Resistance development during serial passage of bacteria producing metallo-β-lactamases. Open symbols, results obtained with BAL30376 (MIC expressed as the concentration of BAL19764); solid symbols, results obtained with meropenem; circles, P. aeruginosa 527; squares, A. baumannii HPA74510; diamonds, S. maltophilia 1AC736; triangles, E. cloacae R947.