Morbidity associated with Pseudomonas aeruginosa bloodstream infections

Pseudomonas aeruginosa population dynamics in a vancomycin-induced murine model of gastrointestinal carriage

Pseudomonas aeruginosa is a common nosocomial pathogen and a major cause of morbidity and mortality in hospitalized patients. Multiple reports highlight that P. aeruginosa gastrointestinal colonization may precede systemic infections by this pathogen. Gaining a deeper insight into the dynamics of P. aeruginosa gastrointestinal carriage is an essential step in managing gastrointestinal colonization and could contribute to preventing bacterial transmission and progression to systemic infection. Here, we present a clinically relevant mouse model relying on parenteral vancomycin pretreatment and a single orogastric gavage of a controlled dose of P. aeruginosa. Robust carriage was observed with multiple clinical isolates, and carriage persisted for up to 60 days. Histological and microbiological examination of mice indicated that this model indeed represented carriage and not infection. We then used a barcoded P. aeruginosa library along with the sequence tag-based analysis of microbial populations (STAMPR) analytic pipeline to quantify bacterial population dynamics and bottlenecks during the establishment of the gastrointestinal carriage. Analysis indicated that most of the P. aeruginosa population was rapidly eliminated in the stomach, but the few bacteria that moved to the small intestine and the cecum expanded rapidly. Hence, the stomach constitutes a significant barrier against gastrointestinal carriage of P. aeruginosa, which may have clinical implications for hospitalized patients.

IMPORTANCE

While Pseudomonas aeruginosa is rarely part of the normal human microbiome, carriage of the bacterium is quite frequent in hospitalized patients and residents of long-term care facilities. P. aeruginosa carriage is a precursor to infection. Options for treating infections caused by difficult-to-treat P. aeruginosa strains are dwindling, underscoring the urgency to better understand and impede pre-infection stages, such as colonization. Here, we use vancomycin-treated mice to model antibiotic-treated patients who become colonized with P. aeruginosa in their gastrointestinal tracts. We identify the stomach as a major barrier to the establishment of gastrointestinal carriage. These findings suggest that efforts to prevent gastrointestinal colonization should focus not only on judicious use of antibiotics but also on investigation into how the stomach eliminates orally ingested P. aeruginosa.

Pseudomonas aeruginosa population dynamics in a vancomycin-induced murine model of gastrointestinal carriage

Pseudomonas aeruginosa is a common nosocomial pathogen and a major cause of morbidity and mortality in hospitalized patients. Multiple reports highlight that P. aeruginosa gastrointestinal colonization may precede systemic infections by this pathogen. Gaining a deeper insight into the dynamics of P. aeruginosa gastrointestinal carriage is an essential step in managing gastrointestinal colonization and could contribute to preventing bacterial transmission and progression to systemic infection. Here, we present a clinically relevant mouse model relying on parenteral vancomycin pretreatment and a single orogastric gavage of a controlled dose of P. aeruginosa. Robust carriage was observed with multiple clinical isolates, and carriage persisted for up to 60 days. Histological and microbiological examination of mice indicated that this model indeed represented carriage and not infection. We then used a barcoded P. aeruginosa library along with the sequence tag-based analysis of microbial populations (STAMPR) analytic pipeline to quantify bacterial population dynamics and bottlenecks during the establishment of the gastrointestinal carriage. Analysis indicated that most of the P. aeruginosa population was rapidly eliminated in the stomach, but the few bacteria that moved to the small intestine and the caecum expanded significantly. Hence, the stomach constitutes a significant barrier against gastrointestinal carriage of P. aeruginosa, which may have clinical implications for hospitalized patients.

Cell-Based Assay to Determine Type 3 Secretion System Translocon Assembly in Pseudomonas aeruginosa Using Split Luciferase

Multi-drug-resistant Pseudomonas aeruginosa poses a serious threat to hospitalized patients. This organism expresses an arsenal of virulence factors that enables it to readily establish infections and disseminate in the host. The Type 3 secretion system (T3SS) and its associated effectors play a crucial role in the pathogenesis of P. aeruginosa, making them attractive targets for the development of novel therapeutic agents. The T3SS translocon, composed of PopD and PopB, is an essential component of the T3SS secretion apparatus. In the properly assembled translocon, the N-terminus of PopD protrudes into the cytoplasm of the target mammalian cell, which can be exploited as a molecular indicator of functional translocon assembly. In this article, we describe a novel whole-cell-based assay that employs the split NanoLuc luciferase detection system to provide a readout for translocon assembly. The assay demonstrates a favorable signal/noise ratio (13.6) and robustness (Z' = 0.67), making it highly suitable for high-throughput screening of small-molecule inhibitors targeting T3SS translocon assembly.

Crossroads of Antimicrobial and Diagnostic Stewardship: Assessing Risks to Develop Clinical Decision Support to Combat Multidrug-Resistant Pseudomonas

Background

Early detection of multidrug-resistant Pseudomonas aeruginosa (MDRP) remains challenging. Existing risk prediction tools are difficult to translate to bedside application. The goal of this study was to develop a simple electronic medical record (EMR)-integrated tool for prediction of MDRP infection.

Methods

This was a mixed-methods study. We conducted a split-sample cohort study of adult critical care patients with P aeruginosa infections. Two previously published tools were validated using c-statistic. A subset of variables based on strength of association and ease of EMR extraction was selected for further evaluation. A simplified tool was developed using multivariable logistic regression. Both c-statistic and theoretical trade-off of over- versus underprescribing of broad-spectrum MDRP therapy were assessed in the validation cohort. A qualitative survey of frontline clinicians assessed understanding of risks for MDRP and potential usability of an EMR-integrated tool to predict MDRP.

Results

The 2 previous risk prediction tools demonstrated similar accuracy in the derivation cohort (c-statistic of 0.76 [95% confidence interval {CI}, .69-.83] and 0.73 [95% CI, .66-.8]). A simplified tool based on 4 variables demonstrated reasonable accuracy (c-statistic of 0.71 [95% CI, .57-.85]) without significant overprescribing in the validation cohort. The risk factors were prior MDRP infection, ≥4 antibiotics prior to culture, infection >3 days after admission, and dialysis. Fourteen clinicians completed the survey. An alert providing context regarding individual patient risk factors for MDRP was preferred.

Conclusions

These results can be used to develop a local EMR-integrated tool to improve timeliness of effective therapy in those at risk of MDRP infections.

Phenotypic and genomic characterization of Pseudomonas aeruginosa isolates recovered from catheter-associated urinary tract infections in an Egyptian hospital

Catheter-associated urinary tract infections (CAUTIs) represent one of the major healthcare-associated infections, and Pseudomonas aeruginosa is a common Gram-negative bacterium associated with catheter infections in Egyptian clinical settings. The present study describes the phenotypic and genotypic characteristics of 31 P. aeruginosa isolates recovered from CAUTIs in an Egyptian hospital over a 3 month period. Genomes of isolates were of good quality and were confirmed to be P. aeruginosa by comparison to the type strain (average nucleotide identity, phylogenetic analysis). Clonal diversity among the isolates was determined; eight different sequence types were found (STs 244, 357, 381, 621, 773, 1430, 1667 and 3765), of which ST357 and ST773 are considered to be high-risk clones. Antimicrobial resistance (AMR) testing according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines showed that the isolates were highly resistant to quinolones [ciprofloxacin (12/31, 38.7 %) and levofloxacin (9/31, 29 %) followed by tobramycin (10/31, 32.5 %)] and cephalosporins (7/31, 22.5 %). Genotypic analysis of resistance determinants predicted all isolates to encode a range of AMR genes, including those conferring resistance to aminoglycosides, β-lactamases, fluoroquinolones, fosfomycin, sulfonamides, tetracyclines and chloramphenicol. One isolate was found to carry a 422 938 bp pBT2436-like megaplasmid encoding OXA-520, the first report from Egypt of this emerging family of clinically important mobile genetic elements. All isolates were able to form biofilms and were predicted to encode virulence genes associated with adherence, antimicrobial activity, anti-phagocytosis, phospholipase enzymes, iron uptake, proteases, secretion systems and toxins. The present study shows how phenotypic analysis alongside genomic analysis may help us understand the AMR and virulence profiles of P. aeruginosa contributing to CAUTIs in Egypt.

Functional Amyloids in Pseudomonas aeruginosa Are Essential for the Proteome Modulation That Leads to Pathoadaptation in Pulmonary Niches

Persistence and survival of Pseudomonas aeruginosa in chronic lung infections is closely linked to the biofilm lifestyle. One biofilm component, functional amyloid of P. aeruginosa (Fap), imparts structural adaptations for biofilms; however, the role of Fap in pathogenesis is still unclear. Conservation of the fap operon encoding Fap and P. aeruginosa being an opportunistic pathogen of lung infections prompted us to explore its role in lung infection. We found that Fap is essential for establishment of lung infection in rats, as its genetic exclusion led to mild focal infection with quick resolution. Moreover, without an underlying cystic fibrosis (CF) genetic disorder, overexpression of Fap reproduced the CF pathotype. The molecular basis of Fap-mediated pulmonary adaptation was explored through surface-associated proteomics in vitro. Differential proteomics positively associated Fap expression with activation of known proteins related to pulmonary pathoadaptation, attachment, and biofilm fitness. The aggregative bacterial phenotype in the pulmonary niche correlated with Fap-influenced activation of biofilm sustainability regulators and stress response regulators that favored persistence-mediated establishment of pulmonary infection. Fap overexpression upregulated proteins that are abundant in the proteome of P. aeruginosa in colonizing CF lungs. Planktonic lifestyle, defects in anaerobic pathway, and neutrophilic evasion were key factors in the absence of Fap that impaired establishment of infection. We concluded that Fap is essential for cellular equilibration to establish pulmonary infection. Amyloid-induced bacterial aggregation subverted the immune response, leading to chronic infection by collaterally damaging tissue and reinforcing bacterial persistence. IMPORTANCE Pseudomonas aeruginosa is inextricably linked with chronic lung infections. In this study, the well-conserved Fap operon was found to be essential for pathoadaptation in pulmonary infection in a rat lung model. Moreover, the presence of Fap increased pathogenesis and biofilm sustainability by modulating bacterial physiology. Hence, a pathoadaptive role of Fap in pulmonary infections can be exploited for clinical application by targeting amyloids. Furthermore, genetic conservation and extracellular exposure of Fap make it a commendable target for such interventions.

Pseudomonas aeruginosa Pneumonia: Evolution of Antimicrobial Resistance and Implications for Therapy

Pseudomonas aeruginosa (PA), a non-lactose-fermenting gram-negative bacillus, is a common cause of nosocomial infections in critically ill or debilitated patients, particularly ventilator-associated pneumonia (VAP), and infections of urinary tract, intra-abdominal, wounds, skin/soft tissue, and bloodstream. PA rarely affects healthy individuals, but may cause serious infections in patients with chronic structural lung disease, comorbidities, advanced age, impaired immune defenses, or with medical devices (e.g., urinary or intravascular catheters, foreign bodies). Treatment of pseudomonal infections is difficult, as PA is intrinsically resistant to multiple antimicrobials, and may acquire new resistance determinants even while on antimicrobial therapy. Mortality associated with pseudomonal VAP or bacteremias is high (> 35%) and optimal therapy is controversial. Over the past three decades, antimicrobial resistance (AMR) among PA has escalated globally, via dissemination of several international multidrug resistant "epidemic" clones. We discuss the importance of PA as a cause of pneumonia including health care-associated pneumonia, hospital-acquired pneumonia, VAP, the emergence of AMR to this pathogen, and approaches to therapy (both empirical and definitive).

Pseudomonas aeruginosa survives in epithelia by ExoS-mediated inhibition of autophagy and mTOR

One major factor that contributes to the virulence of Pseudomonas aeruginosa is its ability to reside and replicate unchallenged inside airway epithelial cells. The mechanism by which P. aeruginosa escapes destruction by intracellular host defense mechanisms, such as autophagy, is not known. Here, we show that the type III secretion system effector protein ExoS facilitates P. aeruginosa survival in airway epithelial cells by inhibiting autophagy in host cells. Autophagy inhibition is independent of mTOR activity, as the latter is also inhibited by ExoS, albeit by a different mechanism. Deficiency of the critical autophagy gene Atg7 in airway epithelial cells, both in vitro and in mouse models, greatly enhances the survival of ExoS-deficient P. aeruginosa but does not affect the survival of ExoS-containing bacteria. The inhibitory effect of ExoS on autophagy and mTOR depends on the activity of its ADP-ribosyltransferase domain. Inhibition of mTOR is caused by ExoS-mediated ADP ribosylation of RAS, whereas autophagy inhibition is due to the suppression of autophagic Vps34 kinase activity.

DNA alternate polymerase PolB mediates inhibition of type III secretion in Pseudomonas aeruginosa

Opportunistic pathogen Pseudomonas aeruginosa uses a variety of virulence factors to cause acute and chronic infections. We previously found that alternate DNA polymerase gene polB inhibits P. aeruginosa pyocyanin production. We investigated whether polB also affects T3SS expression. polB overexpression significantly reduced T3SS transcription and repressed translation of the master T3SS regulator ExsA, while not affecting exsA mRNA transcript abundance. Further, polB does not act through previously described genetic pathways that post-transcriptionally regulate ExsA. Our results show a novel T3SS regulatory component which may lead to development of future drugs to target this mechanism.

Static Growth Promotes PrrF and 2-Alkyl-4(1H)-Quinolone Regulation of Type VI Secretion Protein Expression in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that is frequently associated with both acute and chronic infections. P. aeruginosa possesses a complex regulatory network that modulates nutrient acquisition and virulence, but our knowledge of these networks is largely based on studies with shaking cultures, which are not likely representative of conditions during infection. Here, we provide proteomic, metabolic, and genetic evidence that regulation by iron, a critical metallonutrient, is altered in static P. aeruginosa cultures. Specifically, we observed a loss of iron-induced expression of proteins for oxidative phosphorylation, tricarboxylic acid (TCA) cycle metabolism under static conditions. Moreover, we identified type VI secretion as a target of iron regulation in P. aeruginosa cells under static but not shaking conditions, and we present evidence that this regulation occurs via PrrF small regulatory RNA (sRNA)-dependent production of 2-alkyl-4(1H)-quinolone metabolites. These results yield new iron regulation paradigms in an important opportunistic pathogen and highlight the need to redefine iron homeostasis in static microbial communities.IMPORTANCE Host-mediated iron starvation is a broadly conserved signal for microbial pathogens to upregulate expression of virulence traits required for successful infection. Historically, global iron regulatory studies in microorganisms have been conducted in shaking cultures to ensure culture homogeneity, yet these conditions are likely not reflective of growth during infection. Pseudomonas aeruginosa is a well-studied opportunistic pathogen and model organism for iron regulatory studies. Iron homeostasis is maintained through the Fur protein and PrrF small regulatory sRNAs, the functions of which are highly conserved in many other bacterial species. In the current study, we examined how static growth affects the known iron and PrrF regulons of P. aeruginosa, leading to the discovery of novel PrrF-regulated virulence processes. This study demonstrates how the utilization of distinct growth models can enhance our understanding of basic physiological processes that may also affect pathogenesis.

A Genome-Based Model to Predict the Virulence of Pseudomonas aeruginosa Isolates

Variation in the genome of Pseudomonas aeruginosa, an important pathogen, can have dramatic impacts on the bacterium's ability to cause disease. We therefore asked whether it was possible to predict the virulence of P. aeruginosa isolates based on their genomic content. We applied a machine learning approach to a genetically and phenotypically diverse collection of 115 clinical P. aeruginosa isolates using genomic information and corresponding virulence phenotypes in a mouse model of bacteremia. We defined the accessory genome of these isolates through the presence or absence of accessory genomic elements (AGEs), sequences present in some strains but not others. Machine learning models trained using AGEs were predictive of virulence, with a mean nested cross-validation accuracy of 75% using the random forest algorithm. However, individual AGEs did not have a large influence on the algorithm's performance, suggesting instead that virulence predictions are derived from a diffuse genomic signature. These results were validated with an independent test set of 25 P. aeruginosa isolates whose virulence was predicted with 72% accuracy. Machine learning models trained using core genome single-nucleotide variants and whole-genome k-mers also predicted virulence. Our findings are a proof of concept for the use of bacterial genomes to predict pathogenicity in P. aeruginosa and highlight the potential of this approach for predicting patient outcomes.IMPORTANCE Pseudomonas aeruginosa is a clinically important Gram-negative opportunistic pathogen. P. aeruginosa shows a large degree of genomic heterogeneity both through variation in sequences found throughout the species (core genome) and through the presence or absence of sequences in different isolates (accessory genome). P. aeruginosa isolates also differ markedly in their ability to cause disease. In this study, we used machine learning to predict the virulence level of P. aeruginosa isolates in a mouse bacteremia model based on genomic content. We show that both the accessory and core genomes are predictive of virulence. This study provides a machine learning framework to investigate relationships between bacterial genomes and complex phenotypes such as virulence.

A comparative genomics approach identifies contact-dependent growth inhibition as a virulence determinant

Emerging evidence suggests the Pseudomonas aeruginosa accessory genome is enriched with uncharacterized virulence genes. Identification and characterization of such genes may reveal novel pathogenic mechanisms used by particularly virulent isolates. Here, we utilized a mouse bacteremia model to quantify the virulence of 100 individual P. aeruginosa bloodstream isolates and performed whole-genome sequencing to identify accessory genomic elements correlated with increased bacterial virulence. From this work, we identified a specific contact-dependent growth inhibition (CDI) system enriched among highly virulent P. aeruginosa isolates. CDI systems contain a large exoprotein (CdiA) with a C-terminal toxin (CT) domain that can vary between different isolates within a species. Prior work has revealed that delivery of a CdiA-CT domain upon direct cell-to-cell contact can inhibit replication of a susceptible target bacterium. Aside from mediating interbacterial competition, we observed our virulence-associated CdiA-CT domain to promote toxicity against mammalian cells in culture and lethality during mouse bacteremia. Structural and functional studies revealed this CdiA-CT domain to have in vitro tRNase activity, and mutations that abrogated this tRNAse activity in vitro also attenuated virulence. Furthermore, CdiA contributed to virulence in mice even in the absence of contact-dependent signaling. Overall, our findings indicate that this P. aeruginosa CDI system functions as both an interbacterial inhibition system and a bacterial virulence factor against a mammalian host. These findings provide an impetus for continued studies into the complex role of CDI systems in P. aeruginosa pathogenesis.

Systemic infection facilitates transmission of Pseudomonas aeruginosa in mice

Health care-associated infections such as Pseudomonas aeruginosa bacteremia pose a major clinical risk for hospitalized patients. However, these systemic infections are presumed to be a "dead-end" for P. aeruginosa and to have no impact on transmission. Here, we use a mouse infection model to show that P. aeruginosa can spread from the bloodstream to the gallbladder, where it replicates to extremely high numbers. Bacteria in the gallbladder can then seed the intestines and feces, leading to transmission to uninfected cage-mate mice. Our work shows that the gallbladder is crucial for spread of P. aeruginosa from the bloodstream to the feces during bacteremia, a process that promotes transmission in this experimental system. Further research is needed to test to what extent these findings are relevant to infections in patients.

Long-term Persistence of an Extensively Drug-Resistant Subclade of Globally Distributed Pseudomonas aeruginosa Clonal Complex 446 in an Academic Medical Center

BACKGROUND

Antimicrobial resistance (AMR) is a major challenge in the treatment of infections caused by Pseudomonas aeruginosa. Highly drug-resistant infections are disproportionally caused by a small subset of globally distributed P. aeruginosa sequence types (STs), termed "high-risk clones." We noted that clonal complex (CC) 446 (which includes STs 298 and 446) isolates were repeatedly cultured at 1 medical center and asked whether this lineage might constitute an emerging high-risk clone.

METHODS

We searched P. aeruginosa genomes from collections available from several institutions and from a public database for the presence of CC446 isolates. We determined antibacterial susceptibility using microbroth dilution and examined genome sequences to characterize the population structure of CC446 and investigate the genetic basis of AMR.

RESULTS

CC446 was globally distributed over 5 continents. CC446 isolates demonstrated high rates of AMR, with 51.9% (28/54) being multidrug-resistant (MDR) and 53.6% of these (15/28) being extensively drug-resistant (XDR). Phylogenetic analysis revealed that most MDR/XDR isolates belonged to a subclade of ST298 (designated ST298*) of which 100% (21/21) were MDR and 61.9% (13/21) were XDR. XDR ST298* was identified repeatedly and consistently at a single academic medical center from 2001 through 2017. These isolates harbored a large plasmid that carries a novel antibiotic resistance integron.

CONCLUSIONS

CC446 isolates are globally distributed with multiple occurrences of high AMR. The subclade ST298* is responsible for a prolonged epidemic (≥16 years) of XDR infections at an academic medical center. These findings indicate that CC446 is an emerging high-risk clone deserving further surveillance.

Diversity of Contact-Dependent Growth Inhibition Systems of Pseudomonas aeruginosa

Contact-dependent growth inhibition (CDI) systems are used in bacterial competition to hinder the growth of neighboring microbes. These systems utilize a two-partner secretion mechanism to display the CdiA exoprotein at the bacterial cell surface. CdiA forms a long filamentous stalk that facilitates binding to a target cell and delivery of a C-terminal toxin (CT) domain. This CT domain is processed and delivered into the cytoplasm of a target cell upon contact. CDI systems also encode a cognate immunity protein (CdiI) that protects siblings and resistant targeted cells from intoxication by high-affinity binding to the CT. CdiA CT domains vary among strains within a species, and many alleles encode enzymatic functions that target nucleic acids. This variation is thought to help drive diversity and adaptation within a species. CdiA diversity is well studied in Escherichia coli and several other bacteria, but little is known about the extent of this diversity in Pseudomonas aeruginosa. The purpose of this review is to highlight the variability that exists in CDI systems of P. aeruginosa. We show that this diversity is apparent even among strains isolated from a single geographical region, suggesting that CDI systems play an important role in the ecology of P. aeruginosa.

Impact of Pseudomonas aeruginosa bacteraemia in a tertiary hospital: Mortality and prognostic factors

BACKGROUND AND OBJECTIVES

Pseudomonas aeruginosa bacteraemia is associated with a very high mortality, conditioned by comorbidity, source, severity of the episode and lack of adequate treatment. The aim of the study is to know the mortality and prognostic factors of bacteraemia by P.aeruginosa in our hospital.

PATIENTS AND METHODS

We conducted a retrospective study of P.aeruginosa bacteraemia detected between 2009 and 2014. Epidemiological, clinical and microbiological characteristics were described. A risk factor analysis for mortality was performed.

RESULTS

We analysed 110 episodes of bacteraemia, which was more frequent in men of advanced age and with a history of hospitalisation, comorbidity and immunosuppression. Most of the bacteraemias were secondary (mainly of respiratory or urinary source) and led to a significant clinical deterioration. The presence of antibiotic resistance was very high, with 27.3% of multiresistant strains. Empirical treatment was adequate in 60.0% and 92.3% for definite treatment. Overall mortality was 37.3% and attributable mortality was 29.1%. The most important prognostic factors were Charlson index ≥3, history of haematologic malignancy, neutropenia and previous use of corticosteroids, source of bacteraemia, Pitt index ≥4, renal insufficiency, adequate definite treatment, empiric treatment with piperacillin/tazobactam in severe episodes and focus control.

CONCLUSION

P.aeruginosa bacteraemia is associated with a very high mortality, possibly more related to previous comorbidity and severity of the episode than to the treatment chosen. However, the main goal in management remains to optimise treatment, including focus control.

Bloodstream infections in acute myeloid leukemia patients treated according to the Finnish Leukemia Group AML-2003 protocol - a prospective nationwide study

BACKGROUND

Infections greatly influence the outcome of acute myeloid leukemia (AML) patients receiving intensive treatment. The aim of this study was to establish the incidence, microbial etiology, risk factors and prognosis of bloodstream infections (BSIs) in patients with AML and compare the results with the previous treatment protocol (AML-92).

METHODS

Registery data were gathered prospectively from 357 patients aged 16-65 years recruited on the AML-2003 treatment protocol between November 2003 and November 2011 during different treatment cycles.

RESULTS

Blood culture data were available on 977 treatment episodes, in which there were 503 BSIs (51%). The overall incidence rate (IR) for BSIs (per 1000 hospital days) was 16.7. Twenty patients (5.6%) died due to an infection and 16 of them (80%) had a BSI. The most commonly detected microbes (polymicrobial episodes included) in blood cultures were coagulase-negative staphylococci (CoNS, 24.7%), viridans group streptococci (VGS, 19.1%), enterococci (13.9%) and Enterobacteriacae group (25.9%). The etiology of BSIs varied greatly from treatment cycle to cycle.

CONCLUSIONS

Enterococcal BSIs have increased compared to our previous treatment protocol, and they represent significant pathogens in blood cultures. Infection-related mortality has decreased despite the increase in the IR of BSIs. Enterococci seem to be an increasingly prominent pathogen underlying BSIs in the AML patients, especially during induction therapy (20%).

Pseudomonas aeruginosa Bacteremia among Immunocompetent and Immunocompromised Patients: Relation to Initial Antibiotic Therapy and Survival

Pseudomonas aeruginosa bacteremia occurs mainly in immunocompromised patients. However, P. aeruginosa bacteremia in immunocompetent patients has also been reported. The aim of this study was to evaluate the clinical characteristics of P. aeruginosa bacteremia in relation to the immune status of the patients. The medical records of 126 adult patients with P. aeruginosa bacteremia in Nagasaki University Hospital were retrospectively reviewed between January 2003 and December 2012. Of 126 patients with P. aeruginosa bacteremia, 60 patients (47.6%) were classified as immunocompetent. Mortality in immunocompetent patients tended to be lower than in immunocompromised patients (7-day mortality, 8% vs. 30%, P < 0.01; 30-day mortality, 23% vs. 39%, P = 0.053). Multivariate analysis showed that a higher sequential organ failure assessment score (hazard ratio [HR]: 1.27, P < 0.01) and underlying malignancies (HR: 3.33, P < 0.01) were independently associated with 30-day mortality. Initial antibiotic therapy (HR: 0.21, P < 0.01) and patients' immune status (HR: 0.29, P = 0.02) also had a significant impact on survival. However, there was a significant interaction between these 2 variables (P = 0.03 for interaction). A subgroup analysis showed that in immunocompromised, but not immunocompetent patients, initial appropriate antibiotic therapy was associated with lower mortality (30-day mortality 20.5% vs. 66.7%, P < 0.01 by log-rank test).

Risk factors associated with unfavorable short-term treatment outcome in patients with documented Pseudomonas aeruginosa infection

BACKGROUND

Invasive infections with Pseudomonas aeruginosa (PA) are associated with significant morbidity and mortality. While risk factors for mortality have been identified, their influence on short-term outcomes impacting treatment selection has not been reported.

OBJECTIVES

The objective of this study was to evaluate the relationship between select patient- and treatment-related factors and short-term outcomes in patients with PA pneumonia and/or bacteremia.

SETTING

Large academic medical center in the United States.

METHODS

This IRB-approved single-center, retrospective case-cohort study included patients >18 years of age with culture-confirmed PA bacteremia and/or pneumonia receiving antimicrobial agent(s) active against PA.

MAIN OUTCOME MEASURE

Risk of unfavorable short-term treatment result.

RESULTS

The population consisted of 117 patients (40 [34 %] and 77 [66 %] in the unfavorable and not-unfavorable groups, respectively). Baseline characteristics including age (mean of 63 years), gender (55 % male), Charlson score, creatinine clearance, and body mass index were comparable between groups. Piperacillin/tazobactam was the most common monotherapy antibiotic (46 and 33 % in unfavorable and not-unfavorable groups, respectively). Combination therapy primarily consisted of a beta-lactam plus ciprofloxacin in both unfavorable (10 %) and not-unfavorable (20 %) outcome groups. The preliminary regression model indicated that SIRS, direct ICU admission, and vasopressor therapy were associated with an unfavorable outcome. In addition, patients who received more than two active antimicrobials had a reduced risk of an unfavorable outcome. The final regression model revealed that vasopressor therapy (odds ratio [OR] 6.0; 95 % confidence interval [95 % CI] 2.3, 17) was associated with an unfavorable outcome, while receipt of greater than two active antibiotics was associated with a reduced risk of an unfavorable outcome (OR 0.26; 95 % CI 0.07, 0.83).

CONCLUSIONS

Treatment with more than two agents with activity against PA was associated with a reduced risk of an unfavorable short-term treatment outcome in patients with bacteremia and/or pneumonia.

Bacterial and clinical characteristics of health care- and community-acquired bloodstream infections due to Pseudomonas aeruginosa

Health care-associated infections, including Pseudomonas aeruginosa bloodstream infection, have been linked to delays in appropriate antibiotic therapy and an increased mortality rate. The objective of this study was to evaluate intrinsic virulence, bacterial resistance, and clinical outcomes of health care-associated bloodstream infections (HCABSIs) in comparison with those of community-acquired bloodstream infections (CABSIs) caused by P. aeruginosa. We conducted a retrospective multicenter study of consecutive P. aeruginosa bacteremia patients at two university-affiliated hospitals. Demographic, clinical, and treatment data were collected. Microbiologic analyses included in vitro susceptibility profiles and type III secretory (TTS) phenotypes. Sixty CABSI and 90 HCABSI episodes were analyzed. Patients with HCABSIs had more organ dysfunction at the time of bacteremia (P = 0.05) and were more likely to have been exposed to antimicrobial therapy (P < 0.001) than those with CABSIs. Ninety-two percent of the carbapenem-resistant P. aeruginosa infections were characterized as HCABSIs. The 30-day mortality rate for CABSIs was 26% versus 36% for HCABSIs (P = 0.38). The sequential organ failure assessment score at the time of bacteremia (hazard ratio [HR], 1.2; 95% confidence interval [CI], 1.1 to 1.3) and the TTS phenotype (HR 2.1; 95% CI, 1.1 to 3.9) were found to be independent predictors of the 30-day mortality rate. No mortality rate difference was observed between CABSIs and HCABSIs caused by P. aeruginosa. Severity of illness and expression of TTS proteins were the strongest predictors of the 30-day mortality rate due to P. aeruginosa bacteremia. Future P. aeruginosa bacteremia trials designed to neutralize TTS proteins are warranted.

Elucidating the Pseudomonas aeruginosa fatty acid degradation pathway: identification of additional fatty acyl-CoA synthetase homologues

The fatty acid (FA) degradation pathway of Pseudomonas aeruginosa, an opportunistic pathogen, was recently shown to be involved in nutrient acquisition during BALB/c mouse lung infection model. The source of FA in the lung is believed to be phosphatidylcholine, the major component of lung surfactant. Previous research indicated that P. aeruginosa has more than two fatty acyl-CoA synthetase genes (fadD; PA3299 and PA3300), which are responsible for activation of FAs using ATP and coenzyme A. Through a bioinformatics approach, 11 candidate genes were identified by their homology to the Escherichia coli FadD in the present study. Four new homologues of fadD (PA1617, PA2893, PA3860, and PA3924) were functionally confirmed by their ability to complement the E. coli fadD mutant on FA-containing media. Growth phenotypes of 17 combinatorial fadD mutants on different FAs, as sole carbon sources, indicated that the four new fadD homologues are involved in FA degradation, bringing the total number of P. aeruginosa fadD genes to six. Of the four new homologues, fadD4 (PA1617) contributed the most to the degradation of different chain length FAs. Growth patterns of various fadD mutants on plant-based perfumery substances, citronellic and geranic acids, as sole carbon and energy sources indicated that fadD4 is also involved in the degradation of these plant-derived compounds. A decrease in fitness of the sextuple fadD mutant, relative to the ΔfadD1D2 mutant, was only observed during BALB/c mouse lung infection at 24 h.

Risk factors for pan-resistant Pseudomonas aeruginosa bacteremia and the adequacy of antibiotic therapy

INTRODUCTION

The aim of this study was to determine risk factors for acquiring carbapenem-resistant Pseudomonas aeruginosa bacteremia (CR-PA) and factors associated with in-hospital mortality.

METHODS

Seventy-seven cases of bacteremia caused by P. aeruginosa were evaluated in a hospital with high incidence of CR-PA. Clinical and laboratorial factors, and previous use of antibiotics were also evaluated. In one analysis, CR-PA and carbapenem-susceptible P. aeruginosa (CS-PA) bacteremia were compared. A second analysis compared patients who died with survivors.

RESULTS

Among 77 P. aeruginosa bacteremia, 29 were caused by CR-PA. Admission to the intensive care unit, higher number of total leukocytes, and previous use of carbapenem were statistically associated with CR-PA. In the multivariate analysis, only previous use of carbapenem (including ertapenem) turned out to be a risk factor for CR-PA (p=0.014). The 30-day mortality of patients with P. aeruginosa bloodstream infection was 44.8% for CS-PA and 54.2% for patients with CR-PA (p=0.288). Chronic renal failure, admission to the intensive care unit, mechanical ventilation, and central venous catheter were risk factors for mortality. Incorrect treatment increased mortality of patients with bacteremia caused by CS-PA, but not for CR-SA. The odd ratio of mortality associated with incorrect therapy in patients with CS-PA was 3.30 (1.01-10.82; p=0.043). The mortality of patients with bacteremia caused by CR-PA was unexpectedly similar regardless of antimicrobial treatment adequacy.

CONCLUSION

Appropriate treatment for CS-PA bacteremia initiated within the first 24 hours was associated with lower mortality, but this cannot be extrapolated for CR-PA.

Draft genome sequence of the Pseudomonas aeruginosa bloodstream isolate PABL056

Pseudomonas aeruginosa is an important cause of disease in hospitalized and immunocompromised patients. The genome of P. aeruginosa is among the largest of bacteria pathogenic to humans. We present the draft genome sequence of P. aeruginosa strain PABL056, a human bloodstream isolate with the largest genome yet reported in P. aeruginosa.

Empiric antibiotic selection strategies for healthcare-associated pneumonia, intra-abdominal infections, and catheter-associated bacteremia

Initial selection and early deployment of appropriate/adequate empiric antimicrobial therapy is critical to minimize the significant morbidity and mortality associated with hospital- or healthcare-associated infections (HAIs). Initial empiric therapy that inadequately covers the pathogen(s) causing a serious HAI has been associated with increased mortality, longer hospital stay, and elevated healthcare costs. Moreover, subsequent modification of initial inadequate therapy, later in the disease process when culture results become available, may not remedy the impact of the initial choice. Because of this, it is important that initial empiric therapy covers the most likely pathogens associated with infection in a particular patient, even if this initial regimen turns out to be unnecessarily broad, based on subsequent culture results. The current paradigm for management of serious HAIs is to initiate empiric therapy with a broad-spectrum regimen covering likely pathogens, based on local surveillance and susceptibility data, and presence of risk factors for involvement of a resistant microorganism. Subsequent modification (de-escalation) of the initial regimen becomes possible later, when culture results are available and clinical status can be better assessed, 2 to 4 days after initiation of empiric therapy. When possible, de-escalation and other steps to modify antimicrobial exposure are important for minimizing risk of antimicrobial resistance development. This article examines the general process for selection of initial empiric antibiotic therapy for patients with HAIs, illustrated through 3 case studies dealing with healthcare-associated pneumonia, complicated intra-abdominal infection, and catheter-associated bacteremia, respectively.

Impact of carbapenem resistance and receipt of active antimicrobial therapy on clinical outcomes of Acinetobacter baumannii bloodstream infections

Nosocomial Acinetobacter baumannii bloodstream infections occur with significant prevalence and mortality. The relationship between carbapenem resistance in A. baumannii and patient outcomes remains unclear. A retrospective cohort study was conducted on patients with A. baumannii bacteremia. Outcomes, controlling for confounders, were compared for carbapenem-nonresistant A. baumannii (CNRAB) and carbapenem-resistant A. baumannii (CRAB). The primary outcome studied was all-cause hospital mortality, and the secondary endpoints evaluated were time to mortality, time to negative cultures, and length of stay postinfection for survivors. A total of 79 patients, 37 infected with CRAB and 42 with CNRAB, were studied. Hospital mortality was greater in the CRAB group as determined based on bivariate analysis (P < 0.01); however, this effect was nullified when controlling for relevant confounders with logistic regression and a Cox proportional-hazards model (P = 0.71 and 0.75, respectively). Values for time to mortality and time to negative cultures did not differ between the groups. The median number of days of stay postinfection for survivors was greater for the CRAB group than the CNRAB group (14 versus 6.5; P < 0.01). Patients who received active antimicrobial therapy were less likely to die (93.5% versus 74.2%; P = 0.02), regardless of carbapenem susceptibility classifications, and this result was robust in the multivariate model (P = 0.02). Trends existed for improved outcomes in patients receiving an active beta-lactam, and patients fared worse if they had received a polymyxin as an active agent. Patients with CRAB bloodstream infections were more chronically ill and had more comorbidities. Inactive therapy was more important than carbapenem susceptibility with respect to outcomes, was a strong predictor of death, and is potentially modifiable.

Pseudomonas aeruginosa toxin ExoU induces a PAF-dependent impairment of alveolar fibrin turnover secondary to enhanced activation of coagulation and increased expression of plasminogen activator inhibitor-1 in the course of mice pneumosepsis

Background

ExoU, a Pseudomonas aeruginosa cytotoxin with phospholipase A₂ activity, was shown to induce vascular hyperpermeability and thrombus formation in a murine model of pneumosepsis. In this study, we investigated the toxin ability to induce alterations in pulmonary fibrinolysis and the contribution of the platelet activating factor (PAF) in the ExoU-induced overexpression of plasminogen activator inhibitor-1 (PAI-1).

Methods

Mice were intratracheally instilled with the ExoU producing PA103 P. aeruginosa or its mutant with deletion of the exoU gene. After 24 h, animal bronchoalveolar lavage fluids (BALF) were analyzed and lung sections were submitted to fibrin and PAI-1 immunohistochemical localization. Supernatants from A549 airway epithelial cells and THP-1 macrophage cultures infected with both bacterial strains were also analyzed at 24 h post-infection.

Results

In PA103-infected mice, but not in control animals or in mice infected with the bacterial mutant, extensive fibrin deposition was detected in lung parenchyma and microvasculature whereas mice BALF exhibited elevated tissue factor-dependent procoagulant activity and PAI-1 concentration. ExoU-triggered PAI-1 overexpression was confirmed by immunohistochemistry. In in vitro assays, PA103-infected A549 cells exhibited overexpression of PAI-1 mRNA. Increased concentration of PAI-1 protein was detected in both A549 and THP-1 culture supernatants. Mice treatment with a PAF antagonist prior to PA103 infection reduced significantly PAI-1 concentrations in mice BALF. Similarly, A549 cell treatment with an antibody against PAF receptor significantly reduced PAI-1 mRNA expression and PAI-1 concentrations in cell supernatants, respectively.

Conclusion

ExoU was shown to induce disturbed fibrin turnover, secondary to enhanced procoagulant and antifibrinolytic activity during P. aeruginosa pneumosepsis, by a PAF-dependent mechanism. Besides its possible pathophysiological relevance, in vitro detection of exoU gene in bacterial clinical isolates warrants investigation as a predictor of outcome of patients with P. aeruginosa pneumonia/sepsis and as a marker to guide treatment strategies.

Prevalence and epidemiology of microbial pathogens causing bloodstream infections: results of the OASIS multicenter study

Beginning on April 2007, a prospective multicenter study was performed to investigate prevalence and epidemiology of microbial pathogens causing bloodstream infections (BSIs). Twenty microbiology laboratories participated to the survey over a 1-year period. A total of 11,638 episodes of BSI occurred in 11 202 patients, with 8.5% (n=985) of episodes being polymicrobial. Of 12 781 causative organisms, aerobic Gram-negative bacteria were 47.4% (n=6058), whereas Gram-positives accounted for 43.9% (n=5608). The remaining organisms included fungal species (n=924, 7.2%) and anaerobes (n=191, 1.5%). The most prevalent agents were Escherichia coli (21.7%), Staphylococcus aureus (14.9%), Staphylococcus epidermidis (8.2%), Pseudomonas aeruginosa (7.0%), and Enterococcus faecalis (6.3%). Isolates recovered from patients admitted to medical, surgical, and intensive care units accounted for 62.9%, 17.7%, and 19.4% of cases, respectively. BSIs were classified as hospital-acquired in 67.2% of cases. Compared with previous studies, our data show an increasing role of Gram-negative bacteria among both hospital- and community-acquired blood isolates.

Induced conformational changes in the activation of the Pseudomonas aeruginosa type III toxin, ExoU

ExoU is a 74-kDa, water-soluble toxin injected directly into mammalian cells through the type III secretion system of the opportunistic pathogen, Pseudomonas aeruginosa. Previous studies have shown that ExoU is a Ca(2+)-independent phospholipase that requires a eukaryotic protein cofactor. One protein capable of activating ExoU and serving as a required cofactor was identified by biochemical and proteomic methods as superoxide dismutase (SOD1). In these studies, we carried out site-directed spin-labeling electron paramagnetic resonance spectroscopy to examine the effects of SOD1 and substrate liposomes on the structure and dynamics of ExoU. Local conformational changes within the catalytic site were observed in the presence of substrate liposomes, and were enhanced by the addition of SOD1 in a concentration-dependent manner. Conformational changes in the C-terminal domain of ExoU were observed upon addition of cofactor, even in the absence of liposomes. Double electron-electron resonance experiments indicated that ExoU samples multiple conformations in the resting state. In contrast, addition of SOD1 induced ExoU to adopt a single, well-defined conformation. These studies provide, to our knowledge, the first direct evidence for cofactor- and membrane-induced conformational changes in the mechanism of activation of ExoU.