Clinical Effectiveness of Tetracycline-Class Agents Based Regimens in Patients With Carbapenem-Resistant Acinetobacter baumannii Bacteremia: A Single-Center Retrospective Cohort Study

Comparison of Hypervirulent and Non-Hypervirulent Carbapenem-Resistant Acinetobacter baumannii Isolated from Bloodstream Infections: Mortality, Potential Virulence Factors, and Combination Therapy In Vitro

Hypervirulent carbapenem-resistant Acinetobacter baumannii (hv-CRAB) has emerged in bloodstream infections (BSI). Cases of BSI caused by hv-CRAB (hv-CRAB-BSI) had posed a significant threat to hospitalized patients. In this study, 31 CRAB strains isolated from Chinese BSI patients were analyzed, of which 24 were identified as hv-CRAB-BSI and 7 as non-hv-CRAB-BSI, using the Galleria mellonella infection model. Patients with hv-CRAB-BSI had higher rates of septic shock (79.2% vs. 14.3%, p = 0.004) and mortality (66.7% vs. 14.3%, p = 0.028). All strains were resistant to most antibiotics but sensitive to colistin. Hv-CRAB-BSI showed lower resistance to minocycline than non-hv-CRAB-BSI (54.2% vs. 100%, p = 0.03). Whole-genome sequencing revealed that the detection rates of immune modulation genes ptk and epsA in hv-CRAB-BSI were significantly higher than in non-hv-CRAB-BSI (91.7% vs. 28.6%, p = 0.002). Additionally, all ST457 hv-CRAB-BSI lacked abaR, and all ST1486 non-hv-CRAB-BSI lacked adeG. The checkerboard dilution method assessed the efficacies of various antibiotic combinations, revealing that although synergism was rarely observed, the combination of colistin and minocycline showed the best efficacy for treating CRAB-BSI, regardless of whether the infections were hv-CRAB-BSI or non-hv-CRAB-BSI. These findings highlight the importance of analyzing molecular characteristics and exploring effective treatment strategies for hv-CRAB-BSI.

Ineffectiveness of colistin monotherapy in treating carbapenem-resistant Acinetobacter baumannii Pneumonia: A retrospective single-center cohort study

BACKGROUND

Acinetobacter baumannii, a common carbapenem-resistant gram-negative bacillus, usually causes nosocomial infections. Colistin has been used for carbapenem-resistant A. baumannii (CRAB) infections; however, only a few studies have evaluated colistin as a treatment option compared to appropriate controls. We investigated the effectiveness of colistin monotherapy in treating CRAB pneumonia compared to those treated without an active drug.

METHODS

Adult patients (≥ 18 years) with CRAB isolated from respiratory specimens were screened from September 2017 to August 2022. Only patients with pneumonia treated with colistin monotherapy (colistin group) were included and compared to those without any active antibiotics (no active antibiotics [NAA] group). The primary and secondary outcomes were 30-day all-cause mortality and acute kidney injury within 30 days. The inverse probability of the treatment-weighted Cox proportional hazard model was used to compare mortality between groups.

RESULTS

Among the 826 adult patients with CRAB in their respiratory specimens, 45 and 123 patients were included in the colistin and NAA groups, respectively. Most of the CRAB pneumonia (91.1%) cases were hospital-acquired pneumonia. The 30-day all-cause mortality rates in the colistin and NAA groups were 58.3% and 56.1%, respectively, and no difference was observed after adjustments (adjusted hazard ratio, 0.74; 95% CI, 0.47-1.17). The incidence of acute kidney injury was higher in the colistin group (65.3%) compared to the NAA group (39.0%) (P = 0.143).

CONCLUSIONS

Colistin monotherapy did not significantly improve treatment outcomes for CRAB pneumonia. The development and evaluation of new antimicrobials for CRAB pneumonia should be advocated in clinical practice.