Serious infections caused by enteric gram-negative bacilli--mechanisms of antibiotic resistance and implications for therapy of gram-negative sepsis in the transplanted patient.

The Enterobacteriaceae (eg, Escherichia coli, Klebsiella spp., Enterobacter spp.) are common causes of intraabdominal, respiratory tract, and bloodstream infections in transplant recipients. Antibiotic resistance in these organisms is increasing. The major mechanism of resistance to cephalosporins is beta-lactamase production. The most important beta-lactamases are the inducible group 1 cephalosporinases, which are resistant to beta-lactamase inhibitors, and the plasmid-mediated extended-spectrum beta-lactamases (ESBLs). Organisms producing these beta-lactamases also may be resistant to quinolones and aminoglycosides by different mechanisms. A worrying recent development has been the detection of plasmid-mediated carbapenemases, which can inactivate antibiotics such as imipenem and meropenem. In general, third-generation cephalosporins should be avoided in the therapy of serious infections in transplant recipients because of the common occurrence of cephalospo-rinases in the Enterobacteriaceae. Antibiotic options are becoming more limited as the prevalence of resistance mechanisms in gram-negative bacilli increases.