Tracking carbapenemase-producing bacteria by molecular typing: Population diversity and sampling pitfall.

While typing methods are increasingly refined, the sampling of bacteria to be typed in healthcare-associated infection context retains less attention. Through 2 emblematic cases of in-hospital transmission of extensively drug-resistant bacteria producing carbapenemases, we demonstrate the impact of colony sampling in typing results. Because of intra-population diversity, typing several colonies of same species and resistotype was needed to fully track the transmission among patients. Bacterial population studies could better decipher transmission routes of healthcare-associated bacteria, thereby improving outbreak control.