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Fatal outbreak of an emerging clone of extensively drug-resistant Acinetobacter baumannii with enhanced virulence
Crystal L Jones1, Megan Clancy2, Cary Honnold3
1Department of Wound Infections, Walter Reed Army Institute of Research, Silver Spring, Maryland.
Background:
Severe Acinetobacter baumannii infections in immunocompetent patients are uncommon, and the virulence mechanisms of this organism are not fully understood.
Methods:
Following an outbreak of fatal A. baumannii infections in a cohort of relatively immunocompetent patients (low comorbidity and illness severity scores), isolates were investigated with comparative genomics and in animal models.
Results:
Two unrelated A. baumannii clades were associated with the outbreak. The clone associated with the majority of patient deaths, clade B, is evolutionarily distinct from the 3 international clonal complexes, belongs to multilocus sequence type (MLST) 10, and is most closely related to strains isolated from the Czech Republic, California, and Germany in 1994, 1997, and 2003, respectively. In 2 different murine models, clade B isolates were more virulent than comparator strains, including the highly virulent reference strain AB5075. The most virulent clade B derivative, MRSN 16897, was isolated from the patient with the lowest combined comorbidity/illness severity score. Clade B isolates possess a unique combination of putative virulence genes involved in iron metabolism, protein secretion, and glycosylation, which was leveraged to develop a rapid and specific clinical assay to detect this clade that cannot be distinguished by MLST.
Conclusions:
Clade B warrants continued surveillance and investigation.
Insights
A novel Acinetobacter baumannii clade B caused severe infections in immunocompetent patients. This highly virulent strain possesses unique genes and requires continued surveillance.
Area of Science:
- Microbiology
- Infectious Diseases
- Genomics
Background:
- Severe Acinetobacter baumannii infections in immunocompetent individuals are rare.
- The virulence mechanisms of Acinetobacter baumannii are not fully understood.
Purpose of the Study:
- Investigate the virulence mechanisms of Acinetobacter baumannii during an outbreak in immunocompetent patients.
- Identify distinct genetic clades associated with severe infections.
Main Methods:
- Comparative genomics of Acinetobacter baumannii isolates from a fatal infection outbreak.
- Virulence assessment in murine models.
- Development of a clade-specific diagnostic assay.
Main Results:
- Two distinct Acinetobacter baumannii clades were identified; clade B was associated with most fatalities.
- Clade B exhibited enhanced virulence in murine models compared to reference strains.
- Clade B possesses unique genes for iron metabolism, protein secretion, and glycosylation, enabling specific assay development.
Conclusions:
- Clade B represents a significant Acinetobacter baumannii threat requiring ongoing surveillance.
- Further research into clade B virulence factors is warranted.
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