Bacterial biofilms predominate in both acute and chronic human lung infections

A 'rich-get-richer' mechanism drives patchy dynamics and resistance evolution in antibiotic-treated bacteria

Bacteria in nature often form surface-attached communities that initially comprise distinct subpopulations, or patches. For pathogens, these patches can form at infection sites, persist during antibiotic treatment, and develop into mature biofilms. Evidence suggests that patches can emerge due to heterogeneity in the growth environment and bacterial seeding, as well as cell-cell signaling. However, it is unclear how these factors contribute to patch formation and how patch formation might affect bacterial survival and evolution. Here, we demonstrate that a 'rich-get-richer' mechanism drives patch formation in bacteria exhibiting collective survival (CS) during antibiotic treatment. Modeling predicts that the seeding heterogeneity of these bacteria is amplified by local CS and global resource competition, leading to patch formation. Increasing the dose of a non-eradicating antibiotic treatment increases the degree of patchiness. Experimentally, we first demonstrated the mechanism using engineered Escherichia coli and then demonstrated its applicability to a pathogen, Pseudomonas aeruginosa. We further showed that the formation of P. aeruginosa patches promoted the evolution of antibiotic resistance. Our work provides new insights into population dynamics and resistance evolution during surface-attached bacterial growth.

Pseudomonas aeruginosa senses and responds to epithelial potassium flux via Kdp operon to promote biofilm

Mucosa-associated biofilms are associated with many human disease states, but the host mechanisms promoting biofilm remain unclear. In chronic respiratory diseases like cystic fibrosis (CF), Pseudomonas aeruginosa establishes chronic infection through biofilm formation. P. aeruginosa can be attracted to interspecies biofilms through potassium currents emanating from the biofilms. We hypothesized that P. aeruginosa could, similarly, sense and respond to the potassium efflux from human airway epithelial cells (AECs) to promote biofilm. Using respiratory epithelial co-culture biofilm imaging assays of P. aeruginosa grown in association with CF bronchial epithelial cells (CFBE41o-), we found that P. aeruginosa biofilm was increased by potassium efflux from AECs, as examined by potentiating large conductance potassium channel, BKCa (NS19504) potassium efflux. This phenotype is driven by increased bacterial attachment and increased coalescence of bacteria into aggregates. Conversely, biofilm formation was reduced when AECs were treated with a BKCa blocker (paxilline). Using an agar-based macroscopic chemotaxis assay, we determined that P. aeruginosa chemotaxes toward potassium and screened transposon mutants to discover that disruption of the high-sensitivity potassium transporter, KdpFABC, and the two-component potassium sensing system, KdpDE, reduces P. aeruginosa potassium chemotaxis. In respiratory epithelial co-culture biofilm imaging assays, a KdpFABCDE deficient P. aeruginosa strain demonstrated reduced biofilm growth in association with AECs while maintaining biofilm formation on abiotic surfaces. Furthermore, we determined that the Kdp operon is expressed in vivo in people with CF and the genes are conserved in CF isolates. Collectively, these data suggest that P. aeruginosa biofilm formation can be increased by attracting bacteria to the mucosal surface and enhancing coalescence into microcolonies through aberrant AEC potassium efflux sensed by the KdpFABCDE system. These findings suggest host electrochemical signaling can enhance biofilm, a novel host-pathogen interaction, and potassium flux could be a therapeutic target to prevent chronic infections in diseases with mucosa-associated biofilms, like CF.

Ecological and evolutionary mechanisms driving within-patient emergence of antimicrobial resistance

The ecological and evolutionary mechanisms of antimicrobial resistance (AMR) emergence within patients and how these vary across bacterial infections are poorly understood. Increasingly widespread use of pathogen genome sequencing in the clinic enables a deeper understanding of these processes. In this Review, we explore the clinical evidence to support four major mechanisms of within-patient AMR emergence in bacteria: spontaneous resistance mutations; in situ horizontal gene transfer of resistance genes; selection of pre-existing resistance; and immigration of resistant lineages. Within-patient AMR emergence occurs across a wide range of host niches and bacterial species, but the importance of each mechanism varies between bacterial species and infection sites within the body. We identify potential drivers of such differences and discuss how ecological and evolutionary analysis could be embedded within clinical trials of antimicrobials, which are powerful but underused tools for understanding why these mechanisms vary between pathogens, infections and individuals. Ultimately, improving understanding of how host niche, bacterial species and antibiotic mode of action combine to govern the ecological and evolutionary mechanism of AMR emergence in patients will enable more predictive and personalized diagnosis and antimicrobial therapies.

The L-lactate dehydrogenases of Pseudomonas aeruginosa are conditionally regulated but both contribute to survival during macrophage infection

Pseudomonas aeruginosa is an opportunistic pathogen that thrives in environments associated with human activity, including soil and water altered by agriculture or pollution. Because L-lactate is a significant product of plant and animal metabolism, it is available to serve as a carbon source for P. aeruginosa in the diverse settings it inhabits. Here, we evaluate P. aeruginosa's production and use of its redundant L-lactate dehydrogenases, termed LldD and LldA. We confirm that the protein LldR represses lldD and identify a new transcription factor, called LldS, that activates lldA; these distinct regulators and the genomic contexts of lldD and lldA contribute to their differential expression. We demonstrate that the lldD and lldA genes are conditionally controlled in response to lactate isomers as well as to glycolate and - hydroxybutyrate, which, like lactate, are -hydroxycarboxylates. We also show that lldA is induced when iron availability is low. Our examination of lldD and lldA expression across depth in biofilms indicates a complex pattern that is consistent with the effects of glycolate production, iron availability, and cross-regulation on enzyme preference. Finally, macrophage infection assays revealed that both lldD and lldA contribute to persistence within host cells, underscoring the potential role of L-lactate as a carbon source during P. aeruginosa-eukaryote interactions. Together, these findings help us understand the metabolism of a key resource that may promote P. aeruginosa's success as a resident of contaminated environments and animal hosts.

Optimization of an in vitro Pseudomonas aeruginosa Biofilm Model to Examine Antibiotic Pharmacodynamics at the Air-Liquid Interface

Pseudomonas aeruginosa is an important cause of lower respiratory tract infections, such as ventilator-associated bacterial pneumonia (VABP). Using inhaled antibiotics to treat VABP can achieve high drug concentrations at the infection site while minimizing systemic toxicities. Despite the theoretical advantages, clinical trials have failed to show a benefit for inhaled antibiotic therapy in treating VABP. A potential reason for this discordance is the presence of biofilm-embedded bacteria in lower respiratory tract infections. Drug selection and dosing are often based on data from bacteria grown planktonically. In the present study, an in vitro air-liquid interface pharmacokinetic/pharmacodynamic biofilm model was optimized to evaluate the activity of simulated epithelial lining fluid exposures of inhaled and intravenous doses of polymyxin B and tobramycin against two P. aeruginosa strains. Antibiotic activity was also determined against the P. aeruginosa strains grown planktonically. Our study revealed that inhaled antibiotic exposures were more active than their intravenous counterparts across biofilm and planktonic populations. Inhaled exposures of polymyxin B and tobramycin exhibited comparable activity against planktonic P. aeruginosa. Although inhaled polymyxin B exposures were initially more active against P. aeruginosa biofilms (through 6 h), tobramycin was more active by the end of the experiment (48 h). Together, these data slightly favor the use of inhaled tobramycin for VABP caused by biofilm-forming P. aeruginosa that are not resistant to either antibiotic. The optimized in vitro air-liquid interface pharmacokinetic/pharmacodynamic biofilm model may be beneficial for the development of novel anti-biofilm agents or to optimize antibiotic dosing for infections such as VABP.

Combination treatment to improve mucociliary transport of Pseudomonas aeruginosa biofilms

People with muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often have acute or chronic respiratory infections that are difficult to treat due in part to the accumulation of hyperconcentrated mucus within the airway. Mucus accumulation and obstruction promote chronic inflammation and infection and reduce therapeutic efficacy. Bacterial aggregates in the form of biofilms exhibit increased resistance to mechanical stressors from the immune response (e.g., phagocytosis) and chemical treatments including antibiotics. Herein, combination treatments designed to disrupt the mechanical properties of biofilms and potentiate antibiotic efficacy are investigated against mucus-grown Pseudomonas aeruginosa biofilms and optimized to 1) alter biofilm viscoelastic properties, 2) increase mucociliary transport rates, and 3) reduce bacterial viability. A disulfide bond reducing agent (tris(2-carboxyethyl)phosphine, TCEP), a surfactant (NP40), a biopolymer (hyaluronic acid, HA), a DNA degradation enzyme (DNase), and an antibiotic (tobramycin) are tested in various combinations to maximize biofilm disruption. The viscoelastic properties of biofilms are quantified with particle tracking microrheology and transport rates are quantified in a mucociliary transport device comprised of fully differentiated primary human bronchial epithelial cells. The combination of the NP40 with hyaluronic acid and tobramycin was the most effective at increasing mucociliary transport rates, decreasing the viscoelastic properties of mucus, and reducing bacterial viability. Multimechanistic targeting of biofilm infections may ultimately result in improved clinical outcomes, and the results of this study may be translated into future in vivo infection models.

Dogs can detect an odor profile associated with Staphylococcus aureus biofilms in cultures and biological samples

Introduction

The study investigated the utilization of odor detection dogs to identify the odor profile of Staphylococcus aureus (S. aureus) biofilms in pure in vitro samples and in in vivo biosamples from animals and humans with S. aureus periprosthetic joint infection (PJI). Biofilms form when bacterial communities aggregate on orthopedic implants leading to recalcitrant infections that are difficult to treat. Identifying PJI biofilm infections is challenging, and traditional microbiological cultures may yield negative results even in the presence of clinical signs.

Methods

Dogs were trained on pure in vitro S. aureus biofilms and tested on lacrimal fluid samples from an in vivo animal model (rabbits) and human patients with confirmed S. aureus PJI.

Results

The results demonstrated that dogs achieved a high degree of sensitivity and specificity in detecting the odor profile associated with S. aureus biofilms in rabbit samples. Preliminary results suggest that dogs can recognize S. aureus volatile organic compounds (VOCs) in human lacrimal fluid samples.

Discussion

Training odor detection dogs on in vitro S. aureus, may provide an alternative to obtaining clinical samples for training and mitigates biosecurity hazards. The findings hold promise for culture-independent diagnostics, enabling early disease detection, and improved antimicrobial stewardship. In conclusion, this research demonstrates that dogs trained on in vitro S. aureus samples can identify the consistent VOC profile of PJI S. aureus biofilm infections. The study opens avenues for further investigations into a retained VOC profile of S. aureus biofilm infection. These advancements could revolutionize infectious disease diagnosis and treatment, leading to better patient outcomes and addressing the global challenge of antimicrobial resistance.

MEK1/2 inhibition decreases pro-inflammatory responses in macrophages from people with cystic fibrosis and mitigates severity of illness in experimental murine methicillin-resistant Staphylococcus aureus infection

Chronic pulmonary bacterial infections and associated inflammation remain a cause of morbidity and mortality in people with cystic fibrosis (PwCF) despite new modulator therapies. Therapies targeting host factors that dampen detrimental inflammation without suppressing immune responses critical for controlling infections remain limited, while the development of lung infections caused by antimicrobial resistant bacteria is an increasing global problem, and a significant challenge in CF. Pharmacological compounds targeting the mammalian MAPK proteins MEK1 and MEK2, referred to as MEK1/2 inhibitor compounds, have potential combined anti-microbial and anti-inflammatory effects. Here we examined the immunomodulatory properties of MEK1/2 inhibitor compounds PD0325901, trametinib, and CI-1040 on CF innate immune cells. Human CF macrophage and neutrophil phagocytic functions were assessed by quantifying phagocytosis of serum opsonized pHrodo red E. coli, Staphylococcus aureus, and zymosan bioparticles. MEK1/2 inhibitor compounds reduced CF macrophage pro-inflammatory cytokine production without impairing CF macrophage or neutrophil phagocytic abilities. Wild-type C57BL6/J and Cftr tm1kth (F508del homozygous) mice were used to evaluate the in vivo therapeutic potential of PD0325901 compared to vehicle treatment in an intranasal methicillin-resistant Staphylococcus aureus (MRSA) infection with the community-acquired MRSA strain USA300. In both wild-type and CF mice, PD0325901 reduced inflammation associated body mass loss. Wild-type mice treated with PD0325901 had significant reduction in neutrophil-mediated inflammation compared to vehicle treatment groups, with preserved clearance of bacteria in lung, liver, or spleen 1 day after infection in either wild-type or CF mouse models. In summary, this study provides the first data evaluating the therapeutic potential of MEK1/2 inhibitor to modulate CF immune cells and demonstrates that MEK1/2 inhibitors diminish pro-inflammatory responses without impairing host defense mechanisms required for acute pathogen clearance.

Bacterial aerobic respiration is a major consumer of oxygen in sputum from patients with acute lower respiratory tract infection

Bacterial aerobic respiration may determine the outcome of antibiotic treatment in experimental settings, but the clinical relevance of bacterial aerobic respiration for the outcome of antibiotic treatment has not been tested. Therefore, we hypothesized that bacterial aerobic respiration is higher in sputum from patients with acute lower respiratory tract infections (aLRTI), than in sputum from patients with chronic LRTI (cLRTI), where the bacteria persist despite antibiotic treatment. The bacterial aerobic respiration was determined according to the dynamics of the oxygen (O2 ) concentration in sputum from aLRTI patients (n = 52). This result was evaluated by comparison to previously published data from patients with cLRTI. O2 consumption resulting in anoxic zones was more frequent in sputum with detected bacterial pathogens. The bacterial aerobic respiration in aLRTI sputum approximated 55% of the total O2 consumption, which was significantly higher than previously published for cLRTI. The bacterial aerobic respiration in sputum was higher in aLRTI patients than previously seen in cLRTI patients, indicating the presence of bacteria with a sensitive physiology in aLRTI. These variations in bacterial physiology between aLRTI patients and cLRTI patients may contribute the huge difference in treatment success between the two patient groups.

An Overview of Biofilm-Associated Infections and the Role of Phytochemicals and Nanomaterials in Their Control and Prevention

Biofilm formation is considered one of the primary virulence mechanisms in Gram-positive and Gram-negative pathogenic species, particularly those responsible for chronic infections and promoting bacterial survival within the host. In recent years, there has been a growing interest in discovering new compounds capable of inhibiting biofilm formation. This is considered a promising antivirulence strategy that could potentially overcome antibiotic resistance issues. Effective antibiofilm agents should possess distinctive properties. They should be structurally unique, enable easy entry into cells, influence quorum sensing signaling, and synergize with other antibacterial agents. Many of these properties are found in both natural systems that are isolated from plants and in synthetic systems like nanoparticles and nanocomposites. In this review, we discuss the clinical nature of biofilm-associated infections and some of the mechanisms associated with their antibiotic tolerance. We focus on the advantages and efficacy of various natural and synthetic compounds as a new therapeutic approach to control bacterial biofilms and address multidrug resistance in bacteria.

The role of human extracellular matrix proteins in defining Staphylococcus aureus biofilm infections

Twenty to forty one percent of the world's population is either transiently or permanently colonized by the Gram-positive bacterium, Staphylococcus aureus. In 2017, the CDC designated methicillin-resistant S. aureus (MRSA) as a serious threat, reporting ∼300 000 cases of MRSA-associated hospitalizations annually, resulting in over 19 000 deaths, surpassing that of HIV in the USA. S. aureus is a proficient biofilm-forming organism that rapidly acquires resistance to antibiotics, most commonly methicillin (MRSA). This review focuses on a large group of (>30) S. aureus adhesins, either surface-associated or secreted that are designed to specifically bind to 15 or more of the proteins that form key components of the human extracellular matrix (hECM). Importantly, this includes hECM proteins that are pivotal to the homeostasis of almost every tissue environment [collagen (skin), proteoglycans (lung), hemoglobin (blood), elastin, laminin, fibrinogen, fibronectin, and fibrin (multiple organs)]. These adhesins offer S. aureus the potential to establish an infection in every sterile tissue niche. These infections often endure repeated immune onslaught, developing into chronic, biofilm-associated conditions that are tolerant to ∼1000 times the clinically prescribed dose of antibiotics. Depending on the infection and the immune response, this allows S. aureus to seamlessly transition from colonizer to pathogen by subtly manipulating the host against itself while providing the time and stealth that it requires to establish and persist as a biofilm. This is a comprehensive discussion of the interaction between S. aureus biofilms and the hECM. We provide particular focus on the role of these interactions in pathogenesis and, consequently, the clinical implications for the prevention and treatment of S. aureus biofilm infections.

Biofilms and core pathogens shape the tumor microenvironment and immune phenotype in colorectal cancer

Extensive research has explored the role of gut microbiota in colorectal cancer (CRC). Nonetheless, metatranscriptomic studies investigating the in situ functional implications of host-microbe interactions in CRC are scarce. Therefore, we characterized the influence of CRC core pathogens and biofilms on the tumor microenvironment (TME) in 40 CRC, paired normal, and healthy tissue biopsies using fluorescence in situ hybridization (FISH) and dual-RNA sequencing. FISH revealed that Fusobacterium spp. was associated with increased bacterial biomass and inflammatory response in CRC samples. Dual-RNA sequencing demonstrated increased expression of pro-inflammatory cytokines, defensins, matrix-metalloproteases, and immunomodulatory factors in CRC samples with high bacterial activity. In addition, bacterial activity correlated with the infiltration of several immune cell subtypes, including M2 macrophages and regulatory T-cells in CRC samples. Specifically, Bacteroides fragilis and Fusobacterium nucleatum correlated with the infiltration of neutrophils and CD4+ T-cells, respectively. The collective bacterial activity/biomass appeared to exert a more significant influence on the TME than core pathogens, underscoring the intricate interplay between gut microbiota and CRC. These results emphasize how biofilms and core pathogens shape the immune phenotype and TME in CRC while highlighting the need to extend the bacterial scope beyond CRC pathogens to advance our understanding and identify treatment targets.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

The natriuretic peptide receptor agonist osteocrin disperses Pseudomonas aeruginosa biofilm

Biofilms are highly tolerant to antimicrobials and host immune defense, enabling pathogens to thrive in hostile environments. The diversity of microbial biofilm infections requires alternative and complex treatment strategies. In a previous work we demonstrated that the human Atrial Natriuretic Peptide (hANP) displays a strong anti-biofilm activity toward Pseudomonas aeruginosa and that the binding of hANP by the AmiC protein supports this effect. This AmiC sensor has been identified as an analog of the human natriuretic peptide receptor subtype C (h-NPRC). In the present study, we evaluated the anti-biofilm activity of the h-NPRC agonist, osteocrin (OSTN), a hormone that displays a strong affinity for the AmiC sensor at least in vitro. Using molecular docking, we identified a pocket in the AmiC sensor that OSTN reproducibly docks into, suggesting that OSTN might possess an anti-biofilm activity as well as hANP. This hypothesis was validated since we observed that OSTN dispersed established biofilm of P. aeruginosa PA14 strain at the same concentrations as hANP. However, the OSTN dispersal effect is less marked than that observed for the hANP (-61% versus -73%). We demonstrated that the co-exposure of P. aeruginosa preformed biofilm to hANP and OSTN induced a biofilm dispersion with a similar effect to that observed with hANP alone suggesting a similar mechanism of action of these two peptides. This was confirmed by the observation that OSTN anti-biofilm activity requires the activation of the complex composed by the sensor AmiC and the regulator AmiR of the ami pathway. Using a panel of both P. aeruginosa laboratory reference strains and clinical isolates, we observed that the OSTN capacity to disperse established biofilms is highly variable from one strain to another. Taken together, these results show that similarly to the hANP hormone, OSTN has a strong potential to be used as a tool to disperse P. aeruginosa biofilms.

Emerging strategies to target virulence in Pseudomonas aeruginosa respiratory infections

Pseudomonas aeruginosa is an opportunistic pathogen that is responsible for infections in people living with chronic respiratory conditions, such as cystic fibrosis (CF) and non-CF bronchiectasis (NCFB). Traditionally, in people with chronic respiratory disorders, P. aeruginosa infection has been managed with a combination of inhaled and intravenous antibiotic therapies. However, due in part to the prolonged use of antibiotics in these people, the emergence of multi-drug resistant P. aeruginosa strains is a growing concern. The development of anti-virulence therapeutics may provide a new means of treating P. aeruginosa lung infections whilst also combatting the AMR crisis, as these agents are presumed to exert reduced pressure for the emergence of drug resistance as compared to antibiotics. However, the pipeline for developing anti-virulence therapeutics is poorly defined, and it is currently unclear as to whether in vivo and in vitro models effectively replicate the complex pulmonary environment sufficiently to enable development and testing of such therapies for future clinical use. Here, we discuss potential targets for P. aeruginosa anti-virulence therapeutics and the effectiveness of the current models used to study them. Focus is given to the difficulty of replicating the virulence gene expression patterns of P. aeruginosa in the CF and NCFB lung under laboratory conditions and to the challenges this poses for anti-virulence therapeutic development.

ROS generating BODIPY loaded nanoparticles for photodynamic eradication of biofilms

Bacterial biofilms can pose a serious health risk to humans and are less susceptible to antibiotics and disinfection than planktonic bacteria. Here, a novel method for biofilm eradication based on antimicrobial photodynamic therapy utilizing a nanoparticle in conjunction with a BODIPY derivative as photosensitizer was developed. Reactive oxygen species are generated upon illumination with visible light and lead to a strong, controllable and persistent eradication of both planktonic bacteria and biofilms. One of the biggest challenges in biofilm eradication is the penetration of the antimicrobial agent into the biofilm and its matrix. A biocompatible hydrophilic nanoparticle was utilized as a delivery system for the hydrophobic BODIPY dye and enabled its accumulation within the biofilm. This key feature of delivering the antimicrobial agent to the site of action where it is activated resulted in effective eradication of all tested biofilms. Here, 3 bacterial species that commonly form clinically relevant pathogenic biofilms were selected: Escherichia coli, Staphylococcus aureus and Streptococcus mutans. The development of this antimicrobial photodynamic therapy tool for biofilm eradication takes a promising step towards new methods for the much needed treatment of pathogenic biofilms.

Single cells and bacterial biofilm populations in chronic wound infections

Chronic wounds and chronic ulcers are an increasing problem associated with high health care burden and patient burden. The arrested healing of chronic wounds has, in part, been attributed to the presence of biofilms. Substantial research has documented the presence of biofilms in chronic wounds, and many mechanisms of host-pathogen interactions have been uncovered to explain the arrested healing. However, the paradigm of whether biofilms are only observed in chronic infections was recently challenged when biofilms were also observed in acute infections. Here, we characterize the distribution of bacteria in lower leg wounds with particular emphasis on Pseudomonas aeruginosa and Staphylococcus aureus by confocal laser scanning microscopy combined with PNA-FISH staining and routine culture of bacteria. We show that 40% of wounds contained either P. aeruginosa or S. aureus biofilms and demonstrate the presence of scattered single cells in tissues stained with a universal bacterial PNA-FISH probe. Thus, we demonstrate that chronic wounds do not only harbor bacteria organized in biofilms, but also carry populations of scattered single cells and small cell clusters of only a few bacteria. Our findings may influence diagnostic tools being developed to only target biofilms, where single-cell subpopulations thus may be overlooked and possibly lead to false-negative results.

What's in a name? Characteristics of clinical biofilms

In vitro biofilms are communities of microbes with unique features compared to individual cells. Biofilms are commonly characterized by physical traits like size, adhesion, and a matrix made of extracellular substances. They display distinct phenotypic features, such as metabolic activity and antibiotic tolerance. However, the relative importance of these traits depends on the environment and bacterial species. Various mechanisms enable biofilm-associated bacteria to withstand antibiotics, including physical barriers, physiological adaptations, and changes in gene expression. Gene expression profiles in biofilms differ from individual cells but, there is little consensus among studies and so far, a 'biofilm signature transcriptome' has not been recognized. Additionally, the spatial and temporal variability within biofilms varies greatly depending on the system or environment. Despite all these variable conditions, which produce very diverse structures, they are all noted as biofilms. We discuss that clinical biofilms may differ from those grown in laboratories and found in the environment and discuss whether the characteristics that are commonly used to define and characterize biofilms have been shown in infectious biofilms. We emphasize that there is a need for a comprehensive understanding of the specific traits that are used to define bacteria in infections as clinical biofilms.

Drug delivery strategies for antibiofilm therapy

Although new antibiofilm agents have been developed to prevent and eliminate pathogenic biofilms, their widespread clinical use is hindered by poor biocompatibility and bioavailability, unspecific interactions and insufficient local concentrations. The development of innovative drug delivery strategies can facilitate penetration of antimicrobials through biofilms, promote drug dispersal and synergistic bactericidal effects, and provide novel paradigms for clinical application. In this Review, we discuss the potential benefits of such emerging techniques for improving the clinical efficacy of antibiofilm agents, as well as highlighting the existing limitations and future prospects for these therapies in the clinic.

The non-attached biofilm aggregate

Biofilms have conventionally been perceived as dense bacterial masses on surfaces, following the five-step model of development. Initial biofilm research focused on surface-attached formations, but detached aggregates have received increasing attention in the past decade due to their pivotal role in chronic infections. Understanding their nature sparked fervent discussions in biofilm conferences and scientific literature. This review consolidates current insights on non-attached aggregates, offering examples of their occurrence in nature and diseases. We discuss their formation and dispersion mechanisms, resilience to antibiotics and immune-responses, drawing parallels to surface-attached biofilms. Moreover, we outline available in vitro models for studying non-attached aggregates.

Bacterial biofilms in the human body: prevalence and impacts on health and disease

Bacterial biofilms can be found in most environments on our planet, and the human body is no exception. Consisting of microbial cells encased in a matrix of extracellular polymers, biofilms enable bacteria to sequester themselves in favorable niches, while also increasing their ability to resist numerous stresses and survive under hostile circumstances. In recent decades, biofilms have increasingly been recognized as a major contributor to the pathogenesis of chronic infections. However, biofilms also occur in or on certain tissues in healthy individuals, and their constituent species are not restricted to canonical pathogens. In this review, we discuss the evidence for where, when, and what types of biofilms occur in the human body, as well as the diverse ways in which they can impact host health under homeostatic and dysbiotic states.

Combination Treatment to Improve Mucociliary Transport of Pseudomonas aeruginosa Biofilms

People with muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often have acute or chronic respiratory infections that are difficult to treat due in part to the accumulation of hyperconcentrated mucus within the airway. Mucus accumulation and obstruction promote chronic inflammation and infection and reduce therapeutic efficacy. Bacterial aggregates in the form of biofilms exhibit increased resistance to mechanical stressors from the immune response (e.g., phagocytosis) and chemical treatments including antibiotics. Herein, combination treatments designed to disrupt the mechanical properties of biofilms and potentiate antibiotic efficacy are investigated against mucus-grown Pseudomonas aeruginosa biofilms and optimized to 1) alter biofilm viscoelastic properties, 2) increase mucociliary transport rates, and 3) reduce bacterial viability. A disulfide bond reducing agent (tris(2-carboxyethyl)phosphine, TCEP), a surfactant (NP40), a biopolymer (hyaluronic acid, HA), a DNA degradation enzyme (DNase), and an antibiotic (tobramycin) are tested in various combinations to maximize biofilm disruption. The viscoelastic properties of biofilms are quantified with particle tracking microrheology and transport rates are quantified in a mucociliary transport device comprised of fully differentiated primary human bronchial epithelial cells. The combination of the NP40 with hyaluronic acid and tobramycin was the most effective at increasing mucociliary transport rates, decreasing the viscoelastic properties of mucus, and reducing bacterial viability. Multimechanistic targeting of biofilm infections may ultimately result in improved clinical outcomes, and the results of this study may be translated into future in vivo infection models.

Nontypeable Haemophilus influenzae released from biofilm residence by monoclonal antibody directed against a biofilm matrix component display a vulnerable phenotype

Bacterial biofilms contribute significantly to pathogenesis, recurrence and/or chronicity of the majority of bacterial diseases due to their notable recalcitrance to clearance. Herein, we examined kinetics of the enhanced sensitivity of nontypeable Haemophilus influenzae (NTHI) newly released (NRel) from biofilm residence by a monoclonal antibody against a bacterial DNABII protein (α-DNABII) to preferential killing by a β-lactam antibiotic. This phenotype was detected within 5 min and lasted for ~ 6 h. Relative expression of genes selected due to their known involvement in sensitivity to a β-lactam showed transient up-regulated expression of penicillin binding proteins by α-DNABII NTHI NRel, whereas there was limited expression of the β-lactamase precursor. Transient down-regulated expression of mediators of oxidative stress supported similarly timed vulnerability to NADPH-oxidase sensitive intracellular killing by activated human PMNs. Further, transient up-regulated expression of the major NTHI porin aligned well with observed increased membrane permeability of α-DNABII NTHI NRel, a characteristic also shown by NRel of three additional pathogens. These data provide mechanistic insights as to the transient, yet highly vulnerable, α-DNABII NRel phenotype. This heightened understanding supports continued validation of this novel therapeutic approach designed to leverage knowledge of the α-DNABII NRel phenotype for more effective eradication of recalcitrant biofilm-related diseases.

Druggable redox pathways against Mycobacterium abscessus in cystic fibrosis patient-derived airway organoids

Mycobacterium abscessus (Mabs) drives life-shortening mortality in cystic fibrosis (CF) patients, primarily because of its resistance to chemotherapeutic agents. To date, our knowledge on the host and bacterial determinants driving Mabs pathology in CF patient lung remains rudimentary. Here, we used human airway organoids (AOs) microinjected with smooth (S) or rough (R-)Mabs to evaluate bacteria fitness, host responses to infection, and new treatment efficacy. We show that S Mabs formed biofilm, and R Mabs formed cord serpentines and displayed a higher virulence. While Mabs infection triggers enhanced oxidative stress, pharmacological activation of antioxidant pathways resulted in better control of Mabs growth and reduced virulence. Genetic and pharmacological inhibition of the CFTR is associated with better growth and higher virulence of S and R Mabs. Finally, pharmacological activation of antioxidant pathways inhibited Mabs growth, at least in part through the quinone oxidoreductase NQO1, and improved efficacy in combination with cefoxitin, a first line antibiotic. In conclusion, we have established AOs as a suitable human system to decipher mechanisms of CF-driven respiratory infection by Mabs and propose boosting of the NRF2-NQO1 axis as a potential host-directed strategy to improve Mabs infection control.

ESKAPEE pathogens newly released from biofilm residence by a targeted monoclonal are sensitized to killing by traditional antibiotics

Introduction

The "silent" antimicrobial resistance (AMR) pandemic is responsible for nearly five million deaths annually, with a group of seven biofilm-forming pathogens, known as the ESKAPEE pathogens, responsible for 70% of these fatalities. Biofilm-resident bacteria, as they exist within the disease site, are canonically highly resistant to antibiotics. One strategy to counter AMR and improve disease resolution involves developing methods to disrupt biofilms. These methods aim to release bacteria from the protective biofilm matrix to facilitate their killing by antibiotics or immune effectors. Several laboratories working on such strategies have demonstrated that bacteria newly released from a biofilm display a transient phenotype of significantly increased susceptibility to antibiotics. Similarly, we developed an antibody-based approach for biofilm disruption directed against the two-membered DNABII family of bacterial DNA-binding proteins, which serve as linchpins to stabilize the biofilm matrix. The incubation of biofilms with α-DNABII antibodies rapidly collapses them to induce a population of newly released bacteria (NRel).

Methods

In this study, we used a humanized monoclonal antibody (HuTipMab) directed against protective epitopes of a DNABII protein to determine if we could disrupt biofilms formed by the high-priority ESKAPEE pathogens as visualized by confocal laser scanning microscopy (CLSM) and COMSTAT2 analysis. Then, we demonstrated the potentiated killing of the induced NRel by seven diverse classes of traditional antibiotics by comparative plate count.

Results

To this end, ESKAPEE biofilms were disrupted by 50%-79% using a single tested dose and treatment period with HuTipMab. The NRel of each biofilm were significantly more sensitive to killing than their planktonically grown counterparts (heretofore, considered to be the most sensitive to antibiotic-mediated killing), even when tested at a fraction of the MIC (1/250-1/2 MIC). Moreover, the bacteria that remained within the biofilms of two representative ESKAPEE pathogens after HuTipMab disruption were also significantly more susceptible to killing by antibiotics.

Discussion

New data presented in this study support our continued development of a combinatorial therapy wherein HuTipMab is delivered to a patient with recalcitrant disease due to an ESKAPEE pathogen to disrupt a pathogenic biofilm, along with a co-delivered dose of an antibiotic whose ability to rapidly kill the induced NRel has been demonstrated. This novel regimen could provide a more successful clinical outcome to those with chronic, recurrent, or recalcitrant diseases, while limiting further contribution to AMR.

Antibacterial and Biocompatible Polyethylene Composites with Hybrid Clay Nanofillers

Low-density polyethylene is one of the basic polymers used in medicine for a variety of purposes; so, the relevant improvements in functional properties are discussed here, making it safer to use as devices or implants during surgery or injury. The objective of the laboratory-prepared material was to study the antimicrobial and biocompatible properties of low-density polyethylene composites with 3 wt. % hybrid nanoclay filler. We found that the antimicrobial activity was mainly related to the filler, i.e., the hybrid type, where inorganic clay minerals, vermiculite or montmorillonite, were intercalated with organic chlorhexidine diacetate and subsequently decorated with Ca-deficient hydroxyapatite. After fusion of the hybrid nanofiller with polyethylene, intense exfoliation of the clay layers occurred. This phenomenon was confirmed by the analysis of the X-ray diffraction patterns of the composite, where the original basal peak of the clays decreased or completely disappeared, and the optimal distribution of the filler was observed using the transmission mode of light microscopy. Functional property testing showed that the composites have good antibacterial activity against Staphylococcus aureus, and the biocompatibility prediction demonstrated the formation of Ca- and P-containing particles through an in vitro experiment, thus applicable for medical use.

Nanotherapeutics with immunoregulatory functions for the treatment of bacterial infection

The advent of drug-resistant pathogens results in the occurrence of stubborn bacterial infections that cannot be treated with traditional antibiotics. Antibacterial immunotherapy by reviving or activating the body's immune system to eliminate pathogenic bacteria has confirmed promising therapeutic strategies in controlling bacterial infections. Subsequent studies found that antimicrobial immunotherapy has its own benefits and limitations, such as avoiding recurrence of infection and autoimmunity-induced side effects. Current studies indicate that the various antibacterial therapeutic strategies inducing immune regulation can achieve superior therapeutic efficacy compared with monotherapy alone. Therefore, summarizing the recent advances in nanomedicine with immunomodulatory functions for combating bacterial infections is necessary. Herein, we briefly introduce the crisis caused by drug-resistant bacteria and the opportunity for antibacterial immunotherapy. Then, immune-involved multimodal antibacterial therapy for the treatment of infectious diseases was systematically summarized. Finally, the prospects and challenges of immune-involved combinational therapy are discussed.

Application of a quantitative framework to improve the accuracy of a bacterial infection model

Laboratory models are critical to basic and translational microbiology research. Models serve multiple purposes, from providing tractable systems to study cell biology to allowing the investigation of inaccessible clinical and environmental ecosystems. Although there is a recognized need for improved model systems, there is a gap in rational approaches to accomplish this goal. We recently developed a framework for assessing the accuracy of microbial models by quantifying how closely each gene is expressed in the natural environment and in various models. The accuracy of the model is defined as the percentage of genes that are similarly expressed in the natural environment and the model. Here, we leverage this framework to develop and validate two generalizable approaches for improving model accuracy, and as proof of concept, we apply these approaches to improve models of Pseudomonas aeruginosa infecting the cystic fibrosis (CF) lung. First, we identify two models, an in vitro synthetic CF sputum medium model (SCFM2) and an epithelial cell model, that accurately recapitulate different gene sets. By combining these models, we developed the epithelial cell-SCFM2 model which improves the accuracy of over 500 genes. Second, to improve the accuracy of specific genes, we mined publicly available transcriptome data, which identified zinc limitation as a cue present in the CF lung and absent in SCFM2. Induction of zinc limitation in SCFM2 resulted in accurate expression of 90% of P. aeruginosa genes. These approaches provide generalizable, quantitative frameworks for microbiological model improvement that can be applied to any system of interest.

Protocol to assess metabolic activity of Pseudomonas aeruginosa by measuring heat flow using isothermal calorimetry

Here, we present a protocol for assessing metabolic activity of bacterial populations by measuring heat flow using isothermal calorimetry. We outline the steps for preparing the different growth models of Pseudomonas aeruginosa and performing continuous metabolic activity measurements in the calScreener. We detail simple principal component analysis to differentiate between metabolic states of different populations and probabilistic logistic classification to assess resemblance to wild-type bacteria. This protocol for fine-scale metabolic measurement can aid in understanding microbial physiology. For complete details on the use and execution of this protocol, please refer to Lichtenberg et al. (2022).¹.

Recent Progress of Surface-Enhanced Raman Spectroscopy for Bacteria Detection

There are various pathogenic bacteria in the surrounding living environment, which not only pose a great threat to human health but also bring huge losses to economic development. Conventional methods for bacteria detection are usually time-consuming, complicated and labor-intensive, and cannot meet the growing demands for on-site and rapid analyses. Sensitive, rapid and effective methods for pathogenic bacteria detection are necessary for environmental monitoring, food safety and infectious bacteria diagnosis. Recently, benefiting from its advantages of rapidity and high sensitivity, surface-enhanced Raman spectroscopy (SERS) has attracted significant attention in the field of bacteria detection and identification as well as drug susceptibility testing. Here, we comprehensively reviewed the latest advances in SERS technology in the field of bacteria analysis. Firstly, the mechanism of SERS detection and the fabrication of the SERS substrate were briefly introduced. Secondly, the label-free SERS applied for the identification of bacteria species was summarized in detail. Thirdly, various SERS tags for the high-sensitivity detection of bacteria were also discussed. Moreover, we emphasized the application prospects of microfluidic SERS chips in antimicrobial susceptibility testing (AST). In the end, we gave an outlook on the future development and trends of SERS in point-of-care diagnoses of bacterial infections.

Recent Advances in Monoclonal Antibody-Based Approaches in the Management of Bacterial Sepsis

Sepsis is a life-threatening condition characterized by an uncontrolled inflammatory response to an infectious agent and its antigens. Immune cell activation against the antigens causes severe distress that mediates a strong inflammatory response in vital organs. Sepsis is responsible for a high rate of morbidity and mortality in immunosuppressed patients. Monoclonal antibody (mAb)-based therapeutic strategies are now being explored as a viable therapy option for severe sepsis and septic shock. Monoclonal antibodies may provide benefits through two major strategies: (a) monoclonal antibodies targeting the pathogen and its components, and (b) mAbs targeting inflammatory signaling may directly suppress the production of inflammatory mediators. The major focus of mAb therapies has been bacterial endotoxin (lipopolysaccharide), although other surface antigens are also being investigated for mAb therapy. Several promising candidates for mAbs are undergoing clinical trials at present. Despite several failures and the investigation of novel targets, mAb therapy provides a glimmer of hope for the treatment of severe bacterial sepsis and septic shock. In this review, mAb candidates, their efficacy against controlling infection, with special emphasis on potential roadblocks, and prospects are discussed.

Impact of Growth Rate on the Protein-mRNA Ratio in Pseudomonas aeruginosa

Our understanding of how bacterial pathogens colonize and persist during human infection has been hampered by the limited characterization of bacterial physiology during infection and a research bias toward in vitro, fast-growing bacteria. Recent research has begun to address these gaps in knowledge by directly quantifying bacterial mRNA levels during human infection, with the goal of assessing microbial community function at the infection site. However, mRNA levels are not always predictive of protein levels, which are the primary functional units of a cell. Here, we used carefully controlled chemostat experiments to examine the relationship between mRNA and protein levels across four growth rates in the bacterial pathogen Pseudomonas aeruginosa. We found a genome-wide positive correlation between mRNA and protein abundances across all growth rates, with genes required for P. aeruginosa viability having stronger correlations than nonessential genes. We developed a statistical method to identify genes whose mRNA abundances poorly predict protein abundances and calculated an RNA-to-protein (RTP) conversion factor to improve mRNA predictions of protein levels. The application of the RTP conversion factor to publicly available transcriptome data sets was highly robust, enabling the more accurate prediction of P. aeruginosa protein levels across strains and growth conditions. Finally, the RTP conversion factor was applied to P. aeruginosa human cystic fibrosis (CF) infection transcriptomes to provide greater insights into the functionality of this bacterium in the CF lung. This study addresses a critical problem in infection microbiology by providing a framework for enhancing the functional interpretation of bacterial human infection transcriptome data. IMPORTANCE Our understanding of bacterial physiology during human infection is limited by the difficulty in assessing bacterial function at the infection site. Recent studies have begun to address this question by quantifying bacterial mRNA levels in human-derived samples using transcriptomics. One challenge for these studies is the poor predictivity of mRNA for protein levels for some genes. Here, we addressed this challenge by measuring the transcriptomes and proteomes of P. aeruginosa grown at four growth rates. Our results revealed that the growth rate does not impact the genome-wide correlation of mRNA and protein levels. We used statistical methods to identify the genes for which mRNA and protein were poorly correlated and developed an RNA-to-protein (RTP) conversion factor that improved the predictivity of protein levels across strains and growth conditions. Our results provide new insights into mRNA-protein correlations and tools to enhance our understanding of bacterial physiology from transcriptome data.

Architecture and matrix assembly determinants of Bordetella pertussis biofilms on primary human airway epithelium

Traditionally, whooping cough or pertussis caused by the obligate human pathogen Bordetella pertussis (Bp) is described as an acute disease with severe symptoms. However, many individuals who contract pertussis are either asymptomatic or show very mild symptoms and yet can serve as carriers and sources of bacterial transmission. Biofilms are an important survival mechanism for bacteria in human infections and disease. However, bacterial determinants that drive biofilm formation in humans are ill-defined. In the current study, we show that Bp infection of well-differentiated primary human bronchial epithelial cells leads to formation of bacterial aggregates, clusters, and highly structured biofilms which are colocalized with cilia. These findings mimic observations from pathological analyses of tissues from pertussis patients. Distinct arrangements (mono-, bi-, and tri-partite) of the polysaccharide Bps, extracellular DNA, and bacterial cells were visualized, suggesting complex heterogeneity in bacteria-matrix interactions. Analyses of mutant biofilms revealed positive roles in matrix production, cell cluster formation, and biofilm maturity for three critical Bp virulence factors: Bps, filamentous hemagglutinin, and adenylate cyclase toxin. Adherence assays identified Bps as a new Bp adhesin for primary human airway cells. Taken together, our results demonstrate the multi-factorial nature of the biofilm extracellular matrix and biofilm development process under conditions mimicking the human respiratory tract and highlight the importance of model systems resembling the natural host environment to investigate pathogenesis and potential therapeutic strategies.

Are There Any Changes in the Causative Microorganisms Isolated in the Last Years from Hip and Knee Periprosthetic Joint Infections? Antimicrobial Susceptibility Test Results Analysis

BACKGROUND

PJIs following total hip and knee arthroplasty represent severe complications with broad implications, and with significant disability, morbidity, and mortality. To be able to provide correct and effective management of these cases, an accurate diagnosis is needed. Classically, acute PJIs are characterized by a preponderance of virulent microorganisms, and chronic PJIs are characterized by a preponderance of less-virulent pathogens like coagulase-negative staphylococci or Cutibacterium species. This paper aims to analyze if there are any changes in the causative microorganisms isolated in the last years, as well as to provide a subanalysis of the types of PJIs.

METHODS

In this single-center study, we prospectively included all retrospectively consecutive collected data from patients aged over 18 years that were hospitalized from 2016 through 2022, and patients that underwent a joint arthroplasty revision surgery. A standardized diagnostic protocol was used in all cases, and the 2021 EBJIS definition criteria for PJIs was used.

RESULTS

114 patients were included in our analysis; of them, 67 were diagnosed with PJIs, 12 were acute/acute hematogenous, and 55 were chronic PJIs. 49 strains of gram-positive aerobic or microaerophilic cocci and 35 gram-negative aerobic bacilli were isolated. Overall, Staphylococcus aureus was the most common isolated pathogen, followed by coagulase-negative staphylococci (CoNS). All cases of acute/acute hematogenous PJIs were caused by gram-positive aerobic or microaerophilic cocci pathogens. Both Staphylococcus epidermidis and methicillin-resistant S. aureus were involved in 91.66% of the acute/acute hematogenous PJIs cases. 21.8% of the chronic PJIs cases were caused by pathogens belonging to the Enterobacterales group of bacteria, followed by the gram-negative nonfermenting bacilli group of bacteria, which were involved in 18.4% of the cases. 12 chronic cases were polymicrobial.

CONCLUSION

Based on our findings, empiric broad-spectrum antibiotic therapy in acute PJIs could be focused on the bacteria belonging to the gram-positive aerobic or microaerophilic cocci, but the results should be analyzed carefully, and the local resistance of the pathogens should be taken into consideration.

Pseudomonas aeruginosa aggregation and Psl expression in sputum is associated with antibiotic eradication failure in children with cystic fibrosis

We previously demonstrated that P. aeruginosa isolates that persisted in children with cystic fibrosis (CF) despite inhaled tobramycin treatment had increased anti-Psl antibody binding in vitro compared to those successfully eradicated. We aimed to validate these findings by directly visualizing P. aeruginosa in CF sputum. This was a prospective observational study of children with CF with new-onset P. aeruginosa infection who underwent inhaled tobramycin eradication treatment. Using microbial identification passive clarity technique (MiPACT), P. aeruginosa was visualized in sputum samples obtained before treatment and classified as persistent or eradicated based on outcomes. Pre-treatment isolates were also grown as biofilms in vitro. Of 11 patients enrolled, 4 developed persistent infection and 7 eradicated infection. P. aeruginosa biovolume and the number as well as size of P. aeruginosa aggregates were greater in the sputum of those with persistent compared with eradicated infections (p < 0.01). The amount of Psl antibody binding in sputum was also greater overall (p < 0.05) in samples with increased P. aeruginosa biovolume. When visualized in sputum, P. aeruginosa had a greater biovolume, with more expressed Psl, and formed more numerous, larger aggregates in CF children who failed eradication therapy compared to those who successfully cleared their infection.

Prevalence of biofilms in acute infections challenges a longstanding paradigm

The significance of bacterial biofilm formation in chronic bacterial lung infections has long been recognized [1]. Likewise, chronic biofilm formation on medical devices is well accepted as a nidus for recurrent bacteremia [2,3]. Even though the prevailing paradigm relies on the dominance of planktonic bacteria in acute endobronchial infections, our understanding of the bacterial organization during acute infection is, so far, limited - virtually absent. However, by comparing similar clinical samples, we have recently demonstrated massive bacterial biofilm formation during acute lung infections resembling the immense bacterial biofilm formation during chronic lung infections. These findings pose major challenges to the basic paradigm of chronic infections being dominated by biofilm forming bacteria while acute infections are dominated by planktonic bacteria. As opposed to the similar high amount of bacterial biofilm found in chronic and acute lung infections, we found that the fast bacterial growth in acute lung infections differed from the slow bacterial growth in chronic lung infections. By highlighting these new findings, we review modes of improved treatment of biofilm infections and the relevance of bacterial growth rates for other bacterial biofilm infections than human lung infections.

The Combination of Low-Frequency Ultrasound and Antibiotics Improves the Killing of In Vitro Staphylococcus aureus and Pseudomonas aeruginosa Biofilms

Due to an increase in underlying predisposing factors, chronic wounds have become an increasing burden on healthcare systems worldwide. Chronic infections often contain biofilm-forming bacteria, which are challenging to eradicate due to increased antibiotic tolerance; thus, new and improved therapeutic strategies are warranted. One such strategy is the combination of ultrasound and antibiotics. Therefore, this study aimed to investigate the combinatory effects of low-frequency (50 kHz) ultrasound delivered by specially designed ultrasound patches using flexible piezoelectric material, PiezoPaint™, in combination with antibiotics against biofilms with Staphylococcus aureus and Pseudomonas aeruginosa. The reduction in viable cells in S. aureus and P. aeruginosa biofilms was evaluated post-treatment with fusidic acid, clindamycin, ciprofloxacin, and colistin in combination with ultrasound treatment. Two-hour ultrasound treatment significantly increased the bactericidal effect of all four antibiotics, resulting in a 96−98% and 90−93% reduction in P. aeruginosa and S. aureus, respectively. In addition, an additive effect was observed when extending treatment to 4 h, resulting in >99% and 95−97% reduction in P. aeruginosa and S. aureus, respectively. These results contrasted the lack of effect observed when treating filter-biofilms with antibiotics alone. The combined effect of ultrasound and antibiotic treatment resulted in a synergistic effect, reducing the viability of the clinically relevant pathogens S. aureus and P. aeruginosa. The modularity of the specially designed patches intended for topical treatment holds promising applications as a supplement in chronic wound therapy. Further studies are warranted with clinically isolated strains and other clinically relevant antibiotics before proceeding to studies where safety and applicability are investigated.

Designer Liposomic Nanocarriers Are Effective Biofilm Eradicators

Drug delivery via nanovehicles is successfully employed in several clinical settings, yet bacterial infections, forming microbial communities in the form of biofilms, present a strong challenge to therapeutic treatment due to resistance to conventional antimicrobial therapies. Liposomes can provide a versatile drug-vector strategy for biofilm treatment, but are limited by the need to balance colloidal stability with biofilm penetration. We have discovered a liposomic functionalization strategy, using membrane-embedded moieties of poly[2-(methacryloyloxy)ethyl phosphorylcholine], pMPC, that overcomes this limitation. Such pMPCylation results in liposomic stability equivalent to current functionalization strategies (mostly PEGylation, the present gold-standard), but with strikingly improved cellular uptake and cargo conveyance. Fluorimetry, cryo-electron, and fluorescence microscopies reveal a far-enhanced antibiotic delivery to model Pseudomonas aeruginosa biofilms by pMPC-liposomes, followed by faster cytosolic cargo release, resulting in significantly greater biofilm eradication than either PEGylation or free drug. Moreover, this combination of techniques uncovers the molecular mechanism underlying the enhanced interaction with bacteria, indicating it arises from bridging by divalent ions of the zwitterionic groups on the pMPC moieties to the negatively charged lipopolysaccharide chains emanating from the bacterial membranes. Our results point to pMPCylation as a transformative strategy for liposomal functionalization, leading to next-generation delivery systems for biofilm treatment.

Biofilm antimicrobial susceptibility through an experimental evolutionary lens

Experimental evolution experiments in which bacterial populations are repeatedly exposed to an antimicrobial treatment, and examination of the genotype and phenotype of the resulting evolved bacteria, can help shed light on mechanisms behind reduced susceptibility. In this review we present an overview of why it is important to include biofilms in experimental evolution, which approaches are available to study experimental evolution in biofilms and what experimental evolution has taught us about tolerance and resistance in biofilms. Finally, we present an emerging consensus view on biofilm antimicrobial susceptibility supported by data obtained during experimental evolution studies.

Targeted Anti-Biofilm Therapy: Dissecting Targets in the Biofilm Life Cycle

Biofilm is a crucial virulence factor for microorganisms that causes chronic infection. After biofilm formation, the bacteria present improve drug tolerance and multifactorial defense mechanisms, which impose significant challenges for the use of antimicrobials. This indicates the urgent need for new targeted technologies and emerging therapeutic strategies. In this review, we focus on the current biofilm-targeting strategies and those under development, including targeting persistent cells, quorum quenching, and phage therapy. We emphasize biofilm-targeting technologies that are supported by blocking the biofilm life cycle, providing a theoretical basis for design of targeting technology that disrupts the biofilm and promotes practical application of antibacterial materials.

The biofilm life cycle: expanding the conceptual model of biofilm formation

Bacterial biofilms are often defined as communities of surface-attached bacteria and are typically depicted with a classic mushroom-shaped structure characteristic of Pseudomonas aeruginosa. However, it has become evident that this is not how all biofilms develop, especially in vivo, in clinical and industrial settings, and in the environment, where biofilms often are observed as non-surface-attached aggregates. In this Review, we describe the origin of the current five-step biofilm development model and why it fails to capture many aspects of bacterial biofilm physiology. We aim to present a simplistic developmental model for biofilm formation that is flexible enough to include all the diverse scenarios and microenvironments where biofilms are formed. With this new expanded, inclusive model, we hereby introduce a common platform for developing an understanding of biofilms and anti-biofilm strategies that can be tailored to the microenvironment under investigation.

Breaching Bacterial Biofilm Barriers: Efficient Combinatorial Theranostics for Multidrug-Resistant Bacterial Biofilms with a Novel Penetration-Enhanced AIEgen Probe

The formation of microbial biofilms is acknowledged as a major virulence factor in a range of persistent local infections. Failures to remove biofilms with antibiotics foster the emergence of antibiotic-resistant bacteria and result in chronic infections. As a result, the construction of effective biofilm-inhibiting and biofilm-eradicating chemicals is urgently required. Herein, we designed a water-soluble probe APDIS for membrane-active fluorescence and broad-spectrum antimicrobial actions, particularly against methicillin-resistant Staphylococcus aureus (MRSA), which shows multidrug resistance. In vitro and in vivo experiments demonstrate its high antibacterial effects comparable to vancomycin. Furthermore, it inhibits biofilm formation by effectively killing planktonic bacteria at low inhibitory concentrations, without toxicity to mammalian cells. More importantly, this probe can efficiently penetrate through biofilm barriers and exterminate bacteria that are enclosed within biofilms and startle existing biofilms. In the mouse model of implant-related biofilm infections, this probe exhibits strong antibiofilm activity against MRSA biofilms, thus providing a novel theranostic strategy to disrupt biofilms in vivo effectively. Our results indicate that this probe has the potential to be used for the development of a combinatorial theranostic platform with synergistic enhanced effects for the treatment of multidrug-resistant bacterial infections and antibiofilm medications.

Biofilm aggregates and the host airway-microbial interface

Biofilms are multicellular microbial aggregates that can be associated with host mucosal epithelia in the airway, gut, and genitourinary tract. The host environment plays a critical role in the establishment of these microbial communities in both health and disease. These host mucosal microenvironments however are distinct histologically, functionally, and regarding nutrient availability. This review discusses the specific mucosal epithelial microenvironments lining the airway, focusing on: i) biofilms in the human respiratory tract and the unique airway microenvironments that make it exquisitely suited to defend against infection, and ii) how airway pathophysiology and dysfunctional barrier/clearance mechanisms due to genetic mutations, damage, and inflammation contribute to biofilm infections. The host cellular responses to infection that contribute to resolution or exacerbation, and insights about evaluating and therapeutically targeting airway-associated biofilm infections are briefly discussed. Since so many studies have focused on Pseudomonas aeruginosa in the context of cystic fibrosis (CF) or on Haemophilus influenzae in the context of upper and lower respiratory diseases, these bacteria are used as examples. However, there are notable differences in diseased airway microenvironments and the unique pathophysiology specific to the bacterial pathogens themselves.

The Use of Artificial Sputum Media to Enhance Investigation and Subsequent Treatment of Cystic Fibrosis Bacterial Infections

In cystic fibrosis (CF), mutations in the CF transmembrane conductance regulator protein reduce ionic exchange in the lung, resulting in thicker mucus, which impairs mucociliary function, airway inflammation and infection. The mucosal and nutritional environment of the CF lung is inadequately mimicked by commercially available growth media, as it lacks key components involved in microbial pathogenesis. Defining the nutritional composition of CF sputum has been a long-term goal of in vitro research into CF infections to better elucidate bacterial growth and infection pathways. This narrative review highlights the development of artificial sputum medium, from a viable in vitro method for understanding bacterial mechanisms utilised in CF lung, to uses in the development of antimicrobial treatment regimens and examination of interactions at the epithelial cell surface and interior by the addition of host cell layers. The authors collated publications based on a PubMed search using the key words: “artificial sputum media” and “cystic fibrosis”. The earliest iteration of artificial sputum media were developed in 1997. Formulations since then have been based either on published data or chemically derived from extracted sputum. Formulations contain combinations of mucin, extracellular DNA, iron, amino acids, and lipids. A valuable advantage of artificial sputum media is the ability to standardise media composition according to experimental requirements.

Increased sputum lactate during oral glucose tolerance test in cystic fibrosis

Blood glucose levels exceeding 8 mM are shown to increase glucose levels in airway surface in cystic fibrosis (CF). Moreover, high levels of endobronchial glucose are proposed to increase the growth of common CF bacteria and feed the neutrophil‐driven inflammation. In the infected airways, glucose may be metabolized by glycolysis to lactate by both bacteria and neutrophils. Therefore, we aimed to investigate whether increased blood glucose may fuel the glycolytic pathways of the lung inflammation by determining sputum glucose and lactate during an oral glucose tolerance test (OGTT). Sputum from 27 CF patients was collected during an OGTT. Sputum was collected at fasting and one and two hours following the intake of 75 g of glucose. Only participants able to expectorate more than one sputum sample were included. Glucose levels in venous blood and lactate and glucose content in sputum were analyzed using a regular blood gas analyzer. We collected 62 sputum samples: 20 at baseline, 22 after 1 h, and 20 after 2 h. Lactate and glucose were detectable in 30 (48.4%) and 43 (69.4%) sputum samples, respectively. The sputum lactate increased significantly at 2 h in the OGTT (p = 0.024), but sputum glucose was not changed. As expected, plasma glucose level significantly increased during the OGTT (p < 0.001). In CF patients, sputum lactate increased during an OGTT, while the sputum glucose did not reflect the increased plasma glucose. The increase in sputum lactate suggests that glucose spills over from plasma to sputum where glucose may enhance the inflammation by fueling the anaerobic metabolism in neutrophils or bacteria.

Biofilm Survival Strategies in Chronic Wounds

Bacterial biofilms residing in chronic wounds are thought to have numerous survival strategies, making them extremely difficult to eradicate and resulting in long-term infections. However, much of our knowledge regarding biofilm persistence stems from in vitro models and experiments performed in vivo in animal models. While the knowledge obtained from such experiments is highly valuable, its direct translation to the human clinical setting should be undertaken with caution. In this review, we highlight knowledge obtained from human clinical samples in different aspects of biofilm survival strategies. These strategies have been divided into segments of the following attributes: altered transcriptomic profiles, spatial distribution, the production of extracellular polymeric substances, an altered microenvironment, inter-and intra-species interactions, and heterogeneity in the bacterial population. While all these attributes are speculated to contribute to the enhanced persistence of biofilms in chronic wounds, only some of them have been demonstrated to exist in human wounds. Some of the attributes have been observed in other clinical diseases while others have only been observed in vitro. Here, we have strived to clarify the limitations of the current knowledge in regard to this specific topic, without ignoring important in vitro and in vivo observations.