New and rare pathogens: identification of a Pseudoxanthomonas kaohsiungensis

Background. Although previously isolated from contaminated soils, new opportunistic human pathogens belonging to the genus Pseudoxanthomonas have been described. Analysis of the biological properties of a P. kaohsiungensis strain isolated from the blood indicated that it is a potential human pathogen in immunocompromised patients and not merely a bacterium that produces biosurfactants in the environment.

The aim. To conduct biological characterization, phylogenetic analysis, and protein spectroscopy to identify the P. kaohsiungensis strain, a potential new and rare human pathogen.

Materials and Methods. The P. kaohsiungensis strain IMB-1 was isolated from a child undergoing treatment in a city hospital. The strain was isolated and cultured on blood agar. Morphological and biochemical properties were studied. Ribosomal phylogeny was used for identification; additionally, protein spectra were obtained using MALDI-TOF mass spectrometry.

Results. Small gray colonies were isolated from an enrichment medium from cerebrospinal fluid sample. The cell morphology was Gram-negative rods, oxidase- and catalase-positive. Identification using the NEFERMtest system was inconclusive. The strain was susceptible to increased doses of trimethoprim-sulfamethoxazole. Protein spectrum with a low score and convergence indicated a primary identification as Stenotrophomonas maltophilia. A 1470-bp 16S rRNA gene sequence was assembled using Sanger sequencing. Primary identification using the NCBI database revealed 99.8 % homology to the type strain of the species P. kaohsiungensis. Protein spectra obtained using MALDI-TOF mass spectrometry were processed, and a reference protein profile was generated for identifying P. kaohsiungensis strains.

Conclusion. Difficulties in bacteriological identification of clinically significant new bacterial strains and the lack of reference protein spectra in databases highlight the importance of genomic tools for accurate pathogen identification and characterization and confirm the gold standard of molecular sequencing and ribosomal phylogeny. The obtained results highlight the urgent need to strengthen genomic monitoring and update databases for the rapid identification of opportunistic pathogens.

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