Pseudomonas aeruginosa polymicrobial interactions during lung infection

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.

Furazolidone reduces the pathogenesis of Trueperella pyogenes and Pseudomonas aeruginosa co-infection in a mouse model

The prevalence of abscess disease significantly limits the population expansion of captive forest musk deer, which is an endangered species protected by the legislation of China. Our prior work had demonstrated that Trueperella pyogenes and Pseudomonas aeruginosa are two important microorganisms in causing the abscess disease of forest musk deer, and furazolidone could inhibit the growth and virulence of the pathogens in vitro. In this study, the in vivo protection activity of furazolidone was evaluated by using mouse models chronically infected with T. pyogenes and P. aeruginosa. The results showed that furazolidone treatment significantly increased the survival rates of mice in the co-infection group, all the mice survived at 14 days post-infection. The damage degree of the lung tissues caused by bacterial infection was ameliorated by the treatment of furazolidone from 7 to 14 days post-infection, which also reduced the residual bacterial burden in the lungs. Compared to the untreated control group, the expression levels of genes activated by the quorum-sensing system of P. aeruginosa and the core virulence regulatory genes of T. pyogenes were significantly suppressed by furazolidone. In addition, the results of transcriptomic analyses showed that 270 DEGs were identified in the co-infection group. This finding further revealed that the immune responses of mice could be enhanced by the treatment of furazolidone, and this might also contribute to the clearance of bacteria from the lungs. Therefore, this study clearly reveals the protection activity of furazolidone against P. aeruginosa and T. pyogenes infection, and thus provides a promising candidate in the treatment of abscess disease.

Interspecies surfactants serve as public goods enabling surface motility in Pseudomonas aeruginosa

In most natural environments, bacteria live in polymicrobial communities where secreted molecules from neighboring species alter bacterial behaviors, including motility, but such interactions are understudied. Pseudomonas aeruginosa is a motile opportunistic pathogen that exists in diverse multispecies environments, such as the soil, and is frequently found in human wound and respiratory tract co-infections with other bacteria, including Staphylococcus aureus. Here, we show that P. aeruginosa can co-opt secreted surfactants from other species for flagellar-based surface motility. We found that exogenous surfactants from S. aureus, other bacteria, and interkingdom species enabled P. aeruginosa to switch from swarming to an alternative surface spreading motility on semi-solid surfaces and allowed for the emergence of surface motility on hard agar where P. aeruginosa was otherwise unable to move. Although active flagellar function was required for surface spreading, known motility regulators were not essential, indicating that surface spreading may be regulated by an as yet unknown mechanism. This motility was distinct from the response of most other motile bacterial species in the presence of exogenous surfactants. Mutant analysis indicated that this P. aeruginosa motility was similar to a previously described mucin-based motility, "surfing," albeit with divergent regulation. Thus, our study demonstrates that secreted surfactants from the host as well as neighboring bacterial and interkingdom species act as public goods facilitating P. aeruginosa flagella-mediated surfing-like surface motility, thereby allowing it to access different environmental niches.

IMPORTANCE

Bacterial motility is an important determinant of bacterial fitness and pathogenesis, allowing expansion and invasion to access nutrients and adapt to new environments. Here, we demonstrate that secreted surfactants from a variety of foreign species, including other bacterial species, infection hosts, fungi, and plants, facilitate surface spreading motility in the opportunistic pathogen Pseudomonas aeruginosa that is distinct from established motility phenotypes. This response to foreign surfactants also occurs in Pseudomonas putida, but not in more distantly related bacterial species. Our systematic characterization of surfactant-based surface spreading shows that these interspecies surfactants serve as public goods to enable P. aeruginosa to move and explore environmental conditions when it would be otherwise immotile.

Pseudomonas aeruginosa Alkyl Quinolone Response is dampened by Enterococcus faecalis

The bacterium Pseudomonas aeruginosa is an opportunistic pathogen that can cause lung, skin, wound, joint, urinary tract, and eye infections. While P. aeruginosa is known to exhibit a robust competitive response towards other bacterial species, this bacterium is frequently identified in polymicrobial infections where multiple species survive. For example, in prosthetic joint infections (PJIs), P. aeruginosa can be identified along with other pathogenic bacteria including Staphylococcus aureus, Enterococcus faecalis, and Corynebacterium striatum. Here we have explored the survival and behavior of such microbes and find that E. faecalis readily survives culturing with P. aeruginosa while other tested species do not. In each of the tested conditions, E. faecalis growth remained unchanged by the presence of P. aeruginosa, indicating a unique mutualistic interaction between the two species. We find that E. faecalis proximity leads P. aeruginosa to attenuate competitive behaviors as exemplified by reduced production of Pseudomonas quinolone signal (PQS) and pyocyanin. Reduced alkyl quinolones is important to E. faecalis as it will grow in supernatant from a quinolone mutant but not P. aeruginosa wildtype in planktonic culture. The reduced pyocyanin production of P. aeruginosa is attributable to production of ornithine by E. faecalis , which we recapitulate by adding exogenous ornithine to P. aeruginosa mono-cultures. Similarly, co-culture with an ornithine-deficient strain of E. faecalis leads P. aeruginosa to yield near mono-culture amounts of pyocyanin. Here, we directly demonstrate how notorious pathogens such as P. aeruginosa might persist in polymicrobial infections under the influence of metabolites produced by other bacterial species.

Importance

While we now appreciate that many infections are polymicrobial, we understand little of the specific actions between a given set of microbes to enable combinatorial survival and pathogenesis. The bacteria Pseudomonas aeruginosa and Enterococcus faecalis are both prevalent pathogens in wound, urinary tract, and bacteremic infections. While P. aeruginosa often kills other species in standard laboratory culture conditions, we present here that E. faecalis can be reliably co-cultured with P. aeruginosa. We specifically detail that ornithine produced by E. faecalis reduces the Pseudomonas Quinolone Signal response of P. aeruginosa . This reduction of the Pseudomonas Quinolone Signal response aids E. faecalis growth.

Role of R5 Pyocin in the Predominance of High-Risk Pseudomonas aeruginosa Isolates

Infections with antimicrobial resistant pathogens, such as Pseudomonas aeruginosa, are a frequent occurrence in healthcare settings. Human P. aeruginosa infections are predominantly caused by a small number of sequence types (ST), such as ST235, ST111, and ST175. Although ST111 is recognized as one of the most prevalent high-risk P. aeruginosa clones worldwide and frequently exhibits multidrug-resistant or extensively drug-resistant phenotypes, the basis for this dominance remains unclear. In this study, we used a genome-wide transposon insertion library screen to discover that the competitive advantage of ST111 strains over certain non-ST111 strains is through production of R pyocins. We confirmed this finding by showing that competitive dominance was lost by ST111 mutants with R pyocin gene deletions. Further investigation showed that sensitivity to ST111 R pyocin (specifically R5 pyocin) is caused by deficiency in the O-antigen ligase waaL, which leaves lipopolysaccharide (LPS) bereft of O antigen, enabling pyocins to bind the LPS core. In contrast, sensitivity of waaL mutants to R1 or R2 pyocins depended on additional genomic changes. In addition, we found the PA14 mutants in lipopolysaccharide biosynthesis (waaL, wbpL, wbpM) that cause high susceptibility to R pyocins also exhibit poor swimming motility. Analysis of 5,135 typed P. aeruginosa strains revealed that several international, high-risk sequence types (including ST235, ST111, and ST175) are enriched for R5 pyocin production, indicating a correlation between these phenotypes and suggesting a novel approach for evaluating risk from emerging prevalent P. aeruginosa strains. Overall, our study sheds light on the mechanisms underlying the dominance of ST111 strains and highlighting the role of waaL in extending spectrum of R pyocin susceptibility.

Interactions between Pseudomonas aeruginosa and six opportunistic pathogens cover a broad spectrum from mutualism to antagonism

Bacterial infections often involve more than one pathogen. While it is well established that polymicrobial infections can impact disease outcomes, we know little about how pathogens interact and affect each other's behaviour and fitness. Here, we used a microscopy approach to explore interactions between Pseudomonas aeruginosa and six human opportunistic pathogens that often co-occur in polymicrobial infections: Acinetobacter baumannii, Burkholderia cenocepacia, Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, and Staphylococcus aureus. When following growing microcolonies on agarose pads over time, we observed a broad spectrum of species-specific ecological interactions, ranging from mutualism to antagonism. For example, P. aeruginosa engaged in a mutually beneficial interaction with E. faecium but suffered from antagonism by E. coli. While we found little evidence for active directional growth towards or away from cohabitants, we observed that some pathogens increased growth in double layers in response to competition and that physical forces due to fast colony expansion had a major impact on fitness. Overall, our work provides an atlas of pathogen interactions, highlighting the diversity of potential species dynamics that may occur in polymicrobial infections. We discuss possible mechanisms driving pathogen interactions and offer predictions of how the different ecological interactions could affect virulence.

Hfq-binding small RNA PqsS regulates Pseudomonas aeruginosa pqs quorum sensing system and virulence

Pseudomonas aeruginosa is a widespread nosocomial pathogen with a significant to cause both severe planktonic acute and biofilm-related chronic infections. Small RNAs (sRNAs) are noncoding regulatory molecules that are stabilized by the RNA chaperone Hfq to trigger various virulence-related signaling pathways. Here, we identified an Hfq-binding sRNA in P. aeruginosa PAO1, PqsS, which promotes bacterial pathogenicity and pseudomonas quinolone signal quorum sensing (pqs QS) system. Specifically, PqsS enhanced acute bacterial infections by inducing host cell death and promoting rhamnolipid-regulated swarming motility. Meanwhile, PqsS reduced chronic infection traits including biofilm formation and antibiotic resistance. Moreover, PqsS repressed pqsL transcript, increasing PQS levels for pqs QS. A PQS-rich environment promoted PqsS expression, thus forming a positive feedback loop. Furthermore, we demonstrated that the PqsS interacts and destabilizes the pqsL mRNA by recruiting RNase E to drive degradation. These findings provide insights for future research on P. aeruginosa pathogenesis and targeted treatment.

Pseudomonas aeruginosa: metabolic allies and adversaries in the world of polymicrobial infections

Pseudomonas aeruginosa (PA), an opportunistic human pathogen that is frequently linked with chronic infections in immunocompromised individuals, is also metabolically versatile, and thrives in diverse environments. Additionally, studies report that PA can interact with other microorganisms, such as bacteria, and fungi, producing unique metabolites that can modulate the host immune response, and contribute to disease pathogenesis. This review summarizes the current knowledge related to the metabolic interactions of PA with other microorganisms (Staphylococcus, Acinetobacter, Klebsiella, Enterococcus, and Candida) and human hosts, and the importance of these interactions in a polymicrobial context. Further, we highlight the potential applications of studying these metabolic interactions toward designing better diagnostic tools, and therapeutic strategies to prevent, and treat infections caused by this pathogen.

Roles of Pseudomonas aeruginosa siderophores in interaction with prokaryotic and eukaryotic organisms

Pseudomonas aeruginosa is an opportunistic pathogen that produces two types of siderophores, pyoverdine and pyochelin, that play pivotal roles in iron scavenging from the environment and host cells. P. aeruginosa siderophores can serve as virulence factors and perform various functions. Several bacterial and fungal species are likely to interact with P. aeruginosa due to its ubiquity in soil and water as well as its potential to cause infections in plants, animals, and humans. Siderophores produced by P. aeruginosa play critical roles in iron scavenging for prokaryotic species (bacteria) and eukaryotic hosts (fungi, animals, insects, invertebrates, and plants) as well. This review provides a comprehensive discussion of the role of P. aeruginosa siderophores in interaction with prokaryotes and eukaryotes as well as their underlying mechanisms of action. The evolutionary relationship between P. aeruginosa siderophore recognition receptors, such as FpvA, FpvB, and FptA, and those of other bacterial species has also been investigated.

The past, present and future of polymicrobial infection research: Modelling, eavesdropping, terraforming and other stories

Over the last two centuries, great advances have been made in microbiology as a discipline. Much of this progress has come about as a consequence of studying the growth and physiology of individual microbial species in well-defined laboratory media; so-called "axenic growth". However, in the real world, microbes rarely live in such "splendid isolation" (to paraphrase Foster) and more often-than-not, share the niche with a plethora of co-habitants. The resulting interactions between species (and even between kingdoms) are only very poorly understood, both on a theoretical and experimental level. Nevertheless, the last few years have seen significant progress, and in this review, we assess the importance of polymicrobial infections, and show how improved experimental traction is advancing our understanding of these. A particular focus is on developments that are allowing us to capture the key features of polymicrobial infection scenarios, especially as those associated with the human airways (both healthy and diseased).

Interspecies surfactants serve as public goods enabling surface motility in Pseudomonas aeruginosa

In most natural environments, bacteria live in polymicrobial communities where secreted molecules from neighboring species alter bacterial behaviors including motility, but such interactions are understudied. Pseudomonas aeruginosa is a motile opportunistic pathogen that exists in diverse multispecies environments such as the soil and is frequently found in human wound and respiratory tract co-infections with other bacteria including Staphylococcus aureus. Here we show that P. aeruginosa can co-opt secreted surfactants from other species for flagellar-based surface motility. We found that exogenous surfactants from S. aureus, other bacteria, and interkingdom species enabled P. aeruginosa to switch from swarming to an alternative surface spreading motility on semi-solid surfaces and allowed for the emergence of surface motility on hard agar where P. aeruginosa was otherwise unable to move. This motility was distinct from the response of other motile bacteria in the presence of exogenous surfactants. Mutant analysis indicated that this P. aeruginosa motility was similar to a previously described mucin-based motility, 'surfing', albeit with divergent regulation. Thus, our study demonstrates that secreted surfactants from the host as well as neighboring bacterial and interkingdom species act as public goods facilitating P. aeruginosa flagella-mediated surfing-like surface motility, thereby allowing it to access different environmental niches.

Pseudomonas aeruginosa transcriptome analysis of metal restriction in ex vivo cystic fibrosis sputum

Chronic Pseudomonas aeruginosa lung infections are a feature of cystic fibrosis (CF) that many patients experience even with the advent of highly effective modulator therapies. Identifying factors that impact P. aeruginosa in the CF lung could yield novel strategies to eradicate infection or otherwise improve outcomes. To complement published P. aeruginosa studies using laboratory models or RNA isolated from sputum, we analyzed transcripts of strain PAO1 after incubation in sputum from different CF donors prior to RNA extraction. We compared PAO1 gene expression in this "spike-in" sputum model to that for P. aeruginosa grown in synthetic cystic fibrosis sputum medium to determine key genes, which are among the most differentially expressed or most highly expressed. Using the key genes, gene sets with correlated expression were determined using the gene expression analysis tool eADAGE. Gene sets were used to analyze the activity of specific pathways in P. aeruginosa grown in sputum from different individuals. Gene sets that we found to be more active in sputum showed similar activation in published data that included P. aeruginosa RNA isolated from sputum relative to corresponding in vitro reference cultures. In the ex vivo samples, P. aeruginosa had increased levels of genes related to zinc and iron acquisition which were suppressed by metal amendment of sputum. We also found a significant correlation between expression of the H1-type VI secretion system and CFTR corrector use by the sputum donor. An ex vivo sputum model or synthetic sputum medium formulation that imposes metal restriction may enhance future CF-related studies.IMPORTANCEIdentifying the gene expression programs used by Pseudomonas aeruginosa to colonize the lungs of people with cystic fibrosis (CF) will illuminate new therapeutic strategies. To capture these transcriptional programs, we cultured the common P. aeruginosa laboratory strain PAO1 in expectorated sputum from CF patient donors. Through bioinformatic analysis, we defined sets of genes that are more transcriptionally active in real CF sputum compared to a synthetic cystic fibrosis sputum medium. Many of the most differentially active gene sets contained genes related to metal acquisition, suggesting that these gene sets play an active role in scavenging for metals in the CF lung environment which may be inadequately represented in some models. Future studies of P. aeruginosa transcript abundance in CF may benefit from the use of an expectorated sputum model or media supplemented with factors that induce metal restriction.

Intestinal Bacteroides modulates inflammation, systemic cytokines, and microbial ecology via propionate in a mouse model of cystic fibrosis

Persons with cystic fibrosis (CF), starting in early life, show intestinal microbiome dysbiosis characterized in part by a decreased relative abundance of the genus Bacteroides. Bacteroides is a major producer of the intestinal short chain fatty acid propionate. We demonstrate here that cystic fibrosis transmembrane conductance regulator-defective (CFTR-/-) Caco-2 intestinal epithelial cells are responsive to the anti-inflammatory effects of propionate. Furthermore, Bacteroides isolates inhibit the IL-1β-induced inflammatory response of CFTR-/- Caco-2 intestinal epithelial cells and do so in a propionate-dependent manner. The introduction of Bacteroides-supplemented stool from infants with cystic fibrosis into the gut of CftrF508del mice results in higher propionate in the stool as well as the reduction in several systemic pro-inflammatory cytokines. Bacteroides supplementation also reduced the fecal relative abundance of Escherichia coli, indicating a potential interaction between these two microbes, consistent with previous clinical studies. For a Bacteroides propionate mutant in the mouse model, pro-inflammatory cytokine KC is higher in the airway and serum compared with the wild-type (WT) strain, with no significant difference in the absolute abundance of these two strains. Taken together, our data indicate the potential multiple roles of Bacteroides-derived propionate in the modulation of systemic and airway inflammation and mediating the intestinal ecology of infants and children with CF. The roles of Bacteroides and the propionate it produces may help explain the observed gut-lung axis in CF and could guide the development of probiotics to mitigate systemic and airway inflammation for persons with CF.IMPORTANCEThe composition of the gut microbiome in persons with CF is correlated with lung health outcomes, a phenomenon referred to as the gut-lung axis. Here, we demonstrate that the intestinal microbe Bacteroides decreases inflammation through the production of the short-chain fatty acid propionate. Supplementing the levels of Bacteroides in an animal model of CF is associated with reduced systemic inflammation and reduction in the relative abundance of the opportunistically pathogenic group Escherichia/Shigella in the gut. Taken together, these data demonstrate a key role for Bacteroides and microbially produced propionate in modulating inflammation, gut microbial ecology, and the gut-lung axis in cystic fibrosis. These data support the role of Bacteroides as a potential probiotic in CF.

Co-occurring microflora and mucin drive Pseudomonas aeruginosa diversification and pathoadaptation

While several environmental factors contribute to the evolutionary diversification of the pathogenic bacterium Pseudomonas aeruginosa during cystic fibrosis lung infections, relatively little is known about the impact of the surrounding microbiota. By using in vitro experimental evolution, we show that the presence of Stenotrophomonas maltophilia, Staphylococcus aureus, or them both, prevent the evolution of loss of virulence, which repeatedly occurs in the absence of these species due to mutations in regulators of the Pseudomonas Quinolone Signal quorum sensing system, vqsM and pqsR. Moreover, the strength of the effect of co-occurring species is attenuated through changes in the physical environment by the addition of mucin, resulting in selection for phenotypes resembling those evolved in the absence of the co-occurring species. Together, our findings show that variation in mucosal environment and the surrounding polymicrobial environment can determine the evolutionary trajectory of P. aeruginosa, partly explaining its diversification and pathoadaptation from acute to chronic phenotype during cystic fibrosis lung infections.

Origins of symbiosis: shared mechanisms underlying microbial pathogenesis, commensalism and mutualism of plants and animals

Regardless of the outcome of symbiosis, whether it is pathogenic, mutualistic or commensal, bacteria must first colonize their hosts. Intriguingly, closely related bacteria that colonize diverse hosts with diverse outcomes of symbiosis have conserved host-association and virulence factors. This review describes commonalities in the process of becoming host associated amongst bacteria with diverse lifestyles. Whether a pathogen, commensal or mutualist, bacteria must sense the presence of and migrate towards a host, compete for space and nutrients with other microbes, evade the host immune system, and change their physiology to enable long-term host association. We primarily focus on well-studied taxa, such as Pseudomonas, that associate with diverse model plant and animal hosts, with far-ranging symbiotic outcomes. Given the importance of opportunistic pathogens and chronic infections in both human health and agriculture, understanding the mechanisms that facilitate symbiotic relationships between bacteria and their hosts will help inform the development of disease treatments for both humans, and the plants we eat.

A nosocomial Pseudomonas aeruginosa ST3495 isolated from a wild Burmese python (Python bivittatus) with suppurative pneumonia and bacteremia in Hainan, China

Pseudomonas aeruginosa is a common infectious agent associated with respiratory diseases in boas and pythons, however, the histopathology, resistance and virulence are yet described for this species. In this study, we investigated a dying Burmese python rescued from tropical rainforest in Hainan. Clinical signs were open-mouthed breathing, abnormal shedding and anorexia. Abundant yellow mucopurulent secretions were observed in highly ectatic segmental bronchi by postmortem. Histopathological lesions included systemic pneumonia, enteritis, nephritis and carditis. P. aeruginosa was the only species isolated from heart blood, kidney, trachea and lung. The phenotype analysis demonstrated that the isolates had strong biofilm, and were sensitive to amikacin, spectinomycin, ciprofloxacin, norfloxacin and polymyxin B, moreover, the LD50 of the most virulent isolate was 2.22×105 cfu/mL in a zebrafish model. Molecular epidemiological analysis revealed that the isolates belonged to sequence type 3495, the common gene patterns were toxA + exoSYT + phzIM + plcHN in virulence and catB + blaTEM + ant (3'')-I+ tetA in resistance. This study highlights that P. aeruginosa should be worth more attention in wildlife conservation and raise the public awareness for the cross infection and cross spread between animals and human.

Enzyme Production and Inhibitory Potential of Pseudomonas aeruginosa: Contrasting Clinical and Environmental Isolates

(1) Background: This study summarizes the findings of two studies investigating the inhibitory effects of Pseudomonas aeruginosa strains from clinical and environmental sources against gram-positive and gram-negative bacteria and fungi. The studies also analyzed the correlation between enzyme production and inhibitory effects to gain insights into the antimicrobial capabilities of P. aeruginosa strains; (2) Methods: Both studies employed similar methodologies, including the use of disk diffusion and well diffusion methods to assess the inhibitory effects of P. aeruginosa strains against target pathogens. Enzyme production was analyzed through various biochemical assays to determine the diversity and frequencies of enzyme secretion among the strains; (3) Results: A comparative analysis of enzyme production in P. aeruginosa strains from clinical sources revealed significant variations in enzyme production, with hemolysin and protease being the most commonly produced enzymes. Gelatinase production showed lower rates, whereas chondroitinase and hyaluronidase were absent or occurred less frequently. In contrast, a comparative analysis of enzyme production in environmental isolates showed different patterns, indicating adaptation to environmental conditions. Pyocyanin production was absent in all environmental isolates. The inhibitory effects against gram-positive and gram-negative bacteria varied among different P. aeruginosa strains, with strain-specific variations observed. Limited inhibitory effects were observed against fungi, primarily toward gram-positive bacteria; (4) Conclusions: The findings highlight the strain-specific nature of inhibitory effects and enzyme production in P. aeruginosa strains. The correlation between enzyme production and inhibitory effects against gram-positive bacteria suggest a potential role of specific enzymes, such as hemolysin and protease, in the antimicrobial activity. The complexity of the relationship between enzyme production and the inhibition of different pathogens requires further investigation. The results emphasize the potential of P. aeruginosa strains as sources for antimicrobial strategies, particularly against gram-positive bacteria. Future research should focus on understanding the mechanisms underlying these inhibitory effects and exploring their therapeutic applications.

Analysis of Pseudomonas aeruginosa transcription in an ex vivo cystic fibrosis sputum model identifies metal restriction as a gene expression stimulus

Chronic Pseudomonas aeruginosa lung infections are a distinctive feature of cystic fibrosis (CF) pathology, that challenge adults with CF even with the advent of highly effective modulator therapies. Characterizing P. aeruginosa transcription in the CF lung and identifying factors that drive gene expression could yield novel strategies to eradicate infection or otherwise improve outcomes. To complement published P. aeruginosa gene expression studies in laboratory culture models designed to model the CF lung environment, we employed an ex vivo sputum model in which laboratory strain PAO1 was incubated in sputum from different CF donors. As part of the analysis, we compared PAO1 gene expression in this "spike-in" sputum model to that for P. aeruginosa grown in artificial sputum medium (ASM). Analyses focused on genes that were differentially expressed between sputum and ASM and genes that were most highly expressed in sputum. We present a new approach that used sets of genes with correlated expression, identified by the gene expression analysis tool eADAGE, to analyze the differential activity of pathways in P. aeruginosa grown in CF sputum from different individuals. A key characteristic of P. aeruginosa grown in expectorated CF sputum was related to zinc and iron acquisition, but this signal varied by donor sputum. In addition, a significant correlation between P. aeruginosa expression of the H1-type VI secretion system and corrector use by the sputum donor was observed. These methods may be broadly useful in looking for variable signals across clinical samples.

Repurposing High-Throughput Screening Identifies Unconventional Drugs with Antibacterial and Antibiofilm Activities against Pseudomonas aeruginosa under Experimental Conditions Relevant to Cystic Fibrosis

Pseudomonas aeruginosa is the most common pathogen infecting cystic fibrosis (CF) lungs, causing acute and chronic infections. Intrinsic and acquired antibiotic resistance allow P. aeruginosa to colonize and persist despite antibiotic treatment, making new therapeutic approaches necessary. Combining high-throughput screening and drug repurposing is an effective way to develop new therapeutic uses for drugs. This study screened a drug library of 3,386 drugs, mostly FDA approved, to identify antimicrobials against P. aeruginosa under physicochemical conditions relevant to CF-infected lungs. Based on the antibacterial activity, assessed spectrophotometrically against the prototype RP73 strain and 10 other CF virulent strains, and the toxic potential evaluated toward CF IB3-1 bronchial epithelial cells, five potential hits were selected for further analysis: the anti-inflammatory and antioxidant ebselen, the anticancer drugs tirapazamine, carmofur, and 5-fluorouracil, and the antifungal tavaborole. A time-kill assay showed that ebselen has the potential to cause rapid and dose-dependent bactericidal activity. The antibiofilm activity was evaluated by viable cell count and crystal violet assays, revealing carmofur and 5-fluorouracil as the most active drugs in preventing biofilm formation regardless of the concentration. In contrast, tirapazamine and tavaborole were the only drugs actively dispersing preformed biofilms. Tavaborole was the most active drug against CF pathogens other than P. aeruginosa, especially against Burkholderia cepacia and Acinetobacter baumannii, while carmofur, ebselen, and tirapazamine were particularly active against Staphylococcus aureus and B. cepacia. Electron microscopy and propidium iodide uptake assay revealed that ebselen, carmofur, and tirapazamine significantly damage cell membranes, with leakage and cytoplasm loss, by increasing membrane permeability. IMPORTANCE Antibiotic resistance makes it urgent to design new strategies for treating pulmonary infections in CF patients. The repurposing approach accelerates drug discovery and development, as the drugs' general pharmacological, pharmacokinetic, and toxicological properties are already well known. In the present study, for the first time, a high-throughput compound library screening was performed under experimental conditions relevant to CF-infected lungs. Among 3,386 drugs screened, the clinically used drugs from outside infection treatment ebselen, tirapazamine, carmofur, 5-fluorouracil, and tavaborole showed, although to different extents, anti-P. aeruginosa activity against planktonic and biofilm cells and broad-spectrum activity against other CF pathogens at concentrations not toxic to bronchial epithelial cells. The mode-of-action studies revealed ebselen, carmofur, and tirapazamine targeted the cell membrane, increasing its permeability with subsequent cell lysis. These drugs are strong candidates for repurposing for treating CF lung P. aeruginosa infections.

Structure based virtual screening and molecular dynamics of natural anti-biofilm compounds against SagS response regulator/sensor kinase in Pseudomonas aeruginosa

SagS sensor regulator plays a vital role in biofilm development of Pseudomonas aeruginosa which subsequently makes the cells more tolerant to various antimicrobials. The multidrug resistance (MDR) issue has risen substantially in recent years and is considered a global threat. Therefore, alternative compounds should be unearthed immediately to address the issues related to P. aeruginosa drug resistance for which SagS could be a candidate. The present study is an attempt to screen natural anti-biofilm compounds as the potent inhibitors of SagS. Twenty natural anti-biofilm/quorum sensing inhibiting compounds were retrieved from various literatures with significant inhibitory effects against P. aeruginosa biofilm from in-vitro experiments which were screened using various pharmacokinetic parameters. The screened and three standard drugs were docked against SagS-HisKA using AutoDock 4.2 tool, which were further analysed by MD simulations to understand the binding mode of compounds and dynamic behaviour of the complexes. Two potential anti-biofilm natural compounds, pinocembrin with binding affinity (-7.19 kcal/mol), vestitol (-7.18 kcal/mol) and the standard drug ceftazidime (-8.89 kcal/mol) were selected based on filtered parameters and better binding affinity. The trajectory analysis of MD simulations reflected Pinocembrin in stabilizing the system compared to ceftazidime. The existing reports state that the natural products represent promising source of therapy with least or almost nil adverse effect compared to synthetic drugs which is well collated with our in-silico findings. This investigation can save both time and cost required for in-vitro and in-vivo analysis for designing of a novel anti-biofilm agent against P. aeruginosa biofilm-associated infections.Communicated by Ramaswamy H. Sarma.

Genetic and environmental determinants of surface adaptations in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a well-studied Gram-negative opportunistic bacterium that thrives in markedly varied environments. It is a nutritionally versatile microbe that can colonize a host as well as exist in the environment. Unicellular, planktonic cells of P. aeruginosa can come together to perform a coordinated swarming movement or turn into a sessile, surface-adhered population called biofilm. These collective behaviours produce strikingly different outcomes. While swarming motility rapidly disseminates the bacterial population, biofilm collectively protects the population from environmental stresses such as heat, drought, toxic chemicals, grazing by predators, and attack by host immune cells and antibiotics. The ubiquitous nature of P. aeruginosa is likely to be supported by the timely transition between planktonic, swarming and biofilm lifestyles. The social behaviours of this bacteria viz biofilm and swarm modes are controlled by signals from quorum-sensing networks, LasI-LasR, RhlI-RhlR and PQS-MvfR, and several other sensory kinases and response regulators. A combination of environmental and genetic cues regulates the transition of the P. aeruginosa population to specific states. The current review is aimed at discussing key factors that promote physiologically distinct transitioning of the P. aeruginosa population.

Comparative Genomics of Pseudomonas aeruginosa Strains Isolated from Different Ecological Niches

The Pseudomonas aeruginosa genome can change to adapt to different ecological niches. We compared four genomes from a Mexican hospital and 59 genomes from GenBank from different niches, such as urine, sputum, and environmental. The ST analysis showed that high-risk STs (ST235, ST773, and ST27) were present in the genomes of the three niches from GenBank, and the STs of Mexican genomes (ST167, ST2731, and ST549) differed from the GenBank genomes. Phylogenetic analysis showed that the genomes were clustering according to their ST and not their niche. When analyzing the genomic content, we observed that environmental genomes had genes involved in adapting to the environment not found in the clinics and that their mechanisms of resistance were mutations in antibiotic resistance-related genes. In contrast, clinical genomes from GenBank had resistance genes, in mobile/mobilizable genetic elements in the chromosome, except for the Mexican genomes that carried them mostly in plasmids. This was related to the presence of CRISPR-Cas and anti-CRISPR; however, Mexican strains only had plasmids and CRISPR-Cas. bla_OXA-488 (a variant of bla_OXA50) with higher activity against carbapenems was more prevalent in sputum genomes. The virulome analysis showed that exoS was most prevalent in the genomes of urinary samples and exoU and pldA in sputum samples. This study provides evidence regarding the genetic variability among P. aeruginosa isolated from different niches.

Complications and Treatments of Pseudomonas aeruginosa Infection After Rhinoplasty With Implants: A Clinical Study

BACKGROUND

Pseudomonas aeruginosa is an opportunistic pathogen, and because of its specificity, its treatments appear tricky in postrhinoplasty infections with internal implants. This study summarizes the clinical characteristics and treatment of this type of infections to provide some reference for clinical work.

METHODS

We retrospectively analyzed 10 patients who were diagnosed with a nasal infection of P. aeruginosa after implant nasal augmentation. The results of the bacterial culture and drug sensitivity test of the patients' wound secretions were summarized and analyzed. We summarized the characteristics of the patients' infection and the treatments, and we also summarized the patients' prognosis.

RESULTS

In these 10 cases, their implants included rib cartilage and ear cartilage alone, as well as their own cartilage combined with expanded polytetrafluoroethylene and silicone. All patients developed wound infections within 1 month after rhinoplasty, with bacterial cultures of P. aeruginosa . Prolonged use of sensitive antibiotics, as well as wound dressing changes, failed to keep the infection well under control. Patients whose implant was removed and thoroughly debrided within 1 week of infection did not experience any serious complications. In patients who were infected for >1 week before surgery to remove the implants, complications such as nasal column necrosis and nasal contracture occurred, and later the nasal repair was performed after multiple surgeries.

CONCLUSIONS

For bacterial infections in postrhinoplasty wounds with implants, we recommend early bacterial culture. If the infection is clearly P. aeruginosa , the implant should be removed and thoroughly debrided as soon as possible to avoid serious complications.

LEVEL OF EVIDENCE

Level IV.

Pseudomonas aeruginosa behaviour in polymicrobial communities: The competitive and cooperative interactions conducting to the exacerbation of infections

Pseudomonas aeruginosa is mostly associated with persistent infections and antibiotic resistance as a result of several factors, biofilms one of them. Microorganisms within the polymicrobial biofilm (PMB) reveal various transcriptional profiles and affect each other which might influence their pathogenicity and antibiotic tolerance and subsequent worsening of the biofilm infection. P. aeruginosa within PMB exhibits various behaviours toward other microorganisms, which may enhance or repress the virulence of these microbes. Microbial neighbours, in turn, may affect P. aeruginosa's virulence either positively or negatively. Such interactions among microorganisms lead to emerging persistent and antibiotic-resistant infections. This review highlights the relationship between P. aeruginosa and its microbial neighbours within the PMB in an attempt to better understand the mechanisms of polymicrobial interaction and the correlation between increased exacerbations of infection and the P. aeruginosa-microbe interaction. Researching in the literature that was carried out in vitro either in co-cultures or in the models to simulate the environment at the site of infection suggested that the interplay between P. aeruginosa and other microorganisms is one main reason for the worsening of the infection and which in turn requires a treatment approach different from that followed with P. aeruginosa mono-infection.

Structural modification of the Pseudomonas aeruginosa alkylquinoline cell-cell communication signal, HHQ, leads to benzofuranoquinolines with anti-virulence behaviour in ESKAPE pathogens

Microbial populations have evolved intricate networks of negotiation and communication through which they can coexist in natural and host ecosystems. The nature of these systems can be complex and they are, for the most part, poorly understood at the polymicrobial level. The Pseudomonas Quinolone Signal (PQS) and its precursor 4-hydroxy-2-heptylquinoline (HHQ) are signal molecules produced by the important nosocomial pathogen Pseudomonas aeruginosa . They are known to modulate the behaviour of co-colonizing bacterial and fungal pathogens such as Bacillus atropheaus, Candida albicans and Aspergillus fumigatus. While the structural basis for alkyl-quinolone signalling within P. aeruginosa has been studied extensively, less is known about how structural derivatives of these molecules can influence multicellular behaviour and population-level decision-making in other co-colonizing organisms. In this study, we investigated a suite of small molecules derived initially from the HHQ framework, for anti-virulence activity against ESKAPE pathogens, at the species and strain levels. Somewhat surprisingly, with appropriate substitution, loss of the alkyl chain (present in HHQ and PQS) did not result in a loss of activity, presenting a more easily accessible synthetic framework for investigation. Virulence profiling uncovered significant levels of inter-strain variation among the responses of clinical and environmental isolates to small-molecule challenge. While several lead compounds were identified in this study, further work is needed to appreciate the extent of strain-level tolerance to small-molecule anti-infectives among pathogenic organisms.

Temperature-specific adaptations and genetic requirements in a biofilm formed by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a gram-negative opportunistic pathogen often associated with nosocomial infections that are made more severe by this bacterium's ability to form robust biofilms. A biofilm is a microbial community encompassing cells embedded within an extracellular polymeric substrate (EPS) matrix that is typically secreted by the encased microbial cells. Biofilm formation is influenced by several environmental cues, and temperature fluctuations are likely to be an important stimulus in the lifecycle of P. aeruginosa as it transitions between life in aquatic or soil environments to sites of infection in the human host. Previous work has demonstrated that human body temperature can induce a shift in the biofilm EPS relative to room temperature growth, resulting in an incorporation of a filamentous phage coat protein into the biofilm EPS. In this study, we sought to identify adaptations enabling biofilm formation at room temperature or temperatures mimicking the natural environment of P. aeruginosa (23°C and 30°C) relative to temperatures mimicking life in the human host (37°C and 40°C). We identified higher biofilm: biomass ratios at lower temperatures on certain substrates, which correlated with a higher relative abundance of apparent polysaccharide EPS content. However, the known genes for EPS polysaccharide production in P. aeruginosa PA14 did not appear to be specifically important for temperature-dependent biofilm adaptation, with the pelB gene appearing to be generally important and the algD gene being generally expendable in all conditions tested. Instead, we were able to identify two previously uncharacterized hypothetical proteins (PA14_50070 and PA14_67550) specifically required for biofilm formation at 23°C and/or 30°C relative to temperatures associated with the human host. These unstudied contributors to biofilm integrity may have been previously overlooked since most P. aeruginosa biofilm studies tend to use 37°C growth temperatures. Overall, our study demonstrates that temperature shifts can have dramatic impacts on biofilm structure and highlights the importance of studying environment-specific adaptations in biofilm physiology.

Photo-responsive polymeric micelles for the light-triggered release of curcumin targeting antimicrobial activity

Nanocarriers have been successfully used to solubilize, deliver, and increase the bioavailability of curcumin (CUR), but slow CUR release rates hinder its use as a topical photosensitizer in antimicrobial photodynamic therapy. A photo-responsive polymer (PRP) was designed for the light-triggered release of CUR with an effective light activation-dependent antimicrobial response. The characterization of the PRP was compared with non-responsive micelles comprising Pluronics™ P123 and F127. According to the findings, the PRP formed photo-responsive micelles in the nanometric scale (< 100 nm) with a lower critical micelle concentration (3.74 × 10^-4 M^-1, 5.8 × 10^-4 M^-1, and 7.2 × 10^-6 M^-1 for PRP, F127, P123, respectively, at 25°C) and higher entrapment efficiency of CUR (88.7, 77.2, and 72.3% for PRP, F127, and P123 micelles, respectively) than the pluronics evaluated. The PRP provided enhanced protection of CUR compared to P123 micelles, as demonstrated in fluorescence quenching studies. The light-triggered release of CUR from PRP occurred with UV light irradiation (at 355 nm and 25 mW cm^-2) and a cumulative release of 88.34% of CUR within 1 h compared to 80% from pluronics after 36 h. In vitro studies showed that CUR-loaded PRP was non-toxic to mammal cell, showed inactivation of the pathogenic microorganisms Candida albicans, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus, and decreased biofilm biomass when associated with blue light (455  nm, 33.84 J/cm²). The findings show that the CUR-loaded PRP micelle is a viable option for antimicrobial activity.

You will know by its tail: a method for quantification of heterogeneity of bacterial populations using single-cell MIC profiling

Severe non-healing infections are often caused by multiple pathogens or by genetic variants of the same pathogen exhibiting different levels of antibiotic resistance. For example, polymicrobial diabetic foot infections double the risk of amputation compared to monomicrobial infections. Although these infections lead to increased morbidity and mortality, standard antimicrobial susceptibility methods are designed for homogenous samples and are impaired in quantifying heteroresistance. Here, we propose a droplet-based label-free method for quantifying the antibiotic response of the entire population at the single-cell level. We used Pseudomonas aeruginosa and Staphylococcus aureus samples to confirm that the shape of the profile informs about the coexistence of diverse bacterial subpopulations, their sizes, and antibiotic heteroresistance. These profiles could therefore indicate the outcome of antibiotic treatment in terms of the size of remaining subpopulations. Moreover, we studied phenotypic variants of a S. aureus strain to confirm that the profile can be used to identify tolerant subpopulations, such as small colony variants, associated with increased risks for the development of persisting infections. Therefore, the profile is a versatile instrument for quantifying the size of each bacterial subpopulation within a specimen as well as their individual and joined heteroresistance.

Rapid Synergistic Biofilm Production of Pseudomonas and Candida on the Pulmonary Cell Surface and in Mice, a Possible Cause of Chronic Mixed Organismal Lung Lesions

Due to the possible co-presence of Pseudomonas aeruginosa and Candida albicans (the most common nosocomial pathogens) in lungs, rapid interkingdom biofilm production is possible. As such, PA+CA produced more dominant biofilms on the pulmonary epithelial surface (NCI-H292) (confocal fluorescent extracellular matrix staining) with dominant psl upregulation, as demonstrated by polymerase chain reaction (PCR), after 8 h of experiments than PA alone. With a proteomic analysis, rhamnosyltransferase RhlB protein (Psl-associated quorum-sensing protein) was found to be among the high-abundance proteins in PA+CA than in PA biofilms, supporting psl-mediated biofilms in PA+CA on the cell surface. Additionally, PA+CA increased supernatant cytokines (IL-8 and IL-13, but not TNF-α, IL-6, and IL-10) with a similar upregulation of TLR-4, TLR-5, and TLR-9 (by PCR) compared with PA-stimulated cells. The intratracheal administration of PA+CA induced a greater severity of sepsis (serum creatinine, alanine transaminase, serum cytokines, and histology score) and prominent biofilms (fluorescent staining) with psl upregulation (PCR). In comparison with PA+CA biofilms on glass slides, PA+CA biofilms on biotic surfaces were more prominent (fluorescent staining). In conclusion, PA+CA induced Psl-predominant biofilms on the pulmonary cell surface and in mice with acute pneumonia, and these biofilms were more prominent than those induced by PA alone, highlighting the impact of Candida on rapid interkingdom biofilm production.

Probiotics Administration in Cystic Fibrosis: What Is the Evidence?

In the last 20 years, gut microbiota in patients with cystic fibrosis (CF) has become an object of interest. It was shown that these patients had gut dysbiosis and this could explain not only the intestinal manifestations of the disease but also part of those involving the respiratory tract. The acquisition of previously unknown information about the importance of some bacteria, i.e., those partially or totally disappeared in the gut of CF patients, in the regulation of the activity and function of the gut and the lung was the base to suggest the use of probiotics in CF patients. The main aim of this paper is to discuss the biological basis for probiotic administration to CF patients and which results could be expected. Literature analysis showed that CF intestinal dysbiosis depends on the same genetic mutations that condition the clinical picture of the diseases and is aggravated by a series of therapeutic interventions, such as dietary modifications, the use of antibiotics, and the administration of antacids. All this translates into a significant worsening of the structure and function of organs, including the lung and intestine, already deeply penalized by the genetic alterations of CF. Probiotics can intervene on dysbiosis, reducing the negative effects derived from it. However, the available data cannot be considered sufficient to indicate that these bacteria are essential elements of CF therapy. Further studies that take into account the still unsolved aspects on how to use probiotics are absolutely necessary.

Pseudomonas aeruginosa: Recent Advances in Vaccine Development

Pseudomonas aeruginosa is an important opportunistic human pathogen. Using its arsenal of virulence factors and its intrinsic ability to adapt to new environments, P. aeruginosa causes a range of complicated acute and chronic infections in immunocompromised individuals. Of particular importance are burn wound infections, ventilator-associated pneumonia, and chronic infections in people with cystic fibrosis. Antibiotic resistance has rendered many of these infections challenging to treat and novel therapeutic strategies are limited. Multiple clinical studies using well-characterised virulence factors as vaccine antigens over the last 50 years have fallen short, resulting in no effective vaccination being available for clinical use. Nonetheless, progress has been made in preclinical research, namely, in the realms of antigen discovery, adjuvant use, and novel delivery systems. Herein, we briefly review the scope of P. aeruginosa clinical infections and its major important virulence factors.

CF-Seq, an accessible web application for rapid re-analysis of cystic fibrosis pathogen RNA sequencing studies

Researchers studying cystic fibrosis (CF) pathogens have produced numerous RNA-seq datasets which are available in the gene expression omnibus (GEO). Although these studies are publicly available, substantial computational expertise and manual effort are required to compare similar studies, visualize gene expression patterns within studies, and use published data to generate new experimental hypotheses. Furthermore, it is difficult to filter available studies by domain-relevant attributes such as strain, treatment, or media, or for a researcher to assess how a specific gene responds to various experimental conditions across studies. To reduce these barriers to data re-analysis, we have developed an R Shiny application called CF-Seq, which works with a compendium of 128 studies and 1,322 individual samples from 13 clinically relevant CF pathogens. The application allows users to filter studies by experimental factors and to view complex differential gene expression analyses at the click of a button. Here we present a series of use cases that demonstrate the application is a useful and efficient tool for new hypothesis generation. (CF-Seq: http://scangeo.dartmouth.edu/CFSeq/ ).

The Gut-Lung Axis in Cystic Fibrosis

Cystic fibrosis (CF) is a heritable, multiorgan disease that impacts all tissues that normally express cystic fibrosis transmembrane conductance regulator (CFTR) protein. While the importance of the airway microbiota has long been recognized, the intestinal microbiota has only recently been recognized as an important player in both intestinal and lung health outcomes for persons with CF (pwCF). Here, we summarize current literature related to the gut-lung axis in CF, with a particular focus on three key ideas: (i) mechanisms through which microbes influence the gut-lung axis, (ii) drivers of microbiota alterations, and (iii) the potential for intestinal microbiota remediation.

Priority effects dictate community structure and alter virulence of fungal-bacterial biofilms

Polymicrobial biofilms are a hallmark of chronic wound infection. The forces governing assembly and maturation of these microbial ecosystems are largely unexplored but the consequences on host response and clinical outcome can be significant. In the context of wound healing, formation of a biofilm and a stable microbial community structure is associated with impaired tissue repair resulting in a non-healing chronic wound. These types of wounds can persist for years simmering below the threshold of classically defined clinical infection (which includes heat, pain, redness, and swelling) and cycling through phases of recurrent infection. In the most severe outcome, amputation of lower extremities may occur if spreading infection ensues. Here we take an ecological perspective to study priority effects and competitive exclusion on overall biofilm community structure in a three-membered community comprised of strains of Staphylococcus aureus, Citrobacter freundii, and Candida albicans derived from a chronic wound. We show that both priority effects and inter-bacterial competition for binding to C. albicans biofilms significantly shape community structure on both abiotic and biotic substrates, such as ex vivo human skin wounds. We further show attachment of C. freundii to C. albicans is mediated by mannose-binding lectins. Co-cultures of C. freundii and C. albicans trigger the yeast-to-hyphae transition, resulting in a significant increase in neutrophil death and inflammation compared to either species alone. Collectively, the results presented here facilitate our understanding of fungal-bacterial interactions and their effects on host-microbe interactions, pathogenesis, and ultimately, wound healing.

Basics for Improved Use of Phages for Therapy

Blood-borne therapeutic phages and phage capsids increasingly reach therapeutic targets as they acquire more persistence, i.e., become more resistant to non-targeted removal from blood. Pathogenic bacteria are targets during classical phage therapy. Metastatic tumors are potential future targets, during use of drug delivery vehicles (DDVs) that are phage derived. Phage therapy has, to date, only sometimes been successful. One cause of failure is low phage persistence. A three-step strategy for increasing persistence is to increase (1) the speed of lytic phage isolation, (2) the diversity of phages isolated, and (3) the effectiveness and speed of screening phages for high persistence. The importance of high persistence-screening is illustrated by our finding here of persistence dramatically higher for coliphage T3 than for its relative, coliphage T7, in murine blood. Coliphage T4 is more persistent, long-term than T3. Pseudomonas chlororaphis phage 201phi2-1 has relatively low persistence. These data are obtained with phages co-inoculated and separately assayed. In addition, highly persistent phage T3 undergoes dispersal to several murine organs and displays tumor tropism in epithelial tissue (xenografted human oral squamous cell carcinoma). Dispersal is an asset for phage therapy, but a liability for phage-based DDVs. We propose increased focus on phage persistence—and dispersal—screening.

Pseudomonas aeruginosa biofilms and their partners in crime

Pseudomonas aeruginosa biofilms and the capacity of the bacterium to coexist and interact with a broad range of microorganisms have a substantial clinical impact. This review focuses on the main traits of P. aeruginosa biofilms, such as the structural composition and regulatory networks involved, placing particular emphasis on the clinical challenges they represent in terms of antimicrobial susceptibility and biofilm infection clearance. Furthermore, the ability of P. aeruginosa to grow together with other microorganisms is a significant pathogenic attribute with clinical relevance; hence, the main microbial interactions of Pseudomonas are especially highlighted and detailed throughout this review. This article also explores the infections caused by single and polymicrobial biofilms of P. aeruginosa and the current models used to recreate them under laboratory conditions. Finally, the antimicrobial and antibiofilm strategies developed against P. aeruginosa mono and multispecies biofilms are detailed at the end of this review.

Interspecies Metabolic Complementation in Cystic Fibrosis Pathogens via Purine Exchange

Cystic fibrosis (CF) is a genetic disease frequently associated with chronic lung infections caused by a consortium of pathogens. It is common for auxotrophy (the inability to biosynthesize certain essential metabolites) to develop in clinical isolates of the dominant CF pathogen Pseudomonas aeruginosa, indicating that the CF lung environment is replete in various nutrients. Many of these nutrients are likely to come from the host tissues, but some may come from the surrounding polymicrobial community within the lungs of CF patients as well. To assess the feasibility of nutrient exchange within the polymicrobial community of the CF lung, we selected P. aeruginosa and Staphylococcus aureus, two of the most prevalent species found in the CF lung environment. By comparing the polymicrobial culture of wild-type strains relative to their purine auxotrophic counterparts, we were able to observe metabolic complementation occurring in both P. aeruginosa and S. aureus when grown with a purine-producing cross-species pair. While our data indicate that some of this complementation is likely derived from extracellular DNA freed by lysis of S. aureus by the highly competitive P. aeruginosa, the partial complementation of S. aureus purine deficiency by P. aeruginosa demonstrates that bidirectional nutrient exchange between these classic competitors is possible.

The Impact of Intraspecies and Interspecies Bacterial Interactions on Disease Outcome

The human microbiota is an array of microorganisms known to interact with the host and other microbes. These interactions can be competitive, as microbes must adapt to host- and microorganism-related stressors, thus producing toxic molecules, or cooperative, whereby microbes survive by maintaining homeostasis with the host and host-associated microbial communities. As a result, these microbial interactions shape host health and can potentially result in disease. In this review, we discuss these varying interactions across microbial species, their positive and negative effects, the therapeutic potential of these interactions, and their implications on our knowledge of human well-being.

A Cationic Porphyrin, ZnPor, Disassembles Pseudomonas aeruginosa Biofilm Matrix, Kills Cells Directly, and Enhances Antibiotic Activity of Tobramycin

One of the greatest threats to human health is the rise in antibiotic-resistant bacterial infections. Pseudomonas aeruginosa (PsA) is an "opportunistic" pathogen known to cause life-threatening infections in immunocompromised individuals and is the most common pathogen in adults with cystic fibrosis (CF). We report here a cationic zinc (II) porphyrin, ZnPor, that effectively kills planktonic and biofilm-associated cells of PsA. In standard tests against 16-18 h-old biofilms, concentrations as low as 16 µg/mL resulted in the extensive disruption and detachment of the matrix. The pre-treatment of biofilms for 30 min with ZnPor at minimum inhibitory concentration (MIC) levels (4 µg/mL) substantially enhanced the ability of tobramycin (Tobra) to kill biofilm-associated cells. We demonstrate the rapid uptake and accumulation of ZnPor in planktonic cells even in dedicated heme-uptake system mutants (ΔPhu, ΔHas, and the double mutant). Furthermore, uptake was unaffected by the ionophore carbonyl cyanide m-chlorophenyl hydrazine (CCCP). Cells pre-exposed to ZnPor took up the cell-impermeant dye SYTOXTM Green in a concentration-dependent manner. The accumulation of ZnPor did not result in cell lysis, nor did the cells develop resistance. Taken together, these properties make ZnPor a promising candidate for treating multi-drug-resistant infections, including persistent, antibiotic-resistant biofilms.

Host Adaptation Predisposes Pseudomonas aeruginosa to Type VI Secretion System-Mediated Predation by the Burkholderia cepacia Complex

Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) species are opportunistic lung pathogens of cystic fibrosis (CF) patients. While P. aeruginosa can initiate long-term infections in younger CF patients, Bcc infections only arise in teenagers and adults. Both P. aeruginosa and Bcc use type VI secretion systems (T6SSs) to mediate interbacterial competition. Here, we show P. aeruginosa isolates from teenage and adult CF patients, but not those from young CF patients, are outcompeted by the epidemic Bcc isolate Burkholderia cenocepacia strain AU1054 in a T6SS-dependent manner. The genomes of susceptible P. aeruginosa isolates harbor T6SS-abrogating mutations, the repair of which, in some cases, rendered the isolates resistant. Moreover, seven of eight Bcc strains outcompeted P. aeruginosa strains isolated from the same patients. Our findings suggest certain mutations that arise as P. aeruginosa adapts to the CF lung abrogate T6SS activity, making P. aeruginosa and its human host susceptible to potentially fatal Bcc superinfection.

Niosome-encapsulated tobramycin reduced antibiotic resistance and enhanced antibacterial activity against multidrug-resistant clinical strains of Pseudomonas aeruginosa

In the current study, niosome-encapsulated tobramycin based on Span 60 and Tween 60 was synthesized and its biological efficacies including anti-bacterial, anti-efflux, and anti-biofilm activities were investigated against multidrug resistant (MDR) clinical strains of Pseudomonas aeruginosa. The niosomal formulations were characterized using scanning electron microscopy, transmission electron microscopy, and dynamic light scattering measurement. The encapsulation efficiency was found to be 69.54% ±; 0.67. The prepared niosomal formulations had a high storage stability to 60 days with small changes in size and drug entrapment, which indicates that it is a suitable candidate for pharmaceutical applications. The results of biological study showed the anti-bacterial activity via reduction of antibiotic resistance, enhanced anti-efflux and anti-biofilm activities by more folds in comparison to free tobramycin. In addition, niosome encapsulated tobramycin down-regulated the MexAB-OprM efflux genes, pslA and pelA biofilm related genes in MDR P. aeruginosa strains. The anti-proliferative activity of formulation was evaluated against HEK293 cell lines, which exhibited negligible cytotoxicity against HEK293 cells. The finding of our study shows that encapsulation of tobramycin in niosome enhanced the antibacterial activity and reduced antibiotic resistance in MDR strains of P. aeruginosa comparing to free tobramycin and it can be considered as a favorable drug delivery system.

Current Knowledge and Future Directions in Developing Strategies to Combat Pseudomonas aeruginosa Infection

In the face of growing antimicrobial resistance, there is an urgent need for the development of effective strategies to target Pseudomonas aeruginosa. This metabolically versatile bacterium can cause a wide range of severe opportunistic infections in patients with serious underlying medical conditions, such as those with burns, surgical wounds or people with cystic fibrosis. Many of the key adaptations that arise in this organism during infection are centered on core metabolism and virulence factor synthesis. Interfering with these processes may provide a new strategy to combat infection which could be combined with conventional antibiotics. This review will provide an overview of the most recent work that has advanced our understanding of P. aeruginosa infection. Strategies that exploit this recent knowledge to combat infection will be highlighted alongside potential alternative therapeutic options and their limitations.