Genetic landscape and evolution of Acinetobacter pittii, an underestimated emerging nosocomial pathogen

Area of Science:

• Microbiology
• Genomics
• Epidemiology

Background:

• Acinetobacter pittii is an emerging pathogen in healthcare settings, known for its increasing prevalence and multidrug resistance (MDR).
• Understanding the population structure of A. pittii is crucial for effective transmission tracing and evolutionary studies.
• Current knowledge of A. pittii's population genetics is limited, hindering control efforts.

Purpose of the Study:

• To develop and apply a novel genotyping method, distributed core genome multilocus sequence typing (dcgMLST), for A. pittii.
• To elucidate the genetic diversity, population structure, and evolutionary dynamics of A. pittii.
• To identify key genetic elements, such as plasmids, associated with multidrug resistance in A. pittii.

Main Methods:

• Development of a distributed core genome multilocus sequence typing (dcgMLST) scheme for A. pittii.
• Analysis of 750 A. pittii whole-genome sequences.
• Application of hierarchical clustering (HC) to define population structure at different genetic diversity levels (HC1100 and HC450).
• Investigation of gene gain and loss events within identified lineages.
• Identification and characterization of multidrug-resistant plasmids.

Main Results:

• The dcgMLST scheme effectively resolved A. pittii into distinct hierarchical clusters, corresponding to species-level (HC1100) and natural population-level (HC450) diversity.
• A predominant lineage, HC1100_4, was identified, comprising 33.9% of the analyzed A. pittii strains.
• Specific gene gain and loss events were associated with environmental stress adaptation in the HC1100_4 lineage.
• A cluster of multidrug-resistant plasmids, designated PT_712, was found to be responsible for the dissemination of blaNDM-1 genes within the Acinetobacter genus.

Conclusions:

• The developed dcgMLST provides a robust framework for characterizing A. pittii's genetic diversity and evolutionary trajectory.
• The identified predominant lineage and associated adaptive mechanisms offer insights into A. pittii's success in nosocomial environments.
• The discovery of specific MDR plasmids highlights critical targets for infection control interventions.
• This study lays the groundwork for improved molecular epidemiology, infection control strategies, and public health policies related to A. pittii.