Phage-plasmids produce antibiotic resistant lysogens

Phage-plasmids infect bacterial cell as phages and are maintained in host cells as plasmids. In our study, we used an established workflow to find phage-plasmids in bacterial genomes and found them to be numerous and widespread. Some encode interesting traits such as antibiotic resistance genes (ARGs). ARGs are often found in plasmids, but are very rare in phages. Since phage-plasmids are phages as well, we thus wondered if phage-plasmids can spread ARGs as phages. We conducted experiments on phage-plasmids which we isolated from resistant strains retrieved from the hospital, and confirmed by sequencing that bacteria can become resistant lysogens by acquiring ARG-encoding phage-plasmids. Overall these results show that phage-plasmids are abundant and are capable to transfer accessory genes typical of phages and of plasmids.