Bret L, Chanal-Claris C, Sirot D, Chaibi E B, Labia R, Sirot J
Laboratoire de Bactériologie, Faculté de Médecine, Clermont-Ferrand, France.
Antimicrob Agents Chemother. 1998 May;42(5):1110-4. doi: 10.1128/AAC.42.5.1110.
A clinical strain of Proteus mirabilis (CF09) isolated from urine specimens of a patient displayed resistance to amoxicillin (MIC >4,096 microg/ml), ticarcillin (4,096 microg/ml), cefoxitin (64 microg/ml), cefotaxime (256 microg/ml), and ceftazidime (128 microg/ml) and required an elevated MIC of aztreonam (4 microg/ml). Clavulanic acid did not act synergistically with cephalosporins. Two beta-lactamases with apparent pIs of 5.6 and 9.0 were identified by isoelectric focusing on a gel. Substrate and inhibition profiles were characteristic of an AmpC-type beta-lactamase with a pI of 9.0. Amplification by PCR with primers for ampC genes (Escherichia coli, Enterobacter cloacae, and Citrobacter freundii) of a 756-bp DNA fragment from strain CF09 was obtained only with C. freundii-specific primers. Hybridization results showed that the ampC gene is only chromosomally located while the TEM gene is plasmid located. After cloning of the gene, analysis of the complete nucleotide sequence (1,146 bp) showed that this ampC gene is close to blaCMY-2, from which it differs by three point mutations leading to amino acid substitutions Glu --> Gly at position 22, Trp --> Arg at position 201, and Ser --> Asn at position 343. AmpC beta-lactamases derived from that of C. freundii (LAT-1, LAT-2, BIL-1, and CMY-2) have been found in Klebsiella pneumoniae, E. coli, and Enterobacter aerogenes and have been reported to be plasmid borne. This is the first example of a chromosomally encoded AmpC-type beta-lactamase observed in P. mirabilis. We suggest that it be designated CMY-3.
从一名患者尿液标本中分离出的奇异变形杆菌临床菌株（CF09）对阿莫西林（MIC>4,096微克/毫升）、替卡西林（4,096微克/毫升）、头孢西丁（64微克/毫升）、头孢噻肟（256微克/毫升）和头孢他啶（128微克/毫升）耐药，对氨曲南的MIC升高（4微克/毫升）。克拉维酸与头孢菌素无协同作用。通过凝胶等电聚焦鉴定出两种表观pI分别为5.6和9.0的β-内酰胺酶。底物和抑制谱具有pI为9.0的AmpC型β-内酰胺酶的特征。用针对ampC基因（大肠杆菌、阴沟肠杆菌和弗氏柠檬酸杆菌）的引物通过PCR从CF09菌株扩增出756bp的DNA片段，仅用弗氏柠檬酸杆菌特异性引物获得成功。杂交结果表明，ampC基因仅位于染色体上，而TEM基因位于质粒上。该基因克隆后，对其完整核苷酸序列（1,146bp）进行分析表明，此ampC基因与blaCMY-2相近，二者在三个位点发生点突变，导致第22位氨基酸由Glu变为Gly、第201位由Trp变为Arg、第343位由Ser变为Asn。源自弗氏柠檬酸杆菌的AmpCβ-内酰胺酶（LAT-1、LAT-2、BIL-1和CMY-2）已在肺炎克雷伯菌、大肠杆菌和气杆菌中发现，据报道是质粒携带的。这是在奇异变形杆菌中观察到的染色体编码AmpC型β-内酰胺酶的首个实例。我们建议将其命名为CMY-3。
