The identification of 83 Corynebacterium, 13 Arcanobacterium haemolyticum, and 10 Rhodococcus equi strains by conventional methods (API Coryne complemented with 16S rRNA gene sequence analysis) was compared with matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identification. The correlation between API and MALDI-TOF results was 89%. MALDI-TOF is a rapid and accurate system for identification of the above-mentioned microorganisms. Corynebacteria are widespread throughout nature. Pathogenic Corynebacterium species include Corynebacterium diphtheriae and nondiphtheroid Corynebacterium. The nondiphtheroid Corynebacterium species are found in the mucosa and normal skin flora of humans and animals. Some species, such as Corynebacterium amycolatum, Corynebacterium jeikeium, Corynebacterium striatum, Corynebacterium urealyticum, and Corynebacterium xerosis, are relevant human pathogens, mainly infecting immunocompromised patients (4). The API Coryne V2.0 system (bioMérieux, Marcy l'Etoile, France), complemented with conventional phenotypic testing, is most commonly used in routine laboratories for identification of these microorganisms. However, this method is time-consuming and does not always give reliable identification at the species level (2). Identification by means of 16S rRNA sequencing is more specific but is slow and expensive.Arcanobacterium haemolyticum is an obligate parasite of the pharynx of humans; sporadically, it causes pharyngeal or skin lesions (11). Rhodococcus equi is the most important pathogenic species of the genus Rhodococcus, causing several infections such as necrotizing pneumonia and enteritis, mainly in immunocompromised patients such HIV-positive patients (14). A. haemolyticum and R. equi are also routinely identified using the API Coryne V2.0 system. In the case of R. equi, reliable identification frequently requires confirmation by molecular methods, including PCR and DNA sequencing (7).In recent years, matrix-assisted laser desorption ionizationtime of flight mass spectrometry (MALDI-TOF MS) has been increasingly applied in clinical microbial diagnostics for species identification of bacterial and fungal pathogens (13). MALDI-TOF MS identified successfully at the species level a group of 115 Corynebacterium clinical isolates, including 78 C. diphtheriae and 37 nondiphtheroid corynebacterial isolates (6). In a recent study (3), MALDI-TOF discriminated Corynebacterium aurimucosum from Corynebacterium minutissimum, two closely related Corynebacterium species previously considered difficult to differentiate (5).The aim of this study was to determine whether MALDI-TOF MS can be used as a routine method for fast and reliable identification of Corynebacterium clinical isolates at the species level in our laboratories. Eighty-three clinical strains isolated at the Clinical Microbiology Laboratory, Hospital Universitario Marqués de Valdecilla, Santander, Spain, were initially identified by API Coryne V2.0 and other conventional phenotypic methods (4) as C...
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has lately been implemented as a solid technology for rapid microorganism identification in microbiology laboratories. This study compares two methods for bacterial separation from 85 positive blood culture before MALDI-TOF MS: (1) a conventional method that we used in our laboratory to prepare bacteria for susceptibility testing and (2) a new commercialized technique (Sepsityper). There were no significant differences in the identification of Gram-negative bacilli regardless of the bacterial separation method used. However, identification was greater for Gram-positive cocci when the Sepsityper method was used (84.15% vs. 100% in the identification to a genus level in staphylococci and 57.14% vs. 85.71% in the identification to a genus level of enterococci with the in-house and Sepsityper methods, respectively). Therefore, the Sepsityper method to prepare bacteria from a positive blood culture is more adequate for the further identification of Gram-positive cocci by MALDI-TOF MS.
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