Update on CTX-M-type β-lactamases
2002; Lippincott Williams & Wilkins; Volume: 13; Issue: 2 Linguagem: Inglês
10.1097/00013542-200204000-00003
ISSN1473-5601
AutoresFerrán Navarro, Elisenda Miró,
Tópico(s)Infections and bacterial resistance
ResumoIn the past 10 years an increasing number of members of a family of class A extended-spectrum β-lactamases (ESBL), the CTX-M-type, which are not closely related to TEM, SHV or OXA enzymes, have been detected. The extended-spectrum activity of CTX-M enzymes seems to be an 'intrinsic' enzymatic property of these ESBL, due mainly to the hydrogen-binding pattern and the formation of the hydrophobic core observed near the Ω loop. When we compared CTX-M-type enzymes with other class A β-lactamases, the degree of amino acid identity was found to be lower than 40 %. Among all CTX-M β-lactamases, four different clusters were observed. The homologies among these clusters were quite low, suggesting that they branched off early from an unknown protein or, as was found more recently, from different proteins. The CTX-M-1 cluster could have originated from KLUC-1 of Kluyvera cryocrescens, whereas the CTX-M-2 cluster could have originated from KLUA-1 or KLUA-2 of Kluyvera ascorbata. It has been observed that the insertion sequence IS Ecp1, IS 903 and complex class 1 integron In60 may be implicated in jumping DNA fragments (in these cases containing genes that code for β-lactamases) from chromosomes to plasmids, which could contribute to the rapid spread of these β-lactamases in various species of the family Enterobacteriaceae and in geographically widely distant areas.
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