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Unusual deprivation of compatible solutes in Acinetobacter baumannii
Sabine Zeidler1, Volker Müller1
1Department of Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University, Frankfurt am Main, Germany.
Abstract:
The opportunistic human pathogen Acinetobacter baumannii is one of the leading causes of nosocomial infections. The high prevalence of multidrug-resistant strains, a high adaptability to changing environments and an overall pronounced stress resistance contribute to persistence and spread of the bacteria in hospitals and thereby promote repeated outbreaks. Altogether, the success of A. baumannii is mainly built on adaptation and stress resistance mechanisms, rather than relying on 'true' virulence factors. One of the stress factors that pathogens must cope with is osmolarity, which can differ between the external environment and different body parts of the human host. A. baumannii ATCC 19606T accumulates the compatible solutes glutamate, mannitol and trehalose in response to high salinities. In this work, it was found that most of the solutes vanish immediately after reaching stationary phase, a very unusual phenomenon. While glutamate can be metabolized, mannitol produced by MtlD is excreted to the medium in high amounts. First results indicate that A. baumannii ATCC 19606T undergoes a rapid switch to a dormant state (viable but non-culturable) after disappearance of the compatible solutes. Resuscitation from this state could easily be achieved in PBS or fresh medium.
Insights
Acinetobacter baumannii rapidly loses compatible solutes upon reaching stationary phase, entering a dormant state. This unusual adaptation allows for easy resuscitation, impacting hospital-acquired infection dynamics.
Area of Science:
- Microbiology
- Pathogen Biology
- Bacterial Physiology
Background:
- Acinetobacter baumannii is a major cause of hospital-acquired infections, known for multidrug resistance and adaptability.
- Bacterial success is attributed to stress resistance and adaptation rather than overt virulence factors.
- Osmotic stress is a significant challenge for pathogens adapting to diverse host environments.
Purpose of the Study:
- To investigate the osmotic adaptation mechanisms of Acinetobacter baumannii ATCC 19606T.
- To characterize the dynamics of compatible solute accumulation and disappearance.
- To understand the physiological state following solute depletion.
Main Methods:
- Culturing of Acinetobacter baumannii ATCC 19606T under varying salinity conditions.
- Analysis of compatible solute accumulation (glutamate, mannitol, trehalose) using biochemical assays.
- Monitoring bacterial cell viability and culturability post-stationary phase.
Main Results:
- A. baumannii accumulates glutamate, mannitol, and trehalose in response to high salinity.
- Compatible solutes rapidly vanish upon reaching the stationary phase, an atypical observation.
- Mannitol is excreted into the medium, and glutamate is metabolized.
- Bacteria transition to a viable but non-culturable (dormant) state after solute disappearance.
Conclusions:
- A. baumannii exhibits a unique, rapid switch to a dormant state linked to compatible solute dynamics.
- Excretion of mannitol and metabolism of glutamate are key processes.
- The dormant state is easily reversible, suggesting implications for persistence and treatment strategies.
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