Is it a potential pneumonia pathogen in Pseudomonas putida group? First isolation and identification of Pseudomonas plecoglossicida in clinic and a comparison of pathogenicity with Pseudomonas putida

Purpose: Pseudomonas plecoglossicida belongs to the Pseudomonas putida group and is a common aquatic pathogen that induces visceral lesions in fish. However, it has never been previously isolated from human specimen and associated with human infections. In the study, we first investigated the pathogenicity of Pseudomonas plecoglossicida strain "SXY" isolated from a child with infectious pneumonia. Methods: Using 16S rRNA sequencing, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, and unique biochemical phenotypes, we isolated and identified Pseudomonas plecoglossicida in clinical practice, a highly suspicious pneumonia-related pathogen based on bacteriological examinations and clinical manifestations. Its pathogenicity was assessed and compared with that of Pseudomonas putida clinical strain "ECL" (a recognized pathogen in the Pseudomonas putida group) by a series of in vitro pathogenicity tests (including the growth capacity assay at 37 degree celsius, the lung leukocyte-killing and inflammatory factor release assay, and the whole blood-killing, serum-killing and complement sensitivity assay). Results: All tests demonstrated its ability to cause colonization, infection, and inflammation in the lungs. However, the pathogenicity and risk of bloodstream infection of Pseudomonas plecoglossicida strain "SXY" were limited and weaker than those of Pseudomonas putida strain "ECL". Notably, Pseudomonas plecoglossicida could be incorrectly identified as Pseudomonas putida, based on the biochemical identification of VITEK-2, potentially leading to a high rate of missing infections. Conclusions: Pseudomonas plecoglossicida is a potential and neglected pneumonia pathogen.