Evaluation of in vitro methods for testing tigecycline combinations against carbapenemase-producing K.pneumoniae isolates.

•Agreement between time–kill, chequerboard and three Etest synergy methods was evaluated.•Poor correlation with the time–kill assay was observed for all methods tested.•Etest cross formation showed the best agreement but lacked sensitivity.•Method-related parameters appear to compromise the comparability of synergy testing methods.