Therapeutic considerations in the treatment of respiratory infections caused by ceftazidime-resistant Klebsiella pneumoniae.

Klebsiella pneumoniae are important human pathogens, particularly as causes of nosocomial respiratory tract infections. Intrinsically resistant to ampicillin, in recent years K. pneumoniae strains have acquired resistance to a broad variety of extended-spectrum cephalosporins. This resistance is most commonly mediated by the extended-spectrum beta-lactamases (ESBLs), plasmid-mediated enzymes that have evolved through point mutations in the genes encoding the more susceptible penicillinases TEM-1 and SHV-1. In a small minority of cases, K. pneumoniae have also been found to express extended-spectrum cephalosporin resistance by the elaboration of plasmid-mediated AmpC-type enzymes. These mutant enzymes confer resistance to extended-spectrum cephalosporins, penicillins, and in some cases cefamycins or beta-lactam-beta-lactamase inhibitor combinations. The most reliable and effective antimicrobial treatment of infections caused by these strains are the carbapenems imipenem and meropenem.