The lytic polysaccharide monooxygenase CbpD promotes Pseudomonas aeruginosa virulence in systemic infection

The recently discovered lytic polysaccharide monooxygenases (LPMOs), which cleave polysaccharides by oxidation, have been associated with bacterial virulence, but supporting functional data is scarce. Here we show that CbpD, the LPMO of Pseudomonas aeruginosa, is a chitin-oxidizing virulence factor that promotes survival of the bacterium in human blood. The catalytic activity of CbpD was promoted by azurin and pyocyanin, two redox-active virulence factors also secreted by P. aeruginosa. Homology modeling, molecular dynamics simulations, and small angle X-ray scattering indicated that CbpD is a monomeric tri-modular enzyme with flexible linkers. Deletion of cbpD rendered P. aeruginosa unable to establish a lethal systemic infection, associated with enhanced bacterial clearance in vivo. CbpD-dependent survival of the wild-type bacterium was not attributable to dampening of pro-inflammatory responses by CbpD ex vivo or in vivo. Rather, we found that CbpD attenuates the terminal complement cascade in human serum. Studies with an active site mutant of CbpD indicated that catalytic activity is crucial for virulence function. Finally, profiling of the bacterial and splenic proteomes showed that the lack of this single enzyme resulted in substantial re-organization of the bacterial and host proteomes. LPMOs similar to CbpD occur in other pathogens and may have similar immune evasive functions.

Antimicrobial Effects of Thymosin Beta-4 and Ciprofloxacin Adjunctive Therapy in Pseudomonas aeruginosa Induced Keratitis

Prior work has indicated that thymosin beta 4 (Tβ4) administered with ciprofloxacin markedly improves disease outcome for Pseudomonas aeruginosa (PA)-induced keratitis. As a result, the goal of the current study was to elucidate mechanisms by which Tβ4 mitigates the corneal response; specifically, regarding its bactericidal influence and potential synergy with ciprofloxacin. An in vitro approach was carried out using minimum inhibitory concentration (MIC) assays to assess bactericidal activity against PA. In addition, antimicrobial peptide (AMP) production was evaluated at the mRNA levels using human corneal epithelial cells in response to lipopolysaccharide (LPS) challenge. The results of the MIC assays did not show direct bactericidal activity with Tβ4 alone, although ciprofloxacin exhibited significant killing at concentrations far lower than clinically dosed. Tβ4, however, displayed an indirect effect on bacterial killing, as shown by an upregulation of AMPs and related molecules. The cumulative data from this study indicate an indirect bactericidal role of Tβ4, as well as a synergistic relationship with ciprofloxacin. Furthermore, ciprofloxacin alone was found to influence cellular functions that otherwise have yet to be reported. These results highlight a mechanism of intracellular communication for Tβ4 and further strengthen its development as an adjunct therapy with antibiotics for corneal infections.

Engineering synthetic breath biomarkers for respiratory disease

Human breath contains many volatile metabolites. However, few breath tests are currently used in the clinic to monitor disease due to bottlenecks in biomarker identification. Here we engineered breath biomarkers for respiratory disease by local delivery of protease-sensing nanoparticles to the lungs. The nanosensors shed volatile reporters upon cleavage by neutrophil elastase, an inflammation-associated protease with elevated activity in lung diseases such as bacterial infection and alpha-1 antitrypsin deficiency. After intrapulmonary delivery into mouse models with acute lung inflammation, the volatile reporters are released and expelled in breath at levels detectable by mass spectrometry. These breath signals can identify diseased mice with high sensitivity as early as 10 min after nanosensor administration. Using these nanosensors, we performed serial breath tests to monitor dynamic changes in neutrophil elastase activity during lung infection and to assess the efficacy of a protease inhibitor therapy targeting neutrophil elastase for the treatment of alpha-1 antitrypsin deficiency.

Protease activity sensors noninvasively classify bacterial infections and antibiotic responses

BACKGROUND

Respiratory tract infections represent a significant public health risk, and timely and accurate detection of bacterial infections facilitates rapid therapeutic intervention. Furthermore, monitoring the progression of infections after intervention enables 'course correction' in cases where initial treatments are ineffective, avoiding unnecessary drug dosing that can contribute to antibiotic resistance. However, current diagnostic and monitoring techniques rely on non-specific or slow readouts, such as radiographic imaging and sputum cultures, which fail to specifically identify bacterial infections and take several days to identify optimal antibiotic treatments.

METHODS

Here we describe a nanoparticle system that detects P. aeruginosa lung infections by sensing host and bacterial protease activity in vivo, and that delivers a urinary detection readout. One protease sensor is comprised of a peptide substrate for the P. aeruginosa protease LasA. A second sensor designed to detect elastases is responsive to recombinant neutrophil elastase and secreted proteases from bacterial strains.

FINDINGS

In mice infected with P. aeruginosa, nanoparticle formulations of these protease sensors-termed activity-based nanosensors (ABNs)-detect infections and monitor bacterial clearance from the lungs over time. Additionally, ABNs differentiate between appropriate and ineffective antibiotic treatments acutely, within hours after the initiation of therapy.

INTERPRETATION

These findings demonstrate how activity measurements of disease-associated proteases can provide a noninvasive window into the dynamic process of bacterial infection and resolution, offering an opportunity for detecting, monitoring, and characterizing lung infections. FUND: National Cancer Institute, National Institute of Environmental Health Sciences, National Institutes of Health, National Science Foundation Graduate Research Fellowship Program, and Howard Hughes Medical Institute.

Effect of Nitric Oxide Synthase Inhibition in Experimental Pseudomonas keratitis in Rabbits

Purpose

The aim of this study was to assess the efficacy of the nitric oxide synthase inhibitor L-NG-nitro-arginine-methyleser (L-NAME) in the treatment of experimental Pseudomonas keratitis.

Methods

Twelve young New Zealand white rabbits were given intrastromal injections of Pseudomonas aeruginosa strains. Twenty-four hours later, the rabbits were randomly divided into four groups: group 1 was treated with topical 0.3% ciprofloxacin drops and a single subconjunctival injection of L-NAME (150 mg/kg); group 2 received topical 0.3% ciprofloxacin drops alone; group 3 received a single subconjunctival injection of L-NAME alone; group 4, the control group, was treated with topical balanced salt solution (BSS) drops. One drop of either ciprofloxacin of BSS was applied at each treatment interval. Twenty-six hours after the start of treatment, the eyes were examined by slit lamp to assess inflammation. Aqueous humor specimens were collected from each eye to measure the nitric oxide concentration. Corneas were removed to count bacteria results.

Results

Slit lamp examination cell scores were significantly lower for groups 1 and 3 than groups 2 and 4 eyes (p = 0.002 to p = 0.004). No viable bacteria were detected in the corneas of groups 1 and 2. Group 3 corneas had significantly fewer bacteria (6.33 ± 0.42 × 103) than group 4 (5.94 ± 0.16 × 104) (p < 0.05). Nitric oxide levels in the aqueous humor were significantly lower for group 1 eyes than for groups 2, 3, or 4 (p = 0.02, p = 0.01, and p = 0.003, respectively).

Conclusions

We conclude that nitric oxide synthase inhibitors may be a useful adjunct but are not a replacement for traditional antibiotic drop therapy.

Prevalence of ESBL-producing Pseudomonas aeruginosa isolates in Warsaw, Poland, detected by various phenotypic and genotypic methods

Knowledge of the prevalence of ESBL enzymes among P. aeruginosa strains compared to the Enterobacteraiceae family is limited. The phenotypic tests recommended by EUCAST for the detection of ESBL-producing Enterobacteriaceae are not always suited for P. aeruginosa strains. This is mainly due to the presence of other families of ESBLs in P. aeruginosa isolates more often than in Enterobacteriaceae, production of natural AmpC cephalosporinase and its overexpression, and co-production of metallo-β-lactamases. The aim of this study was to determine the occurrence of ESBLs in P. aeruginosa isolated from patients from hospitals in Warsaw, to evaluate the ESBL production of these isolates using currently available phenotypic tests, their modifications, multiplex PCR and molecular typing of ESBL-positive isolates by PFGE. Clinical isolates of P. aeruginosa were collected in 2000-2014 from four Warsaw hospitals. Based on the data obtained in this study, we suggest using three DDST methods with inhibitors, such as clavulanic acid, sulbactam and imipenem, to detect ESBL-producing P. aeruginosa strains. Depending on the appearance of the plates, we suggest a reduction in the distance between discs with antibiotics to 15 mm and the addition of boronic acid at 0.4 mg per disc. The analysed isolates carried genes encoding ESBL from the families VEB (69 isolates with VEB-9), GES (6 with GES-1, 1 GES-5, 5 GES-13 and 2 with GES-15), OXA-2 (12 with OXA-15, 1 OXA-141, 1 OXA-210, 1 OXA-543 and 1 with OXA-544) and OXA-10 (5 isolates with OXA-74 and one with OXA-142). The most important result of this study was the discovery of three new genes, bla_GES-15, bla_OXA-141 and bla_OXA-142; their nucleotide sequences have been submitted to the NCBI GenBank. It is also very important to note that this is the first report on the epidemiological problem of VEB-9-producing bacterial strains, not only in Poland but also worldwide.

Role of inducers in detection of blaPDC-mediated oxyimino-cephalosporin resistance in Pseudomonas aeruginosa

BACKGROUND & OBJECTIVES

Pseudomonas aeruginosa possessing chromosomally inducible blaPDCalong with other intrinsic mechanism causes infection with high mortality rate. It is difficult to detect inducible AmpC enzymes in this organism and is usually overlooked by routine testing that may lead to therapeutic failure. Therefore, three different inducers were evaluated in the present study to assess their ability of induction of blaPDCin P. aeruginosa.

METHODS

A total of 189 consecutive Pseudomonas isolates recovered from different clinical specimens (November 2011-April 2013) were selected for the study. Isolates were screened with cefoxitin for AmpC β-lactamases and confirmed by modified three-dimensional extract test (M3DET). Inductions were checked using three inducers, namely, clavulanic acid, cefoxitin and imipenem along with ceftazidime. Molecular screening of AmpC β-lactamase genes was performed by PCR assay. Antimicrobial susceptibility and minimum inhibitory concentrations (MICs) were determined, and repetitive extragenic palindromic-PCR of all blaPDCharbouring isolates was performed.

RESULTS

Inducible phenotype was observed in 42 (24.3%) of 97 (56%) isolates confirmed by M3DET. Among these, 22 isolates harboured chromosomal blaPDCgene, and cocarriage of both chromosomal and plasmid-mediated blaAmpC genes was observed in seven isolates. Cefoxitin-ceftazidime-based test gave good sensitivity and specificity for detecting inducible AmpC enzymes. Isolates harbouring blaPDCshowed high MIC against all tested cephalosporins and monobactam. DNA fingerprinting of these isolates showed 22 different clones of P. aeruginosa.

INTERPRETATION & CONCLUSIONS

P. aeruginosa harbouring inducible (chromosomal) and plasmid-mediated AmpC β-lactamase is a matter of concern as it may limit therapeutic option. Using cefoxitin-ceftazidime-based test is simple and may be used for detecting inducible AmpC β-lactamase amongst P. aeruginosa.

The Pig: A Relevant Model for Evaluating the Neutrophil Serine Protease Activities during Acute Pseudomonas aeruginosa Lung Infection

The main features of lung infection and inflammation are a massive recruitment of neutrophils and the subsequent release of neutrophil serine proteases (NSPs). Anti-infectious and/or anti-inflammatory treatments must be tested on a suitable animal model. Mice models do not replicate several aspects of human lung disease. This is particularly true for cystic fibrosis (CF), which has led the scientific community to a search for new animal models. We have shown that mice are not appropriate for characterizing drugs targeting neutrophil-dependent inflammation and that pig neutrophils and their NSPs are similar to their human homologues. We induced acute neutrophilic inflammatory responses in pig lungs using Pseudomonas aeruginosa, an opportunistic respiratory pathogen. Blood samples, nasal swabs and bronchoalveolar lavage fluids (BALFs) were collected at 0, 3, 6 and 24 h post-insfection (p.i.) and biochemical parameters, serum and BAL cytokines, bacterial cultures and neutrophil activity were evaluated. The release of proinflammatory mediators, biochemical and hematological blood parameters, cell recruitment and bronchial reactivity, peaked at 6h p.i.. We also used synthetic substrates specific for human neutrophil proteases to show that the activity of pig NSPs in BALFs increased. These proteases were also detected at the surface of lung neutrophils using anti-human NSP antibodies. Pseudomonas aeruginosa-induced lung infection in pigs results in a neutrophilic response similar to that described for cystic fibrosis and ventilator-associated pneumonia in humans. Altogether, this indicates that the pig is an appropriate model for testing anti-infectious and/or anti-inflammatory drugs to combat adverse proteolytic effects of neutrophil in human lung diseases.

The Pseudomonas aeruginosa Exoenzyme Y: A Promiscuous Nucleotidyl Cyclase Edema Factor and Virulence Determinant

Exoenzyme Y (ExoY) was identified as a component of the Pseudomonas aeruginosa type 3 secretion system secretome in 1998. It is a common contributor to the arsenal of type 3 secretion system effectors, as it is present in approximately 90% of Pseudomonas isolates. ExoY has adenylyl cyclase activity that is dependent upon its association with a host cell cofactor. However, recent evidence indicates that ExoY is not just an adenylyl cyclase; rather, it is a promiscuous cyclase capable of generating purine and pyrimidine cyclic nucleotide monophosphates. ExoY's enzymatic activity causes a characteristic rounding of mammalian cells, due to microtubule breakdown. In endothelium, this cell rounding disrupts cell-to-cell junctions, leading to loss of barrier integrity and an increase in tissue edema. Microtubule breakdown seems to depend upon tau phosphorylation, where the elevation of cyclic nucleotide monophosphates activates protein kinases A and G and causes phosphorylation of endothelial microtubule associated protein tau. Phosphorylation is a stimulus for tau release from microtubules, leading to microtubule instability. Phosphorylated tau accumulates inside endothelium as a high molecular weight, oligomeric form, and is then released from the cell. Extracellular high molecular weight tau causes a transmissible cytotoxicity that significantly hinders cellular repair following infection. Thus, ExoY may contribute to bacterial virulence in at least two ways; first, by microtubule breakdown leading to loss of endothelial cell barrier integrity, and second, by promoting release of a high molecular weight tau cytotoxin that impairs cellular recovery following infection.

GBA2-encoded β-glucosidase activity is involved in the inflammatory response to Pseudomonas aeruginosa

Current anti-inflammatory strategies for the treatment of pulmonary disease in cystic fibrosis (CF) are limited; thus, there is continued interest in identifying additional molecular targets for therapeutic intervention. Given the emerging role of sphingolipids (SLs) in various respiratory disorders, including CF, drugs that selectively target the enzymes associated with SL metabolism are under development. Miglustat, a well-characterized iminosugar-based inhibitor of β-glucosidase 2 (GBA2), has shown promise in CF treatment because it reduces the inflammatory response to infection by P. aeruginosa and restores F508del-CFTR chloride channel activity. This study aimed to probe the molecular basis for the anti-inflammatory activity of miglustat by examining specifically the role of GBA2 following the infection of CF bronchial epithelial cells by P. aeruginosa. We also report the anti-inflammatory activity of another potent inhibitor of GBA2 activity, namely N-(5-adamantane-1-yl-methoxy)pentyl)-deoxynojirimycin (Genz-529648). In CF bronchial cells, inhibition of GBA2 by miglustat or Genz-529648 significantly reduced the induction of IL-8 mRNA levels and protein release following infection by P. aeruginosa. Hence, the present data demonstrate that the anti-inflammatory effects of miglustat and Genz-529648 are likely exerted through inhibition of GBA2.

Intoxication of host cells by the T3SS phospholipase ExoU: PI(4,5)P2-associated, cytoskeletal collapse and late phase membrane blebbing

Pseudomonas aeruginosa is an opportunistic pathogen that is associated with hospital-acquired infections, ventilator-associated pneumonia, and morbidity of immunocompromised individuals. A subpopulation of P. aeruginosa encodes a protein, ExoU, which exhibits acute cytotoxicity. Toxicity is directly related to the phospholipase A2 activity of the protein after injection into the host cytoplasm via a type III secretion system. ExoU enzymatic activity requires eukaryotic cofactors, ubiquitin or ubiquitin-modified proteins. When administered extracellularly, ExoU is unable to intoxicate epithelial cells in culture, even in the presence of the cofactor. Injection or transfection of ExoU is necessary to observe the acute cytotoxic response. Biochemical approaches indicate that ExoU possesses high affinity to a multifunctional phosphoinositide, phosphatidylinositol 4,5-bisphosphate or PI(4,5)P2 and that it is capable of utilizing this phospholipid as a substrate. In eukaryotic cells, PI(4,5)P2 is mainly located in the cytoplasmic side of the plasma membrane and anchors adaptor proteins that are involved in cytoskeletal structures, focal adhesions, and plasma membranes. Time-lapse fluorescent microscopy analyses of infected live cells demonstrate that ExoU intoxication correlates with intracellular damage in the early phases of infection, such as disruption of focal adhesions, cytoskeletal collapse, actin depolymerization, and cell rounding. At later time points, a membrane blebbing phenotype was prominent prior to the loss of the plasma membrane integrity and barrier function. Membrane blebbing appears to accelerate membrane rupture and the release of intracellular markers. Our data suggest that in eukaryotic host cells, intracellular ExoU targets and hydrolyzes PI(4,5)P2 on the plasma membrane, causing a subsequent disruption of cellular structures and membrane integrity.

Host-specific enzyme-substrate interactions in SPM-1 metallo-β-lactamase are modulated by second sphere residues

Pseudomonas aeruginosa is one of the most virulent and resistant non-fermenting Gram-negative pathogens in the clinic. Unfortunately, P. aeruginosa has acquired genes encoding metallo-β-lactamases (MβLs), enzymes able to hydrolyze most β-lactam antibiotics. SPM-1 is an MβL produced only by P. aeruginosa, while other MβLs are found in different bacteria. Despite similar active sites, the resistance profile of MβLs towards β-lactams changes from one enzyme to the other. SPM-1 is unique among pathogen-associated MβLs in that it contains “atypical” second sphere residues (S84, G121). Codon randomization on these positions and further selection of resistance-conferring mutants was performed. MICs, periplasmic enzymatic activity, Zn(II) requirements, and protein stability was assessed. Our results indicated that identity of second sphere residues modulates the substrate preferences and the resistance profile of SPM-1 expressed in P. aeruginosa. The second sphere residues found in wild type SPM-1 give rise to a substrate selectivity that is observed only in the periplasmic environment. These residues also allow SPM-1 to confer resistance in P. aeruginosa under Zn(II)-limiting conditions, such as those expected under infection. By optimizing the catalytic efficiency towards β-lactam antibiotics, the enzyme stability and the Zn(II) binding features, molecular evolution meets the specific needs of a pathogenic bacterial host by means of substitutions outside the active site.

The presence of Zn(II)-containing metallo-β-lactamases (MβLs) that confer resistance to all penicillins, cephalosporins and carbapenems in Pseudomonas aeruginosa adds significantly to the threat of this pathogen in our health care system. SPM-1 is an MβLs widely distributed in South America and only found in P. aeruginosa. In common with all MβLs, the active site residues are highly conserved. In this work we asked the following question: how would substrate specificity evolve in SPM-1 if the active site residues are highly uniform and do not permit substitutions. To this end, we explored the role of two amino acids (S84 and G121) that are outside the active site (second sphere) and are unique in the SPM-1 β-lactamase. We discovered that replacing these amino acids impacts resistance to cephalosporins and carbapenems and that this resistance profile depends on the enzymatic behavior and the availability of Zn(II) in the environment. This work demonstrates how protein evolution by means of subtle substitutions outside the active site meets the specific needs of a pathogenic bacterial host.

The protein kinases TPL2 and EGFR contribute to ERK1/ERK2 hyperactivation in CFTRΔF508-expressing airway epithelial cells exposed to Pseudomonas aeruginosa

Excessive inflammation and Pseudomonas aeruginosa infection are two major characteristics of cysticfibrosis (CF) lung disease. In this manuscript, we describe a novel mechanism of ERK1/ERK2 activationand CXCL8 expression in airway epithelial cells (AECs) lacking functional CFTR. In both non-CF and CFAECs, the protein kinase TPL2 is required for ERK1/ERK2 MAPK activation. However, we have found that EGFR is strongly phosphorylated in the airway epithelium of CF lung and contributes to ERK1/ERK2 MAPK activation in CF AECs exposed to P. aeruginosa diffusible material (PsaDM). Moreover, PsaDM stimulates the expression of the EGFR pro-ligand HB-EGF more strongly, and in a sustained manner, in CF AECs compared to non-CF cells. Finally, although both non-CF and CF AECs expresses CXCL8 in response to PsaDM, the levels of CXCL8 are higher and EGFR plays a more important role in regulating CXCL8 synthesis in CF AECs. Together, our finding shows that in addition to the TLR-mediated TPL2 activation of ERK1/ERK2, an additional pathway contributing to ERK1/ERK2 activation is triggered by infection of CF AECs: the EGFR signaling pathway. This second pathway may contribute to excessive inflammation observed in CF.

[Epidemiologic diagnostic of nosocomial suppurative-septic infections of Pseudomonas etiology based on intraspecies typing of causative agent]

AIM

Scientific justification of optimization of epidemiologic diagnostic of suppurative-septic infection (SSI) caused by Pseudomonas aeruginosa based on comparability of antibiotic sensitivity and beta-lactamase production.

MATERIALS AND METHODS

Intraspecies typing of 37 P. aeruginosa strains isolated during microbiological monitoring of 106 patients and 131 objects of clinical environment of surgical and obstetrician hospitals by using a complex ofphenotypic and molecular-biological methods including determination of sensitivity to antibiotics by serial dilutions method and PCR-diagnostics with determination of TEM, SHV, CTX, OXA, MBL, VIM genes was performed.

RESULTS

P. aeruginosa strains combined into groups by isolation location during studies turned out to be heterogeneous by sensitivity to antibiotics and beta-lactamase production that allowed to form subgroups of strains by focality attribute. Isolates recovered from different SSI foci had significant differences in minimal inhibitory concentration (MIC) reaching 1024 times. MIC parameter within subgroups did not exceed 8 - 16 consequent dilutions.

CONCLUSION

Use of a complex of phenotypic and molecular-biologic methods of causative agent typing including determination of sensitivity to antibiotics by serial dilutions method and evaluation of beta-lactamase production allowed to establish a mechanism of development of SSI epidemic process caused by P. aeruginosa, detect origins and reservoirs of infection in hospital, modes and factors of transmission and reach maximum justification of epidemiologic control and prophylaxis measures of localization of foci of nosocomial infections of pseudomonas etiology.

Human cysteine cathepsins are not reliable markers of infection by Pseudomonas aeruginosa in cystic fibrosis

Cysteine cathepsins have emerged as new players in inflammatory lung disorders. Their activities are dramatically increased in the sputum of cystic fibrosis (CF) patients, suggesting that they are involved in the pathophysiology of CF. We have characterized the cathepsins in CF expectorations and evaluated their use as markers of colonization by Pseudomonas aeruginosa. The concentrations of active cathepsins B, H, K, L and S were the same in P. aeruginosa-positive (19 Ps+) and P. aeruginosa-negative (6 Ps−) samples, unlike those of human neutrophil elastase. Also the cathepsin inhibitory potential and the cathepsins/cathepsin inhibitors imbalance remained unchanged and similar (∼2-fold) in the Ps+ and Ps− groups (p<0.001), which correlated with the breakdown of their circulating cystatin-like inhibitors (kininogens). Procathepsins, which may be activated autocatalytically, are a potential proteolytic reservoir. Immunoblotting and active-site labeling identified the double-chain cathepsin B, the major cathepsin in CF sputum, as the main molecular form in both Ps+ and Ps− samples, despite the possible release of the ∼31 kDa single-chain form from procathepsin B by sputum elastase. Thus, the hydrolytic activity of cysteine cathepsins was not correlated with bacterial colonization, indicating that cathepsins, unlike human neutrophil elastase, are not suitable markers of P. aeruginosa infection.

Prevalence of metallo-β-lactamase-producing Pseudomonas aeruginosa isolated from diabetic foot ulcer patients

Metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa strains have been reported to be an important cause of nosocomial infections. There is not enough information from India regarding their prevalence in diabetic foot ulcer (DFU) patients. The present study was undertaken over a period of two year from December 2008 to March 2011 to study the incidence of MBL producing P. aeruginosa isolated from 162 DFU patients with various grades of ulcer (Texas classification). Forty isolates of P. aeruginosa were obtained from patients. These isolates were subjected to susceptibility testing to anti-pseudomonal drugs as per Clinical Laboratory and Standards Institute (CLSI) guidelines, and were further screened for the production of MBL by disc potentiation testing using ethylenediaminetetraacetic acid (EDTA)-impregnated imipenem and meropenem discs. Of the 40 isolates of P. aeruginosa, 22 (55%) isolates were found resistant to carbapenems (imipenem) and 18 (81.1%) were found to be MBL producers using imipenem+(EDTA) and 15(68.1%) by meropenem+EDTA. This rapid dissemination of MBL producers is worrisome and necessitates the implementation of not just surveillance studies but also proper and judicious selection of antibiotics, especially carbapenems.

Metallo beta-lactamase producing pseudomonas species--a major cause of concern among hospital associated urinary tract infection

Multidrug resistant pseudomonas strains are isolated in high frequency from urinary samples in hospitalised patients. With the occurrence of extended spectrum beta-lactamases (ESBLs) and metallo beta-lactamase (MBL)-producing Pseudomonas aeruginosa being increasingly reported worldwide, this study evaluated the resistance pattern of pseudomonad strains to carbapenam and other antipseudomonal antibiotics isolated from patients with hospital associated urinary tract infections along with clinical usefulness of various MBL screening methods (combined disc diffusion test, E-test and modified Hodge test). Presence of ESBL and AmpC beta-lactamases in the isolates was also determined. Of the 87 isolates, 81 (93.1%) were Pseudomonas aeruginosa, 4 (4.6%) were Pseudomonas putida, 2 (2.3%) were Burkholderia cepacia. Thirty-one isolates (35.6%) were resistant to imipenem and 61% of these 31 isolates, were MBL producers by combined disc diffusion test, while 48% were detected by E-test method. Overall, in 30% and 54% strains, production of AmpC and ESBL respectively was observed.

YfiBNR mediates cyclic di-GMP dependent small colony variant formation and persistence in Pseudomonas aeruginosa

During long-term cystic fibrosis lung infections, Pseudomonas aeruginosa undergoes genetic adaptation resulting in progressively increased persistence and the generation of adaptive colony morphotypes. This includes small colony variants (SCVs), auto-aggregative, hyper-adherent cells whose appearance correlates with poor lung function and persistence of infection. The SCV morphotype is strongly linked to elevated levels of cyclic-di-GMP, a ubiquitous bacterial second messenger that regulates the transition between motile and sessile, cooperative lifestyles. A genetic screen in PA01 for SCV-related loci identified the yfiBNR operon, encoding a tripartite signaling module that regulates c-di-GMP levels in P. aeruginosa. Subsequent analysis determined that YfiN is a membrane-integral diguanylate cyclase whose activity is tightly controlled by YfiR, a small periplasmic protein, and the OmpA/Pal-like outer-membrane lipoprotein YfiB. Exopolysaccharide synthesis was identified as the principal downstream target for YfiBNR, with increased production of Pel and Psl exopolysaccharides responsible for many characteristic SCV behaviors. An yfi-dependent SCV was isolated from the sputum of a CF patient. Consequently, the effect of the SCV morphology on persistence of infection was analyzed in vitro and in vivo using the YfiN-mediated SCV as a representative strain. The SCV strain exhibited strong, exopolysaccharide-dependent resistance to nematode scavenging and macrophage phagocytosis. Furthermore, the SCV strain effectively persisted over many weeks in mouse infection models, despite exhibiting a marked fitness disadvantage in vitro. Exposure to sub-inhibitory concentrations of antibiotics significantly decreased both the number of suppressors arising, and the relative fitness disadvantage of the SCV mutant in vitro, suggesting that the SCV persistence phenotype may play a more important role during antimicrobial chemotherapy. This study establishes YfiBNR as an important player in P. aeruginosa persistence, and implicates a central role for c-di-GMP, and by extension the SCV phenotype in chronic infections.

During long-term chronic infections of cystic fibrosis patients, Pseudomonas aeruginosa adapts to the lung environment, generating various different morphotypes including small colony variants (SCVs), small, strongly adherent colonies whose appearance correlates with persistence of infection. The SCV morphology is strongly associated with increased levels of the signaling molecule cyclic di-GMP. In this study we investigated the connection between cyclic di-GMP, SCV and persistence of infection. Following a genetic screen for mutants that displayed SCV morphologies, we identified and characterized the YfiBNR system. YfiN is a membrane-bound cyclic di-GMP producing enzyme, whose activity is tightly controlled by YfiR and YfiB. Cyclic di-GMP produced by YfiN boosts exopolysaccharide synthesis, generating an SCV morphotype upon YfiR-mediated release of YfiN repression. The resulting YfiN-mediated SCV morphotype is highly resistant to macrophage phagocytosis in vitro, suggesting a role for the SCV phenotype in immune system evasion. Consistent with this, YfiN de-repression increased the persistence of P. aeruginosa in long-term infections in a mouse model. The observation that the addition of antibiotics decreased the number of suppressors, and the relative fitness disadvantage of the YfiN-mediated SCV morphotype in liquid culture, suggested that SCV-mediated persistence might be favored during antimicrobial chemotherapy.

Side chain SAR of bicyclic beta-lactamase inhibitors (BLIs). 1. Discovery of a class C BLI for combination with imipinem

Bridged monobactam beta-lactamase inhibitors were prepared and evaluated as potential partners for combination with imipenem to overcome class C beta-lactamase mediated resistance. The (S)-azepine analog 2 was found to be effective in both in vitro and in vivo assays and was selected for preclinical development.

Matrix metalloproteases in bronchoalveolar lavage fluid of patients with type III Pseudomonas aeruginosa pneumonia

OBJECTIVES

In patients with ventilator-associated pneumonia (VAP), Pseudomonas aeruginosa type III (TTSS) secreting isolates have been linked to poor clinical outcomes. Differential expression of matrix metalloproteinases (MMPs) induced by type III effector proteins may herald an irreversible lung injury.

METHODS

Serial bronchoalveolar lavage fluids collected from 41 patients with P. aeruginosa at onset of VAP, day 4, and day 8 after antibiotic therapy were assayed for MMP-8, MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and alpha-2 macroglobulin levels.

RESULTS

At the onset of VAP, isolates secreting ExoU had the highest MMP-9 levels. The response to antimicrobial therapy showed a differential drop in MMPs with significant decrease in MMP-8 and MMP-9 levels on days 4 and 8 in patients with TTSS(-) compared to TTSS(+) phenotype. The ratio of MMP-9/TIMP-1 was significantly associated with alpha-2 macroglobulin at end of therapy (r=0.4, p=0.02). Patients who survived had a lower MMP-9/TIMP-1 ratio than those who died (p=0.003).

CONCLUSIONS

VAP linked to P. aeruginosa Type III phenotype portrays a divergent antibiotic treatment response in regards to the concentrations of metalloproteinases in the alveolar space. The imbalance between MMP-9 and TIMP-1 may determine the intensity of alveolocapillary damage and ultimate outcome of P. aeruginosa VAP.

Serine protease inhibitor 6-deficient mice have increased neutrophil immunity to Pseudomonas aeruginosa

Inflammation is a localized, protective response to trauma or microbial invasion that destroys the injurious agent and the injured tissue. Neutrophil elastase (NE), a serine protease stored in the azurophil granules of polymorphonuclear neutrophils, digests microbes after phagocytosis. NE can also digest microbes extracellularly but is associated with tissue damage and inflammatory disease. In this study, we show that polymorphonuclear neutrophils from mice deficient in serine protease inhibitor 6, a weak intracellular NE inhibitor, had increased susceptibility to self-inflicted lysis because of increased NE activity. The resulting transient increase in local extracellular NE activity was within a narrow range that resulted in the clearance of Pseudomonas aeruginosa but did not damage the lung. Therefore, deficiency in a weak intracellular inhibitor of NE results in an acute inflammatory response that protects from P. aeruginosa but does not cause lung disease.

[Spreading and mechanisms of antimicrobial resistance of microorganisms, producing beta-lactamases. Phenotypical screening for MBL producers (carbapenemases B1) among strains of Pseudomonas genus, isolated in cases of nosocomial infections]

Intrahospital strains (215) of the bacterial genus Pseudomonas isolated from patients of 30 Medical centers of 15 Russian regions have been investigated for antibiotic resistance. The bacterial cultures resistant to imipenem and/or meropenem were considered as metallo-beta-lactamase (MBL) producers. Production of subclass B1 MBL (carbapenemases) was evaluated by means of the double-disk approximation test using MBL inhibitor, EDTA. There were 55 P. aeroginosa strains (25.6%) resistant to imipenem and meropenem simultaneously; 19 isolates (8.8%) of P. aeroginosa were characterized by synergism between carbapenem and EDTA. The subclass B1 MBL producers are widely distributed in the intrahospital strain obtained from Moscow, Yaroslavl, Ekaterinburg, Omsk, and Tomsk hospitals.

Induction and function of lipocalin prostaglandin D synthase in host immunity

Although mainly expressed in neuronal cells, lipocalin-type PGD synthase (L-PGDS) is detected in the macrophages infiltrated to atherosclerotic plaques. However, the regulation and significance of L-PGDS expression in macrophages are unknown. Here, we found that treatment of macrophages with bacterial endotoxin (LPS) or Pseudomonas induced L-PGDS expression. Epigenetic suppression of L-PGDS expression in macrophages blunted a majority of PGD(2) produced after LPS treatment. Chromatin immunoprecipitation assays show that L-PGDS induction was regulated positively by AP-1, but negatively by p53. L-PGDS expression was detected in whole lung and alveolar macrophages treated with LPS or Pseudomonas. L-PGDS overexpressing transgenic mice improved clearance of Pseudomonas from the lung compared with nontransgenic mice. Similarly, intratracheal instillation of PGD(2) enhanced removal of Pseudomonas from the lung in mice. In contrast, L-PGDS knockout mice were impaired in their ability to remove Pseudomonas from the lung. Together, our results identify induction of L-PGDS expression by inflammatory stimuli or bacterial infection, the regulatory mechanism of L-PGDS induction, and the protective role of L-PGDS expression in host immune response. Our study suggests a potential therapeutic usage of L-PGDS or PGD(2) against Pseudomonas pneumonia.

Corneal virulence of Pseudomonas aeruginosa elastase B and alkaline protease produced by Pseudomonas putida

PURPOSE

To measure the specific virulence contributions of two Pseudomonas aeruginosa proteases, elastase B and alkaline protease, when expressed separately by Pseudomonas putida in a rabbit model of bacterial keratitis.

METHODS

P. putida KT2440 was transformed with plasmids that enabled the extracellular production of either elastase or alkaline protease. Protease expression was confirmed by zymography and immunoblotting. P. putida expressing elastase, alkaline protease, or vector alone was injected intrastromally (10(3) colony forming units [CFU]) into rabbit corneas (n=6). Infected eyes were graded by slit-lamp examination (SLE) at 20, 24, 28, and 32 hr postinfection (PI). Rabbits were sacrificed at 33 hr PI, and the log CFU (+/-SEM) per cornea was determined.

RESULTS

SLE scores for eyes infected with P. putida producing elastase were significantly higher than those infected with vector alone at all time points (p<or=0.008). SLE scores for eyes infected with P. putida producing alkaline protease were not significantly higher than the control (p>or=0.1), but small erosions formed in 33% of corneas. At both 24 and 28 hr PI, the SLE scores for corneas infected with P. putida producing elastase were significantly higher than those infected with P. putida producing alkaline protease (p<or=0.002).

CONCLUSIONS

Elastase production by P. putida caused significant increases in SLE scores whereas expression of alkaline protease caused limited corneal erosions. This suggests that the production of elastase during P. aeruginosa keratitis enhances ocular pathology, whereas alkaline protease production contributes to limited corneal erosion.

Bacterial clearance ofPseudomonas aeruginosa is enhanced by the inhibition of COX-2

Prostanoids generated by COX-2 are involved in the regulation of inflammation but their exact role in the innate immune response has not been defined. We investigated whether COX-2 is involved in host defense against Pseudomonas aeruginosa pneumonia. In vitro studies, in a macrophage cell line, showed that cytotoxic strain of P aeruginosa (PA103) induced significant COX-2 protein expression and enzymatic function. In vivo data showed that infection with PA103 increased COX-2 protein production in whole lung tissue compared to mice that were infected with mutant bacteria that lack ExoU (DeltaU) or ExoU and ExoT (DeltaUT). COX-2(-/-) mice had accentuated clearance of cytotoxic P. aeruginosa from the lungs. We further tested the effects of COX-2 products such as prostaglandin E(2) on the function of phagocytic cells. Our studies indicate that prostaglandin E(2) may be involved through interacting with the EP2 receptors in modulating the host response because treatment of macrophages with prostaglandin E(2) suppressed production of reactive oxygen species. Furthermore there was enhanced bacterial clearance in EP2 receptor(-/-) mice compared to the wild-type controls. Thus it is possible that inhibition of COX-2 or EP2 receptors could be an effective adjunctive treatment for severe or resistant P. aeruginosa pneumonia.

Emergence and dissemination of multidrug resistant clones of Pseudomonas aeruginosa producing VIM-2 metallo-beta-lactamase in Belgium

Emergence of carbapenem-hydrolysing metallo-beta-lactamase (MBL) in Pseudomonas aeruginosa has been described worldwide. Infection with MBL-producing strains represents a therapeutic problem due to their resistance to all beta-lactams except monobactams. Several types of MBL enzymes have been identified in P. aeruginosa among which the VIM-type enzymes appear as the most prevalent in Europe with more than 12 allelic variants.

Induction of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs correlates with outcome of acute experimental pseudomonal keratitis

This study aimed to investigate expressions and sources of matrix metalloproteinases (MMP)-2 and MMP-9, and of tissue inhibitors of MMP (TIMP)-1 and TIMP-2 in experimental Pseudomonas aeruginosa keratitis in rabbits. Pseudomonal keratitis was induced in New Zealand white rabbits, and macroscopic and microscopic examinations were performed at appropriate time points (3, 9, 12, 18, 24, 72 h). Expressions and sources of MMP-2, 9, and TIMP-1, 2 were determined using immunohistochemistry, gelatin zymography, ELISA, and RT-PCR. A typical corneal ulcer with a ring abscess was observed 12-72 h post-infection (p.i.) with P. aeruginosa. In microscopic examinations, massive inflammatory cell (mostly polymorphonuclear leukocytes, PMNs) infiltration and liquefactive necrosis were characteristic features. MMP-2 was constitutively expressed in keratocytes, and its expression was not apparently enhanced after pseudomonal infection as evidenced by zymography, immunostaining, and RT-PCR. However, MMP-9 and its activated form were induced, and were significantly enhanced 12-24 h p.i. MMP-9 appeared to derive from PMNs rather than from resident corneal cells. TIMP-1 was expressed in PMNs, macrophages, and keratocytes, and its expression was enhanced 72 h p.i. Although TIMP-2 was constitutively expressed as seen by immunostaining and RT-PCR, its concentration was below detection limits during the experiments. We demonstrated that MMP-9 was one of the important factors for corneal tissue destruction, because it was induced and significantly expressed in keratocytes and inflammatory cells after pseudomonal infection. Although TIMP-1 was expressed in later stages of infection, enhancement and activation of MMP-9 were much faster and stronger than those of TIMP-1, thereby facilitating tissue destruction leading to corneal ulceration.

IL-23 mediates inflammatory responses to mucoid Pseudomonas aeruginosa lung infection in mice

Patients with cystic fibrosis (CF) develop chronic Pseudomonas aeruginosa lung infection with mucoid strains of P. aeruginosa; these infections cause significant morbidity. The immunological response in these infections is characterized by an influx of neutrophils to the lung and subsequent lung damage over time; however, the underlying mediators to this response are not well understood. We recently reported that IL-23 and IL-17 were elevated in the sputum of patients with CF who were actively infected with P. aeruginosa; however, the importance of IL-23 and IL-17 in mediating this inflammation was unclear. To understand the role that IL-23 plays in initiating airway inflammation in response to P. aeruginosa, IL-23p19(-/-) (IL-23 deficient) and wild-type (WT) mice were challenged with agarose beads containing a clinical, mucoid isolate of P. aeruginosa. Levels of proinflammatory cytokines, chemokines, bacterial dissemination, and inflammatory infiltrates were measured. IL-23-deficient mice had significantly lower induction of IL-17, keratinocyte-derived chemokine (KC), and IL-6, decreased bronchoalveolar lavage (BAL) neutrophils, metalloproteinase-9 (MMP-9), and reduced airway inflammation than WT mice. Despite the reduced level of inflammation in IL-23p19(-/-) mice, there were no differences in the induction of TNF and interferon-gamma or in bacterial dissemination between the two groups. This study demonstrates that IL-23 plays a critical role in generating airway inflammation observed in mucoid P. aeruginosa infection and suggests that IL-23 could be a potential target for immunotherapy to treat airway inflammation in CF.

Identification of superoxide dismutase as a cofactor for the pseudomonas type III toxin, ExoU

Pseudomonas aeruginosa is an opportunistic pathogen that uses a type III secretion system and four effector proteins to avoid innate immune responses. ExoS, ExoT, ExoY, and ExoU all possess enzymatic activities that disrupt host cellular physiology and prevent bacterial clearance by host defense mechanisms. The specificity of these toxins for eukaryotic cells depends on the presence of substrate targets and eukaryotic cofactors responsible for effector activation. We used a combined biochemical and proteomic approach to identify Cu(2+), Zn(2+)-superoxide dismutase (SOD1) as a cofactor that activates the phospholipase activity of ExoU. Recombinant ExoU (rExoU) was activated in a dose-dependent manner by either bovine liver SOD1 or the yeast ortholog, Sod1p, but not by either Fe or Mn-containing SODs from E. coli or small molecule SOD mimetics. Inhibitor studies indicated that SOD enzymatic activity was not required for the activation of rExoU. The physical interaction between rExoU and SOD was demonstrated by capture techniques using either of the two proteins immobilized onto the solid phase. Identification of SOD as a cofactor allowed us to develop a new assay using a fluorescent substrate to measure the phospholipase activity of rExoU. The ability of SOD to act as a cytoplasmic cofactor stimulating ExoU phospholipase activity has significant implications for the biological activity of the toxin. Further elucidation of the structural mechanism of ExoU activation by this eukaryotic cofactor may provide a rational approach to the design of inhibitors that can diminish tissue damage during infection by ExoU-producing strains of P. aeruginosa.

Src kinase Lyn is crucial for Pseudomonas aeruginosa internalization into lung cells

Lyn is an important B cell signaling kinase of the Src tyrosine kinase family with a broad range of functions from cytoskeletal changes to induction of apoptosis. However, the role of Lyn in infectious diseases is not clear. Here, we demonstrate that Lyn activation by phosphorylation significantly impacted invasion of an alveolar epithelial cell line, primary lung cells, and rat lungs by Pseudomonas aeruginosa (PA), a common opportunistic lung pathogen affecting individuals with deficient lung immunity. Our results indicate that activation of Lyn and its interaction with rafts and TLR2, played an important role in the initial stages of PA interaction with host cells. The role of Lyn was further evaluated using the pharmacologic Src-specific inhibitor PP2, a dominant negative mutant, and finally confirmed with Lyn-deficient (Lyn(-/-)) bone marrow-derived mast cells. Inhibition of Lyn's function by above approaches prevented PA internalization. Moreover, blocking of Lyn also affected downstream events: induction of inflammatory cytokines and apoptosis. This report brings out a new role of Lyn in infectious diseases and indicates potential new targets for prevention and treatment of infections.

The peptidoglycan-degrading property of lysozyme is not required for bactericidal activity in vivo

Lysozyme is an abundant, cationic antimicrobial protein that plays an important role in pulmonary host defense. Increased concentration of lysozyme in the airspaces of transgenic mice enhanced bacterial killing whereas lysozyme deficiency resulted in increased bacterial burden and morbidity. Lysozyme degrades peptidoglycan in the bacterial cell wall leading to rapid killing of Gram-positive organisms; however, this mechanism cannot account for the protective effect of lysozyme against Gram-negative bacteria. The current study was therefore designed to test the hypothesis that the catalytic activity (muramidase activity) of lysozyme is not required for bacterial killing in vivo. Substitution of serine for aspartic acid at position 53 (D53S) in mouse lysozyme M completely ablated muramidase activity. Muramidase-deficient recombinant lysozyme (LysM(D53S)) killed both Gram-positive and Gram-negative bacteria in vitro. Targeted expression of LysM(D53S) in the respiratory epithelium of wild-type (LysM(+/+)/LysM(D53S)) or lysozyme M(null) mice (LysM(-/-)/LysM(D53S)) resulted in significantly elevated lysozyme protein in the airspaces without any increase in muramidase activity. Intratracheal challenge of transgenic mice with Gram-positive or Gram-negative bacteria resulted in a significant increase in bacterial burden in LysM(-/-) mice that was completely reversed by targeted expression of LysM(D53S). These results indicate that the muramidase activity of lysozyme is not required for bacterial killing in vitro or in vivo.

Adenoviral gene transfer of a mutant surfactant enzyme ameliorates pseudomonas-induced lung injury

Surfactant deficiency is an important contributor to the acute respiratory distress syndrome, a disorder that commonly occurs after bacterial sepsis. CTP:phosphocholine cytidylyltransferase (CCTalpha) is the rate-limiting enzyme required for the biosynthesis of dipalmitoylphosphatidylcholine (DPPC), the major phospholipid of surfactant. In this study, a cDNA encoding a novel, calpain-resistant mutant CCTalpha enzyme was delivered intratracheally in mice using a replication-deficient adenovirus 5 CTP:phosphocholine cytidylyltransferase construct (Ad5-CCT(Penta)) in models of bacterial sepsis. Ad5-CCT(Penta) gene transfer produced high-level CCTalpha gene expression, increased alveolar surfactant (DPPC) levels and improved lung surface tension and pressure-volume relationships relative to control mice. Pseudomonas aeruginosa (PA103) decreased DPPC synthesis, in part, via calpain-mediated degradation of CCTalpha. Deleterious effects of Pseudomonas on surfactant were lessened after infection with a mutant strain lacking the type III exotoxin, Exo U. Replication-deficient adenovirus 5 CTP:phosphocholine cytidylyltransferase gene delivery improved lung biophysical properties by optimizing surface activity in this Pseudomonas model of proteinase-mediated lung injury. The studies are the first demonstration of in vivo gene transfer of a lipogenic enzyme resulting in improved lung mechanics. The studies suggest that augmentation of DPPC synthesis via gene delivery of CCTalpha can attenuate impaired lung function in surfactant-deficient states such as bacterial sepsis.

Matrix metalloproteinase-9 amplifies the immune response to Pseudomonas aeruginosa corneal infection

PURPOSE

The purpose of this study was to determine the role of matrix metalloproteinases (MMP) in Pseudomonas aeruginosa keratitis.

METHODS

Gene array and selective real-time PCR examined MMP expression in the cornea of susceptible (C57BL/6, B6) versus resistant (BALB/c) mice before and after infection; zymography tested enzyme activity for MMP-2 and -9. Clinical score, Langerhans cell (LC), and Neutrophil (PMN) quantitation were done in recombinant (r) MMP-9, antibody neutralized, and MMP-9(-/-) mice. The chemotactic potential of MMP-9 was tested in a Boyden chamber assay; light and transmission microscopy and immunostaining for collagen IV and MMP-9 were used to examine the effects and the source of MMP-9 after infection. ELISA was used to assess IL-1beta and MIP-2 levels.

RESULTS

Gene array (confirmed by PCR) revealed sixfold more MMP-9, and zymography showed greater enzyme activity in the infected cornea of B6 over BALB/c mice. rMMP-9 injection of BALB/c mice enhanced, whereas MMP-9 antibody neutralization in B6 mice and its absence in MMP-9(-/-) mice decreased corneal disease. MMP-9(-/-) and antibody neutralized mice had fewer LCs in cornea; rMMP-9-treated mice had more. A myeloperoxidase (MPO) assay showed a similar pattern for PMN. MMP-9 was not chemotactic for LC or PMN. The basement membrane was more intact in MMP-9(-/-) over wild-type infected mice and correlated with staining for collagen IV; PMN was a source of MMP-9. IL-1beta and MIP-2 were increased in rMMP-9 but decreased in MMP-9 antibody neutralized and MMP-9(-/-) over control groups.

CONCLUSIONS

MMP-9 regulates immune function in cornea by proteolysis, potentiating P. aeruginosa keratitis by degrading collagen IV and upregulating chemotactic cytokines/chemokines IL-1beta and MIP-2.

Characterization of poxB, a chromosomal-encoded Pseudomonas aeruginosa oxacillinase

Pseudomonas aeruginosa is the major pathogen associated with morbidity and mortality of patients with cystic fibrosis. One of the reasons for the failure of beta-lactam antibiotic regimens appears to be mediated by de-regulation of the ampC gene, encoding the chromosomal Ambler's Class C beta-lactamase. Currently, the AmpC is the only known chromosomal beta-lactamase whose expression is regulated by a transcriptional regulator, AmpR. We generated an ampC mutation in the prototypic P. aeruginosa strain PAO1. The mutation in ampC did not abolish the beta-lactamase activity entirely suggesting the expression of yet another unreported beta-lactamase. Our genomic analysis revealed the presence of an open reading frame encoding a protein with high homology to the Class D beta-lactamases, commonly known as oxacillinases. The gene was named poxB for Pseudomonas oxacillinase. Cloning and expression of poxB in Escherichia coli conferred beta-lactam resistance to the host. We detected the presence of poxB both in clinical and environmental isolates. Our studies show that P. aeruginosa possesses two beta-lactamases, AmpC and PoxB, which contribute to its resistance against a wide spectrum of beta-lactam antibiotics.

Human and murine paraoxonase 1 are host modulators of Pseudomonas aeruginosa quorum-sensing

The pathogenic bacterium Pseudomonas aeruginosa uses acyl-HSL quorum-sensing signals to regulate genes controlling virulence and biofilm formation. We found that paraoxonase 1 (PON1), a mammalian lactonase with an unknown natural substrate, hydrolyzed the P. aeruginosa acyl-HSL 3OC12-HSL. In in vitro assays, mouse serum-PON1 was required and sufficient to degrade 3OC12-HSL. Furthermore, PON2 and PON3 also degraded 3OC12-HSL effectively. Serum-PON1 prevented P. aeruginosa quorum-sensing and biofilm formation in vitro by inactivating the quorum-sensing signal. Although 3OC12-HSL production by P. aeruginosa was important for virulence in a mouse sepsis model, Pon1-knock-out mice were paradoxically protected. These mice showed increased levels of PON2 and PON3 mRNA in epithelial tissues suggesting a possible compensatory mechanism. Thus, paraoxonase interruption of bacterial communication represents a novel mechanism to modulate quorum-sensing by bacteria. The consequences for host immunity are yet to be determined.

Detection of metallo betalactamase producing Pseudomonas aeruginosa in hospitalized patients

BACKGROUND & OBJECTIVE

Metallo beta-lactamase (MBL)-mediated resistance to carbapenems is an emerging threat in hospital isolates of Pseudomonas aeruginosa. Though there are several screening methods to detect this enzyme production, the National Committee for Clinical Laboratory Standards (NCCLS) does not have performance standards documented so far. There is not enough information from the Indian subcontinent regarding the prevalence and the screening methods for these enzymes. The present study was undertaken to detect MBL in nosocomial isolates of P. aeruginosa by two screening methods.

METHODS

Fifty consecutive P. aeruginosa isolates obtained from hospitalized patients were subjected to susceptibility testing to antipseudomonal drugs by disc diffusion, and minimum inhibitory concentration (MIC) of imipenem was determined. The production of MBL was detected by 4-fold reduction in MIC with imipenem-ethylene diamine tetraacetic acid (EDTA) and the zone size enhancement with EDTA impregnated imipenem and ceftazidime discs.

RESULTS

Sixteen per cent of the isolates tested were resistant to imipenem by disc diffusion method of which 87.5 per cent exhibited a zone size enhancement with EDTA impregnated imipenem and ceftazidime discs as well as a 4-fold reduction in MIC with imipenem EDTA. The imipenem susceptible isolates (84%) had normal MIC values and exhibited no zone diameter enhancement with EDTA impregnated antibiotic discs.

INTERPRETATION & CONCLUSION

MBL-mediated imipenem resistance in P. aeruginosa is a cause for concern in the therapy of critically ill patients. The two confirmatory methods i.e., zone diameter enhancement with EDTA impregnated imipenem and ceftazidime discs and 4-fold reduction in MIC with imipenem EDTA combination are equally effective for their detection.

Regulation of Pseudomonas aeruginosa corneal infection in IL-1 beta converting enzyme (ICE, caspase-1) deficient mice

PURPOSE

Antibody neutralization studies have shown that in Pseudomonas aeruginosa corneal infection, IL-1 beta is critical to regulation of the host inflammatory response, but mechanisms remain undetermined. To elucidate these mechanisms, caspase-1 knockout (ICE(-/-)) mice, that do not release mature IL-1 beta after endotoxin challenge, were tested.

METHODS

Clinical scores, MPO activity (for PMN quantitation), bacterial plate count, semiquantitative RT-PCR, ELISA and TUNEL staining were used to characterize the inflammatory response after infection in knockout and C57BL/6 (B6) wild type mice.

RESULTS

Clinical scores were significantly reduced in ICE(-/-) vs. B6 mice at 3, 5 and 7 days postinfection (p.i.). The decreased inflammatory response of ICE(-/-) mice was striking at 1 day p.i., and bacterial load also was significantly reduced in the cornea of the knockout mice at 3-7 days p.i. Knockout mice exhibited significantly increased mRNA and protein levels for IL-1Ra, the physiological regulator of IL-1 activity, and in addition, a significant increase in the number of apoptotic cells were quantitated in the corneal epithelium of ICE(-/-) vs. B6 mice at 1 day p.i.

CONCLUSIONS

These data provide evidence that bacterial infection in the cornea of ICE(-/-) mice induces a reduced inflammatory response by: reduction in PMN and cytokines and chemokines that attract these cells to the cornea; enhanced apoptotic cell death in the infected epithelium; and increased IL-1Ra levels. The data also confirm the importance of IL-1 regulation in this model and suggest that ICE inhibition may be an attractive ancillary therapeutic strategy to control the host response to this pathogen.

Pseudomonas aeruginosa causes acute lung injury via the catalytic activity of the patatin-like phospholipase domain of ExoU

OBJECTIVE

Acute lung injury in Pseudomonas aeruginosa pneumonia depends primarily on ExoU toxin being delivered directly into the eukaryotic cell cytosol through the type III secretion system. The amino-acid sequence of ExoU has a potato patatin-like phospholipase domain, similar to the sequence of mammalian Ca-independent phospholipase A2. We examined whether the acute lung injury caused by cytotoxic P. aeruginosa was dependent on the patatin-like phospholipase domain of ExoU.

DESIGN

Laboratory investigation using an established mouse model for P. aeruginosa pneumonia with quantitative measurements of acute lung injury and mortality.

SETTING

University experimental research laboratory.

SUBJECTS

Balb/c mice.

INTERVENTIONS

First, a site-directional mutation was introduced in the predicted catalytically active site of the patatin-like phospholipase domain of recombinant ExoU protein. The effect of the mutation on the catalytic activity of ExoU was tested by the in vitro lysophospholipase A assay. Second, the same site-directional mutation was introduced into the exoU gene of P. aeruginosa PA103. Mice were intratracheally infected with either a wild-type P. aeruginosa strain PA103 or an isogenic mutant containing the mutation in exoU. Acute epithelial lung injury, lung edema, bacteremia, and mortality were evaluated quantitatively.

MEASUREMENTS AND MAIN RESULTS

Recombinant ExoU had lysophospholipase A activity. Site-directional mutations in the predicted catalytic site of ExoU caused a loss of the lysophospholipase A activity. Whereas the airspace instillation of PA103 caused acute lung injury and death of the infected mice, the airspace instillation of isogenic mutants secreting catalytically inactive ExoU were noncytotoxic and did not cause acute lung injury or death of the infected mice.

CONCLUSION

Virulent P. aeruginosa causes acute lung injury and death by the cytotoxic activity derived from the patatin-like phospholipase domain of ExoU.

Aerosol treatment with MNEI suppresses bacterial proliferation in a model of chronic Pseudomonas aeruginosa lung infection

Neutrophil elastase is present at high levels in airway fluid of patients with cystic fibrosis (CF), and is responsible for considerable inflammatory damage. Human monocyte/neutrophil elastase inhibitor (MNEI), a 42-kDa serpin protein, is an effective inhibitor of neutrophil elastase, cathepsin G, and proteinase-3, related proteases released from inflammatory neutrophils. We hypothesized that recombinant MNEI would reduce inflammatory damage and enhance bacterial clearance from the lung in an animal model of chronic Pseudomonas aeruginosa infection. In vitro studies showed that MNEI causes dose-dependent inhibition of the activity of rat neutrophil elastase. Recombinant MNEI was administered daily by aerosolization to rats previously inoculated with agar beads containing P. aeruginosa to initiate chronic infection. Administered MNEI was partially recovered in lavage fluid of treated rats as a 66-kDa complex with protease indicative of in vivo inhibition of elastase or a related protease. Aerosol treatment with MNEI significantly decreased the extent of inflammatory injury, quantified as the histopathology score. MNEI, which had no bactericidal effect on P. aeruginosa in vitro, significantly enhanced clearance of bacteria from infected rat lungs. The reduction of histopathology scores and enhancement of bacterial killing were evident 6 hr after a single aerosol treatment with MNEI. These findings indicate an important function of MNEI in protecting innate antimicrobial defense. Similar results were previously obtained for aerosolized prolastin (alpha1-antitrypsin), indicating that enhanced bacterial clearance by MNEI is due to inhibition of neutrophil protease. These findings demonstrate the value of this nonantibiotic protease inhibitor as an adjunct for the treatment and prevention of the infection component of CF lung disease.

Structure/function studies on a S-adenosyl-L-methionine-dependent uroporphyrinogen III C methyltransferase (SUMT), a key regulatory enzyme of tetrapyrrole biosynthesis

The crystallographic structure of the Pseudomonas denitrificans S-adenosyl-L-methionine-dependent uroporphyrinogen III methyltransferase (SUMT), which is encoded by the cobA gene, has been solved by molecular replacement to 2.7A resolution. SUMT is a branchpoint enzyme that plays a key role in the biosynthesis of modified tetrapyrroles by controlling flux to compounds such as vitamin B(12) and sirohaem, and catalysing the transformation of uroporphyrinogen III into precorrin-2. The overall topology of the enzyme is similar to that of the SUMT module of sirohaem synthase (CysG) and the cobalt-precorrin-4 methyltransferase CbiF and, as with the latter structures, SUMT has the product S-adenosyl-L-homocysteine bound in the crystal. The roles of a number of residues within the SUMT structure are discussed with respect to their conservation either across the broader family of cobalamin biosynthetic methyltransferases or within the sub-group of SUMT members. The D47N, L49A, F106A, T130A, Y183A and M184A variants of SUMT were generated by mutagenesis of the cobA gene, and tested for SAM binding and enzymatic activity. Of these variants, only D47N and L49A bound the co-substrate S-adenosyl-L-methionine. Consequently, all the mutants were severely restricted in their capacity to synthesise precorrin-2, although both the D47N and L49A variants produced significant quantities of precorrin-1, the monomethylated derivative of uroporphyrinogen III. The activity of these variants is interpreted with respect to the structure of the enzyme.

Up-regulation and localization of asparagine synthetase in tomato leaves infected by the bacterial pathogen Pseudomonas syringae

Nitrogen metabolism is one aspect of basic metabolism, which is still quite unknown in the field of plant-pathogen interactions. Evidence derived from previous studies conducted in our laboratory strongly suggests that during microbial pathogenesis an important nitrogen mobilization process takes place in diseased tissues. Here we describe the expression pattern of asparagine synthetase (AS; EC 6.3.5.4) in tomato leaves infected by the bacterial pathogen Pseudomonas syringae pv. tomato. Using an homologous AS cDNA probe isolated by RT-PCR from infected leaves, we have observed a high level induction of AS expression during the course of infection. Concomitantly, a single AS polypeptide also accumulated in response to bacterial infection. Furthermore, immunohistochemical analysis of AS in infected leaves revealed a strong immunostaining in phloem cells of the main vascular bundles and in secondary veins of the leaf blade. These data correlate with those previously reported for expression of a cytosolic isoform of glutamine synthetase (GS1) also induced during development of the infectious process. Taken together, our results suggest the existence of a GS1/AS pathway representing a metabolic route for transferring ammonium released from protein catabolism into asparagine, an amino acid that may have a major role in nitrogen mobilization from diseased tissues.

Murine ocular heparanase expression before and during infection with Pseudomonas aeruginosa

PURPOSE

To demonstrate the constitutive expression and regulation of heparanase (heparan sulfate endoglycosidase) in the normal mouse eye and in mice intracorneally infected with Pseudomonas aeruginosa.

METHODS

Naïve (unimmunized) and immunized C57BL/6J mice were infected with P. aeruginosa, and corneal heparanase gene and protein expression were detected by semiquantitative RT-PCR and immunoblot analysis. Immunohistochemistry was also applied to characterize corneal heparanase in naïve mice.

RESULTS

Heparanase mRNA and protein expression were detected in uninfected corneas of C57BL/6J mice. Immunohistochemical studies indicated heparanase protein expression was primarily in the corneal epithelium before corneal infection and was also in the corneal stroma after infection. Immunohistochemical studies of uninfected and infected whole eyes of naïve mice indicated heparanase protein expression in most layers of the retina, but the expression did not appear to be upregulated during corneal infection. Staining was most intense in the inner photoreceptor layer of the retina.

CONCLUSIONS

Heparanase was constitutively expressed in both the corneal epithelium and several retinal layers before intracorneal infection with P. aeruginosa. Temporal upregulation of corneal heparanase protein expression was detected in naïve mice during infection, most likely due to heparanase positive infiltrating cells, but the protein was not upregulated in corneas from immunized mice because they had a lower inflammatory response, associated with the restoration of corneal clarity. There did not appear to be temporal upregulation of heparanase expression in the retina of infected mice, as determined by immunohistochemistry.

Neutrophil serine proteinases cleave bacterial flagellin, abrogating its host response-inducing activity

After bacterial infection, neutrophils dominate the cellular infiltrate. Their main function is assumed to be killing invading pathogens and resolving the inflammation they cause. Activated neutrophils are also known to release a variety of molecules, including the neutrophil serine proteinases, extracellularly. The release of these proteinases during inflammation creates a proteolytic environment where degradation of different molecules modulates the inflammatory response. Flagellin, the structural component of flagella on many bacterial species, is a virulence factor with a strong proinflammatory activity on epithelial cells and other cell types. In this study we show that both human and mouse neutrophil serine proteinases cleave flagellin from Pseudomonas aeruginosa and other bacterial species. More important, cleavage of P. aeruginosa flagellin by the neutrophil serine proteinases neutrophil elastase and cathepsin G resulted in loss of the biological activity of this virulence factor, as evidenced by the lack of innate host defense gene expression in human epithelial cells. The finding that flagellin is susceptible to cleavage by neutrophil serine proteinases suggests a novel role for these enzymes in the inflammatory response to infection. Not only can these enzymes kill bacteria, but they also degrade their virulence factors to halt the inflammatory response they trigger.

Pulmonary cytochrome P-450 2J4 is reduced in a rat model of acute Pseudomonas pneumonia

We previously reported that the levels of epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE) are depressed in microsomes prepared from lungs of rats with acute Pseudomonas pneumonia. We also showed a potential role for cytochrome P-450 (CYP) metabolites of arachidonic acid (AA) in contractile responses of both normal pulmonary arteries and pulmonary arteries from rats with pneumonia. The CYP2J subfamily enzymes (endogenous source of EETs and HETEs) are constitutively expressed in human and rat lungs where they are localized in vascular smooth muscle and endothelium. The purpose of this study was to determine if CYP2J proteins are modified in pneumonia. Pseudomonas organisms were injected via a tracheostomy in the lungs of rats. Later (44 h), lungs were frozen, and microsomes were prepared from pneumonia and control rat lung homogenates. Lung microsomal proteins were then immunoblotted with anti-CYP2B1/2B2, anti-CYP4A, anti-CYP2J9pep2 (which reacts with rat CYP2J3), anti-CYP2J6pep1 (which reacts with rat CYP2J4), anti-CYP2J2pep4, or anti-CYP2J2pep3 (both of which react with all known CYP2J isozymes). Western blotting revealed a prominent 55-kDa band with anti-CYP2J2pep3, anti-CYP2J2pep4, and anti-CYP2J6pep1 (but not anti-CYP2J9pep2) that was reduced in pneumonia compared with control lung microsomes. The CYP2B bands (51-52 kDa) were less prominent and not different between pneumonia and control lungs. CYP4A proteins (20-HETE sources) were not detected in rat lung microsomes. Therefore, rat lung contains a protein with immunological characteristics similar to CYP2J4, and this CYP is reduced after pneumonia. We speculate that CYP2J (but not CYP2B) enzymes and their AA metabolic products (EETs) are involved in the modulation of pulmonary vascular tone in pneumonia in rats.

Role of elastase in a mouse model of chronic respiratory Pseudomonas aeruginosa infection that mimics diffuse panbronchiolitis

Pseudomonas aeruginosa frequently colonizes the respiratory tract of patients suffering from cystic fibrosis (CF) and diffuse panbronchiolitis (DPB). However, the relationship between lung inflammation and extracellular products of P. aeruginosa is not well-defined. To assess the role of elastase released by P. aeruginosa in DPB, a murine model of DPB was employed in this study. Mice were inoculated with either P. aeruginosa PAO1 or PAO-E64; the latter produces elastase with greatly reduced enzymic activity. Throughout the 90-day experiments, counts of viable bacteria from the PAO1- and PAO-E64-infected mice were found to be equivalent. However, the number of lymphocytes isolated from the lungs of PAO-E64-infected mice was significantly lower than the number isolated from the lungs of PAO1-infected animals. Histopathological examination of the lungs of mice infected by PAO1 on day 90 revealed an intense accumulation of chronic respiratory cells surrounding the bronchi, in sharp contrast to the more localized inflammatory response found in those mice infected by PAO-E64. These data suggest that P. aeruginosa elastase (PE) is a potent inflammatory factor in a mouse model of DPB and that the control of PE release by P. aeruginosa may be beneficial for patients with DPB.

Regulation of MMPs and TIMPs by IL-1beta during corneal ulceration and infection

PURPOSE

This study was conducted to investigate the role of IL-1beta in the regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in a mouse model of experimental keratitis and corneal injury.

METHODS

Mice were injected subconjunctivally with 10 micro g of anti-mouse IL-1beta antibody 2 hours before challenge with Pseudomonas aeruginosa (strain 6294). Control animals received an equal volume and concentration of isotype control antibody at the same time. Eyes were enucleated at 0, 8, 24, and 72 hours, after bacterial challenge and processed for histologic examination. Some eyes were homogenized and used to evaluate production of MMP-2, MMP-9, TIMP-1, and TIMP-2 protein, by zymography and reverse zymography.

RESULTS

Injury without bacterial infection resulted in increases in both MMP-2 and -9 and a slight but significant downregulation of TIMP-1. Administration of anti-IL-1beta just before injury and without bacterial infection resulted in a significant reduction in expression of MMP-2 (at 8 hours), MMP-9 (at 8 hours), TIMP-1 (at 8 and 72 hours), and TIMP-2 (at 8 hours). Mice treated with anti-IL-1beta antibody, before bacterial challenge, demonstrated markedly reduced corneal damage compared with the severe corneal injury and massive neutrophil infiltration observed in infected mice treated with control antibody. Administration of the neutralizing anti-IL-1beta antibody resulted in a significant reduction of MMP-9 and a change in the time course of TIMP-1 and -2 expression. The reduction in MMP-9 by anti-IL-1beta during infection was much greater than the reduction without infection.

CONCLUSIONS

The results imply that IL-1beta has a central role in corneal destruction during bacterial keratitis and suggests that targeting IL-1beta may be a novel therapeutic strategy for microbial keratitis.

Effects of dietary arginine supplementation on antibody production and antioxidant enzyme activity in burned mice

This study investigated the effect of arginine (Arg) supplementation on specific antibody production and antioxidant enzyme activities in burned mice vaccinated with detoxified Pseudomonas exotoxin A linked with the outer membrane proteins I and F, named PEIF. Also, the survival rate of burned mice complicated with Pseudomonas aeruginosa was evaluated. Experiment 1: Thirty BALB/c mice were assigned to two groups. One group was fed a control diet with casein as the protein source, while the other group was supplemented with 2% Arg in addition to casein. The two groups were isonitrogenous. The mice were immunized twice with PEIF, and the production of specific antibodies against PEIF was measured every week. After 8 weeks, all mice received a 30% body surface area burn injury. Mice were sacrificed 24h after the burn. The antioxidant enzyme activities and lipid peroxides in the tissues as well as the specific antibody production were analyzed. Experiment 2: Twenty-eight mice were divided into two groups and vaccinated as described in experiment 1. After the burn the mice were infected with P. aeruginosa, and the survival rate was observed for 8 days. The results demonstrated that antioxidant enzyme activities and lipid peroxides in tissues were significantly lower in the Arg group than in the control group after the burn. The production of specific antibodies against P. aeruginosa significantly increased in the Arg group at 4 and 7 weeks after immunization, and 24h after the burn. The survival rates of vaccinated burned mice after bacterial infection did not significantly differ between the two groups. These results suggest that vaccinating mice with Arg supplementation may enhance humoral immunity and attenuate the oxidative stress induced by burn injury. However, Arg supplementation did not improve survival in vaccinated mice complicated with P. aeruginosa infection.

Type 2 nitric oxide synthase and protein nitration in chronic lung infection

Inflammation in the lung can lead to increased expression of inducible nitric oxide synthase (iNOS) and enhanced NO production. It has been postulated that the resultant highly reactive NO metabolites may have an important role in host defence, although they might also contribute to tissue damage. However, in a number of inflammatory lung diseases, including bronchiectasis, iNOS expression is increased but no elevation of airway NO can be detected. A potential explanation for this finding is that NO is rapidly scavenged by reaction with superoxide radicals, forming peroxynitrite, which is preferentially metabolized via nitration and nitrosation reactions. To test this hypothesis, anaesthetized, specific pathogen-free rats were inoculated with Pseudomonas aeruginosa incorporated into agar beads (chronically infected group) or sterile agar beads (control group). Ten to 15 days later, the lungs were isolated and fixed. Pseudomonas organisms were isolated from the lungs of the chronically infected group. These lungs showed extensive inflammatory cell infiltration and tissue damage, which were not observed in control lungs. Expression of iNOS was increased in the chronically infected group when compared with the control group. However, the mean number of cells staining for nitrotyrosine in the chronically infected group was not significantly different from that in the controls, nor was there an excess of nitrotyrosine, nitrate, nitrite or nitrosothiol concentrations in the infected lungs. Thus, no evidence was found of increased NO metabolites in chronically infected lungs, including products of the peroxynitrite pathway. These findings suggest that chronic infection does not cause increased iNOS activity in the lung, despite increased expression of iNOS.