Current viewpoint on the epidemiology of nonfermenting Gram-negative bacterial strains

Respiratory dysbiosis as prognostic biomarker of disease severity for adults with community-acquired pneumonia requiring mechanical ventilation

OBJETIVES

To ascertain the role of the lung microbiome in the development of severe pneumonia and its potential as a biomarker for disease progression.

METHODS

BAL samples from 34 adults with severe community-acquired pneumonia (CAP) (17 viral, 8 viral coinfected with bacteria and 9 bacterial) admitted to the ICU for acute respiratory failure between 2019 and 2021 were collected within the first 48 h of admission to the ICU. The microbiome was characterized via the Ion 16S Metagenomics Kit and the Ion Torrent sequencing platform. Clinical factors, including survival, mechanical ventilation duration, blood biomarkers and organ failure in terms of acute respiratory distress syndrome (ARDS), shock or acute renal failure, were correlated with microbiome characteristics.

RESULTS

The microbiome diversity in patients with viral pneumonia was significantly greater than that in patients with bacterial or coinfected pneumonia: the Shannon diversity index was 3.75 (Q1-Q3: 2.5-4.1) versus 0.4 (Q1-Q3: 0.2-1.3) and 0.48 (Q1-Q3: 0.3-1.1), respectively (p < 0.05). The microbiome diversity index was associated with severity-of-illness (APACHE II), independent of the etiology of pneumonia (B coefficient -1.845; p < 0.01). Patients with severe viral CAP who developed ARDS had a lower presence of Proteobacteria, and those who were complicated with ventilator-associated pneumonia had a higher prevalence of Acinetobacter at admission. The mortality of patients with bacterial or coinfected pneumonia was 35%. In coinfected patients, the diversity index was associated with the development of shock.

CONCLUSION

Patients with severe CAP have low respiratory microbiome diversity, indicating that respiratory microbiome diversity is a potential biomarker of disease severity.

Clinical Characteristics of Patients Who Acquired Gram-Negative Bacteria During Ceftazidime-Avibactam Therapy

INTRODUCTION

Ceftazidime-avibactam (CZA) is recommended to treat infections caused by carbapenem-resistant Enterobacterales and Pseudomonas aeruginosa with difficult-to-treat resistance. The selective pressure of CZA results in the isolation of multidrug-resistant Gram-negative bacteria (MDR-GNB), causing superinfection or hospital-wide spread. We aimed to study the clinical characteristics of patients who acquired GNB during CZA treatment.

METHODS

Adult patients treated with CZA for ≥ 5 days for proven or suspected MDR-GNB were retrospectively enrolled at Taipei Veterans General Hospital between December 2019 and June 2021. GNB acquisition was defined as new GNB species resulting in infection or colonization isolated during the period from 5 days after the initiation of CZA until the end of treatment. Clinical features were compared between patients who acquired GNB from clinical specimen and those who did not. Multivariable analysis was used to explore risk factors for acquisition of GNB and 28-day mortality in patients who acquired GNB.

RESULTS

Among 321 patients treated with CZA, 68 GNB were identified in 55 patients (17.1%). Elizabethkingia species (n = 15) was the most common GNB, followed by Acinetobacter species (n = 13) and Burkholderia cenocepacia (n = 11). The presence of diabetes mellitus, and mechanical ventilation were independent risk factors for GNB acquisition. There was a statistically nonsignificant trend toward increased 28-day mortality in patients with GNB acquisition compared to those without (38.2% vs. 27.8%, P = 0.105). Cerebrovascular disease and acquired GNB resulting in infection were associated with 28-day mortality in patients who acquired GNB.

CONCLUSIONS

Elizabethkingia species, Acinetobacter species, and B. cenocepacia were the major GNB acquired during CZA treatment. A trend toward increased mortality was observed in patients with GNB acquisition during CZA treatment. Further studies on optimal treatments for these patients were warranted.

Cefiderocol treatment for patients infected by Stenotrophomonas maltophilia, Burkholderia cepacia complex and Achromobacter spp.: subgroup analysis from the PERSEUS study

PURPOSE

This subgroup analysis of the PERSEUS study aimed to describe the effectiveness of cefiderocol treatment in the early access programme in Spain in patients infected by Stenotrophomonas maltophilia, Burkholderia cepacia complex (Bcc) or Achromobacter species.

METHODS

In the retrospective, observational, multicentre PERSEUS study in Spain, the effectiveness and safety of cefiderocol treatment administered for at least 72 h up to 28 days in patients infected by Gram-negative bacteria, except Acinetobacter spp., in the early access programme was investigated. Patient demographics and baseline clinical characteristics, cefiderocol use, clinical cure at end of treatment, all-cause mortality at Day 28 were the main outcomes.

RESULTS

A total of 20 patients had S. maltophilia infections, and 14 patients had other rare glucose non-fermenters (Bcc 8, Achromobacter spp. 5, Ralstonia mannitolilytica 1). The median (interquartile range [IQR]) age was 60.5 (48.0-65.5) years and 49.5 (33.0-59.0) years for patients with S. maltophilia and other rare non-fermenters, respectively. The majority of patients had respiratory tract infections (S. maltophilia 55%; other rare non-fermenters 71.4%), and median (IQR) duration of cefiderocol treatment was 10.0 (6.5-13.5) days and 8.0 (6-14) days, respectively. Clinical cure rates were 70%, 62.5% and 80.0% for patients with S. maltophilia, Bcc and Achromobacter spp., respectively. Corresponding 28-day all-cause mortality rates were 30.0%, 37.5% and 40.0%, respectively. One patient with R. mannitolilytica had clinical cure and survived to Day 28.

CONCLUSIONS

Cefiderocol is an important addition to the limited treatment options for patients infected by these rare glucose non-fermenting Gram-negative bacteria.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT05789199 (Registration date: 16 February 2023).

Clinical and microbiological features of positive blood culture episodes caused by non-fermenting gram-negative bacilli other than Pseudomonas and Acinetobacter species (2020-2023)

INTRODUCTION

Non-fermenting Gram-negative bacilli (NFGNB) other than Pseudomonas aeruginosa and Acinetobacter baumannii complex are pathogens of interest due to their ability to cause health-care associated infections and display complex drug resistance phenotypes. However, their clinical and microbiological landscape is still poorly characterized.

METHODS

Observational retrospective study including all hospitalized patients presenting with a positive positive blood culture (BC) episode caused by less common NFGNB over a four-year period (January 2020-December 2023). Clinical-microbiological features and factors associated with mortality were investigated.

RESULTS

Sixty-six less common NFGNB isolates other than Pseudomonas and Acinetobacter species causing 63 positive BC episodes were recovered from 60 patients. Positive BC episodes were predominantly sustained by Stenotrophomonas maltophilia (49.2%) followed by Achromobacter species (15.9%) that exhibited the most complex resistance phenotype. Positive BC episodes had bloodstream infection criteria in 95.2% of cases (60 out 63), being intravascular device (30.2%) and respiratory tract (19.1%) the main sources of infection. Fourteen-day, 30-day, and in-hospital mortality rates were 6.4%, 9.5%, and 15.9%, respectively. The longer time from admission to the positive BC episode, older age, diabetes, admission due to sepsis, and higher Charlson Comorbidity Index were identified as the main predictors of in-hospital mortality.

CONCLUSIONS

Positive BC episodes sustained by NFGNB other than Pseudomonas and Acinetobacter species were predominantly sustained by Stenotrophomonas maltophilia and Achromobacter species, having bloodstream infection criteria in the vast majority of cases. Factors that have emerged to be associated with mortality highlighted how these species may have more room in prolonged hospitalisation and at the end of life for patients with chronic organ diseases.

Novel Antibiotics for Gram-Negative Nosocomial Pneumonia

Nosocomial pneumonia, including hospital-acquired pneumonia and ventilator-associated pneumonia, is the leading cause of death related to hospital-acquired infections among critically ill patients. A growing proportion of these cases are attributed to multi-drug-resistant (MDR-) Gram-negative bacteria (GNB). MDR-GNB pneumonia often leads to delayed appropriate treatment, prolonged hospital stays, and increased morbidity and mortality. This issue is compounded by the increased toxicity profiles of the conventional antibiotics required to treat MDR-GNB infections. In recent years, several novel antibiotics have been licensed for the treatment of GNB nosocomial pneumonia. These novel antibiotics are promising therapeutic options for treatment of nosocomial pneumonia by MDR pathogens with certain mechanisms of resistance. Still, antibiotic resistance remains an evolving global crisis, and resistance to novel antibiotics has started emerging, making their judicious use crucial to prolong their shelf-life. This article presents an up-to-date review of these novel antibiotics and their current role in the antimicrobial armamentarium. We critically present data for the pharmacokinetics/pharmacodynamics, the in vitro spectrum of antimicrobial activity and resistance, and in vivo data for their clinical and microbiological efficacy in trials. Where possible, available data are summarized specifically in patients with nosocomial pneumonia, as this cohort may exhibit 'critical illness' physiology that affects drug efficacy.

Stenotrophomonas maltophilia: The Landscape in Critically Ill Patients and Optimising Management Approaches

The aim of this review is to synthesise the key aspects of the epidemiology, current microbiological diagnostic challenges, antibiotic resistance rates, optimal antimicrobial management, and most effective prevention strategies for Stenotrophomonas maltophilia (SM) in the intensive care unit (ICU) population. In recent years, resistance surveillance data indicate that SM accounts for less than 3% of all healthcare-associated infection strains, a percentage that doubles in the case of ventilator-associated pneumonia (VAP). Interestingly, SM ranks as the third most isolated non-glucose fermenter Gram-negative bacilli (NFGNB). Although this NFGNB genus has usually been considered a bystander and colonising strain, recently published data warn about its potential role as a causative pathogen of severe infections, particularly pneumonia and bloodstream infections (BSI), not only for the classical immunocompromised susceptible host patients but also for critically ill ones even without overt immunosuppression. Indeed, it has been associated with crude 28-day mortality as high as 54.8%, despite initial response following targeted therapy. Additionally, alongside its intrinsic resistance to a wide range of common antimicrobials, various worldwide and local surveillance studies raise concerns about an increase in ICU settings regarding resistance to first-line drugs such as cotrimoxazole or tigecycline. This scenario alerts ICU physicians to the need to reconsider the best stewardship approach when SM is isolated in obtained samples from critically ill patients. Despite the coverage of this multidrug-resistant bacterium (MDRB) provided by some traditional and a non-negligible number of current pipeline antimicrobials, an ecological and cost-effective strategy is needed in the present era.

Co-Administration of High-Dose Nebulized Colistin for Acinetobacter baumannii Bacteremic Ventilator-Associated Pneumonia: Impact on Outcomes

Acinetobacter baumannii (A. baumannii) is a difficult-to-treat (DTR) pathogen that causes ventilator-associated pneumonia (VAP) associated with high mortality. To improve the outcome of DTR A. Baumannii VAP, nebulized colistin (NC) was introduced with promising but conflicting results on mortality in earlier studies. Currently, NC is used at a much higher daily dose compared to the past. Nevertheless, there is little evidence on the effect of high-dose NC on the outcomes of A. baumannii VAPs, especially in the current era where the percentage of colistin-resistant A. baumannii strains is rising. We conducted a retrospective study comparing bacteremic A. baumannii VAP patients who were treated with and without NC co-administration and were admitted in the Intensive Care Unit of University Hospital of Ioannina from March 2020 to August 2023. Overall, 59 patients (21 and 38 with and without NC coadministration, respectively) were included. Both 28-day and 7-day mortalities were significantly lower in the patient group treated with NC (52.4% vs. 78.9%, p 0.034 and 9.5% vs. 47.4%, p 0.003, respectively). Patients treated with NC had a higher percentage of sepsis resolution by day 7 (38.1% vs. 13.5%, p 0.023) and were more likely to be off vasopressors by day 7 (28.6% vs. 8.1%, p 0.039). The addition of NC in the treatment regime of A. baumannii VAP decreased mortality.