Isolation and characterization of novel plasmid-dependent phages infecting bacteria carrying diverse conjugative plasmids

Plasmid-dependent phages infect bacteria carrying conjugative plasmids by recognizing the plasmid-encoded pilus. Despite the high abundance of conjugative plasmids in diverse environments, plasmid-dependent phages have not been widely studied. Since conjugative plasmids often carry antimicrobial resistance genes (ARGs), interfering with conjugation could reduce the spread of ARGs and avoid the appearance of multiresistant superbugs. Our aim was to isolate and characterize plasmid-dependent phages able to infect bacteria carrying diverse conjugative plasmids belonging to the most common plasmid families among Gram-negative pathogens. We isolated two lytic phages from wastewater using an avirulent strain of Salmonella enterica carrying the conjugative IncN plasmid pKM101. Both phages, named Lu221 and Hi226, are novel dsDNA viruses within the class Caudoviricetes with genomes of approximately 76 kb. They showed broad host range infecting Escherichia coli, S. enterica, Kluyvera sp., and Enterobacter sp. carrying conjugative plasmids. They recognize plasmid-encoded receptors from 12 out of 15 tested plasmids, all of them carrying resistance determinants. Phages Lu221 and Hi226 could have the potential to help combat the antimicrobial resistance crisis by reducing ARGs present in conjugative plasmids.