GlossaryOXA (for “oxacillin-hydrolyzing”) β-lactamases represented one of the most prevalent plasmid-encoded β-lactamase families in the late 1970s and early 1980s (129, 132, 198). When the molecular class D OXA β-lactamases were placed in a separate molecular class from the other serine β-lactamases (76), they had been identified mainly in the Enterobacteriaceae and P. aeruginosa (23, 144) and were functionally described as penicillinases capable of hydrolyzing oxacillin and cloxacillin (21). They were in general poorly inhibited by clavulanic acid and EDTA and known to have a large amount of variability in amino acid sequences (22). OXA-11, the first extended-spectrum variant of OXA-10 (previously known as PSE-2), was described in 1993 (61). The extended-spectrum variants OXA-11, OXA-15, OXA-18, and OXA-45 had hydrolysis rates for ceftazidime that varied from 1% to 1,150% relative to the hydrolysis rate of penicillin, but imipenem hydrolysis was not detected (38, 61, 162, 205). Currently there have been 102 unique OXA sequences identified (http://www.lahey.org/Studies/), of which 9 are extended spectrum β-lactamases and at least 37 are considered to be carbapenemases
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