Liu Zhenru, Ling Baodong, Zhou Liming
J Chemother. 2015 Aug;27(4):207-12. doi: 10.1179/1973947814Y.0000000190. Epub 2014 Apr 27.
Multidrug-resistant Acinetobacter baumannii has become a worldwide problem, and methylation of 16S rRNA has recently emerged as a new mechanism of resistance to aminoglycosides, which is mediated by a newly recognized group of 16S rRNA methylases. 16S rRNA methylase confers a high-level resistance to all 4,6-substituted deoxystreptamine aminoglycosides that are currently used in clinical practice. Some of the A. baumannii isolates have been found to coproduce extended-spectrum beta-lactamases (ESBLs), contributing to their multidrug resistance. The aim of this study was to detect the determinants of the 16S rRNA methylase genes armA, rmtA, rmtB, rmtC, rmtD, rmtE, and npmA, the modifying enzyme genes aac(6')-Ib, ant(3″)-Ia, aph(3')-I, and the extended-spectrum beta-lactamase genes bla(TEM), bla(SHV), and bla(CTX-M-3) among A. baumannii isolates in northeastern Sichuan, China. Minimum inhibitory concentrations (MICs) of 21 different antimicrobial agents against the A. baumannii isolates were determined. The clinical isolates showed a high level of resistance (MIC≧256 μg/ml) to aminoglycosides, which ranged from 50·1 to 83·8%. The resistances to meropenem and imipenem, two of the beta-lactam antibiotics and the most active antibiotics against A. baumannii, were 9·1 and 8·2%, respectively. Among 60 amikacin-resistant isolates, only the 16S rRNA methylase gene armA was found to be prevalent (66·7%), but the other 16S rRNA methylase genes rmtA, rmtB, rmtC, rmtD, rmtE, and npmA were not detected. The prevalences of the modifying enzyme genes aac (6')-Ib, ant (3″)-Ia, and aph (3')-I were 51·7, 81·7, and 58·3%, respectively, which are different from a previous study in which the occurrences of these genes were 3, 64, and 72%, respectively. Among the 40 isolates that were armA-positive, the prevalences of bla(TEM), bla(SHV), and bla(CTX-M-3) genes were detected for the first time in China, and their occurrences were 45, 65, and 52·5%, respectively. In all, A. baumannii with all the 16S rRNA methylase, modifying enzyme, and ESBL genes is extremely prevalent in northeastern Sichuan, China, posing a serious clinical concern with a major therapeutic threat in the future.
多重耐药鲍曼不动杆菌已成为一个全球性问题，16S rRNA甲基化最近成为对氨基糖苷类耐药的一种新机制，这是由一组新发现的16S rRNA甲基化酶介导的。16S rRNA甲基化酶赋予对目前临床使用的所有4,6-取代脱氧链霉胺氨基糖苷类高水平耐药。已发现一些鲍曼不动杆菌分离株可共同产生超广谱β-内酰胺酶（ESBLs），这导致了它们的多重耐药性。本研究的目的是检测中国四川东北部鲍曼不动杆菌分离株中16S rRNA甲基化酶基因armA、rmtA、rmtB、rmtC、rmtD、rmtE和npmA、修饰酶基因aac(6')-Ib、ant(3″)-Ia、aph(3')-I以及超广谱β-内酰胺酶基因bla(TEM)、bla(SHV)和bla(CTX-M-3)的决定因素。测定了21种不同抗菌药物对鲍曼不动杆菌分离株的最低抑菌浓度（MICs）。临床分离株对氨基糖苷类呈现高水平耐药（MIC≧256 μg/ml），耐药率在50·1%至83·8%之间。对美罗培南和亚胺培南这两种β-内酰胺类抗生素且是对鲍曼不动杆菌最有效的抗生素的耐药率分别为9·1%和8·2%。在60株对阿米卡星耐药的分离株中，仅发现16S rRNA甲基化酶基因armA普遍存在（66·7%），但未检测到其他16S rRNA甲基化酶基因rmtA（、rmtB、rmtC、rmtD、rmtE和npmA。修饰酶基因aac(6')-Ib、ant(3″)-Ia和aph(3')-I的流行率分别为51·7%、81·7%和58·3%，这与之前的一项研究不同，在该研究中这些基因的发生率分别为3%、64%和72%。在40株armA阳性分离株中，bla(TEM)、bla(SHV)和bla(CTX-M-3)基因的流行率在中国首次被检测到，其发生率分别为45%、65%和52·5%。总体而言，携带所有16S rRNA甲基化酶、修饰酶和ESBL基因的鲍曼不动杆菌在中国四川东北部极为普遍，对未来临床构成严重威胁且是重大治疗挑战。
