Detection of carbapenemase activities of Bacteroides fragilis strains with matrix-assisted laser desorption ionization – Time of flight mass spectrometry (MALDI-TOF MS)

•MALDI-TOF MS was applied to detect carbapenemases of Bacteroides fragilis strains.•Only the selected cfiA-positive strains displayed ertapenem hydrolysis within 2.5 h.•Hydrolysis correlates with the presence of the cfiA gene, but not with the IS elements.•Ertapenem is a sensitive substrate to detect B. fragilis carbapenemase activities.

Today resistance against carbapenems is considered an emerging problem in Bacteroides fragilis. Carbapenemase activities produced by aerobic bacteria have been detected by looking at hydrolysis of carbapenems with MALDI-TOF MS, but this technique was never used for anaerobic bacteria. We have developed a protocol for detection and verification of carbapenemase production in B. fragilis within 2.5 h. Twenty-eight strains of B. fragilis were tested. Of the sixteen cfiA-positive strains all showed hydrolysis of ertapenem, whereas the twelve cfiA-negative strains showed no hydrolysis. Ertapenem hydrolysis could be inhibited with 2,6-Pyridinecarboxylic acid (DPA) in all cfiA-positive strains, verifying the presence of the metallo-beta-lactamase. Here we show a rapid way to detect carbapenemase activities of B. fragilis strains.