Plasmid-mediated extended-spectrum β-lactamases in organisms other than Klebsiella pneumoniae and Escherichia coli: A hidden reservoir of transferable resistance genes

Conclusions

Resistance due to AmpC β-lactamases and ESBLs in gramnegative bacillary pathogens is a growing and important problem and is tied to extensive use of extended-spectrum cephalosporins The emergence of these β-lactamases is then amplified by spread of resistant clones or resistant genes among patients within institutions or among patients who move between institutions within a region. Genes encoding β-lactamases are frequently linked to resistance genes for other classes of antibiotics. Thus, use of any one class of antibiotic may select for emergence of resistance to another. Treatment of infections caused by these multidrug-resistant pathogens is often problematic. One strategy to circumvent β-lactamase production has been use of β-lactam/β-lactamase inhibitor combinations, but AmpC β-lactamases and hyperproduction of ESBLs evade this therapeutic strategy. Use of carbapenems and cefepime, which are the most stable of all β-lactam antibiotics to hydrolysis by ESBLs and AmpC β-lactamases, can be expected eventually to select for emergence of resistance to these drugs as well.

Traditional isolation precautions that include use of gloves and gown have been shown to be effective during contact with the patient infected or colonized with ESBLproducing K. pneumoniae or E. coli. However, if infection control efforts are directed only at those isolates that the laboratory is capable of identifying as ESBL-producers, the presence in an institutional setting of undetected plasmidencoded ESBLs in Enterobacteriaceae, other than K. pneumoniae and E. coli, will likely be an epidemiologic hazard. A patient infected with these organisms is a hidden reservoir of plasmid-encoded resistance genes that can spread among different species of Enterobacteriaceae. Development of rapid assays to detect the presence of these resistance genes would be a major asset. Control measures that may be effective include early detection of ESBLs in any Enterobacteriaceae, especially Enterobacter species or P. aeruginosa; universal glove use and hand hygiene; cohorting of colonized or infected patients; implementation of control measures simultaneously in all health care facilities linked by patient transfers; and of greatest importance, control of unnecessary and inappropriate antibiotic use.