Extended Spectrum Beta- Lactamases: A Minireview of Clinical Relevant Groups

Within the ESBL family the most common genes are temoneira (blaTEM) and sulfhydryl variable (blaSHV) with increasing reports of cefotaximase (blaCTX-M) [4]. The blaSHV and the blaTEM subgroups arise from mutational changes due to point mutations in the genes resulting in subtypes. Examples include blaSHV which differs from blaSHV-1 due to a single mutation of an amino acid from glycine to serine at position 238 (G238S) [5] while the same mutation in the blaTEM gene is referred to as blaTEM-2 [6]. BlaCTX-M is becoming more prevalent, acquired on a plasmid from Kluyvera species, over 125 different subtypes of the blaCTX-M gene have been described with blaCTX-M-15 most predominant around the globe associated with clonal spread [7,8]. Other less familiar genes within the ESBLs include blaOXA, blaPER, blaVEB, blaCME, blaTLA, blaSFO and blaGES to name a few. BlaOXA differs from the blaOXA-10 by one amino acid mutation, either S73D or G157D. The blaPER enzyme is mainly found in Turkey and South America, the genes blaVEB, blaCME and blaTLA are closely related to the blaPER gene [5], blaSFO is closely related to class A beta-lactamases [5]. ESBLs can be categorized into four different classes: A, B, C and D. Class A denotes a serine enzyme betalactamase, class B refers to metallo-beta-lactamases, class C represents cephalosporinases and class D enzymes are oxacillin-hydrolyzing enzymes [2,9].