectively). We found no difference between infections with and without intra-cranial involvement. Conclusions: Bone flap removal and parenteral antibiotic agents remain important in the management of SSI after craniotomy and were associated with less relapse in our study. More studies are needed to better determine the optimal treatment of this infection.

Bacterial Biofilm Growth on 3D-Printed Materials

Recent advances in 3D printing have led to a rise in the use of 3D printed materials in prosthetics and external medical devices. These devices, while inexpensive, have not been adequately studied for their ability to resist biofouling and biofilm buildup. Bacterial biofilms are a major cause of biofouling in the medical field and, therefore, hospital-acquired, and medical device infections. These surface-attached bacteria are highly recalcitrant to conventional antimicrobial agents and result in chronic infections. During the COVID-19 pandemic, the U.S. Food and Drug Administration and medical officials have considered 3D printed medical devices as alternatives to conventional devices, due to manufacturing shortages. This abundant use of 3D printed devices in the medical fields warrants studies to assess the ability of different microorganisms to attach and colonize to such surfaces. In this study, we describe methods to determine bacterial biofouling and biofilm formation on 3D printed materials. We explored the biofilm-forming ability of multiple opportunistic pathogens commonly found on the human body including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus to colonize eight commonly used polylactic acid (PLA) polymers. Biofilm quantification, surface topography, digital optical microscopy, and 3D projections were employed to better understand the bacterial attachment to 3D printed surfaces. We found that biofilm formation depends on surface structure, hydrophobicity, and that there was a wide range of antimicrobial properties among the tested polymers. We compared our tested materials with commercially available antimicrobial PLA polymers.

Artificial Sweeteners Negatively Regulate Pathogenic Characteristics of Two Model Gut Bacteria, E. coli and E. faecalis

Artificial sweeteners (AS) are synthetic sugar substitutes that are commonly consumed in the diet. Recent studies have indicated considerable health risks which links the consumption of AS with metabolic derangements and gut microbiota perturbations. Despite these studies, there is still limited data on how AS impacts the commensal microbiota to cause pathogenicity. The present study sought to investigate the role of commonly consumed AS on gut bacterial pathogenicity and gut epithelium-microbiota interactions, using models of microbiota (Escherichia coli NCTC10418 and Enterococcus faecalis ATCC19433) and the intestinal epithelium (Caco-2 cells). Model gut bacteria were exposed to different concentrations of the AS saccharin, sucralose, and aspartame, and their pathogenicity and changes in interactions with Caco-2 cells were measured using in vitro studies. Findings show that sweeteners differentially increase the ability of bacteria to form a biofilm. Co-culture with human intestinal epithelial cells shows an increase in the ability of model gut bacteria to adhere to, invade and kill the host epithelium. The pan-sweet taste inhibitor, zinc sulphate, effectively blocked these negative impacts. Since AS consumption in the diet continues to increase, understanding how this food additive affects gut microbiota and how these damaging effects can be ameliorated is vital.

Surgical Site Infections after glioblastoma surgery: results of a multicentric retrospective study

BACKGROUND

The effects of surgical site infections (SSI) after glioblastoma surgery on patient outcomes are understudied. The aim of this retrospective multicenter study was to evaluate the impact of SSI on the survival of glioblastoma patients.

METHODS

Data from SSI cases after glioblastoma surgeries between 2009 and 2016 were collected from 14 French neurosurgical centers. Collected data included patient demographics, previous medical history, risk factors, details of the surgical procedure, radiotherapy/chemotherapy, infection characteristics, and infection management. Similar data were collected from gender- and age-paired control individuals.

RESULTS

We used the medical records of 77 SSI patients and 58 control individuals. 13 were excluded. Our analyses included data from 64 SSI cases and 58 non-infected glioblastoma patients. Infections occurred after surgery for primary tumors in 38 cases (group I) and after surgery for a recurrent tumor in 26 cases (group II). Median survival was 381, 633, and 547 days in patients of group I, group II, and the control group, respectively. Patients in group I had significantly shorter survival compared to the other two groups (p < 0.05). The one-year survival rate of patients who developed infections after surgery for primary tumors was 50%. Additionally, we found that SSIs led to postoperative treatment discontinuation in 30% of the patients.

DISCUSSION

Our findings highlighted the severity of SSIs after glioblastoma surgery, as they significantly affect patient survival. The establishment of preventive measures, as well as guidelines for the management of SSIs, is of high clinical importance.

The Development of a Pipeline for the Identification and Validation of Small-Molecule RelA Inhibitors for Use as Anti-Biofilm Drugs

Biofilm infections have no approved effective medical treatments and can only be disrupted via physical means. This means that any biofilm infection that is not addressable surgically can never be eliminated and can only be managed as a chronic disease. Therefore, there is an urgent need for the development of new classes of drugs that can target the metabolic mechanisms within biofilms which render them recalcitrant to traditional antibiotics. Persister cells within the biofilm structure may play a large role in the enhanced antibiotic recalcitrance of bacteria biofilms. Biofilm persister cells can be resistant to up to 1000 times the minimal inhibitory concentrations of many antibiotics, as compared to their planktonic envirovars; they are thought to be the prokaryotic equivalent of metazoan stem cells. Their metabolic resistance has been demonstrated to be an active process induced by the stringent response that is triggered by the ribosomally-associated enzyme RelA in response to amino acid starvation. This 84-kD pyrophosphokinase produces the “magic spot” alarmones, collectively called (p)ppGpp. These alarmones act by directly regulating transcription by binding to RNA polymerase. These transcriptional changes lead to a major shift in cellular function to both upregulate oxidative stress-combating enzymes and down regulate major cellular functions associated with growth and replication. These changes in gene expression produce the quiescent persister cells. In this work, we describe a hybrid in silico laboratory pipeline for identifying and validating small-molecule inhibitors of RelA for use in the combinatorial treatment of bacterial biofilms as re-potentiators of classical antibiotics.

Evidence for inoculum size and gas interfaces as critical factors in bacterial biofilm formation on magnesium implants in an animal model

Infections of medical implants caused by bacterial biofilms are a major clinical problem. Bacterial colonization is predicted to be prevented by alkaline magnesium surfaces. However, in experimental animal studies, magnesium implants prolonged infections. The reason for this peculiarity likely lies within the ‒still largely hypothetical‒ mechanism by which infection arises. Investigating subcutaneous magnesium implants infected with bioluminescent Pseudomonas aeruginosa via in vivo imaging, we found that the rate of implant infections was critically dependent on a surprisingly high quantity of injected bacteria. At high inocula, bacteria were antibiotic-refractory immediately after infection. High cell densities are known to limit nutrient availability, restricting proliferation and trigger quorum sensing which could both contribute to the rapid initial resistance. We propose that gas bubbles such as those formed during magnesium corrosion, can then act as interfaces that support biofilm formation and permit long-term survival. This model could provide an explanation for the apparent ineffectiveness of innovative contact-dependent bactericidal implant surfaces in patients. In addition, the model points toward air bubbles in tissue, either by inclusion during surgery or by spontaneous gas bubble formation later on, could constitute a key risk factor for clinical implant infections.

Natural history of ventriculostomy-related infection under appropriate treatment and risk factors of poor outcome: a retrospective study

OBJECTIVE

The authors aimed to describe the natural history of ventriculostomy-related infections (VRIs) under appropriate treatment and to assess risk factors for poor outcome.

METHODS

All patients older than 18 years in whom an external ventricular drain (EVD) had been implanted and who had developed a VRI requiring treatment were included in this retrospective study. D0 was defined as the first day of antibiotic administration. Clinical and biological parameters were compared each day beginning with D1 and ending with D10 to those of D0. The authors defined D0 in a control group as the day a CSF culture came back positive, without any sign of infection. The authors then searched for poor prognostic factors in the VRI group.

RESULTS

Among 567 patients requiring an EVD between January 2007 and October 2017, 39 developed a VRI. Most were monomicrobial infections, and 47 microbes were responsible (45% were gram-positive cocci). Clinical parameters differed significantly from the control group during the first 2 days and then returned to baseline. The CSF parameters differed significantly from the control group for a longer period, returning to baseline after 5 days. CSF sterilization occurred in a median time of 2 days. An intrathecal route or EVD exchange was not associated with a poor outcome. No clinical or biological parameter between D3 and D5 was linked to outcome.

CONCLUSIONS

Clinical status improved faster than CSF parameters (before and after D5, respectively). Some CSF parameters remained abnormal until D10. Body temperature and microbiological cultures normalized faster than other parameters.

Management and prevention of cranioplasty infections

BACKGROUND

Infection may complicate the outcome of cranial repair with significant additional morbidity, related to hospitalization, surgery and long antibiotic therapy, that may become even dramatic in case of multi-resistant germs and in particular in the paediatric population. Additionally, the economic costs for the health system are obvious. Moreover, surgical decisions concerning the timing of cranioplasty and choice of the material may be strongly affected by the risk of infection. Despite, management and prevention of cranioplasty infections are not systematically treated through the literature so far.

METHODS

We reviewed pertinent literature dealing with cranioplasty infection starting from the diagnosis to treatment options, namely conservative versus surgical ones. Our institutional bundle, specific to the paediatric population, is also presented. This approach aims to significantly reduce the risk of infection in first-line cranioplasty and redo cranioplasty after previous infection.

CONCLUSIONS

A thorough knowledge and understanding of risk factors may lead to surgical strategies and bundles, aiming to reduce infectious complications of cranioplasty. Finally, innovation in materials used for cranial repair should also aim to enhance the antimicrobial properties of these inert materials.

Gram-Positive Rods on a Cerebrospinal Fluid Gram Stain

Cerebrospinal fluid (CSF) access device placement in the pediatric population presents challenges due to the development of infections following placement, access or revision, and/or shunt malfunctions. Here we report an unusual pediatric case of L. monocytogenes ventriculitis/VP shunt (VPS) infection and associated pseudocyst with an emphasis on the importance of VPS removal in clearing the infection due to biofilm formation.

A new model for biofilm formation and inflammatory tissue reaction: intraoperative infection of a cranial implant with Staphylococcus aureus in rats

BACKGROUND

Implant failure is a severe and frequent adverse event in all areas of neurosurgery. It often involves infection with biofilm formation, accompanied by inflammation of surrounding tissue, including the brain, and bone loss. The most common bacteria involved are Staphylococcus aureus. We here test whether intraoperative infection of intracranial screws with Staphylococcus aureus would lead to biofilm formation and inflammatory tissue reaction in rats.

METHODS

Two titanium screws were implanted in the cranium of Sprague-Dawley rats, anesthetized with xylazine (4 mg/kg) and ketamine (75 mg/kg). Prior to the implantation of the screws, Staphylococcus aureus was given in the drill holes; controls received phosphate-buffered saline (PBS). Rats were euthanized 2, 10 and 21 days after surgery to remove the screws for analysis of biofilm formation with a confocal laser scanning microscope. The surrounding tissue composed of soft tissue and bone, as well as the underlying brain tissue, was evaluated for inflammation, bone remodeling, foreign body reaction and fibrosis after H&E staining.

RESULTS

Intraoperative application of Staphylococcus aureus leads to robust and stable biofilm formation on the titanium implants on days 10 and 21 after surgery, while no bacteria were found in controls. This was accompanied by a substantial inflammatory response of peri-implant tissue after infection, also affecting the underlying brain tissue.

CONCLUSIONS

Intraoperative infection of implants with Staphylococcus aureus in rats may be useful as a tool to model new implant materials and surfaces on biofilm formation and inflammatory tissue reaction in vivo.

2017 Infectious Diseases Society of America's Clinical Practice Guidelines for Healthcare-Associated Ventriculitis and Meningitis

The Infectious Diseases Society of America (IDSA) Standards and Practice Guidelines Committee collaborated with partner organizations to convene a panel of 10 experts on healthcare-associated ventriculitis and meningitis. The panel represented pediatric and adult specialists in the field of infectious diseases and represented other organizations whose members care for patients with healthcare-associated ventriculitis and meningitis (American Academy of Neurology, American Association of Neurological Surgeons, and Neurocritical Care Society). The panel reviewed articles based on literature reviews, review articles and book chapters, evaluated the evidence and drafted recommendations. Questions were reviewed and approved by panel members. Subcategories were included for some questions based on specific populations of patients who may develop healthcare-associated ventriculitis and meningitis after the following procedures or situations: cerebrospinal fluid shunts, cerebrospinal fluid drains, implantation of intrathecal infusion pumps, implantation of deep brain stimulation hardware, and general neurosurgery and head trauma. Recommendations were followed by the strength of the recommendation and the quality of the evidence supporting the recommendation. Many recommendations, however, were based on expert opinion because rigorous clinical data are not available. These guidelines represent a practical and useful approach to assist practicing clinicians in the management of these challenging infections.

Biofilm-associated infection: the hidden face of cerebrospinal fluid shunt malfunction

Diagnosis of cerebrospinal fluid (CSF) shunt infection is difficult. Growing evidence links this pattern to biofilm-associated infections (BAI). Biofilm may explain the indolent development of the infection, and the poor efficiency of traditional microbiologic methods. We report the case of a patient admitted for hydrocephalus associated to CSF shunt malfunction. None of the clinical, serum, or CSF laboratory findings were in favor of an infectious process. Only scanning electron microscopy (SEM) revealed the presence of biofilm. Hence, despite a broad CSF shunt infection definition, some infections could remain undiagnosed by the traditional approach. This study is the first to provide some direct evidence for bacterial biofilm-associated CSF shunt infection.

Successful treatment of biofilm infections using shock waves combined with antibiotic therapy

Many bacteria secrete a highly hydrated framework of extracellular polymer matrix on suitable substrates and embed within the matrix to form a biofilm. Bacterial biofilms are observed on many medical devices, endocarditis, periodontitis and lung infections in cystic fibrosis patients. Bacteria in biofilm are protected from antibiotics and >1,000 times of the minimum inhibitory concentration may be required to treat biofilm infections. Here, we demonstrated that shock waves could be used to remove Salmonella, Pseudomonas and Staphylococcus biofilms in urinary catheters. The studies were extended to a Pseudomonas chronic pneumonia lung infection and Staphylococcus skin suture infection model in mice. The biofilm infections in mice, treated with shock waves became susceptible to antibiotics, unlike untreated biofilms. Mice exposed to shock waves responded to ciprofloxacin treatment, while ciprofloxacin alone was ineffective in treating the infection. These results demonstrate for the first time that, shock waves, combined with antibiotic treatment can be used to treat biofilm infection on medical devices as well as in situ infections.

Clinical and microbiological aspects of biofilm-associated surgical site infections

While microbial biofilms have been recognized as being ubiquitous in nature for the past 40 years, it has only been within the past 20 years that clinical practitioners have realized that biofilm play a significant role in both device-related and tissue-based infections. The global impact of surgical site infections (SSIs) is monumental and as many as 80 % of these infections may involve a microbial biofilm. Recent studies suggest that biofilm- producing organisms play a significant role in persistent skin and soft tissue wound infections in the postoperative surgical patient population. Biofilm, on an organizational level, allows bacteria to survive intrinsic and extrinsic defenses that would inactivate the dispersed (planktonic) bacteria. SSIs associated with biomedical implants are notoriously difficult to eradicate using antibiotic regimens that would typically be effective against the same bacteria growing under planktonic conditions. This biofilm-mediated phenomenon is characterized as antimicrobial recalcitrance, which is associated with the survival of a subset of cells including "persister" cells. The ideal method to manage a biofilm-mediated surgical site wound infection is to prevent it from occurring through rational use of antibiotic prophylaxis, adequate skin antisepsis prior to surgery and use of innovative in-situ irrigation procedures; together with antimicrobial suture technology in an effort to promote wound hygiene at the time of closure; once established, biofilm removal remains a significant clinical problem.

Ventricular shunt infections: immunopathogenesis and clinical management

Ventricular shunts are the most common neurosurgical procedure performed in the United States. This hydrocephalus treatment is often complicated by infection of the device with biofilm-forming bacteria. In this review, we discuss the pathogenesis of shunt infection, as well as the implications of the biofilm formation on treatment and prevention of these infections. Many questions remain, including the contribution of glia and the impact of inflammation on developmental outcomes following infection. Immune responses within the CNS must be carefully regulated to contain infection while minimizing bystander damage; further study is needed to design optimal treatment strategies for these patients.

Filaments in curved streamlines: Rapid formation of Staphylococcus aureus biofilm streamers

Biofilms are surface-associated conglomerates of bacteria that are highly resistant to antibiotics. These bacterial communities can cause chronic infections in humans by colonizing, for example, medical implants, heart valves, or lungs. Staphylococcus aureus, a notorious human pathogen, causes some of the most common biofilm-related infections. Despite the clinical importance of S. aureus biofilms, it remains mostly unknown how physical effects, in particular flow, and surface structure influence biofilm dynamics. Here we use model microfluidic systems to investigate how environmental factors, such as surface geometry, surface chemistry, and fluid flow affect biofilm development in S. aureus. We discovered that S. aureus rapidly forms flow-induced, filamentous biofilm streamers, and furthermore if surfaces are coated with human blood plasma, streamers appear within minutes and clog the channels more rapidly than if the channels are uncoated. To understand how biofilm streamer filaments reorient in flows with curved streamlines to bridge the distances between corners, we developed a mathematical model based on resistive force theory of slender filaments. Understanding physical aspects of biofilm formation in S. aureus may lead to new approaches for interrupting biofilm formation of this pathogen.

From in vitro to in vivo Models of Bacterial Biofilm-Related Infections

The influence of microorganisms growing as sessile communities in a large number of human infections has been extensively studied and recognized for 30–40 years, therefore warranting intense scientific and medical research. Nonetheless, mimicking the biofilm-life style of bacteria and biofilm-related infections has been an arduous task. Models used to study biofilms range from simple in vitro to complex in vivo models of tissues or device-related infections. These different models have progressively contributed to the current knowledge of biofilm physiology within the host context. While far from a complete understanding of the multiple elements controlling the dynamic interactions between the host and biofilms, we are nowadays witnessing the emergence of promising preventive or curative strategies to fight biofilm-related infections. This review undertakes a comprehensive analysis of the literature from a historic perspective commenting on the contribution of the different models and discussing future venues and new approaches that can be merged with more traditional techniques in order to model biofilm-infections and efficiently fight them.

Pilot-study on the influence of carrier gas and plasma application (open resp. delimited) modifications on physical plasma and its antimicrobial effect against Pseudomonas aeruginosa and Staphylococcus aureus

INTRODUCTION

Physical plasma is a promising new technology regarding its antimicrobial effects. This is especially accounting for treatment of bacterial infection of chronic wounds. Plasma can be generated with different carrier gases causing various biological effects. Screening of different carrier gases and plasma generation setups is therefore needed to find suitable compositions for highly effective antimicrobial plasma treatments and other applications.

METHOD

The plasma source used was a radio-frequency plasma jet which generates tissue tolerable plasma (TTP). The study compared the antimicrobial efficacy of air, argon, or helium plasma alone or admixed with 0.1%, 0.5%, and 1% oxygen against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). Treatment took place in an environmentally open and delimited system. Therefore, bacteria were plated on agar and treated with plasma in a punctiform manner. The resulting inhibition zones were measured and the reduction factors were calculated by colony counting, respectively.

RESULTS

For S. aureus and P. aeruginosa, inhibition zones and overall reduction of colony forming units (CFU) on the agar plate were observed while an accumulative reduction of CFU dominated for S. aureus. The highest antimicrobial effect was shown in form of an inhibition zone for argon plasma with 0.1% oxygen admixture for both species. S. aureus was more sensitive for helium plasma with >0.1% oxygen admixture compared to P. aeruginosa which in turn was more sensitive for argon plasma with and without oxygen. The efficacy of air plasma was very low in comparison to the other gases. The treatment in a closed system predominantly enhanced the antimicrobial effect. The effect intensity varied for each treatment time and gas mixtures.

DISCUSSION

As expected, the antimicrobial effect mostly increased when increasing oxygen admixture to the carrier gases. The variation in bacterial growth and inhibition after exposure to different plasma gas compositions could be due to a varying generation of reactive oxygen species or radiation.

CONCLUSION

The applied plasma in a "closed system" accumulates bactericidal plasma species and might increase antimicrobial efficacy in clinical settings as in wound management involving multi-drug resistant bacteria.

Synergistic antibacterial efficacy of early combination treatment with tobramycin and quorum-sensing inhibitors against Pseudomonas aeruginosa in an intraperitoneal foreign-body infection mouse model

OBJECTIVES

Quorum sensing (QS)-deficient Pseudomonas aeruginosa biofilms formed in vitro are more susceptible to tobramycin than QS-proficient P. aeruginosa biofilms, and combination treatment with a QS inhibitor (QSI) and tobramycin shows synergistic effects on the killing of in vitro biofilms. We extended these results to an in vivo P. aeruginosa foreign-body biofilm model. The effect of treatment initiated prophylactically was compared with treatment initiated 11 days post-insertion.

METHODS

Silicone tube implants pre-colonized with wild-type P. aeruginosa were inserted into the peritoneal cavity of BALB/c mice. Mice were treated with intraperitoneal or subcutaneous injections of the QSIs furanone C-30, ajoene or horseradish juice extract in combination with tobramycin. Mice were euthanized on day 1, 2, 3 or 14 post-infection for the estimation of quantitative bacteriology, histopathology and cytokine measurements.

RESULTS

Combination treatment of P. aeruginosa resulted in a significantly lower cfu per implant as compared with the placebo groups for all QSIs tested. For early-initiated treatment, a significant difference in clearing was also observed between the combination group and the single-treatment groups, and between the placebo group and the single-treatment groups. In one case a significant difference in clearing was found between the two single-treatment groups.

CONCLUSIONS

Synergistic antimicrobial efficacy could be achieved when treating mice with both a QSI and tobramycin, resulting in an increased clearance of P. aeruginosa in a foreign-body infection model. Our study highlights the important prospects in developing an early combinatory treatment strategy for chronic infections.

Adherence of Streptococcus pneumoniae to polystyrene plates and epithelial cells and the antiadhesive potential of albumin and xylitol

Aimed to prevent Streptococcus pneumoniae biofilm infections, we studied the adherence of nine pneumococcal strains to polystyrene plates and on epithelial cells and the antiadhesive effect of albumin and xylitol. The adherence was variable among strains, but there was a good correlation between their adherent ability and binding to abiotic material and cells. Strains of serotypes 6B and 23F were the most adherent organisms, whereas serotype 3 strains were the least adherent. Human serum albumin (HSA) enhanced bacterial growth at low concentrations (0.5-2.5%) but inhibited it at 10%. Xylitol inhibited bacterial growth of all strains at concentrations ranging from 5 to 15%. Exposure to 0.5-5% HSA in solubilized form and to 5% HSA precoating of plates diminished adherence to polystyrene >80% for all strains, except for serotype 3 strains. Contrarily, 0.5 and 5% xylitol did not diminish significantly pneumococcal adherence to polystyrene plates or on epithelial cells. Our results suggest that 1) the potential application of HSA coatings on medical devices to inhibit pneumococcal adherence and 2) the possible beneficial effect of xylitol in preventing some pneumococcal infections could be because of its antimicrobial activity rather than to an antiadhesive effect.

Direct demonstration of Staphylococcus biofilm in an external ventricular drain in a patient with a history of recurrent ventriculoperitoneal shunt failure

External ventricular drains (EVD) are associated with a high infection rate. Early detection of infection is frequently problematic due to a lack of clinical signs and the time period required for culturing. Bacterial biofilms have been suggested to play an important role in the infection of EVD, but direct evidence is as yet lacking. We report the case of a 17- year-old male with Dandy-Walker malformation who presented with headache, nausea and drowsiness; a CT scan revealed enlarged ventricles. The patient had a history of ventriculoperitoneal shunt revision 3 weeks prior to admission. The shunt was removed on suspicion of infection and an EVD placed. Daily surveillance cultures through the EVD were negative and the EVD was replaced on day 5. Examination of the initial EVD by confocal microscopy demonstrated clear intraluminal biofilm formation; molecular analysis by PCR identified Staphylococcus aureus resident on the catheter. To our knowledge, this is the first direct demonstration of an intraluminal biofilm compromising an EVD. Despite the presence of biofilm on this catheter, the patient demonstrated no clinical signs of infection, and the routine surveillance culture was negative. Undetected biofilm may pose a latent risk on EVD and other neurosurgical catheters.

Characterization of biofilm formed by human-derived nanoparticles

AIM

Microbial biofilm matrix contains polysaccharides and proteins and can require extracellular nucleic acids for initial formation. Experiments were designed to identify infectious pathogens in human aneurysms and to characterize biofilm formed by calcified human arterial-derived nanoparticles.

MATERIALS & METHOD

A total of 26 different microbial pathogens were isolated from 48 inflammatory aneurysms. Consistent amounts (0.49 McFarland units) of nanoparticles derived from similar tissue were seeded into 24-well plates and cultured for 21 days in the absence (control) or presence of RNase, tetracycline or gentamicin.

RESULTS

Control biofilm developed within 14 days, as detected by concanavalin A and BacLight Green staining. The formation of biofilm in wells treated with RNase was not different from the control; however, gentamicin partially inhibited and tetracycline completely inhibited biofilm formation. Therefore, nanoparticle biofilm retains some characteristics of conventional bacterial biofilm and requires protein-calcium interactions, although extracellular RNA is not required.

CONCLUSION

This model system may also allow study of nanosized vesicles derived from donor tissue, including any microbes present, and could provide a useful tool for in vitro investigation of nanoparticle biofilm formation.

Inactivation of the rhlA gene in Pseudomonas aeruginosa prevents rhamnolipid production, disabling the protection against polymorphonuclear leukocytes

Many of the virulence factors produced by the opportunistic human pathogen Pseudomonas aeruginosa are quorum-sensing (QS) regulated. Among these are rhamnolipids, which have been shown to cause lysis of several cellular components of the human immune system, e.g. monocyte-derived macrophages and polymorphonuclear leukocytes (PMNs). We have previously shown that rhamnolipids produced by P. aeruginosa cause necrotic death of PMNs in vitro. This raises the possibility that rhamnolipids may function as a 'biofilm shield'in vivo, which contributes significantly to the increased tolerance of P. aeruginosa biofilms to PMNs. In the present study, we demonstrate the importance of the production of rhamnolipids in the establishment and persistence of P. aeruginosa infections, using an in vitro biofilm system, an intraperitoneal foreign-body model and a pulmonary model of P. aeruginosa infections in mice. Our experimental data showed that a P. aeruginosa strain, unable to produce any detectable rhamnolipids due to an inactivating mutation in the single QS-controlled rhlA gene, did not induce necrosis of PMNs in vitro and exhibited increased clearance compared with its wild-type counterpart in vivo. Conclusively, the results support our model that rhamnolipids are key protective agents of P. aeruginosa against PMNs.

The sociobiology of biofilms

Biofilms are densely packed communities of microbial cells that grow on surfaces and surround themselves with secreted polymers. Many bacterial species form biofilms, and their study has revealed them to be complex and diverse. The structural and physiological complexity of biofilms has led to the idea that they are coordinated and cooperative groups, analogous to multicellular organisms. We evaluate this idea by addressing the findings of microbiologists from the perspective of sociobiology, including theories of collective behavior (self-organization) and social evolution. This yields two main conclusions. First, the appearance of organization in biofilms can emerge without active coordination. That is, biofilm properties such as phenotypic differentiation, species stratification and channel formation do not necessarily require that cells communicate with one another using specialized signaling molecules. Second, while local cooperation among bacteria may often occur, the evolution of cooperation among all cells is unlikely for most biofilms. Strong conflict can arise among multiple species and strains in a biofilm, and spontaneous mutation can generate conflict even within biofilms initiated by genetically identical cells. Biofilms will typically result from a balance between competition and cooperation, and we argue that understanding this balance is central to building a complete and predictive model of biofilm formation.

Biofilm and the role of the ica operon and aap in Staphylococcus epidermidis isolates causing neurosurgical meningitis

Fifty-five Staphylococcus epidermidis isolates, classified as contaminants or causing device-related meningitis, from external ventricular drain (EVD) and non-EVD cerebrospinal fluid specimens were characterized. Thirty-three of 42 (78.6%) meningitis isolates were PCR-positive for ica and aap, known determinants of polysaccharide- and protein-mediated biofilm production, whereas five of 13 (38.5%) contaminants were ica- and aap-negative; 71.4% of meningitis isolates and 84.6% of contaminants produced biofilm. ica+aap+ meningitis isolates produced more biofilm than ica+aap- isolates (p 0.0020). ica+aap- isolates did not produce more biofilm than ica-aap+ isolates (p 0.4368). Apparently, ica and aap are associated with biofilm production in S. epidermidis device-related meningitis isolates.

High-density targeting of a viral multifunctional nanoplatform to a pathogenic, biofilm-forming bacterium

Nanomedicine directed at diagnosis and treatment of infections can benefit from innovations that have substantially increased the variety of available multifunctional nanoplatforms. Here, we targeted a spherical, icosahedral viral nanoplatform to a pathogenic, biofilm-forming bacterium, Staphylococcus aureus. Density of binding mediated through specific protein-ligand interactions exceeded the density expected for a planar, hexagonally close-packed array. A multifunctionalized viral protein cage was used to load imaging agents (fluorophore and MRI contrast agent) onto cells. The fluorescence-imaging capability allowed for direct observation of penetration of the nanoplatform into an S. aureus biofilm. These results demonstrate that multifunctional nanoplatforms based on protein cage architectures have significant potential as tools for both diagnosis and targeted treatment of recalcitrant bacterial infections.

Adherence of Streptococcus pneumoniae to polystyrene plates, effect of serum on adhesion, and virulence in the gerbil otitis media model

The adherence of 11 pneumococcal strains to polystyrene was studied and expressed as the number of colony-forming units (CFU) recovered per 10(6)CFU of initial inoculum. Three strains were considered as strong adherent (>100CFU/10(6)), three as medium adherent (10-100CFU/10(6)), and five as low adherent (<10CFU/10(6)). All serotype 3 strains were low adherent whilst serotypes 23F and 19F behaved as strong or medium adherent. The impact of gerbil sera on adherence of six selected pneumococcal strains (one strong adherent, one medium adherent, and four low adherents) to abiotic material was also studied under two experimental conditions. In the presence of sera, the adherence ability of the strong, medium, and one low adherent strains decreased significantly. On the other hand, the adherence significantly increased in all strains when sera were removed following preincubation of bacteria exposed to sera, although such increase was statistically significant for five of them. Finally, the ability of two (one strong adherent and one low adherent) strains to induce otitis media in gerbils was also evaluated; the strong adherent strain behaved significantly more virulent than the less adherent in terms of ear damage and animal weight loss.

Impact of Pseudomonas aeruginosa quorum sensing on biofilm persistence in an in vivo intraperitoneal foreign-body infection model

Pseudomonas aeruginosa is an opportunistic human pathogen that causes chronic biofilm-based infections in host organisms. P. aeruginosa employs quorum sensing (QS) to control expression of its virulence, and to establish and maintain chronic infections. Under such conditions, the biofilm mode of growth contributes significantly to P. aeruginosa tolerance to the action of the innate and adaptive defence system and numerous antibiotics. In the present study, an in vivo foreign-body infection model was established in the peritoneal cavity of mice. Experimental data showed that QS-deficient P. aeruginosa are cleared more rapidly from silicone implants as compared to their wild-type counterparts. Concurrently, treatment with the QS inhibitor furanone C-30 of mice harbouring implants colonized with the wild-type P. aeruginosa resulted in a significantly faster clearing of the implants as compared to the placebo-treated group. These results were obtained with both an inbred (BALB/c) and an outbred (NMRI) mouse strain. The present results support a model by which functional QS systems play a pivotal role in the ability of bacteria to resist clearing by the innate immune system and strongly suggest that the efficiency of the mouse innate defence against biofilm-forming P. aeruginosa is improved when the bacteria are treated with QS drugs that induce QS deficiency.

Insight into Biofilm-Associated Microbial Life

Microbes cohabit our planet and are engaged in a struggle for survival though on a microscopic scale. This endeavor allows them to develop and devise means for survival and proliferation. One such strategy is the formation of biofilms leading to establishment of a protected community. Such multi-communities may consist of harmful and pathogenic microbes, and they may cause economic problems and threats to human health. Biofilms are formed when microorganisms are typically attached to support surfaces. Biofilm-associated cells are sessile and differentiated from their suspended counterparts by generation of an extracellular polymeric substance matrix, reduced growth rates, and the up- and downregulation of specific genes. Biofilm formation is a complex process regulated by diverse characteristics of the growth medium, substratum, and cell surface. Development of strategies to control or prevent biofilms requires a thorough understanding of the biofilm development process. Biofilm research has witnessed exponential growth, and exciting findings have been reported. This has led us to visualize some previously un-thought-of and fascinating events. This article aims to provide an overview of biofilm research and associated challenges.