ABSTRACT
Fast and reliable discrimination of methicillin-resistant Staphylococcus aureus (MRSA) isolates is essential in identifying an outbreak. Molecular typing methods, such as S. aureus protein A (spa) typing, multi locus sequence typing (MLST) and pulse field gel electrophoresis (PFGE) are generally used for this purpose. These methods are all relatively time-consuming and not performed routinely in all laboratories. The aim of this study is to examine whether MALDI-TOF MS can be used as a fast, simple and easily implemented method for first-line discrimination of MRSA isolates. Mass spectra from 600 clinical MRSA isolates were included in the study, representing 89 spa types, associated with 16 different known clonal complexes. All spectra were obtained directly from colony material obtained from overnight cultures without prior protein extraction. We identified 43 useful discriminatory m/z-values (peaks) and used a concept of arranging these peaks into pairs or small clusters within a small mass range, allowing for quality control of the spectra obtained. Using this concept we could reproducibly characterise and arrange the isolates into 26 MALDI-TOF groups, which strongly correlated with spa types and clonal complexes. The results of this study clearly show that MALDI-TOF MS can be used for first-line discrimination of MRSA isolates, using a simple and fast method that is easy to implement as part of routine testing.
Subject(s)
Bacterial Typing Techniques/methods , Methicillin-Resistant Staphylococcus aureus/classification , Methicillin-Resistant Staphylococcus aureus/isolation & purification , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods , Cluster Analysis , Disease Outbreaks , Humans , Methicillin-Resistant Staphylococcus aureus/chemistry , Molecular Epidemiology/methods , Phenotype , Reproducibility of Results , Staphylococcal Infections/epidemiology , Staphylococcal Infections/microbiology , Time FactorsABSTRACT
We report two cases of bacteremia with the anaerobic bacterium Ruminococcus gnavus. In both cases, the bacteremia was associated with diverticular disease. Preliminary conventional identification suggested peptostreptococci, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis did not produce scores high enough for species identification. Finally, the bacteria were identified by 16S rRNA gene sequencing.
