Molecular Surveillance of Acinetobacter baumannii : Clonal Analysis and Substitution Dynamics in Hospital Setting
Antimicrobial Resistance
Genomics
Molecular Surveillance
Acinetobacter baumannii represents one of the most epidemiologically important pathogens in hospital environments, classified as a priority pathogen by the World Health Organization. This genomic and epidemiological analysis examines in detail the circulation of this pathogen in a specific hospital setting, revealing patterns of clonal substitution, resistance mechanisms, and dynamics that challenge both infection control protocols and available therapeutic strategies.
Epidemiological and Resistance Profile
Acinetobacter baumannii is a gram-negative non-fermenting bacillus that has emerged as a nosocomial pathogen of critical importance. Its increasing prevalence is directly associated with its ability to acquire multiple resistance mechanisms, often encoded on mobile genetic elements that facilitate its spread among different strains and clones.
Epidemiological Impact
With a reported mortality rate of 56% in patients with multiresistant strain infections, A. baumannii represents a significant burden of hospital morbidity and mortality.
Temporal Distribution of Isolates
Temporal analysis of A. baumannii isolates reveals circulation patterns suggestive of multiple introduction events followed by nosocomial transmission.
Genetic Arsenal: Resistance Mechanisms
Genomic analysis reveals multiple resistance genes distributed across the chromosome and plasmids. The simultaneous presence of multiple mechanisms explains the multiresistant phenotype observed in clinical isolates.
Classification of Resistance Mechanisms
Intrinsic Resistance
Inherent to the species, including reduced permeability and chromosomal efflux pumps (Ade ABC).
Acquired Resistance
Genes located on plasmids or integrons, such as
bla
OXA-23
and
bla
NDM-1
.
Clonal Dynamics: Substitution and Transmission
Molecular typing analysis identifies the initial predominance of clone A (72% of isolates), followed by gradual substitution by clone B following infection control intervention, demonstrating the efficacy of implemented measures.
Substitution Analysis
Case Studies: Transmission Dynamics
Case 1: Intra-Hospital Transmission (Clone A)
The 18 Clone A isolates, recovered between September and October 2024, originated from different departments (ICU, general medicine, surgery). Next-generation sequencing (NGS) analysis suggests a common ancestor with only 2-5 single nucleotide polymorphism (SNP) differences, indicating recent dissemination from a common introduction event.
Implication: Failure of isolation measures or infection control between departments.
Case 2: Post-Intervention Substitution (Clone B)
Following implementation of intensified infection control protocols (contact isolation, improved hand hygiene, daily environmental cleaning), Clone A gradually disappeared and was replaced by Clone B between November 2024 and January 2025.
Clone B maintains a similar resistance phenotype (OXA-23+, NDM-1-) but with significant genomic differences (>500 SNP, suggestive of a divergent lineage or new introduction).
Implication: Partial success of control measures, but resurgence of another clone with similar resistance characteristics.
Conclusions and Recommendations
This molecular surveillance analysis of A. baumannii in a hospital setting demonstrates the need for an integrated approach combining genomic sequencing, epidemiological surveillance, and infection control measures. Although interventions succeeded in reducing the prevalence of the initial dominant clone, the resurgence of alternative strains with similar resistance profiles underscores the importance of:
- Sustained implementation of infection control measures
- Continuous genomic surveillance to detect epidemiological changes
- Regular evaluation of intervention efficacy
- Multidisciplinary communication between infectious diseases, microbiology, and infection control
- Development of alternative therapeutic strategies for non-susceptible cases