Creation of an In-House Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Corynebacterineae Database Overcomes Difficulties in Identification of Nocardia farcinica Clinical Isolates

Abstract

Nocardiosis is a rare disease that is caused by Gram-positive actinobacteria of theNocardiagenus and affects predominantly immunocompromised patients. In its disseminated form, it has a predilection for the central nervous system and is associated with high mortality rates. Therefore, prompt identification of the pathogen is critical. Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry is a relatively novel technique used for identification of microorganisms. In this work, an upgraded MALDI-TOF Biotyper database containingCorynebacterineaerepresentatives of strains deposited in the Polish Collection of Microorganisms was created and used for identification of the strain isolated from a nocardial brain abscess, mimicking a brain tumor, in an immunocompetent patient. Testing with the API Coryne system initially incorrectly identifiedRhodococcussp., while chemotaxonomic tests, especially mycolic acid analysis, enabled correctNocardiaidentification only at the genus level. Subsequent sequence analysis of 16S rRNA andsecA1genes confirmed the identification. To improve the accuracy of the results, an in-house database was constructed using optimized parameters; with the use of the database, the strain was eventually identified asNocardia farcinica. Clinical laboratories processing various clinical strains can upgrade a commercial database to improve and to accelerate the results obtained. This is especially important in the case ofNocardia, for which valid microbial diagnosis remains challenging; reference laboratories are often required to identify and to survey these rare actinobacteria.