[show abstract][hide abstract] ABSTRACT: Activated T lymphocytes are abundant in the airway during lung allograft rejection. Based on respiratory viral studies, it is the current paradigm that T cells cannot divide in the airway, and that their accumulation in the lumen of the respiratory tract is the exclusive result of recruitment from other sites, such as mediastinal lymph nodes. Here, we show that CD8(+) T cell activation and proliferation can occur in the airway after orthotopic lung transplantation. We also demonstrate that airway epithelium expresses major histocompatibility class I predominantly on the apical surface, both in vitro and in vivo, and initiates CD8(+) T cell responses in a polarized fashion, favoring luminal activation. Our data identify a unique site for CD8(+) T cell activation after lung transplantation, and suggest that attenuating these responses may provide a clinically relevant target.
American Journal of Respiratory Cell and Molecular Biology 06/2011; 44(6):749-54. · 4.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cilia are traditionally classified as motile or primary. Motile cilia are restricted to specific populations of well-differentiated epithelial cells, including those in the airway, brain ventricles, and oviducts. Primary cilia are nonmotile, solitary structures that are present in many cell types, and often have sensory functions such as in the retina and renal tubules. Primary cilia were also implicated in the regulation of fundamental processes in development. Rare depictions of primary cilia in embryonic airways led us to hypothesize that primary cilia in airway cells are temporally related to motile ciliogenesis. We identified primary cilia in undifferentiated, cultured airway epithelial cells from mice and humans and in developing lungs. The solitary cilia in the airways express proteins considered unique to primary cilia, including polycystin-1 and polycystin-2. A temporal analysis of airway epithelial cell differentiation showed that cells with primary cilia acquire markers of motile ciliogenesis, suggesting that motile ciliated cells originate from primary ciliated cells. Whereas motile ciliogenesis requires Foxj1, primary ciliogenesis does not, and the expression of Foxj1 was associated with a loss of primary cilia, just before the appearance of motile cilia. Primary cilia were not found in well-differentiated airway epithelial cells. However, after injury, they appear in the luminal layer of epithelium and in basal cells. The transient nature of primary cilia, together with the temporal and spatial patterns of expression in the development and repair of airway epithelium, suggests a critical role of primary cilia in determining outcomes during airway epithelial cell differentiation.
American Journal of Respiratory Cell and Molecular Biology 12/2010; 43(6):731-9. · 4.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Activated T lymphocytes are abundant in the airway during lung allograft rejection. Based on respiratory viral studies, it is the current paradigm that T cells cannot divide in the airway and that their accumulation in the lumen of the respiratory tract is the exclusive result of recruitment from other sites, such as mediastinal lymph nodes. Here we show that CD8(+) T cell activation and proliferation can occur in the airway after orthotopic lung transplantation. We also demonstrate that airway epithelium expresses MHC Class I predominantly on the apical surface, both in vitro and in vivo, and initiates CD8(+) T cell responses in a polarized fashion favoring luminal activation. Our data identify a unique site for CD8(+) T cell activation after lung transplantation and suggest that attenuating these responses may provide a clinically relevant target.
American Journal of Respiratory Cell and Molecular Biology 09/2010; · 4.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Viral bronchiolitis is the leading cause of hospitalization in young infants. It is associated with the development of childhood asthma and contributes to morbidity and mortality in the elderly. Currently no therapies effectively attenuate inflammation during the acute viral infection, or prevent the risk of post-viral asthma. We hypothesized that early treatment of a paramyxoviral bronchiolitis with azithromycin would attenuate acute and chronic airway inflammation.
Mice were inoculated with parainfluenza type 1, Sendai Virus (SeV), and treated daily with PBS or azithromycin for 7 days post-inoculation. On day 8 and 21 we assessed airway inflammation in lung tissue, and quantified immune cells and inflammatory mediators in bronchoalveolar lavage (BAL).
Compared to treatment with PBS, azithromycin significantly attenuated post-viral weight loss. During the peak of acute inflammation (day 8), azithromycin decreased total leukocyte accumulation in the lung tissue and BAL, with the largest fold-reduction in BAL neutrophils. This decreased inflammation was independent of changes in viral load. Azithromycin significantly attenuated the concentration of BAL inflammatory mediators and enhanced resolution of chronic airway inflammation evident by decreased BAL inflammatory mediators on day 21.
In this mouse model of paramyxoviral bronchiolitis, azithromycin attenuated acute and chronic airway inflammation. These findings demonstrate anti-inflammatory effects of azithromycin that are not related to anti-viral activity. Our findings support the rationale for future prospective randomized clinical trials that will evaluate the effects of macrolides on acute viral bronchiolitis and their long-term consequences.
Respiratory research 01/2010; 11:90. · 3.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: The canonical Wnt/β-catenin pathway plays crucial roles in various aspects of lung morphogenesis and regeneration/repair. Here, we examined the lung phenotype and function in mice lacking the Wnt/β-catenin antagonist Chibby (Cby). In support of its inhibitory role in canonical Wnt signaling, expression of β-catenin target genes is elevated in the Cby(-/-) lung. Notably, Cby protein is prominently associated with the centrosome/basal body microtubule structures in embryonic lung epithelial progenitor cells, and later enriches as discrete foci at the base of motile cilia in airway ciliated cells. At birth, Cby(-/-) lungs are grossly normal but spontaneously develop alveolar airspace enlargement with reduced proliferation and abnormal differentiation of lung epithelial cells, resulting in altered pulmonary function. Consistent with the Cby expression pattern, airway ciliated cells exhibit a marked paucity of motile cilia with apparent failure of basal body docking. Moreover, we demonstrate that Cby is a direct downstream target for the master ciliogenesis transcription factor Foxj1. Collectively, our results demonstrate that Cby facilitates proper postnatal lung development and function.
PLoS ONE 01/2010; 5(10):e13600. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Silver is a centuries-old antibiotic agent currently used to treat infected burns. The sensitivity of a wide range of drug-resistant microorganisms to silver killing suggests that it may be useful for treating refractory lung infections. Toward this goal, we previously developed a methylated caffeine silver acetate compound, SCC1, that exhibits broad-spectrum antimicrobial activity against clinical strains of bacteria in vitro and when nebulized to lungs in mouse infection models. Preclinical testing of high concentrations of SCC1 in primary culture mouse tracheal epithelial cells (mTEC) showed selective ciliated cell death. Ciliated cell death was induced by both silver- and copper-containing compounds but not by the methylated caffeine portion of SCC1. We hypothesized that copper transporting P-type ATPases, ATP7A and ATP7B, play a role in silver detoxification in the airway. In mTEC, ATP7A was expressed in non-ciliated cells, whereas ATP7B was expressed only in ciliated cells. The exposure of mTEC to SCC1 induced the trafficking of ATP7B, but not ATP7A, suggesting the presence of a cell-specific silver uptake and detoxification mechanisms. Indeed, the expression of the copper uptake protein CTR1 was also restricted to ciliated cells. A role of ATP7B in silver detoxification was further substantiated when treatment of SCC1 significantly increased cell death in ATP7B shRNA-treated HepG2 cells. In addition, mTEC from ATP7B(-/-) mice showed enhanced loss of ciliated cells compared to wild type. These studies are the first to demonstrate a cell type-specific expression of the Ag+/Cu+ transporters ATP7A, ATP7B, and CTR1 in airway epithelial cells and a role for ATP7B in detoxification of these metals in the lung.
Toxicology and Applied Pharmacology 12/2009; 243(3):315-22. · 3.98 Impact Factor
[show abstract][hide abstract] ABSTRACT: The pathogenesis of infection with Burkholderia cepacia complex (Bcc) organisms may be linked to its capacity to invade respiratory epithelium.
An antibiotic exclusion assay was used to study B. dolosa AU4459 and B. cenocepacia J2315 invasion into wild-type (WT) and CFTR-deficient respiratory epithelial cells. Inhibitors were used to evaluate Bcc invasion dependency on host microtubule (mt) and microfilament (mf) systems.
B. dolosa entered WT-CFTR cells with 5-fold greater efficiency than CFTR deficient cells (25% vs 5%, respectively). Invasion dropped to <0.5% after either mf or mt inhibition. B. cenocepacia entered WT (0.05%) and CFTR-deficient cells (0.07%) with similarly low efficiencies, which significantly decreased with either mf or mt inhibition (0.008% and 0.002%, respectively).
B. dolosa and B. cenocepacia enter respiratory epithelial cells in a mf and mt dependent fashion. Mutated CFTR leads to less internalization of B. dolosa, but not B. cenocepacia.
Journal of cystic fibrosis: official journal of the European Cystic Fibrosis Society 11/2009; 9(1):36-43. · 3.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Polymer chemistry offers the possibility of synthesizing multifunctional nanoparticles which incorporate moieties that enhance diagnostic and therapeutic targeting of cargo delivery to the lung. However, since rules for predicting particle behavior following modification are not well-defined, it is essential that probes for tracking fate in vivo are also included. Accordingly, we designed polyacrylamide-based hydrogel particles of differing sizes, functionalized with a nona-arginine cell-penetrating peptide (Arg(9)), and labeled with imaging components to assess lung retention and cellular uptake after intratracheal administration. Radiolabeled microparticles (1-5 microm diameter) and nanoparticles (20-40 nm diameter) without and with Arg(9) showed diffuse airspace distribution by positron emission tomography imaging. Biodistribution studies revealed that particle clearance and extrapulmonary distribution was, in part, size dependent. Microparticles were rapidly cleared by mucociliary routes but, unexpectedly, also through the circulation. In contrast, nanoparticles had prolonged lung retention enhanced by Arg(9) and were significantly restricted to the lung. For all particle types, uptake was predominant in alveolar macrophages and, to a lesser extent, lung epithelial cells. In general, particles did not induce local inflammatory responses, with the exception of microparticles bearing Arg(9). Whereas microparticles may be advantageous for short-term applications, nanosized particles constitute an efficient high-retention and non-inflammatory vehicle for the delivery of diagnostic imaging agents and therapeutics to lung airspaces and alveolar macrophages that can be enhanced by Arg(9). Importantly, our results show that minor particle modifications may significantly impact in vivo behavior within the complex environments of the lung, underscoring the need for animal modeling.
[show abstract][hide abstract] ABSTRACT: The expanding clinical challenge of respiratory tract infections due to resistant bacteria necessitates the development of new forms of therapy. The development of a compound composed of silver coupled to a methylated caffeine carrier (silver carbene complex 1 [SCC1]) that demonstrated in vitro efficacy against bacteria, including drug-resistant organisms, isolated from patients with respiratory tract infections was described previously. The findings of current in vitro studies now suggest that bactericidal concentrations of SCC1 are not toxic to airway epithelial cells in primary culture. Thus, it was hypothesized that SCC1 could be administered by the aerosolized route to concentrate delivery to the lung while minimizing systemic toxicity. In vivo, aerosolized SCC1 delivered to mice resulted in mild aversion behavior, but it was otherwise well tolerated and did not cause lung inflammation following administration over a 5-day period. The therapeutic efficacy of SCC1 compared to that of water was shown in a 3-day prophylaxis protocol, in which mice infected with a clinical strain of Pseudomonas aeruginosa had increased survival, decreased amounts of bacteria in the lung, and a lower prevalence of bacteremia. Similarly, by using an airway infection model in which bacteria were impacted in the airways by agarose beads, the administration of SCC1 was significantly superior to water in decreasing the lung bacterial burden and the levels of bacteremia and markers of airway inflammation. These observations indicate that aerosolized SCC1, a novel antimicrobial agent, warrants further study as a potential therapy for bacterial respiratory tract infections.
Antimicrobial Agents and Chemotherapy 06/2009; 53(8):3285-93. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: Definitive conclusions regarding the antiinflammatory effects of macrolide antibiotics for treatment of asthma are difficult to formulate since their beneficial effects may be related to their antimicrobial action. We hypothesized that azithromycin possesses distinct antiinflammatory properties and tested this assumption in a noninfectious mouse model of allergic asthma.
To induce allergic airway inflammation, 7-week-old BALB/cJ mice underwent intraperitoneal ovalbumin sensitization on days 0 and 7 followed by an intranasal challenge on day 14. Mice were treated with azithromycin or phosphate-buffered saline (PBS) solution on days 13 through 16. On day 17, airway inflammation was assessed by quantifying leukocytes in the airway, expression of multiple inflammatory mediators in the BAL fluid, and mucous cell metaplasia. In a separate set of experiments, azithromycin or PBS solution treatment were initiated after the ovalbumin challenge. Each experiment was repeated 3 times (a total of 9 to 11 mice in each group).
Compared to treatment with PBS solution, azithromycin attenuated the ovalbumin-dependent airway inflammation. We observed a decrease in total leukocytes in the lung tissue and BAL fluid. In addition, azithromycin attenuated the expression of cytokines (eg, interleukin [IL]-13 and IL-5) and chemokines (eg, CCL2, CCL3, and CCL4) in the BAL fluid and abrogated the extent of mucous cell metaplasia. Similar antiinflammatory effects were observed when azithromycin treatment was initiated after the ovalbumin challenge.
In this noninfectious mouse model of allergic asthma, azithromycin attenuated allergic airway inflammation. These findings demonstrate an antiinflammatory effect of azithromycin and suggest azithromycin may have beneficial effects in treating noninfectious airway inflammatory diseases, including asthma.
[show abstract][hide abstract] ABSTRACT: The genetic basis for virulence and host switching in influenza A viruses (FLUAV) is largely unknown. Because the hemagglutinin (HA) protein is a determinant of these properties, HA evolution was mapped in an experimental model of mouse lung adaptation. Variants of prototype A/Hong Kong/1/68 (H3N2) (wild-type [wt] HK) human virus were selected in both longitudinal and parallel studies of lung adaptation. Mapping of HA mutations found in 11 independently derived mouse-adapted populations of wt HK identified 27 mutations that clustered within two distinct regions in or near the globular frameworks of the HA1 and HA2 subunits. The adaptive mutations demonstrated multiple instances of convergent evolution involving four amino acid positions (162, 210, and 218 in HA1 and 154 in HA2). By use of reverse genetics, convergent HA mutations were shown to affect cell tropism by enhancing infection and replication in primary mouse tracheal epithelial cells in vitro and mouse lung tissue in vivo. Adaptive HA mutations were multifunctional, affecting both median pH of fusion and receptor specificity. Specific mutations within both adaptive regions were shown to increase virulence in a mouse lung model. The occurrence of mutations in the HA1 and HA2 adaptive regions of natural FLUAV host range and virulent variants of avian and mammalian viruses is discussed. This study has identified adaptive sites and regions within the HA1 and HA2 subunits that may guide future studies of viral adaptation and evolution in nature.
Journal of Virology 11/2008; 82(23):11599-608. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: A protective immune response to a respiratory viral infection requires a series of coordinated cellular and molecular responses. We have previously demonstrated that increased expression of airway epithelial cell interleukin (IL)-12 p80, a macrophage chemoattractant, is associated with human respiratory viral infection and mediates post-viral mortality in the mouse. To better understand the role of IL-12 p80-dependent macrophage chemotaxis in mediating viral immunity, we generated a transgenic mouse strain utilizing a promoter to drive IL-12 p40 gene expression in the airway epithelium. This transgenic strain secreted biologically active IL-12 p80 in a lung-specific manner, and demonstrated a selective increase in the number of resident, unactivated airway macrophages at baseline. Following infection with a sublethal dose of mouse parainfluenza virus type 1 (Sendai virus), the transgenic mice demonstrated an earlier peak and decline in the number of airway inflammatory cells. The transgenic mice were resistant to a lethal dose of virus and this viral resistance was dependent on the increased number of airway macrophages at baseline as partial depletion prior to infection abrogated this phenotype. The survival advantage in the transgenic mice was independent of viral load but was associated with a more rapid decline in the number of airway inflammatory cells and concentrations of multiple chemokines including the CC chemokine ligand 2 (CCL2)/JE, CCL3/macrophage inflammatory protein (MIP)-1alpha, CCL4/MIP-1beta, and CCL5/RANTES. Collectively, these results suggest that IL-12 p80-driven increases in the number of resident airway macrophages prime the host for a protective immune response that can confer increased survival following a lethal respiratory viral infection.
[show abstract][hide abstract] ABSTRACT: Autosomal dominant polycystic kidney disease (ADPKD) is a common disease with several known extrarenal manifestations, although no known pulmonary features. The formation of renal cysts in ADPKD has been attributed to dysfunction of primary cilia and the primary cilia-related proteins polycystin-1 (in 85% of cases) and polycystin-2 in renal epithelial cells. The goals of this study were to characterize the normal expression of polycystin-1 in the motile cilia of airway epithelial cells and to evaluate lung structure in ADPKD patients.
Airway epithelium from non-ADPKD patients was immunostained to localize polycystin-1 expression, and lung tissue from ADPKD patients was examined for pathologic changes. CT scans from ADPKD patients (n = 95) and a control group of non-ADPKD chronic kidney disease patients (n = 95) were retrospectively reviewed for the presence of bronchiectasis using defined criteria.
Immunostaining revealed polycystin-1 expression in the motile cilia of non-ADPKD airway epithelial cells. Lung tissue from one of five available ADPKD patient autopsies revealed histologic changes of bronchiectasis. Review of CT scans revealed a threefold-increased prevalence of bronchiectasis in the ADPKD group compared to the control group (37% vs 13%, p = 0.002).
ADPKD patients demonstrate an increased prevalence of radiographic bronchiectasis, a previously unrecognized manifestation of the disease. This association suggests that patients with primary cilia-associated diseases may be at risk for airway disease.
[show abstract][hide abstract] ABSTRACT: Biopharmaceuticals, such as proteins and DNA, have demonstrated their potential to prevent and cure diseases. The success of such therapeutic agents hinges upon their ability to cross complex barriers in the body and reach their target intact. In order to reap the full benefits of these therapeutic agents, a delivery vehicle capable of delivering cargo to all cell types, both phagocytic and non-phagocytic, is needed. This article presents the synthesis and evaluation of a microparticle delivery vehicle capable of cell penetration and sub-cellular triggered release of an encapsulated payload. pH-sensitive polyacrylamide particles functionalized with a polyarginine cell-penetrating peptide (CPP) were synthesized. The incorporation of a CPP into the microparticles led to efficient uptake by non-phagocytic cells in culture. In addition, the CPP-modified particles showed no cytotoxic effects at concentrations used in this study. The results suggest that these particles may provide a vehicle for the successful delivery of therapeutic agents to various cell types.
[show abstract][hide abstract] ABSTRACT: Lung transplantation remains the only therapeutic option for many patients suffering from end-stage pulmonary disease. Long-term success after lung transplantation is severely limited by the development of bronchiolitis obliterans. The murine heterotopic tracheal transplantation model has been widely used for studies investigating pathogenesis of obliterative airway disease and immunosuppressive strategies to prevent its development. Despite its utility, this model employs proximal airway that lacks airflow and is not vascularized. We have developed a novel model of orthotopic vascularized lung transplantation in the mouse, which leads to severe vascular rejection in allogeneic strain combinations. Here we characterize differences in the fate of airway epithelial cells in nonimmunosuppressed heterotopic tracheal and vascularized lung allograft models over 28 days. Up-regulation of growth factors that are thought to be critical for the development of airway fibrosis and interstitial collagen deposition were similar in both models. However, while loss of airway epithelial cells occurred in the tracheal model, airway epithelium remained intact and fully differentiated in lung allografts, despite profound vascular rejection. Moreover, we demonstrate expression of the anti-apoptotic protein Bcl-2 in airway epithelial cells of acutely rejected lung allografts. These findings suggest that in addition to alloimmune responses, other stimuli may be required for the destruction of airway epithelial cells. Thus, the model of vascularized mouse lung transplantation may provide a new and more physiologic experimental tool to study the interaction between immune and nonimmune mechanisms affecting airway pathology in lung allografts.
American Journal of Respiratory Cell and Molecular Biology 01/2008; 37(6):625-30. · 4.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: Programs that direct cellular differentiation are dependent on the strict temporal expression of regulatory factors that can be provided by Rho GTPases. Ciliogenesis is a complex sequence of events involving the generation and docking of basal bodies at the apical membrane, followed by ciliary axoneme generation. Although a cilia proteome has been assembled, programs that direct ciliated cell differentiation are not well established, particularly in mammalian systems. Using mouse primary culture airway epithelial cells, we identified a critical stage of ciliogenesis requiring the temporal establishment of an apical web-like structure of actin for basal body docking and subsequent axoneme growth. Apical web formation and basal body docking were prevented by interruption of actin remodeling and were dependent on RhoA activation. Additional evidence for this program was provided by analysis of Foxj1-null mice that failed to dock basal bodies and lacked apical actin. Foxj1 expression coincided with actin web formation, activated RhoA and RhoB, and persisted despite RhoA inhibition, suggesting that Foxj1 promoted RhoA during ciliogenesis. Apical ezrin localization was also dependent on Foxj1, actin remodeling, and RhoA, but was not critical for ciliogenesis. Thus, temporal Foxj1 and RhoA activity are essential regulatory events for cytoskeletal remodeling during mammalian ciliogenesis.
[show abstract][hide abstract] ABSTRACT: Ciliated airway epithelial cells are critical for mucosal barrier function, including host defense against pathogens. This cell population is often the primary target and thereby the first line of defense against many common respiratory viruses. It is also the precursor for mucous cells and thereby promotes mucociliary clearance of infectious and other noxious agents. Cells with motile cilia in other organs (e.g., brain and reproductive organs) may also have roles in development and reproduction. However, definitive proof of ciliated cell function is hampered by the lack of strategies to specifically target this cell population for loss of function in vivo. To this end, cell type-specific gene promoters have been combined with the Cre/LoxP system to disrupt genes in airway and alveolar epithelial cell populations expressing surfactant protein C (SP-C) or Clara cell secretory protein (CCSP). By contrast, an analogous system to disrupt gene function in ciliated airway epithelial cells was still needed. Here we report the generation and analysis of mouse lines with a FOXJ1 promoter driving the Cre recombinase and show that this system mediates genomic recombination specifically in ciliated cells. The pattern of recombination recapitulates endogenous FOXJ1 promoter function, being restricted to ciliated cells present in pulmonary airways as well as choroid plexus, ependyma, oviduct, and testis. This transgenic mouse system thereby offers a new strategy for specific knockouts of genes in ciliated cells. It should prove extremely useful for defining ciliated cell function in airway mucosal immunity as well as development and reproduction.
American Journal of Respiratory Cell and Molecular Biology 06/2007; 36(5):515-9. · 4.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: The pathogenesis of many lung diseases involves neutrophilic inflammation. Neutrophil functions, in turn, are critically dependent on glucose uptake and glycolysis to supply the necessary energy to meet these functions. In this study, we determined the effects of p38 mitogen-activated protein kinase and hypoxia-inducible factor (HIF)-1, as well as their potential interaction, on the expression of membrane glucose transporters and on glucose uptake in murine neutrophils. Neutrophils were harvested and purified from C57BL/6 mice and stimulated with lipopolysaccharide (LPS) in the presence or absence of specific p38 and HIF-1 inhibitors. Glucose uptake was measured as the rate of [3H]deoxyglucose (DG) uptake. We identified GLUT-1 in mouse neutrophils, but neither GLUT-3 nor GLUT-4 were detected using Western blot analysis, even after LPS stimulation. LPS stimulation did not increase GLUT-1 protein levels but did cause translocation of GLUT-1 from the cell interior to the cell surface, together with a dose-dependent increase in [3H]DG uptake, indicating that glucose uptake is regulated in these cells. LPS also activated both p38 and the HIF-1 pathway. Inhibitors of p38 and HIF-1 blocked GLUT-1 translocation and [3H]DG uptake. These data suggest that LPS-induced increases in neutrophil glucose uptake are mediated by GLUT-1 translocation to the cell surface in response to sequential activation of neutrophil p38 and HIF-1alpha in neutrophils. Given that neutrophil function and glucose metabolism are closely linked, control of the latter may represent a new target to ameliorate the deleterious effects of neutrophils on the lungs.
[show abstract][hide abstract] ABSTRACT: Pseudomonas aeruginosa is an important bacterial pathogen, particularly as a cause of infections in hospitalised patients, immunocompromised hosts and patients with cystic fibrosis. Surveillance of nosocomial P. aeruginosa infections has revealed trends of increasing antimicrobial resistance, including carbapenem resistance and multidrug resistance. Mechanisms of antimicrobial resistance include multidrug efflux pumps, ss-lactamases and downregulation of outer membrane porins. Mechanisms of virulence include secreted toxins and the ability to form biofilms. The effective treatment of infections caused by P. aeruginosa includes prevention when possible, source control measures as necessary and prompt administration of appropriate antibacterial agents. Antibacterial de-escalation should be pursued in patients with an appropriate clinical response, especially when antibacterial susceptibilities are known. Multidrug-resistant P. aeruginosa may require treatment with less commonly used antibacterials (e.g. colistin), but newer anti-pseudomonal antibacterials are expected to be available in the near future.