Extended-Spectrum Beta-Lactamase Producing Escherichia coli: Increasing Incidence of a Resistant Pathogen

Definitions: Beta-lactam antimicrobials are characterized by having a four-membered cyclic amide (beta-lactam ring) as part of their chemical structure (Figure 1) [1]. This broad group includes the penicillins, cephalosporins, carbapenems, and monobactams [1]. All beta-lactams have a similar mechanism of action; they inhibit bacterial cell wall synthesis [1]. Resistance to beta-lactam antimicrobials may be mediated by several mechanisms. Among clinically important gram-negative bacteria, antimicrobial resistance is commonly the result of beta-lactamase production [2]. Beta-lactamases are enzymes capable of hydrolyzing beta-lactam antimicrobials, thereby inactivating them [2]. There are hundreds of different beta-lactamase enzymes which differ in terms of the specific beta-lactam antimicrobials they are able to inactivate [2]. Extended-spectrum beta-lactamases (ESBLs) are beta-lactamase enzymes capable of hydrolyzing extended-spectrum/third generation cephalosporins (e.g., ceftriaxone and/or ceftazidime) [2,3]. They do not hydrolyze carbapenems and are susceptible, in turn, to inhibition by conventional beta-lactamase inhibitors (clavulanate) [2,4]. ESBL-producing Escherichia coli typically demonstrate resistance to penicillins, cephalosporins (first, second, and third generation), and monobactams [2,4,5]. They remain susceptible to carbapenems and may or may not be susceptible to beta-lactam/beta-lactamase inhibitor combinations [2,4,5]. However, it is important to note that there are many different types of ESBL enzymes and the susceptibility profile of a given clinical isolate will depend on the specific enzyme present.