Comparative analysis and distribution of pP9014, a novel drug resistance IncP-1 plasmid from Photobacterium damselae subsp. piscicida

Photobacterium damselae subsp. piscicida, a causative agent of pseudotuberculosis, often harbours resistance plasmids (R plasmids) that facilitate horizontal gene transfer of drug resistance genes. R plasmid pP9014 was isolated from P. damselae subsp. piscicida and its complete nucleotide sequence was determined using Next Generation Sequencing technology. A protein network analysis was conducted to determine the relatedness of protein coding sequences, and ClustalW was used for the full nucleotide sequences. The occurrence of pP9014-like plasmids compared with pP99-018-like plasmids in a specific region was determined using probes for their transfer regions. pP9014 is 55 851 bp long with an overall GC content of 44.4% encoding 61 open reading frames (ORFs) including antimicrobial resistance genes and two conjugative transfer regions (Tra and Trb). The backbone showed highest similarity to Marinobacter adhaerens pHP-42 and Methylophaga sp. JAM7. pP9014 is similar to several IncP plasmids but forms a different subgroup. pP9014 is a unique plasmid in P. damselae subsp. piscicida and was not commonly found in drug-resistant P. damselae subsp. piscicida isolated from different areas and years in Japan. Plasmids similar to the previously reported pP99-018 are more widely distributed. This rarity suggests that plasmids similar to pP99-018 are more compatible with γ-proteobacteria. pP9014 is the first reported IncP-1 plasmid from fish pathogens. Its similarity to other IncP plasmids isolated from soil and human pathogens suggests that plasmids of the IncP-1 incompatibility group are vectors for the transfer of drug resistance genes among diverse environments.