Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Laboratorio di Fisiologia e Biotecnologia dei Microrganismi, Universitá di Siena, I-53100 Siena, Italy.
Antimicrob Agents Chemother. 2010 Apr;54(4):1547-54. doi: 10.1128/AAC.01252-09. Epub 2010 Feb 1.
Aeromonas enteropelogenes (formerly A. tructi) was described to be an ampicillin-susceptible and cephalothin-resistant Aeromonas species, which suggests the production of a cephalosporinase. Strain ATCC 49803 was susceptible to amoxicillin, cefotaxime, and imipenem but resistant to cefazolin (MICs of 2, 0.032, 0.125, and >256 microg/ml, respectively) and produced an inducible beta-lactamase. Cefotaxime-resistant mutants (MIC, 32 microg/ml) that showed constitutive beta-lactamase production could be selected in vitro. The gene coding for the cephalosporinase of A. enteropelogenes ATCC 49803 was cloned, and its biochemical properties were investigated. Escherichia coli transformants showing resistance to various beta-lactams carried a 3.5-kb plasmid insert whose sequence revealed a 1,146-bp open reading frame (ORF) encoding a class C beta-lactamase, named TRU-1, showing the highest identity scores with A. punctata CAV-1 (75%), A. salmonicida AmpC (75%), and A. hydrophila CepH (71%). The bla(TRU-1) locus includes open reading frames (ORFs) showing significant homology with genes found in the genomes of other Aeromonas species, although it exhibits a different organization, as reflected by the presence of additional ORFs located downstream of the beta-lactamase gene in the A. hydrophila and A. salmonicida genomes. Specific PCR assays were negative for cphA-like and bla(OXA-12)-like genes in three A. enteropelogenes ATCC strains. Purified TRU-1 showed a broad substrate profile, efficiently hydrolyzing benzylpenicillin, cephalothin, cefoxitin, and, although with significantly lower turnover rates, oxyiminocephalosporins. Cephaloridine and cefepime were poorly recognized by the enzyme, as reflected by the high K(m) values observed with these substrates. Thus far, A. enteropelogenes represents the only known example of an Aeromonas species that produces only one beta-lactamase belonging to molecular class C.
产气肠杆菌（以前称为 A. tructi）被描述为一种对氨苄西林敏感但头孢噻吩耐药的气单胞菌，这表明其产生了头孢菌素酶。菌株 ATCC 49803 对阿莫西林、头孢噻肟和亚胺培南敏感，但对头孢唑林耐药（MIC 分别为 2、0.032、0.125 和 >256μg/ml），并产生诱导型β-内酰胺酶。在体外可选择产生头孢菌素酶的表型稳定的头孢噻肟耐药突变株（MIC 为 32μg/ml）。克隆了产气肠杆菌 ATCC 49803 的头孢菌素酶基因，并对其生化特性进行了研究。对各种β-内酰胺类药物耐药的大肠杆菌转化子携带一个 3.5kb 的质粒插入片段，其序列揭示了一个 1146bp 的开放阅读框（ORF），编码一种 C 类β-内酰胺酶，命名为 TRU-1，与 A. punctata CAV-1（75%）、A. salmonicida AmpC（75%）和 A. hydrophila CepH（71%）的同源性最高。bla(TRU-1)基因座包括与其他气单胞菌基因组中发现的基因具有显著同源性的开放阅读框（ORFs），尽管其组织不同，这反映在 A. hydrophila 和 A. salmonicida 基因组中β-内酰胺酶基因下游存在额外的 ORFs。在 3 株产气肠杆菌 ATCC 菌株中，特定的 PCR 检测对 cphA 样和 bla(OXA-12)样基因均为阴性。纯化的 TRU-1 显示出广泛的底物谱，可有效水解苯唑西林、头孢噻吩、头孢西丁和氧肟头孢菌素，尽管其周转率明显较低。头孢菌素和头孢吡肟的酶识别较差，这反映在这些底物观察到的高 K(m)值上。迄今为止，产气肠杆菌是唯一已知的仅产生一种属于 C 类分子的β-内酰胺酶的气单胞菌属物种。
