Preferential selection of IMP and VIM metallo-beta-lactamases by imipenem in Pseudomonas aeruginosa

Mixed populations of Pseudomonas aeruginosa, comprising a carbapenem-susceptible and a carbapenem-resistant strain, containing either the IMP or VIM beta-lactamases, were exposed to imipenem. They developed resistance to both imipenem and meropenem. When the same mixed populations were exposed to meropenem, only the mixture containing the VIM beta- lactamases became resistant to both car-bapenems.