Etiology of Ventilator-Associated Pneumonia

A PilZ domain protein interacts with the transcriptional regulator HinK to regulate type VI secretion system in Pseudomonas aeruginosa

Type VI secretion systems (T6SS) are bacterial macromolecular complexes that secrete effectors into target cells or the extracellular environment, leading to the demise of adjacent cells and providing a survival advantage. Although studies have shown that the T6SS in Pseudomonas aeruginosa is regulated by the Quorum Sensing system and second messenger c-di-GMP, the underlying molecular mechanism remains largely unknown. In this study, we discovered that the c-di-GMP-binding adaptor protein PA0012 has a repressive effect on the expression of the T6SS HSI-I genes in P. aeruginosa PAO1. To probe the mechanism by which PA0012 (renamed TssZ, Type Six Secretion System -associated PilZ protein) regulates the expression of HSI-I genes, we conducted yeast two-hybrid screening and identified HinK, a LasR-type transcriptional regulator, as the binding partner of TssZ. The protein-protein interaction between HinK and TssZ was confirmed through co-immunoprecipitation assays. Further analysis suggested that the HinK-TssZ interaction was weakened at high c-di-GMP concentrations, contrary to the current paradigm wherein c-di-GMP enhances the interaction between PilZ proteins and their partners. Electrophoretic mobility shift assays revealed that the non-c-di-GMP-binding mutant TssZR5A/R9A interacts directly with HinK and prevents it from binding to the promoter of the quorum-sensing regulator pqsR. The functional connection between TssZ and HinK is further supported by observations that TssZ and HinK impact the swarming motility, pyocyanin production, and T6SS-mediated bacterial killing activity of P. aeruginosa in a PqsR-dependent manner. Together, these results unveil a novel regulatory mechanism wherein TssZ functions as an inhibitor that interacts with HinK to control gene expression.

Quantitative Determination of Unbound Piperacillin and Imipenem in Biological Material from Critically Ill Using Thin-Film Microextraction-Liquid Chromatography-Mass Spectrometry

β-Lactam antibiotics are most commonly used in the critically ill, but their effective dosing is challenging and may result in sub-therapeutic concentrations that can lead to therapy failure and even promote antimicrobial resistance. In this study, we present the analytical tool enabling specific and sensitive determination of the sole biologically active fraction of piperacillin and imipenem in biological material from the critically ill. Thin-film microextraction sampling technique, followed by rapid liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis, was optimized and validated for the quantitative determination of antibiotics in blood and bronchoalveolar lavage (BAL) specimens collected from intensive care unit (ICU) patients suffering from ventilation-associated pneumonia (n = 18 and n = 9, respectively). The method was optimized and proved to meet the criteria of US Food and Drug Administration (FDA) guidelines for bioanalytical method validation. Highly selective, sensitive, accurate and precise analysis by means of thin-film microextraction–LC-MS/MS, which is not affected by matrix-related factors, was successfully applied in clinical settings, revealing poor penetration of piperacillin and imipenem from blood into BAL fluid (reflecting the site of bacterial infection), nonlinearity in antibiotic binding to plasma-proteins and drug-specific dependence on creatinine clearance. This work demonstrates that only a small fraction of biologically active antibiotics reach the site of infection, providing clinicians with a high-throughput analytical tool for future studies on personalized therapeutic drug monitoring when tailoring the dosing strategy to an individual patient.

Epidemiology and Outcomes of Community-Acquired Escherichia coli Pneumonia

Background

E. coli is an under-recognized cause of bacterial community-acquired pneumonia (CAP). The objective of this study was to describe the epidemiology, risk factors, and outcomes of community-acquired Escherichia coli pneumonia in comparison with other gram-negative and pneumococcal pneumonias.

Methods

We conducted a large retrospective cohort study of adult patients admitted with pneumonia to 173 US hospitals included in the Premier Research database from July 2010 to June 2015. Patients were included if they had a principal diagnosis code for pneumonia or a principal diagnosis of respiratory failure or sepsis with a secondary diagnosis of pneumonia and had a positive blood or respiratory culture obtained on hospital day 1. The primary outcome was in-hospital case fatality. Secondary outcomes included intensive care unit admission, invasive mechanical ventilation, and use of vasopressors.

Results

Of 8680 patients with pneumonia and positive blood or respiratory cultures, 1029 (7.7%) had E. coli CAP. Patients with E. coli pneumonia were older and more likely to have a principal diagnosis of sepsis. Patients with E. coli pneumonia had significantly higher case fatality than patients with pneumococcal pneumonia (adjusted odds ratio, 1.55; 95% CI, 1.23–1.97), but it was not significantly different than other gram-negative pneumonias (adjusted odds ratio, 1.06; 95% CI, 0.85–1.32). Approximately 36% of the isolates were resistant to fluoroquinolones; 9.3% were resistant to ceftriaxone.

Conclusions

E. coli is an important cause of severe CAP; with mortality that was higher than pneumococcal pneumonia but similar to other gram-negative pneumonias. The rate of fluoroquinolone resistance was high, and empiric fluoroquinolones should be used with caution in these patients.

Acidosis exacerbates in vivo IL-1-dependent inflammatory responses and neutrophil recruitment during pulmonary Pseudomonas aeruginosa infection

Acidic microenvironments commonly occur at sites of inflammation and bacterial infections. In the context of a Pseudomonas aeruginosa infection, we previously demonstrated that acidosis enhances the cellular proinflammatory interleukin (IL)-1β response in vitro. However, how pH alterations affect in vivo IL-1β responses and subsequent IL-1-driven inflammation during infection with P. aeruginosa is unclear. Here, we report that acidosis enhances in vivo IL-1β production and downstream IL-1 receptor-dependent responses during infection with P. aeruginosa in models of acute pneumonia and peritonitis. Importantly, we demonstrate that infection with P. aeruginosa within an acidic environment leads to enhanced production of a subset of proinflammatory cytokines, including chemokine (C-X-C) motif ligand 1, IL-6, and chemokine (C-C motif) ligand 2, and increased neutrophil recruitment. Furthermore, with the use of IL-1 receptor type 1-deficient mice, we identify the contribution of the IL-1 signaling pathway to the acidosis-enhanced inflammatory response and pathology. These data provide insights into the potential benefit of pH regulation during bacterial infections to control disease progression and immunopathology.

Acidosis increases the susceptibility of respiratory epithelial cells to Pseudomonas aeruginosa-induced cytotoxicity

Bacterial infection can lead to acidosis of the local microenvironment, which is believed to exacerbate disease pathogenesis; however, the mechanisms by which changes in pH alter disease progression are poorly understood. We test the hypothesis that acidosis enhances respiratory epithelial cell death in response to infection with Pseudomonas aeruginosa Our findings support the idea that acidosis in the context of P. aeruginosa infection results in increased epithelial cell cytotoxicity due to ExoU intoxication. Importantly, enforced maintenance of neutral pH during P. aeruginosa infection demonstrates that cytotoxicity is dependent on the acidosis. Investigation of the underlying mechanisms revealed that host cell cytotoxicity correlated with increased bacterial survival during an acidic infection that was due to reduced bactericidal activity of host-derived antimicrobial peptides. These findings extend previous reports that the activities of antimicrobial peptides are pH-dependent and provide novel insights into the consequences of acidosis on infection-derived pathology. Therefore, this report provides the first evidence that physiological levels of acidosis increase the susceptibility of epithelial cells to acute Pseudomonas infection and demonstrates the benefit of maintaining pH homeostasis during a bacterial infection.

Pseudomonas aeruginosa Enolase Influences Bacterial Tolerance to Oxidative Stresses and Virulence

Pseudomonas aeruginosa is a Gram negative opportunistic pathogenic bacterium, which causes acute and chronic infections. Upon entering the host, bacteria alter global gene expression to adapt to host environment and avoid clearance by the host. Enolase is a glycolytic enzyme involved in carbon metabolism. It is also a component of RNA degradosome, which is involved in RNA processing and gene regulation. Here, we report that enolase is required for the virulence of P. aeruginosa in a murine acute pneumonia model. Mutation of enolase coding gene (eno) increased bacterial susceptibility to neutrophil mediated killing, which is due to reduced tolerance to oxidative stress. Catalases and alkyl hydroperoxide reductases play a major role in protecting the cell from oxidative damages. In the eno mutant, the expression levels of catalases (KatA and KatB) were similar as those in the wild type strain in the presence of H₂O₂, however, the expression levels of alkyl hydroperoxide reductases (AhpB and AhpC) were significantly reduced. Overexpression of ahpB but not ahpC in the eno mutant fully restored the bacterial resistance to H₂O₂ as well as neutrophil mediated killing, and partially restored bacterial virulence in the murine acute pneumonia model. Therefore, we have identified a novel role of enolase in the virulence of P. aeruginosa.

Ventilator-associated Pneumonia caused by commensal oropharyngeal Flora; [corrected] a retrospective Analysis of a prospectively collected Database

Background

The significance of commensal oropharyngeal flora (COF) as a potential cause of ventilator-associated pneumonia (VAP) is scarcely investigated and consequently unknown. Therefore, the aim of this study was to explore whether COF may cause VAP.

Methods

Retrospective clinical, microbiological and radiographic analysis of all prospectively collected suspected VAP cases in which bronchoalveolar lavage fluid exclusively yielded ≥ 10⁴ cfu/ml COF during a 9.5-year period. Characteristics of 899 recent intensive care unit (ICU) admissions were used as a reference population.

Results

Out of the prospectively collected database containing 159 VAP cases, 23 patients were included. In these patients, VAP developed after a median of 8 days of mechanical ventilation. The patients faced a prolonged total ICU length of stay (35 days [P < .001]), hospital length of stay (45 days [P = .001]), and a trend to higher mortality (39 % vs. 26 %, [P = .158]; standardized mortality ratio 1.26 vs. 0.77, [P = .137]) compared to the reference population. After clinical, microbiological and radiographic analysis, COF was the most likely cause of respiratory deterioration in 15 patients (9.4 % of all VAP cases) and a possible cause in 2 patients.

Conclusion

Commensal oropharyngeal flora appears to be a potential cause of VAP in limited numbers of ICU patients as is probably associated with an increased length of stay in both ICU and hospital. As COF-VAP develops late in the course of ICU admission, it is possibly associated with the immunocompromised status of ICU patients.

Drug-resistant ventilator associated pneumonia in a tertiary care hospital in Saudi Arabia

BACKGROUND:

There is a wide geographic and temporal variability of bacterial resistance among microbial causes of ventilator-associated pneumonia (VAP). The contribution of multi-drug resistant (MDR) pathogens to the VAP etiology in Saudi Arabia was never studied. We sought to examine the extent of multiple-drug resistance among common microbial causes of VAP.

MATERIALS AND METHODS:

We conducted a retrospective susceptibility study in the adult intensive care unit (ICU) of King Abdulaziz Medical City, Riyadh, Saudi Arabia. Susceptibility results of isolates from patients diagnosed with VAP between October 2004 and June 2009 were examined. The US National Healthcare Safety Network definition of MDR was adopted.

RESULTS:

A total of 248 isolates including 9 different pathogens were included. Acinetobacter spp. was highly (60-89%) resistant to all tested antimicrobials, including carbapenems (three- and four-class MDR prevalence were 86% and 69%, respectively). Pseudomonas aeruginosa was moderately (13-31%) resistant to all tested antimicrobials, including antipseudomonal penicillins (three- and four-class MDR prevalence were 13% and 10%, respectively). With an exception of ampicillin (fully resistant), Klebsiella spp. had low (0-13%) resistance to other tested antimicrobials with no detected MDR. Staphylococcus aureus was fully susceptible to vancomycin with 42% resistance to oxacillin. There were significant increasing trends of MDR Acinetobacter spp. however not P. aeruginosa during the study. Resistant pathogens were associated with worse profile of ICU patients but not patients’ outcomes.

CONCLUSION:

Acinetobacter in the current study was an increasingly resistant VAP-associated pathogen more than seen in many parts of the world. The current finding may impact local choice of initial empiric antibiotics.

Risk of developing pneumonia is enhanced by the combined traits of fluoroquinolone resistance and type III secretion virulence in respiratory isolates of Pseudomonas aeruginosa

OBJECTIVES

To determine the differential association of host characteristics, antimicrobial resistance, and type III secretion system virulence of Pseudomonas aeruginosa isolates with respiratory syndromes in hospitalized adult patients.

DESIGN

Retrospective, cohort study.

SETTING

Community teaching hospital.

PATIENTS

Two hundred eighteen consecutive adult patients with respiratory culture positive for P. aeruginosa between January 2005 to January 2010.

INTERVENTIONS

Medical charts were reviewed to obtain demographic, laboratory, radiographic, and clinical information. Isolates were assayed by polymerase chain reaction for genes encoding the type III secretion system effectors (ExoU, ExoS, and PcrV) and for strain relatedness using randomly amplified polymorphic DNA analysis. Levofloxacin susceptibility was determined by broth microdilution. Patients were grouped by colonization, bronchitis, or pneumonia and were compared for differential risk of developing the clinical syndrome with respect to host and microbial characteristics.

MEASUREMENTS AND MAIN RESULTS

Half of the study cohort (54%, 117 of 218) had pneumonia, 32% (70 of 218) had bronchitis, and 14% (31 of 218) had colonization; in-hospital mortality was 35%, 11%, and 0%, respectively. Host factors strongly associated with pneumonia development were residence in long-term care facility, healthcare-associated acquisition of P. aeruginosa, higher Acute Physiology and Chronic Health Evaluation II score, presence of enteral feeding tube, mechanical ventilation, and recent history of pneumonia. Fluoroquinolone-resistant (57% vs 34%, 16%; p < 0.0001) and multidrug-resistant (36% vs 26%, 7%; p = 0.0045) strains were more likely to cause pneumonia than bronchitis or colonization, respectively. Analysis of host and microbial factors in a multivariate regression model yielded the combined traits of fluoroquinolone resistance and gene encoding the type III secretion system ExoU effector in P. aeruginosa as the single most significant predictor of pneumonia development.

CONCLUSIONS

These results suggest that fluoroquinolone-resistant phenotype in a type III secretion system exoU strain background contributes toward the pathogenesis of P. aeruginosa in pneumonia.

Hypercapnia impairs lung neutrophil function and increases mortality in murine pseudomonas pneumonia

Hypercapnia, an elevation of the level of carbon dioxide (CO2) in blood and tissues, is a marker of poor prognosis in chronic obstructive pulmonary disease and other pulmonary disorders. We previously reported that hypercapnia inhibits the expression of TNF and IL-6 and phagocytosis in macrophages in vitro. In the present study, we determined the effects of normoxic hypercapnia (10% CO2, 21% O2, and 69% N2) on outcomes of Pseudomonas aeruginosa pneumonia in BALB/c mice and on pulmonary neutrophil function. We found that the mortality of P. aeruginosa pneumonia was increased in 10% CO2-exposed compared with air-exposed mice. Hypercapnia increased pneumonia mortality similarly in mice with acute and chronic respiratory acidosis, indicating an effect unrelated to the degree of acidosis. Exposure to 10% CO2 increased the burden of P. aeruginosa in the lungs, spleen, and liver, but did not alter lung injury attributable to pneumonia. Hypercapnia did not reduce pulmonary neutrophil recruitment during infection, but alveolar neutrophils from 10% CO2-exposed mice phagocytosed fewer bacteria and produced less H2O2 than neutrophils from air-exposed mice. Secretion of IL-6 and TNF in the lungs of 10% CO2-exposed mice was decreased 7 hours, but not 15 hours, after the onset of pneumonia, indicating that hypercapnia inhibited the early cytokine response to infection. The increase in pneumonia mortality caused by elevated CO2 was reversible when hypercapnic mice were returned to breathing air before or immediately after infection. These results suggest that hypercapnia may increase the susceptibility to and/or worsen the outcome of lung infections in patients with severe lung disease.

The value of chlorhexidine gluconate wipes and prepacked washcloths to prevent the spread of pathogens--a systematic review

BACKGROUND

Use of chlorhexidine gluconate wipes and pre-packed washcloths has been described for preventing pathogen spread in healthcare settings.

AIM

To assess the impact of chlorhexidine washcloths/wipes in preventing the spread of pathogens.

METHODS

Extensive and structured literature search from studies in Google Academic, Cochrane Library, Web of Science, Pubmed and Cinahl from their inception until November 2012.

FINDINGS

Final analysis included 15 studies, 9 of which were randomised controlled trials. The most frequent setting was the intensive care unit. In intensive care units, a significant reduction of bloodstream infection was associated with intervention and 3 studies revealed a decrease in blood culture contamination. One study showed a decrease in staff and environmental contamination and no increase in chlorhexidine resistance with intervention. Positive blood cultures for multiple pathogens also declined with intervention. In a paediatric intensive care unit, intervention decreased bacteraemia and catheter-associated bloodstream infection. In hospital wards, intervention was associated to a 64% reduction of pathogen transmission. One study had no statistically significant results. Pre-surgical chlorhexidine use significantly decreased bacterial colonisation but had no impact on surgical site infections. Regarding maternal and perinatal setting, one study did not show reduction of early onset neonatal sepsis and pathogen transmission. Another study of vaginal and neonatal decolonisation with chlorhexidine wiping revealed significant reduction in colonisation. One study concluded that single and multiple umbilical cord cleansing reduced the likelihood for a positive swab in 25% and 29%, respectively. Neonatal wiping maintained low levels of skin colonisation for a 24h period, for multiple pathogens.

CONCLUSION

Current evidence supports the usefulness of chlorhexidine washcloths and wipes in an intensive care, hospital and pre-surgical setting. More studies are required to encourage its use for prevention of perinatal and neonatal transmission of pathogens.

Improved outcome of ventilator-associated pneumonia caused by methicillin-resistant Staphylococcus aureus in a trauma population

BACKGROUND

The treatment of ventilator-associated pneumonia (VAP) secondary to methicillin-resistant Staphylococcus aureus (MRSA) remains controversial.

METHODS

We performed a review of all blunt trauma patients diagnosed with MRSA VAP from June 2005 to June 2011. VAP for the first 3 years was diagnosed by sputum aspiration and treated with vancomycin. For the last 3 years of the study period, VAP was diagnosed with bronchoalveolar lavage and treated with linezolid.

RESULTS

MRSA VAP patients treated with vancomycin had an average hospital length of stay (LOS) of 49 days (range 9-99 days), an average intensive care unit (ICU) LOS of 43 days (range 6-98 days), and average ventilator days of 34.4 (range 3-76 days). Seventeen MRSA VAP patients treated with linezolid had an average hospital LOS of 27 days (range 11-61), an average ICU LOS of 22 days (range 10-42) days, and average ventilator days of 16.6 (range 2-42).

CONCLUSIONS

Trauma patients who develop MRSA VAP appear to have fewer ventilator days and shorter ICU and hospital LOS when treated with linezolid.

High prevalence of multidrug-resistant nonfermenters in hospital-acquired pneumonia in Asia

RATIONALE

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) remain important causes of morbidity and mortality. Increasing antimicrobial resistance has aroused the concern of the failure of antibiotic treatment.

OBJECTIVES

To determine the distribution of the bacterial isolates of HAP and VAP, their antimicrobial resistance patterns, and impact of discordant antibiotic therapy on clinical outcome in Asian countries

METHODS

A prospective surveillance study was conducted in 73 hospitals in 10 Asian countries from 2008-2009. A total of 2,554 cases with HAP or VAP in adults were enrolled and 2,445 bacterial isolates were collected from 1,897 cases. Clinical characteristics and antimicrobial resistance profiles were analyzed.

MEASUREMENT AND MAIN RESULTS

Major bacterial isolates from HAP and VAP cases in Asian countries were Acinetobacter spp., Pseudomonas aeruginosa, Staphylococcus aureus, and Klebsiella pneumoniae. Imipenem resistance rates of Acinetobacter and P. aeruginosa were 67.3% and 27.2%, respectively. Multidrug-resistant rates were 82% and 42.8%, and extensively drug-resistant rates were 51.1% and 4.9%. Multidrug-resistant rate of K. pneumoniae was 44.7%. Oxacillin resistance rate of S. aureus was 82.1%. All-cause mortality rate was 38.9%. Discordant initial empirical antimicrobial therapy increased the likelihood of pneumonia-related mortality (odds ratio, 1.542; 95% confidence interval, 1.127-2.110).

CONCLUSIONS

Acinetobacter spp., P. aeruginosa, S. aureus, and K. pneumoniae are the most frequent isolates from adults with HAP or VAP in Asian countries. These isolates are highly resistant to major antimicrobial agents, which could limit the therapeutic options in the clinical practice. Discordant initial empirical antimicrobial therapy significantly increases the likelihood of pneumonia-related mortality.

Pseudomonas aeruginosa cytotoxin ExoU is injected into phagocytic cells during acute pneumonia

ExoU, a cytotoxin translocated into host cells via the type III secretion system of Pseudomonas aeruginosa, is associated with increased mortality and disease severity. We previously showed that impairment of recruited phagocytic cells allowed survival of ExoU-secreting P. aeruginosa in the lung. Here we analyzed types of cells injected with ExoU in vivo using translational fusions of ExoU with a beta-lactamase reporter (ExoU-Bla). Cells injected with ExoU-Bla were detectable in vitro but not in vivo, presumably due to the rapid cytotoxicity induced by the toxin. Therefore, we used a noncytotoxic ExoU variant, designated ExoU(S142A)-Bla, to analyze injection in vivo. We determined that phagocytic cells in the lung were frequently injected with ExoU(S142A). Early during infection, resident macrophages constituted the majority of cells into which ExoU was injected, but neutrophils and monocytes became the predominant types of cells into which ExoU was injected upon recruitment into the lung. We observed a modest preference for injection into neutrophils over injection into other cell types, but in general the repertoire of injected immune cells reflected the relative abundance of these cells in the lung. Our results indicate that phagocytic cells in the lung are injected with ExoU and support the hypothesis that ExoU-mediated impairment of phagocytes has a role in the pathogenesis of pneumonia caused by P. aeruginosa.

Role of tigecycline in the control of a carbapenem-resistant Acinetobacter baumannii outbreak in an intensive care unit

The incidence of Acinetobacter baumannii infection has greatly increased over recent decades with infections occurring more in critically ill hospitalised patients. Hospital outbreaks of multiple antibiotic-resistant strains are posing an increasing threat to public health. Three different outbreaks of multidrug-resistant A. baumannii (MRAB) infections involving 24 patients, aged 16-75 years occurred in the intensive care unit in the course of one year. The isolates were cultured from clinical samples and identified using automated Vitek II ID system and the API 20NE system. Susceptibility testing was done by the E-test method. Molecular typing of the isolates was determined by pulsed-field electrophoresis. Screening of both patients and the environment was carried out. The acquisition time, i.e. the time of admission to time of acquiring infection, ranged from 3 to 31 days. All isolates were multiply resistant (MRAB), including resistance to carbapenems (MRAB-C) in the majority of cases but susceptible to tigecycline, with a minimum inhibitory concentration (MIC(90)) of 2 microg/mL. The overall mortality rate was 16.7%. Time-to-clearance of the MRAB-C was 8.3 days in the first outbreak, when tigecycline was not used, and 2.8 and 3.1 days during the second and third outbreaks, respectively, when tigecycline was used, and all but one patient survived. Environmental screening revealed gross contamination of many surfaces and equipment within the unit. The outbreak strains belonged to two distinct clones (D and E) whereas the 14 environmental strains belonged to three distinct groups (A-C). The outbreak of infections treated with tigecycline was successfully eliminated in conjunction with an aggressive infection control strategy.

Pseudomonas aeruginosa induces localized immunosuppression during pneumonia

Hospital-acquired bacterial pneumonia is a common and serious complication of modern medical care. Many aspects of such infections remain unclear, including the mechanisms by which invading pathogens resist clearance by the innate immune response and the tendency of the infections to be polymicrobial. Here, we used a mouse model of infection to show that Pseudomonas aeruginosa, a leading cause of hospital-acquired pneumonia, interferes with the ability of recruited phagocytic cells to eradicate bacteria from the lung. Early in infection, phagocytic cells, predominantly neutrophils, are recruited to the lungs but are incapacitated when they enter the airways by the P. aeruginosa toxin ExoU. The resulting paucity of functioning phagocytes allows P. aeruginosa to persist within the lungs and results in local immunosuppression that facilitates superinfection with less-pathogenic bacteria. Together, our results provide explanations for previous reports linking ExoU-secreting P. aeruginosa with more severe pulmonary infections and for the tendency of hospital-acquired pneumonia to be polymicrobial.

Ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a significant clinical infection affecting up to one-third of patients requiring mechanical ventilation, and is associated with significant attributable morbidity and mortality. Clinicians should have a heightened clinical suspicion for VAP with diagnostic goals focusing on accuracy; gathering of lower respiratory tract culture; and appropriate and timely initial antibiotic therapy. Early and adequate antibiotic therapy is important to optimize the management of patients with VAP. The incidence and etiologic patterns of the major pathogens causing VAP must be taken into account when making empiric antibiotic therapy choices. Subsequent de-escalation and prescription of an appropriate duration of therapy guided by clinical response and culture results may lead to decreased morbidity and future antibiotic resistance.

Direct E-test (AB Biodisk) of respiratory samples improves antimicrobial use in ventilator-associated pneumonia

BACKGROUND

Ventilator-associated pneumonia is the most frequently observed nosocomial infection in intensive care units, and it is associated with high morbidity and mortality. Early microbiological diagnosis and the initial administration of appropriate antimicrobial therapy are associated with decreased mortality and potentially reduced costs. Our study evaluates the clinical and financial impact of performing rapid antimicrobial susceptibility tests directly on samples obtained from the lower respiratory tract.

METHODS

A prospective, randomized study was performed over a 2-year period. Patients who had a lower respiratory tract infection that was acquired during mechanical ventilation and for whom samples obtained from the respiratory tract were sent for culture were randomized to 1 of 2 groups. Samples were cultured for the control group, and results were reported using standard procedures. Samples were also cultured for the test subject group using standard procedures, but in addition, a rapid antibiogram was immediately performed by placing E-test antibiotic strips (AB Biodisk) directly on respiratory tract samples. Patients in the E-test group received a preliminary laboratory report when it became available. The 2 patient groups were compared according to the following variables: type and severity of underlying conditions, total days of antimicrobial use, number of defined daily doses, cost of acquisition of the antimicrobial agent per episode, days of fever, days receiving mechanical ventilation, days in the intensive care unit, incidence of Clostridium difficile-associated diarrhea, and mortality.

RESULTS

Reporting a rapid E-test was associated with fewer days of fever, fewer days of antibiotic administration until resolution of the episode of ventilator-associated pneumonia, decreased antibiotic consumption, less C. difficile-associated diarrhea, lower costs of antimicrobial agents, and fewer days receiving mechanical ventilation.

CONCLUSIONS

A rapid E-test of respiratory tract samples improves antimicrobial use in cases of ventilator-associated pneumonia.

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Levofloxacin in the treatment of ventilator-associated pneumonia

The use of levofloxacin in critically ill patients has progressively increased since commercial marketing of the drug in 1999, despite the fact that few studies have been designed to assess the use of levofloxacin in this population. Pharmacological characteristics, broad spectrum of activity, and tolerability account for the high interest in the drug for the treatment of different infectious diseases, including ventilator-associated pneumonia (VAP), and the recommendation of levofloxacin in guidelines developed by a number of scientific societies. According to pharmacokinetic-pharmacodynamic data, it seems reasonable to assume that an increase in activity follows from a larger dose, so that 500 mg/12 h is adequate in patients with VAP. In critically ill patients with VAP, levofloxacin monotherapy is indicated for empirical treatment of patients with early onset pneumonia without risk factors for multiresistant pathogens, and in combination therapy for late onset VAP or for patients at risk for multiresistant pathogens. The use of levofloxacin in combination therapy is supported by multiple reasons, including: increased empirical coverage in infections with suspected intracellular pathogens; substitution for more toxic antimicrobial agents (e.g., aminoglycosides) in patients with renal dysfunction and in those at risk for renal insufficiency; and severity of systemic response to infection (septic shock) that justifies multiple treatment with better tolerated antibiotics. The availability of the oral formulation allows sequential therapy, switching from the intravenous route to the oral route. Levofloxacin is well tolerated by critically ill patients, with few adverse events of mild to moderate severity.

Gram-negative bacterial pneumonia: aetiology and management

PURPOSE OF REVIEW

Recent articles of clinical and investigational interest on Gram-negative pneumonia, particularly hospital-acquired and ventilator-associated pneumonia, are reviewed.

RECENT FINDINGS

The high rate of respiratory infections due to Gram-negative bacteria in late-onset ventilator-associated pneumonia has been repeatedly documented. The predominant pathogens are Pseudomonas aeruginosa and Acinetobacter baumannii. On the other hand, the frequency of Gram-negative bacteria in community-acquired pneumonia and in early-onset ventilator-associated pneumonia is increasing. Patients with risk factors for infection with resistant pathogens should initially receive a combination therapy that covers a broad spectrum, and, as soon as the pathogen and the susceptibilities are available, treatment should be simplified to a more targeted one (with the possible exception of P. aeruginosa pneumonia). Adequate dosing is of great importance and the use of pharmacodynamic/pharmacokinetic principles when prescribing antibiotics increases effectiveness. The optimal duration of therapy remains unknown; several studies have supported the use of shorter courses of treatment. Alternative treatment approaches (e.g. vaccines) are under investigation.

SUMMARY

The increasing frequency of resistant Gram-negative bacteria and the shortage of newer antibiotics in the pipeline with activity against Gram-negative bacteria is of concern. Early effective antimicrobial treatment is a key for the resolution of infection and improved survival.

Neumonía nosocomial causada por Staphylococcus aureus resistente a meticilina

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly common cause of hospital acquired pneumonia (HAP) and the second most frequently isolated pathogen from patients who die from HAP. High-risk units for MRSA colonization such as intensive care (ICU's) are the most affected. Multiple risk factors for transmission of MRSA have been identified, including colonization pressure and severity of illness at ICU admission. On the other hand, the most important predisposing factor for MRSA infection is prolonged mechanical ventilation and/or previous antibiotic therapy. Controlling the spread of MRSA remains a major challenge for hospitals. Screening programs, together with contact precautions for cases with MRSA and judicious antimicrobial use are major factors for a successful control. Early appropriate initial therapy is of crucial importance and improves outcome. The standard therapy has been glycopeptides but, in spite of its in vitro activity, mortality in critically ill patients treated with glycopeptides has consistently been reported high, mainly due to their poor lung penetration. Linezolid shows better clinical cure and survival rates, but further studies are needed. As the treatment options for MRSA pneumonia are limited and inadequate, development of more effective drugs is mandatory.

Treatment of multidrug resistant Acinetobacter

PURPOSE OF REVIEW

Acinetobacter baumannii-calcoaceticus complex has become a serious nosocomial pathogen due to its persistence in the hospital environment and its broad antimicrobial resistance patterns. This review summarizes the most recent literature pertaining to the clinical management of infections with this bacteria emphasizing in-vitro antimicrobial resistance patterns and antimicrobial efficacy in animals and humans.

RECENT FINDINGS

Although this pathogen can be associated with an elevated crude mortality, it only contributes to this mortality in a subset of high-risk patients. Determining in-vitro activity of antimicrobial agents can be problematic due to conflicting results sometimes obtained through different testing methods. There is no simple answer as to the most appropriate antimicrobial therapy secondary to lack of adequate studies. Imipenem/cilastatin, amikacin, ampicillin/sulbactam, colistin, rifampin, and tetracyclines are typically active against these bacteria. It is also not clear if combination therapy is more effective than monotherapy. In cases in which A. baumannii-calcoaceticus complex bacteria are resistant to all available agents, we have prolonged infusion times, increased drug dose, and altered route of instillation, such as nebulized therapy for pulmonary infections with mixed results. A primary goal of A. baumannii-calcoaceticus complex management should be to prevent initial colonization and subsequent infection by adequate infection control.

SUMMARY

The A. baumannii-calcoaceticus complex continues to play a significant role in our healthcare systems. Prompt and adequate therapy with agents having in-vitro activity is required once it is established that the bacteria represents infection and not colonization. Aggressive infection control policies should be enforced when this pathogen is identified.