Hall L M, Livermore D M, Gur D, Akova M, Akalin H E
Department of Medical Microbiology, London Hospital Medical College, United Kingdom.
Antimicrob Agents Chemother. 1993 Aug;37(8):1637-44. doi: 10.1128/AAC.37.8.1637.
Pseudomonas aeruginosa ABD, which was isolated in October 1991 from blood cultures of a burn patient in Turkey, was resistant to cephalosporins, particularly ceftazidime (MIC, 512 micrograms/ml), penicillins, aztreonam, and meropenem, but not to imipenem. Cephalosporin and penicillin resistance transferred to P. aeruginosa PU21 and was associated with a beta-lactamase with a pI of 6.4 encoded by a 100-MDa plasmid designated pMLH52. Like extended-spectrum TEM and SHV beta-lactamases, this enzyme hydrolyzed penicillins and newer cephalosporins but did not hydrolyze cefoxitin or carbapenems. However, it differed from TEM and SHV derivatives in being a potent oxacillinase, and its encoding gene did not hybridize with probes to TEM and SHV genes. To characterize the enzyme, libraries of total DNA were cloned into plasmid pUC19 and were transformed into Escherichia coli DH5 alpha. Recombinant plasmids that gave ceftazidime resistance all contained a 3.65-kb BamHI fragment. Deletions from this fragment allowed the beta-lactamase gene to be located on a 1.4-kb section of DNA, which contained an open reading frame of 798 bases. This encoded a protein that was deduced to differ from PSE-2 beta-lactamase only in having serine instead of asparagine at position 143 and aspartate instead of glycine at position 157. It is concluded that the resistance of isolate ABD dependent on an extended-spectrum variant of the PSE-2 enzyme. The ability of this enzyme to cause ceftazidime resistance dependent primarily on a low Km for the compound; Vmax remained low. It is proposed that PSE-2 should be transferred to the OXA group as OXA-10 and that the new enzyme be designated OXA-11.
1991年10月从土耳其一名烧伤患者的血培养物中分离出的铜绿假单胞菌ABD，对头孢菌素耐药，尤其是对头孢他啶（MIC，512微克/毫升）、青霉素、氨曲南和美罗培南耐药，但对亚胺培南不耐药。头孢菌素和青霉素耐药性转移至铜绿假单胞菌PU21，并与一种由名为pMLH52的100-MDa质粒编码的pI为6.4的β-内酰胺酶相关。与超广谱TEM和SHVβ-内酰胺酶一样，这种酶可水解青霉素和新型头孢菌素，但不能水解头孢西丁或碳青霉烯类。然而，它与TEM和SHV衍生物不同，是一种强效苯唑西林酶，其编码基因与TEM和SHV基因的探针不杂交。为了鉴定该酶，将总DNA文库克隆到质粒pUC19中，并转化到大肠杆菌DH5α中。赋予头孢他啶耐药性的重组质粒均含有一个3.65-kb的BamHI片段。该片段的缺失使β-内酰胺酶基因定位在一段1.4-kb的DNA上，该DNA包含一个798个碱基的开放阅读框。这编码了一种蛋白质，推断该蛋白质与PSE-2β-内酰胺酶的区别仅在于第143位为丝氨酸而非天冬酰胺，第157位为天冬氨酸而非甘氨酸。得出结论，分离株ABD的耐药性取决于PSE-2酶的超广谱变体。这种酶导致头孢他啶耐药的能力主要取决于该化合物的低Km；Vmax仍然较低。建议将PSE-2转移到OXA组，命名为OXA-10，新酶命名为OXA-11。
