Epidemiology of Extended-spectrum ß-lactamase (ESBL)-Producing Enteric Gram-negative Bacilli in Swiss Children

Background & Rationale:

Increasing resistance to antibiotics is a growing problem in public health and is associated with treatment failures, increased health care costs, and prolonged hospital stays. Over the past years, one mechanism of resistance has been of particular concern: ESBL, which is produced mainly by Escherichia coli and Klebsiella species but also found in other gram negative bacteria. ESBLs are plasmid-encoded ß-lactamases conferring resistance to penicillins, cephalosporins and aztreonam.

ESBL-producing enterobacteria are usually susceptible to carbapenems, such as ertapenem, imipenem or meropenem. Thus, treatment with carbapenems remains safe if the presence of ESBL is recognized. However, the confirmation of ESBL is not always a routine procedure in all laboratories. Furthermore, ESBL strains with high resistance to ertapenem and decreased activity to imipenem and meropenem have already been described. The mechanism among these strains however, appears to be a combination of the expression of ESBL and impermeability or increased efflux for carbapenems. Infection with ESBL-producing E. coli or K. pneumoniae is potentially hazardous for patients. Mortality is significantly higher following a bloodstream infection caused by ESBL producing E. coli compared to non-ESBL producing strains.

ESBLs are encoded on plasmids: classically, these plasmid mediated enzymes have been of the TEM and SHV type. However, in recent years CTX-M-type ESBLs have been increasingly identified worldwide throughout the world. CTX-M enzymes predominantly hydrolyze cefotaxime, but are weakly active against ceftazidime. However, some ESBLs of the CTX-M family also display increased hydrolytic activities against ceftazidime, as is the case for CTXM-15 and CTX-M-32.

The prevalence of ESBL producing enterobacteria and particularly E. coli has significantly increased in recent years. This increase is primarily due to the spread of ESBL of the CTX-M-type. Genes encoding CTX-M enzymes are associated with mobile genetic elements allowing these enzymes to spread throughout the community. Well established primer sets are used in polymerase chain reaction (PCR) tests for the detection of the blaTEM, blaSHV, and blaCTX-M genes, and are used to differentiate ESBL strains.