When MALDI-TOF MS and 16S rRNA gene sequencing are not enough: identification of Gordonia hongkongensis causing bloodstream infection.

Abstract

Background: Gordonia spp. are gram-positive aerobic bacilli whose infections in humans are rare and typically affect immunocompromised hosts and those with indwelling medical devices. Conventional identification systems frequently misidentify Gordonia species. Here, we present a bloodstream infection caused by Gordonia hongkongensis.

Case summary: A 76-year-old man with metastatic colorectal adenocarcinoma receiving oral chemotherapy presented with febrile syndrome and acute diarrhea, unresponsive to prior antimicrobial therapy. Blood cultures were positive for gram-positive rods, which grew producing pink-to-orange pigmented colonies. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and 16S rRNA gene sequencing could not distinguish the isolate at the species level, identifying it as belonging to the genus Gordonia. Owing to the limitations of these methods, whole-genome sequencing (WGS) was performed, which revealed G. hongkongensis as the causative pathogen. Updating the MALDI-TOF MS database with the main spectral profiles enabled the correct identification of the isolate upon reanalysis. Empirical antimicrobial therapy with piperacillin-tazobactam was initiated before organism identification and susceptibility testing. After a 7-day course of treatment, the patient showed clinical improvement and resolution of fever.

Conclusion: Human infections with G. hongkongensis are rare. This case underscores the diagnostic challenges associated with Gordonia species and emphasizes the role of WGS in accurately identifying emerging pathogens. Increased awareness and improved diagnostic tools are essential for a better understanding and management of Gordonia infections.