The treatment of gram-negative bacteremia is increasingly complicated by the occurrence of multidrug resistant gram-negative bacilli strains. Normally susceptible bacteria may become resistant to antimicrobial agents through mutation and selection or acquisition from other bacteria of genetic information that encodes resistance. Enterobacterial resistance to third-generation cephalosporins is typically caused by production of extended-spectrum beta-lactamases . CTX-Ms are one of the means of antibiotic resistant marker transfer among members of Enterobacteriaceae. Continous surveillance will be necessary to monitor the evolution of extended spectrum beta-lactamases and to verify whether the CTX-M type ESBLs will eventually prevail over the TEM-type ESBLs, which are still widespread, in some areas. The present work unveils the increasing role of the bla-CTX-M ?-lactamases in antibiotic resistance and the significance of appropriate treatment for infections caused by coliforms. Further studies are needed, however, to determine whether antibiotic policies or other measures can halt or lower the level of horizontal transfer that occurs in a hospital or community.