Clinical epidemiology, treatment and prognostic factors of extensively drug-resistant Acinetobacter baumannii ventilator-associated pneumonia in critically ill patients

Antimicrobial efficacy of eravacycline against emerging extensively drug-resistant (XDR) Acinetobacter baumannii isolates

PURPOSE

Drug-resistant Acinetobacter baumannii is an emerging threat. This study has been conducted to observe the efficacy of eravacycline along with the RND-efflux pump system.

METHODS

A cross-sectional study was done collecting 48 clinical isolates of Acinetobacter baumannii. MICs of 15 antibiotics were detected along with BMD of tigecycline and eravacycline. PCR products of drug-resistant regulatory genes were sequenced and analyzed.

RESULTS

Of the total 48 Isolates, 35 (72.91%) were XDR and 13 (27.08%) were MDR. Out of all, 60.41% of isolates were found to be susceptible to eravacycline by BMD according to both FDA and EUCAST guidelines. A 2-fold decline of MIC50/90 was observed with the use of eravacycline compared to tigecycline. RND-efflux genes like AdeC in 30 (62.5%) isolates and Regulatory gene AdeS in 29 (60.41%) isolates were detected, explaining the existing resistance mechanism.

CONCLUSIONS

XDR Acinetobacter poses an escalating threat due to its resistance to multiple antibiotics, raising serious concerns in healthcare settings. Eravacycline is an encouraging new drug for empirical use in severe infection caused due to the same. Molecular investigation and strict antimicrobial stewardship should be followed to control the emergence, and a better understanding of mechanisms of resistance to prevent the spread of drug-resistant isolates.

Sub-minimum inhibitory concentrations (sub-MICs) of colistin on Acinetobacter baumannii biofilm formation potency, adherence, and invasion to epithelial host cells: an experimental study in an Iranian children's referral hospital

Here, we described the efficacy of colistin sub-minimum inhibitory concentrations (sub-MICs) on biofilm-forming activity, host epithelial cell adherence, and invasion capacity of Acinetobacter baumannii strains collected from children admitted to the Children's Medical Center Hospital. Biofilm formation potency of A. baumannii clinical isolates was measured using a 96-well microtiter plate assay. Distribution of biofilm-related genes, including bap, abaI, ompA, csuE, and blaPER-1, was detected by PCR. The mRNA expression level of ompA and csuE was measured by qPCR in the presence of ¼ and ½ MICs of colistin. A. baumannii adhesion and invasion to eukaryotic host cells were phenotypically assayed at sub-MICs of colistin. Eighty percent (56/70) and 35.7% (25/70) of A. baumannii isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes, respectively. The strong, moderate, and weak biofilm producers of A. baumannii were 37.1% (26/70), 32.8%, (23/70), and 22.8% (16/70), respectively. The frequencies of biofilm-associated genes were 100% for abaI, ompA, and csuE, followed by 22.8% (16/70) and 24.3% (17/70) for bap and blaPER-1, respectively. The downregulation of csuE and ompA expression levels was observed in the sub-MIC of colistin. In vitro cell culture study showed a decreased capability of A. baumannii to adhere to the human epithelial cells at sub-inhibitory doses of colistin; however, none of the isolates could invade HEp-2 cells. Our study showed that the genes encoding biofilm-associated proteins undergo downregulation in expression levels after exposure to sub-MICs of colistin in A. baumannii. Longitudinal in vivo studies are needed to fully understand the clinical aspects of pathogenicity mechanisms and evolutionary dynamics of drug resistance.IMPORTANCESince the toxicity of colistin is dose dependent, there is a focus on strategies that reduce the dose while maintaining the therapeutic effect of the drug. Our findings about sub-inhibitory doses of colistin provide a novel insight into the logical use of colistin to treat and control Acinetobacter baumannii-related infections in clinical practice.

Development and clinical empirical validation of the chronic critical illness prognosis prediction model

BACKGROUND

The evolution of critical care medicine and nursing has aided and enabled the rescue of a large number of patients from numerous life-threatening diseases. However, in many cases, patient health may not be quickly restored, and the long-term prognosis may not be optimistic.

OBJECTIVES

In this study, we aimed to develop and validate a prediction model for accurate, precise, and objective identification of the severity of chronic critical illness (CCI) in patients.

METHODS

We used a retrospective case-control and prospective cohort study with no interventions. Patients diagnosed with CCI admitted to the ICU of a large metropolitan public hospital were selected. In the case-control study, 344 patients (case: 172; control:172) were enrolled to develop the prognosis prediction model of chronic critical illness (PPCCI Model); 88 patients (case:44; control: 44) in a prospective cohort study, served as the validation cohort. The discrimination of the model was measured using the area under the curve (AUC) of the receiver operating characteristic curve (ROC).

RESULTS

Age, prolonged mechanical ventilation (PMV), sepsis or other severe infections, Glasgow Coma Scale (GCS), mean artery pressure (MAP), heart rate (HR), respiratory rate (RR), oxygenation index (OI), and active bleeding were the nine predictors included in the model. In both cohorts, the PPCCI model outperformed the Acute Physiology And Chronic Health Evaluation II (APACHE II), Modified Early Warning Score (MEWS), and Sequential Organ Failure Assessment (SOFA) in identifying deceased patients with CCI (development cohort: AUC, 0.934; 95%CI, 0.908-0.960; validation cohort: AUC, 0.965; 95% CI, 0.931-0.999).

CONCLUSION

The PPCCI model can provide ICU medical staff with a standardized measurement tool for assessing the condition of patients with CCI, enabling them to allocate ward monitoring resources rationally and communicate with family members.

Differential proteomic analysis and pathogenic effects of outer membrane vesicles derived from Acinetobacter baumannii under normoxia and hypoxia

Acinetobacter baumannii is a major causative agent of nosocomial infections and its outer membrane vesicles (AbOMVs) have been shown to be involved in pathogenicity by transporting virulence factors and transferring information for communication between pathogens and host cells. Despite the fact that the infected sites of A. baumannii such as lungs and skin soft tissues are hypoxic, most studies on AbOMV virulence have used AbOMVs prepared under aerobic conditions. The present study aims to elucidate the protein profile and pathogenic impact of AbOMVs released under hypoxic condition. AbOMVs were isolated from A. baumannii under normoxic and hypoxic conditions, and their protein profiles were compared. The different effects of both normoxic and hypoxic AbOMVs in cytokine response from mouse macrophages, cytotoxicity to the human lung epithelial cells, and bacterial invasion were then investigated. Our results showed that A. baumannii under hypoxia released larger amounts of OMVs with different protein profiles. Although the cytotoxic effect of AbOMVs from normoxia and hypoxia were comparable, AbOMVs from normoxia induced higher TNF-α production and invasion of Staphylococcus aureus and Pseudomonas aeruginosa than those from hypoxia. On the other hand, AbOMVs significantly enhanced A. baumannii invasion into lung epithelial cells in a dose-dependent manner. These results clearly demonstrate that AbOMVs released from normoxic and hypoxic have different impacts in pathogenesis. This finding provides new insight into the complex interactions between A. baumannii, coinfecting pathogens and host cells via OMVs, in particular the different pathogenic effects of AbOMVs under normoxic and hypoxic conditions.

Impact of Molecular Syndromic Diagnosis of Severe Pneumonia in the Management of Critically Ill Patients

The impact of syndromic molecular diagnosis in the management of nosocomial infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) pathogens has been incompletely characterized. We evaluated the performance of a molecular syndromic platform (BioFire FilmArray-Pneumonia plus Panel) in patients with pneumonia in the intensive care unit (ICU) of a University Hospital in Greece over a 2-year period. We evaluated 79 consecutive patients diagnosed with pneumonia in the ICU (2018-2020), including 55 patients with ventilator associated pneumonia (VAP). We included 40 control patients diagnosed with pneumonia in the ICU the year before the study (2017-2018). We identified 16 cases of VAP due to XDR bacterial pathogens. We found an excellent agreement (89.4% 76/85 reported results) between the results of syndromic platform and conventional cultures of tracheal aspirates. The molecular syndromic test significantly improved time to diagnosis versus conventional culture (3.5 h vs 72 h, P < 0.0001), and identified new pathogens not detected by cultures in 49% of the cases. However, three cases of pneumonia with targets not included in the molecular platform, were not detected. Implementation of the molecular syndromic facilitated treatment modification from broad to narrow spectrum antimicrobial therapy, resulting in significant reductions in antibiotic consumption in the study group compared to the control group, without a negative impact in patient outcome. The implementation of syndromic molecular diagnosis in critically ill patients with pneumonia is associated with timely and improved diagnosis and has significant impact on reduction of antibiotic consumption. IMPORTANCE The impact of syndromic molecular diagnosis in the management of nosocomial infections caused by MDR/XDR pathogens has been incompletely characterized. We evaluated the performance of a molecular syndromic platform (BioFire FilmArray -Pneumonia plus Panel) in 79 patients with pneumonia in the intensive care unit (ICU) of a University Hospital in Greece over a 2-year period (2018-2020) compared to 40 control patients diagnosed with pneumonia in the ICU the year before the study (2017-2018). Importantly, implementation of syndromic pneumonia panel improved time to diagnosis, identified new pathogens not detected by cultures in 49% of the cases and resulted in a significant reduction in antibiotic consumption compared to the year before initiation of the study without a negative impact in mortality of patients. Collectively, our study demonstrates the positive value of PCR syndromic testing in the management of pneumonia in ICUs high rates of MDR/XDR nosocomial pathogens.

Acinetobacter baumannii: Pathogenesis, virulence factors, novel therapeutic options and mechanisms of resistance to antimicrobial agents with emphasis on tigecycline

WHAT IS KNOWN AND OBJECTIVE

Acinetobacter baumannii is one of the most important nosocomial pathogens with the ability to cause infections such as meningitis, pneumonia, urinary tract, septicaemia and wound infections. A wide range of virulence factors are responsible for pathogenesis and high mortality of A. baumannii including outer membrane proteins, lipopolysaccharide, capsule, phospholipase, nutrient- acquisition systems, efflux pumps, protein secretion systems, quarom sensing and biofilm production. These virulence factors contribute in pathogen survival in stressful conditions and antimicrobial resistance.

COMMENT

According to the World Health Organization (WHO), A. baumannii is one of the most resistant pathogens of ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa and Enterobacter spp.). In recent years, resistance to a wide range of antibiotics in A. baumannii has significantly increased and the high emergence of extensively drug resistant (XDR) isolates is challenging. Among therapeutic antibiotics, resistance to tigecycline as a last resort antibiotic has become a global concern. Several mechanisms are involved in tigecycline resistance, the most important of which is RND (Resistance-Nodulation-Division) family efflux pumps overexpression. The development of new therapeutic strategies to confront A. baumannii infections has been very promising in recent years.

WHAT IS NEW AND CONCLUSION

In the present review we highlight microbiological and virulence traits in A. baumannii and peruse the tigecycline resistance mechanisms and novel therapeutic options. Among the novel therapeutic strategies we focus on combination therapy, drug repurposing, novel antibiotics, bacteriophage therapy, antimicrobial peptides (AMPs), human monoclonal antibodies (Hu-mAbs), nanoparticles and gene editing.

Evaluating the Efficacy of Eravacycline and Omadacycline against Extensively Drug-Resistant Acinetobacter baumannii Patient Isolates

For decades, the spread of multidrug-resistant (MDR) Acinetobacter baumannii has been rampant in critically ill, hospitalized patients. Traditional antibiotic therapies against this pathogen have been failing, leading to rising concerns over management options for patients. Two new antibiotics, eravacycline and omadacycline, were introduced to the market and have shown promising results in the treatment of Gram-negative infections. Since these drugs are newly available, there is limited in vitro data about their effectiveness against MDR A. baumannii or even susceptible strains. Here, we examined the effectiveness of 22 standard-of-care antibiotics, eravacycline, and omadacycline against susceptible and extensively drug-resistant (XDR) A. baumannii patient isolates from Cooper University Hospital. Furthermore, we examined selected combinations of eravacycline or omadacycline with other antibiotics against an XDR strain. We demonstrated that this collection of strains is largely resistant to monotherapies of carbapenems, fluoroquinolones, folate pathway antagonists, cephalosporins, and most tetracyclines. While clinical breakpoint data are not available for eravacycline or omadacycline, based on minimum inhibitory concentrations, eravacycline was highly effective against these strains. The aminoglycoside amikacin alone and in combination with eravacycline or omadacycline yielded the most promising results. Our comprehensive characterization offers direction in the treatment of this deadly infection in hospitalized patients.

Clinical Features and Outcomes of Monobacterial and Polybacterial Episodes of Ventilator-Associated Pneumonia Due to Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant A. baumannii (MDRAB) VAP has high morbidity and mortality, and the rates are constantly increasing globally. Mono- and polybacterial MDRAB VAP might differ, including outcomes. We conducted a single-center, retrospective (January 2014−December 2016) study in the four ICUs (12−18−24 beds each) of a reference Lithuanian university hospital, aiming to compare the clinical features and the 30-day mortality of monobacterial and polybacterial MDRAB VAP episodes. A total of 156 MDRAB VAP episodes were analyzed: 105 (67.5%) were monomicrobial. The 30-day mortality was higher (p < 0.05) in monobacterial episodes: overall (57.1 vs. 37.3%), subgroup with appropriate antibiotic therapy (50.7 vs. 23.5%), and subgroup of XDR A. baumannii (57.3 vs. 36.4%). Monobacterial MDRAB VAP was associated (p < 0.05) with Charlson comorbidity index ≥3 (67.6 vs. 47.1%), respiratory comorbidities (19.0 vs. 5.9%), obesity (27.6 vs. 9.8%), prior hospitalization (58.1 vs. 31.4%), prior antibiotic therapy (99.0 vs. 92.2%), sepsis (88.6 vs. 76.5%), septic shock (51.9 vs. 34.6%), severe hypoxemia (23.8 vs. 7.8%), higher leukocyte count on VAP onset (median [IQR] 11.6 [8.4−16.6] vs. 10.9 [7.3−13.4]), and RRT need during ICU stay (37.1 vs. 17.6%). Patients with polybacterial VAP had a higher frequency of decreased level of consciousness (p < 0.05) on ICU admission (29.4 vs. 14.3%) and on VAP onset (29.4 vs. 11.4%). We concluded that monobacterial MDRAB VAP had different demographic/clinical characteristics compared to polybacterial and carried worse outcomes. These important findings need to be validated in a larger, prospective study, and the management implications to be further investigated.

Recommendations and guidelines for the treatment of infections due to multidrug resistant organisms

Antimicrobial drug resistance is one of the major threats to global health. It has made common infections increasingly difficult or impossible to treat, and leads to higher medical costs, prolonged hospital stays and increased mortality. Infection rates due to multidrug-resistant organisms (MDRO) are increasing globally. Active agents against MDRO are limited despite an increased in the availability of novel antibiotics in recent years. This guideline aims to assist clinicians in the management of infections due to MDRO. The 2019 Guidelines Recommendations for Evidence-based Antimicrobial agents use in Taiwan (GREAT) working group, comprising of infectious disease specialists from 14 medical centers in Taiwan, reviewed current evidences and drafted recommendations for the treatment of infections due to MDRO. A nationwide expert panel reviewed the recommendations during a consensus meeting in Aug 2020, and the guideline was endorsed by the Infectious Diseases Society of Taiwan (IDST). This guideline includes recommendations for selecting antimicrobial therapy for infections caused by carbapenem-resistant Acinetobacter baumannii, carbapenem-resistant Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, and vancomycin-resistant Enterococcus. The guideline takes into consideration the local epidemiology, and includes antimicrobial agents that may not yet be available in Taiwan. It is intended to serve as a clinical guide and not to supersede the clinical judgment of physicians in the management of individual patients.

Antimicrobial Random Peptide Mixtures Eradicate Acinetobacter baumannii Biofilms and Inhibit Mouse Models of Infection

Antibiotic resistance is one of the greatest crises in human medicine. Increased incidents of antibiotic resistance are linked to clinical overuse and overreliance on antibiotics. Among the ESKAPE pathogens, Acinetobacter baumannii, especially carbapenem-resistant isolates, has emerged as a significant threat in the context of blood, urinary tract, lung, and wound infections. Therefore, new approaches that limit the emergence of antibiotic resistant A. baumannii are urgently needed. Recently, we have shown that random peptide mixtures (RPMs) are an attractive alternative class of drugs to antibiotics with strong safety and pharmacokinetic profiles. RPMs are antimicrobial peptide mixtures produced by incorporating two amino acids at each coupling step, rendering them extremely diverse but still defined in their overall composition, chain length, and stereochemistry. The extreme diversity of RPMs may prevent bacteria from evolving resistance rapidly. Here, we demonstrated that RPMs rapidly and efficiently kill different strains of A. baumannii, inhibit biofilm formation, and disrupt mature biofilms. Importantly, RPMs attenuated bacterial burden in mouse models of acute pneumonia and soft tissue infection and significantly reduced mouse mortality during sepsis. Collectively, our results demonstrate RPMs have the potential to be used as powerful therapeutics against antibiotic-resistant A. baumannii.

Treatment of extensively-drug resistant (XDR) Acinetobacter and impact on clinical outcomes in U.S. veterans affairs (VA) medical centers

BACKGROUND

Guidelines for treatment of resistant Acinetobacter baumannii (AB) are limited, leaving a knowledge gap in best practices for treatment. This study described treatments and outcomes of extensively-drug resistant (XDR) AB.

METHODS

Retrospective cohort study including patients with XDRAB (non-susceptible to at least 1 agent in all but 2 or fewer classes) and antibiotic treatment between 2012 and 2018 at Veterans Affairs Medical Centers. Descriptive statistics summarized antibiotics; propensity score adjusted regression models were fit to compare outcomes.

RESULTS

Two hundred and seventy-six patients with 439 XDRAB cultures and Gram-negative targeted antibiotic treatment were included. One hundred and eighteen (43%) patients received monotherapy while 158 (57%) received combination therapy, most commonly including a carbapenem (n = 106, 67%) and polymyxin (n = 66, 42%). One hundred and eighty-four (67%) patients received inadequate treatment. In adjusted models, combination therapy did not decrease the odds of in-hospital (aOR 1.24, 95%CI 0.60-2.59) or 30-day (aOR 1.43, 95%CI 0.86-2.38) mortality, or median postculture length of stay (aIRR 1.11, 95%CI 0.86-1.43). Likewise, receipt of inadequate treatment was not associated with poorer outcomes.

CONCLUSIONS

In this national cohort of patients with XDRAB, neither combination therapy nor receipt of adequate treatment improved outcomes. Further research is needed on optimal management of this difficult-to-treat pathogen with few effective antibiotic options.

Replication initiator proteins of Acinetobacter baumannii plasmids: An update note

The bioinformatic analysis that we made of 492 Acinetobacter baumannii plasmid sequences identified 418 genes encoding Replication Initiator (Rep) proteins that fell into at least fourteen groups according to the protein domains that they contained. The most abundant group of Rep proteins contained a Rep_3 superfamily domain, followed by Rep proteins containing Replicase/PriCT_1 superfamily domains, and then by Reps possessing only an HTH_MerR-SF superfamily domain. The remaining eleven groups contain only a few members. To evaluate the diversity of these Rep proteins, we classify them using the current scheme of GR homology groups, which contains 34 groups. However, we needed to create 22 additional GR homology groups to capture all the Rep protein diversity of the plasmid collection. Finally, our bioinformatic analysis suggests that a large fraction of the plasmids seem to have a restricted host range limited to Acinetobacter species, except for those belonging to GR38 that have a very wide host range. To facilitate the future analysis of the Rep proteins, we included a list of the DNA and protein sequences, in fasta format, of the representatives of each one of the GR homology groups.

Overexpression of the adeB Efflux Pump Gene in Tigecycline-Resistant Acinetobacter baumannii Clinical Isolates and Its Inhibition by (+)Usnic Acid as an Adjuvant

Acinetobacter species are among the most life-threatening Gram-negative bacilli, causing hospital-acquired infections, and they are associated with high morbidity and mortality. They show multidrug resistance that acts via various mechanisms. In Acinetobacter baumannii, efflux pump-mediated resistance to many antimicrobial compounds, including tigecycline, has been widely reported. Natural compounds have been used for their various pharmacological properties, including anti-efflux pump activity. The present study aimed to evaluate the efflux pump-mediated resistance mechanism of Acinetobacter baumannii and the effect of (+)Usnic acid as an efflux pump inhibitor with tigecycline. For detecting the efflux pump activity of tigecycline-resistant Acinetobacter baumannii isolates, microbroth dilution method and real-time quantitative reverse transcription–polymerase chain reaction was used. (+)Usnic acid was added to tigecycline and tested by the checkerboard method to evaluate its efficacy as an efflux pump inhibitor. qRT-PCR analysis was carried out to show the downregulation of the efflux pump in the isolates. Out of 42 tigecycline-resistant Acinetobacter baumannii isolates, 19 showed efflux pump activity. All 19 strains expressed the adeB gene. (+)Usnic acid as an adjuvant showed better efficacy in lowering the minimum inhibitory concentration compared with the conventional efflux pump inhibitor, carbonyl cyanide phenylhydrazone.

Systematic review and meta-analysis of the proportion and associated mortality of polymicrobial (vs monomicrobial) pulmonary and bloodstream infections by Acinetobacter baumannii complex

BACKGROUND

Differentiating Acinetobacter baumannii complex (ABC) infection from colonization remains difficult and further complicated in polymicrobial infections.

PURPOSE

To assess the frequency of polymicrobial ABC infections and associated mortality. We hypothesized a lower mortality in polymicrobial infections if ABC isolation reflects colonization in some polymicrobial infections.

METHODS

A systematic review was conducted in PubMed, Scopus and CENTRAL for studies reporting ABC pulmonary and bloodstream infections. The proportion of infections that were polymicrobial and the magnitude of the association between polymicrobial (vs monomicrobial) infection and mortality were estimated with meta-analyses.

RESULTS

Based on 80 studies (9759 infections) from 23 countries, the pooled proportion of polymicrobial infection was 27% (95% CI 22-31%) and was similarly high for bloodstream and pulmonary infections. Polymicrobial infection was variably and insufficiently defined in most (95%) studies. Considerable heterogeneity (I² = 95%) was observed that persisted in subgroup analyses and meta-regressions. Based on 17 studies (2675 infections), polymicrobial infection was associated with lower 28-day mortality (OR = 0.75, 95% CI 0.58-0.98, I² = 36%). However, polymicrobial infection was not associated with in-hospital mortality (OR = 0.97, 95% CI 0.69-1.35, I² = 0%) based on 14 studies (953 infections). The quality of evidence (GRADE) for the association of polymicrobial (vs monomicrobial) infection with mortality was low and at high risk of bias.

CONCLUSION

Polymicrobial ABC infections are common and may be associated with lower 28-day mortality. Considering the heterogeneity of polymicrobial infections and limitations of the available literature, more research is required to clarify the clinical impact of polymicrobial (vs monomicrobial) ABC infection.

Pandrug-resistant Gram-negative bacteria: a systematic review of current epidemiology, prognosis and treatment options

BACKGROUND

The literature on the epidemiology, mortality and treatment of pandrug-resistant (PDR) Gram-negative bacteria (GNB) is scarce, scattered and controversial.

OBJECTIVES

To consolidate the relevant literature and identify treatment options for PDR GNB infections.

METHODS

A systematic search in MEDLINE, Scopus and clinical trial registries was conducted. Studies reporting PDR clinical isolates were eligible for review if susceptibility testing for all major antimicrobials had been performed. Characteristics and findings of retrieved studies were qualitatively synthesized.

RESULTS

Of 81 studies reviewed, 47 (58%) were published in the last 5 years. The reports reflected a worldwide dissemination of PDR GNB in 25 countries in 5 continents. Of 526 PDR isolates reported, Pseudomonas aeruginosa (n=175), Acinetobacter baumannii (n=172) and Klebsiella pneumoniae (n=125) were most common. PDR GNB were typically isolated in ICUs, but several studies demonstrated wider outbreak potential, including dissemination to long-term care facilities and international spread. All-cause mortality was high (range 20%-71%), but appeared to be substantially reduced in studies reporting treatment regimens active in vitro. No controlled trial has been performed to date, but several case reports and series noted successful use of various regimens, predominantly synergistic combinations, and in selected patients increased exposure regimens and newer antibiotics.

CONCLUSIONS

PDR GNB are increasingly being reported worldwide and are associated with high mortality. Several treatment regimens have been successfully used, of which synergistic combinations appear to be most promising and often the only available option. More pharmacokinetic/pharmacodynamic and outcome studies are needed to guide the use of synergistic combinations.

Is pandrug-resistance in A. baumannii a transient phenotype? Epidemiological clues from a 4-year cohort study at a tertiary referral hospital in Greece

Pandrug-resistant A. baumannii (PDRAB) is increasingly being reported but remains rare. Several case studies show that A. baumannii can acquire resistance to last resort antibiotics during treatment by single-step chromosomal mutations. However, re-emergence of the ancestral susceptible strain after withdrawal of antibiotics has been described, possibly due to fitness cost associated with acquired resistance. Therefore, PDRAB may be a transient phenotype. Epidemiological data to show this process in larger cohorts are currently lacking. In this study of 91 hospitalized patients with PDRAB we showed the frequent (60%) isolation of non-PDRAB, often susceptible only to colistin, aminoglycosides and/or tigecycline, preceding and/or following PDRAB isolation. However, the isolation of PDRAB in two outpatients, 25 and 36 days after their discharge from the hospital, suggests the potential of some PDRAB strains to persist even in the absence of antimicrobial pressure.

Excess mortality due to pandrug-resistant Acinetobacter baumannii infections in hospitalized patients

BACKGROUND

Pandrug-resistant Acinetobacter baumannii (PDRAB) is increasingly being reported as a nosocomial pathogen worldwide, but determining its clinical impact is challenging.

AIM

To assess the spectrum of excess mortality attributable to PDRAB infection in acute care settings.

METHODS

This four-year cohort study was conducted in a tertiary-care referral hospital in Greece to estimate excess in-hospital mortality due to PDRAB infection by comparing patients infected to those colonized with PDRAB by means of competing risks survival analysis.

FINDINGS

The study cohort comprised 91 patients (median age: 67 years; 77% men). For most patients, PDRAB was first isolated in the intensive care unit (ICU) (N = 51; 57%) or following ICU discharge (N = 26; 29%). Overall in-hospital mortality was 68% (95% confidence interval (CI): 57.5-77.5%). PDRAB-infected patients (N = 62; 68%) and PDRAB-colonized patients (N = 29; 32%) had similar baseline characteristics, but the absolute excess risk of 30-day mortality in infected patients compared to colonized patients was 34% (95% CI: 14-54%). Multivariable competing risks regression showed that PDRAB infection significantly increased the daily hazard of 30-day in-hospital death (cause-specific hazard ratio (csHR): 3.10; 95% CI: 1.33-7.21) while simultaneously decreasing the daily rate of discharge (csHR: 0.24; 95% CI: 0.08-0.74), thereby leading to longer hospitalization. Stronger effects were observed for bloodstream infections.

CONCLUSION

New effective antimicrobials would be expected to prevent mortality in one of every three patients treated for PDRAB infection and reduce their length of hospitalization. However, available therapeutic options remain extremely limited and emphasis on preventing healthcare-associated transmission of PDRAB is ever more important.

Intravenous colistin use for infections due to MDR Gram-negative bacilli in critically ill paediatric patients: a systematic review and meta-analysis

BACKGROUND

Data are limited regarding the clinical effectiveness and safety of intravenous colistin for treatment of infections due to MDR Gram-negative bacilli (GNB) in paediatric ICUs (PICUs).

METHODS

Systematic review of intravenous colistin use in critically ill paediatric patients with MDR-GNB infection in PubMed, Scopus and EMBASE (up to 31 January 2018).

RESULTS

Out of 1181 citations, 7 studies were included on the use of intravenous colistin for 405 patients in PICUs. The majority of patients were diagnosed with lower respiratory tract infections, Acinetobacter baumannii being the predominant pathogen. Colistin dosages ranged between 2.6 and 18 mg/kg/day, with only one case reporting a loading dose. Emergence of colistin resistance during treatment was reported in two cases. Nephrotoxicity and neurotoxicity were reported in 6.1% and 0.5%, respectively, but concomitant medications and severe underlying illness limited our ability to definitively associate use of colistin with nephrotoxicity. Crude mortality was 29.5% (95% CI = 21.7%-38.1%), whereas infection-related mortality was 16.6% (95% CI = 12.2%-21.5%).

CONCLUSIONS

While the reported incidence of adverse events related to colistin was low, reported mortality rates for infections due to MDR-GNB in PICUs were notable. In addition to severity of disease and comorbidities, inadequate daily dosage and the absence of a loading dose may have contributed to mortality. As the use of colistin for treatment of MDR-GNB infections increases, it is imperative to understand whether optimal dosing of colistin in paediatric patients differs across different age groups. Thus, future studies to establish the pharmacokinetic properties of colistin in different paediatric settings are warranted.

Development of Different Methods for Preparing Acinetobacter baumannii Outer Membrane Vesicles Vaccine: Impact of Preparation Method on Protective Efficacy

Acinetobacter baumannii (A. baumannii) is becoming a common global concern due to the emergence of multi-drug or pan-drug resistant strains. Confronting the issue of antimicrobial resistance by developing vaccines against the resistant pathogen is becoming a common strategy. In this study, different methods for preparing A. baumannii outer membrane vesicles (AbOMVs) vaccines were developed. sOMV (spontaneously released AbOMV) was extracted from the culture supernatant, while SuOMV (sucrose-extracted AbOMV) and nOMV (native AbOMV) were prepared from the bacterial cells. Three AbOMVs exhibited significant differences in yield, particle size, protein composition, and LPS/DNA content. To compare the protective efficacy of the three AbOMVs, groups of mice were immunized either intramuscularly or intranasally with each AbOMV. Vaccination via both routes conferred significant protection against lethal and sub-lethal A. baumannii challenge. Moreover, intranasal vaccination provided more robust protection, which may be attributed to the induction of significant sIgA response in mucosal sites. Among the three AbOMVs, SuOMV elicited the highest level of protective immunity against A. baumannii infection, whether intramuscular or intranasal immunization, which was characterized by the expression of the most profound specific serum IgG or mucosal sIgA. Taken together, the preparation method had a significant effect on the yield, morphology, and composition of AbOMVs, that further influenced the protective effect against A. baumannii infection.

The Current Epidemiological Landscape of Ventilator-associated Pneumonia in the Intensive Care Unit: A Multicenter Prospective Observational Study in China

Background

Ventilator-associated pneumonia (VAP) is among the most important hospital-acquired infections in the intensive-care unit setting. However, clinical data regarding the epidemiology of VAP in China are limited.

Methods

A multicenter, longitudinal, observational study was performed from March 2013 to December 2015 to prospectively collect data on patients diagnosed with VAP. Specifically, patients supported by invasive mechanical ventilation for longer than 48 hours were included. Clinical data were recorded for each VAP patient. The exact pathogen distribution and the incidence of VAP were calculated. Risk factors associated with mortality were analyzed using univariate and multivariate regression analyses.

Results

A total of 2492 patients received mechanical ventilation for longer than 48 hours and were enrolled in the study. A total of 129 (5.0%) patients fulfilled the VAP criteria, and 38 (29.5%) patients were diagnosed with early-onset VAP. The incidence of VAP was 4.5 per 1000 ventilation days, with a 28-day mortality rate of 45%. Individual pathogens, including 115 bacteria and 2 fungi, were identified in 117 (90.7%) enrollees, and 87 (75.7%) bacteria were multidrug-resistant organisms. Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa were the most commonly detected pathogens causing VAP. No difference in the distribution of pathogens was observed between early- and late-onset VAP or between surviving and non-surviving patients. Multivariate regression revealed that older ages and Sequential Organ Failure Assessment Scores were correlated with increased 28-day mortality rates.

Conclusions

High pathogen resistance and mortality were found in both early- and late-onset VAP.

Clinical Trials Registration

NCT01943331.

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.

Monotherapy versus combination therapy for multidrug-resistant Gram-negative infections: Systematic Review and Meta-Analysis

Infections caused by carbapenemase-producing, multidrug-resistant (MDR), or extensively drug-resistant (XDR) Gram-negative bacteria constitute a major therapeutic challenge. Whether combination antibiotic therapy is superior to monotherapy remains unknown. In this systematic review and meta-analysis OVID MEDLINE, EMBASE, PubMed, The Cochrane Library, and Scopus databases were searched for randomized controlled trials (RCTs) and observational studies published by December 2016 comparing mono- with combination antibiotic therapy for infections with carbapenemase-producing, MDR, or XDR Gram-negative bacteria. Mortality and clinical cure rates served as primary and secondary outcome measures, respectively. Of 8847 initially identified studies, 53 studies – covering pneumonia (n = 10 studies), blood stream (n = 15), osteoarticular (n = 1), and mixed infections (n = 27) - were included. 41% (n = 1848) of patients underwent monotherapy, and 59% (n = 2666) combination therapy. In case series/cohort studies (n = 45) mortality was lower with combination- vs. monotherapy (RR 0.83, CI 0.73–0.93, p = 0.002, I² = 24%). Subgroup analysis revealed lower mortality with combination therapy with at least two in-vitro active antibiotics, in blood stream infections, and carbapenemase-producing Enterobacteriaceae. No mortality difference was seen in case-control studies (n = 6) and RCTs (n = 2). Cure rates did not differ regardless of study type. The two included RCTs had a high and unknown risk of bias, respectively. 16.7% (1/6) of case-control studies and 37.8% (17/45) of cases series/cohort studies were of good quality, whereas quality was poor in the remaining studies. In conclusion, combination antimicrobial therapy of multidrug-resistant Gram-negative bacteria appears to be superior to monotherapy with regard to mortality.

A systematic review of the global seasonality of infections caused by Acinetobacter species in hospitalized patients

BACKGROUND

Acinetobacter is a leading multidrug resistant pathogen in hospitals worldwide that has been seen to exhibit periodic surges during summer months. However, winter peaks and lack of seasonality have also been noted.

OBJECTIVES

To systematically collate and examine the evidence describing seasonal patterns in the incidence of Acinetobacter infection in hospitalized patients.

DATA SOURCES

MEDLINE/Ovid, EMBASE, Scopus and Web of Science.

STUDY ELIGIBILITY CRITERIA

Longitudinal observational studies investigating seasonal variation in the incidence of Acinetobacter infection.

PARTICIPANTS

Patients receiving hospital care.

INTERVENTIONS

Routine hospital care.

METHODS

Systematic review with narrative evidence synthesis structured around clinical and methodological heterogeneity and internal validity of retrieved studies, seasonal patterns and risk factors detected, and stated hypotheses of mechanisms underlying seasonality. To examine consistency in reported seasonal patterns across different conditions, monthly incidence data were extracted, standardised, weighted and presented graphically.

RESULTS

Twenty-five studies reporting 37006 cases of Acinetobacter infection or colonization during 1954 months of follow-up were reviewed. Standardised monthly incidence data pooled across studies exhibited a global seasonal pattern with an incidence peak in summer/warmer months and a trough in winter/colder months. This seasonal pattern remained consistent under different weighting schemes accounting for study size, length of follow-up and overall quality assessment rating. Seasonality persisted in different clinical settings and for different types and sources of infection. Nine studies provided consistent evidence of temperature-associated variation in Acinetobacter incidence, while there were controversial findings regarding other environmental variables. No study detected patient-related or clinical practice-related seasonal variation in Acinetobacter incidence.

CONCLUSIONS

Despite substantial clinical and methodological heterogeneity in retrieved studies, a consistent global seasonal pattern in Acinetobacter infection incidence was evident in this review. This merits attention when designing or evaluating infection control interventions in hospitals. Future research should focus on elucidating driving mechanisms underlying the observed seasonality.

Clinical experience with tigecycline in the treatment of hospital-acquired pneumonia caused by multidrug resistant Acinetobacter baumannii

Background

Tigecycline, with broad in vitro antibacterial activity, has been widely used off-label for nosocomial pneumonia caused by multi-drug resistant Acinetobacter baumannii (MDRAB). However, many concerns have been raised about the efficacy of tigecycline treatment as the inconsistent results from previous clinical studies.

Methods

This retrospective study evaluated the outcome of adult patients with monomicrobial MDRAB nosocomial pneumonia treated with tigecycline between 2015 and 2017. Results.

A total of 77 patients was eligible for this study, and the overall clinical success and 30-day survival rates were 70.03 and 70.13%, respectively, however, the microbiological eradication rate was relatively low (48%). Multivariate analysis indicated that shorter duration of tigecycline use associated with increased clinical failure, whereas higher CURB65 scores, mechanical ventilation and tigecycline resistant to MDRAB have significant association with 30-day mortality.

Conclusions

Our results suggest that tigecycline is one of the potential choices for the treatment of hospital-acquired pneumonia caused by MDRAB, especially with a MIC≤2 mg/L. In addition, a longer duration of tigecycline treatment may be required to insure better clinical outcomes.

Ventilator-Associated Pneumonia due to Drug-Resistant Acinetobacter baumannii: Risk Factors and Mortality Relation with Resistance Profiles, and Independent Predictors of In-Hospital Mortality

Background and objectives: High mortality and healthcare costs area associated with ventilator-associated pneumonia (VAP) due to Acinetobacter baumannii (A. baumannii). The data concerning the link between multidrug-resistance of A. baumannii strains and outcomes remains controversial. Therefore, we aimed to identify the relation of risk factors for ventilator-associated pneumonia (VAP) and mortality with the drug resistance profiles of Acinetobacter baumannii (A. baumannii) and independent predictors of in-hospital mortality. Methods: A retrospective ongoing cohort study of 60 patients that were treated for VAP due to drug-resistant A. baumannii in medical-surgical intensive care units (ICU) over a two-year period was conducted. Results: The proportions of multidrug-resistant (MDR), extensively drug-resistant (XDR), and potentially pandrug-resistant (pPDR) A. baumannii were 13.3%, 68.3%, and 18.3%, respectively. The SAPS II scores on ICU admission were 42.6, 48.7, and 49 (p = 0.048); hospital length of stay (LOS) prior to ICU was 0, one, and two days (p = 0.036), prior to mechanical ventilation (MV)—0, 0, and three days (p = 0.013), and carbapenem use prior to VAP—50%, 29.3%, and 18.2% (p = 0.036), respectively. The overall in-hospital mortality rate was 63.3%. In MDR, XDR, and pPDR A. baumannii VAP groups, it was 62.5%, 61.3%, and 72.7% (p = 0.772), respectively. Binary logistic regression analysis showed that female gender (95% OR 5.26; CI: 1.21–22.83), SOFA score on ICU admission (95% OR 1.28; CI: 1.06–1.53), and RBC transfusion (95% OR 5.98; CI: 1.41–25.27) were all independent predictors of in-hospital mortality. Conclusions: The VAP risk factors: higher SAPS II score, increased hospital LOS prior to ICU, and MV were related to the higher resistance profile of A. baumannii. Carbapenem use was found to be associated with the risk of MDR A. baumannii VAP. Mortality due to drug-resistant A. baumannii VAP was high, but it was not associated with the A. baumannii resistance profile. Female gender, SOFA score, and RBC transfusion were found to be independent predictors of in-hospital mortality.

Acinetobacter baumannii Ventilator-Associated Pneumonia: Clinical Efficacy of Combined Antimicrobial Therapy and in vitro Drug Sensitivity Test Results

Objective: To evaluate therapeutic efficacy of different combined antimicrobial treatments against Acinetobacter baumannii ventilator-associated pneumonia (VAP). Methods: Clinical outcomes were retrospectively analyzed to elucidate the efficacy of four combined antimicrobial regimens. The chessboard and micro broth dilution methods determined the minimum inhibitory concentrations (MICs) of four antiseptic drugs singly used and combined two drugs against 36 isolates of multidrug-resistant (MDR) A. baumannii. Results: The incidence of VAP was approximately 6.9% (237/3424) between January 1, 2015 and December 31, and 35.9% (85/237) of the cases were caused by A. baumannii. Among these cases, 60 belonged to AB-VAP, for whom antimicrobial treatment plan was centralized and clinical data was complete. Moreover, all 60 strains of A. baumannii were MDR bacteria from reports microbiological laboratory. Resistance rate was lowest for amikacin (68.3%) and ampicillin sulbactam (71.7%). Resistance rate for imipenem increased from 63.2 to 90.9% during the 3 years. However, in these 60 cases of AB-VAP, the combination between 4 antibiotics was effective in most cases: the effective rate was 75% (18/24) for sulbactam combined with etilmicin, 71.4% (10/14) for sulbactam combined with levofloxacin, 72.7% (8/11) for meropenem combined with etilmicin, and 63.6% (7/11) for meropenem combined with levofloxacin. There was no statistical difference between four regimens (P > 0.05). Sulbactam combined with etilmicin decreased 1/2 of MIC50 and MIC90 of sulbactam while the decreases in etilmicin were more obviously than single drug. When adopting meropenem combined with levofloxacin or etilmicin, the MIC of meropenem reduced to 1/2 of that in applying single drug. As for sulbactam or meropenem combined with levofloxacin, it also lessened the MIC50 of levofloxacin to 1/2 of that for single drug. FIC results suggested that the effects of four combined antimicrobial regimens were additive or unrelated. When sulbactam was combined with etimicin, the additive effect was 63.89%. Conclusion: Drug combination sensitivity test in vitro may be helpful for choosing antimicrobial treatment plans. Sulbactam or meropenem as the basis of treatment regimens can function as the alternatives against AB-VAP. Sulbactam combined with etimicin has been regarded as a recommended regimen in Suizhou, Hubei, China.

Acinetobacter etiology respiratory tract infections associated with mechanical ventilation: what impacts on the prognosis? A retrospective cohort study

INTRODUCTION

Acinetobacter species treatment often represents a challenge. The main objective of this study is identify predictors of ICU mortality in patients submitted to mechanical ventilation (MV).

MATERIALS AND METHODS

Retrospective cohort study. Patients with MV > 48 h who developed a respiratory tract positive culture for Acinetobacter were included, and distinguished among colonized, ventilator-associated pneumonia (VAP) or ventilator-associated tracheobronchitis (VAT) patients. Primary outcome was ICU mortality.

RESULTS

153 patients were in MV and presented positive culture for Acinetobacter calcoaceticus-baumanii complex, 70 of them with VAP, 59 with VAT and 24 patients were colonized. The factors related to ICU mortality were VAP (OR 2.2, 95% CI 1.1-4.5) and shock at the time of diagnosis (OR 4.8, 95% CI 1.8-2.3). In multivariate analysis, only SOFA score at the time of diagnosis (OR 1.06, 95% CI 1.03-1.09) was related with ICU mortality. A paired-matched analysis was performed to assess effect of dual therapy on outcomes, and no effect was found in terms of clinical cure, ICU or hospital mortality or duration of antimicrobial therapy.

CONCLUSIONS

Previous comorbidities and degree of associated organic injury seem to be more important factors in the prognosis than double antibiotic therapy in patients with Acinetobacter-related respiratory infection.

Incidence and characteristics of ventilator-associated pneumonia in a regional non-tertiary Australian intensive care unit: protocol for a retrospective clinical audit study

INTRODUCTION

Ventilator-associated pneumonia (VAP) is a medical complication associated with prolonged mechanical ventilation. Most studies looking at VAP originate from major, tertiary intensive care units (ICUs). Our understanding of VAP in regional hospitals is limited. Given that patient characteristics often differ between metropolitan and regional centres, it is important to investigate VAP in a regional non-tertiary ICU. This project will establish and report the incidence, case characteristics and outcomes including mortality and length of stay related to VAP in a regional non-tertiary Australian ICU. Furthermore, it will compare the incidence of VAP in accordance with consultant diagnosed cases in the medical record, and by a post hoc screening of all cases against a list of previously published diagnostic criteria.

METHODS AND ANALYSIS

This retrospective clinical audit study will screen medical records from the period 1 January 2013 to 31 December 2016. All cases requiring mechanical ventilation for ≥72 hours will be screened against previously reported diagnostic criteria for VAP. At the same time, their medical records will be screened for a documented diagnosis of VAP.

ETHICS AND DISSEMINATION

This study has been granted ethical approval from the Central Queensland Hospital and Health Service (CQHHS) Human Research Ethics Committee (HREC/17/QCQ/11) and the Central Queensland University Human Research Ethics Committee (H17/05-102). This study will be submitted for publication in a peer-reviewed scientific journal and presented at internal workshops (within Queensland Health) and national and/or international scientific conferences.

Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities

Acinetobacter baumannii, once considered a low-category pathogen, has emerged as an obstinate infectious agent. The scientific community is paying more attention to this pathogen due to its stubbornness to last resort antimicrobials, including carbapenems, colistin, and tigecycline, its high prevalence of infections in the hospital setting, and significantly increased rate of community-acquired infections by this organism over the past decade. It has given the fear of pre-antibiotic era to the world. To further enhance our understanding about this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

Defining the potency of amikacin against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii derived from Chinese hospitals using CLSI and inhalation-based breakpoints

OBJECTIVES

We report the in vitro activity of amikacin and comparators against Gram-negative bacteria collected from blood and respiratory specimens in China during a 1-year period between December 2015 and December 2016.

MATERIALS AND METHODS

Minimum inhibitory concentrations (MICs) were determined by agar dilution methods using Clinical and Laboratory Standards Institute (CLSI) guidelines, and susceptibility was assessed using CLSI breakpoints, except for tigecycline against Enterobacteriaceae. A pharmacodynamic threshold MIC ≤ 256 mg/L was also applied for amikacin since its inhalation formulation has demonstrated activity up to these MICs.

RESULTS

For Escherichia coli, including extended-spectrum beta-lactamase (ESBL)-producing isolates (45.7% of population), amikacin demonstrated excellent activity (93.0%-94.7% susceptible) similar to tigecycline, piperacillin/tazobactam, and the carbapenems. Against Klebsiella pneumoniae, only tigecycline retained susceptibility >90%; amikacin inhibited 83.7% and 71.1% of the total and ESBL-producing (24.2%) populations at its breakpoint, respectively. Amikacin susceptibility against Pseudomonas aeruginosa was 91.1%, and only polymyxin B (100%) achieved higher susceptibility rates. Susceptibility declined to 80.9% and 54.5% against carbapenem- and multidrug-resistant (MDR) isolates, respectively. Finally, MDR was very common (84.0%) among Acinetobacter baumannii, with amikacin susceptibility at 30.5% for all isolates and 17.3% for MDR isolates. Since the majority of the amikacin-resistant isolates had amikacin MICs > 256 mg/L, the use of the inhalation pharmacodynamic threshold did not substantially improve the CLSI susceptible value.

CONCLUSION

Amikacin portrayed comparable or better susceptibility rates to most of the tested antibiotics against E. coli, K. pneumoniae, P. aeruginosa, and A. baumannii in China. As few isolates had MICs of 32-256 mg/L, use of the CLSI breakpoint and inhalation pharmacodynamic threshold yielded similar overall susceptibilities.

Risk factors for mortality in ICU patients with Acinetobacter baumannii ventilator-associated pneumonia: impact of bacterial cytotoxicity

Background

Acinetobacter baumannii (A. baumannii) ventilator-associated pneumonia (VAP) in intensive care unit (ICU) is associated with high morbidity and mortality in patients with critical illness. However, the literatures that focused on the short-term prognosis and the risk factors for mortality are limited. The aim of this study was to evaluate the risk factors for mortality in ICU patients with A. baumannii VAP.

Methods

A retrospective cohort study was conducted in the medical/surgical ICU at Zhongshan Hospital in Shanghai, China. Adult patients meeting the criteria of A. baumannii VAP from January 2012 to October 2015 were enrolled. Apart from collecting clinical and microbiologic data, we performed biofilm-formation and cytotoxicity testing using A. baumannii strains which are isolated from patients. Multivariate logistic regression analysis was used to determine the independent risk factors for 30-day mortality in ICU.

Results

Seventy-eight patients were included in this study. The 30-day mortality rate in ICU for the patients was 37.2%. Multivariate analysis revealed that short-term mortality was significantly associated with prior surgery [OR, 0.277; 95% confidence interval (CI), 0.089-0.866; P=0.027], higher APACHEII score (OR, 1.140; 95% CI, 1.007-1.291; P=0.038) and an increased bacterial cytotoxicity (OR, 1.029 ; 95% CI, 1.001-1.058; P=0.047).

Conclusions

The main finding of our study was that increased bacterial cytotoxicity might be a risk factor for short-term mortality in ICU patients with A. baumannii VAP.

Colistin versus Colistin Combined with Ampicillin-Sulbactam for Multiresistant Acinetobacter baumannii Ventilator-associated Pneumonia Treatment: An Open-label Prospective Study

Background:

Retrospective studies have reported good clinical success rates using colistin as monotherapy to treat Acinetobacter baumannii ventilator-associated pneumonia (VAP), comparable to that obtained with colistin combined with other antibiotics. However, inadequate penetration into the pulmonary parenchyma for colistin has been shown in animal models.

Aim:

The aim of the study was to study prospectively the outcome, measured as clinical response and survival, of intravenously administered colistin versus colistin combined with high-dose ampicillin-sulbactam in Intensive Care Unit (ICU) patients with multiresistant A. baumannii VAP.

Methods and Subjects:

This prospective, open-label, randomized study included consecutive patients who developed microbiologically documented VAP due to A. baumannii with carbapenem-resistant strains but susceptible to colistin and ampicillin-sulbactam. Seventy-four patients were screened, but finally, 39 participants were enrolled and finished the study Patients received colistin (Group A – 19 patients) or colistin and ampicillin/sulbactam (Group B – 20 patients). The clinical response of VAP was assessed on day 4^th to 5^th of treatment (early response). If therapy was considered unsuccessful after this period, ampicillin/sulbactam was added in Group A or changed therapy in B.

Results:

Early cure rates in Group A and B were 15.8% and 70%, respectively (P = 0.001). Multiple regression analysis revealed that combination treatment (odds ratio [OR]: 43.6, 95% confidence interval [CI]: 3.594–530.9) and Sequential Organ Failure Assessment score <8 (OR: 0.022, 95% CI: 0.001–0.43) were independently associated with favorable clinical response. APACHE II score ≤15 (OR: 0.049, 95% CI: 0.003–0.0942) and an early favorable response to treatment (OR: 244.4, 95% CI: 2.151–27850.9) were associated with survival and discharge from ICU.

Conclusion:

Combination therapy with colistin and a high dose of ampicillin/sulbactam was associated with a more favorable clinical response to VAP due to carbapenem-resistant A. baumannii than colistin monotherapy.

Clinical and Pathophysiological Overview of Acinetobacter Infections: a Century of Challenges

Acinetobacter is a complex genus, and historically, there has been confusion about the existence of multiple species. The species commonly cause nosocomial infections, predominantly aspiration pneumonia and catheter-associated bacteremia, but can also cause soft tissue and urinary tract infections. Community-acquired infections by Acinetobacter spp. are increasingly reported. Transmission of Acinetobacter and subsequent disease is facilitated by the organism's environmental tenacity, resistance to desiccation, and evasion of host immunity. The virulence properties demonstrated by Acinetobacter spp. primarily stem from evasion of rapid clearance by the innate immune system, effectively enabling high bacterial density that triggers lipopolysaccharide (LPS)-Toll-like receptor 4 (TLR4)-mediated sepsis. Capsular polysaccharide is a critical virulence factor that enables immune evasion, while LPS triggers septic shock. However, the primary driver of clinical outcome is antibiotic resistance. Administration of initially effective therapy is key to improving survival, reducing 30-day mortality threefold. Regrettably, due to the high frequency of this organism having an extreme drug resistance (XDR) phenotype, early initiation of effective therapy is a major clinical challenge. Given its high rate of antibiotic resistance and abysmal outcomes (up to 70% mortality rate from infections caused by XDR strains in some case series), new preventative and therapeutic options for Acinetobacter spp. are desperately needed.

Photodynamic antimicrobial chemotherapy with the novel amino acid-porphyrin conjugate 4I: In vitro and in vivo studies

Photodynamic antimicrobial chemotherapy (PACT), as a novel and effective therapeutic modality to eradicate drug resistant bacteria without provoking multidrug resistance, has attracted increasing attention. This study examined the antimicrobial efficacy of the novel cationic amino acid-porphyrin conjugate 4I with four lysine groups against two different clinical isolated strains (drug sensitive and multidrug resistant) of the Acinetobacter baumannii species and its toxicity on murine dermal fibroblasts in vitro, as well as the therapeutic effect of PACT on acute, potentially lethal multidrug resistant strain excisional wound infections in vivo. The PACT protocol exposed 4I to illumination, exhibiting high antimicrobial efficacy on two different strains due to a high yield of reactive oxygen species (ROS) and non-selectivity to microorganisms. The photoinactivation effects of 4I against two different strains were dose-dependent. At 3.9 μM and 7.8 μM, PACT induced 6 log units of inactivation of sensitive and multidrug resistant strains. In contrast, 4I alone and illumination alone treatments had no visibly antimicrobial effect. Moreover, cytotoxicity tests revealed the great safety of the photosensitizer 4I in mice. In the in vivo study, we found 4I-mediated PACT was not only able to kill bacteria but also accelerated wound recovery. Compared with non-treated mice, over 2.89 log reduction of multidrug resistant Acinetobacter baumannii strain was reached in PACT treat mice at 24 h post-treatment. These results imply that 4I-mediated PACT therapy is an effective and safe alternative to conventional antibiotic therapy and has clinical potential for superficial drug-resistant bacterial infections.

Anticipating the Unpredictable: A Review of Antimicrobial Stewardship and Acinetobacter Infections

Acinetobacter remains one of the most challenging pathogens in the field of infectious diseases owing primarily to the uniqueness and multiplicity of its resistance mechanisms. This resistance often leads to devastatingly long delays in time to appropriate therapy and increased mortality for patients afflicted with Acinetobacter infections. Selecting appropriate empiric and definitive antibacterial therapy for Acinetobacter is further complicated by the lack of reliability in commercial antimicrobial susceptibility testing devices and limited breakpoint interpretations for available agents. Existing treatment options for infections due to Acinetobacter are limited by a lack of robust efficacy and safety data along with concerns regarding appropriate dosing, pharmacokinetic/pharmacodynamic targets, and toxicity. Antimicrobial stewardship programs are essential to combat this unpredictable pathogen through use of infection prevention, rapid diagnostics, antibiogram-optimized treatment regimens, and avoidance of overuse of antimicrobials. The drug development pipeline includes several agents with encouraging in vitro activity against Acinetobacter, but their place in therapy and contribution to the armamentarium against this pathogen remain to be defined. The objective of this review is to highlight the unique challenge of treating infections due to Acinetobacter and summarize recent literature regarding optimal antimicrobial treatment for this pathogen. The drug development pipeline is also explored for future potentially effective treatment options.