A newly isolated Pseudomonas otitidis phage, vB_PotS-PotUPM1 from tilapia in Malaysia

A new Pseudomonas species, Pseudomonas otitidis was first known as an otic infectious agent in human. The presence of an inherent metallo-beta-lactamase gene and its recent emergence in aquaculture underscore its potential zoonotic pathogenicity. The present study is aimed to characterize P. otitidis NK1 and its bacteriophage vB_PotS-PotUPM1 (PotUPM1), which were isolated from an infected tilapia fish farm in Malaysia. P. otitidis NK1 showed beta-hemolysis on blood agar and is resistant to several antibiotics. Its genome size was 6067,534 bp, with an average nucleotide identity of less than 99 % to all P. otitidis genome assemblies in GenBank, making it a novel strain of P. otitidis. The phage PotUPM1 has a latent period of 45 min and a burst size of 405 phage particles per bacterium. It effectively inhibited the growth of P. otitidis NK1 even at a low multiplicity of infection of 0.001 up to 9-hour post-inoculation. Transmission electron microscopy showed that it has a prolate head and a long, non-contractile tail, resembling those in the Siphoviridae family. Based on bioinformatic analysis, PotUPM1 has no resistance or virulence genes and is a lysogenic phage based on the presence of an integrase gene in the phage genome. Similarity analysis showed that PotUPM1 may represent a novel viral species with less than 95 % nucleotide sequence similarity to other characterized phages. The findings of this study could provide an insight on the occurrence of P. otitidis in the aquaculture industry and lay a basis for the application of phage or phagederived proteins against pathogenic P. otitidis to alleviate antimicrobial resistance.