Acinetobacter baumannii ventilator-associated pneumonia: epidemiology, clinical characteristics, and prognosis factors

Hospital-acquired and ventilator-associated pneumonia caused by multidrug-resistant Gram-negative pathogens: Understanding epidemiology, resistance patterns, and implications with COVID-19

The ongoing spread of antimicrobial resistance has complicated the treatment of bacterial hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP). Gram-negative pathogens, especially those with multidrug-resistant profiles, including Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Pseudomonas aeruginosa, and Acinetobacter spp., are important culprits in this type of infections. Understanding the determinants of resistance in pathogens causing pneumonia is ultimately stressing, especially in the shadows of the COVID-19 pandemic, when bacterial lung infections are considered a top priority that has become urgent to revise. Globally, the increasing prevalence of these pathogens in respiratory samples represents a significant infection challenge, with major limitations of treatment options and poor clinical outcomes. This review will focus on the epidemiology of HAP and VAP and will present the roles and the antimicrobial resistance patterns of implicated multidrug-resistant (MDR) Gram-negative pathogens like carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Pseudomonas aeruginosa (CRPA), carbapenem-resistant Enterobacterales (CRE), as well as colistin-resistant Gram-negative pathogens and extended-spectrum β-lactamase (ESBL)-producing Enterobacterales. While emerging from the COVID-19 pandemic, perspectives and conclusions are drawn from findings of HAP and VAP caused by MDR Gram-negative bacteria in patients with COVID-19.

Using time-series chest radiographs and laboratory data by machine learning for identifying pulmonary infection and colonization of Acinetobacter baumannii

BACKGROUND

Accurately distinguishing between pulmonary infection and colonization in patients with Acinetobacter baumannii is of utmost importance to optimize treatment and prevent antibiotic abuse or inadequate therapy. An efficient automated sorting tool could prompt individualized interventions and enhance overall patient outcomes. This study aims to develop a robust machine learning classification model using a combination of time-series chest radiographs and laboratory data to accurately classify pulmonary status caused by Acinetobacter baumannii.

METHODS

We proposed nested logistic regression models based on different time-series data to automatically classify the pulmonary status of patients with Acinetobacter baumannii. Advanced features were extracted from the time-series data of hospitalized patients, encompassing dynamic pneumonia indicators observed on chest radiographs and laboratory indicator values recorded at three specific time points.

RESULTS

Data of 152 patients with Acinetobacter baumannii cultured from sputum or alveolar lavage fluid were retrospectively analyzed. Our model with multiple time-series data demonstrated a higher performance of AUC (0.850, with a 95% confidence interval of [0.638-0.873]), an accuracy of 0.761, a sensitivity of 0.833. The model, which only incorporated a single time point feature, achieved an AUC of 0.741. The influential model variables included difference in the chest radiograph pneumonia score.

CONCLUSION

Dynamic assessment of time-series chest radiographs and laboratory data using machine learning allowed for accurate classification of colonization and infection with Acinetobacter baumannii. This demonstrates the potential to help clinicians provide individualized treatment through early detection.

How to treat severe Acinetobacter baumannii infections

PURPOSE OF REVIEW

To update the management of severe Acinetobacter baumannii infections (ABI), particularly those caused by multi-resistant isolates.

RECENT FINDINGS

The in vitro activity of the various antimicrobial agents potentially helpful in treating ABI is highly variable and has progressively decreased for many of them, limiting current therapeutic options. The combination of more than one drug is still advisable in most circumstances. Ideally, two active first-line drugs should be used. Alternatively, a first-line and a second-line drug and, if this is not possible, two or more second-line drugs in combination. The emergence of new agents such as Cefiderocol, the combination of Sulbactam and Durlobactam, and the new Tetracyclines offer therapeutic options that need to be supported by clinical evidence.

SUMMARY

The apparent limitations in treating infections caused by this bacterium, the rapid development of resistance, and the serious underlying situation in most cases invite the search for alternatives to antibiotic treatment, the most promising of which seems to be bacteriophage therapy.

Droperidol as a potential inhibitor of acyl-homoserine lactone synthase from A. baumannii: insights from virtual screening, MD simulations and MM/PBSA calculations

Acinetobacter baumannii belongs to the ESKAPE family of pathogens and is a multi-drug resistant, gram-negative bacteria which follows the anaerobic form of respiration. A. baumannii is known to be the causative agent of hospital-related infections such as pneumonia, meningitis, endocarditis, septicaemia and a plethora of infections such as urinary tract infections found primarily in immunocompromised patients. These attributes of A. baumannii make it a priority pathogen against which potential therapeutic agents need to be developed. A. baumannii employs the formation of a biofilm to insulate its colonies from the outer environment, which allows it to grow under harsh environmental conditions and develop resistance against various drug molecules. Acyl-homoserine lactone synthase (AHLS) is an enzyme involved in the quorum-sensing pathway in A. baumannii, which is responsible for the synthesis of signal molecules known as acyl-homoserine lactones, which trigger the signalling pathway to regulate the factors involved in biofilm formation and regulation. The present study utilised a homology-modelled structure of AHLS to virtually screen it against the ZINC in trial/FDA-approved drug molecule library to find a subset of potential lead candidates. These molecules were then filtered based on Lipinski's, toxicological and ADME properties, binding affinity, and interaction patterns to delineate lead molecules. Finally, three promising molecules were selected, and their estimated binding affinity values were corroborated using AutoDock 4.2. The identified molecules and a control molecule were subsequently subjected to MD simulations to mimic the physiological conditions of protein ligand-binding interaction under the influence of a GROMOS forcefield. The global and essential dynamics analyses and MM/PBSA based binding free energy computations suggested Droperidol and Cipargamin as potential inhibitors against the binding site of AHLS from A. baumannii. The binding free energy calculations based on the MM/PBSA method showed excellent results for Droperidol (- 50.02 ± 4.67 kcal/mol) and Cipargamin (- 42.29 ± 4.05 kcal/mol).

Natural Antibodies Mediate Protection Against Acinetobacter baumannii Respiratory Infections

BACKGROUND

Acinetobacter baumannii causes a wide range of dangerous infections due to the emergence of pandrug-resistant strains. Therefore, there is a need for alternative therapeutics to treat these infections, including those targeting the host immune responses. However, immune responses, especially the humoral response against this pathogen, are poorly understood.

METHODS

This study investigated the lymphocyte-mediated innate immune resistance to A. baumannii AB5075 pulmonary infection using B- and T-cell-deficient (Rag2-/-) mice, the protective effect of natural antibodies (NAbs), and the expression of complement-mediated responses using a mouse pneumonia model.

RESULTS

Our results showed that intranasally infected Rag2-/- mice are impaired in clearing bacteria from lung, liver, and spleen at 24 hours postinfection compared to wildtype mice. Animal pretreatment with normal mouse serum or purified antibodies from naive mice rescued Rag2-/- mice from infection. Analysis of C3 complement protein binding demonstrated that NAbs increased C3 protein deposition on A. baumannii cells, indicating the activation of the classical complement pathway by NAbs.

CONCLUSIONS

Overall, our study shows that NAbs mediate innate immune resistance against A. baumannii, a finding that may lead to the development of effective therapies against human infections caused by this antibiotic-resistant A. baumannii.

Carbapenem-Resistant Acinetobacter spp Infection in Critically Ill Patients With Limited Treatment Options: A Descriptive Study of Cefiderocol Therapy During the COVID-19 Pandemic

Background

Carbapenem-resistant Acinetobacter baumannii infections are difficult to treat and are a significant public health threat due to intrinsic/acquired resistance and limited treatment options.

Methods

A retrospective, observational cohort study in patients receiving cefiderocol via Shionogi's early access program for Acinetobacter spp infections (1 April 2020-30 April 2021; 27 sites; Italy, Spain, Germany, France). Primary outcome was clinical success, defined as clinical resolution of infection at day 14 or day 28 survival.

Results

Overall, 147 patients were included. Primary infection sites were respiratory (65.3%) and bloodstream (unknown source [15.6%]; catheter-related [10.9%]); 24.5% of patients had polymicrobial infection. Of 136 patients in intensive care (92.5%), 85.3% (116/136) received mechanical ventilation. Septic shock (55.6% [70/126]) and coronavirus disease 2019 (COVID-19) (81.6%) were prevalent. Prior to cefiderocol, 85.0% of patients received gram-negative treatment, 61.2% received ≥2 antimicrobials, and most received colistin (58.5%; median duration, 11.5 days). Cefiderocol monotherapy was used in 30.6% of patients. Clinical success rate was 53.1% and was higher in patients without septic shock (62.5%), without COVID-19 (77.8%), and with lower Sequential Organ Failure Assessment (SOFA) scores (quartile 1 [median, 3; range, 0-5]: 82.9%). Day 28 survival was 44.9% and was higher in patients without septic shock (60.7%), without COVID-19 (59.3%), with lower SOFA score (quartile 1: 82.9%), and receiving first-line cefiderocol (68.2% [15/22]). Resolution of infection at day 14 occurred in 39.5% of patients.

Conclusions

Despite use in complex patients with limited treatment options and high septic shock/COVID-19 rates, cefiderocol treatment was associated with an overall clinical success rate of 53%.

Antibiotic resistance in hospital-acquired ESKAPE-E infections in low- and lower-middle-income countries: a systematic review and meta-analysis

Antimicrobial resistance (AMR) and hospital-acquired infections (HAIs) are global health challenges. The burden of antibiotic resistance in HAIs is still unclear in low- and lower-middle-income countries (L-LMICs). This study summarizes recent data on antibiotic resistance in priority HAIs (ESKAPE-E) in L-LMICs and compares them with data from high-income countries (HICs). EMBASE, Web of Science, and Global Index Medicus were searched for studies on AMR patterns in HAIs published from 01/2010 to 10/2020. Random-effects meta-analyses were performed to obtain pooled estimates. In total, 163 eligible studies were included in the review and meta-analysis. The pooled methicillin resistance proportion in Staphylococcus aureus was 48.4% (95% confidence interval [95%CI] 41·7-55·2, n = 80). Pooled carbapenem resistance proportions were high in Gram-negative pathogens: Escherichia coli: 16·6% (95%CI 10·7-23·4, n = 60); Klebsiella pneumoniae: 34·9% (95%CI 24·6-45·9, n = 50); Pseudomonas aeruginosa: 37.1% (95%CI 24·6-45·9, n = 56); Enterobacter spp.: 51·2% (95%CI 27·5-74·7, n = 7); and Acinetobacter baumannii (complex): 72·4% (95%CI 62·1-81·7%, n = 36). A higher resistance proportions were observed for third-generation cephalosporins: Klebsiella pneumoniae: 78·7% (95%CI 71·5-85·2, n = 46); Escherichia coli: 78·5% (95%CI 72·1-84·2%, n = 58); and Enterobacter spp.: 83·5% (95%CI 71·9-92·8, n = 8). We observed a high between-study heterogeneity (I2  >  80%), which could not be explained by our set of moderators. Pooled resistance proportions for Gram-negative pathogens were higher in L-LMICs than regional and national estimates from HICs. Patients in resource-constrained regions are particularly affected by AMR. To combat the high resistance to critical antibiotics in L-LMICs, and bridge disparities in health, it is crucial to strengthen local surveillance and the health systems in general.

Molecular Characterization and Antibiogram of Acinetobacter baumannii Clinical Isolates Recovered from the Patients with Ventilator-Associated Pneumonia

A 2-year prospective study carried out on ventilator-associated pneumonia (VAP) patients in the intensive care unit at a tertiary care hospital, Hail, Kingdom of Saudi Arabia (KSA), revealed a high prevalence of extremely drug-resistant (XDR) Acinetobacter baumannii. About a 9% increase in the incidence rate of A. baumannii occurred in the VAP patients between 2019 and 2020 (21.4% to 30.7%). In 2019, the isolates were positive for IMP-1 and VIM-2 (31.1% and 25.7%, respectively) as detected by PCR. In comparison, a higher proportion of isolates produced NDM-1 in 2020. Here, we observed a high proportion of resistant ICU isolates towards the most common antibiotics in use. Colistin sensitivity dropped to 91.4% in the year 2020 as compared to 2019 (100%). Thus, the finding of this study has a highly significant clinical implementation in the clinical management strategies for VAP patients. Furthermore, strict implementation of antibiotic stewardship policies, regular surveillance programs for antimicrobial resistance monitoring, and screening for genes encoding drug resistance phenotypes have become imperative.

An extensive computational study to identify potential inhibitors of Acyl-homoserine-lactone synthase from Acinetobacter baumannii (strain AYE)

A member of the ESKAPE family of pathogens, A. baumannii, is an opportunistic gram-negative multidrug-resistant bacterium. A. baumannii is a ubiquitous coccobacillus involved in various hospital-related infections such as wound infections, pneumonia, urinary tract infections, septicaemia, endocarditis and ventilator assisted pneumonia and accounts for approximately 1-2% of all nosocomial bloodstream infections; hence it becomes imperative to identify potential therapeutic agents against the dreadful pathogen. The quorum-sensing pathway becomes an attractive drug target due to its role in biofilm regulation and formation, which provides the bacteria insulation from the harsh environment. A crucial protein in biofilm formation and regulation is Acyl-homoserine-lactone synthase (AHLS), responsible for producing signal molecules that trigger the signalling pathway for biofilm formation and regulation. The current study modeled the three-dimensional structure of AHLS in A. baumannii (strain AYE) followed by high-throughput virtual screening of the enamine-AC small-molecule database to identify lead molecules against its acylated-ACP (Acyl Carrier Protein) substrate-binding site. Based on the estimated binding affinity, estimated inhibition constant, ADME analysis and interaction patterns of the screened molecules, three lead candidates (Z815888654, Z2416029019, Z3766992625) were identified along with a control molecule (J8-C8). These molecules were then subjected to molecular dynamics simulations where the physiological effect of ligand binding on the protein was virtually predicted and analysed. The MM/PBSA based binding free energy calculations showed favourable results for Z815888654 (-22.77 ± 2.94 kcal/mol), Z2416029019 (-33.68 ± 2.63 kcal/mol), Z3766992625 (-21.44 ± 3.40 kcal/mol). The study employed global and essential dynamics analyses, MM/PBSA based binding free energy, free energy landscape and dynamic cross-correlation matrix to suggest Z815888654, Z2416029019 and Z3766992625 as potential inhibitors against the acylated-ACP substrate-binding site in AHLS from A. baumannii.

Synergistic Inhibitory Effect of Polymyxin B in Combination with Ceftazidime against Robust Biofilm Formed by Acinetobacter baumannii with Genetic Deficiency in AbaI/AbaR Quorum Sensing

Carbapenem resistance of Acinetobacter baumannii poses challenges to public health. Biofilm contributes to the persistence of A. baumannii cells. This study was designed to investigate the genetic relationships among carbapenem resistance, polymyxin resistance, multidrug resistance, biofilm formation, and surface-associated motility and evaluate the antibiofilm effect of polymyxin in combination with other antibiotics. A total of 103 clinical A. baumannii strains were used to determine antibiotic susceptibility, biofilm formation capacity, and motility. Enterobacterial repetitive intergenic consensus (ERIC)-PCR fingerprinting was used to determine the genetic variation among strains. The distribution of 17 genes related to the resistance-nodulation-cell division (RND)-type efflux, autoinducer-receptor (AbaI/AbaR) quorum sensing, oxacillinases (OXA)-23, and insertion sequence of ISAba1 element was investigated. The representative strains were chosen to evaluate the gene transcription and the antibiofilm activity by polymyxin B (PB) in combination with merapenem, levofloxacin, and ceftazidime, respectively. ERIC-PCR-dependent fingerprints were found to be associated with carbapenem resistance and multidrug resistance. The presence of bla_OXA-23 was found to correlate with genes involved in ISAba1 insertion, AbaI/AbaR quorum sensing, and AdeABC efflux. Carbapenem resistance was observed to be negatively correlated with biofilm formation and positively correlated with motility. PB in combination with ceftazidime displayed a synergistic antibiofilm effect against robust biofilm formed by an A. baumannii strain with deficiency in AbaI/AbaR quorum sensing. Our results not only clarify the genetic correlation among carbapenem resistance, biofilm formation, and pathogenicity in a certain level but also provide a theoretical basis for clinical applications of polymyxin-based combination of antibiotics in antibiofilm therapy. IMPORTANCE Deeper explorations of molecular correlation among antibiotic resistance, biofilm formation, and pathogenicity could provide novel insights that would facilitate the development of therapeutics and prevention against A. baumannii biofilm-related infections. The major finding that polymyxin B in combination with ceftazidime displayed a synergistic antibiofilm effect against robust biofilm formed by an A. baumannii strain with genetic deficiency in AbaI/AbaR quorum sensing further provides a theoretical basis for clinical applications of antibiotics in combination with quorum quenching in antibiofilm therapy.

Rescuing Tetracycline Class Antibiotics for the Treatment of Multidrug-Resistant Acinetobacter baumannii Pulmonary Infection

Acinetobacter baumannii causes high mortality in ventilator-associated pneumonia patients, and antibiotic treatment is compromised by multidrug-resistant strains resistant to β-lactams, carbapenems, cephalosporins, polymyxins, and tetracyclines. Among COVID-19 patients receiving ventilator support, a multidrug-resistant A. baumannii secondary infection is associated with a 2-fold increase in mortality. Here, we investigated the use of the 8-hydroxyquinoline ionophore PBT2 to break the resistance of A. baumannii to tetracycline class antibiotics. In vitro, the combination of PBT2 and zinc with either tetracycline, doxycycline, or tigecycline was shown to be bactericidal against multidrug-resistant A. baumannii, and any resistance that did arise imposed a fitness cost. PBT2 and zinc disrupted metal ion homeostasis in A. baumannii, increasing cellular zinc and copper while decreasing magnesium accumulation. Using a murine model of pulmonary infection, treatment with PBT2 in combination with tetracycline or tigecycline proved efficacious against multidrug-resistant A. baumannii. These findings suggest that PBT2 may find utility as a resistance breaker to rescue the efficacy of tetracycline-class antibiotics commonly employed to treat multidrug-resistant A. baumannii infections. IMPORTANCE Within intensive care unit settings, multidrug-resistant (MDR) Acinetobacter baumannii is a major cause of ventilator-associated pneumonia, and hospital-associated outbreaks are becoming increasingly widespread. Antibiotic treatment of A. baumannii infection is often compromised by MDR strains resistant to last-resort β-lactam (e.g., carbapenems), polymyxin, and tetracycline class antibiotics. During the on-going COVID-19 pandemic, secondary bacterial infection by A. baumannii has been associated with a 2-fold increase in COVID-19-related mortality. With a rise in antibiotic resistance and a reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. Rescuing the efficacy of existing therapies for the treatment of MDR A. baumannii infection represents a financially viable pathway, reducing time, cost, and risk associated with drug innovation.

Adverse clinical outcomes associated with carbapenem-resistant Acinetobacter (CRA) infections: a systematic review and meta-analysis

Background

Carbapenem-resistant Acinetobacter (CRA) infections have been associated with increased morbidity and mortality in hospitalized patients. This systematic review and meta-analysis aimed to quantify the association between CRA infections and adverse clinical outcomes.

Methods

Three databases (i.e. PubMed, EMBASE and Scopus) were searched for epidemiological studies that compared mortality, severe sepsis or shock, or bacteraemia among adult inpatients with CRA infections and those with carbapenem-susceptible Acinetobacter (CSA) infections. The pooled ORs for the three outcomes were estimated using the inverse variance heterogeneity model.

Results

Thirty-four studies were included. Patients with CRA infections had higher odds of mortality (31 studies, OR = 2.10, 95% CI: 1.58–2.79, I²=60.6%) and severe sepsis or septic shock (7 studies, OR = 1.51, 95% CI: 1.09–2.09, I²=0%) compared with CSA-infected patients. There was no difference in the odds of bacteraemia (four studies, OR = 1.39, 95% CI: 0.79–2.46, I²=38.1%). CRA-infected patients presented with worse comorbidity at admission (e.g. APACHE score) (eight studies, standardized mean difference = 0.25, 95% CI: −0.01 to 0.52) and had lower frequency of appropriate antibiotic therapy. Results were consistent when pooling 16 study-adjusted risk estimates for mortality. There was no difference in risk of mortality from CRA infection when compared across geographical regions, country income, median year of enrolment and day of mortality from infection onset.

Conclusions

CRA-infected patients had worse clinical outcomes. This might be due to delay in appropriate antibiotic therapy, patients being sicker at admission and CRA strains potentially being more virulent than CSA strains. Improving appropriateness of antibiotic therapy in CRA-infected patients could reduce adverse clinical outcomes.

Predictive Performance of Risk Factors for Multidrug-Resistant Pathogens in Nosocomial Pneumonia

Rationale: In 2017, the International European Respiratory Society/European Society of Intensive Care Medicine/European Society of Clinical Microbiology and Infectious Diseases/Latin American Thoracic Society (European) guidelines defined new risk factors for multidrug-resistant (MDR) pathogens in patients with nosocomial pneumonia.Objectives: To assess the predictive performance of these newly defined risk factors for MDR pathogens.Methods: We enrolled 507 adult patients with nosocomial pneumonia who were treated in six intensive care units at the Hospital Clinic of Barcelona in Spain. Of the 503 patients at high MDR pathogen and mortality risk, 275 (54%) had no septic shock and 228 (46%) had septic shock.Results: Admission to hospital settings with high rates of MDR pathogens (n = 421; 83%) and prior antibiotic use (n = 399; 79%) showed the highest prevalence in the overall population, with sensitivities of 92% and 85% and negative predictive values of 85% and 82%, respectively. However, low specificities and low positive predictive values were found. Previous respiratory MDR pathogen isolation was less common (n = 17; 3%) but presented a specificity and positive predictive value of 100%. The area under the receiver operating characteristic curve was less than 0.6 for all risk factors and combinations.Conclusions: The risk factors proposed by the European Respiratory Society/European Society of Intensive Care Medicine/European Society of Clinical Microbiology and Infectious Diseases/Latin American Thoracic Society showed low accuracy for predicting MDR pathogens in intensive care unit acquired pneumonia (ICU-AP). Admission to hospital settings with high rates of MDR pathogens and prior antibiotic use were the most prevalent risk factors, with a high sensitivity for predicting these microorganisms; prior positive cultures for MDR pathogens showed high specificity but very low sensitivity. Combinations of risk factors did not show any great accuracy for predicting these microorganisms. Further studies assessing combined strategies of risk stratification and complementary methods are now warranted.

Retrospective Assessment of Ventilator-Associated Pneumonias due to Acinetobacter baumannii in an Oncology Hospital

Objectives:

Ventilator-associated pneumonia (VAP) is associated with significant morbidity and mortality in critically ill patients and leads to increases in health-care costs. However, it is preventable, and hospitals can decrease VAP rates. This study aims to retrospectively assess VAP rates in the intensive care unit of Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital of the University of Health Sciences, with reference to Acinetobacter baumannii, one of the causative organisms.

Methods:

This study enrolled a total of 2277 patients hospitalized between the years of 2011 and 2015. The required data were collected by reviewing medical files of the patients through computerized hospital databases. VAP rate and ventilator utilization (VU) ratio were calculated using the United States Center for Disease Control National Healthcare Safety Network methodology.

Results:

Of the study patients, 302 (13.26%) were seen to have developed VAP. Among these patients, 191 (63.25%) were microbiologically diagnosed VAP caused by A. baumannii. Pooled means of VU ratio and VAP rate were 0.70 and 22.91, respectively.

Conclusion:

The results of this study will motivate the infection control committee of the study hospital to assess current infection control program and strategies so that high VAP rate in the study intensive care unit can be reduced to the minimum possible level.

Compassionate mesenchymal stem cell treatment in a severe COVID-19 patient: a case report

COVID-19 presentations range from cold-like symptoms to severe symptoms with the development of acute respiratory distress syndrome (ARDS). We report on a severe COVID-19 patient who was mechanically ventilated and who developed ARDS and bacterial infection. Because of rapid clinical deterioration and the exhaustion of other treatment options, the family and attending physicians requested a compassionate use of adult allogeneic bone marrow-derived mesenchymal stem cells (MSC) in addition to commonly used immunosuppressive, antiviral, and supportive therapy. The clinical course is discussed thoroughly, with a special emphasis on the safety and effect of MSC therapy. Compassionate MSC treatment, given in three rounds, affected ARDS regression. The patient was discharged from the intensive care unit after 31 days and from hospital after 49 days in a good general condition. MSC treatment was not associated with any side effects and was well tolerated in a three-week period; therefore, it should be studied in larger trials and considered for compassionate use.

Anti-biofilm and anti-virulence effects of zerumbone against Acinetobacter baumannii

Acinetobacter baumannii is a multidrug-resistant opportunistic pathogen that affects patients with a compromised immune system and is becoming increasingly important as a hospital-derived infection. This pathogen is difficult to treat owing to its intrinsic multidrug resistance and ability to form antimicrobial-tolerant biofilms. In the present study, we aimed to assess the potential use of zerumbone as a novel anti-biofilm and/or anti-virulence agent against A. baumannii. The results showed that zerumbone at sub-inhibitory doses decreased biofilm formation and disrupted established A. baumannii biofilms. The zerumbone-induced decrease in biofilm formation was dose-dependent based on the results of microtitre plate biofilm assays and confocal laser scanning microscopy. In addition, our data validated the anti-virulence efficacy of zerumbone, wherein it significantly interfered with the motility of A. baumannii. To support these phenotypic results, transcriptional analysis revealed that zerumbone downregulated the expression of biofilm- and virulence-associated genes (adeA, adeB, adeC and bap) in A. baumannii. Overall, our findings suggested that zerumbone might be a promising bioactive agent for the treatment of biofilm- and virulence-related infections caused by multidrug-resistant A. baumannii.

Outcomes of Adjunctive Therapy with Intravenous Cefoperazone-Sulbactam for Ventilator-Associated Pneumonia Due to Carbapenem-Resistant Acinetobacter baumannii

Introduction

The efficacy of adjunctive therapy with cefoperazone-sulbactam (CEP-SUL) for ventilator-associated pneumonia (VAP) due to carbapenem-resistant A. baumannii (CRAB) is unclear.

Methods

We retrospectively analyzed the therapeutic effect of adding CEP-SUL to standard regimens for VAP due to CRAB. Patients with VAP due to CRAB strains that were susceptible to CEP-SUL were enrolled into the study. The patients were divided into two groups: those who receive cefoperazone-sulbactam (CEP-SUL⁺), and those who did not receive cefoperazone-sulbactam (CEP-SUL). Mortality rates and resource utilization of these two groups were compared. Factors associated with mortality were explored.

Results

Eighty patients were enrolled into the study, 52 CEP-SUL⁺ and 28 CEP-SUL^-. The baseline characteristics of the two groups were comparable, except for median Acute Physiology and Chronic Health Evaluation (APACHE) II score which was significantly higher for CEP-SUL⁺. Thirty-day, and in-hospital mortality rates for CEP-SUL⁺ were significantly lower than CEP-SUL^- with values of 35%, 39% and 61%, 68%, for CEP-SUL⁺ and CEP-SUL^-, respectively. The survival rate for CEP-SUL⁺ was significantly higher compared with CEP-SUL^- (P < 0.001). The number of hospital days, ventilator days since diagnosis of VAP and hospital costs were lower for CEP-SUL⁺.

Conclusion

Overall results suggested that patients with VAP due to CRAB strains who received adjunctive therapy with CEP-SUL had lower mortality rates and resource utilization compared with CEP-SUL^-.

Enhanced bacterial killing with colistin/sulbactam combination against carbapenem-resistant Acinetobacter baumannii

AIMS

Polymyxin-based combination therapy is often used to treat carbapenem-resistant Acinetobacter baumannii (A. baumannii) infections. Although sulbactam is intrinsically active against A. baumannii, few studies have investigated colistin/sulbactam combinations against carbapenem-resistant A. baumannii.

METHODS

Whole genome sequencing was undertaken on eight carbapenem-resistant (colistin-susceptible) isolates of A. baumannii from Chinese patients. Bacterial killing of colistin and sulbactam, alone and in combination, was examined with checkerboard (all isolates) and static and dynamic time-kill studies (three isolates). In the dynamic studies, antibiotics were administered in various clinically-relevant dosing regimens that mimicked patient pharmacokinetics.

RESULTS

The eight isolates consisted of ST195, ST191 and ST208 belonging to clonal complex 208, which is the most epidemic clonal type of A. baumannii globally. All isolates possessed Acinetobacter-derived cephalosporinase (ADC-61 or ADC-78) and seven of eight isolates contained the carbapenem-resistance gene bla_OXA-23. The colistin/sulbactam combination was synergistic against two of eight isolates in checkerboard studies. In time-kill studies, rapid bacterial killing of ca. 3-6 log₁₀ CFU/mL was observed with colistin monotherapy, followed by steady regrowth. Sulbactam monotherapy was generally ineffective. Substantially enhanced bacterial killing was observed with colistin/sulbactam combinations in both static and dynamic models, especially with the higher sulbactam concentration (2 g) and/or longer sulbactam infusion time (2 hours) in the dynamic model.

CONCLUSIONS

This study was the first to use a pharmacokinetics/pharmacodynamics model to investigate synergistic activity of colistin/sulbactam combinations against A. baumannii. It showed that clinically-relevant dosing regimens of colistin combined with sulbactam may substantially improve bacterial killing of multidrug-resistant and carbapenem-resistant A. baumannii.

The Association Between Empirical Antibiotic Treatment and Mortality in Severe Infections Caused by Carbapenem-resistant Gram-negative Bacteria: A Prospective Study

Background

Empirical colistin should be avoided. We aimed to evaluate the association between covering empirical antibiotics (EAT) and mortality for infections caused by carbapenem-resistant gram-negative bacteria (CRGNB).

Methods

This was a secondary analysis of a randomized controlled trial, including adults with bloodstream infections, pneumonia, or urosepsis caused by CRGNB. All patients received EAT followed by covering targeted therapy. The exposure variable was covering EAT in the first 48 hours. The outcome was 28-day mortality. We adjusted the analyses by multivariable regression analysis and propensity score matching.

Results

The study included 406 inpatients with severe CRGNB infections, mostly Acinetobacter baumannii (312/406 [77%]). Covering EAT was given to 209 (51.5%) patients, mostly colistin (n = 200). Patients receiving noncovering EAT were older, more frequently unconscious and dependent, carrying catheters, and mechanically ventilated with pneumonia. Mortality was 84 of 197 (42.6%) with noncovering vs 96 of 209 (45.9%) with covering EAT (P = .504). Covering EAT was not associated with survival in the adjusted analysis; rather, there was a weak association with mortality (odds ratio [OR], 1.37; 95% confidence interval [CI], 1.02-1.84). Results were similar for colistin monotherapy and colistin-carbapenem combination EAT. In the propensity score-matched cohort (n = 338) covering antibiotics were not significantly associated with mortality (OR, 1.42; 95% CI, .91-2.22). Similar results were obtained in an analysis of 14-day mortality.

Conclusions

Empirical use of colistin before pathogen identification, with or without a carbapenem, was not associated with survival following severe infections caused by CRGNBs, mainly A. baumannii.

Acinetobacter Pneumonia: Improving Outcomes With Early Identification and Appropriate Therapy

In an era of increasing antimicrobial resistance, Acinetobacter distinguishes itself as one of the most resistant Gram-negative bacteria responsible for significant morbidity and mortality. New solutions are needed to combat the detrimental effects of increasing rates of antimicrobial resistance. Using empiric broad-spectrum antibiotics in patients deemed at risk for infections caused by multidrug-resistant pathogens may protect against attributable mortality, but this temporary solution furthers the risk of antimicrobial resistance. In this article we will review relevant strategies to aid with early identification and appropriate treatment of Acinetobacter pneumonia while preserving antibiotic susceptibility.

Incidence and costs of ventilator-associated pneumonia in the adult intensive care unit of a tertiary referral hospital in Mexico

BACKGROUND

Ventilator-associated pneumonia (VAP) is defined as pneumonia that occurs after 48 hours of endotracheal intubation and initiation of mechanical ventilation. The aim of this work was to use a micro-costing method to calculate the costs generated in 2017 for the care of patients with VAP at the Hospital Juárez de México.

METHODS

We performed a cross-sectional, retrospective, analytical, and observational study of the databases of the registry of health care-associated infections (HAIs) in 2017, in addition to a micro-costing study.

RESULTS

We studied 48 VAP cases in an adult intensive care unit (AICU). In this period, 1668 ventilator days were identified, with an incidence rate of 28.8 per 1000 days. All cases were caused by multidrug-resistant (MDR) bacteria and the costs of their care exceeded the average costs for the use of antimicrobials. By calculating the profit on return as an association measure, we found that VAP caused by MDR bacteria confers 9 times the risk of increasing the costs of care above the expected average.

CONCLUSIONS

The cost for a case of VAP in the AICU is high and has an impact on the institutional budget. Control measures to prevent the spread of bacteria, particularly MDR bacteria, must be put into place in order to avoid increases in hospital stay costs and mortality.

Acinetobacter infections: a retrospective study to determine inhospital mortality rate and clinical factors associated with mortality

A retrospective case series of acinetobacter infections at a tertiary hospital in Nairobi was conducted to determine the mortality rate and factors associated with mortality. Over an eight-year period, 80 clinically significant infections were identified. The majority of infections were ventilator-associated pneumonia (40%) and bloodstream infections (30%). Eighty-six percent of the isolates were multi-drug resistant. The mortality rate in the study cohort was 45%. Twelve patients grew Acinetobacter spp. within 48 h of hospitalization, and three of these patients had no prior healthcare contact. The mean Sequential Organ Failure Assessment score was associated with mortality from acinetobacter infections.

Circulation of imipenem-resistant Acinetobacter baumannii ST10, ST2 and ST3 in a university teaching hospital from Tehran, Iran

PURPOSE

Multi-drug resistant (MDR) Acinetobacter baumannii has introduced a worldwide health crisis. The purposes of this study were to characterize the clonal relatedness among MDR clinical strains and to introduce a new two-locus typing method confirmed by multi-locus sequence typing (MLST).

METHODOLOGY

In this study, we determined antimicrobial resistance, detected genes associated with carbapenem resistance and characterized clonal relatedness among 99 clinical isolates extracted from 82 hospitalized inpatients in a university hospital.

RESULTS

Of the 99 A. baumannii isolates, 92.9% (92/99) were resistant to imipenem and 97.9% (97/99) had an MDR profile. We found that the high prevalence of blaVIM [94.9% (94/99)] and blaOXA-23-like [93.93% (93/99)] is the main mechanism of carbapenem resistance. This study proposes a new two-locus typing (blaOXA-51-like and ampC) method for the rapid identification of clonal complexes (CCs). The results of this method and confirmation by MLST show that clinical isolates carry blaOXA-68 as well as ampC-10 or ampC-20 genes belonging to CC10 (ST10); blaOXA-66 and ampC-2 belonging to CC2 (ST2); and blaOXA-71 and ampC-3 belonging to CC3 (ST3). One isolate had blaOXA-90 with an undetermined allele number of ampC belonging to ST513.

CONCLUSION

The high prevalence of MDR strains and the circulation of four limited clones, including ST10 (45/99), ST2 (41/99), ST3 (12/99) and ST513 (1/99), in the clinical setting highlights the importance of a rigorous infection control programme. The two-locus typing method has more discrimination than the application of each method separately and it could be applied for the rapid determination of the CC without performing MLST.

New Delhi metallo-β-lactamase-producing Acinetobacter isolates among late-onset VAP patients: multidrug-resistant pathogen and poor outcome

Background

Acinetobacter spp. are increasingly important microbes involved in late-onset ventilator-associated pneumonia (VAP).

Purpose

The aims of this study were to determine the prevalence of New Delhi metallo-β-lactamase (MβL) (blaNDM-1)-producing Acinetobacter spp. among late-onset VAP patients in different intensive care units (ICUs) of Menoufia and Kasr Al Ainy University Hospitals, to investigate the possible risk factors contributing to the acquisition of blaNDM-1-producing Acinetobacter infection, and to correlate between antimicrobial resistance pattern and therapeutic efficacy as well as clinical outcomes of these patients.

Materials and methods

Sixty-four Acinetobacter isolates were collected from mechanically ventilated patients with suspected late-onset VAP and subjected to antimicrobial susceptibility testing. The modified Hodge test (MHT) and combined disk tests (CDT) were applied for blaNDM-1 MβL detection. Acinetobacter isolates with phenotypically confirmed MβLs production were subjected to a PCR assay to verify the presence of blaNDM-1 gene. The most obvious risk factors for acquisition of carbapenem resistance in VAP patients and treatment outcomes were also analyzed.

Results

Out of 64 Acinetobacter isolates, 42 (65.6%) proved to be blaNDM-1 positive. The sensitivity and specificity of MHT were 52.38% and 41.67%, while for CDT they were 92.86% and 83.33%, respectively. Acinetobacter isolates showed high susceptibility to colistin (85.7%). The clinical response was better among VAP patients who received combined carbapenem plus colistin therapy than those who received colistin alone. Relapse of infection was detected in 12.5% (8/64) of VAP cases. The reported mortality reached 46.8% (30/64) of which 27 (64.3%) were infected with blaNDM-1-positive isolates. Prolonged duration of mechanical ventilation, longer hospital and ICU stays, and prior exposure to antibiotic therapy were by far the most important factors predisposing to carbapenem resistance among VAP patients.

Conclusion

A worldwide spread of Acinetobacter spp. expressing carbapenemases represents a significant threat to the medical community. The current study addressed the high prevalence of blaNDM-1-producing Acinetobacter isolates among late-onset VAP patients.

Ten-year surveillance study of ventilator-associated pneumonia at a tertiary care center in Lebanon

BACKGROUND

Ventilator-associated pneumonia (VAP) is associated with significant adverse outcomes in critically-ill patients admitted to the Intensive Care Unit (ICU). Systematic data from Lebanon on VAP are not available and large epidemiological studies from the region are scarce.

METHODS

We conducted a retrospective study over a 10-year period at the American University of Beirut Medical Center (AUBMC), a tertiary referral center in Lebanon in order to describe the incidence, microbiology, and temporal trends of VAP in the medical/surgical ICU.

RESULTS

A total of 162 patients developed VAP over the study period and the overall incidence of VAP was 7.9 per 1000 ventilator-days. There was a statistically significant decrease over time in the incidence of VAP, from 13.1 in 2008 to 1.1 per 1000 ventilator-days in 2017. Multidrug-resistant (MDR) Acinetobacter spp. was the predominant pathogen, both in early- as well as late-onset VAP, followed by Pseudomonas aeruginosa.

CONCLUSIONS

Following significant efforts from the Infection Control and Prevention Program, a considerable reduction in the incidence of VAP was achieved at AUBMC. The predominance of MDR Acinetobacter spp. should be taken into consideration when deciding on empirical therapy in patients with VAP.

Appropriateness of empiric antimicrobial therapy with imipenem/colistin in severe septic patients: observational cohort study

BACKGROUND

Empiric antimicrobial therapy (EAMT) using imipenem/colistin is commonly prescribed as a first line therapy in critically ill patients with severe sepsis. We aimed to assess the appropriateness of prescribing imipenem/colistin as EAMT in ICU patients.

METHODS

A 3-year observational prospective study included ICU patients that required imipenem/colistin as EAMT. The EAMT was assessed according to microbiological and clinical outcomes. The outcomes were: delay in apyrexia, delay in the decrease of the biological inflammatory parameters (BIP), the requirement for vasoactive agents, bacteriological eradication, length of stay, ventilator days and 30-day mortality.

RESULTS

79 administrations of EAMT in 70 patients were studied. EAMT was appropriate in 52% of the studied cases. An ICU stay > 6 days was related to inappropriateness, and chronic respiratory failure was associated with appropriateness. In the appropriate EAMT group, we showed: earlier apyrexia, shorter delay in the decrease of the BIP and a reduced significant vasopressors requirement. Furthermore, EAMT improved survival with a median gain of 4 days. Inappropriate EAMT increased the mortality risk by six. The acquisition of NI in ICU was also an independent factor of mortality.

CONCLUSIONS

EAMT using imipenem-colistin was appropriate in half of the cases and inappropriateness was associated with an increased ICU mortality risk.

Efficacy and toxicity of high-dose nebulized colistin for critically ill surgical patients with ventilator-associated pneumonia caused by multidrug-resistant Acinetobacter baumannii

PURPOSE

Few studies have compared nebulized and intravenous (IV) colistin for multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa pneumonia. This study compared the nephrotoxicity and clinical outcomes for these two delivery routes.

METHODS

This study retrospectively compared 95 critically ill surgical patients who were diagnosed with Acinetobacter baumannii ventilator associated pneumonia and received colistin between March 2013 and January 2016.

RESULTS

The most common diagnoses were brain hemorrhage (27.4%), traumatic brain injury (20%), traumatic thoracic injury (15.8%), and secondary peritonitis (11.6%). Compared to the IV group, the nebulizer group was significantly older (60.0 vs. 67.5years, p=0.010), had higher APACHE II scores (16.3 vs. 19.9, p=0.001), and more frequently had diabetes mellitus (6.8% vs. 21.6%, p=0.043). Nephrotoxicity was more common in the IV group (60.5% vs. 15.7%, p<0.0001). Both groups had similar microbiological and clinical outcomes (p=0.921 and p=0.719, respectively). Patients with nephrotoxicity exhibited prolonged IV or nebulized colistin treatment and more frequent combination with vancomycin. Nephrotoxicity was independently associated with IV delivery (odds ratio: 8.48, 95% confidence interval: 2.95-24.39, p<0.0001).

CONCLUSIONS

Nebulized colistin may have less nephrotoxicity and provide similar clinical results, compared to IV colistin.

Colistin Dosage without Loading Dose Is Efficacious when Treating Carbapenem-Resistant Acinetobacter baumannii Ventilator-Associated Pneumonia Caused by Strains with High Susceptibility to Colistin

OBJECTIVES

This study aims to analyze the mortality and the length of ICU stay (LOS) of A. baumannii VAP compared to respiratory colonization in patients with mechanical ventilation (MV).

METHODS

A prospective cohort study was performed in an ICU of adult patients (February 2010-June 2011). One hundred patients on MV with A. baumannii in lower respiratory airways were recruited, and classified as VAP or airways colonization according to CPIS criteria, with a punctuation ≥6. LOS, 30-days mortality, A. baumannii bacteremia, and clinical features including antibiotic therapy were recorded. Multivariate analysis (linear and Cox regression) and survival analysis (Kaplan-Meier curves) were performed.

RESULTS

Fifty-seven VAP and 43 colonized A. baumannii patients were analyzed. Among the A. baumannii strains, 99% were non-susceptible to carbapenems and the MIC90 of colistin was 0.12 mg/l. Therapy was appropriate in 94.6% of VAP patients, most of them with colistin 6 MIU/day, although in 13 (23.6%) cases colistin was started 48 hours after the onset of VAP. Mortality was similar in both groups (VAP 24.6% vs. colonized 27.9%, p = 0.7). Bacteremia and acute kidney insufficiency were associated with decreased survival (p = 0.02 and p = 0.04, respectively) in VAP patients. LOS was 21.5 (11.5-42.75) vs. 9 (6-22) days for VAP and colonized patients (p = 0.004). VAP (p = 0.003) and age (p = 0.01) were independently related to a longer LOS.

CONCLUSIONS

Multidrug-resistant A. baumannii VAP treated with colistin does not have a different mortality compared to lower airways colonization, among patients on mechanical-ventilation, in a setting of high susceptibility to colistin of A. baumannii.

Use of Ventilator Bundle and Staff Education to Decrease Ventilator-Associated Pneumonia in Intensive Care Patients

BACKGROUND

Ventilator-associated pneumonia (VAP), one of the most common hospital-acquired infections, has a high mortality rate.

OBJECTIVES

To evaluate the incidence of VAP in a multidisciplinary intensive care unit and to examine the effects of the implementation of ventilator bundles and staff education on its incidence.

METHODS

A 24-month-long before/after study was conducted, divided into baseline, intervention, and postintervention periods. VAP incidence and rate, the microbiological profile, duration of mechanical ventilation, and length of stay in the intensive care unit were recorded and compared between the periods.

RESULTS

Of 1097 patients evaluated, 362 met the inclusion criteria. The baseline VAP rate was 21.6 per 1000 ventilator days. During the postintervention period, it decreased to 11.6 per 1000 ventilator days (P = .01). Length of stay in the intensive care unit decreased from 36 to 27 days (P = .04), and duration of mechanical ventilation decreased from 26 to 21 days (P = .06).

CONCLUSIONS

VAP incidence was high in a general intensive care unit in a Greek hospital. However, implementation of a ventilator bundle and staff education has decreased both VAP incidence and length of stay in the unit.

Breath analysis for noninvasively differentiating Acinetobacter baumannii ventilator-associated pneumonia from its respiratory tract colonization of ventilated patients

A number of multiresistant pathogens including Acinetobacter baumannii (A. baumannii) place a heavy burden on ventilator-associated pneumonia (VAP) patients in intensive care units (ICU). It is critically important to differentiate between bacterial infection and colonization to avoid prescribing unnecessary antibiotics. Quantitative culture of lower respiratory tract (LRT) specimens, however, requires invasive procedures. Nowadays, volatile organic compounds (VOCs) have been studied in vitro and in vivo to identify pathogen-derived biomarkers. Therefore, an exploratory pilot study was conceived for a proof of concept that the appearance and level of A. baumannii-derived metabolites might be correlated with the presence of the pathogen and its ecological niche (i.e. the infection and colonization states) in ICU ventilated patients. Twenty patients with A. baumannii VAP (infection group), 20 ventilated patients with LRT A. baumannii colonization (colonization group) and 20 ventilated patients with neurological disorders, but without pneumonia or A. baumannii colonization (control group) were enrolled in the in vivo pilot study. A clinical isolate of A. baumannii strains was used for the in vitro culture experiment. The adsorptive preconcentration (solid-phase microextraction fiber and Tenax(®) TA) and analysis technique of gas chromatography-mass spectrometry were applied in the studies. Breath profiles could be visually differentiated between A. baumannii cultivation in vitro and culture medium, and among in vivo groups. In the in vitro experiment, nine compounds of interest (2,5-dimethyl-pyrazine, 1-undecene, isopentyl 3-methylbutanoate, decanal, 1,3-naphthalenediol, longifolene, tetradecane, iminodibenzyl and 3-methyl-indene) in the headspace were found to be possible A. baumannii derivations. While there were eight target VOCs (1-undecene, nonanal, decanal, 2,6,10-trimethyl-dodecane, 5-methyl-5-propyl-nonane, longifolene, tetradecane and 2-butyl-1-octanol) exhibiting characteristics of A. baumannii VAP derivations. The selected VOC profile in vivo could be adopted to efficiently differentiate the presence of LRT A. baumannii from its absence, and LRT A. baumannii infection from its colonization (AUC  =  0.89 and 0.88, respectively). It is not feasible to simply transfer the metabolic biomarkers from the in vitro condition to in vivo. The direct detection of exhaled A. baumannii-derived VOCs may be adopted for an early alert of the LRT bacterial presence in ventilated ICU patients, and even in different parasitic states of A. baumannii (i.e. infection and colonization). However, further refinement and validation are required before its clinical use.

Efficacy and toxicity of aerosolised colistin in ventilator-associated pneumonia: a prospective, randomised trial

Background

Cases of ventilator-associated pneumonia (VAP) due to multidrug-resistant (MDR) gram-negative bacilli (GNB) mainly Acinetobacter baumannii, Pseudomonas aeruginosa and enterobacteria are common in hospitalised patients of Tunisian intensive care units (ICUs). Parenteral colistin has been used for the therapy of VAP caused by MDR GNB at Tunisian hospitals over the past few years with a favourable clinical response. However, its use fell out of favour because of the reported drug-related nephrotoxicity and neurotoxicity.

Objectives

To determine whether aerosolised (AS) colistin was beneficial and safe in therapy of gram-negative VAP.

Methods

This was a randomised, single-blind study, in 149 critically ill adults who developed gram-negative VAP. Included patients were divided into two groups whether they received AS colistin (intervention group; n = 73) or intravenous (IV) colistin (control group; n = 76). AS colistin was given as 4 million units (MU) by nebulisation three times per 24 h. IV colistin was given as a loading dose of 9 MU followed by 4.5 MU two times per 24 h. Patients were followed during 28 days. Primary outcome was cure of VAP assessed at day 14 of therapy and defined as resolution of clinical signs of VAP and bacteriological eradication. Secondary outcomes were incidence of acute renal failure (ARF), mechanical ventilation length, ICU length of stay and 28-day mortality. Results were analysed based on intention-to-treat concept.

Results

The patient’s baseline characteristics and distribution of pathogens VAP in both groups were similar. The clinical cure rate was 67.1 % in AS group and 72 % in IV group (p = 0.59). When administered in monotherapy or in combination, the AS regimen was as effective as IV regimen. Patients in AS group had significantly lower incidence of ARF (17.8 vs 39.4 %, p = 0.004), more favourable improvement of P/F ratio (349 vs 316 at day 14, p = 0.012), shortened time to bacterial eradication (TBE) (9.89 vs 11.26 days, p = 0.023) and earlier weaning from ventilator in ICU survivors with a mean gain in ventilator-free days of 5 days. No difference was shown in the length of stay and the 28-day mortality.

Conclusion

Aerosolised colistin seems to be beneficial. It provided a therapeutic effectiveness non-inferior to parenteral colistin in therapy of MDR bacilli VAP with a lower nephrotoxicity, a better improvement of P/F ratio, a shortened bacterial eradication time and earlier weaning from ventilator in ICU survivors.

Trial registration ClinicalTrials.gov Identifier: NCT02683603

Efficacy and Toxicity of High-Dose Colistin in Multidrug-Resistant Gram-Negative Bacilli Infections: A Comparative Study of a Matched Series

BACKGROUND

Colistimethate sodium (CMS) is the commercialized form of colistin that is effective against multiresistant Gram-negative bacilli. Its main side effects are nephrotoxicity and neurotoxicity. Pharmacodynamic dosages showed that they were infratherapeutic. Therefore, strategies with higher doses were proposed. The aim of this study was to assess the efficiency and toxicity of higher-dose CMS by comparing two treatment strategies: high-dose CMS versus standard-dose CMS.

METHODS

A prospective and comparative study of two matched groups was conducted. Fourty-six patients in each group were matched for age, severity and nature of infection. In the high-dose colistin group, CMS was administered at a loading dose of 9 MIU followed by a maintenance dose of 4.5 MIU/12 h. In the second group, retrospectively analyzed, colistin was administered at 6 MIU/day. For each group, clinical results, bacteriological eradication and daily creatinine clearance were recorded. Primary outcome measures were clinical cure defined as disappearance of infectious signs and eradication of microorganisms in all the follow-up cultures. Secondary outcome measures were incidence of acute renal failure and mortality.

RESULTS

Ninety-two patients were analyzed by matching. There was a higher cure rate in the high-dose group (63 vs. 41.3%, p = 0.04). No higher risk of nephrotoxicity was found by increasing daily doses of colistin (32.2 versus 26%, p = 0.64). Similarly, there was no significant difference in the time to onset of renal failure (8.32 vs. 11 days, p = 1) or in the requirement of hemodialysis (26.6 vs. 41%, p = 1).

CONCLUSION

The high-dose colistin regimen is more efficient, without significant renal or neurological toxicity.

Nosocomial Acinetobacter pneumonia: Treatment and prognostic factors in 356 cases

BACKGROUND AND OBJECTIVE

Acinetobacter baumannii and A. baumannii/calcoaceticus complex are commonly encountered pathogens in nosocomial infections. This study aimed to evaluate the treatment and prognostic risk factors in nosocomial pneumonia caused by these microorganisms.

METHODS

The study was conducted retrospectively in Uludag University Hospital and included 356 adult non-neutropenic patients with nosocomial pneumonia.

RESULTS

Of the subjects, 94.9% (n = 338) had ventilator-associated pneumonia. The clinical response rate was 57.2%, the 14-day mortality 39.6% and the 30-day mortality 53.1%. The significant independent risk factors for the 30-day mortality were severe sepsis (OR, 2.60; 95% CI: 1.49-4.56; P = 0.001), septic shock (OR, 6.12; 95% CI: 2.75-13.64; P < 0.001), APACHE II score ≥ 20 (OR, 2.12; 95% CI: 1.28-3.50; P = 0.003) and empiric monotherapy (OR, 1.63; 95% CI: 1.00-2.64; P = 0.048). Multi-trauma (OR, 2.50; 95% CI: 1.11-5.68; P = 0.028) was found to be a protective factor. In patients with a clinical pulmonary infection score (CPIS) > 6 on the third day of treatment, both the 14- and 30-day mortality rates were high (P < 0.001, P < 0.001). Also, the 14- and 30-day mortality rates were significantly higher in the patients treated with empiric monotherapy compared with combination therapy (48/93 (51.6%)-46/123 (37.4%), P = 0.037 and 62/93 (66.7%)-65/123 (52.8%), P = 0.041, respectively) in pneumonia caused by imipenem-resistant strains.

CONCLUSION

Mortality rates were high in pneumonia caused by imipenem-resistant A. baumannii or A. baumannii/calcoaceticus complex. In the units with a high level of carbapenem resistance, antibiotic combinations should be considered for empiric therapy.

Biofilm Formation Caused by Clinical Acinetobacter baumannii Isolates Is Associated with Overexpression of the AdeFGH Efflux Pump

Chronic wound infections are associated with biofilm formation, which in turn has been correlated with drug resistance. However, the mechanism by which bacteria form biofilms in clinical environments is not clearly understood. This study was designed to investigate the biofilm formation potency of Acinetobacter baumannii and the potential association of biofilm formation with genes encoding efflux pumps, quorum-sensing regulators, and outer membrane proteins. A total of 48 clinically isolated A. baumannii strains, identified by enterobacterial repetitive intergenic consensus (ERIC)-PCR as types A-II, A-III, and A-IV, were analyzed. Three representative strains, which were designated A. baumannii ABR2, ABR11, and ABS17, were used to evaluate antimicrobial susceptibility, biofilm inducibility, and gene transcription (abaI, adeB, adeG, adeJ, carO, and ompA). A significant increase in the MICs of different classes of antibiotics was observed in the biofilm cells. The formation of a biofilm was significantly induced in all the representative strains exposed to levofloxacin. The levels of gene transcription varied between bacterial genotypes, antibiotics, and antibiotic concentrations. The upregulation of adeG correlated with biofilm induction. The consistent upregulation of adeG and abaI was detected in A-III-type A. baumannii in response to levofloxacin and meropenem (1/8 to 1/2× the MIC), conditions which resulted in the greatest extent of biofilm induction. This study demonstrates a potential role of the AdeFGH efflux pump in the synthesis and transport of autoinducer molecules during biofilm formation, suggesting a link between low-dose antimicrobial therapy and a high risk of biofilm infections caused by A. baumannii. This study provides useful information for the development of antibiofilm strategies.

Prognostic factors associated with mortality of drug-resistant Acinetobacter baumannii ventilator-associated pneumonia

Background

Ventilator-associated pneumonia (VAP) caused by drug-resistant Acinetobacter baumannii is associated with high mortality in critically ill patients. We identified the prognostic factors of 30-day mortality in patients with VAP caused by drug-resistant A. baumannii and compared survival outcomes among multidrug-resistant (MDR), extensively drug-resistant (XDR) and pandrug-resistant (PDR) A. baumannii VAP.

Methods

A retrospective cohort study was conducted in the Medical Intensive Care Unit at Chiang Mai University Hospital, Thailand. All adult patients diagnosed with A. baumannii VAP between 2005 and 2011 were eligible. Univariable and multivariable Cox’s proportional hazards regression were performed to identify the prognostic factors of 30-day mortality.

Results

A total of 337 patients with microbiologically confirmed A. baumannii VAP were included. The proportion of drug-sensitive (DS), MDR, XDR, and PDR A. baumannii were 9.8%, 21.4%, 65.3%, and 3.6%, respectively. The 30-day mortality rates were 21.2%, 31.9%, 56.8%, and 66.7%, respectively. The independent prognostic factors were SOFA score >5 (hazard ratio (HR) = 3.33, 95% confidence interval (CI) 1.94–5.72, P < 0.001), presence of septic shock (HR = 2.66, 95% CI 1.71–4.12, P < 0.001), Simplified Acute Physiology Score (SAPS) II >45 (HR = 1.58, 95% CI 1.01–2.46, P = 0.045), and inappropriate initial antibiotic treatment (HR = 1.53, 95% CI 1.08–2.20, P = 0.016).

Conclusions

Drug-resistant A. baumannii, particularly XDR and PDR, was associated with a high mortality rate. Septic shock, high SAPS II, high SOFA score, and inappropriate initial antibiotic treatment were independent prognostic factors for 30-day mortality.

Molecular mechanisms of sulbactam antibacterial activity and resistance determinants in Acinetobacter baumannii

Sulbactam is a class A β-lactamase inhibitor with intrinsic whole-cell activity against certain bacterial species, including Acinetobacter baumannii. The clinical use of sulbactam for A. baumannii infections is of interest due to increasing multidrug resistance in this pathogen. However, the molecular drivers of its antibacterial activity and resistance determinants have yet to be precisely defined. Here we show that the antibacterial activities of sulbactam vary widely across contemporary A. baumannii clinical isolates and are mediated through inhibition of the penicillin-binding proteins (PBPs) PBP1 and PBP3, with very low frequency of resistance; the rare pbp3 mutants with high levels of resistance to sulbactam are attenuated in fitness. These results support further investigation of the potential clinical utility of sulbactam.

Ventilator-associated pneumonia: epidemiology and prognostic indicators of 30-day mortality

We conducted a retrospective cohort study in the medical intensive care unit of Chaing Mai University Hospital to describe the epidemiology of ventilator-associated pneumonia (VAP) and identify prognostic indicators of 30-day VAP mortality. A total of 621 patients diagnosed with VAP between January 2005 and December 2011 were included. The overall 30-day mortality rate was 44.4%. The major causative pathogens were Acinetobacter baumannii (54.3%), Pseudomonas aeruginosa (35.2%), and methicillin-resistant Staphylococcus aureus (15.1%). Most A. baumannii (90.2%) comprised drug-resistant strains. Identified prognostic indicators were co-morbid malignancy (hazard ratio [HR] = 1.60; 95% confidence interval [CI] 1.02-2.42; P = 0.040), septic shock (HR = 2.51; 95% CI, 1.60-4.00; P < 0.001), Simplified Acute Physiology Score II >45 (HR = 1.62; 95% CI, 1.03-2.56; P = 0.041), Sequential Organ Failure Assessment score >5 (HR = 3.40; 95% CI 2.00-5.81; P < 0.001), and delayed inappropriate empirical antibiotic treatment (HR = 2.23; 95% CI, 1.12-4.45; P = 0.022). VAP was associated with high mortality. The major causative pathogen was drug-resistant A. baumannii. Therefore, early detection of VAP by surveillance in mechanically ventilated patients leading to earlier treatment may improve patient outcomes. Guidelines for prescribing appropriate empirical antibiotics to cover drug-resistant bacteria could be established using local epidemiological data.

Draft Genome Sequence of an International Clonal Lineage 1 Acinetobacter baumannii Strain from Argentina

In the last few years Acinetobacter baumannii has emerged worldwide as an important nosocomial pathogen in medical institutions. Here, we present the draft genome sequence of the international clonal lineage 1 (ICL1) A. baumannii strain A144 that was isolated in a hospital in Buenos Aires City in the year 1997. The strain is susceptible to carbapenems and resistant to trimethoprim and gentamicin.