Multidrug Resistant Acinetobacter Isolates Release Resistance Determinants Through Contact-Dependent Killing and
Clay S Crippen1, Michael J Rothrock Jr2, Susan Sanchez3
1Department of Microbiology and Complex Carbohydrate Research Center, University of Georgia, Athens, GA, United States.
Abstract:
Antimicrobial resistance is an ancient bacterial defense mechanism that has rapidly spread due to the frequent use of antibiotics for disease treatment and livestock growth promotion. We are becoming increasingly aware that pathogens, such as members of the genus Acinetobacter, are precipitously evolving drug resistances through multiple mechanisms, including the acquisition of antibiotic resistance genes. In this study, we isolated three multidrug resistant Acinetobacter species from birds on a free-range farm. Acinetobacter radioresistens, Acinetobacter lwoffii, and Acinetobacter johnsonii were isolated from hens, turkeys and ducks and were resistant to 14 clinically relevant antibiotics, including several listed by the World Health Organization as essential medicines. Co-culturing any of the three Acinetobacter species with Acinetobacter baumannii resulted in contact-dependent release of intact resistance determinants. We also isolated several lytic bacteriophages and selected two of these phages to be included in this study based on differences in plaquing characteristics, nucleic acid content and viral morphology. Both phages released host DNA, including antibiotic resistance genes during cell lysis and we demonstrated that these resistance determinants were transferable to a naïve strain of Escherichia coli. This study demonstrates that contact-dependent competition between bacterial species can readily contribute to DNA release into the environment, including antibiotic resistance determinants. We also highlight that the constant lysis and turnover of bacterial populations during the natural lifecycle of a lytic bacteriophage is an underappreciated mechanism for the liberation of DNA and subsequent genetic exchange.
Insights
Antimicrobial resistance spreads rapidly. This study shows bacterial competition and bacteriophages release antibiotic resistance genes, facilitating their transfer to other bacteria.
Area of Science:
- Microbiology
- Genetics
- Environmental Science
Background:
- Antimicrobial resistance (AMR) is a growing global health threat, driven by antibiotic use in medicine and agriculture.
- Pathogenic bacteria like *Acinetobacter* species rapidly evolve resistance through gene acquisition.
- Free-range farming environments can harbor multidrug-resistant bacteria.
Purpose of the Study:
- To investigate mechanisms of antibiotic resistance gene dissemination in *Acinetobacter* species.
- To explore the role of bacterial interactions and bacteriophages in releasing resistance determinants.
- To assess the transferability of these determinants to other bacterial species.
Main Methods:
- Isolation and identification of multidrug-resistant *Acinetobacter* species from poultry.
- Antibiotic susceptibility testing against 14 clinically relevant antibiotics.
- Co-culturing experiments to observe contact-dependent DNA release.
- Isolation and characterization of lytic bacteriophages.
- Demonstration of antibiotic resistance gene transfer to *Escherichia coli*.
Main Results:
- Three multidrug-resistant *Acinetobacter* species (*A. radioresistens*, *A. lwoffii*, *A. johnsonii*) were isolated from poultry.
- These isolates exhibited resistance to numerous essential antibiotics.
- Contact-dependent competition and bacteriophage-mediated lysis released bacterial DNA, including antibiotic resistance genes.
- These genes were successfully transferred to a recipient *E. coli* strain.
Conclusions:
- Bacterial interactions and bacteriophage activity are significant, yet underappreciated, mechanisms for releasing antibiotic resistance genes into the environment.
- These processes contribute to the spread of antimicrobial resistance through horizontal gene transfer.
- Understanding these mechanisms is crucial for developing strategies to combat AMR.
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