Challenges in the identification of Chryseobacterium indologenes and Elizabethkingia meningoseptica in cases of nosocomial infections and patients with cystic fibrosis

Abstract

Rare nonfermenting Gram-negative bacilli, such as Chryseobacterium indologenes and Elizabethkingia meningoseptica, have clinical importance in nosocomial infections and cystic fibrosis (CF), and their identification is a challenge to microbiology laboratories. Thus, the objective of this study was to verify the performance of phenotypic and mass spectrometry (matrix-assisted desorption ionization-time of flight mass spectrometry, MALDI-TOF MS) methods to identify C. indologenes and E. meningoseptica. In this context, the results obtained with phenotypic methods-namely manual biochemical and automated VITEK 2 (bioMérieux, Marcy l'Etoile, France) and Phoenix tests (Becton Dickinson (BD), San Diego, CA, USA)-and by MALDI-TOF MS-namely MALDI-TOF VITEK MS (MALDI-MS; bioMérieux) and MALDI-TOF BioTyper (MALDI-BD; BD)-of 22 isolates (blood cultures of patients with nosocomial infection (n = 15) and from patients with CF (n = 7)), initially identified as C. indologenes and E. meningoseptica, were compared. As result, using the manual phenotypic method, it was possible to identify the species level in 18/22; no identification was found in 4/22. There was a low agreement level between manual and VITEK 2 automated phenotypic methods when considering the genus level. The greatest agreement for genus-level identification occurred in MALDI-TOF MS equipment (15/22). When comparing all methods to identify the 22 isolates, there was agreement of 4/22 at the genus level and of 4/22 at the species level. In conclusion, there is low agreement level among identification methods of C. indologenes and E. meningoseptica. Although MALDI-TOF MS equipment shows a higher agreement level among them, results present low levels of confidence.

Keywords: Bacterial identification; MALDI-TOF MS; Phoenix; VITEK 2; phenotypic methods.