Mortality and the increase in length of stay attributable to the acquisition of Acinetobacter in critically ill patients

Sequence-Specific Electrochemical Genosensor for Rapid Detection of blaOXA-51-like Gene in Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) are phenotypically indistinguishable from the Acinetobacter calcoaceticus−A. baumannii (ACB) complex members using routine laboratory methods. Early diagnosis plays an important role in controlling A. baumannii infections and this could be assisted by the development of a rapid, yet sensitive diagnostic test. In this study, we developed an enzyme-based electrochemical genosensor for asymmetric PCR (aPCR) amplicon detection of the blaOXA-51-like gene in A. baumannii. A. baumanniiblaOXA-51-like gene PCR primers were designed, having the reverse primer modified at the 5′ end with FAM. A blaOXA-51-like gene sequence-specific biotin labelled capture probe was designed and immobilized using a synthetic oligomer (FAM-labelled) deposited on the working electrode of a streptavidin-modified, screen-printed carbon electrode (SPCE). The zot gene was used as an internal control with biotin and FAM labelled as forward and reverse primers, respectively. The blaOXA-51-like gene was amplified using asymmetric PCR (aPCR) to generate single-stranded amplicons that were detected using the designed SPCE. The amperometric current response was detected with a peroxidase-conjugated, anti-fluorescein antibody. The assay was tested using reference and clinical A. baumannii strains and other nosocomial bacteria. The analytical sensitivity of the assay at the genomic level and bacterial cell level was 0.5 pg/mL (1.443 µA) and 103 CFU/mL, respectively. The assay was 100% specific and sensitive for A. baumannii. Based on accelerated stability performance, the developed genosensor was stable for 1.6 years when stored at 4 °C and up to 28 days at >25 °C. The developed electrochemical genosensor is specific and sensitive and could be useful for rapid, accurate diagnosis of A. baumannii infections even in temperate regions.

Efficacy of Eravacycline Versus Best Previously Available Therapy for Adults With Pneumonia Due to Difficult-to-Treat Resistant (DTR) Acinetobacter baumannii

BACKGROUND

Multidrug-resistant Acinetobacter baumannii remains challenging to treat. Although eravacycline has in vitro activity against this pathogen, there are no studies evaluating outcomes.

OBJECTIVE

To assess the efficacy of eravacycline compared with best previously available therapy in adults with difficult-to-treat resistant (DTR) A. baumannii pneumonia.

METHODS

This was a retrospective study of adults hospitalized for pneumonia with DTR A. baumannii. Patients receiving eravacycline were compared with those receiving best previously available therapy. The primary outcome was 30-day in-hospital mortality. Secondary outcomes included clinical cure at Day 14, hospital and intensive care unit (ICU) length of stay, microbiologic cure, and readmission within 90 days with a positive A. baumannii respiratory culture.

RESULTS

Ninety-three patients were included, with 27 receiving eravacycline. Eravacycline was associated with higher 30-day mortality (33% vs 15%; P = 0.048), lower microbiologic cure (17% vs 59%; P = 0.004), and longer durations of mechanical ventilation (10.5 vs 6.5 days; P = 0.016). At baseline, eravacycline patients had more A. baumannii bacteremia and coinfection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Among bacteremic patients, all 4 receiving eravacycline died by Day 30 and both patients receiving best previously available therapy survived. Upon exclusion of patients with bacteremia and SARS-CoV-2, there were no differences between the groups across any outcomes.

CONCLUSIONS

Eravacycline-based combination therapy had similar outcomes to best previously available combination therapy for adults with DTR A. baumannii pneumonia. However, eravacycline should be used with caution in the setting of bacteremia as outcomes were poor in this population.

Association of capsular polysaccharide locus 2 with prognosis of Acinetobacter baumannii bacteraemia

Acinetobacter baumannii causes healthcare-associated infections worldwide. Capsular polysaccharide (CPS) is shown an important virulence factor of A. baumannii both in vitro and in vivo. Capsule locus 2 (KL2) for CPS is the most common KL type and is associated with carbapenem resistance. It is unclear whether KL2 is related to the clinical outcome of invasive A. baumannii infection. Here we had followed patients with A. baumannii bacteraemia prospectively between 2009 and 2014. One-third of the unduplicated blood isolates were randomly selected each year for microbiological and clinical studies. The KL2 gene cluster was identified using polymerase chain reaction. A total of 148 patients were enrolled randomly. Eighteen isolates (12.2%) carried KL2, and 130 isolates (87.8%) didn’t. Compared with non-KL2 isolates, KL2 isolates had significantly higher resistance to imipenem, sulbactam, and tigecycline. Compared with the non-KL group, in the KL2 group, the hospital stay before development of bacteraemia was longer (P < 0.001), a higher percentage had pneumonia (P = 0.004), and the white blood cell count was lower (P = 0.03). Infection with KL2 A. baumannii predicted mortality (adjusted hazard ratio [aHR], 2.03; 95% confidence interval [CI], 1.09–3.78; P = 0.03), independently of the Pitt bacteraemia score (aHR, 1.34; 95% CI, 1.23–1.46; P < 0.001) and leucopenia (aHR, 2.16; 95% CI, 1.30–3.57; P = 0.003). Thrombocytopenia contributed to the effect of KL2 on mortality in bacteraemia (Sobel test P = 0.01). Large-scale studies are warranted to confirm these findings and the underlying mechanisms deserve further investigation.

Importance of control groups when delineating antibiotic use as a risk factor for carbapenem resistance, extreme-drug resistance, and pan-drug resistance in Acinetobacter baumannii and Pseudomonas aeruginosa: A systematic review and meta-analysis

BACKGROUND

Carbapenem-resistant (CR), extremely drug-resistant (XDR), and pan-drug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa pose a huge clinical threat. This study reviews the impact of control groups on the association of antecedent antibiotic use and the acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa.

METHODS

Studies investigating the role of antibiotics as a risk factor for CR/XDR/PDR A. baumannii and P. aeruginosa acquisition in adult hospitalized patients from 1950 to 2016 were identified in the databases. These were divided into two groups: antibiotic-resistant versus antibiotic-sensitive pathogens (group I); antibiotic-resistant versus no infection (group II). A random-effects model was performed.

RESULTS

Eighty-five studies (46 A. baumannii, 38 P. aeruginosa, and one of both) involving 22 396 patients were included. CR was investigated in 60 studies, XDR in 20 studies, and PDR in two studies. Prior antibiotic exposure was associated with significant acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa in both groups I and II (p<0.05). Antibiotic classes implicated in both groups included aminoglycosides, carbapenems, glycopeptides, and penicillins. Cephalosporin use was not associated with resistance in either group. Fluoroquinolone exposure was only associated with resistance in group I but not group II.

CONCLUSIONS

Control groups play an important role in determining the magnitudes of risk estimates for risk factor studies, hence careful selection is necessary. Antibiotic exposure increases the acquisition of highly resistant A. baumannii and P. aeruginosa, thus appropriate antibiotic use is imperative.

Postoperative infection caused by Acinetobacter baumannii misdiagnosed as a free-living amoeba species in a humeral head hemiarthroplasty patient: a case report

BACKGROUND

Acinetobacter baumannii is ubiquitous, facultative intracellular, and opportunistic bacterial pathogen. Its unique abilities allow it to survive in a diverse range of environments, including health care settings, leading to nosocomial infections. And its exceptional ability to develop resistance to multiple antibiotics leaves few drug options for treatment. It has been recognized as a leading cause of nosocomial pneumonia and bacteremia over the world.

CASE PRESENTATION

In this case, a 73-year-old woman presented with a Neer Group VI proximal humeral fracture. Six hours after a successfully performed hemiarthroplasty, she developed continuous fever. Clinical examination revealed that the vitals were regular. Laboratory and radiographic examinations revealed only elevated procalcitonin levels. Blood culture revealed no bacterial or fungal growth. Cooling treatment and empirical broad-spectrum antibiotic therapy showed no apparent effect.

CONCLUSIONS

We report a postoperative infection caused by Acinetobacter baumannii. The infectious pathogen was identified via molecular DNA sequencing and was initially misidentified as a free-living amoeba species upon microscopic examinations. The patient was mistreated with antiamebic combination therapy. Her symptoms persisted for over 4 months and were eventually followed by her death.

Pneumonia in Trauma Patients

Purpose of Review

This article reviews the new definitions of pneumonia, discusses risk factors for pneumonia among trauma patients, presents the latest evidence for prevention strategies, discusses the best ways to make the diagnosis, and reviews the microbiology and treatment for trauma patients with pneumonia.

Recent Findings

Pneumonia can be prevented by decreasing the duration of mechanical ventilation using daily paired spontaneous awakening and breathing trials, but not with early tracheostomy placement. Other useful prevention strategies include semirecumbent positioning and oral care. Mini-BAL is a sensitive and specific means of securing the diagnosis of pneumonia that does not require a physician to be present and is therefore especially useful in busy trauma centers.

Summary

Pneumonia is a frequent complication among trauma patients. Risk factors are largely unmodifiable. However, trauma centers can institute routine daily paired spontaneous awakening and breathing trials to decrease the duration of ventilation and incidence of pneumonia. Future research is needed to further characterize the microbiology of pneumonia among trauma patients.

Clinical and Economic Evaluation of Multidrug-Resistant Acinetobacter baumannii Colonization in the Intensive Care Unit

Background

The clinical and economic impact of multidrug-resistant (MDR) Acinetobacter baumannii colonization remains unclear. This study aimed to estimate and compare the mortality rates, length of stay (LOS), and hospitalization costs in the intensive care unit (ICU) for MDR A. baumannii colonized patients and a matched population.

Materials and Methods

We performed a retrospective propensity score matched cohort study comparing the outcomes of patients with MDR A. baumannii colonization with those of uncolonized subjects matched at the time they were admitted to the ICU between January 2012 and December 2014.

Results

During the study period, 375 (7.5%) of the 4,779 patients were colonized with MDR A. baumannii. One hundred and twenty-two MDR A. baumannii colonized patients were compared with 122 uncolonized patients using propensity score matching. MDR A. baumannii colonized patients were likely to have a higher mortality rate compared to uncolonized patients (49.2% vs 32.0%; odds ratio [OR], 3.64). A longer ICU LOS and total admission days were observed in the MDR A. baumannii colonized patient group (4.14 and 4.67 days increase, OR 1.41 and 1.19). MDR A. baumannii colonization patients had an average extra ICU and total admission cost of $1,179 (₩1,261,334) and $1,333 (₩1,422,032) according to a multivariable regression model (OR, 1.27 and 1.17). Multivariable analysis identified the factors affecting ICU cost, which included, MDR A. baumannii colonization (OR = 1.33; P = 0.001), ICU LOS (OR = 1.97; P <0.001), valvular heart disease (OR = 1.12; P = 0.005), invasive devices (OR = 1.15; P = 0.018), and surgery (OR = 1.1; P <0.001).

Conclusion

MDR A. baumannii colonization was associated with increased mortality, LOS, and costs in the ICU. A strict infection control program including preemptive isolation for high-risk groups would be helpful for reducing the burden of this infection.

Can the Cost of Distal Vascular Reconstruction be Reduced Without Sacrificing Quality? Analysis of 500 Cases

The goal of clinical pathways is to reduce the cost of the hospitalization while maintaining acceptable results (patency, morbidity, and mortality). Patients who present with lower extremity revascularization pose a difficult problem, for they have significant comorbid medical disease. In this study the authors analyze their results and the treatment cost for patients undergoing lower extremity revascularization before and after the institution of clinical pathways.

Data were collected independently by the hospital financial office, and surgical outcomes were derived from the prospectively collected computerized vascular registry. Data were analyzed for 12 months before and after institution of pathways. Cost, length of stay (LOS), and use of ancillary service as well as mortality, morbidity, and patency rates were evaluated. During each period, patients were selectively admitted to the intensive care unit based on perioperative risk factors independent of the pathway.

Three hundred ninety-nine patients with distal reconstructions were placed on the path during this time period. These were compared to a group of 286 patients who were not on the path in the year prior. The LOS decreased from 14.3 days to 9.2 days. Electrolyte laboratory panels decreased from 12 draws per patient per admission to two draws per patient per admission. This trend was also seen in complete blood count (11.8 to 6.8), glucose (12.6 to 2.1), and electrolytes (12.2 to 1.8). Perioperative mortality rates were similar (2.5% vs 1.9%) with no change in morbidity rates. Total cost for hospitalization decreased by 27% after institution of the clinical pathway.

From these data, the authors can demonstrate that the institution of clinical pathways not only decreased total cost, use of ancillary laboratory tests, and LOS but also did not negatively impact on outcome.

Concurrent Outbreak of Multidrug-Resistant and Susceptible Subclones of Acinetobacter baumannii Affecting Different Wards of a Single Hospital

Background and Objective:

Acinetobacter baumannii has emerged as an opportunistic pathogen among acutely ill patients, especially those with thermal injury. A prospective 8-month study was conducted to describe the clinical and molecular epidemiology of multidrug-resistant A. baumannii affecting a single hospital.

Methods:

Univariate analysis comparing Smal macrorestriction patterns of A. baumannii generated by pulsed-field gel electrophoresis (PFGE) versus clinical and demographic risk factors.

Results:

A total of 200 isolates from 76 patients were collected, of which 185 isolates from 76 patients were analyzed by PFGE. A total of 17 distinct PFGE clonal types were identified. One clonal type (strain A) represented 129 isolates from 49 patients. A group of related clonal types (strain A variants) were identified as 40 isolates from 20 patients. The only risk factor other than geographic location associated with the presence of strain A was prior treatment with antibiotics active against gram-negative bacteria (P = .0015). The two clonal types differed in antibiotic resistance profiles: 25% of strain A isolates, the dominant strain in the burn unit, were susceptible to at least one antibiotic tested. In contrast, approximately 80% of the other strain types were susceptible to at least one antibiotic and were cultured from patients admitted elsewhere in the hospital. No combination of antibiotics was observed to yield additive or synergistic activity.

Conclusion:

Clonally related strains of Acinetobacter that differ in susceptibility patterns may coexist within a single hospital, dependent on the selective pressure related to antibiotic exposure.

Biofilm Formation and Motility Depend on the Nature of the Acinetobacter baumannii Clinical Isolates

Acinetobacter baumannii is a nosocomial pathogen involved in various infections ranging from minor soft-tissue infections to more severe infections such as ventilator-associated pneumonia and bacteremia. The severity and the type of infections depend on the genetic and phenotypic variations of the strains. In this study, we compared the extent of biofilm formation and motility displayed by 60 multidrug-resistant A. baumannii clinical strains isolated from blood and sputum samples from patients from Southern India. Our results showed that isolates from the sputum samples formed significantly more robust biofilm compared to the blood isolates. On the other hand, we observed that the blood isolates were more motile than the sputum isolates. To the best of our knowledge, this is the first study that systematically evaluated the correlation between these two phenotypic traits and the nature of the isolates.

Combatting resistance in intensive care: the multimodal approach of the Spanish ICU "Zero Resistance" program

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2015 and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/annualupdate2015. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Nosocomial Outbreak of Infection With Pan–Drug-ResistantAcinetobacter baumanniiin a Tertiary Care University Hospital

Objective.

TO describe what is, to our knowledge, the first nosocomial outbreak of infection with pan–drug-resistant (including colistin-resistant)Acinetobacter baumannii,to determine the risk factors associated with these types of infections, and to determine their clinical impact.

Design.

Nested case-control cohort study and a clinical-microbiological study.

Setting.

A 1,521-bed tertiary care university hospital in Seville, Spain.

Patients.

Case patients were inpatients who had a pan-drug-resistantA. baumanniiisolate recovered from a clinical or surveillance sample obtained at least 48 hours after admission to an intensive care unit (ICU) during the time of the epidemic outbreak. Control patients were patients who were admitted to any of the “boxes” (ie, rooms that partition off a distinct area for a patient's bed and the equipment needed to care for the patient) of an ICU for at least 48 hours during the time of the epidemic outbreak.

Results.

All the clinical isolates had similar antibiotic susceptibility patterns (ie, they were resistant to all the antibiotics tested, including Colistin), and, on the basis of repetitive extragenic palindromic-polymerase chain reaction, it was determined that all of them were of the same clone. The previous use of quinolones and glycopeptides and an ICU stay were associated with the acquisition of infection or colonization with pan-drug-resistant A.baumannii.To control this outbreak, we implemented the following multicomponent intervention program: the performance of environmental decontamination of the ICUs involved, an environmental survey, a revision of cleaning protocols, active surveillance for colonization with pan-drug-resistantA. baumannii,educational programs for the staff, and the display of posters that illustrate contact isolation measures and antimicrobial use recommendations.

Conclusions.

We were not able to identify the common source for these cases of infection, but the adopted measures have proven to be effective at controlling the outbreak.

Abattoirs as non-hospital source of extended spectrum beta lactamase producers: confirmed by the double disc synergy test and characterized by matrix-assisted laser desorption/ionization time of flight mass spectrometry

In this study, the presence of extended spectrum beta lactamase (ESBL) producing organisms in abattoirs, a non-hospital community was investigated. The presence of ESBL-producing phenotypes was confirmed by the Double Disc Synergy Test (DDST). Out of the 99 isolates screened for ESBL, 28 (28.3%) were confirmed positive. The positive isolates were characterised by using Matrix-Assisted Laser Desorption/Ionization Time of flight Mass Spectrometry. 50% of the isolates were Pseudomonas spp., the rest were different species of Acinetobacter, Stenotrophomonas and Achromobacter. Pseudomonas monteilli and Pseudomonas putida were the most occurring in the intestine. The entire positive ESBL producers were subjected to plasmid curing to ascertain the location of the resistant marker. The result of the plasmid curing indicated that the resistant genes were chromosomally borne. The findings have therefore established the presence of ESBL producing organisms in the gut of animals from abattoirs and the table were the meat are sold, and its rate of occurrence is comparable to hospital ICUs. Abattoir communities could probably be a source of human infection with ESBL expressing pathogens and possible transfer to non-ESBL producers.

Draft Genome Sequence of Multidrug-Resistant Acinetobacter baumannii Strain MMC4, Isolated from a Patient in Tennessee

Acinetobacter baumannii multidrug-resistant strain MMC4 was isolated from a bronchoalveolar lavage fluid sample from a patient in Nashville, TN, USA. Here, we report a draft genome sequence with a size of 3,985,367 bp, an average G+C content of 39.8%, and 3,863 predicted protein-coding sequences.

Epidemiology of severe sepsis

Severe sepsis is a leading cause of death in the United States and the most common cause of death among critically ill patients in non-coronary intensive care units (ICU). Respiratory tract infections, particularly pneumonia, are the most common site of infection, and associated with the highest mortality. The type of organism causing severe sepsis is an important determinant of outcome, and gram-positive organisms as a cause of sepsis have increased in frequency over time and are now more common than gram-negative infections.

Recent studies suggest that acute infections worsen pre-existing chronic diseases or result in new chronic diseases, leading to poor long-term outcomes in acute illness survivors. People of older age, male gender, black race, and preexisting chronic health conditions are particularly prone to develop severe sepsis; hence prevention strategies should be targeted at these vulnerable populations in future studies.

Trauma is associated with a better prognosis in intensive care patients with Acinetobacter infections

PURPOSE

Acinetobacter baumannii has emerged as a common cause of infection in war-related trauma, civilian trauma and other surgical emergencies. The aim of this study was to determine prognostic factors especially trauma, in critically ill surgical patients with Acinetobacter spp. infection in a reference emergency ICU.

METHODS

A retrospective review of medical records was conducted for all patients admitted to the ICU who developed Acinetobacter spp. infection from January 2007 to December 2009. Bivariate and multivariate analyses were made for 36 patients. The end-point analyzed was the in-hospital mortality.

RESULTS

The initial analysis revealed a majority of young (43.6 years ± 17.1) men (92 %), trauma victims (78 %) and an in-hospital mortality of 30 %. Patients who had not suffered trauma presented with other surgical conditions and were on average older than trauma patients (57 ± 12 versus 40 ± 16 years). The overall APACHE II score average was 15.3. The ventilator-associated pneumonia was the main Acinetobacter infection diagnosed. In bivariate analysis lower Glasgow coma scale (p = 0.01) was associated with increased chance of death and being victim of trauma was a protecting factor (OR: 0.16; 95 % CI: 0.03-0.89). Receiving adequate treatment made no difference to outcome (OR: 0.55; 95 % CI: 0.05-3.15). Multivariate analysis showed that only the presence of trauma was independently associated with prognosis and was a protecting factor.

CONCLUSION

Trauma was a marker of good prognosis in emergency ICU patients with Acinetobacter spp. infection.

Expression, crystallization and preliminary X-ray crystallographic analysis of alanine racemase from Acinetobacter baumannii OXA-23

Acinetobacter baumannii has received much attention owing to its exceptional ability to develop resistance to currently available antibiotics. Alanine racemase (ALR) catalyzes the racemization of L-alanine to D-alanine with pyridoxal 5'-phosphate (PLP) as a cofactor. The D-alanine product is an essential component of the bacterial cell wall and ALR is a potential target for the development of novel antibacterial drugs. The alr gene from A. baumannii was cloned and the protein (AbALR) was expressed, purified and crystallized. The AbALR crystal diffracted to 2.3 Å resolution and belonged to the primitive orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 55.1, b = 85.0, c = 167.7 Å. Two protomers were present in the asymmetric unit, with a corresponding V(M) value of 2.3 Å(3) Da(-1) and a solvent content of 47.5%.

A systematic quantitative proteomic examination of multidrug resistance in Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii strains have been examined at the DNA sequence level, but seldom using large-scale quantitative proteomics. We have compared the proteome of the multidrug resistant strain BAA-1605, with the proteome of the drug-sensitive strain ATCC 17978, using iTRAQ labeling and online 2D LC/MS/MS for peptide/protein identification. Of 1484 proteins present in at least 2 of 4 independent experiments, 114 are 2-fold to 66-fold more abundant in BAA-1605, and 99 are 2-fold to 50-fold less abundant. Proteins with 2-fold or greater abundance in the multidrug resistant strain include drug-, antibiotic-, and heavy metal-resistance proteins, stress-related proteins, porins, membrane transporters, proteins important for acquisition of foreign DNA, biofilm-related proteins, cell-wall and exopolysaccharide-related proteins, lipoproteins, metabolic proteins, and many with no annotated function. The porin CarO, inactivated in carbapenem-resistant strains, is 2.3-fold more abundant in BAA-1605. Likewise, the porin OmpW, less abundant in carbapenem- and colistin-resistant A. baumannii strains, is 3-fold more abundant in BAA-1605. Nine proteins, all present in the drug-sensitive strain but from 2.2-fold to 16-fold more abundant in the MDR strain, can potentially account for the observed resistance of BAA-1605 to 18 antibiotics.

BIOLOGICAL SIGNIFICANCE

Multidrug resistant (MDR) strains of the pathogen Acinetobacter baumannii are a significant cause of hospital-acquired infections, are associated with increased mortality and length of stay, and may be a major factor underlying the spread of this pathogen, which is difficult to eradicate from clinical settings. To obtain a better understanding of antimicrobial resistance mechanisms in MDR A. baumannii, we report the first large scale 2D LC/MS/MS-based quantitative proteomics comparison of a drug-sensitive strain and an MDR strain of this pathogen. Ca. 20% of the expressed proteome changes 2-fold or more between the compared strains, including 42 proteins with literature or informatics annotations related to resistance mechanisms, modification of xenobiotics, or drug transport. Other categories of proteins differing 2-fold or more between strains include stress-response related proteins, porins, OMPs, transporters and secretion-related proteins, cell wall- and expolysaccharide-related proteins, lipoproteins, and DNA- and plasmid-related proteins. While the compared strains also differ in other aspects than multi-drug resistance, the observed differences, combined with protein functional annotation, suggest that complex protein expression changes may accompany the MDR phenotype. Expression changes of nine proteins in the MDR strain can potentially account for the observed resistance to 18 antibiotics.

Successful management of nosocomial ventriculitis and meningitis caused by extensively drug-resistant Acinetobacter baumannii in Austria

Nosocomial infections caused by the Gram-negative coccobacillus Acinetobacter baumannii have substantially increased over recent years. Because Acinetobacter is a genus with a tendency to quickly develop resistance to multiple antimicrobial agents, therapy is often complicated, requiring the return to previously used drugs. The authors report a case of meningitis due to extensively drug-resistant A baumannii in an Austrian patient who had undergone neurosurgery in northern Italy. The case illustrates the limits of therapeutic options in central nervous system infections caused by extensively drug-resistant pathogens.

Using the rate of bacterial clearance determined by real-time polymerase chain reaction as a timely surrogate marker to evaluate the appropriateness of antibiotic usage in critical patients with Acinetobacter baumannii bacteremia

OBJECTIVE

Bacteremia caused by Acinetobacter baumannii is becoming more frequent among critically ill patients, and has been associated with high mortality and prolonged hospital stay. Multidrug resistance and delay in blood culture have been shown to be significant barriers to appropriate antibiotic treatment. Quantitative polymerase chain reaction assays were recently used to monitor bacterial loads; we hypothesized that the rate of bacterial clearance determined by quantitative polymerase chain reaction can be used as a timely surrogate marker to evaluate the appropriateness of antibiotic usage.

DESIGN

Prospective observational study.

SETTING

University hospital and research laboratory.

PATIENTS

Patients with culture-proven A. baumannii bacteremia in the intensive care units were prospectively enrolled from April 2008 to February 2009.

INTERVENTIONS

Plasmid Oxa-51/pCRII-TOPO, which contained a 431-bp fragment of the A. baumannii-specific Oxa-51 gene in a pCRII-TOPO vector, was used as the standard. Sequential bacterial DNA loads in the blood were measured by a quantitative polymerase chain reaction assay.

MEASUREMENTS AND MAIN RESULTS

We enrolled 51 patients with A. baumannii bacteremia, and examined 318 sequential whole blood samples. The initial mean bacterial load was 2.15 log copies/mL, and the rate of bacterial clearance was 0.088 log copies/mL/day. Multivariate linear regression using the generalized estimation equation approach revealed that the use of immunosuppressants was an independent predictor for slower bacterial clearance (coefficient, 1.116; p<.001), and appropriate antibiotic usage was an independent predictor for more rapid bacterial clearance (coefficient, -0.995; p<.001). Patients with a slower rate of bacterial clearance experienced higher in-hospital mortality (odds ratio, 2.323; p=.04)

CONCLUSIONS

Immunosuppression and appropriate antibiotic usage were independent factors affecting the rate of clearance of A. baumannii bacteremia in critical patients. These findings highlight the importance of appropriate antibiotic usage and development of effective antibiotics against A. baumannii in an era of emerging antibiotic resistance. The rate of bacterial clearance could serve as a timely surrogate marker for evaluating the appropriateness of antibiotics.

Comparative proteomics of inner membrane fraction from carbapenem-resistant Acinetobacter baumannii with a reference strain

Acinetobacter baumannii has been identified by the Infectious Diseases Society of America as one of the six pathogens that cause majority of hospital infections. Increased resistance of A.baumannii even to the latest generation of β-lactams like carbapenem is an immediate threat to mankind. As inner-membrane fraction plays a significant role in survival of A.baumannii, we investigated the inner-membrane fraction proteome of carbapenem-resistant strain of A.baumannii using Differential In-Gel Electrophoresis (DIGE) followed by DeCyder, Progenesis and LC-MS/MS analysis. We identified 19 over-expressed and 4 down-regulated proteins (fold change>2, p<0.05) in resistant strain as compared to reference strain. Some of the upregulated proteins in resistant strain and their association with carbapenem resistance in A.baumannii are: i) β-lactamases, AmpC and OXA-51: cleave and inactivate carbapenem ii) metabolic enzymes, ATP synthase, malate dehydrogenase and 2-oxoglutarate dehydrogenase: help in increased energy production for the survival and iii) elongation factor Tu and ribosomal proteins: help in the overall protein production. Further, entry of carbapenem perhaps is limited by controlled production of OmpW and low levels of surface antigen help to evade host defence mechanism in developing resistance in A.baumannii. Present results support a model for the importance of proteins of inner-membrane fraction and their synergistic effect in the mediation of resistance of A.baumannii to carbapenem.

Acinetobacter baumannii: human infections, factors contributing to pathogenesis and animal models

Acinetobacter baumannii has emerged as a medically important pathogen because of the increasing number of infections produced by this organism over the preceding three decades and the global spread of strains with resistance to multiple antibiotic classes. In spite of its clinical relevance, until recently, there have been few studies addressing the factors that contribute to the pathogenesis of this organism. The availability of complete genome sequences, molecular tools for manipulating the bacterial genome, and animal models of infection have begun to facilitate the identification of factors that play a role in A. baumannii persistence and infection. This review summarizes the characteristics of A. baumannii that contribute to its pathogenesis, with a focus on motility, adherence, biofilm formation, and iron acquisition. In addition, the virulence factors that have been identified to date, which include the outer membrane protein OmpA, phospholipases, membrane polysaccharide components, penicillin-binding proteins, and outer membrane vesicles, are discussed. Animal models systems that have been developed during the last 15 years for the study of A. baumannii infection are overviewed, and the recent use of these models to identify factors involved in virulence and pathogenesis is highlighted.

Clinical characteristics and outcomes of bacteremia due to different genomic species of Acinetobacter baumannii complex in patients with solid tumors

PURPOSE

Acinetobacter baumannii, Acinetobacter genomic species 3 (AGS 3), and Acinetobacter genomic species sensu Tjernberg and Ursing (AGS 13TU) are phenotypically indistinguishable and are often reported together as the A. baumannii complex (ABC). Few studies have investigated the difference in outcome caused by these different species, and all involved heterogeneous groups of patients. This study aimed to delineate whether there are differences in the clinical characteristics and outcome among patients with solid tumors and bacteremia caused by A. baumannii or two other non-baumannii ABC species (AGS 3 plus AGS 13TU).

METHODS

Patients with solid tumors and ABC bacteremia over a period of 5 years in a medical center were identified. The patient data were retrospectively reviewed and analyzed.

RESULTS

We identified 103 patients with ABC bacteremia during the study period. Bacteremia was due to A. baumannii in 30 patients, AGS 3 in 24 patients, and AGS 13TU in 49 patients. Among the 103 patients with ABC bacteremia, recent stay in the intensive care unit (ICU) (p = 0.008) was independently associated with the acquisition of A. baumannii bacteremia. Multivariate analysis revealed that bacteremia caused by A. baumannii (hazard ratio [HR] 2.990, 95% confidence interval [CI], 1.021-8.752, p = 0.046) and Acute Physiology and Chronic Health Evaluation (APACHE) II score ≥21 (HR 4.623, 95% CI 1.348-15.859, p = 0.015) were independent factors associated with 14-day mortality.

CONCLUSIONS

Infection with A. baumannii and a high APACHE II score (≥21) might be associated with poor outcome in patients with solid tumors and ABC bacteremia.

Outcomes in patients infected with carbapenem-resistant Acinetobacter baumannii and treated with tigecycline alone or in combination therapy

PURPOSE

Acinetobacter baumannii is a non-fermenting aerobic gram-negative bacteria and one of the important nosocomial pathogens, especially in intensive care units (ICUs). In recent years, multidrug-resistant (MDR) isolates have been an emerging problem, with limited therapeutic options. Tigecycline is a novel antimicrobial, with its in vitro activity against most gram-positive and gram-negative pathogens.

METHODS

This is a retrospective study that was conducted in a tertiary care hospital with 550 beds in Ankara, Turkey, from January 2009 to July 2010. Thirty-three patients who had carbapenem-resistant Acinetobacter spp. infections and received tigecycline alone or in combination with other antibiotics for at least 3 days were included.

RESULTS

The median age of the patients was 62 (18-87) years. All of the patients were diagnosed and treated in the ICU. Clinical responses were observed in 23 patients (69.7%). Ten patients (30%) had clinical failure. There was no significant difference between ventilator-associated pneumonia (VAP) and bloodstream infection (BSI) in terms of clinical or microbiological outcome (p > 0.05). The microbiological response rate was 50%. Superinfection was detected in 13 patients (43.3%) and Pseudomonas aeruginosa was the most frequently isolated pathogen. The 30-day overall mortality rate and attributable mortality rates were 57.6 and 24.2%, respectively. The attributable mortality rate was higher in the group in which microbiological eradication was not provided.

CONCLUSIONS

Although it is approved by the Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal infections, complicated skin and soft tissue infections, and community-acquired bacterial pneumonia, emerged resistance of Acinetobacter spp. and limited therapeutic options left physicians no choice but to use tigecycline for off-label indications.

Outer membrane vesicles as an acellular vaccine against Acinetobacter baumannii

Acinetobacter baumannii produces different types of infections including pneumonia, meningitis, and bloodstream infections. The optimal treatment of these infections has been complicated by the global emergence of multidrug resistant strains, requiring the development of novel approaches for treatment and prevention. Outer membrane vesicles are outpouchings of the bacterial outer membrane that are secreted from numerous pathogenic Gram-negative bacteria. In the present study, we describe the isolation of outer membrane vesicles from A. baumannii and their use as a vaccine in a mouse model of disseminated sepsis. Immunization produced a robust antibody response against multiple bacterial antigens which consisted of antigen-specific IgG and IgM. In addition, both IgG1 and IgG2c subtypes were produced by immunization. Immunized mice had lower tissue bacterial loads and lower serum levels of the pro-inflammatory cytokines IL-6 and IL-1β post-infection compared to control mice. Importantly, vaccination protected mice from challenge with the ATCC 19606 strain and provided protection against two clinical isolates, including a pan-resistant strain. These results indicate that vaccination with outer membrane vesicles may be a viable strategy for preventing A. baumannii infection.

Economic value of Acinetobacter baumannii screening in the intensive care unit

Although Acinetobacter baumannii (A. baumannii) is an increasingly common nosocomial pathogen that can cause serious infections in the intensive care unit (ICU), most ICUs do not actively screen admissions for this pathogen. We developed an economic computer simulation model to determine the potential cost-consequences to the hospital of implementing routine A. baumannii screening of ICU admissions and isolating those patients who tested positive, comparing two screening methods, sponge and swab, with each other and no screening. Sensitivity analyses varied the colonization prevalence, percentage of colonized individuals who had active A. baumannii infections, A. baumannii reproductive rate (R), and contact isolation efficacy. Both screening methods were cost-effective for almost all scenarios tested, yielding cost-savings ranging from -$1 to -$1563. Sponge screening was not cost-saving when colonization prevalence was ≤1%, probability of infection ≤30%, R ≤ 0.25, and contact isolation efficacy ≤25%. Swab screening was not cost-saving under these same conditions when the probability of infection was ≤40%. Sponge screening tended to be more cost-saving than swab screening (additional savings ranged from $1 to $421). Routine A. baumannii screening of ICU patients may save costs for hospitals.

Influence of genospecies of Acinetobacter baumannii complex on clinical outcomes of patients with acinetobacter bacteremia

BACKGROUND

acinetobacter baumannii complex infections are increasing in prevalence and are associated with a high mortality. Biochemical classification tests cannot differentiate A. baumannii (genospecies 2) from other genospecies. Genospecies typing offers a potential tool to determine whether there are major differences in pathogenicity among the genospecies.

METHODS

adult patients with A. baumannii complex bacteremia in intensive care units were prospectively observed from January 2007 through July 2009. A. baumannii complex was identified by biochemical methods and the Phoenix bacterial identification system. Genospecies were identified by 16S-23S ribosomal RNA intergenic-spacer sequencing.

RESULTS

among the 135 patients with A. baumannii complex bacteremia, 87 (64.4%) had isolates that belonged to genospecies 2, 36 (26.7%) had isolates that belonged to genospecies 13TU, and 12 (8.9%) had isolates that belonged to genospecies 3. Patients with A. baumannii (genospecies 2) bacteremia were more likely to have pneumonia than were patients with bacteremia due to genospecies 13TU (63.2 % vs 27.8%; P =.001), whereas patients with bacteremia due to genospecies 13TU were more likely to have primary bacteremia (69.4% vs 20.7%; P <.001). Genospecies 2 was less susceptible to antibiotics than were other genospecies. It was associated with a higher rate of mortality than was genospecies 13TU (58.6% vs 16.7%; P < .001). On multivariate analysis, genospecies 2 was an independent predictor of mortality (odds ratio, 5.46; 95% confidence interval, 2.00-14.91; P = .001).

CONCLUSIONS

genospecies 2 of the A. baumannii complex was associated with greater resistance to antibiotics and higher mortality among bacteremic patients, compared with other genospecies, especially genospecies 13TU. These findings emphasize the need to focus on genospecies to better understand the pathogenesis and epidemiology of infections caused by the A. baumannii complex.

High and increasing Oxa-51 DNA load predict mortality in Acinetobacter baumannii bacteremia: implication for pathogenesis and evaluation of therapy

Background

While quantification of viral loads has been successfully employed in clinical medicine and has provided valuable insights and useful markers for several viral diseases, the potential of measuring bacterial DNA load to predict outcome or monitor therapeutic responses remains largely unexplored. We tested this possibility by investigating bacterial loads in Acinetobacter baumannii bacteremia, a rapidly increasing nosocomial infection characterized by high mortality, drug resistance, multiple and complicated risk factors, all of which urged the need of good markers to evaluate therapeutics.

Methods and Findings

We established a quantitative real-time PCR assay based on an A. baumannii-specific gene, Oxa-51, and conducted a prospective study to examine A. baumannii loads in 318 sequential blood samples from 51 adults patients (17 survivors, 34 nonsurvivors) with culture-proven A. baumannii bacteremia in the intensive care units. Oxa-51 DNA loads were significantly higher in the nonsurvivors than survivors on day 1, 2 and 3 (P = 0.03, 0.001 and 0.006, respectively). Compared with survivors, nonsurvivors had higher maximum Oxa-51 DNA load and a trend of increase from day 0 to day 3 (P<0.001), which together with Pitt bacteremia score were independent predictors for mortality by multivariate analysis (P = 0.014 and 0.016, for maximum Oxa-51 DNA and change of Oxa-51 DNA, respectively). Kaplan-Meier analysis revealed significantly different survival curves in patients with different maximum Oxa-51 DNA and change of Oxa-51 DNA from day 0 to day 3.

Conclusions

High Oxa-51 DNA load and its initial increase could predict mortality. Moreover, monitoring Oxa-51 DNA load in blood may provide direct parameters for evaluating new regimens against A. baumannii in future clinical studies.

Infection reduction strategies including antibiotic stewardship protocols in surgical and trauma intensive care units are associated with reduced resistant gram-negative healthcare-associated infections

BACKGROUND

Resistance to broad-spectrum antibiotics by gram-negative organisms is increasing. Resistance demands more resource utilization and is associated with patient morbidity and death. We describe the implementation of infection reduction protocols, including antibiotic stewardship, and assess their impact on multi-drug-resistant (MDR) healthcare-acquired gram-negative infections.

METHODS

Combined infection reduction and antibiotic stewardship protocols were implemented in the surgical and trauma intensive care units at Vanderbilt University Hospital beginning in 2002. The components of the program were: (1) Protocol-specific empiric and therapeutic antibiotics for healthcare-acquired infections; (2) surgical antibiotic prophylaxis protocols; and (3) quarterly rotation/limitation of dual antibiotic classes. Continuous healthcare-acquired infection surveillance was conducted by independent practitioners using National Heath Safety Network criteria. Linear regression analysis was used to estimate trends in MDR gram-negative healthcare-acquired infections.

RESULTS

A total of 1,794 gram-negative pathogens were isolated from healthcare-acquired infections during the eight-year observation period. The proportion of healthcare-acquired infections caused by MDR gram-negative pathogens decreased from 37.4% (2001) to 8.5% (2008), whereas the proportion of healthcare-acquired infections caused by pan-sensitive pathogens increased from 34.1% to 53.2%. The rate of total healthcare-associated infections per 1,000 patient-days that were caused by MDR gram-negative pathogens declined by -0.78 per year (95% confidence interval [CI] -1.28, -0.27). The observed rate of healthcare-acquired infections per 1,000 patient days attributable to specific MDR gram-negative pathogens decreased over time: Pseudomonas -0.14 per year (95% CI -0.20, -0.08), Acinetobacter-0.49 per year (95% CI -0.77, -0.22), and Enterobacteriaceae -0.14 per year (95% CI -0.26, -0.03).

CONCLUSION

Implementation of an antibiotic stewardship protocol as a component of an infection reduction campaign was associated with a decrease in resistant gram-negative healthcare-acquired infections in intensive care units. These results further support widespread implementation of such initiatives.

The impact of Acinetobacter baumannii infections on outcome in trauma patients: a matched cohort study

OBJECTIVE

To determine the impact of Acinetobacter baumannii infection on the outcome of trauma patients.

DESIGN AND SETTING

A retrospective 1:2-matched cohort study. Level I trauma intensive care unit patients with confirmed Acinetobacter baumannii infection were defined as cases.

PATIENTS

Thirty-one Acinetobacter baumannii patients were matched to 62 controls with evidence of infection caused by other microorganisms.

MEASUREMENTS AND MAIN RESULTS

There were 12 matching criteria, including focus of infection, demographics, severity, and characteristics of injury. In-hospital mortality rate, intensive care unit length of stay, and complications of Acinetobacter baumannii including multidrug-resistant strains in patients were compared to those of their controls; 81% had hospital-acquired pneumonia, 13% had bloodstream infections, and 6% had urinary tract infections in both groups. Acinetobacter baumannii cultures were multidrug resistant in 42% (13/31) of cases. The initial empirical antibiotic therapy was adequate in 71% (22/31). Although the in-hospital mortality was higher in the Acinetobacter baumannii group (16% vs. 13%; odds ratio, 1.23; 95% confidence interval, 0.38-4.36; p = .67), the difference did not reach statistical significance. Using the test of equivalence or clinical indifference, the impact of an Acinetobacter baumannii infection on mortality is inconclusive. This applies also to multidrug-resistant strains. Overall intensive care unit stay was prolonged for Acinetobacter baumannii when compared to controls (median, [range], 28 [7-181] days vs. 17 [2-130] days, respectively; p = .05). ARDS and acute liver failure were more frequent in the Acinetobacter baumannii group compared to the control group (35% vs. 15%; odds ratio, 3.24; 95% confidence interval, 1.17-5.48; p = .02 and 26% vs. 10%; odds ratio, 3.25; 95% confidence interval, 3.25-10.40; p = .04).

CONCLUSIONS

In this single-center experience, Acinetobacter baumannii infection, including multidrug-resistant strains, has inconclusive impact on mortality in a cohort of trauma patients. Larger studies are needed to support a definite conclusion. Acinetobacter baumannii infection was, however, associated with a longer intensive care unit stay and a higher rate of organ failure.

Vaccination with outer membrane complexes elicits rapid protective immunity to multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii causes pneumonias, bacteremias, and skin and soft tissue infections, primarily in the hospitalized setting. The incidence of infections caused by A. baumannii has increased dramatically over the last 30 years, while at the same time the treatment of these infections has been complicated by the emergence of antibiotic-resistant strains. Despite these trends, no vaccines or antibody-based therapies have been developed for the prevention of A. baumannii infection. In this study, an outer membrane complex vaccine consisting of multiple surface antigens from the bacterial membrane of A. baumannii was developed and tested in a murine sepsis model. Immunization elicited humoral and cellular responses that were able to reduce postinfection bacterial loads, reduce postinfection proinflammatory cytokine levels in serum, and protect mice from infection with human clinical isolates of A. baumannii. A single administration of the vaccine was able to elicit protective immunity in as few as 6 days postimmunization. In addition, vaccine antiserum was used successfully to therapeutically rescue naïve mice with established infection. These results indicate that prophylactic vaccination and antibody-based therapies based on an outer membrane complex vaccine may be viable approaches to preventing the morbidity and mortality caused by this pathogen.

Multidrug resistant Acinetobacter baumannii: a descriptive study in a city hospital

Background

Multidrug resistant Acinetobacter baumannii, (MRAB) is an important cause of hospital acquired infection. The purpose of this study is to determine the risk factors for MRAB in a city hospital patient population.

Methods

This study is a retrospective review of a city hospital epidemiology data base and includes 247 isolates of Acinetobacter baumannii (AB) from 164 patients. Multidrug resistant Acinetobacter baumannii was defined as resistance to more than three classes of antibiotics. Using the non-MRAB isolates as the control group, the risk factors for the acquisition of MRAB were determined.

Results

Of the 247 AB isolates 72% (177) were multidrug resistant. Fifty-eight percent (143/247) of isolates were highly resistant (resistant to imipenem, amikacin, and ampicillin-sulbactam). Of the 37 patients who died with Acinetobacter colonization/infection, 32 (86%) patients had the organism recovered from the respiratory tract. The factors which were found to be significantly associated (p ≤ 0.05) with multidrug resistance include the recovery of AB from multiple sites, mechanical ventilation, previous antibiotic exposure, and the presence of neurologic impairment. Multidrug resistant Acinetobacter was associated with significant mortality when compared with sensitive strains (p ≤ 0.01). When surgical patients (N = 75) were considered separately, mechanical ventilation and multiple isolates remained the factors significantly associated with the development of multidrug resistant Acinetobacter. Among surgical patients 46/75 (61%) grew a multidrug resistant strain of AB and 37/75 (40%) were resistant to all commonly used antibiotics including aminoglycosides, cephalosporins, carbepenems, extended spectrum penicillins, and quinolones. Thirty-five percent of the surgical patients had AB cultured from multiple sites and 57% of the Acinetobacter isolates were associated with a co-infecting organism, usually a Staphylococcus or Pseudomonas. As in medical patients, the isolation of Acinetobacter from multiple sites and the need for mechanical ventilation were significantly associated with the development of MRAB.

Conclusions

The factors significantly associated with MRAB in both the general patient population and surgical patients were mechanical ventilation and the recovery of Acinetobacter from multiple anatomic sites. Previous antibiotic use and neurologic impairment were significant factors in medical patients. Colonization or infection with MRAB is associated with increased mortality.

Long-term control of hospital-wide, endemic multidrug-resistant Acinetobacter baumannii through a comprehensive "bundle" approach

BACKGROUND

Acinetobacter baumannii (Ab) is emerging as a multidrug-resistant (MDR) nosocomial pathogen of considerable clinical importance. Data on the efficacy of infection control measures in endemic situations are lacking. Here, we investigated the impact of a long-term multifaceted "bundle" approach in controlling endemic MDR Ab in a 950-bed tertiary care center.

METHODS

Ongoing staff education, promotion of hand hygiene, strict Contact and Isolation Precautions, environmental cleaning, and targeted active surveillance in high-risk areas during periods of likely transmission and contamination were initiated in this program. To assess the efficacy of our interventions, we recorded (before and after the intervention) the epidemiologic and clinical features of MDR Ab infections and determined the clonal relationship among MDR Ab bloodstream isolates by pulsed-field gel electrophoresis.

RESULTS

Before the "bundle" was instituted, the rate of colonization/infection was 0.82 cases per 100 admissions (1994-1995). Colonization/infection rates showed a sustained decrease after implementation of the control program in 1995 to 0.46 in 1996-1997 and to 0.21 in 1998-2003 (P < .001). Coincident with the institution of this program, the rate of bacteremia because of MDR Ab decreased 6-fold during the 8-year observation period. A notable change in the clonal distribution of the MDR Ab isolates was also demonstrated.

CONCLUSION

The implementation of a comprehensive and multifaceted infection control program ("bundle") in a tertiary care center effectively controlled the spread and clinical impact of MDR Ab.

Treatment of pan-drug resistant Acinetobacter baumannii

The objective of this study was to investigate the role of sulbactam in the treatment of pan-drug resistant Acinetobacter baumannii (PDRAB). We studied 89 patients with PDRAB infection treated with different antibiotic regimens. Group A (n = 39) were treated with carbapenem with sulbactam and group B (n = 30) with second and third generation cephalosporins, antipseudomonas penicillins, or fluoroquinolones with aminoglycosides. We also studied the MICs for 48 PDRAB strains by using antimicrobial agents with and without sulbactam. The clinical outcomes of the 2 groups did not differ significantly, either in terms of resolution of infection (25/59, 42% in group A vs 12/30, 40% in group B) or survival (35/59, 59% vs 17/30, 57%). However, the MICs indicated that 16 of the 48 strains were sensitive to imipenem/sulbactam, compared with only 2 of the 48 to imipenem alone. The addition of sulbactam thus reversed the response in 30% (14/46) of strains initially resistant or only intermediate sensitive to imipenem. The MICs for meropenem/sulbactam were in the sensitive range for 8 of 48 strains compared to only 3 of the meropenem alone, indicating an 11% (5/45) reversal rate when sulbactam was added to meropenem. For the 38 isolates initially resistant to both carbapenems alone, imipenem/sulbactam reversed the resistance in 16% (6/38), while meropenem/sulbactam did so in only 3% (1/38). Thus, the carbapenem-sulbactam combinations did not clearly improve clinical outcome, but they did demonstrate lower MICs for the PDRAB strains tested. It may be that aggressive, early treatment of A. baumannii infections with these agents might prevent the emergence of PDRAB strains.

Acinetobacter baumannii: emergence of a successful pathogen

Acinetobacter baumannii has emerged as a highly troublesome pathogen for many institutions globally. As a consequence of its immense ability to acquire or upregulate antibiotic drug resistance determinants, it has justifiably been propelled to the forefront of scientific attention. Apart from its predilection for the seriously ill within intensive care units, A. baumannii has more recently caused a range of infectious syndromes in military personnel injured in the Iraq and Afghanistan conflicts. This review details the significant advances that have been made in our understanding of this remarkable organism over the last 10 years, including current taxonomy and species identification, issues with susceptibility testing, mechanisms of antibiotic resistance, global epidemiology, clinical impact of infection, host-pathogen interactions, and infection control and therapeutic considerations.

Hydrocortisone therapy for patients with septic shock

BACKGROUND

Hydrocortisone is widely used in patients with septic shock even though a survival benefit has been reported only in patients who remained hypotensive after fluid and vasopressor resuscitation and whose plasma cortisol levels did not rise appropriately after the administration of corticotropin.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled trial, we assigned 251 patients to receive 50 mg of intravenous hydrocortisone and 248 patients to receive placebo every 6 hours for 5 days; the dose was then tapered during a 6-day period. At 28 days, the primary outcome was death among patients who did not have a response to a corticotropin test.

RESULTS

Of the 499 patients in the study, 233 (46.7%) did not have a response to corticotropin (125 in the hydrocortisone group and 108 in the placebo group). At 28 days, there was no significant difference in mortality between patients in the two study groups who did not have a response to corticotropin (39.2% in the hydrocortisone group and 36.1% in the placebo group, P=0.69) or between those who had a response to corticotropin (28.8% in the hydrocortisone group and 28.7% in the placebo group, P=1.00). At 28 days, 86 of 251 patients in the hydrocortisone group (34.3%) and 78 of 248 patients in the placebo group (31.5%) had died (P=0.51). In the hydrocortisone group, shock was reversed more quickly than in the placebo group. However, there were more episodes of superinfection, including new sepsis and septic shock.

CONCLUSIONS

Hydrocortisone did not improve survival or reversal of shock in patients with septic shock, either overall or in patients who did not have a response to corticotropin, although hydrocortisone hastened reversal of shock in patients in whom shock was reversed. (ClinicalTrials.gov number, NCT00147004.)

The increasing role of Acinetobacter species as nosocomial pathogens

Among gram-negative organisms playing a significant role in nosocomial infections, Acinetobacter species have attracted increasing attention in intensive care units during the past two decades. Acinetobacter species are implicated in a wide spectrum of infections (eg, bacteremia, nosocomial pneumonia, urinary tract infections, secondary meningitis, superinfections in burn patients). One of the most striking features of Acinetobacter species is their extraordinary ability to develop multiple resistance mechanisms against major antibiotic classes. They have become resistant to broad-spectrum β-lactams (third-generation cephalosporins, carboxypenicillins, and increasingly to carbapenems); they produce a wide range of aminoglycoside-inactivating enzymes; and most strains are resistant to fluoroquinolones. In Acinetobacter nosocomial infections, the major problems confronting clinicians in intensive care units are related to the severity of Acinetobacter nosocomial infections and to resistance to major antibiotic classes of these organisms.