Microbial cause of ICU-acquired pneumonia: hospital-acquired pneumonia versus ventilator-associated pneumonia.

PURPOSE OF REVIEW: Successful treatment of patients with hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) remains a difficult and complex undertaking. Better knowledge of the pathogens involved in that setting may allow reassessment of our current modalities of therapy and definition of better protocols. RECENT FINDINGS: Microorganisms responsible for HAP/VAP differ according to geographic areas, ICU patients' specific characteristics, durations of hospital and ICU stays before onset of the disease, and risk factors for MDR pathogens. However, a number of studies have shown that Gram-negative bacilli (GNB) - particularly Pseudomonas aeruginosa and Enterobacteriaceae - cause many of the respiratory infections in this setting, with minimal differences between HAP and VAP, indicating that the cause depends more on the underlying clinical condition of patients rather than previous intubation. SUMMARY: When selecting initial antimicrobial therapy in patients with HAP/VAP, more attention should be paid to individual risk factors for MDR pathogens, severity of the clinical situation, and the local epidemiology than to the type of pneumonia.

How bacteria hack the matrix and dodge the bullets of immunity.

Haemophilus influenzae, Moraxella catarrhalis and Pseudomonas aeruginosa are common Gram-negative pathogens associated with an array of pulmonary diseases. All three species have multiple adhesins in their outer membrane, i.e. surface structures that confer the ability to bind to surrounding cells, proteins or tissues. This mini-review focuses on proteins with high affinity for the components of the extracellular matrix such as collagen, laminin, fibronectin and vitronectin. Adhesins are not structurally related and may be lipoproteins, transmembrane porins or large protruding trimeric auto-transporters. They enable bacteria to avoid being cleared together with mucus by attaching to patches of exposed extracellular matrix, or indirectly adhering to epithelial cells using matrix proteins as bridging molecules. As more adhesins are being unravelled, it is apparent that bacterial adhesion is a highly conserved mechanism, and that most adhesins target the same regions on the proteins of the extracellular matrix. The surface exposed adhesins are prime targets for new vaccines and the interactions between proteins are often possible to inhibit with interfering molecules, e.g heparin. In conclusion, this highly interesting research field of microbiology has unravelled host-pathogen interactions with high therapeutic potential.

The role of mass spectrometry analysis in bacterial effector characterization.

Many secreted bacterial effector proteins play a critical role in host-pathogen interactions by mediating a variety of post-translational modifications, some of which do not occur natively within the eukaryotic proteome. The characterization of bacterial effector protein activity remains an important step to understanding the subversion of host cell biology during pathogen infection and although molecular biology and immunochemistry remain critical tools for gaining insights into bacterial effector functions, increasingly mass spectrometry (MS) and proteomic approaches are also playing an indispensable role. The focus of this editorial is to highlight the strengths of specific MS approaches and their utility for the characterization of bacterial effector activity. With the capability of new generation MS instrumentation, MS-based technologies can provide information that is inaccessible using traditional molecular or immunochemical approaches.

Molecular ß-Lactamase Characterization of Aerobic Gram-Negative Pathogens Recovered from Patients Enrolled in the Ceftazidime-Avibactam Phase 3 Trials for Complicated Intra-abdominal Infections, with Efficacies Analyzed against Susceptible and Resistant Subsets.

The correlation of the clinical efficacy of ceftazidime-avibactam (plus metronidazole) with that of meropenem was evaluated in subjects infected with Gram-negative isolates having characterized ß-lactam resistance mechanisms from the complicated intra-abdominal infection (cIAI) phase 3 clinical trials. Enterobacteriaceae isolates displaying ceftriaxone and/or ceftazidime MIC values of ≥2 µg/ml and Pseudomonas aeruginosa isolates with ceftazidime MIC values of ≥16 µg/ml were characterized for extended-spectrum-ß-lactamase (ESBL) content. Enterobacteriaceae and P. aeruginosa isolates with imipenem and meropenem MIC values of ≥2 and ≥8 µg/ml, respectively, were tested for carbapenemase genes. The primary efficacy endpoint was clinical cure at test of cure (TOC) among the members of the microbiologically modified intention-to-treat (mMITT) population. A total of 14.5% (56/387) and 18.8% (74/394) of patients in the ceftazidime-avibactam and meropenem arms had isolates that met the MIC screening criteria at the baseline visit, respectively. CTX-M variants alone (29.7%; 41/138) or in combination with OXA-1/30 (35.5%; 49/138), most commonly, blaCTX-M group 1 variants (79/90; 87.8%), represented the ß-lactamases most frequently observed among Enterobacteriaceae isolates. Among the patients infected with pathogens that did not meet the screening criteria, 82.2% showed clinical cure in the ceftazidime-avibactam group versus 85.9% in the meropenem group. Among patients infected with any pathogens that met the MIC screening criteria, clinical cure rates at TOC were 87.5% and 86.5% for the ceftazidime-avibactam and meropenem groups, respectively. Ceftazidime-avibactam had clinical cure rates of 92.5% to 90.5% among patients infected with ESBL- and/or carbapenemase-producing Enterobacteriaceae strains at the baseline visit, while meropenem showed rates of 84.9% to 85.4%. The ceftazidime-avibactam and meropenem groups had cure rates of 75.0% and 86.7%, respectively, among patients having any pathogens producing AmpC enzymes. The efficacy of ceftazidime-avibactam was similar to that of meropenem for treatment of cIAI caused by ESBL-producing organisms. (This study has been registered at ClinicalTrials.gov under registration no. NCT01499290 and NCT01500239.).

Traqueobronquitis por Elizabethkingia meningoseptica en una paciente portadora de traqueostomía / Tracheobronchitis by Elizabethkingia meningoseptica in a patient with tracheostomy

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Intraventricular and lumbar intrathecal administration of antibiotics in postneurosurgical patients with meningitis and/or ventriculitis in a serious clinical state.

OBJECT: To date, reports on the clinical efficacy of intraventricularly and intrathecally administered antibiotics for the treatment of neurosurgical ventriculitis and meningitis in adults are limited. The authors aimed to evaluate the efficacy and safety of the intraventricular (IVT) and lumbar intrathecal (IT) administration of antibiotics in critically ill neurosurgical patients. METHODS: Thirty-four postneurosurgical patients with meningitis and ventriculitis were studied. Intraventricular/lumbar intrathecal antibiotics were administered due to positive CSF cultures persisting despite the use of intravenous antibiotics. The time period until CSF sterilization, changes in clinical state, and efficacy of different routes of antibiotic administration were evaluated. RESULTS: The mean time necessary to obtain CSF sterilization was 2.9 ± 2.7 days (range 1-12 days). The CSF cultures became negative within 24 hours after the administration of IVT/IT antibiotics in 17 patients (50%) and up to 48 hours in a further 6 patients (18%). The clinical outcome of patients assessed by the modified Rankin Scale improved in 17 patients (50%), stayed unchanged in 10 patients (29%), and was impaired in 1 patient (3%). Six patients (18%) died; however, 2 of them died due to reasons not directly related to meningitis or ventriculitis, so the overall mortality rate for meningitis and/or ventriculitis was 11.8% in this group of patients. All patients with ventriculitis (n = 4) were treated by antibiotics administered via the IVT route. The average time to CSF sterilization was 6.5 days in the patients with ventriculitis. Thirty patients had clinical signs of meningitis without ventriculitis. Despite the higher ratio of unfavorable Gram-negative meningitis in the subgroup of patients treated via lumbar drainage, the mean duration of CSF sterilization was 2.2 days compared with 2.6 days in the subgroup treated via external ventricular drainage, a difference that was not statistically significant (p = 0.3). Adverse effects of IVT/IT antibiotics appeared in 3 of 34 patients and were of low clinical significance. CONCLUSIONS: Intraventricular/lumbar intrathecal antibiotics can lead to very quick CSF sterilization in postneurosurgical patients with meningitis and ventriculitis. The relapse rate of meningitis and/or ventriculitis is also very low among patients treated by IVT/IT antibiotics. Intraventricular/lumbar intrathecal administration of antibiotics appears to be an effective and safe treatment for infections of the CNS caused by multidrug-resistant organisms. In patients with signs of ventriculitis, the authors prefer the IVT route of antibiotics. This study did not prove a lower efficacy of administration of antibiotics via lumbar drainage compared with the ventricular route in patients with meningitis.

Gram-negative versus Gram-positive bacteremia: what is more alarmin(g)?

Gram-negative bacteremia has been associated with severe sepsis, although the exact mechanism and pathophysiological differences among bacterial species are not well understood. In the previous issue of Critical Care, Abe and colleagues report results of a retrospective study that show a significantly higher incidence of Gram-negative bacteremia among adult intensive care unit patients with septic shock than in those with sepsis or severe sepsis. In this study, C-reactive protein and IL-6 levels were significantly higher in Gram-negative bacteremia than in Gram-positive bacteremia. These observations suggest a distinct immunopathophysiologic behavior of sepsis in patients with Gram-negative bacteremia that may influence clinical outcomes. Future research exploring new biomarkers and danger signals and further characterizing differences in the virulence mechanisms between Gram-negative and Gram-positive bacteria appears promising and could lead to new therapeutics and to improved clinical outcomes.

Species distribution and antimicrobial susceptibility of gram-negative aerobic bacteria in hospitalized cancer patients.

BACKGROUND: Nosocomial infections pose significant threats to hospitalized patients, especially the immunocompromised ones, such as cancer patients. METHODS: This study examined the microbial spectrum of gram-negative bacteria in various infection sites in patients with leukemia and solid tumors. The antimicrobial resistance patterns of the isolated bacteria were studied. RESULTS: The most frequently isolated gram-negative bacteria were Klebsiella pneumonia (31.2%) followed by Escherichia coli (22.2%). We report the isolation and identification of a number of less-frequent gram negative bacteria (Chromobacterium violacum, Burkholderia cepacia, Kluyvera ascorbata, Stenotrophomonas maltophilia, Yersinia pseudotuberculosis, and Salmonella arizona). Most of the gram-negative isolates from Respiratory Tract Infections (RTI), Gastro-intestinal Tract Infections (GITI), Urinary Tract Infections (UTI), and Bloodstream Infections (BSI) were obtained from leukemic patients. All gram-negative isolates from Skin Infections (SI) were obtained from solid-tumor patients. In both leukemic and solid-tumor patients, gram-negative bacteria causing UTI were mainly Escherichia coli and Klebsiella pneumoniae, while gram-negative bacteria causing RTI were mainly Klebsiella pneumoniae. Escherichia coli was the main gram-negative pathogen causing BSI in solid-tumor patients and GITI in leukemic patients. Isolates of Escherichia coli, Klebsiella, Enterobacter, Pseudomonas, and Acinetobacter species were resistant to most antibiotics tested. There was significant imipenem -resistance in Acinetobacter (40.9%), Pseudomonas (40%), and Enterobacter (22.2%) species, and noticeable imipinem-resistance in Klebsiella (13.9%) and Escherichia coli (8%). CONCLUSION: This is the first study to report the evolution of imipenem-resistant gram-negative strains in Egypt. Mortality rates were higher in cancer patients with nosocomial Pseudomonas infections than any other bacterial infections. Policies restricting antibiotic consumption should be implemented to avoid the evolution of newer generations of antibiotic resistant-pathogens.

Emerging gram-negative antibiotic resistance: daunting challenges, declining sensitivities, and dire consequences.

Emerging antibiotic resistance has created a major public health dilemma, compounded by a dearth of new antibiotic options. Multidrug-resistant Gram-negative organisms have received less attention than Gram-positive threats, such as methicillin-resistant Staphylococcus aureus, but are just as menacing. Pathogens such as Pseudomonas aeruginosa and Acinetobacter baumannii employ a variety of resistance mechanisms and are associated with dangerous nosocomial outbreaks. In some cases these pathogens have expressed resistance to all clinically available compounds. The emergence of extended-spectrum beta-lactamase-producing organisms in the community has raised alarm. Furthermore, the carbapenems, currently the most successful class of antibiotics, are showing signs of vulnerability. While the search for new antibiotic options continues, there is urgent need to employ strategies that will slow the development of resistance to the current armamentarium, such as avoiding prolonged antibiotic use or under-dosing, using pharmacokinetic and pharmacodynamic principles to choose dosing regimens, and encouraging early and aggressive empirical therapy, followed by de-escalation and narrowing the antimicrobial spectrum when culture results become available.

Factors affecting the bacteriology of deep neck infection: a retrospective study of 128 patients.

CONCLUSIONS: Broad-spectrum antibiotics are advocated for treating deep neck infection. Anaerobic coverage is necessary, especially in odontogenic cases. The presence of diabetes, infection of the parotid space and an obvious odontogenic source of infection can aid in determining the causative organisms. OBJECTIVES: This study aimed to analyze the bacteriology in deep neck infections and identify the factors that influenced the causative pathogens. MATERIALS AND METHODS: The records of 212 patients who were diagnosed as having deep neck infections at the National Taiwan University Hospital between 1997 and 2003 were reviewed; 128 patients with bacterial isolation from their pus cultures were enrolled. RESULTS: The cultures of 46 patients (35.9%) were polymicrobial. Viridans Streptococcus was the most commonly isolated organism (38.3%), followed by Klebsiella pneumoniae (32.0%) and Peptostreptococcus (17.2%). The most common organism in 44 diabetic patients was K. pneumoniae (54.5%), versus viridans streptococcus (48.8%) in 84 nondiabetic patients. In patients with dental sources of infections, the culture rate of anaerobes was 59.3%; in upper airway infections and other sources of infections they were 22.7% and 21.5%, respectively (Chi(2) test, p = 0.0008). The differences in age, sex, and climate did not show any significant changes in the common causative pathogens. Common pathogens in the infection of parapharyngeal, submandibular, and extended spaces were the same as viridans streptococcus, but in the parotid space K. pneumoniae was the most common pathogen.

The changing pathogens of complicated parapneumonic effusions or empyemas in a medical intensive care unit.

OBJECTIVES: To assess the incidence, pathogens, and outcome of complicated parapneumonic effusions or empyemas in a medical intensive care unit (MICU) patients with pleural effusions. DESIGN AND SETTING: Prospective study of febrile MICU patients with pleural effusion carried out in a tertiary care hospital between April 2001 and September 2003. PATIENTS: The study included 175 patients with a temperature above 38 degrees for more than 8 h with evidence of pleural effusion confirmed by chest radiography and ultrasound. INTERVENTION: Routine thoracentesis and effusion cultures. RESULTS: The prevalence of complicated parapneumonic effusions or thoracic empyemas in febrile MICU patients with pleural effusions was 45% (78/175). A total of 78 micro-organisms were isolated from the pleural fluid of 58 patients (positive microbiological culture 74%) including aerobic Gram-negative (n=45), aerobic Gram-positive (n=23), anaerobic (n=5), Myobacterium tuberculosis (n=3), and Candida (n=2). The infection-related mortality rate of complicated parapneumonic effusions or empyemic patients in the MICU was 41% (32/78). CONCLUSION: The development of complicated parapneumonic effusions or thoracic empyemas in MICU patients is a high-mortality disease. The increasing incidence of aerobic Gram-negative pathogens in empyema has become a more urgent problem.

The lipid A palmitoyltransferase PagP: molecular mechanisms and role in bacterial pathogenesis.

Palmitoylated lipid A can both protect pathogenic bacteria from host immune defences and attenuate the activation of those same defences through the TLR4 signal transduction pathway. A palmitate chain from a phospholipid is incorporated into lipid A by an outer membrane enzyme PagP, which is an 8-stranded antiparallel beta-barrel preceded by an amino-terminal amphipathic alpha-helix. The PagP barrel axis is tilted by 25 degrees with respect to the membrane normal. An interior hydrophobic pocket in the outer leaflet-exposed half of the molecule functions as a hydrocarbon ruler that allows the enzyme to distinguish palmitate from other acyl chains found in phospholipids. Internalization of a phospholipid palmitoyl group within the barrel appears to occur by lateral diffusion from the outer leaflet through non-hydrogen-bonded regions between beta-strands. The MsbA-dependent trafficking of lipids from the inner membrane to the outer membrane outer leaflet is necessary for lipid A palmitoylation in vivo. The mechanisms by which bacteria regulate pagP gene expression strikingly reflect the corresponding pathogenic lifestyle of the bacterium. Variations on PagP structure and function can be illustrated with the known homologues from Gram-negative bacteria, which include pathogens of humans and other mammals in addition to pathogens of insects and plants. The PagP enzyme is potentially a target for the development of anti-infective agents, a probe of outer membrane lipid asymmetry, and a tool for the synthesis of lipid A-based vaccine adjuvants and endotoxin antagonists.

Etiology of ventilator-associated pneumonia.

This review focuses on the top ten causes of ventilator-associated pneumonia (VAP), updating an earlier study. These pathogens have specific risk factors, different patterns of clinical resolution, and a wide range of attributable mortality. The discussion herein analyzes these aspects, placing particular emphasis on risk factors, attributable mortality, resistance, and the implications for management.

Imipenem resistance in nonfermenters causing nosocomial urinary tract infections.

Nonfermenting gram-negative bacilli (nonfermenters) have emerged as important nosocomial pathogens causing opportunistic infections in immunocompromised hosts. These organisms show high level of resistance to b-lactam agents, fluoroquinolones and aminoglycosides. Imipenem is a carbapenem antibiotic, which can be very useful for treatment of infections caused by nonfermenters. Eighty-five nonfermenters causing nosocomial UTI were tested for MIC to imipenem by agar dilution method. Resistance to other antimicrobial agents was compared between imipenem sensitive (S) and resistance (R) groups. Overall 36.4% of nonfermenters were resistant to imipenem. Forty two percent of P. aeruginosa and 18.5% of Acinetobacter baumanii were imipenem resistant. Other nonfermenters showed variable resistance, resistance in Alcaligenes spp. being very high. More than 70% of the nonfermenters were resistant to ceftazidime, gentamicin and ciprofloxacin. Piperacillin and amikacin had the best in vitro susceptibility. No significant difference was found in the antibiotic susceptibility profile among imipenem sensitive (S) or resistant (R) strains.

Diversity of Gram negative bacteria antagonistic against major pathogens of rice from rice seed in the tropic environment.

With the use of a seed washing technique, more than 4000 Gram negative bacteria were isolated by two improved isolation methods from 446 batches of 1 kg rice seed samples obtained from 22 provinces in the Philippines. They were initially characterized on the basis of colony morphology and results of biochemical and pathogenicity tests. Six hundred and fifty-two strains were further identified by Biolog, from which 133 were selected for fatty acid methylester (FAME) analysis together with 80 standard reference strains. Sixteen species or types of Pseudomonas and 17 genera of non-pseudomonads were identified, more than one third of which have not been recorded in rice. The most predominant species observed were P.putida and P. fulva. About 17% of the strains of Pseudomonas and 2% of the non pseudomonads were antagonistic to one or more fungal or bacterial pathogens of rice. Rice seed is an important source of biological control agents.

Non-fermenters in human infections.

One thousand and one hundred thirty non-fermenting gram negative bacteria were isolated from various samples. Of these, Pseudomonas aeruginosa was the commonest isolate (72.83%) followed by Acinetobacter anitratus (8.4%), Alcaligenes faecalis (7.6%), Acinetobacter lwoffi (4.4%), Pseudomonas flourescens (2.4%), Schwanella putrefaciens (1.6%), Stenotrophomonas maltophilia (1.6%), Pseudomonas putida (0.4%), Bravundimonas vesicularis (0.4%) and Flavobacterium meningosepticum (0.4%). Antibiotic sensitivity pattern showed multiple drug resistance pattern with majority of the isolates being resistance to two or more drugs.

Fusospirochetal superinfection of pre-existing oral lesion in patients with acquired immunodeficiency syndrome.

Three patients with AIDS presented with nonbleeding, painful, fetid, oral ulcers overlaid with a grayish-black semiadherent membrane at the sites of a pre-existing lesion. These lesions persisted despite treatment directed toward the primary etiology (cytomegalovirus, Kaposi's sarcoma). Gram- and Giemsa-stained smears of teased membrane fragments revealed an impressive bacterial flora with fusiforms and Borrelia-type spirochetes. Prompt treatment with penicillin brought amelioration of symptoms and sloughing of the overlaying membrane.

A two-component system in Ralstonia (Pseudomonas) solanacearum modulates production of PhcA-regulated virulence factors in response to 3-hydroxypalmitic acid methyl ester.

Expression of virulence factors in Ralstonia solanacearum is controlled by a complex regulatory network, at the center of which is PhcA, a LysR family transcriptional regulator. We report here that expression of phcA and production of PhcA-regulated virulence factors are affected by products of the putative operon phcBSR(Q). phcB is required for production of an extracellular factor (EF), tentatively identified as the fatty acid derivative 3-hydroxypalmitic acid methyl ester (3-OH PAME), but a biochemical function for PhcB could not be deduced from DNA sequence analysis. The other genes in the putative operon are predicted to encode proteins homologous to members of two-component signal transduction systems: PhcS has amino acid similarity to histidine kinase sensors, whereas PhcR and OrfQ are similar to response regulators. PhcR is quite unusual because its putative output domain strongly resembles the histidine kinase domain of a sensor protein. Production of the PhcA-regulated factors exopolysaccharide I, endoglucanase, and pectin methyl esterase was reduced 10- to 100-fold only in mutants with a nonpolar insertion in phcB [which express phcSR(Q) in the absence of the EF]; simultaneously, expression of phcA was reduced fivefold. Both a wild-type phenotype and phcA expression were restored by addition of 3-OH PAME to growing cultures. Mutants with polar insertions in phcB or lacking the entire phcBSR(Q) region produced wild-type levels of PhcA-regulated virulence factors. The genetic data suggest that PhcS and PhcR function together to regulate expression of phcA, but the biochemical mechanism for this is unclear. At low levels of the EF, it is likely that PhcS phosphorylates PhcR, and then PhcR interacts either with PhcA (which is required for full expression of phcA) or an unknown component of the signal cascade to inhibit expression of phcA. When the EF reaches a threshold concentration, we suggest that it reduces the ability of PhcS to phosphorylate PhcR, resulting in increased expression of phcA and production of PhcA-regulated factors.

Rapid induction by wounding and bacterial infection of an S gene family receptor-like kinase gene in Brassica oleracea.

A receptor-like kinase, SRK, has been implicated in the autoincompatible response that leads to the rejection of self-pollen in Brassica plants. SRK is encoded by one member of a multigene family, which includes several receptor-like kinase genes with patterns of expression very different from that of SRK but of unknown function. Here, we report the characterization of a novel member of the Brassica S gene family, SFR2. RNA gel blot analysis demonstrated that SFR2 mRNA accumulated rapidly in response both to wounding and to infiltration with either of two bacteria: Xanthomonas campestris, a pathogen, and Escherichia coli, a saprophyte. SFR2 mRNA also accumulated rapidly after treatment with salicylic acid, a molecule that has been implicated in plant defense response signaling pathways. A SFR2 promoter and reporter gene fusion was introduced into tobacco and was shown to be induced by bacteria of another genus, Ralstonia (Pseudomonas) solanacearum. The accumulation of SFR2 mRNA in response to wounding and pathogen invasion is typical of a gene involved in the defense responses of the plant. The rapidity of SFR2 mRNA accumulation is consistent with SFR2 playing a role in the signal transduction pathway that leads to induction of plant defense proteins, such as pathogenesis-related proteins or enzymes of phenylpropanoid metabolism.