The immune system vs. Pseudomonas aeruginosa biofilms

Hematological Picture of Rabbits Immunized with Pseudomonas aeruginosa

The current study was established to find out the role of immunization of Pseudomonas aeruginosa-whole sonicated antigen in adult white fur domestic rabbits. To achieve this goal, fifteen rabbits were allocated into 3 groups, the first group was immunized with P. aeruginosa–whole sonicated antigen and challenged with viable pathogenic P. aeruginosa; the second group (control negative) was treated with phosphate buffer saline and the third group was injected with viable pathogenic P. aeruginosa (control positive). The results demonstrated increasing levels of the measured parameters blood picture (total WBCs, lymphocytes, and granulocytes, RBCs and hemoglobin concentrations) in the first group compared with control negative group (T test was used). In contrast, a sharp fall was noted in total thrombocytes (platelets) count in the first group compared with control negative group. It can be concluded that immunization with P. aeruginosa– whole sonicated antigen may consider as a potent reproducible effective immunogen model for experimental immunological studies in rabbits.

The Extracellular Polysaccharide Matrix of Pseudomonas aeruginosa Biofilms Is a Determinant of Polymorphonuclear Leukocyte Responses

Bacterial biofilms may cause chronic infections due to their ability to evade clearance by the immune system and antibiotics. The persistent biofilms induce a hyperinflammatory state that damages the surrounding host tissue. Knowledge about the components of biofilms that are responsible for provoking the harmful but inefficient immune response is limited. Flagella are known to stimulate the response of polymorphonuclear leukocytes (PMNs) to planktonic solitary bacteria. However, we provide evidence that flagella are not a prerequisite for the response of PMNs to Pseudomonas aeruginosa biofilms. Instead, we found that extracellular matrix polysaccharides in P. aeruginosa biofilms play a role in the response of PMNs toward biofilms. Using a set of P. aeruginosa mutants with the ability to produce a subset of matrix exopolysaccharides, we found that P. aeruginosa biofilms with distinct exopolysaccharide matrix components elicit distinct PMN responses. In particular, the PMNs respond aggressively toward a biofilm matrix consisting of both Psl and alginate exopolysaccharides. These findings are relevant for therapeutic strategies aimed at dampening the collateral damage associated with biofilm-based infections.

Silver Sulfadiazine Eradicates Antibiotic-Tolerant Staphylococcus aureus and Pseudomonas aeruginosa Biofilms in Patients with Infected Diabetic Foot Ulcers

Infections are among the most frequent and challenging events in diabetic foot ulcers (DFUs). Pathogenic bacteria growing in biofilms within host tissue are highly tolerant to environmental and chemical agents, including antibiotics. The present study was aimed at assessing the use of silver sulfadiazine (SSD) for wound healing and infection control in 16 patients with DFUs harboring biofilm-growing Staphylococcus aureus and Pseudomonas aeruginosa. All patients received a treatment based on a dressing protocol including disinfection, cleansing, application of SSD, and application of nonadherent gauze, followed by sterile gauze and tibio-breech bandage, in preparation for toilet surgery after 30 days of treatment. Clinical parameters were analyzed by the T.I.M.E. classification system. In addition, the activity of SSD against biofilm-growing S. aureus and P. aeruginosa isolates was assessed in vitro. A total of 16 patients with S. aureus and P. aeruginosa infected DFUs were included in the study. Clinical data showed a statistically significant (p < 0.002) improvement of patients' DFUs after 30 days of treatment with SSD with significant amelioration of all the parameters analyzed. Notably, after 30 days of treatment, resolution of infection was observed in all DFUs. In vitro analysis showed that both S. aureus and P. aeruginosa isolates developed complex and highly structured biofilms. Antibiotic susceptibility profiles indicated that biofilm cultures were significantly (p ≤ 0.002) more tolerant to all tested antimicrobials than their planktonic counterparts. However, SSD was found to be effective against fully developed biofilms of both S. aureus and P. aeruginosa at concentrations below those normally used in clinical preparations (10 mg/mL). These results strongly suggest that the topical administration of SSD may represent an effective alternative to conventional antibiotics for the successful treatment of DFUs infected by biofilm-growing S. aureus and P. aeruginosa.

Corneal Infection Models: Tools to Investigate the Role of Biofilms in Bacterial Keratitis

Bacterial keratitis is a corneal infection which may cause visual impairment or even loss of the infected eye. It remains a major cause of blindness in the developing world. Staphylococcus aureus and Pseudomonas aeruginosa are common causative agents and these bacterial species are known to colonise the corneal surface as biofilm populations. Biofilms are complex bacterial communities encased in an extracellular polymeric matrix and are notoriously difficult to eradicate once established. Biofilm bacteria exhibit different phenotypic characteristics from their planktonic counterparts, including an increased resistance to antibiotics and the host immune response. Therefore, understanding the role of biofilms will be essential in the development of new ophthalmic antimicrobials. A brief overview of biofilm-specific resistance mechanisms is provided, but this is a highly multifactorial and rapidly expanding field that warrants further research. Progression in this field is dependent on the development of suitable biofilm models that acknowledge the complexity of the ocular environment. Abiotic models of biofilm formation (where biofilms are studied on non-living surfaces) currently dominate the literature, but co-culture infection models are beginning to emerge. In vitro, ex vivo and in vivo corneal infection models have now been reported which use a variety of different experimental techniques and animal models. In this review, we will discuss existing corneal infection models and their application in the study of biofilms and host-pathogen interactions at the corneal surface.

Residue L193P Mutant of RpoS Affects Its Activity During Biofilm Formation in Salmonella Pullorum

The role of alternative sigma factor RpoS in regulating biofilm formation may differ in various Salmonella Pullorum strains. In this study, the biofilm-forming ability of two Salmonella Pullorum strains S6702 and S11923-3 were compared. The biofilm forming ability of S11923-3 was much stronger than that of S6702. After knocking out the rpoS gene, S11923-3ΔrpoS had significantly reduced biofilm while S6702ΔrpoS demonstrated similar biofilm compared with each parent strain. The analysis of RpoS sequences indicated two amino acid substitutions (L193P and R293C) between S6702 and S11923-3 RpoS. A complementation study confirmed that the expression of S11923-3 RpoS rather than S6702 RpoS could restore the biofilm-forming ability of ΔrpoS strains and the L193P mutation contributed to the restoration of the biofilm-forming ability. Further study indicated that RpoS with the L193P mutant had significantly improved expression level and binding activity to RNAP and csgD gene promoter, which increased the efficacy of the csgD gene promoter and biofilm-forming ability. Therefore, the L193P mutation of RpoS is critical for stronger biofilm formation of Salmonella Pullorum.

Early IL-2 treatment of mice with Pseudomonas aeruginosa pneumonia induced PMN-dominating response and reduced lung pathology

IL-2 is a pro-inflammatory and a Th1 inducing cytokine, which is important for activation of the cell-mediated immunity. IL-2 in serum and sputum has been observed to be reduced in cystic fibrosis (CF) patients. The present IL-2 treatment study of Pseudomonas aeruginosa (PA) lung infected mice was performed in order to evaluate the effect of IL-2 supplement. One hundred-and-twenty female BALB/c mice were divided into three groups: 1) IL-2 treatment/infection (TIG), 2) non-treatment/infection (NTIG), and 3) IL-2 treatment/non-infection (TNIG). The mice were challenged intra-tracheally with PA (PAO579) embedded in seaweed alginate to resemble the biofilm mode of growth. At day 0 and 1, the treatment groups received IL-2 s.c. Mice were killed on day 1 or 2, and cytokine production, lung pathology, and quantitative lung bacteriology were estimated. IL-2 treatment of infected mice reduced the number of mice with signs of macroscopic lung pathology at day 2 (p < 0.05). The reduced macroscopic pathology was paralleled by a reduced IL-1β and TNF-α. In contrast, an increased PMN response at day 2 was observed in the IL-2 treated mice (p < 0.01). This was preceded by a significantly higher degree of microscopic inflammation at day 1 (p < 0.02). The IL-12 levels decreased in both groups of infected mice at day 2 (p < 0.01), however, significantly more in the IL-2 treated mice (p < 0.02). In accordance, but surprisingly, IFN-γ was significantly reduced in the IL-2 treated PA infected group at day 2 (p < 0.05). The present results indicate that early IL-2 treatment prolongs the PMN response but also reduces pro-inflammatory IL-1β and TNF-α and macroscopic signs of pathology.

Bacterial aggregate size determines phagocytosis efficiency of polymorphonuclear leukocytes

The ability of bacteria to aggregate and form biofilms impairs phagocytosis by polymorphonuclear leukocytes (PMNs). The aim of this study was to examine if the size of aggregates is critical for successful phagocytosis and how bacterial biofilms evade phagocytosis. We investigated the live interaction between PMNs and Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Staphylococcus epidermidis using confocal scanning laser microscopy. Aggregate size significantly affected phagocytosis outcome and larger aggregates were less likely to be phagocytized. Aggregates of S. epidermidis were also less likely to be phagocytized than equally-sized aggregates of the other three species. We found that only aggregates of approx. 5 μm diameter or smaller were consistently phagocytosed. We demonstrate that planktonic and aggregated cells of all four species significantly reduced the viability of PMNs after 4 h of incubation. Our results indicate that larger bacterial aggregates are less likely to be phagocytosed by PMNs and we propose that, if the aggregates become too large, circulating PMNs may not be able to phagocytose them quickly enough, which may lead to chronic infection.

The zone model: A conceptual model for understanding the microenvironment of chronic wound infection

In 2008, two articles in Wound Repair and Regeneration changed the clinical perspective on chronic wounds. They stated that chronic wounds that do not heal contain bacterial biofilms and that these biofilms may be one of the reasons for the nonhealing properties of the wounds. However, we still do not understand the exact role biofilms play in the halted healing process, and we are not able to successfully treat them. The reason for this could be that in vivo biofilms differ substantially from in vitro biofilms, and that most of the knowledge about biofilms originates from in vitro research. In this article, we introduce the zone model as a concept for understanding bacterial behavior and the impact of the microenvironment on both the host and the bacteria. Until now, identification of bacteria, gene expression, and postscript regulation have been looking at a bulk of bacteria and averaging the behavior of all the bacteria. As the zone model dictates that every single bacterium reacts to its own microenvironment, the model may facilitate the planning of future research with improved clinical relevance. The zone model integrates physiology and biology from single cells, microbial aggregates, local host response, surrounding tissue, and the systemic context of the whole host. Understanding the mechanisms behind the actions and reactions by a single bacterium when interacting with other neighboring bacteria cells, other microorganisms, and the host will help us overcome the detrimental effects of bacteria in chronic wounds. Furthermore, we propose use of the terminology "bacterial phenotype" when describing the actions and reactions of bacteria, and the term "biofilms" to describe the morphology of the bacterial community.

Three new polyacetylene glycosides (PAGs) from the aerial part of Launaea capitata (Asteraceae) with anti-biofilm activity against Staphylococcus aureus

Four polyacetylenic glycosides, three of which are new, together with two known flavonoids were isolated from the methanol extract of the aerial parts of Launaea capitate, designated bidensyneoside A1 (1), 6´-O-acetyl-bidensyneoside A1 (2), bidensyneoside E (3), bidensyneoside F (4), luteolin (5) and luteolin-7-glucoside (6) also known as cynaroside. Their structures were elucidated by comprehensive analysis of 1D, 2D-NMR and HR-MS data. The absolute configuration of the bidensyneosides was determined by Mosher ester analysis and the optical rotation values. The isolated compounds were tested against biofilm formation of Staphylococcus aureus as well as against several pathogens including Gram-positive bacteria, Gram-negative bacteria, fungi and yeasts. Furthermore, they were tested for their cytotoxicity against two cancer cell lines L929 and KB-3-1. Compound 4 showed moderate inhibition of S. aureus biofilm formation with 30% and 25% at 256 and 128 μg/mL, respectively, while compounds 1 and 5 showed weak inhibition with 20% at 256 μg/mL. Compound 5 showed moderate cytotoxicity against both cell lines L929 and KB-3-1, with IC₅₀ values of 18 μg/mL.

Development of Pseudomonas aeruginosa Biofilms in Partial-Thickness Burn Wounds Using a Sprague-Dawley Rat Model

We used a modified Walker–Mason scald burn rat model to demonstrate that Pseudomonas aeruginosa, a common opportunistic pathogen in the burn ward and notable biofilm former, establishes biofilms within deep partial-thickness burn wounds in rats.

Deep partial-thickness burn wounds, ~10% of the TBSA, were created in anesthetized male Sprague-Dawley rats (350–450 g; n = 84). Immediately post-burn, 100 µl of P. aeruginosa in phosphate-buffered saline at 1 × 10³, 1 × 10⁴, or 1 × 10⁵ cells/wound was spread over the burn surface . At 1, 3, 7, and 11 days post-burn, animals were euthanized and blood and tissue were collected for complete blood counts, colony-forming unit (CFU) counts, biofilm gene expression, histology, scanning electron microscopy (SEM), and myeloperoxidase activity in the burn eschar.

P. aeruginosa developed robust biofilm wound infections, plateauing at ~1 × 10⁹ CFU/g burn tissue within 7 days regardless of inoculum size. Expression of Pseudomonas alginate genes and other virulence factors in the infected wound indicated formation of mature P. aeruginosa biofilm within the burn eschar. Compared to un-inoculated wounds, P. aeruginosa infection caused both local and systemic immune responses demonstrated by changes in systemic neutrophil counts, histology, and myeloperoxidase activity within the burn wound. Additionally, SEM showed P. aeruginosa enmeshed within an extracellular matrix on the burn surface as well as penetrating 500–600 µm deep into the eschar.

P. aeruginosa establishes biofilms within deep partial-thickness burn wounds and invades deep into the burned tissue. This new in vivo biofilm infection model is valuable for testing novel anti-biofilm agents to advance burn care.

The Battle of Probiotics and Their Derivatives Against Biofilms

Biofilm-related infections have been a major clinical problem and include chronic infections, device-related infections and malfunction of medical devices. Since biofilms are not fully available for the human immune system and antibiotics, they are difficult to eradicate and control; therefore, imposing a global threat to human health. There have been avenues to tackle biofilms largely based on the disruption of their adhesion and maturation. Nowadays, the use of probiotics and their derivatives has gained a growing interest in battling against pathogenic biofilms. In the present review, we have a close look at probiotics with the ultimate objective of inhibiting biofilm formation and maturation. Overall, insights into the mechanisms by which probiotics and their derivatives can be used in the management of biofilm infections would be warranted.

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.

Harnessing bacterial interactions to manage infections: a review on the opportunistic pathogen Pseudomonas aeruginosa as a case example

During infections, bacterial pathogens can engage in a variety of interactions with each other, ranging from the cooperative sharing of resources to deadly warfare. This is especially relevant in opportunistic infections, where different strains and species often co-infect the same patient and interact in the host. Here, we review the relevance of these social interactions during opportunistic infections using the human pathogen Pseudomonas aeruginosa as a case example. In particular, we discuss different types of pathogen-pathogen interactions, involving both cooperation and competition, and elaborate on how they impact virulence in multi-strain and multi-species infections. We then review evolutionary dynamics within pathogen populations during chronic infections. We particuarly discuss how local adaptation through niche separation, evolutionary successions and antagonistic co-evolution between pathogens can alter virulence and the damage inflicted on the host. Finally, we outline how studying bacterial social dynamics could be used to manage infections. We show that a deeper appreciation of bacterial evolution and ecology in the clinical context is important for understanding microbial infections and can inspire novel treatment strategies.

Differential Effects of Growth Medium Salinity on Biofilm Formation of Two Salmonella enterica Strains

ABSTRACT

Salmonella enterica is a prominent foodborne pathogen, including diverse serotypes that are prolific biofilm formers. Its ability to form biofilm can be affected by multiple environmental factors. In this study, the effect of salinity on biofilm formation by S. enterica was evaluated by using two recently isolated strains of Salmonella serotypes Enteritidis and Newport. Although supplementing the growth medium with a low concentration (0.5 to 2%) of sodium chloride (NaCl) slightly enhanced biofilm formation for the strain S. enterica serovar Enteritidis 110, it sharply reduced or abolished biofilm formation by the strain S. enterica serovar Newport 193. This differential effect of salinity on S. enterica strains of different serotypes was poorly correlated with inhibition of planktonic growth but strongly correlated with cell motility. Examining genes known to affect biofilm formation showed that the expression of adrA, csgD, and fliC, which encode proteins required for surface adhesion and cell motility, was significantly downregulated with salinity increase in Salmonella Newport 193 but not in Salmonella Enteritidis 110. Therefore, it is plausible that the differential effect of salinity on biofilm formation by Salmonella Enteritidis 110 and Salmonella Newport 193 resulted from the differential regulation to genes required for cell adherence and motility.

HIGHLIGHTS

Clinical Impact of Antibiotics for the Treatment of Pseudomonas aeruginosa Biofilm Infections

Bacterial biofilms are highly recalcitrant to antibiotic therapies due to multiple tolerance mechanisms. The involvement of Pseudomonas aeruginosa in a wide range of biofilm-related infections often leads to treatment failures. Indeed, few current antimicrobial molecules are still effective on tolerant sessile cells. In contrast, studies increasingly showed that conventional antibiotics can, at low concentrations, induce a phenotype change in bacteria and consequently, the biofilm formation. Understanding the clinical effects of antimicrobials on biofilm establishment is essential to avoid the use of inappropriate treatments in the case of biofilm infections. This article reviews the current knowledge about bacterial growth within a biofilm and the preventive or inducer impact of standard antimicrobials on its formation by P. aeruginosa. The effect of antibiotics used to treat biofilms of other bacterial species, as Staphylococcus aureus or Escherichia coli, was also briefly mentioned. Finally, it describes two in vitro devices which could potentially be used as antibiotic susceptibility testing for adherent bacteria.

Haemophilus influenzae and Haemophilus parainfluenzae occurrence in the ear effusion in pediatric patients prone to recurrent respiratory tract infections (RRTI) and with otitis media with effusion (OME)

Introduction. Haemophilus influenzae and Haemophilus parainfluenzae are known as human-restricted respiratory microbiota representatives. The aim of the present paper was to assay haemophili prevalence in middle ear effusion specimens in pediatric patients with otitis media with effusion (OME).

Methods. A total of 86 ear effusion specimens (from the left and right ear independently) were collected from 43 pediatric patients with OME. For comparison, 58 nasopharyngeal specimens were taken from 58 pediatric patients prone to recurrent respiratory tract infections (RRTI). Isolation and identification of haemophili biotypes and antimicrobial susceptibility was accomplished by standard microbiological methods. The cell surface hydrophobicity (CSH) of isolates was assayed by the method of aggregation in ammonium sulfate (SAT).

Results. Haemophili were isolated in 25.6% (11/43) of all OME patients: in 5/43 (11.6%)– H. influenzae (biotypes II, III), in 5/43 (11.6%) – H. parainfluenzae, in 1/43 (2.3%) – both species were found. Haemophili-positive nasopharyngeal specimen was found in 27/58 (46.6%) RRTI patients: in 19/58 (32.8%) – H. influenzae, in 8/58 (13.8%) – H. parainfluenzae. About 90% of all haemophili isolates were characterised by extreme to strong CSH. Antimicrobial resistance occurred mainly among H. parainfluenzae (80%) and to a much lower percentage among H. influenzae (33.3%) isolates. The obtained data suggest that both H. influenzae and H. parainfluenzae can be involved in pathology of OME in pediatric patients. The high cell surface hydrophobicity can affect on the haemophili prevalence and ear colonization, and induces predisposition to the presence of these bacteria as a biofilm that serves as a virulence factor with great importance for the survival of these opportunistic bacteria and their persistence in the ear environment.

Cytokine Levels in the In Vitro Response of T Cells to Planktonic and Biofilm Corynebacterium amycolatum

Unravelling of the interplay between the immune system and non-diphtheria corynebacteria would contribute to understanding their increasing role as medically important microorganisms. We aimed at the analysis of pro- (TNF, IL-1β, IL-6, IL-8, and IL-12p70) and anti-inflammatory (IL-10) cytokines produced by Jurkat T cells in response to planktonic and biofilm Corynebacterium amycolatum. Two reference strains: C. amycolatum ATCC 700207 (R-CA), Staphylococcus aureus ATCC 25923 (R-SA), and ten clinical strains of C. amycolatum (C-CA) were used in the study. Jurkat T cells were stimulated in vitro by the planktonic-conditioned medium (PCM) and biofilm-conditioned medium (BCM) derived from the relevant cultures of the strains tested. The cytokine concentrations were determined in the cell culture supernatants using the flow cytometry. The levels of the cytokines analyzed were lower after stimulation with the BCM when compared to the PCM derived from the cultures of C-CA; statistical significance (p < 0.05) was observed for IL-1β, IL-12 p70, and IL-10. Similarly, planktonic R-CA and R-SA stimulated a higher cytokine production than their biofilm counterparts. The highest levels of pro-inflammatory IL-8, IL-1β, and IL-12p70 were observed after stimulation with planktonic R-SA whereas the strongest stimulation of anti-inflammatory IL-10 was noted for the BCM derived from the mixed culture of both reference species. Our results are indicative of weaker immunostimulatory properties of the biofilm C. amycolatum compared to its planktonic form. It may play a role in the persistence of biofilm-related infections. The extent of the cytokine response can be dependent on the inherent virulence of the infecting microorganism.

Pigmentosins from Gibellula sp. as antibiofilm agents and a new glycosylated asperfuran from Cordyceps javanica

In the course of our exploration of the Thai invertebrate-pathogenic fungi for biologically active metabolites, pigmentosin A (1) and a new bis(naphtho-α-pyrone) derivative, pigmentosin B (2), were isolated from the spider-associated fungus Gibellula sp. Furthermore, a new glycosylated asperfuran 3, together with one new (6) and two known (4 and 5) cyclodepsipeptides, was isolated from Cordyceps javanica. The pigmentosins 1 and 2 showed to be active against biofilm formation of Staphylococcus aureus DSM1104. The lack of toxicity toward the studied microorganism and cell lines of pigmentosin B (2), as well as the antimicrobial effect of pigmentosin A (1), made them good candidates for further development for use in combination therapy of infections involving biofilm-forming S. aureus. The structure elucidation and determination of the absolute configuration were accomplished using a combination of spectroscopy, including 1D and 2D NMR, HRMS, Mosher ester analysis, and comparison of calculated/experimental ECD spectra. A chemotaxonomic investigation of the secondary metabolite profiles using analytical HPLC coupled with diode array detection and mass spectrometry (HPLC-DAD-MS) revealed that the production of pigmentosin B (2) was apparently specific for Gibellula sp., while the glycoasperfuran 3 was specific for C. javanica.

Sensing the unreachable: challenges and opportunities in biofilm detection

Bacteria can attach to essentially all materials and form multicellular biofilms with high-level tolerance to antimicrobials. Detrimental biofilms are responsible for a variety of problems ranging from food and water contamination, bio-corrosion, to drug resistant infections. Besides the challenges in control, biofilms are also difficult to detect due to the lack of biofilm-specific biomarkers and methods for non-destructive imaging. In this article, we present a concise review of recent advancements in this field, with a focus on medical device-associated infections. We also discuss the technologies that have potential for non-destructive detection of bacterial biofilms.

Hijacking of immune defences by biofilms: a multifront strategy

Biofilm formation by pathogens and opportunistic bacteria is the basis of persistent or recurrent infections. Up to 80% of bacterial infections in humans are associated with biofilms. Despite the efficiency of the evolved and complex human defence system against planktonic bacteria, biofilms are capable of subverting host defences. The immune system is not completely effective in opposing bacteria and preventing infection. Increasing attention is being focussed on the mechanisms enabling bacterial biofilms to skew the coordinate action of humoral and cell mediated responses. Knowledge of the interactions between biofilm bacteria and the immune system is critical to effectively address biofilm infections, which have multiplied over the years with the spread of biomaterials in medicine. In this article, the latest information on the interactions between bacterial biofilms and immune cells is examined and the areas where of information is still lacking are explored.

Establishment of Chronic Typhoid Infection in a Mouse Carriage Model Involves a Type 2 Immune Shift and T and B Cell Recruitment to the Gallbladder

The existence of chronic typhoid carriers has been in the public eye for over 100 years in part because of the publicity around Typhoid Mary. Additionally, it has been known for decades that the gallbladder is the main site of persistence and recently that gallstones play a key role. Despite this, very little is known about the physiological conditions that allow Salmonella enterica serovar Typhi to persist in the gallbladder. In this study, we analyze the transcriptional profile of the gallbladder in a mouse model of chronic carriage. We found a shift from an early proinflammatory immune response toward a later anti-inflammatory response, which could explain the stalemate that allows Salmonella persistence. Interestingly, we found a 10-fold increase in the number of Salmonella-specific T cells in mice with gallstones. This work moves us closer to understanding the mechanistic basis of chronic carriage, with a goal toward eradication of the disease.

Typhoid fever, caused primarily by Salmonella enterica serovar Typhi (S. Typhi), is a life-threatening systemic disease responsible for significant morbidity and mortality worldwide. Three to 5% of individuals infected with S. Typhi become chronic carriers due to bacterial persistence in the gallbladder. We have demonstrated that Salmonella forms biofilms on gallstones to establish gallbladder carriage. However, an in-depth molecular understanding of chronic carriage in the gallbladder, from the perspective of both the pathogen and host, is poorly defined. To examine the dynamics of the gallbladder in response to Salmonella infection, we performed transcriptional profiling in the mouse gallbladder at early (7 days) and chronic (21 days) time points. Transcriptome sequencing (RNA-Seq) revealed a shift from a Th1 proinflammatory response at 7 days postinfection (dpi) toward an anti-inflammatory Th2 response by 21 dpi, characterized by increased levels of immunoglobulins and the Th2 master transcriptional regulator, GATA3. Additionally, bioinformatic analysis predicted the upstream regulation of characteristic Th2 markers, including interleukin-4 (IL-4) and Stat6. Immunohistochemistry and fluorescence-activated cell sorter (FACS) analysis confirmed a significant increase in lymphocytes, including T and B cells, at 21 dpi in mice with gallstones. Interestingly, the levels of Salmonella-specific CD4 T cells were 10-fold higher in the gallbladder of mice with gallstones at 21 dpi. We speculate that the biofilm state allows Salmonella to resist the initial onslaught of the Th1 inflammatory response, while yet undefined events influence a switch in the host immunity toward a more permissive type 2 response, enabling the establishment of chronic infection.

The cooling tower water microbiota: Seasonal dynamics and co-occurrence of bacterial and protist phylotypes

Cooling towers for heating, ventilation and air conditioning are ubiquitous in the built environment. Often located on rooftops, their semi-open water basins provide a suitable environment for microbial growth. They are recognized as a potential source of bacterial pathogens and have been associated with disease outbreaks such as Legionnaires' disease. While measures to minimize public health risks are in place, the general microbial and protist community structure and dynamics in these systems remain largely elusive. In this study, we analysed the microbiome of the bulk water from the basins of three cooling towers by 16S and 18S rRNA gene amplicon sequencing over the course of one year. Bacterial diversity in all three towers was broadly comparable to other freshwater systems, yet less diverse than natural environments; the most abundant taxa are also frequently found in freshwater or drinking water. While each cooling tower had a pronounced site-specific microbial community, taxa shared among all locations mainly included groups generally associated with biofilm formation. We also detected several groups related to known opportunistic pathogens, such as Legionella, Mycobacterium, and Pseudomonas species, albeit at generally low abundance. Although cooling towers represent a rather stable environment, microbial community composition was highly dynamic and subject to seasonal change. Protists are important members of the cooling tower water microbiome and known reservoirs for bacterial pathogens. Co-occurrence analysis of bacteria and protist taxa successfully captured known interactions between amoeba-associated bacteria and their hosts, and predicted a large number of additional relationships involving ciliates and other protists. Together, this study provides an unbiased and comprehensive overview of microbial diversity of cooling tower water basins, establishing a framework for investigating and assessing public health risks associated with these man-made freshwater environments.

Polysaccharide Galactan Inhibits Pseudomonas aeruginosa Biofilm Formation but Protects Pre-formed Biofilms from Antibiotics

Microorganisms residing within a biofilm become more tolerant to antibiotics and other types of adverse impact, and biofilm formation by pathogenic bacteria is an important problem of current medicine. Polysaccharides that prevent biofilm formation are among the promising candidates to help tackle this problem. Earlier we demonstrated the ability of a potato polysaccharide galactan to inhibit biofilm formation by a Pseudomonas aeruginosa clinical isolate. Here we investigate the effect of potato galactan on P. aeruginosa biofilms in more detail. Microscopic analysis indicated that the galactan did not interfere with the adhesion of bacterial cells to the substrate but prevented the build-up of bacterial biomass. Moreover, the galactan not only inhibited biofilm formation, but partially destroyed pre-formed biofilms. Presumably, this activity of the galactan was due to the excessive aggregation of bacterial cells, which prohibited the formation and maintenance of proper biofilm architecture, or due to some other mechanisms of biofilm structure remodeling. This led to an unexpected effect, i.e., P. aeruginosa biofilms treated with an antibiotic and the galactan retained more viable bacterial cells compared to biofilms treated with the antibiotic alone. Galactan is the first polysaccharide demonstrated to exert such effect on bacterial biofilms.

Cystic Fibrosis and Pseudomonas aeruginosa: the Host-Microbe Interface

In human pathophysiology, the clash between microbial infection and host immunity contributes to multiple diseases. Cystic fibrosis (CF) is a classical example of this phenomenon, wherein a dysfunctional, hyperinflammatory immune response combined with chronic pulmonary infections wreak havoc upon the airway, leading to a disease course of substantial morbidity and shortened life span. Pseudomonas aeruginosa is an opportunistic pathogen that commonly infects the CF lung, promoting an accelerated decline of pulmonary function. Importantly, P. aeruginosa exhibits significant resistance to innate immune effectors and to antibiotics, in part, by expressing specific virulence factors (e.g., antioxidants and exopolysaccharides) and by acquiring adaptive mutations during chronic infection. In an effort to review our current understanding of the host-pathogen interface driving CF pulmonary disease, we discuss (i) the progression of disease within the primitive CF lung, specifically focusing on the role of host versus bacterial factors; (ii) critical, neutrophil-derived innate immune effectors that are implicated in CF pulmonary disease, including reactive oxygen species (ROS) and antimicrobial peptides (e.g., LL-37); (iii) P. aeruginosa virulence factors and adaptive mutations that enable evasion of the host response; and (iv) ongoing work examining the distribution and colocalization of host and bacterial factors within distinct anatomical niches of the CF lung.

Investigation of the effect of different environmental conditions on biofilm structure of Salmonella enterica serotype Virchow via FTIR spectroscopy

This study aims to describe the content of polymeric matrix components under different incubation temperatures and pH levels. Optimal biofilm production of 15 S. Virchow isolates occurred following the incubation in LB^-NaCl for 72 h, at pH 6.6 and 20 °C. The expression of csgA, csgD, adrA and bcsA genes at 20 °C, 25 °C and 30 °C in S. Virchow DMC18 was analyzed, and it was discovered that the maximum production of cellulose and curli fimbriae occurred at 20 °C. The physical characteristics of pellicle structure of S. Virchow DMC18 was determined as rigid at 20 °C, while becoming fragile at higher temperatures. FTIR analyses confirmed the obtained molecular findings. The intensities of the 16 different peaks originating from carbohydrate, protein, and nucleic acid in the spectra of biofilm samples significantly diminished (p < 0.05) with the increasing temperature. The highest intensities of lipids and carbohydrates were observed at 20 °C indicating the changes in cell surface properties.

Evidence of a microbial etiology for sialoliths

OBJECTIVES

Sialolithiasis is the primary etiology for parotid and submandibular swelling, potentially resulting in discomfort, bacterial infections, and hospitalization. The etiology of sialolith formation is unknown. Currently, the proposed etiologies range from inflammation, coalescence of organic molecules, sialomicrolith formation, pH changes, and biofilm formation. In this study, we performed a descriptive analysis of images obtained through electron microscopy of sialoliths. Based on our findings and descriptive analysis, we hypothesize that sialolith formation is likely multifactorial and begins with biofilm formation. Biofilm formation then triggers a host immune response, and it is the interaction of biofilm with host immune cells and calcium nanoparticles that forms the nidus and creates a favorable environment for calcium precipitation.

METHODS

Sialoliths were extracted from patients and imaged under light and scanning electron microscopy. Specimens for light microscopy were prepared using a diamond saw. Specimens for electron microscopy were freeze-fractured, thus providing an undisturbed view of the core of the sialolith.

RESULTS

We were able to identify clear evidence of biofilm caves at the core of each sialolith. These biofilm caves were complex with the presence of bacteria and dehydrated extrapolysaccharide matrix, host cells (immune cells, platelets and erythrocytes), and calcium nanoparticles.

CONCLUSION

The etiology of sialolith formation is likely multifactorial. We propose that biofilm formation within a single salivary gland or duct leads to local ductal injury, which results in the influx of host immune cells that interact with the biofilm and calcium nanoparticles, creating a scaffold upon which further calcium deposition can occur.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:69-74, 2020.

Virulence gene profiles, biofilm formation, and antimicrobial resistance of Vibrio cholerae non-O1/non-O139 bacteria isolated from West Bengal, India

Vibrio cholerae is the causative agent of acute dehydrating diarrhoeal disease cholera. Among 71 V. cholerae non-O1/non-O139 isolates, all yielded negative results for ctxA, ctxB and tcpA genes in PCR assay. Few strains were positive for stn (28.38%), and ompU (31.08%) genes. While all isolates were negative for ace gene, only two were positive for zot gene. All strains expressed toxR and toxT genes. It was also found that all isolates were slime-producer and these were capable of forming moderate to high biofilm. Biofilm formation was controlled positively by the transcriptional regulators VpsR and VpsT and was regulated negatively by HapR, as well as CRP regulatory complex. These isolates were resistant to ampicillin, furazolidone, doxycycline, vancomycin, erythromycin, while these were susceptible to ciprofloxacin, gentamycin, kanamycin, polymixin B, norfloxacin, chloramphenicol, sulphamethoxazole-trimethoprim, tetracycline, nalidixic acid, and streptomycin. Indeed, 69.01% isolates were resistant to multiple antibiotics (MAR: resistance to 3 or more antibiotics). Treatment protocols for cholera patients should be based on local antibiogram data.

Calcium-mediated Protein Folding and Stabilization of Salmonella Biofilm-associated Protein A

Biofilm-associated proteins (BAPs) are important for early biofilm formation (adhesion) by bacteria and are also found in mature biofilms. BapA from Salmonella is a ~386-kDa surface protein, comprising 27 tandem repeats predicted to be bacterial Ig-like (BIg) domains. Such tandem repeats are conserved for BAPs across different bacterial species, but the function of these domains is not completely understood. In this work, we report the first study of the mechanical stability of the BapA protein. Using magnetic tweezers, we show that the folding of BapA BIg domains requires calcium binding and the folded domains have differential mechanical stabilities. Importantly, we identify that >100 nM concentration of calcium is needed for folding of the BIg domains, and the stability of the folded BIg domains is regulated by calcium over a wide concentration range from sub-micromolar (μM) to millimolar (mM). Only at mM calcium concentrations, as found in the extracellular environment, do the BIg domains have the saturated mechanical stability. BapA has been suggested to be involved in Salmonella invasion, and it is likely a crucial mechanical component of biofilms. Therefore, our results provide new insights into the potential roles of BapA as a structural maintenance component of Salmonella biofilm and also Salmonella invasion.

Rapid diversification of Pseudomonas aeruginosa in cystic fibrosis lung-like conditions

Chronic infection of the cystic fibrosis (CF) airway by the opportunistic pathogen Pseudomonas aeruginosa is the leading cause of morbidity and mortality for adult CF patients. Prolonged infections are accompanied by adaptation of P. aeruginosa to the unique conditions of the CF lung environment, as well as marked diversification of the pathogen into phenotypically and genetically distinct strains that can coexist for years within a patient. Little is known, however, about the causes of this diversification and its impact on patient health. Here, we show experimentally that, consistent with ecological theory of diversification, the nutritional conditions of the CF airway can cause rapid and extensive diversification of P. aeruginosa Mucin, the substance responsible for the increased viscosity associated with the thick mucus layer in the CF airway, had little impact on within-population diversification but did promote divergence among populations. Furthermore, in vitro evolution recapitulated traits thought to be hallmarks of chronic infection, including reduced motility and increased biofilm formation, and the range of phenotypes observed in a collection of clinical isolates. Our results suggest that nutritional complexity and reduced dispersal can drive evolutionary diversification of P. aeruginosa independent of other features of the CF lung such as an active immune system or the presence of competing microbial species. We suggest that diversification, by generating extensive phenotypic and genetic variation on which selection can act, may be a key first step in the development of chronic infections.

Salmonella and Campylobacter biofilm formation: a comparative assessment from farm to fork

It takes several steps to bring food from the farm to the fork (dining table), and contamination with food-borne pathogens can occur at any point in the process. Campylobacter spp. and Salmonella spp. are the main microorganisms responsible for foodborne disease in the EU. These two pathogens are able to persist throughout the food supply chain thanks to their ability to form biofilms. Owing to the high prevalence of Salmonella and especially of Campylobacter in the food supply chain and the huge efforts of food authorities to reduce these levels, it is of great importance to fully understand their mechanisms of persistence. Diverse studies have evaluated the biofilm-forming capacity of foodborne pathogens isolated at different steps of food production. Nonetheless, the principal obstacle of these studies is to reproduce the real conditions that microorganisms encounter in the food supply chain. While there are a wide number of Salmonella biofilm studies, information on Campylobacter biofilms is still limited. A comparison between the two microorganisms could help to develop new research in the field of Campylobacter biofilms. Therefore, this review evaluates relevant work in the field of Salmonella and Campylobacter biofilms and the applicability of the data obtained from these studies to real working conditions. © 2018 Society of Chemical Industry.

Regulation of Virus-Associated Lymphoma Growth and Gene Expression by Bacterial Quorum-Sensing Molecules

Kaposi's sarcoma-associated herpesvirus (KSHV) can cause several human cancers, including primary effusion lymphoma (PEL), which frequently occur in immunocompromised patients. KSHV-infected patients often suffer from polymicrobial infections caused by opportunistic bacterial pathogens. Therefore, it is crucial to understand how these coinfecting microorganisms or their secreted metabolites may affect KSHV infection and the pathogenesis of virus-associated malignancies. Quorum sensing (QS), a cell density-based intercellular communication system, employs extracellular diffusible signaling molecules to regulate bacterial virulence mechanisms in a wide range of bacterial pathogens, such as Pseudomonas aeruginosa, which is one of the most common opportunistic microorganisms found in immunocompromised individuals. In this study, we evaluated and compared the influence on PEL growth and the host/viral interactome of the major QS signaling molecules [N-(3-oxododecanoyl)-l-homoserine lactone (OdDHL), N-butyrylhomoserine lactone (BHL), and 2-heptyl-3-hydroxy-4-quinolone (PQS)] in conditioned medium from wild-type (wt) and QS mutant laboratory strains as well as clinical isolates of P. aeruginosa Our data indicate that P. aeruginosa coinfection may facilitate virus dissemination and establishment of new infection and further promote tumor development through effectively inducing viral lytic gene expression by its QS systems.IMPORTANCE Currently, most studies about KSHV infection and/or virus-associated malignancies depend on pure culture systems or immunodeficient animal models. However, the real situation should be much more complicated in KSHV-infected immunocompromised patients due to frequent polymicrobial infections. It is important to understand the interaction of KSHV and coinfecting microorganisms, especially opportunistic bacterial pathogens. Here we report for the first time that P. aeruginosa and its quorum-sensing signaling molecules display a complicated impact on KSHV-associated lymphoma growth as well as the intracellular host/viral gene expression profile. Our data imply that targeting of coinfecting pathogens is probably necessary during treatment of virus-associated malignancies in these immunocompromised patients.

Chronic biofilm-based infections: skewing of the immune response

Many of the deadliest bacterial diseases that plague humanity in the modern age are caused by bacterial biofilms that produce chronic infections. However, most of our knowledge of the host immune response comes from the study of planktonic pathogens. While there are similarities in the host response to planktonic and biofilm bacteria, specific immune responses toward biofilms have not been well studied; the only apparent difference is the inability to clear the bacteria allowing the biofilm infection to become chronic. In some cases, the biofilms skew T-cell response toward a balance that allows a stalemate between the host and the pathogen, in which the infection can become persistent. In this minireview, we will summarize well-known examples of this phenomena as well as some emerging studies that may indicate that this situation is much more common than initially thought.

The Microbial Endocrinology of Pseudomonas aeruginosa: Inflammatory and Immune Perspectives

Pseudomonas aeruginosa is a major pathogen responsible for both acute and chronic infection. Known as a colonising pathogen of the cystic fibrosis (CF) lung, it is implicated in other settings such as bronchiectasis. It has the ability to cause acute disseminated or localised infection particularly in the immunocompromised. Human hormones have been highlighted as potential regulators of bacterial virulence through crosstalk between analogous "quorum sensing" (QS) systems present in the bacteria that respond to mammalian hormones. Pseudomonas aeruginosa is known to utilise interconnected QS systems to coordinate its virulence and evade various aspects of the host immune system activated in response to infection. Several human hormones demonstrate an influence on P. aeruginosa growth and virulence. This inter-kingdom signalling, termed "microbial endocrinology" has important implications for host-microbe interaction during infection and, potentially opens up novel avenues for therapeutic intervention. This phenomenon, supported by the existence of sexual dichotomies in both microbial infection and chronic lung diseases such as CF is potentially explained by sex hormones and their influence on the infective process. This review summarises our current understanding of the microbial endocrinology of P. aeruginosa, including its endogenous QS systems and their intersection with human endocrinology, pathogenesis of infection and the host immune system.

Enhancing the anti-biofilm activity of 5-aryl-2-aminoimidazoles through nature inspired dimerisation

The increased tolerance of biofilms against disinfectants and antibiotics has stimulated research into new methods of biofilm prevention and eradication. In our previous work, we have identified the 5-aryl-2-aminoimidazole core as a scaffold that demonstrates preventive activity against biofilm formation of a broad range of bacterial and fungal species. Inspired by the dimeric nature of natural 2-aminoimidazoles of the oroidin family, we investigated the potential of dimers of our decorated 5-aryl-2-aminoimidazoles as biofilm inhibitors. A synthetic approach towards 2-aminoimidazole dimers linked by an alkyl chain was developed and a total of 48 dimers were synthesized. The linkers were introduced at two different positions, the N1-position or the N2-position, and the linker length and the substitution of the 5-phenyl ring (H, F, Cl, Br) were varied. Although, no clear correlation between linker length and biofilm inhibition was observed, a strong increase in anti-biofilm activity for almost all N1,N1'-linked dimers was obtained, compared to the respective monomers against Salmonella Typhimurium, Escherichia coli and Staphylococcus aureus. The N2,N2'-linked dimers, having a H- or F-substitution, were also found to show a strong increase in anti-biofilm activity compared to the respective monomers against these three bacterial species and against Pseudomonas aeruginosa. In addition, the obtained growth measurements suggest a broad concentration range with specific biofilm inhibition and no effect on the planktonic growth against Salmonella Typhimurium and Pseudomonas aeruginosa.

The Consequences of Being in an Infectious Biofilm: Microenvironmental Conditions Governing Antibiotic Tolerance

The main driver behind biofilm research is the desire to understand the mechanisms governing the antibiotic tolerance of biofilm-growing bacteria found in chronic bacterial infections. Rather than genetic traits, several physical and chemical traits of the biofilm have been shown to be attributable to antibiotic tolerance. During infection, bacteria in biofilms exhibit slow growth and a low metabolic state due to O₂ limitation imposed by intense O₂ consumption of polymorphonuclear leukocytes or metabolically active bacteria in the biofilm periphery. Due to variable O₂ availability throughout the infection, pathogen growth can involve aerobic, microaerobic and anaerobic metabolism. This has serious implications for the antibiotic treatment of infections (e.g., in chronic wounds or in the chronic lung infection of cystic fibrosis patients), as antibiotics are usually optimized for aerobic, fast-growing bacteria. This review summarizes knowledge about the links between the microenvironment of biofilms in chronic infections and their tolerance against antibiotics.

Unveiling and Characterizing Early Bilateral Interactions between Biofilm and the Mouse Innate Immune System

A very substantial progress has been made in our understanding of infectious diseases caused by invasive bacteria. Under their planktonic forms, bacteria transiently reside in the otherwise sterile mammal body tissues, as the physiological inflammation insures both their clearance and repair of any tissue damage. Yet, the bacteria prone to experience planktonic to biofilm developmental transition still need to be studied. Of note, sessile bacteria not only persist but also concur preventing the effectors and regulators of the physiological inflammation to operate. Thus, it is urgent to design biologically sound experimental approaches aimed to extract, at the earliest stage, immune signatures of mono-bacteria planktonic to biofilm developmental transition in vivo and ex vivo. Indeed, the transition is often the first event to which succeeds the “chronicization” process whereby classical bacteria-targeting therapies are no more efficacious. An in vivo model of micro-injection of Staphylococcus aureus planktonic or biofilm cells in the ear pinna dermis of laboratory transgenic mice with fluorescent immune cells is proposed. It allows visualizing, in real time, the range of the early interactions between the S. aureus and myeloid cell subsets- the resident macrophages and dendritic cells, the recruited neutrophil granulocytes/polymorphonuclear neutrophils, monocytes otherwise known to differentiate as macrophages or dendritic cells. One main objective is to extract contrasting immune signatures of the modulation of the physiological inflammation with respect to the two bacterial lifestyles.

Treating tuberculosis with high doses of anti-TB drugs: mechanisms and outcomes

Tuberculosis (TB) is considered as one of the most serious threats to public health in many parts of the world. The threat is even more severe in the developing countries where there is a lack of advanced medical amenities and contemporary anti-TB drugs. In such situations, dosage optimization of existing medication regimens seems to be the only viable option. Therapeutic drug monitoring study results suggest that high-dose treatment regimens can compensate the low serum concentration of anti-TB drugs and shorten the therapy duration. The article presents a critical review on the possible changes that occur in the host and the pathogen upon the administration of standard and high-dose regimens. Some of the most common factors that are responsible for low anti-TB drug concentrations in the serum are differences in hosts' body weight, metabolic processing of the drug, malabsorption and/or drug-drug interaction. Furthermore, failure to reach the cavitary pulmonary and extrapulmonary tissues also contributes to the therapeutic inefficiency of the drugs. In such conditions, administration of higher doses can help in compensating the pathogenic outcomes of enhancement of the pathogen's physical barriers, efflux pumps and genetic mutations. The present article also presents a summary of the recorded treatment outcomes of clinical trials that were conducted to test the efficacy of administration of high dose of anti-tuberculosis drugs. This review will help physicians across the globe to understand the underlying pathophysiological changes (including side effects) that dictate the clinical outcomes in patients administered with standard and/or high dose anti-TB drugs.

Biofilm formation and antibiotic susceptibility in dispersed cells versus planktonic cells from clinical, industry and environmental origins

We examined the cell-surface physicochemical properties, the biofilm formation capability and the antibiotic susceptibility in dispersed cells (from an artificial biofilm of alginate beads) and compared with their planktonic (free-swimming) counterparts. The strains used were from different origins, such as clinical (Acinetobacter baumannii AB4), cosmetic industry (Klebsiella oxytoca EU213, Pseudomonas aeruginosa EU190), and environmental (Halomonas venusta MAT28). In general, dispersed cells adhered better to surfaces (measured as the "biofilm index") and had a greater hydrophobicity [measured as the microbial affinity to solvents (MATS)] than planktonic cells. The susceptibility to two antibiotics (ciprofloxacin and tetracycline) of dispersed cells was higher compared with that of their planktonic counterparts (tested by the "bactericidal index"). Dispersed and planktonic cells exhibited differences in cell permeability, especially in efflux pump activity, which could be related to the differences observed in susceptibility to antibiotics. At 1 h of biofilm formation in microtiter plates, dispersed cells treated with therapeutic concentration of ciprofloxacin yielded a lower biofilm index than the control dispersed cells without ciprofloxacin. With respect to the planktonic cells, the biofilm index was similar with and without the ciprofloxacin treatment. In both cases there were a reduction of the number of bacteria measured as viable count of the supernatant. The lower biofilm formation in dispersed cells with ciprofloxacin treatment may be due to a significant increase of biofilm disruption with respect to the biofilm from planktonic cells. From a clinical point of view, biofilms formed on medical devices such as catheters, cells that can be related to an infection were the dispersed cells. Our results showed that early treatment with ciprofloxacin of dispersed cells could diminishe bacterial dispersion and facilitate the partial elimination of the new biofilm formed.

A novel small RNA is important for biofilm formation and pathogenicity in Pseudomonas aeruginosa

The regulation of biofilm development requires multiple mechanisms and pathways, but it is not fully understood how these are integrated. Small RNA post-transcriptional regulators are a strong candidate as a regulatory mechanism of biofilm formation. More than 200 small RNAs in the P. aeruginosa genome have been characterized in the literature to date; however, little is known about their biological roles in the cell. Here we describe the identification of the novel regulatory small RNA, SrbA. This locus was up-regulated 45-fold in P. aeruginosa strain PA14 biofilm cultures. Loss of SrbA expression in a deletion strain resulted in a 66% reduction in biofilm mass. Furthermore, the mortality rate over 72 hours in C. elegans infections was reduced to 39% when infected with the srbA deletion strain compared to 78% mortality when infected with the parental wild-type P. aeruginosa strain. There was no significant effect on culture growth or adherence to surfaces with loss of SrbA expression. Also loss of SrbA expression had no effect on antibiotic resistance to ciprofloxacin, gentamicin, and tobramycin. We conclude that SrbA is important for biofilm formation and full pathogenicity of P. aeruginosa.

Low-Dose Nitric Oxide as Targeted Anti-biofilm Adjunctive Therapy to Treat Chronic Pseudomonas aeruginosa Infection in Cystic Fibrosis

Despite aggressive antibiotic therapy, bronchopulmonary colonization by Pseudomonas aeruginosa causes persistent morbidity and mortality in cystic fibrosis (CF). Chronic P. aeruginosa infection in the CF lung is associated with structured, antibiotic-tolerant bacterial aggregates known as biofilms. We have demonstrated the effects of non-bactericidal, low-dose nitric oxide (NO), a signaling molecule that induces biofilm dispersal, as a novel adjunctive therapy for P. aeruginosa biofilm infection in CF in an ex vivo model and a proof-of-concept double-blind clinical trial. Submicromolar NO concentrations alone caused disruption of biofilms within ex vivo CF sputum and a statistically significant decrease in ex vivo biofilm tolerance to tobramycin and tobramycin combined with ceftazidime. In the 12-patient randomized clinical trial, 10 ppm NO inhalation caused significant reduction in P. aeruginosa biofilm aggregates compared with placebo across 7 days of treatment. Our results suggest a benefit of using low-dose NO as adjunctive therapy to enhance the efficacy of antibiotics used to treat acute P. aeruginosa exacerbations in CF. Strategies to induce the disruption of biofilms have the potential to overcome biofilm-associated antibiotic tolerance in CF and other biofilm-related diseases.

Attenuation of quorum-sensing-dependent virulence factors and biofilm formation by medicinal plants against antibiotic resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa use small signaling molecules such as acyl homoserine lactones (AHLs), which play an important role in release virulence factors and toxin for further establishment of host infection. Thus, involving with the QS system would provide alternative ways of preventing the pathogenicity. In the present study, totally six medicinal plants (Terminalia bellerica, Celastrus paniculatus, Kingiodendron pinnatum, Schleichera oleosa, Melastoma malabathricum, Garcinia gummi-gutta) were screened for anti-QS activity using biomonitor strain of Chromobacterium violaceum CV12472. The primary screening of antimicrobial activity of all the plant extracts have inhibited the growth of tested bacterial species. Of these at the sub-minimum inhibitory concentration the methanol extract of T. bellerica (0.0625–0.5 mg/ml) has significantly inhibited violacein production (20.07–66.22%) in C. violaceum (CV12472). Consequently, the extract of T. bellerica has reduced the production of pyocyanin, exopolysaccharide and biofilm formation in P. aeruginosa strains. Fluorescence and scanning electron microscopy analysis confirmed the reduction of biofilm formation in P. aeruginosa strains when treated with T. bellerica. GC–MS analysis showed the active compounds inhibited the production of virulence factors of P. aeruginosa. The results suggest the possible use of this T. bellerica as an anti-QS and anti-biofilm agent to control Pseudomonas infection. Interference of QS provides an important means for the inhibition of bacterial virulence and thus aids in treatment strategies.

Biofilms and host response - helpful or harmful

Biofilm infections are one of the modern medical world's greatest challenges. Probably, all non-obligate intracellular bacteria and fungi can establish biofilms. In addition, there are numerous biofilm-related infections, both foreign body-related and non-foreign body-related. Although biofilm infections can present in numerous ways, one common feature is involvement of the host response with significant impact on the course. A special characteristic is the synergy of the innate and the acquired immune responses for the induced pathology. Here, we review the impact of the host response for the course of biofilm infections, with special focus on cystic fibrosis, chronic wounds and infective endocarditis.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.

Bioengineering a bacterial pathogen to assemble its own particulate vaccine capable of inducing cellular immunity

Many bacterial pathogens naturally form cellular inclusions. Here the immunogenicity of polyhydroxyalkanoate (PHA) inclusions and their use as particulate vaccines delivering a range of host derived antigens was assessed. Our study showed that PHA inclusions of pathogenic Pseudomonas aeruginosa are immunogenic mediating a specific cell-mediated immune response. Protein engineering of the PHA inclusion forming enzyme by translational fusion of epitopes from vaccine candidates outer membrane proteins OprI, OprF, and AlgE mediated self-assembly of PHA inclusions coated by these selected antigens. Mice vaccinated with isolated PHA inclusions produced a Th1 type immune response characterized by antigen-specific production of IFN-γ and IgG2c isotype antibodies. This cell-mediated immune response was found to be associated with the production of functional antibodies reacting with cells of various P. aeruginosa strains as well as facilitating opsonophagocytic killing. This study showed that cellular inclusions of pathogenic bacteria are immunogenic and can be engineered to display selected antigens suitable to serve as particulate subunit vaccines against infectious diseases.

Bacterial Lysis through Interference with Peptidoglycan Synthesis Increases Biofilm Formation by Nontypeable Haemophilus influenzae

Most, if not all, bacteria form a biofilm, a multicellular structure that protects them from antimicrobial actions of the host immune system and affords resistance to antibiotics. The latter is especially disturbing with the increase in multiresistant bacterial clones worldwide. Bacterial biofilm formation is a multistep process that starts with surface adhesion, after which attached bacteria divide and give rise to biomass. The actual steps required for Haemophilus influenzae biofilm formation are largely not known. We show that interference with peptidoglycan biosynthesis increases biofilm formation because of the release of bacterial genomic DNA. Subinhibitory concentrations of β-lactam antibiotics, which are often prescribed to treat H. influenzae infections, increase biofilm formation through a similar mechanism. Therefore, when β-lactam antibiotics do not reach their MIC in vivo, they might not only drive selection for β-lactam-resistant clones but also increase biofilm formation and resistance to other antimicrobial compounds.

Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen that mainly causes otitis media in children and community-acquired pneumonia or exacerbations of chronic obstructive pulmonary disease in adults. A large variety of studies suggest that biofilm formation by NTHi may be an important step in the pathogenesis of this bacterium. However, the underlying mechanisms involved in this process are poorly elucidated. In this study, we used a transposon mutant library to identify bacterial genes involved in biofilm formation. The growth and biofilm formation of 4,172 transposon mutants were determined, and the involvement of the identified genes in biofilm formation was validated in in vitro experiments. Here, we present experimental data showing that increased bacterial lysis, through interference with peptidoglycan synthesis, results in elevated levels of extracellular DNA, which increased biofilm formation. Interestingly, similar results were obtained with subinhibitory concentrations of β-lactam antibiotics, known to interfere with peptidoglycan synthesis, but such an effect does not appear with other classes of antibiotics. These results indicate that treatment with β-lactam antibiotics, especially for β-lactam-resistant NTHi isolates, might increase resistance to antibiotics by increasing biofilm formation.

IMPORTANCE Most, if not all, bacteria form a biofilm, a multicellular structure that protects them from antimicrobial actions of the host immune system and affords resistance to antibiotics. The latter is especially disturbing with the increase in multiresistant bacterial clones worldwide. Bacterial biofilm formation is a multistep process that starts with surface adhesion, after which attached bacteria divide and give rise to biomass. The actual steps required for Haemophilus influenzae biofilm formation are largely not known. We show that interference with peptidoglycan biosynthesis increases biofilm formation because of the release of bacterial genomic DNA. Subinhibitory concentrations of β-lactam antibiotics, which are often prescribed to treat H. influenzae infections, increase biofilm formation through a similar mechanism. Therefore, when β-lactam antibiotics do not reach their MIC in vivo, they might not only drive selection for β-lactam-resistant clones but also increase biofilm formation and resistance to other antimicrobial compounds.