Multidrug resistant Acinetobacter isolates release resistance determinants through contact-dependent killing and bacteriophage lysis

Authors: CRIPPEN, CLAY - University Of Georgia; PALTRY, ROBERT - University Of Georgia; Rothrock, Michael; SANCHEZ, SUSAN - University Of Georgia; SZYMANSKI, CHRISTINE - University Of Georgia

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2020
Publication Date: 8/14/2020
Citation: Crippen, C., Paltry, R.T., Rothrock Jr, M.J., Sanchez, S., Szymanski, C.M. 2020. Multidrug resistant Acinetobacter isolates release resistance determinants through contact-dependent killing and bacteriophage lysis. Frontiers in Microbiology. 11:1918.

Interpretive Summary: Antibiotic resistance is an ancient bacterial defense mechanism that is rapidly spreading due to the frequent use of antibiotics by healthcare providers for disease treatment and by farmers for livestock growth promotion. We are becoming increasingly aware that bacteria such as Acinetobacter baumannii are rapidly 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. A. radioresistens, A. lwoffii and A. johnsonii were isolated from hens, turkeys and ducks and were resistant to 14 clinically relevant antibiotics, including several on the World Health Organization’s list of essential medicines. Co-culturing any of the three Acinetobacter species with A. baumannii resulted in contact-dependent release of both plasmid and genomic DNA, presumably through type VI secretion system (T6SS) mediated cell killing. We also isolated several lytic bacteriophages and selected two of these phages to be included in this study, based on plaquing characteristics, nucleic acid content and viral morphology. Both phages released host DNA, including antibiotic resistance genes during cell lysis. Our study demonstrates that contact-dependent warfare between bacterial species can readily contribute to the release of DNA into the environment, including antibiotic resistance determinants. We also emphasize 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.

Technical Abstract: Antibiotic resistance is an ancient bacterial defense mechanism that is rapidly spreading due to the frequent use of antibiotics by healthcare providers for disease treatment and by farmers for livestock growth promotion. We are becoming increasingly aware that bacteria such as Acinetobacter baumannii are rapidly 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. A. radioresistens, A. lwoffii and A. johnsonii were isolated from hens, turkeys and ducks and were resistant to 14 clinically relevant antibiotics, including several on the World Health Organization’s list of essential medicines. Co-culturing any of the three Acinetobacter species with A. baumannii resulted in contact-dependent release of both plasmid and genomic DNA, presumably through type VI secretion system (T6SS) mediated cell killing. We also isolated several lytic bacteriophages and selected two of these phages to be included in this study, based on plaquing characteristics, nucleic acid content and viral morphology. Both phages released host DNA, including antibiotic resistance genes during cell lysis. Our study demonstrates that contact-dependent warfare between bacterial species can readily contribute to the release of DNA into the environment, including antibiotic resistance determinants. We also emphasize 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.