Differentiation of cfiA -Negative and cfiA -Positive Bacteroides fragilis Isolates by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

Carbapenem resistance in Bacteroides fragilis is associated with cfiA -encoded class B metallo-beta-lactamase. cfiA -negative and cfiA -positive isolates belong to genotypically distinct groups. Of a total of 248 B. fragilis isolates included in this study, 214 were susceptible, 10 were intermediate, and 24 were resistant to meropenem. We show that matrix-assisted laser desorption ionization–time of flight mass spectrometry is able to differentiate between cfiA -negative and cfiA -positive isolates and predict carbapenem resistance in a routine laboratory setting.