Nosocomial pneumonia: epidemiology, pathogenesis, diagnosis, treatment and prevention

Novel dual regulators of Pseudomonas aeruginosa essential for productive biofilms and virulence

Gene regulation network in Pseudomonas aeruginosa is complex. With a relatively large genome (6.2 Mb), there is a significant portion of genes that are proven or predicted to be transcriptional regulators. Many of these regulators have been shown to play important roles in biofilm formation and maintenance. In this study, we present a novel transcriptional regulator, PA1226, which modulates biofilm formation and virulence in P. aeruginosa. Mutation in the gene encoding this regulator abolished the ability of P. aeruginosa to produce biofilms in vitro, without any effect on the planktonic growth. This regulator is also essential for the in vivo fitness and pathogenesis in both Drosophila melanogaster and BALB/c mouse lung infection models. Transcriptome analysis revealed that PA1226 regulates many essential virulence genes/pathways, including those involved in alginate, pili, and LPS biosynthesis. Genes/operons directly regulated by PA1226 and potential binding sequences were identified via ChIP-seq. Attempts to confirm the binding sequences by electrophoretic mobility shift assay led to the discovery of a co-regulator, PA1413, via co-immunoprecipitation assay. PA1226 and PA1413 were shown to bind collaboratively to the promoter regions of their regulons. A model is proposed, summarizing our finding on this novel dual-regulation system.

A realist analysis of hospital patient safety in Wales: applied learning for alternative contexts from a multisite case study

Background

Hospital patient safety is a major social problem. In the UK, policy responses focus on the introduction of improvement programmes that seek to implement evidence-based clinical practices using the Model for Improvement, Plan-Do-Study-Act cycle. Empirical evidence that the outcomes of such programmes vary across hospitals demonstrates that the context of their implementation matters. However, the relationships between features of context and the implementation of safety programmes are both undertheorised and poorly understood in empirical terms.

Objectives

This study is designed to address gaps in conceptual, methodological and empirical knowledge about the influence of context on the local implementation of patient safety programmes.

Design

We used concepts from critical realism and institutional analysis to conduct a qualitative comparative-intensive case study involving 21 hospitals across all seven Welsh health boards. We focused on the local implementation of three focal interventions from the 1000 Lives+patient safety programme: Improving Leadership for Quality Improvement, Reducing Surgical Complications and Reducing Health-care Associated Infection. Our main sources of data were 160 semistructured interviews, observation and 1700 health policy and organisational documents. These data were analysed using the realist approaches of abstraction, abduction and retroduction.

Setting

Welsh Government and NHS Wales.

Participants

Interviews were conducted with 160 participants including government policy leads, health managers and professionals, partner agencies with strategic oversight of patient safety, advocacy groups and academics with expertise in patient safety.

Main outcome measures

Identification of the contextual factors pertinent to the local implementation of the 1000 Lives+patient safety programme in Welsh NHS hospitals.

Results

An innovative conceptual framework harnessing realist social theory and institutional theory was produced to address challenges identified within previous applications of realist inquiry in patient safety research. This involved the development and use of an explanatory intervention–context–mechanism–agency–outcome (I-CMAO) configuration to illustrate the processes behind implementation of a change programme. Our findings, illustrated by multiple nested I-CMAO configurations, show how local implementation of patient safety interventions are impacted and modified by particular aspects of context: specifically, isomorphism, by which an intervention becomes adapted to the environment in which it is implemented; institutional logics, the beliefs and values underpinning the intervention and its source, and their perceived legitimacy among different groups of health-care professionals; and the relational structure and power dynamics of the functional group, that is, those tasked with implementing the initiative. This dynamic interplay shapes and guides actions leading to the normalisation or the rejection of the patient safety programme.

Conclusions

Heightened awareness of the influence of context on the local implementation of patient safety programmes is required to inform the design of such interventions and to ensure their effective implementation and operationalisation in the day-to-day practice of health-care teams. Future work is required to elaborate our conceptual model and findings in similar settings where different interventions are introduced, and in different settings where similar innovations are implemented.

Funding

The National Institute for Health Research Health Services and Delivery Research programme.

Magnetic fields suppress Pseudomonas aeruginosa biofilms and enhance ciprofloxacin activity

Due to the refractory nature of pathogenic microbial biofilms, innovative biofilm eradication strategies are constantly being sought. Thus, this study addresses a novel approach to eradicate Pseudomonas aeruginosa biofilms. Magnetic nanoparticles (MNP), ciprofloxacin (Cipro), and magnetic fields were systematically evaluated in vitro for their relative anti-biofilm contributions. Twenty-four-hour biofilms exposed to aerosolized MNPs, Cipro, or a combination of both, were assessed in the presence or absence of magnetic fields (Static one-sided, Static switched, Oscillating, Static + oscillating) using changes in bacterial metabolism, biofilm biomass, and biofilm imaging. The biofilms exposed to magnetic fields alone exhibited significant metabolic and biomass reductions (p < 0.05). When biofilms were treated with a MNP/Cipro combination, the most significant metabolic and biomass reductions were observed when exposed to static switched magnetic fields (p < 0.05). The exposure of P. aeruginosa biofilms to a static switched magnetic field alone, or co-administration with MNP/Cipro/MNP + Cipro appears to be a promising approach to eradicate biofilms of this bacterium.

Blocking phosphatidylcholine utilization in Pseudomonas aeruginosa, via mutagenesis of fatty acid, glycerol and choline degradation pathways, confirms the importance of this nutrient source in vivo

Pseudomonas aeruginosa can grow to very high-cell-density (HCD) during infection of the cystic fibrosis (CF) lung. Phosphatidylcholine (PC), the major component of lung surfactant, has been hypothesized to support HCD growth of P. aeruginosa in vivo. The phosphorylcholine headgroup, a glycerol molecule, and two long-chain fatty acids (FAs) are released by enzymatic cleavage of PC by bacterial phospholipase C and lipases. Three different bacterial pathways, the choline, glycerol, and fatty acid degradation pathways, are then involved in the degradation of these PC components. Here, we identified five potential FA degradation (Fad) related fadBA-operons (fadBA1-5, each encoding 3-hydroxyacyl-CoA dehydrogenase and acyl-CoA thiolase). Through mutagenesis and growth analyses, we showed that three (fadBA145) of the five fadBA-operons are dominant in medium-chain and long-chain Fad. The triple fadBA145 mutant also showed reduced ability to degrade PC in vitro. We have previously shown that by partially blocking Fad, via mutagenesis of fadBA5 and fadDs, we could significantly reduce the ability of P. aeruginosa to replicate on FA and PC in vitro, as well as in the mouse lung. However, no studies have assessed the ability of mutants, defective in choline and/or glycerol degradation in conjunction with Fad, to grow on PC or in vivo. Hence, we constructed additional mutants (ΔfadBA145ΔglpD, ΔfadBA145ΔbetAB, and ΔfadBA145ΔbetABΔglpD) significantly defective in the ability to degrade FA, choline, and glycerol and, therefore, PC. The analysis of these mutants in the BALB/c mouse lung infection model showed significant inability to utilize PC in vitro, resulted in decreased replication fitness and competitiveness in vivo compared to the complement strain, although there was little to no variation in typical virulence factor production (e.g., hemolysin, lipase, and protease levels). This further supports the hypothesis that lung surfactant PC serves as an important nutrient for P. aeruginosa during CF lung infection.

Midkine is expressed and differentially processed during chronic obstructive pulmonary disease exacerbations and ventilator-associated pneumonia associated with Staphylococcus aureus infection

Staphylococcus aureus is sometimes isolated from the airways during acute exacerbations of chronic obstructive pulmonary disease (COPD) but more commonly recognized as a cause of ventilator-associated pneumonia (VAP). Antimicrobial proteins, among them midkine (MK), are an important part of innate immunity in the airways. In this study, the levels and possible processing of MK in relation to S. aureus infection of the airways were investigated, comparing COPD and VAP, thus comparing a state of disease with preceding chronic inflammation and remodeling (COPD) with acute inflammation (that is, VAP). MK was detected in the small airways and alveoli of COPD lung tissue but less so in normal lung tissue. MK at below micromolar concentrations killed S. aureus in vitro. Proteolytic processing of MK by the staphylococcal metalloprotease aureolysin (AL), but not cysteine protease staphopain A (SA), resulted in impaired bactericidal activity. Degradation was seen foremost in the COOH-terminal portion of the molecule that harbors high bactericidal activity. In addition, MK was detected in sputum from patients suffering from VAP caused by S. aureus but less so in sputum from COPD exacerbations associated with the same bacterium. Recombinant MK was degraded more rapidly in sputum from the COPD patients than from the VAP patients and a greater proteolytic activity in COPD sputum was confirmed by zymography. Taken together, proteases of both bacteria and the host contribute to degradation of the antibacterial protein MK, resulting in an impaired defense of the airways, in particular, in COPD where the state of chronic inflammation could be of importance.

Alcohol-based hand rub and ventilator-associated pneumonia after elective neurosurgery: An interventional study

Background:

Interventional studies on the effect of alcohol-based hand rub on ventilator-associated pneumonia (VAP) among neurosurgical patients are scarce.

Aim:

To observe the effect of alcohol-based hand rub on tracheobronchial colonization and VAP after elective neurosurgical procedures.

Materials and Methods:

An interventional study using a “before–after” design in a tertiary care center in Kerala. Two 9-month study periods were compared; between these periods, an infection control protocol incorporating an alcohol-based hand rub was implemented for a period of 3 months and continued thereafter. Consecutive patients who required mechanical ventilation after neurosurgery between January and September 2006 and 2007, respectively, were included. Outcome measures included VAP rate, tracheobronchial colonization rate, profile of microorganisms and patient survival.

Results:

A total of 352 patients were on mechanical ventilator for a varying period of 1–125 days. The patients in the control and intervention groups were similar with regard to sex, age and type of neurosurgery. Tracheobronchial colonization was seen in 86 (48.6%) of 177 in the control group and 73 (41.7%) of 175 among the intervention group (P = 0.195). The VAP rates in the control and intervention groups were 14.03 and 6.48 per 1000 ventilator days (P = 0.08). The predominant organisms causing VAP and tracheobronchial colonization were Klebsiella and Pseudomonas aeruginosa, respectively, in both groups. Patient survival rates were 87.6% (control) and 92% (intervention).

Conclusion:

Clinical results indicated a better outcome, showing a reduction in tracheobronchial colonization rate and VAP rate, although this was not statistically significant.

Multiple FadD acyl-CoA synthetases contribute to differential fatty acid degradation and virulence in Pseudomonas aeruginosa

A close interconnection between nutrient metabolism and virulence factor expression contributes to the pathophysiology of Pseudomonas aeruginosa as a successful pathogen. P. aeruginosa fatty acid (FA) degradation is complicated with multiple acyl-CoA synthetase homologs (FadDs) expressed in vivo in lung tissue during cystic fibrosis infections. The promoters of two genetically linked P. aeruginosa fadD genes (fadD1 and fadD2) were mapped and northern blot analysis indicated they could exist on two different transcripts. These FadDs contain ATP/AMP signature and FA-binding motifs highly homologous to those of the Escherichia coli FadD. Upon introduction into an E. coli fadD^-/fadR^- double mutant, both P. aeruginosa fadDs functionally complemented the E. coli fadD^-/fadR^- mutant, allowing degradation of different chain-length FAs. Chromosomal mutagenesis, growth analysis, induction studies, and determination of kinetic parameters suggested that FadD1 has a substrate preference for long-chain FAs while FadD2 prefers shorter-chain FAs. When compared to the wild type strain, the fadD2 mutant exhibited decreased production of lipase, protease, rhamnolipid and phospholipase, and retardation of both swimming and swarming motilities. Interestingly, fadD1 mutant showed only increased swarming motility. Growth analysis of the fadD mutants showed noticeable deficiencies in utilizing FAs and phosphatidylcholine (major components of lung surfactant) as the sole carbon source. This defect translated into decreased in vivo fitness of P. aeruginosa in a BALB/c mouse lung infection model, supporting the role of lipids as a significant nutrient source for this bacterium in vivo.

Hospital-acquired pneumonia: pathophysiology, diagnosis, and treatment

Hospital-acquired pneumonia (HAP) is one of the most common causes of nosocomial infection, morbidity, and mortality in hospitalized patients. Many patient- and disease-specific factors contribute to the pathophysiology of HAP, particularly in the surgical population. Risk-factor modification and inpatient prevention strategies can have a significant impact on the incidence of HAP. While the best diagnostic strategy remains a subject of some debate, prompt and appropriate antimicrobial therapy in patients suspected of having HAP has been shown to significantly decrease mortality. Because the pathogens responsible for HAP are frequently more virulent and have greater resistance to commonly used antimicrobials than other pathogens, clinicians must have knowledge of the resistance patterns at their institutions to choose appropriate therapy.

The long-chain fatty acid sensor, PsrA, modulates the expression of rpoS and the type III secretion exsCEBA operon in Pseudomonas aeruginosa

The Pseudomonas aeruginosa PsrA autorepressor has dual roles as a repressor of the fadBA5beta-oxidation operon and an activator of the stationary-phase sigma factor rpoS and exsCEBA operon of the type III secretion system (TTSS). Previously, we demonstrated that the repression of the fadBA5 operon by PsrA is relieved by long-chain fatty acids (LCFAs). However, the signal affecting the activation of rpoS and exsC via PsrA is unknown. In this study, microarray and gene fusion data suggested that LCFA (e.g. oleate) affected the expression of rpoS and exsC. DNA binding studies confirmed that PsrA binds to the rpoS and exsC promoter regions. This binding was inhibited by LCFA, indicating that LCFA directly affects the activation of these two genes through PsrA. LCFA decreased rpoS and exsC expression, resulting in increased N-(butyryl)-l-homoserine-lactone quorum sensing signal and decreased ExoS/T production respectively. Based on the crystal structure of PsrA, site-directed mutagenesis of amino acid residues, within the hydrophobic channel thought to accommodate LCFA, created two LCFA-non-responsive PsrA mutants. The binding and activation of rpoS and exsC by these PsrA mutants was no longer inhibited by LCFA. These data support a mechanistic model where LCFAs influence PsrA regulation to control LCFA metabolism and some virulence genes in P. aeruginosa.

The Pseudomonas aeruginosa PsrA responds to long-chain fatty acid signals to regulate the fadBA5 beta-oxidation operon

Beta-oxidative enzymes for fatty acid degradation (Fad) of long-chain fatty acids (LCFAs) are induced in vivo during lung infection in cystic fibrosis patients, and this may contribute to nutrient acquisition and pathogenesis of Pseudomonas aeruginosa. The promoter region of one P. aeruginosa beta-oxidation operon, fadBA5 (PA3014 and PA3013), was mapped. Focusing on the transposon mutagenesis of strain PAO1 carrying the P(fadBA5)-lacZ fusion, a regulator for the fadBA5 operon was identified to be PsrA (PA3006). Transcriptome analysis of the DeltapsrA mutant indicated its importance in regulating beta-oxidative enzymes. These microarray data were confirmed by real-time RT-PCR analyses of the fadB5 and lipA (encoding a lipase) genes. Induction of the fadBA5 operon was demonstrated to respond to novel LCFA signals, and this induction required the presence of PsrA, suggesting that LCFAs bind to PsrA to derepress fadBA5. Electrophoretic mobility shift assays indicate specific binding of PsrA to the fadBA5 promoter region. This binding is disrupted by specific LCFAs (C(18:1)(Delta9), C(16:0), C(14:0) and, to a lesser extent, C(12:0)), but not by other medium- or short-chain fatty acids or the first intermediate of beta-oxidation, acyl-CoA. It is shown here that PsrA is a fadBA5 regulator that binds and responds to LCFA signals in P. aeruginosa.

Nurses’ Implementation of Guidelines for Ventilator-Associated Pneumonia From the Centers for Disease Control and Prevention

• Background Ventilator-associated pneumonia accounts for 47% of infections in patients in intensive care units. Adherence to the best nursing practices recommended in the 2003 guidelines for the prevention of ventilator-associated pneumonia from the Centers for Disease Control and Prevention should reduce the risk of ventilator-associated pneumonia.

• Objective To evaluate the extent to which nurses working in intensive care units implement best practices when managing adult patients receiving mechanical ventilation.

• Methods Nurses attending education seminars in the United States completed a 29-item questionnaire about the type and frequency of care provided.

• Results Twelve hundred nurses completed the questionnaire. Most (82%) reported compliance with hand-washing guidelines, 75% reported wearing gloves, half reported elevating the head of the bed, a third reported performing subglottic suctioning, and half reported having an oral care protocol in their hospital. Nurses in hospitals with an oral care protocol reported better compliance with hand washing and maintaining head-of-bed elevation, were more likely to regularly provide oral care, and were more familiar with rates of ventilator-associated pneumonia and the organisms involved than were nurses working in hospitals without such protocols.

• Conclusions The guidelines for the prevention of ventilator-associated pneumonia from the Centers for Disease Control and Prevention are not consistently or uniformly implemented. Practices of nurses employed in hospitals with oral care protocols are more often congruent with the guidelines than are practices of nurses employed in hospitals without such protocols. Significant reductions in rates of ventilator-associated pneumonia may be achieved by broader implementation of oral care protocols.

Prevalência e prognóstico dos pacientes com pneumonia associada à ventilação mecânica em um hospital universitário

OBJETIVO: Determinar prevalência de pneumonia associada à ventilação mecânica em unidade de terapia intensiva, fatores associados e evolução. MÉTODOS: Foram avaliados 278 pacientes sob ventilação mecânica por mais de 24 horas prospectivamente em hospital universitário. RESULTADOS: Desenvolveram a doença 38,1% dos pacientes, 35,7 casos/1.000 dias de ventilação mecânica: 45,3% por bacilos gram negativos, Pseudomonas aeruginosa (22%) o mais comum e 43,4% por germes multi-resistentes. O grupo com pneumonia associada à ventilação mecânica teve maiores tempos de ventilação mecânica, desmame, permanência no hospital e na unidade de terapia intensiva (p < 0,001); atelectasia, síndrome do desconforto respiratório agudo, pneumotórax, sinusite, traqueobronquite e infecção multirresistente foram mais comuns (p < 0,05). Letalidades na unidade de terapia intensiva e no hospital foram semelhantes. Fatores associados à doença (razão de chances; intervalo de confiança 95%): sinusite aguda (38,8; 3,4 - 441), ventilação mecânica >10 dias (7,7; 4,1 - 14,2), imunodepressão (4,3; 1,3 - 14,3), síndrome do desconforto respiratório agudo (3,5; 1,4 - 9,0), atelectasia (3,0; 1,2 - 7,3), parada cardiorrespiratória (0,18; 0,05 - 0,66) e hemorragia digestiva alta (0,07; 0,009 - 0,62]. Fatores associados ao óbito hospitalar: insuficiência renal crônica (26,1; 1,9 - 350,7), admissão prévia na unidade de terapia intensiva (15,6; 1,6 - 152,0), simplified acute physiologic score II > 50 pontos (11,9; 3,4 - 42,0) e idade > 55 anos (4,4; 1,6 - 12,3). CONCLUSÃO: A pneumonia associada à ventilação mecânica aumentou tempos de ventilação mecânica, permanência na unidade de terapia intensiva e no hospital, número de complicações, mas não a letalidade.

Bench-to-bedside review: Therapeutic options and issues in the management of ventilator-associated bacterial pneumonia

Despite progress in the diagnosis, prevention and therapy for hospital-acquired infections, ventilator-associated pneumonia (VAP) continues to complicate the course of a significant proportion of patients receiving mechanical ventilation. Mortality rates among patients with VAP have been reported to be as high as 72%, and the morbidity associated with VAP is also considerable, adding days to the hospital stay and increasing health care costs. Appropriate initial antimicrobial therapy for patients with VAP has been shown to reduce mortality rates and improve outcomes; therefore, rapid identification of infected patients and timely, accurate selection of effective antimicrobial agents are important clinical goals. The primary organisms responsible for VAP include Enterobacteriaceae, Pseudomonas aeruginosa and Staphylococcus aureus. However, aetiologies differ considerably between intensive care units, and the increase in antibiotic resistance and nosocomial outbreaks worldwide have presented clinicians with a serious dilemma with respect to selecting appropriate empirical therapy. To date, no optimal antimicrobial regimen for the treatment of VAP has been identified, largely because none of the currently marketed antibiotics has a sufficiently extended spectrum of activity to cover all of the potential key pathogens. More active, less toxic antibacterial agents are still needed, in particular to combat problematic pathogens such as multiresistant Gram-negative bacilli and resistant Gram-positive organisms (e.g. methicillin-resistant S aureus).

Nosocomial Pneumonia

Nosocomial pneumonia (NP) is defined as pneumonia that develops within 48 hours or more of hospital admission and which was not developing at the time of admission. Nosocomial pneumonia, also known as hospital-acquired pneumonia (HAP), is the second most common hospital infection, while ventilator-associated pneumonia represents the most common intensive care unit (ICU) infection. Nosocomial pneumonia significantly contributes to morbidity, mortality, and escalating healthcare costs because of increases in antibiotic prescription and administration, length of ICU stay, and length of hospital stay. Aspiration and colonization of the upper respiratory tract seem to be the major pathogenetic mechanisms for the development of NP, either in intubated or spontaneously breathing patients. The microbiology of NP depends on the timing of onset. In early-onset NP, the responsible pathogens are generally endogenous community-acquired pathogens. In late-onset NP, the responsible microbes include potentially multi-drug-resistant nosocomial organisms residing in oropharyngeal or gastric contents. Important risk factors for development of NP include coma, intubation, prolonged mechanical ventilation, repeated intubations, supine positioning, and long-term antibiotic use. The most significant preventive measures include routine hand washing and avoidance of (1) the supine position, (2) inappropriate antibiotics, and (3) overuse of H2-antagonists for stress ulcer prophylaxis. Accurate diagnosis of NP is difficult and controversial, warranting consideration for the application of invasive quantitative culture techniques over tracheal aspirates. Empiric antibiotic treatment should be prompt, starting on clinical suspicion, and based on local ICU pathogen epidemiology and antibiotic resistance patterns and on a deescalating antibiotic strategy. Innovative antibiotic strategies, such as antibiotic rotation, to help prevent the emergence of multi-drug-resistant pathogens and improve survival should be considered.

Changes in genetic types and population dynamics of Moraxella catarrhalis in hospitalized children are not associated with an exacerbation of existing disease

Pulsed-field gel electrophoresis typing was performed on a retrospective set of 129 Moraxella catarrhalis isolates obtained over a 20 month period from 70 children admitted to, or presenting at, the Erasmus University Medical Center, Rotterdam, The Netherlands. The mean age of the children (at the end of the study) was 2.5 years, with a range of 6 months to 15 years. Fifty-one different M. catarrhalis types were isolated from the hospitalized children, with 31 % (22/70) being infected with two particularly prevalent M. catarrhalis types. These two prevalent types also exhibited different protein profiles. The majority (72%; 16/22) of the children infected with these two predominant types had spent at least 1 week on two paediatric intensive care wards. No exacerbation of existing disease or new disease was observed in children who experienced M. catarrhalis type changes.