Update on the treatment of Pseudomonas aeruginosa pneumonia

Haplotype analysis of the germacrene A synthase gene and association with cynaropicrin content and biological activities in Cynara cardunculus

Cynara cardunculus: L. represents a natural source of terpenic compounds, with the predominant molecule being cynaropicrin. Cynaropicrin is gaining interest since it has been correlated to anti-hyperlipidaemia, antispasmodic and cytotoxicity activity against leukocyte cancer cells. The objective of this work was to screen a collection of C. cardunculus, from different origins, for new allelic variants in germacrene A synthase (GAS) gene involved in the cynaropicrin biosynthesis and correlate them with improved cynaropicrin content and biological activities. Using high-resolution melting, nine haplotypes were identified. The putative impact of the identified allelic variants in GAS protein was evaluated by bioinformatic tools and polymorphisms that putatively lead to protein conformational changes were described. Additionally, cynaropicrin and main pentacyclic triterpenes contents, and antithrombin, antimicrobial and antiproliferative activities were also determined in C. cardunculus leaf lipophilic-derived extracts. In this work we identified allelic variants with putative impact on GAS protein, which are significantly associated with cynaropicrin content and antiproliferative activity. The results obtained suggest that the identified polymorphisms should be explored as putative genetic markers correlated with biological properties in Cynara cardunculus.

Management of multidrug-resistant Pseudomonas aeruginosa in the intensive care unit: state of the art

Pseudomonas aeruginosa (PA) is one of the most important causes of healthcare-related infections among Gram-negative bacteria. The best therapeutic approach is controversial, especially for multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains as well as in the setting of most severe patients, such as in the intensive care unit (ICU). Areas covered: This article addresses several points. First, the main microbiological aspects of PA, focusing on its wide array of resistance mechanisms. Second, risk factors and the worse outcome linked to MDR-PA infection. Third, the pharmacological peculiarity of ICU patients, that makes the choice of a proper antimicrobial therapy difficult. Eventually, the current therapeutic options against MDR-PA are reviewed, taking into account the main variables that drive antimicrobial optimization in critically ill patients. Literature search was carried out using Pubmed and Web of Science. Expert commentary: Methodologically rigorous studies are urgently needed to clarify crucial aspects of the treatment against MDR-PA, namely monotherapy versus combination therapy in empiric and targeted settings. In the meanwhile, useful options are represented by newly approved drugs, such as ceftolozane/tazobactam and ceftazidime/avibactam. In critically ill patients, at least as empirical approach, a combination therapy is a prudent choice when a MDR-PA strain is suspected.

Risk factors for carbapenem-nonsusceptible Pseudomonas aeruginosa: Case-control study

The objective of this case case-control study was to identify risk factors for carbapenem-nonsusceptible Pseudomonas aeruginosa in adult acute care hospitalized patient at 2 large academic medical centers. Risk factors were evaluated using logistic regression within a generalized estimating equations framework to account for clustering of patients within study site. Of 1161 total isolates, 271 (23.3%) were carbapenem-nonsusceptible of which respiratory was the most common source (54.3%). In the multivariable model, intra-abdominal (P < 0.0001) and respiratory (P = 0.0014) sources were associated with a higher odds for carbapenem nonsusceptibility when compared to urine source. Prior positive culture (P < 0.0001), use of an antipseudomonal carbapenem in the prior 30 days (P < 0.0001) and culture collection in the intensive care unit (P < 0.0001) were also associated with increased odds for carbapenem-nonsusceptibility. Further studies to validate these findings are warranted.

Antimicrobial activities of LCB10-0200, a novel siderophore cephalosporin, against the clinical isolates of Pseudomonas aeruginosa and other pathogens

Infections caused by multidrug-resistant bacteria, including Pseudomonas aeruginosa, are threatening public health worldwide. Therefore, a novel antibacterial agent is needed to treat these infections. Here, we investigated the in vitro and in vivo activities of a novel siderophore-conjugated cephalosporin, LCB10-0200, against the clinical isolates of Gram-negative bacteria, including multidrug-resistant P. aeruginosa. In vitro susceptibility to LCB10-0200 was assessed by performing a two-fold agar dilution method, as described by the Clinical and Laboratory Standards Institute. LCB10-0200 showed the most potent antibacterial activity against P. aeruginosa clinical isolates, including β-lactamase-producing strains. Moreover, LCB10-0200 showed better antibacterial activity against recently isolated clinical isolates than its comparators, except colistin. The in vivo activity of LCB10-0200 was examined using four mouse models of systemic, thigh, respiratory tract, and urinary tract infections. LCB10-0200 was more effective than ceftazidime in treating systemic, thigh, respiratory tract, and urinary tract infections caused by drug-susceptible and drug-resistant P. aeruginosa strains in these mouse models. Thus, the potent in vitro and in vivo activities of LCB10-0200 observed in the present study indicate that it has the potential for treating infections caused by Gram-negative bacteria, including P. aeruginosa.

nBioChip, a Lab-on-a-Chip Platform of Mono- and Polymicrobial Biofilms for High-Throughput Downstream Applications

With an estimated 80% of infections being associated with a biofilm mode of growth and the ensuing recalcitrance of these biofilms with respect to conventional antibiotic treatment leading to high mortality rates, there is a dire and unmet need for the development of novel approaches to prevent, treat, and control these infections. Both bacteria and fungi are capable of forming biofilms that are inherently fragile and often polymicrobial in nature, which further complicates treatment. In this work, we showcase a nanobiofilm chip as a convenient platform for culturing several hundreds of mono- or polymicrobial biofilms and for susceptibility testing. This platform enables true ultra-high-throughput screening for antimicrobial drug discovery or diagnostics or for addressing fundamental issues in microbiology.

Current in vitro techniques for the culture of microorganisms, and particularly of delicate microbial biofilms, are still mostly limited to low-density plates and manual labor and are not amenable to automation and true high-throughput (HT) applications. We have developed a novel fully automated platform for the formation of mono- and polymicrobial biofilms of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans at the nanoscale level. The nBioChip is robotically printed, robustly handled, and scanned using a standard microarray reader. Using this technique, hundreds to thousands of identical nanobiofilms encapsulated in hydrogel spots were cultured on microscope slides. The spots can withstand the washing steps involved in screening assays. The miniaturized biofilms demonstrated characteristics similar to those displayed by conventionally formed macroscopic biofilms, including (i) three-dimensional architectural features, (ii) synthesis of exopolymeric matrix material, and (iii) elevated resistance to antibiotic treatment. On the basis of our results, the nBioChip can generate reliable high-throughput antimicrobial susceptibility testing (HT-AST) in 12 to 18 h. The chip serves as a proof-of-concept universal platform for high-throughput drug screening and other downstream applications and furthers understanding of microbial interactions in mixed-species communities at the nanoscale level.

IMPORTANCE With an estimated 80% of infections being associated with a biofilm mode of growth and the ensuing recalcitrance of these biofilms with respect to conventional antibiotic treatment leading to high mortality rates, there is a dire and unmet need for the development of novel approaches to prevent, treat, and control these infections. Both bacteria and fungi are capable of forming biofilms that are inherently fragile and often polymicrobial in nature, which further complicates treatment. In this work, we showcase a nanobiofilm chip as a convenient platform for culturing several hundreds of mono- or polymicrobial biofilms and for susceptibility testing. This platform enables true ultra-high-throughput screening for antimicrobial drug discovery or diagnostics or for addressing fundamental issues in microbiology.

Effect of aquo-alchoholic extract of Glycyrrhiza glabra against Pseudomonas aeruginosa in Mice Lung Infection Model

The prevalence of lung infection caused by Pseudomonas aeruginosa strains that are classified as multi-drug resistant has increased considerably and is mainly attributed to relative insufficiency of potent chemotherapeutic modalities. The present study was conducted to evaluate the antimicrobial activity of aquo-alcoholic extract of Glycyrrhiza glabra against the P. aeruginosa causing lung infection in Swiss albino mice. The study involves evaluation of lethal dose of P. aeruginosa in Swiss albino mice and analysis of disease manifestation that includes bacteremia, hypothermia, reduction in body weight and other parameters for 48h of infection. Physical manifestations of infected mice showed a significant decline in body temperature that is 29±0.57°C (at 48th h) from 38.81±0.33°C (0h) and 30% weight loss was observed at the end of the study. Further the efficacy of G. glabra extract against lung infection induced with the calculated lethal dose was evaluated by employing bacteremia, histopathology and radiological analysis. Bacterial burden showed that 2.30±0.02 Log10CFU/mL at day 7, a significant decline in the bacterial load as compared to day 1 when the bacterial burden was found to be 3.32±0.1 Log10CFU/mL. Histopathological results showed more diffuse and patchy accumulation of inflammatory cells within the alveolar space also the infiltrates were noted in all the lung section of infected mice. In treated animal group improved lung histology was seen with the exudates were less seen in D1 dose (20mg/kg) and disappeared in D2 dose (80mg/kg). The study clearly declares that the G. glabra extract is effective against lung infection caused by P. aeruginosa at dose of 80mg/kg. The LCMS results revealed that the extract contains Glycyrrhizin, Stigmasterol and Ergosterol, Licochalcone and Glabridin. The current study expected to further exploit the biomedical properties of this extract in the preparation of a potent regimen against such threatening pathogen.

Epidihydropinidine, the main piperidine alkaloid compound of Norway spruce (Picea abies) shows promising antibacterial and anti-Candida activity

This study reports for the first time promising antibacterial and antifungal effects of epidihydropinidine, the major piperidine alkaloid in the needles and bark of Norway spruce, Picea abies (L.) Karsten. Epidihydropinidine was growth inhibitory against all bacterial and fungal strains used in our investigation, showing the lowest MIC value of 5.37μg/mL against Pseudomonas aeruginosa, Enterococcus faecalis, Candida glabrata and C. albicans. Epidihydropinidine was nearly three times more active than tetracycline against P. aeruginosa and E. faecalis. Promising antibacterial effects were also recorded against Staphylococcus aureus and Bacillus cereus (MIC 10.75μg/mL) as well as against Salmonella enterica (MIC and MBC 43μg/mL). Our preliminary results suggest that epidihydropinidine as well related alkaloids of Norway spruce could be powerful candidates for new antibiotics and for preventing food spoilage.

Pseudomonas aeruginosa Ventilator-Associated Pneumonia Induces Lung Injury through TNF-α/c-Jun NH2-Terminal Kinase Pathways

Ventilator-associated pneumonia (VAP) is a common nosocomial infection among intensive care unit (ICU) patients. Pseudomonas aeruginosa (PA) is the most common multidrug-resistant Gram-negative pathogen and VAP caused by PA carries a high rate of morbidity and mortality. This study examined the molecular mechanism of PA VAP-induced lung injury. C57BL/6 wild-type (WT) mice and JNK1 knockout (JNK1^-/-) mice received mechanical ventilation (MV) for 3 h at 2 days after receiving nasal instillation of PA. The WT and JNK1^-/- mice also received MV after the induction of lung injury by instillation of supernatants from PA-stimulated alveolar macrophages (AMs). AMs isolated from WT, IκB-kinase (IKK)β^ΔMye (IKKβ was selectively deleted in macrophages), and JNK1^-/- mice were ex vivo stimulated with live PA and supernatants were collected for cytokine assay. Intranasal instillation of 10⁶ PA enhanced MV-induced NF-κB DNA binding activity in the lungs and nitrite levels in BALF. MV after PA instillation significantly increased the expression of ICAM and VCAM in the lungs and TNF-α, IL-1β, and IL-6 levels in bronchoalveolar lavage fluid (BALF) of WT mice, but not in JNK1^-/- mice. MV after supernatant instillation induced more total protein concentration in BALF and neutrophil sequestration in the lungs in WT mice than JNK1^-/- mice and cytokine assay of supernatants indicated that TNF-α is a critical regulator of PA VAP-induced lung injury. Ex vivo PA stimulation induced TNF-α production by AMs from WT as well as JNK1^-/- mice but not IKKβ^ΔMye mice. In summary, PA colonization plays an important role in PA VAP-induced lung injury through the induction of JNK1-mediated inflammation. These results suggest that the pathogenesis mechanism of PA VAP involves production of TNF-α through activation of IKK/NF-κB pathways in AMs and JNK signaling pathway in the lungs.

Pseudomonas aeruginosa colonization enhances ventilator-associated pneumonia-induced lung injury

Background

Pseudomonas aeruginosa (PA) is the single-most common pathogen of ventilator-associated pneumonia (VAP). Large quantities of PA in the trachea of ventilated patients are associated with an increased risk of death. However, the role of PA colonization in PA VAP-induced lung injury remains elusive. This study examined the effect and mechanism of PA colonization in VAP-induced lung injury.

Methods

C57BL/6 wild-type (WT) and c-Jun N-terminal kinase knockout (JNK1^−/−) mice received mechanical ventilation for 3 h at 2 days after receiving nasal instillation of PA (1 × 10⁶ colony forming unit) or normal saline.

Results

Intranasal instillation of PA or mechanical ventilation induced the expression of interleukin-6 (IL-6) in the lungs. Phospho-JNK protein expression in the lungs was significantly increased in mice receiving mechanical ventilation after PA instillation as compared with those receiving ventilation alone. Mechanical ventilation after PA instillation significantly increased the expression of tumor necrosis factor-α (TNF-α), IL-1β, and macrophage inflammatory protein-2 (MIP-2) proteins; neutrophil sequestration; and TNF-α, IL-1β, and IL-6 levels in the lungs of WT mice, but not in JNK1^−/− mice.

Conclusion

PA colonization plays an important role in PA VAP-induced lung injury through the induction of JNK1-mediated inflammation. PA-induced VAP causes lung injury through JNK signaling pathway in the lungs. JNK inhibition in ICU patients with higher percentages of PA colonization may reduce VAP-induced lung injury and mortality.

The inhibition of Pseudomonas aeruginosa biofilm formation by micafungin and the enhancement of antimicrobial agent effectiveness in BALB/c mice

Micafungin inhibits biofilm formation by impeding 1,3-β-D-glucan synthesis in Candida albicans. Since Pseudomonas aeruginosa also has 1,3-β-D-glucan in its cell wall, this study assessed the effects of antibacterial agents in vitro and in vivo on micafungin-treated biofilm-forming P. aeruginosa isolates. After treatment with micafungin as well as with a panel of four antibacterial agents, biofilm production was significantly reduced as measured by spectrophotometry. The relative mRNA transcription levels for the genes encoding pellicles (pelC) and cell wall 1,3-β-D-glucan (ndvB), which were measured by quantitative reverse transcription PCR (qRT-PCR), significantly decreased with micafungin treatment. In vivo, the survival rates of P. aeruginosa-infected BALB/c mice significantly increased after combined treatment with micafungin and each of the antibacterial agents. Of these treatments, the combination of micafungin with levofloxacin had the highest survival rate; this combination was the most effective treatment against P. aeruginosa-induced infection.

Crystal structure of YeaZ from Pseudomonas aeruginosa

The Pseudomonas aeruginosa PA3685 locus encodes a conserved protein that shares 49% sequence identity with Escherichia coli YeaZ, which was recently reported as involved in the biosynthesis of threonylcarbamoyl adenosine (t(6)A), a universal modified tRNA nucleoside. Many YeaZ orthologues were reported as "essential for life" among various bacterial species, suggesting a critical role for both these proteins and for the t(6)A biosynthetic pathway. We provide here evidences that PA3685 protein (PaYeaZ) is essential. Additionally, we describe its purification, crystallization, and crystallographic structure. The crystal structure shows that PaYeaZ is composed of two domains one of which is the platform to form protein-protein interaction involved either in homodimeric assembly or in the formation of the multiprotein complex required for the synthesis of t(6)A. These features make the PaYeaZ protein a potential target candidate for the design of novel inhibitors able to hinder the complex formation and expected to abolish the crucial activity of t(6)A synthesis.

Aloe vera Gel: Effective Therapeutic Agent against Multidrug-Resistant Pseudomonas aeruginosa Isolates Recovered from Burn Wound Infections

Objective. Aloe vera is an herbal medicinal plant with biological activities, such as antimicrobial, anticancer, anti-inflammatory, and antidiabetic ones, and immunomodulatory properties. The purpose of this study was investigation of in vitro antimicrobial activity of A. vera gel against multidrug-resistant (MDR) Pseudomonas aeruginosa isolated from patients with burn wound infections. Methods. During a 6-month study, 140 clinical isolates of P. aeruginosa were collected from patients admitted to the burn wards of a hospital in Tehran, Iran. Antimicrobial susceptibility test was carried out against the pathogens using the A. vera gel and antibiotics (imipenem, gentamicin, and ciprofloxacin). Results. The antibiogram revealed that 47 (33.6%) of all isolates were MDR P. aeruginosa. The extract isolated from A. vera has antibacterial activity against all of isolates. Also, 42 (89.4%) isolates were inhibited by A. vera gel extract at minimum inhibitory concentration (MIC) ≤ 200 µg/mL. MIC value of A. vera gel for other isolates (10.6%) was 800 µg/mL. All of MDR P. aeruginosa strains were inhibited by A. vera at similar MIC₅₀ and MIC₉₀ 200 µg/mL. Conclusion. Based on our results, A. vera gel at various concentrations can be used as an effective antibacterial agent in order to prevent wound infection caused by P. aeruginosa.

Phylogenetic study of metallo-β-lactamase producing multidrug resistant Pseudomonas aeruginosa isolates from burn patients

The present study was carried out to understand the clonal relationship using enterobacteriaceae repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) among metallo-β-lactamase (MBL) producing multidrug resistant Pseudomonas aeruginosa isolates from burn victims and their susceptibility to commonly used anti-pseudomonal agents. In the present study 94 non-duplicate P. aeruginosa strains from the wound samples of burn patients were included. Identification of the isolates was done by biochemical methods and antibiotic sensitivity was done by disc diffusion method following CLSI (Clinical Laboratory Standard Institute) guidelines. By using imipenem (IPM)-EDTA disk diffusion/double disc synergy method carbapenem resistant organisms were tested for MBL. To define the clonal relationship ERIC-PCR was used. Of the 94 isolates, 18 (19.14%) were found resistant to IPM and MBL production was shown 11 (11.70%) by the IPM-EDTA disc diffusion method. From dendrogram of the ERIC-PCR profile four major clusters were obtained (A, B, C and D). Cluster B contained the majority of the isolates (6 strains 1, 4, 8, 9, 10 and 11). This study using ERIC-PCR of randomly collected isolates exhibits high genetic diversity which rules out cross contamination frequency.

Disarming Pseudomonas aeruginosa virulence factor LasB by leveraging a Caenorhabditis elegans infection model

The emergence of antibiotic resistance places a sense of urgency on the development of alternative antibacterial strategies, of which targeting virulence factors has been regarded as a "second generation" antibiotic approach. In the case of Pseudomonas aeruginosa infections, a proteolytic virulence factor, LasB, is one such target. Unfortunately, we and others have not been successful in translating in vitro potency of LasB inhibitors to in vivo efficacy in an animal model. To overcome this obstacle, we now integrate in silico and in vitro identification of the mercaptoacetamide motif as an effective class of LasB inhibitors with full in vivo characterization of mercaptoacetamide prodrugs using Caenorhabditis elegans. We show that one of our mercaptoacetamide prodrugs has a good selectivity profile and high in vivo efficacy, and confirm that LasB is a promising target for the treatment of bacterial infections. In addition, our work highlights that the C. elegans infection model is a user-friendly and cost-effective translational tool for the development of anti-virulence compounds.

Liposomal antibiotic formulations for targeting the lungs in the treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that causes serious lung infections in cystic fibrosis, non-cystic fibrosis bronchiectasis, immunocompromised, and mechanically ventilated patients. The arsenal of conventional antipseudomonal antibiotic drugs include the extended-spectrum penicillins, cephalosporins, carbapenems, monobactams, polymyxins, fluoroquinolones, and aminoglycosides but their toxicity and/or increasing antibiotic resistance are of particular concern. Improvement of existing therapies against Pseudomonas aeruginosa infections involves the use of liposomes - artificial phospholipid vesicles that are biocompatible, biodegradable, and nontoxic and able to entrap and carry hydrophilic, hydrophobic, and amphiphilic molecules to the site of action. The goal of developing liposomal antibiotic formulations is to improve their therapeutic efficacy by reducing drug toxicity and/or by enhancing the delivery and retention of antibiotics at the site of infection. The focus of this review is to appraise the current progress of the development and application of liposomal antibiotic delivery systems for the treatment pulmonary infections caused by P. aeruginosa.

Pseudomonas aeruginosa septicemia causes death following liposuction with allogenic fat transfer and gluteal augmentation

Cosmetic surgery to improve aesthetic and body conditions is becoming increasingly popular worldwide. In 2013, the American Society of Plastic Surgeons (ASPS) reported that one of the top five cosmetic procedures in the US is liposuction with over 200,000 procedures per year. This type of surgery is regarded as a minimal risk operation. Since surgical complications are not often reported, liposuction is usually performed in outpatient clinics. Fatality after cosmetic liposuction surgery is also relatively rare. This case report presents a death following cosmetic liposuction with allogenic fat transfer and gluteal augmentation. The medico-legal autopsy, pathology, and postmortem microbiology examinations reveal that septicemia by Pseudomonas aeruginosa was the definite cause of death. Surgical risk assessment and pathogenesis of the organism was reviewed.

Structural changes and differentially expressed genes in Pseudomonas aeruginosa exposed to meropenem-ciprofloxacin combination

The effect of a meropenem-ciprofloxacin combination (MCC) on the susceptibility of multidrug-resistant (MDR) Pseudomonas aeruginosa (MRPA) clinical isolates was determined using checkerboard and time-kill curve techniques. Structural changes and differential gene expression that resulted from the synergistic action of the MCC against one of the P. aeruginosa isolates (1071-MRPA]) were evaluated using electron microscopy and representational difference analysis (RDA), respectively. The differentially expressed, SOS response-associated, and resistance-associated genes in 1071-MRPA exposed to meropenem, ciprofloxacin, and the MCC were monitored by quantitative PCR. The MCC was synergistic against 25% and 40.6% of MDR P. aeruginosa isolates as shown by the checkerboard and time-kill curves, respectively. The morphological and structural changes that resulted from the synergistic action of the MCC against 1071-MRPA were a summation of the effects observed with each antimicrobial alone. One exception included outer membrane vesicles, which were seen in a greater amount upon ciprofloxacin exposure but were significantly inhibited upon MCC exposure. Cell wall- and DNA repair-associated genes were differentially expressed in 1071-MRPA exposed to meropenem, ciprofloxacin, and the MCC. However, some of the RDA-detected, resistance-associated, and SOS response-associated genes were expressed at significantly lower levels in 1071-MRPA exposed to the MCC. The MCC may be an alternative for the treatment of MDR P. aeruginosa. The effect of this antimicrobial combination may be not only the result of a summation of the effects of meropenem and ciprofloxacin but also a result of differential action that likely inhibits protective mechanisms in the bacteria.

Lactonase-expressing Lactobacillus plantarum NC8 attenuates the virulence factors of multiple drug resistant Pseudomonas aeruginosa in co-culturing environment

Pseudomonas aeruginosa possesses an arcade of both cell-associated and extracellular cytotoxic virulence factors which are regulated by a multi-component quorum sensing system. Many research studies report success of lactonase in combating the pathogenicity of P. aeruginosa but delivery of lactonase remains a challenge. The present study aims at developing a delivery vehicle for lactonase. Lactobacillus plantarum NC8 was used as host for aiiA (Bacillus thuringiensis 4A3 lactonase gene) using pSIP409 expression vector. pSIP409: aiiA construct was stably maintained in L. plantarum NC8. Co-culturing of multi-drug resistant (MDR) clinical isolates of P. aeruginosa and PAO1 with recombinant L. plantarum NC8 led to significant reduction (p < 0.001) in extracellular virulence factors like pyocyanin, protease, elastase and rhamnolipids in P. aeruginosa and also showed significant reduction in adhesion of P. aeruginosa strains to uroepithelial cells in vitro. This study shows the heterologous expression of AiiA lactonase in L. plantarum NC8. Co-culturing of lactonase expressing L. plantarum NC8 with MDR P. aeruginosa strains led to attenuation of their virulence significantly. These results underscore the potential application of recombinant L. plantarum NC8 with anti-quorum sensing properties to control infections caused by multidrug resistant P. aeruginosa.

VE-cadherin cleavage by LasB protease from Pseudomonas aeruginosa facilitates type III secretion system toxicity in endothelial cells

Infection of the vascular system by Pseudomonas aeruginosa (Pa) occurs during bacterial dissemination in the body or in blood-borne infections. Type 3 secretion system (T3SS) toxins from Pa induce a massive retraction when injected into endothelial cells. Here, we addressed the role of type 2 secretion system (T2SS) effectors in this process. Mutants with an inactive T2SS were much less effective than wild-type strains at inducing cell retraction. Furthermore, secretomes from wild-types were sufficient to trigger cell-cell junction opening when applied to cells, while T2SS-inactivated mutants had minimal activity. Intoxication was associated with decreased levels of vascular endothelial (VE)-cadherin, a homophilic adhesive protein located at endothelial cell-cell junctions. During the process, the protein was cleaved in the middle of its extracellular domain (positions 335 and 349). VE-cadherin attrition was T3SS-independent but T2SS-dependent. Interestingly, the epithelial (E)-cadherin was unaffected by T2SS effectors, indicating that this mechanism is specific to endothelial cells. We showed that one of the T2SS effectors, the protease LasB, directly affected VE-cadherin proteolysis, hence promoting cell-cell junction disruption. Furthermore, mouse infection with Pa to induce acute pneumonia lead to significant decreases in lung VE-cadherin levels, whereas the decrease was minimal with T2SS-inactivated or LasB-deleted mutant strains. We conclude that the T2SS plays a pivotal role during Pa infection of the vascular system by breaching the endothelial barrier, and propose a model in which the T2SS and the T3SS cooperate to intoxicate endothelial cells.

Crystal structure of FliC flagellin from Pseudomonas aeruginosa and its implication in TLR5 binding and formation of the flagellar filament

Pseudomonas aeruginosa is one of leading opportunistic pathogens in humans and its movement is driven by a flagellar filament that is constituted through the polymerization of a single protein, FliC flagellin (paFliC). paFliC is an essential virulence factor for the colonization of P. aeruginosa. paFliC activates innate immune responses via its recognition by Toll-like receptor 5 (TLR5) and adaptive immunity in the host. Thus, paFliC has been a vaccine candidate to prevent P. aeruginosa infection, particularly for cystic fibrosis patients. To provide structural information on paFliC and its flagellar filament, we have determined the crystal structure of paFliC, which contains the conserved D1 and variable D2 domains, at 2.1 Å resolution. As observed for Salmonella FliC, the paFliC D1 domain is folded into a rod-shaped structure, and paFliC was demonstrated by gel filtration and native PAGE analyses to directly interact with TLR5. Moreover, a structural model of the paFliC-TLR5 complex suggests that paFliC D1 would provide major TLR5-binding sites, similar to Salmonella FliC. In contrast to the D1 domain, the paFliC D2 domain exhibits a unique structure of two β-sheets and one α-helix that has not been found in other flagellins. An in silico construction of a flagellar filament based on the packing of paFliC in the crystal suggests that the D2 domain would be exposed to solution and could play an important role in immunogenicity. Our biophysical and structure-based modeling study on paFliC, the paFliC-TLR5 complex, and the paFliC filament could contribute to the improvement of vaccine design to control P. aeruginosa infection.

Analysis of integrons and associated gene cassettes in clinical isolates of multidrug resistant Pseudomonas aeruginosa from Southwest Nigeria

Background

Multidrug resistant Pseudomonas aeruginosa harbours integrons and other mobile genetic elements such as plasmids and transposons, which easily disseminate antibiotic resistance genes among clinical strains of P. aeruginosa.

Methodology

Plasmid extraction of 54 clinical isolates of P. aeruginosa was carried out by alkaline lysis method; and plasmid size estimation was done by using E. coli V517 standard plasmid marker. Fifty-four clinical strains of P. aeruginosa were isolated from 5 hospitals in 3 Southwestern states of Nigeria between March and September 2010. Plasmid extraction of isolates was carried out by alkaline lysis method; and plasmid size estimation was done by using E. coli V517 standard plasmid marker. PCR amplification for the 3 classes of resistance integrons, and gene cassette characterization were carried out using specific primers and by sequencing of PCR products. Conjugal mating of the integron positive P. aeruginosa strains with E. coli DH5α was performed to demonstrate transferability of integrons and gene cassettes.

Result

Agarose gel electrophoresis of plasmid DNA revealed that all the 54 P. aeruginosa harboured 1–4 plasmids with sizes ranging from 2.2 – >58 kb. Class 1 integron was identified in 31 (57%) strains; but none of them carried class 2 and class 3 integrons. High prevalence of aadA gene conferring resistance to streptomycin/spectinomycin was detected in the strains positive for class 1 integron. Sequencing of the 1.6 kb and 1.2 kb amplified band of gene cassettes revealed the presence of aadA6-orfD and aadA13 respectively.

Conclusion

This study demonstrates the presence of plasmids and integrons harbouring resistance gene cassettes, which may collectively constitute an efficient system for dissemination of resistance genes in P. aeruginosa. Disturbingly, the rapid and unabated spread of class 1 integron-associated multidrug resistant P. aeruginosa in Southwest Nigeria may greatly hamper successful treatment of infections caused by such strains. This necessitates the establishment of functional antimicrobial resistance surveillance programmes in Nigeria.

Partially-desulfated heparin improves survival in Pseudomonas pneumonia by enhancing bacterial clearance and ameliorating lung injury

Nosocomial pneumonia (NP, or hospital-acquired pneumonia) is associated with infections originating from hospital-borne pathogens. Persistent microbial presence and acute lung injury are common features of these infections, contributing to the high mortality rates and excessive financial burden for these patients. Pseudomonas aeruginosa (PA), a gram-negative opportunistic pathogen, is one of the prominent pathogens associated with NP. PA pneumonia is characterized by excessive secretion of inflammatory cytokines, neutrophil infiltration, and subsequent lung damage. The persistent presence of PA along with overwhelming inflammatory response is suggestive of impairment in innate immunity. High mobility group box 1 (HMGB1), a recently discovered potent pro-inflammatory cytokine, plays an important role in PA lung infections by compromising innate immunity via impairing phagocyte function through toll-like receptors (TLR) TLR2 and TLR4. ODSH (2-O, 3-O-desulfated heparin), a heparin derivative with significant anti-inflammatory properties but minimal anti-coagulatory effects, has been shown to reduce neutrophilic lung injury in the absence of active microbial infections. This study examined the effects of ODSH on PA pneumonia. This study demonstrates that ODSH not only reduced PA-induced lung injury, but also significantly increased bacterial clearance. The ameliorated lung injury, together with the increased bacterial clearance, resulted in marked improvement in the survival of these animals. The resulting attenuation in lung injury and improvement in bacterial clearance were associated with decreased levels of airway HMGB1. Furthermore, binding of HMGB1 to its receptors TLR2 and TLR4 was blunted in the presence of ODSH. These data suggest that ODSH provides a potential novel approach in the adjunctive treatment of PA pneumonia.

In vivo efficacy of biapenem with ME1071, a novel metallo-β-lactamase (MBL) inhibitor, in a murine model mimicking ventilator-associated pneumonia caused by MBL-producing Pseudomonas aeruginosa

ME1071, a maleic acid derivative, is a novel, specific inhibitor of metallo-β-lactamases (MBLs). In vitro, ME1071 can potentiate the activity of carbapenems against MBL-producing Pseudomonas aeruginosa. To confirm the clinical efficacy of ME1071 in ventilator-associated pneumonia (VAP) caused by MBL-producing P. aeruginosa, a mouse model that mimics VAP by placement of a plastic tube in the bronchus was used. Biapenem (100 mg/kg) or ME1071 plus biapenem (each 100 mg/kg) was administered intraperitoneally every 12 h beginning at 12 h after inoculation. Survival was evaluated over 7 days. At 30 h post infection, mice were sacrificed and the numbers of viable bacteria in the lungs and bronchoalveolar lavage fluid (BALF) were compared. Histopathological analysis of lung specimens was also performed. The pharmacokinetics of ME1071 was analysed after initial treatment. The ME1071 plus biapenem combination group displayed significantly longer survival compared with the control and biapenem monotherapy groups (P<0.05). Furthermore, the number of viable bacteria in the lungs was significantly lower in the combination group (P<0.05). Histopathological examination of lung specimens indicated that progression of lung inflammation was prevented in the combination group. Furthermore, total cell and neutrophil counts, as well as cytokine levels, in BALF were significantly decreased (P<0.05) in the combination group. The percentage time above the MIC (%T>MIC) for biapenem without ME1071 was 0% in plasma; however, this value was elevated to 10.8% with ME1071. These results suggest that ME1071 is potent and effective for treatment of VAP caused by MBL-producing P. aeruginosa.

Successful management of multidrug-resistant Pseudomonas aeruginosa pneumonia after kidney transplantation in a dog

An 8-year-old male mongrel dog that had undergone renal transplantation was presented 25 days later with an acute cough, anorexia and exercise intolerance. During the investigation, neutrophilic leukocytosis was noted, and thoracic radiographs revealed caudal lung lobe infiltration. While being treated with two broad-spectrum antibiotics, clinical signs worsened. Pneumonia due to infection with multidrug-resistant (MDR) Pseudomonas (P.) aeruginosa, sensitive only to imipenem and amikacin, was confirmed by bacteria isolation. After treatment with imipenem-cilastatin without reducing the immunosuppressant dose, clinical signs completely resolved. During the 2-year follow-up period, no recurrence was observed. To the best of authors' knowledge, this is the first report of pneumonia caused by MDR P. aeruginosa in a renal recipient dog and successful management of this disease.

Adaptation-based resistance to siderophore-conjugated antibacterial agents by Pseudomonas aeruginosa

Multidrug resistance in Gram-negative bacteria has become so threatening to human health that new antibacterial platforms are desperately needed to combat these deadly infections. The concept of siderophore conjugation, which facilitates compound uptake across the outer membrane by hijacking bacterial iron acquisition systems, has received significant attention in recent years. While standard in vitro MIC and resistance frequency methods demonstrate that these compounds are potent, broad-spectrum antibacterial agents whose activity should not be threatened by unacceptably high spontaneous resistance rates, recapitulation of these results in animal models can prove unreliable, partially because of the differences in iron availability in these different methods. Here, we describe the characterization of MB-1, a novel siderophore-conjugated monobactam that demonstrates excellent in vitro activity against Pseudomonas aeruginosa when tested using standard assay conditions. Unfortunately, the in vitro findings did not correlate with the in vivo results we obtained, as multiple strains were not effectively treated by MB-1 despite having low MICs. To address this, we also describe the development of new in vitro assays that were predictive of efficacy in mouse models, and we provide evidence that competition with native siderophores could contribute to the recalcitrance of some P. aeruginosa isolates in vivo.

Impact of antibiotic use on carbapenem resistance in Pseudomonas aeruginosa: is there a role for antibiotic diversity?

In this study, we aimed to evaluate the relationship between the rates of resistance of Pseudomonas aeruginosa to carbapenems and the levels and diversity of antibiotic consumption. Data were retrospectively collected from 20 acute care hospitals across 3 regions of Switzerland between 2006 and 2010. The main outcome of the present study was the rate of resistance to carbapenems among P. aeruginosa. Putative predictors included the total antibiotic consumption and carbapenem consumption in defined daily doses per 100 bed days, the proportion of very broad-spectrum antibiotics used, and the Peterson index. The present study confirmed a correlation between carbapenem use and carbapenem resistance rates at the hospital and regional levels. The impact of diversifying the range of antibiotics used against P. aeruginosa resistance was suggested by (i) a positive correlation in multivariate analysis between the above-mentioned resistance and the proportion of consumed antibiotics having a very broad spectrum of activity (coefficient = 1.77; 95% confidence interval, 0.58 to 2.96; P < 0.01) and (ii) a negative correlation between the resistance and diversity of antibiotic use as measured by the Peterson homogeneity index (coefficient = -0.52; P < 0.05). We conclude that promoting heterogeneity plus parsimony in the use of antibiotics appears to be a valuable strategy for minimizing the spread of carbapenem resistance in P. aeruginosa in hospitals.

Rational use of aminoglycosides--review and recommendations by the Swedish Reference Group for Antibiotics (SRGA)

The Swedish Reference Group for Antibiotics (SRGA) has carried out a risk-benefit analysis of aminoglycoside treatment based on clinical efficacy, antibacterial spectrum, and synergistic effect with beta-lactam antibiotics, endotoxin release, toxicity, and side effects. In addition, SRGA has considered optimal dosage schedules and advice on serum concentration monitoring, with respect to variability in volume of drug distribution and renal clearance. SRGA recommends that aminoglycoside therapy should be considered in the following situations: (1) progressive severe sepsis and septic shock, in combination with broad-spectrum beta-lactam antibiotics, (2) sepsis without shock, in combination with broad-spectrum beta-lactam antibiotics if the infection is suspected to be caused by multi-resistant Gram-negative pathogens, (3) pyelonephritis, in combination with a beta-lactam or quinolone until culture and susceptibility results are obtained, or as monotherapy if a serious allergy to beta-lactam or quinolone antibiotics exists, (4) serious infections caused by multi-resistant Gram-negative bacteria when other alternatives are lacking, and (5) endocarditis caused by difficult-to-treat pathogens when monotherapy with beta-lactam antibiotics is not sufficient. Amikacin is generally more active against extended-spectrum beta-lactamase (ESBL)-producing and quinolone-resistant Escherichia coli than other aminoglycosides, making it a better option in cases of suspected infection caused by multidrug-resistant Enterobacteriaceae. Based on their resistance data, local drug committees should decide on the choice of first-line aminoglycoside. Unfortunately, aminoglycoside use is rarely followed up with audiometry, and in Sweden we currently have no systematic surveillance of adverse events after aminoglycoside treatment. We recommend routine assessment of adverse effects, including hearing loss and impairment of renal function, if possible at the start and after treatment with aminoglycosides, and that these data should be included in hospital patient safety surveillance and national quality registries.

Impact of adequate empirical combination therapy on mortality from bacteremic Pseudomonas aeruginosa pneumonia

BACKGROUND

Pseudomonas aeruginosa has gained an increasing amount of attention in the treatment of patients with pneumonia. However, the benefit of empirical combination therapy for pneumonia remains unclear. We evaluated the effects of adequate empirical combination therapy and multidrug-resistance in bacteremic Pseudomonas pneumonia on the mortality.

METHODS

A retrospective cohort study was performed at the 2,700-bed tertiary care university hospital. We reviewed the medical records of patients with bacteremic pneumonia between January 1997 and February 2011. Patients who received either inappropriate or appropriate empirical therapy were compared by using marginal structural model. Furthermore, we investigated the direct impact of combination therapy on clinical outcomes in patients with monomicrobial bacteremic pneumonia.

RESULTS

Among 100 consecutive patients with bacteremic Pseudomonas pneumonia, 65 patients were classified in the adequate empirical therapy group, 32 of whom received monotherapy and 33 combination therapy. In the marginal structural model, only inadequate therapy was significantly associated with 28-day mortality (p = 0.02), and multidrug-resistance was not a significant risk factor.To examine further the direct impact of combination therapy, we performed a subgroup analysis of the 65 patients who received adequate therapy. Multivariate logistic regression analysis identified absence of septic shock at the time of bacteremia (OR, 0.07; 95% CI, 0.01-0.49; p = 0.008), and adequate combination therapy (OR, 0.05; 95% CI, 0.01-0.34; p = 0.002) as variables independently associated with decreased all-cause 28-day mortality.

CONCLUSIONS

Our study suggests that adequate empirical combination therapy can decrease mortality in patients with bacteremic Pseudomonas pneumonia.

A novel virulence strategy for Pseudomonas aeruginosa mediated by an autotransporter with arginine-specific aminopeptidase activity

The opportunistic human pathogen, Pseudomonas aeruginosa, is a major cause of infections in chronic wounds, burns and the lungs of cystic fibrosis patients. The P. aeruginosa genome encodes at least three proteins exhibiting the characteristic three domain structure of autotransporters, but much remains to be understood about the functions of these three proteins and their role in pathogenicity. Autotransporters are the largest family of secreted proteins in Gram-negative bacteria, and those characterised are virulence factors. Here, we demonstrate that the PA0328 autotransporter is a cell-surface tethered, arginine-specific aminopeptidase, and have defined its active site by site directed mutagenesis. Hence, we have assigned PA0328 with the name AaaA, for arginine-specific autotransporter of P. aeruginosa. We show that AaaA provides a fitness advantage in environments where the sole source of nitrogen is peptides with an aminoterminal arginine, and that this could be important for establishing an infection, as the lack of AaaA led to attenuation in a mouse chronic wound infection which correlated with lower levels of the cytokines TNFα, IL-1α, KC and COX-2. Consequently AaaA is an important virulence factor playing a significant role in the successful establishment of P. aeruginosa infections.

We present a new Pseudomonas aeruginosa virulence factor that promotes chronic skin wound infections. We propose the name AaaA for this cell-surface tethered autotransporter. This arginine-specific aminopeptidase confers a growth advantage upon P. aeruginosa, providing a fitness advantage by creating a supply of arginine in chronic wounds where oxygen availability is limited and biofilm formation is involved. To our knowledge, this is the first mechanistic evidence linking the upregulation of genes involved in arginine metabolism with pathogenicity of P. aeruginosa, and we propose potential underlying mechanisms. The superbug P. aeruginosa is the leading cause of morbidity in cystic fibrosis patients. The ineffective host immune response to bacterial colonization is likely to play a critical role in the demise of these patients, making the possibility that AaaA could interface with the innate immune system, influencing the activity of iNOS and consequently the host's defence against invading pathogens. The surface localisation of AaaA makes it accessible to inhibitors that could reduce growth of P. aeruginosa during colonisation and alter biofilm formation, potentially improving the efficacy of current antimicrobials. Indeed, structurally related aminopeptidases play a central role in several disease states (stroke, diabetes, cancer, HIV and neuropsychiatric disorders), and inhibitors alleviate symptoms.

Antibacterial efficacy of temperate phage-mediated inhibition of bacterial group motilities

Phage therapy against bacterial pathogens has been resurrected as an alternative and supplementary anti-infective modality. Here, we observed that bacterial group motilities were impaired in Pseudomonas aeruginosa strain PA14 lysogens for some temperate siphophages; the PA14 lysogens for DMS3 and MP22 were impaired in swarming motility, whereas the PA14 lysogen for D3112 was impaired in twitching motility. The swarming and twitching motilities of PA14 were also affected in the presence of MP22 and D3112, respectively. The in vitro killing activities of D3112 and MP22 toward PA14 did not differ, and neither did their in vivo persistence in the absence of bacterial infections in mice as well as in flies. Nevertheless, administration of D3112, not MP22, significantly reduced the mortality and the bacterial burdens in murine peritonitis-sepsis and Drosophila systemic infection caused by PA14. Taken together, we suggest that a temperate phage-mediated twitching motility inhibition might be comparably effective to control the acute infections caused by P. aeruginosa.

Intrapulmonary penetration of ceftolozane/tazobactam and piperacillin/tazobactam in healthy adult subjects

OBJECTIVES

Appropriate antibiotic exposure at the site of infection is important for clinically effective therapy. This study compared the epithelial lining fluid (ELF) penetration of ceftolozane/tazobactam, which has potent in vitro activity against many Gram-negative pathogens causing nosocomial pneumonia, with that of piperacillin/tazobactam in healthy adult volunteers.

METHODS

In this Phase 1, open-label trial, 51 healthy adult subjects were randomized to receive three doses of either ceftolozane/tazobactam 1.5 g administered every 8 h via a 60 min infusion or piperacillin/tazobactam 4.5 g administered every 6 h via a 30 min infusion. Serial blood samples were obtained for determination of plasma drug concentrations. Bronchoscopy and bronchoalveolar lavage were performed at pre-specified timepoints in five subjects per timepoint in each treatment group to determine the ELF drug concentration. The penetration of individual analytes into the ELF was determined from the ratio of the area under the plasma concentration-time curve in ELF to that in plasma (AUC(ELF)/AUC(plasma)).

RESULTS

Plasma and ELF concentrations of ceftolozane, piperacillin and tazobactam increased rapidly, reaching maximal concentrations at the end of the infusion. Mean maximum concentration and AUC from time 0 to the end of the dosing interval (AUC(0-τ)) for ceftolozane in ELF were 21.8 mg/L and 75.1 mg·h/L, respectively. Corresponding values for piperacillin were 58.8 mg/L and 94.5 mg·h/L. The ELF/plasma AUC ratio for ceftolozane was 0.48 compared with 0.26 for piperacillin.

CONCLUSION

This study demonstrated that ceftolozane penetrated well into the ELF following parenteral administration of ceftolozane/tazobactam.

High prevalence of extended-spectrum β-lactamase-producing pathogens: results of a surveillance study in two hospitals in Ujjain, India

BACKGROUND

Recent reports of the rapid evolution of bacterial resistance in India require urgent antibiotic stewardship programs. This study aimed to define the magnitude and pattern of resistance of bacterial pathogens to guide empirical therapy.

METHODS

We prospectively collected consecutive, clinically significant, and nonduplicate bacterial isolates from each patient from two hospitals in Ujjain, India. The antibiotic susceptibility of the bacteria was tested using a disc diffusion method as recommended by the Clinical and Laboratory Standards Institute.

RESULTS

A total of 716 pathogens were isolated from 2568 patients (median age, 25 years; range, 0 days to 92 years). Gram-negative infections were predominant (62%). The isolated pathogens included Staphylococcus aureus (n = 221; 31%), Escherichia coli (n = 149; 21%), Pseudomonas aeruginosa (n = 127; 18%), and Klebsiella pneumoniae (n = 107; 15%). Common diagnoses included abscesses (56%), urinary tract infections (14%), blood stream infections (10%), pneumonia (10%), and vaginal infections (10%). In E. coli isolates, 69% (95% confidence interval [CI] 61.6-76.6) were extended-spectrum β-lactamase (ESBL) producers and 41% (95% CI 31.6-50.5) of K. pneumoniae isolates were ESBL producers. These isolates had a high resistance to fluoroquinolones and β-lactams, except for imipenem and piperacillin-tazobactam. Salmonella typhi remained sensitive to third-generation cephalosporins. Methicillin-resistant S. aureus (MRSA) constituted 30% of all S. aureus isolates and showed resistance to ciprofloxacin (81%), cotrimoxazole (76%), and levofloxacin (60%).

CONCLUSION

Our results showed a high prevalence of ESBL among Gram-negative bacterial isolates and a high prevalence of MRSA among S. aureus isolates. Carbapenems provided the broadest coverage for Gram-negative bacteria, while glycopeptides were the most effective against MRSA; however, both classes of drugs need to be used judiciously. This study will help in planning future antibiotic stewardship programs.

In vivo efficacy and pharmacokinetics of biapenem in a murine model of ventilator-associated pneumonia with Pseudomonas aeruginosa

Biapenem (BIPM) has high bactericidal activity against Pseudomonas aeruginosa and similar activity in vitro as meropenem (MEPM). We used a murine model to examine the efficacy of biapenem against ventilator-associated pneumonia (VAP) caused by P. aeruginosa. Mice were treated by intraperitoneal injection with 100 mg/kg BIPM or MEPM every 12 h beginning 12 h after inoculation with P. aeruginosa. Survival was evaluated for 7 days, and 24 h after infection, lung histopathology was analyzed and the number of viable bacteria in the lungs and blood was counted. In addition, the pharmacokinetics of BIPM and MEPM were analyzed after the initial treatment. BIPM and MEPM significantly prolonged survival compared to control (P < 0.05). The lungs of mice treated with BIPM or MEPM had significantly fewer viable bacteria (3.54 ± 0.28 vs. 3.77 ± 0.14 log(10) CFU/ml) than in the lungs of control mice (6.65 ± 0.57 log(10) CFU/ml) (P < 0.05). Furthermore, viable bacteria were not detected in the blood of mice treated with BIPM or MEPM (control 2.85 ± 0.85 log(10) CFU/ml) (P < 0.05). Histopathological examination of lung specimens indicated that BIPM and MEPM prevent the progression of lung inflammation, including alveolar neutrophil infiltration and hemorrhage. The % time above MIC for BIPM and MEPM was 15.4% and 18.3% in plasma and 19.8% and 19.8% in lungs, respectively. These results show that BIPM and MEPM significantly prolongs survival and reduces the number of viable bacteria in a murine model of VAP caused by P. aeruginosa. Therefore, BIPM might be a potent and effective treatment for VAP caused by this bacterium.

A retrospective observational study on the efficacy of colistin by inhalation as compared to parenteral administration for the treatment of nosocomial pneumonia associated with multidrug-resistant Pseudomonas aeruginosa

Background

Colistin is used as last treatment option for pneumonia associated with multidrug-resistant (MDR) Pseudomonas spp.. Literature about the best administration mode (inhalation versus parenteral treatment) is lacking.

Methods

A retrospective study of 20 intensive care patients with a pneumonia associated with MDR P. aeruginosa receiving colistin sulphomethate sodium (Colistineb^®) between 2007 and 2009 was performed. A strain was considered multidrug-resistant if it was resistant to at least 6 of the following antibiotics: piperacillin-tazobactam, ceftazidime, cefepime, meropenem, aztreonam, ciprofloxacin, and amikacin. The administration mode, predicted mortality based on the SAPS3 score, SOFA score at onset of the colistin treatment, clinical and microbiological response, and mortality during the episode of the infection were analysed. The non parametric Kruskal-Wallis and Fisher's Exact test were used for statistical analysis of respectively the predicted mortality/SOFA score and mortality rate.

Results

Six patients received colistin by inhalation only, 5 were treated only parenterally, and 9 by a combination of both administration modes. All patients received concomitant beta-lactam therapy. The mean predicted mortalities were respectively 72%, 68%, and 69% (p = 0.91). SOFA scores at the onset of the treatment were also comparable (p = 0.87). Clinical response was favorable in all patients receiving colistin by inhalation (6/6) and in 40% (2/5) of the patients receiving colistin parenterally (p = 0.06). In the patients with colistin administered both via inhalation and parenterally, clinical response was favorable in 78% of the patients (7/9) (p = 0.27 as compared to the treatment group receiving colistin only parenterally). When all patients with inhalation therapy were compared to the group without inhalation therapy, a favorable clinical response was present in respectively 87% and 40% (p = 0.06). In none of the patients, the Pseudomonas spp. was eradicated from the follow-up cultures.

All patients in the parenterally treated group died. None of the patients receiving colistin by inhalation, and 3 of 9 patients of the combination group eventually died (p = 0.002 and p = 0.03 respectively as compared to the group receiving colistin only parenterally).

Conclusions

Aerosolized colistin could be beneficial as adjunctive treatment for the management of pneumonia due to MDR P. aeruginosa.

Pneumonia due to Pseudomonas aeruginosa: part II: antimicrobial resistance, pharmacodynamic concepts, and antibiotic therapy

Pseudomonas aeruginosa carries a notably higher mortality rate than other pneumonia pathogens. Because of its multiple mechanisms of antibiotic resistance, therapy has always been challenging. This problem has been magnified in recent years with the emergence of multidrug-resistant (MDR) pathogens often unharmed by almost all classes of antimicrobials. The objective of this article is to assess optimal antimicrobial therapy based on in vitro activity, animal studies, and pharmacokinetic/pharmacodynamic (PK/PD) observations so that evidence-based recommendations can be developed to maximize favorable clinical outcomes. Mechanisms of antimicrobial resistance of P aeruginosa are reviewed. A selective literature review of laboratory studies, PK/PD concepts, and controlled clinical trials of antibiotic therapy directed at P aeruginosa pneumonia was performed. P aeruginosa possesses multiple mechanisms for inducing antibiotic resistance to antimicrobial agents. Continuous infusion of antipseudomonal β-lactam antibiotics enhances bacterial killing. Although the advantages of combination therapy remain contentious, in vitro and animal model studies plus selected meta-analyses of clinical trials support its use, especially in the era of MDR. Colistin use and the role of antibiotic aerosolization are reviewed. An evidence-based algorithmic approach based on severity of illness, Clinical Pulmonary Infection Score, and combination antibiotic therapy is presented; clinical outcomes may be improved, and the emergence of MDR pathogens should be minimized with this approach.

Multi-Functional Characteristics of the Pseudomonas aeruginosa Type III Needle-Tip Protein, PcrV; Comparison to Orthologs in other Gram-negative Bacteria

Pseudomonas aeruginosa possesses a type III secretion system (T3SS) to intoxicate host cells and evade innate immunity. This virulence-related machinery consists of a molecular syringe and needle assembled on the bacterial surface, which allows delivery of T3 effector proteins into infected cells. To accomplish a one-step effector translocation, a tip protein is required at the top end of the T3 needle structure. Strains lacking expression of the functional tip protein fail to intoxicate host cells. P. aeruginosa encodes a T3S that is highly homologous to the proteins encoded by Yersinia spp. The needle-tip proteins of Yersinia, LcrV, and P. aeruginosa, PcrV, share 37% identity and 65% similarity. Other known tip proteins are AcrV (Aeromonas), IpaD (Shigella), SipD (Salmonella), BipD (Burkholderia), EspA (EPEC, EHEC), Bsp22 (Bordetella), with additional proteins identified from various Gram-negative species, such as Vibrio and Bordetella. The tip proteins can serve as a protective antigen or may be critical for sensing host cells and evading innate immune responses. Recognition of the host microenvironment transcriptionally activates synthesis of T3SS components. The machinery appears to be mechanically controlled by the assemblage of specific junctions within the apparatus. These junctions include the tip and base of the T3 apparatus, the needle proteins and components within the bacterial cytoplasm. The tip proteins likely have chaperone functions for translocon proteins, allowing the proper assembly of translocation channels in the host membrane and completing vectorial delivery of effector proteins into the host cytoplasm. Multi-functional features of the needle-tip proteins appear to be intricately controlled. In this review, we highlight the functional aspects and complex controls of T3 needle-tip proteins with particular emphasis on PcrV and LcrV.

Pharmacokinetics and safety of panobacumab: specific adjunctive immunotherapy in critical patients with nosocomial Pseudomonas aeruginosa O11 pneumonia

OBJECTIVES

Nosocomial Pseudomonas aeruginosa pneumonia remains a major concern in critically ill patients. We explored the potential impact of microorganism-targeted adjunctive immunotherapy in such patients.

PATIENTS AND METHODS

This multicentre, open pilot Phase 2a clinical trial (NCT00851435) prospectively evaluated the safety, pharmacokinetics and potential efficacy of three doses of 1.2 mg/kg panobacumab, a fully human monoclonal anti-lipopolysaccharide IgM, given every 72 h in 18 patients developing nosocomial P. aeruginosa (serotype O11) pneumonia.

RESULTS

Seventeen out of 18 patients were included in the pharmacokinetic analysis. In 13 patients receiving three doses, the maximal concentration after the third infusion was 33.9 ± 8.0 μg/mL, total area under the serum concentration-time curve was 5397 ± 1993 μg h/mL and elimination half-life was 102.3 ± 47.8 h. Panobacumab was well tolerated, induced no immunogenicity and was detected in respiratory samples. In contrast to Acute Physiology and Chronic Health Evaluation II (APACHE II) prediction, all 13 patients receiving three doses survived, with a mean clinical resolution in 9.0 ± 2.7 days. Two patients suffered a recurrence at days 17 and 20.

CONCLUSIONS

These data suggest that panobacumab is safe, with a pharmacokinetic profile similar to that in healthy volunteers. It was associated with high clinical cure and survival rates in patients developing nosocomial P. aeruginosa O11 pneumonia. We concluded that these promising results warrant further trials.