Challenges and New Therapeutic Approaches in the Management of Chronic Wounds

Chronic non-healing wounds are estimated to cost the US healthcare $28-$31 billion per year. Diabetic ulcers, arterial and venous ulcers, and pressure ulcers are some of the most common types of chronic wounds. The burden of chronic wounds continues to rise due to the current epidemic of obesity and diabetes and the increase in elderly adults in the population who are more vulnerable to chronic wounds than younger individuals. This patient population is also highly vulnerable to debilitating infections caused by opportunistic and multi-drug resistant pathogens. Reduced microcirculation, decreased availability of cytokines and growth factors that promote wound closure and healing, and infections by multi-drug resistant and biofilm forming microbes are some of the critical factors that contribute to the development of chronic non-healing wounds. This review discusses novel approaches to understand chronic wound pathology and methods to improve chronic wound care, particularly when chronic wounds are infected by multi-drug resistant, biofilm forming microbes.

Pf Bacteriophage and Their Impact on Pseudomonas Virulence, Mammalian Immunity, and Chronic Infections

Pf bacteriophage are temperate phages that infect the bacterium Pseudomonas aeruginosa, a major cause of chronic lung infections in cystic fibrosis (CF) and other settings. Pf and other temperate phages have evolved complex, mutualistic relationships with their bacterial hosts that impact both bacterial phenotypes and chronic infection. We and others have reported that Pf phages are a virulence factor that promote the pathogenesis of P. aeruginosa infections in animal models and are associated with worse skin and lung infections in humans. Here we review the biology of Pf phage and what is known about its contributions to pathogenesis and clinical disease. First, we review the structure, genetics, and epidemiology of Pf phage. Next, we address the diverse and surprising ways that Pf phages contribute to P. aeruginosa phenotypes including effects on biofilm formation, antibiotic resistance, and motility. Then, we cover data indicating that Pf phages suppress mammalian immunity at sites of bacterial infection. Finally, we discuss recent literature implicating Pf in chronic P. aeruginosa infections in CF and other settings. Together, these reports suggest that Pf bacteriophage have direct effects on P. aeruginosa infections and that temperate phages are an exciting frontier in microbiology, immunology, and human health.

2018 international consensus meeting on musculoskeletal infection: Summary from the biofilm workgroup and consensus on biofilm related musculoskeletal infections

Biofilm-associated implant-related bone and joint infections are clinically important due to the extensive morbidity, cost of care and socioeconomic burden that they cause. Research in the field of biofilms has expanded in the past two decades, however, there is still an immense knowledge gap related to many clinical challenges of these biofilm-associated infections. This subject was assigned to the Biofilm Workgroup during the second International Consensus Meeting on Musculoskeletal Infection held in Philadelphia USA (ICM 2018) (https://icmphilly.com). The main objective of the Biofilm Workgroup was to prepare a consensus document based on a review of the literature, prepared responses, discussion, and vote on thirteen biofilm related questions. The Workgroup commenced discussing and refining responses prepared before the meeting on day one using Delphi methodology, followed by a tally of responses using an anonymized voting system on the second day of ICM 2018. The Working group derived consensus on information about biofilms deemed relevant to clinical practice, pertaining to: (1) surface modifications to prevent/inhibit biofilm formation; (2) therapies to prevent and treat biofilm infections; (3) polymicrobial biofilms; (4) diagnostics to detect active and dormant biofilm in patients; (5) methods to establish minimal biofilm eradication concentration for biofilm bacteria; and (6) novel anti-infectives that are effective against biofilm bacteria. It was also noted that biomedical research funding agencies and the pharmaceutical industry should recognize these areas as priorities. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Current Methods for Molecular Epidemiology Studies of Implant Infections

Over the last few decades, the number of surgical procedures involving prosthetic materials has greatly multiplied, along with the rising medical and economic impact of implant-associated infections. The need to appropriately counteract and deal with this phenomenon has led to growing efforts to elucidate the etiology, pathogenesis and epidemiology of these types of infections, characterized by opportunistic pathogens. Molecular epidemiology studies have progressively emerged as a leading multitask tool to identify and fingerprint bacterial strains, unveil the complex clonal nature of important pathogens, detect outbreak events, track the origin of the infections, assess the clinical significance of individual strain types, survey their distribution, recognize associations of strain types with specific virulence determinants and/or pathological conditions, assess the role played by the specific components of the virulon, and reveal the phylogeny and the mechanisms through which new strain types have emerged. Despite the many advances that have been made thanks to these flourishing new approaches to molecular epidemiology, a number of critical aspects remain challenging. In this paper, we briefly discuss the current limitations and possible developments of molecular epidemiology methods in the investigation and surveillance of implant infections.

Determinants for persistence of Pseudomonas aeruginosa in hospitals: interplay between resistance, virulence and biofilm formation

Pseudomonas aeruginosa (Pa) is one of the major bacterial pathogens causing nosocomial infections. During the past few decades, multidrug-resistant (MDR) and extensively drug-resistant (XDR) lineages of Pa have emerged in hospital settings with increasing numbers. However, it remains unclear which determinants of Pa facilitated this spread. A total of 211 clinical XDR and 38 susceptible clinical Pa isolates (nonXDR), as well as 47 environmental isolates (EI), were collected at the Heidelberg University Hospital. We used RAPD PCR to identify genetic clusters. Carriage of carbapenamases (CPM) and virulence genes were analyzed by PCR, biofilm formation capacity was assessed, in vitro fitness was evaluated using competitive growth assays, and interaction with the host's immune system was analyzed using serum killing and neutrophil killing assays. XDR isolates showed significantly elevated biofilm formation (p < 0.05) and higher competitive fitness compared to nonXDR and EI isolates. Thirty percent (62/205) of the XDR isolates carried a CPM. Similarities in distribution of virulence factors, as well as biofilm formation properties, between CPM+ Pa isolates and EI and between CPM- and nonXDR isolates were detected. Molecular typing revealed two distinct genetic clusters within the XDR population, which were characterized by even higher biofilm formation. In contrast, XDR isolates were more susceptible to the immune response than nonXDR isolates. Our study provides evidence that the ability to form biofilms is an outstanding determinant for persistence and endemic spread of Pa in the hospital setting.

Residence in biofilms allows Burkholderia cepacia complex (Bcc) bacteria to evade the antimicrobial activities of neutrophil-like dHL60 cells

Bacteria of the Burkholderia cepacia complex (Bcc) persist in the airways of people with cystic fibrosis (CF) despite the continuous recruitment of neutrophils. Most members of Bcc are multidrug resistant and can form biofilms. As such, we sought to investigate whether biofilm formation plays a role in protecting Bcc bacteria from neutrophils. Using the neutrophil-like, differentiated cell line, dHL60, we have shown for the first time that Bcc biofilms are enhanced in the presence of these cells. Biofilm biomass was greater following culture in the presence of dHL60 cells than in their absence, likely the result of incorporating dHL60 cellular debris into the biofilm. Moreover, we have demonstrated that mature biofilms (cultured for up to 72 h) induced necrosis in the cells. Established biofilms also acted as a barrier to the migration of the cells and masked the bacteria from being recognized by the cells; dHL60 cells expressed less IL-8 mRNA and secreted significantly less IL-8 when cultured in the presence of biofilms, with respect to planktonic bacteria. Our findings provide evidence that biofilm formation can, at least partly, enable the persistence of Bcc bacteria in the CF airway and emphasize a requirement for anti-biofilm therapeutics.

Pseudomonas aeruginosa lasI/rhlI quorum sensing genes promote phagocytosis and aquaporin 9 redistribution to the leading and trailing regions in macrophages

Pseudomonas aeruginosa controls production of its multiple virulence factors and biofilm development via the quorum sensing (QS) system. QS signals also interact with and affect the behavior of eukaryotic cells. Host water homeostasis and aquaporins (AQP) are essential during pathological conditions since they interfere with the cell cytoskeleton and signaling, and hereby affect cell morphology and functions. We investigated the contribution of P. aeruginosa QS genes lasI/rhlI to phagocytosis, cell morphology, AQP9 expression, and distribution in human macrophages, using immunoblotting, confocal, and nanoscale imaging. Wild type P. aeruginosa with a functional QS system was a more attractive prey for macrophages than the lasI/rhlI mutant lacking the production of QS molecules, 3O-C₁₂-HSL, and C₄-HSL, and associated virulence factors. The P. aeruginosa infections resulted in elevated AQP9 expression and relocalization to the leading and trailing regions in macrophages, increased cell area and length; bacteria with a functional QS system lasI/rhlI achieved stronger responses. We present evidence for a new role of water fluxes via AQP9 during bacteria–macrophage interaction and for the QS system as an important stimulus in this process. These novel events in the interplay between P. aeruginosa and macrophages may influence on the outcome of infection, inflammation, and development of disease.

Immune defense against S. epidermidis biofilms: components of the extracellular polymeric substance activate distinct bactericidal mechanisms of phagocytic cells

Bacteria, organized in biofilms, are a common cause of relapsing or persistent infections and the ultimate cause of implant-associated osteomyelitis. Bacterial biofilms initiate a prominent local inflammatory response with infiltration of polymorphonuclear neutrophils (PMN), the main protagonists of the local innate host defense against bacteria. In our previous work we found that PMN recognize and adhere to biofilms, and that phagocytosis and degranulation of bactericidal substances, such as lactoferrin, were initiated. In contrast to the situation with planktonic bacteria, opsonization of biofilms with immunoglobulin and complement was not required for PMN activation, suggesting that biofilms contain signaling components for PMN. In the present study we identified in the bacteria-free extracellular substance of Staphylococcus epidermidis biofilms protein fractions that activated PMN in vitro.

Host Defence against Bacterial Biofilms: “Mission Impossible”?

Bacteria living as biofilms have been recognised as the ultimate cause of persistent and destructive inflammatory processes. Biofilm formation is a well-organised, genetically-driven process, which is well characterised for numerous bacteria species. In contrast, the host response to bacterial biofilms is less well analysed, and there is the general believe that bacteria in biofilms escape recognition or eradication by the immune defence. In this review the host response to bacterial biofilms is discussed with particular focus on the role of neutrophils because these phagocytic cells are the first to infiltrate areas of bacterial infection, and because neutrophils are equipped with a wide arsenal of bactericidal and toxic entities. I come to the conclusion that bacterial biofilms are not inherently protected against the attack by neutrophils, but that control of biofilm formation is possible depending on a timely and sufficient host response.

Interactions of Staphylococci with Osteoblasts and Phagocytes in the Pathogenesis of Implant-Associated Osteomyelitis

In spite of great advancements in the field of biomaterials and in surgical techniques, the implant of medical devices is still associated with a high risk of bacterial infection. Implant-associated osteomyelitis is a deep infection of bone around the implant. The continuous inflammatory destruction of bone tissues characterizes this serious bone infectious disease. Staphylococcus aureus and Staphylococcus epidermidis are the most prevalent etiologic agents of implant-associated infections, together with the emerging pathogen Staphylococcus lugdunensis. Various interactions between staphylococci, osteoblasts, and phagocytes occurring in the peri-prosthesis environment play a crucial role in the pathogenesis of implant-associated osteomyelitis. Here we focus on two main events: internalization of staphylococci into osteoblasts, and bacterial interactions with phagocytic cells.

N-Acylhomoserine lactones are potent neutrophil chemoattractants that act via calcium mobilization and actin remodeling

In gram-negative bacteria, cell-cell communication based on HSL QS molecules is known to coordinate the production of virulence factors and biofilms. These bacterial signals can also modulate human immune cell behavior. Using a Transwell migration assay, we found that human primary neutrophils are strongly stimulated by 3O-C(12)-HSL and -C(10)-HSL but not C(4)-HSL in a concentration-dependent manner. Moreover, 3O-C(12)-HSL and -C(10)-HSL activate PLCγ1 but not -γ2, mobilize intracellular calcium, and up-regulate IP(3)R. These changes were paralleled by F-actin accumulation, primarily in the leading edge of neutrophils, as evidenced by phalloidin staining and confocal microscopy. F- and G-actin isolation and quantification by immunoblotting revealed that the F/G-actin ratio was increased significantly after treatment with all three HSLs. Furthemore, 3O-C(12)-HSL- and 3O-C(10)-HSL treatment resulted in phosphorylation of Rac1 and Cdc42. In contrast, C(4)-HSL had negligible influence on the phosphorylation status of PLC and Rac1/Cdc42 and failed to attract neutrophils and induce calcium release. The calcium inhibitor thapsigargin, which blocks ER calcium uptake, strongly prevented neutrophil migration toward 3O-C(12)-HSL and -C(10)-HSL. These findings show that the bacterial QS molecules 3O-C(12)-HSL and -C(10)-HSL may attract human neutrophils to the sites of bacterial infection and developing biofilms. Indeed, recognition of HSL QS signals by neutrophils may play a critical role in their recruitment during infections.

Phagocytosis of staphylococci biofilms by polymorphonuclear neutrophils: S. aureus and S. epidermidis differ with regard to their susceptibility towards the host defense

Bacteria organized in biofilms are a common cause of relapsing or persistent infections. In patients receiving orthopedic implants, such as endoprostheses or osteosynthesis materials, Staphylococcus aureus and S. epidermidis are prevalent and it is widely assumed that bacteria in biofilms are not only relatively resistant towards antibiotics and biocides, but also towards host defense mechanisms. In that context, we addressed the question how polymorphonuclear neutrophils (PMN), the "first line defense" against bacterial infection, interact with biofilms generated in vitro. By time-lapse video microscopy, we observed migration of PMN towards the biofilms. In the case of S. aureus, the PMN moved across the biofilm and took up bacteria as they moved along. On S. epidermidis, in contrast, the PMN were rather immobile, and phagocytosis was limited to bacteria in the immediate vicinity. By labeling the bacteria within the biofilm with H-thymidine we found that S. aureus biofilms were more sensitive towards the PMN attack than S. epidermidis. Following phagocytosis of either bacteria strain, the PMN underwent apoptosis, in line with the dogma, that phagocytosis induces programmed cell-death in order to prevent spilling of the bactericidal and cytotoxic entities. In conclusion, biofilms are not inherently protected against the attack by phagocytic cells; their sensitivity, however, varies among bacterial strains, presumably due to properties of the extracellular biofilm matrix affecting the motility of PMN on the film.

Host defence against Staphylococcus aureus biofilms infection: phagocytosis of biofilms by polymorphonuclear neutrophils (PMN)

Bacteria organised in biofilms are a common cause of relapsing or persistent infections, particularly in patients receiving medical implants such as ventilation tubes, indwelling catheters, artificial heart valves, endoprostheses, or osteosynthesis materials. Bacteria in biofilms are relatively resistant towards antibiotics and biocides, and--according to the current dogma--towards the host defence mechanisms as well. In that context, we addressed the question, how polymorphonuclear neutrophils (PMN), the "first line defence" against bacterial infection, would interact with Staphylococcus aureus biofilms generated in vitro. By time-lapse video microscopy and confocal laser scan microscopy we observed a migration of PMN towards and into the biofilms, as well as clearance of biofilms by phagocytosis. By labelling the bacteria within the biofilm with (3)H thymidine, and by cytofluorometry we could confirm and quantify clearance and phagocytosis of biofilm as well. Of note, the extent of biofilm clearance depended on its maturation state: developing "young" biofilms were more sensitive towards the attack by PMN compared to mature biofilms. In conclusion, contrary to the current dogma, S. aureus biofilms are not inherently protected against the host defence.

Still stuck in the slime

The role of biofilm in implant infections and the genetic control of its production are still giving rise to great interest and controversial new results are continuing to emerge from widespread investigations. Bacteria embedded in biofilms are more resistant to most antibiotics. Hypotheses regarding the mechanisms of antibiotic multi-resistance in biofilm are brought to light, including the onset of persister cells during the attachment of bacteria to implant surfaces.This 2008 special issue ''Focus on Implant Infections'', presents new strategies for combating biofilm infections,such as the use of staphylococcal quorum-sensing inhibitors or the ''bioelectric effect'': the phenomenon by which electric current can enhance the activity of some antimicrobial agents against bacteria in biofilms.