Differences in the changes in resistance patterns to third and fourth-generation cephalosporins and piperacillin/tazobactam among Klebsiella pneumoniae and Escherichia coli clinical isolates following a restriction policy in a Greek tertiary care hospital - Petrikkos, G; Markogiannakis, A; Papaparaskevas, J (Int J Antimicrob Agents, 2007)