Dampening Host Sensing and Avoiding Recognition inPseudomonas aeruginosaPneumonia

Pseudomonas aeruginosais an opportunistic pathogen and causes a wide range of acute and chronic infections.P. aeruginosainfections are kept in check by an effective immune surveillance in the healthy host, while any imbalance or defect in the normal immune response can manifest in disease. Invasive acute infection in the immunocompromised patients is mediated by potent extracellular and cell bound bacterial virulence factors. Life-threatening chronic infection in cystic fibrosis patients is maintained by pathogenic variants that contribute to evade detection and clearance by the immune system. Here, we reviewed the molecular basis of receptor-mediated recognition ofP. aeruginosaand their role in initiating inflammation and the colonization. In addition, the consequence of theP. aeruginosagenetic adaptation for the antibacterial defence and the maintaining of chronic infection are discussed.

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Mutational Analysis of RetS, an Unusual Sensor Kinase-Response Regulator Hybrid Required for Pseudomonas aeruginosa Virulence

Infection and Immunity ◽

10.1128/iai.00575-06 ◽

2006 ◽

Vol 74 (8) ◽

pp. 4462-4473 ◽

Cited By ~ 53

Author(s):

Michelle A. Laskowski ◽

Barbara I. Kazmierczak

Keyword(s):

Pseudomonas Aeruginosa ◽

Mutational Analysis ◽

Response Regulator ◽

Acute Infection ◽

Opportunistic Pathogen ◽

Sensor Kinase ◽

Chronic Infections ◽

Reciprocal Regulation ◽

Wide Range

ABSTRACT Pseudomonas aeruginosa is an opportunistic pathogen capable of causing both acute and chronic infections in a wide range of hosts. Expression of the type III secretion system (T3SS) proteins is correlated with virulence in models of acute infection, while downregulation of the T3SS and upregulation of genes important for biofilm formation are observed during chronic infections. RetS, a hybrid sensor kinase-response regulator protein of P. aeruginosa, plays a key role in the reciprocal regulation of virulence factors required for acute versus chronic infection and is postulated to act in concert with two other sensor kinase-response regulator hybrids, GacS and LadS. This work examines the roles of the putative sensing and signal transduction domains of RetS in induction of the T3SS in vitro and in a murine model of acute pneumonia. We identify distinct signaling roles for the tandem receiver domains of RetS and present evidence suggesting that RetS may serve as a substrate for another sensor kinase. Phenotypes associated with RetS alleles lacking periplasmic and/or transmembrane domains further indicate that the periplasmic domain of RetS may transmit a signal that inhibits RetS activity during acute infections.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1721270115 ◽

2018 ◽

Vol 115 (42) ◽

pp. 10714-10719 ◽

Cited By ~ 20

Author(s):

Alana Schick ◽

Rees Kassen

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Chronic Infection ◽

Opportunistic Pathogen ◽

Chronic Infections ◽

Evolutionary Diversification ◽

Nutritional Conditions ◽

Patient Health ◽

Rapid Diversification

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.

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Significance of a Positive Toxoplasma Immunoglobulin M Test Result in the United States

Journal of Clinical Microbiology ◽

10.1128/jcm.01663-15 ◽

2015 ◽

Vol 53 (11) ◽

pp. 3601-3605 ◽

Cited By ~ 39

Author(s):

Reshika Dhakal ◽

Kiran Gajurel ◽

Christelle Pomares ◽

Jeanne Talucod ◽

Cynthia J. Press ◽

...

Keyword(s):

United States ◽

Chronic Infection ◽

Serological Test ◽

Acute Infection ◽

The United States ◽

Immunoglobulin M ◽

Reference Laboratory ◽

Test Results ◽

Chronic Infections ◽

Content Type

A positiveToxoplasmaimmunoglobulin M (IgM) result is often interpreted as a marker of an acute infection. However, IgM can persist for several years, andToxoplasmacommercial IgM diagnostic test kits can yield a number of false-positive results. For these reasons, a chronicToxoplasmainfection can be erroneously classified as an acute infection, resulting in serious adverse consequences, especially in pregnant women, leading to emotional distress and unnecessary interventions, including termination of pregnancy. Interpretation ofToxoplasmaserology at a reference laboratory can help differentiate a recently acquired infection from a chronic infection. Serological test results for 451 patients with positiveToxoplasmaIgM and IgG test results obtained at nonreference laboratories (NRLs) that were referred to Palo Alto Medical Foundation Toxoplasma Serology Laboratory (PAMF-TSL) to determine whether the patient was acutely or chronically infected were retrospectively reviewed. PAMF-TSL results established that of the 451 patients, 335 (74%) had a chronic infection, 100 (22%) had an acute infection, and 7 (2%) were not infected, and for 9 (2%), results were indeterminate. PositiveToxoplasmaIgM and IgG test results obtained at NRLs cannot accurately distinguish between acute and chronic infections. To do so, testing at reference laboratories is required, as mandated in 1997 in a letter from the Food and Drug Administration (FDA) to clinicians and laboratories in the United States.

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Evolutionary Genomics of Niche-Specific Adaptation to the Cystic Fibrosis Lung in Pseudomonas aeruginosa

Molecular Biology and Evolution ◽

10.1093/molbev/msaa226 ◽

2020 ◽

Author(s):

Jeremy R Dettman ◽

Rees Kassen

Keyword(s):

Cystic Fibrosis ◽

Pseudomonas Aeruginosa ◽

Positive Selection ◽

Chronic Infection ◽

Iron Homeostasis ◽

Acute Infection ◽

Whole Genome Sequence ◽

Chronic Infections ◽

Environmental Strain ◽

Single Strain

Abstract The comparative genomics of the transition of the opportunistic pathogen Pseudomonas aeruginosa from a free-living environmental strain to one that causes chronic infection in the airways of cystic fibrosis (CF) patients remain poorly studied. Chronic infections are thought to originate from colonization by a single strain sampled from a diverse, globally distributed population, followed by adaptive evolution to the novel, stressful conditions of the CF lung. However, we do not know whether certain clades are more likely to form chronic infections than others and we lack a comprehensive view of the suite of genes under positive selection in the CF lung. We analyzed whole-genome sequence data from 1,000 P. aeruginosa strains with diverse ecological provenances including the CF lung. CF isolates were distributed across the phylogeny, indicating little genetic predisposition for any one clade to cause chronic infection. Isolates from the CF niche experienced stronger positive selection on core genes than those derived from environmental or acute infection sources, consistent with recent adaptation to the lung environment. Genes with the greatest differential positive selection in the CF niche include those involved in core cellular processes such as metabolism, energy production, and stress response as well as those linked to patho-adaptive processes such as antibiotic resistance, cell wall and membrane modification, quorum sensing, biofilms, mucoidy, motility, and iron homeostasis. Many genes under CF-specific differential positive selection had regulatory functions, consistent with the idea that regulatory mutations play an important role in rapid adaptation to novel environments.

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A Large-Scale Whole-Genome Comparison Shows that Experimental Evolution in Response to Antibiotics Predicts Changes in Naturally Evolved Clinical Pseudomonas aeruginosa

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01619-19 ◽

2019 ◽

Vol 63 (12) ◽

Cited By ~ 6

Author(s):

Samuel J. T. Wardell ◽

Attika Rehman ◽

Lois W. Martin ◽

Craig Winstanley ◽

Wayne M. Patrick ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Experimental Evolution ◽

Large Scale ◽

Opportunistic Pathogen ◽

Clinical Isolates ◽

Genome Comparison ◽

Chronic Infections ◽

Content Type ◽

Large Deletions ◽

Wide Range

ABSTRACT Pseudomonas aeruginosa is an opportunistic pathogen that causes a wide range of acute and chronic infections. An increasing number of isolates have mutations that make them antibiotic resistant, making treatment difficult. To identify resistance-associated mutations, we experimentally evolved the antibiotic-sensitive strain P. aeruginosa PAO1 to become resistant to three widely used antipseudomonal antibiotics, namely, ciprofloxacin, meropenem, and tobramycin. Mutants could tolerate up to 2,048-fold higher concentrations of antibiotics than strain PAO1. Genome sequences were determined for 13 mutants for each antibiotic. Each mutant had between 2 and 8 mutations. For each antibiotic, at least 8 genes were mutated in multiple mutants, demonstrating the genetic complexity of resistance. For all three antibiotics, mutations arose in genes known to be associated with resistance but also in genes not previously associated with resistance. To determine the clinical relevance of mutations uncovered in this study, we analyzed the corresponding genes in 558 isolates of P. aeruginosa from patients with chronic lung disease and in 172 isolates from the general environment. Many genes identified through experimental evolution had predicted function-altering changes in clinical isolates but not in environmental isolates, showing that mutated genes in experimentally evolved bacteria can predict those that undergo mutation during infection. Additionally, large deletions of up to 479 kb arose in experimentally evolved meropenem-resistant mutants, and large deletions were present in 87 of the clinical isolates. These findings significantly advance understanding of antibiotic resistance in P. aeruginosa and demonstrate the validity of experimental evolution in identifying clinically relevant resistance-associated mutations.

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Clinical S. aureus Isolates Vary in Their Virulence to Promote Adaptation to the Host

Toxins ◽

10.3390/toxins11030135 ◽

2019 ◽

Vol 11 (3) ◽

pp. 135 ◽

Cited By ~ 8

Author(s):

Lorena Tuchscherr ◽

Christine Pöllath ◽

Anke Siegmund ◽

Stefanie Deinhardt-Emmer ◽

Verena Hoerr ◽

...

Keyword(s):

Treatment Strategies ◽

Bacterial Virulence ◽

Chronic Infections ◽

Host Pathogen Interaction ◽

Genotypic Analysis ◽

Wide Range ◽

Severe Infections ◽

Small Colony ◽

Low Cytotoxicity ◽

Infection Types

Staphylococcus aureus colonizes epithelial surfaces, but it can also cause severe infections. The aim of this work was to investigate whether bacterial virulence correlates with defined types of tissue infections. For this, we collected 10–12 clinical S. aureus strains each from nasal colonization, and from patients with endoprosthesis infection, hematogenous osteomyelitis, and sepsis. All strains were characterized by genotypic analysis, and by the expression of virulence factors. The host–pathogen interaction was studied through several functional assays in osteoblast cultures. Additionally, selected strains were tested in a murine sepsis/osteomyelitis model. We did not find characteristic bacterial features for the defined infection types; rather, a wide range in all strain collections regarding cytotoxicity and invasiveness was observed. Interestingly, all strains were able to persist and to form small colony variants (SCVs). However, the low-cytotoxicity strains survived in higher numbers, and were less efficiently cleared by the host than the highly cytotoxic strains. In summary, our results indicate that not only destructive, but also low-cytotoxicity strains are able to induce infections. The low-cytotoxicity strains can successfully survive, and are less efficiently cleared from the host than the highly cytotoxic strains, which represent a source for chronic infections. The understanding of this interplay/evolution between the host and the pathogen during infection, with specific attention towards low-cytotoxicity isolates, will help to optimize treatment strategies for invasive and therapy-refractory infection courses.

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Impact of Engineered Expression of Mitochondrial Association Factor 1b on Toxoplasma gondii Infection and the Host Response in a Mouse Model

mSphere ◽

10.1128/msphere.00471-18 ◽

2018 ◽

Vol 3 (5) ◽

Cited By ~ 2

Author(s):

Elizabeth D. English ◽

Jon P. Boyle

Keyword(s):

Toxoplasma Gondii ◽

Chronic Infection ◽

Acute Infection ◽

Chronic Phase ◽

Parasite Burden ◽

Cytokine Signaling ◽

Parasite Protein ◽

Content Type ◽

Life Threatening ◽

The Impact

ABSTRACT The opportunistic intracellular parasite Toxoplasma gondii causes a lifelong chronic infection capable of reactivating in immunocompromised individuals, which can lead to life-threatening complications. Following invasion of the host cell, host mitochondria associate with the parasitophorous vacuole membrane. This phenotype is T. gondii strain specific and is mediated by expression of a host mitochondrial association-competent (HMA+) paralog of the parasite protein mitochondrial association factor 1 (MAF1b). Previous work demonstrated that expression of MAF1b in strains that do not normally associate with host mitochondria increases their fitness during acute infection in vivo. However, the impact of MAF1b expression during chronic T. gondii infection is unclear. In this study, we assess the impact of MAF1b expression on cyst formation and cytokine production in mice. Despite generally low numbers of cysts generated by the in vitro culture-adapted strains used in this study, we find that parasites expressing MAF1b have higher numbers of cysts in the brains of chronically infected mice and that MAF1b+ cyst burden significantly increases during the course of chronic infection. Consistent with this, mice infected with MAF1b+ parasites have higher levels of the serum cytokines RANTES and VEGF (vascular endothelial growth factor) at day 57 postinfection, although this could be due to higher parasite burden at this time point rather than direct manipulation of these cytokines by MAF1b. Overall these data indicate that MAF1b expression may also be important in determining infection outcome during the chronic phase, either by directly altering the cytokine/signaling environment or by increasing proliferation during the acute and/or chronic phase. IMPORTANCE The parasite Toxoplasma gondii currently infects approximately one-third of the world’s population and causes life-threatening toxoplasmosis in individuals with undeveloped or weakened immune systems. Current treatments are unable to cure T. gondii infection, leaving infected individuals with slow-growing tissue cysts for the remainder of their lives. Previous work has shown that expression of the parasite protein mitochondrial association factor 1 (MAF1b) is responsible for the association of T. gondii parasites with host mitochondria and provides a selective advantage during acute infection. Here we examine the impact of MAF1b expression during chronic T. gondii infection. We find that mice infected with MAF1b-expressing parasites have higher cyst burden and cytokine levels than their wild-type counterparts. A better understanding of the genes involved in establishing and maintaining chronic infection will aid in discovering effective therapeutics for chronically infected individuals.

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Pseudomonas aeruginosa Forms Biofilms in Acute Infection Independent of Cell-to-Cell Signaling

Infection and Immunity ◽

10.1128/iai.00586-07 ◽

2007 ◽

Vol 75 (8) ◽

pp. 3715-3721 ◽

Cited By ~ 108

Author(s):

J. Andy Schaber ◽

W. Jeffrey Triffo ◽

Sang Jin Suh ◽

Jeffrey W. Oliver ◽

Mary Catherine Hastert ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Bacterial Colonization ◽

Acute Infection ◽

Opportunistic Pathogen ◽

Confocal Scanning Laser Microscopy ◽

Chronic Infections ◽

Signaling Mechanism ◽

Confocal Scanning Laser

ABSTRACT Biofilms are bacterial communities residing within a polysaccharide matrix that are associated with persistence and antibiotic resistance in chronic infections. We show that the opportunistic pathogen Pseudomonas aeruginosa forms biofilms within 8 h of infection in thermally injured mice, demonstrating that biofilms contribute to bacterial colonization in acute infections as well. Using light, electron, and confocal scanning laser microscopy, P. aeruginosa biofilms were visualized within burned tissue surrounding blood vessels and adipose cells. Although quorum sensing (QS), a bacterial signaling mechanism, coordinates differentiation of biofilms in vitro, wild-type and QS-deficient P. aeruginosa strains formed similar biofilms in vivo. Our findings demonstrate that P. aeruginosa forms biofilms on specific host tissues independently of QS.

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Roles of Two-Component Systems in Pseudomonas aeruginosa Virulence

International Journal of Molecular Sciences ◽

10.3390/ijms222212152 ◽

2021 ◽

Vol 22 (22) ◽

pp. 12152

Author(s):

Maria Sultan ◽

Rekha Arya ◽

Kyeong Kyu Kim

Keyword(s):

Pseudomonas Aeruginosa ◽

Virulence Factors ◽

Opportunistic Pathogen ◽

Secretion Systems ◽

Chronic Infections ◽

Potential Threat ◽

Wide Range ◽

Component Systems ◽

Two Component ◽

Two Component Systems

Pseudomonas aeruginosa is an opportunistic pathogen that synthesizes and secretes a wide range of virulence factors. P. aeruginosa poses a potential threat to human health worldwide due to its omnipresent nature, robust host accumulation, high virulence, and significant resistance to multiple antibiotics. The pathogenicity of P. aeruginosa, which is associated with acute and chronic infections, is linked with multiple virulence factors and associated secretion systems, such as the ability to form and utilize a biofilm, pili, flagella, alginate, pyocyanin, proteases, and toxins. Two-component systems (TCSs) of P. aeruginosa perform an essential role in controlling virulence factors in response to internal and external stimuli. Therefore, understanding the mechanism of TCSs to perceive and respond to signals from the environment and control the production of virulence factors during infection is essential to understanding the diseases caused by P. aeruginosa infection and further develop new antibiotics to treat this pathogen. This review discusses the important virulence factors of P. aeruginosa and the understanding of their regulation through TCSs by focusing on biofilm, motility, pyocyanin, and cytotoxins.

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β-lactam Resistance in Pseudomonas aeruginosa: Current Status, Future Prospects

Pathogens ◽

10.3390/pathogens10121638 ◽

2021 ◽

Vol 10 (12) ◽

pp. 1638

Author(s):

Karl A. Glen ◽

Iain L. Lamont

Keyword(s):

Pseudomonas Aeruginosa ◽

Cell Division ◽

Biofilm Formation ◽

Opportunistic Pathogen ◽

Current Status ◽

Future Prospects ◽

Penicillin Binding Protein ◽

Chronic Infections ◽

Penicillin Binding Proteins ◽

Wide Range

Pseudomonas aeruginosa is a major opportunistic pathogen, causing a wide range of acute and chronic infections. β-lactam antibiotics including penicillins, carbapenems, monobactams, and cephalosporins play a key role in the treatment of P. aeruginosa infections. However, a significant number of isolates of these bacteria are resistant to β-lactams, complicating treatment of infections and leading to worse outcomes for patients. In this review, we summarize studies demonstrating the health and economic impacts associated with β-lactam-resistant P. aeruginosa. We then describe how β-lactams bind to and inhibit P. aeruginosa penicillin-binding proteins that are required for synthesis and remodelling of peptidoglycan. Resistance to β-lactams is multifactorial and can involve changes to a key target protein, penicillin-binding protein 3, that is essential for cell division; reduced uptake or increased efflux of β-lactams; degradation of β-lactam antibiotics by increased expression or altered substrate specificity of an AmpC β-lactamase, or by the acquisition of β-lactamases through horizontal gene transfer; and changes to biofilm formation and metabolism. The current understanding of these mechanisms is discussed. Lastly, important knowledge gaps are identified, and possible strategies for enhancing the effectiveness of β-lactam antibiotics in treating P. aeruginosa infections are considered.

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