Service de Microbiologie, UNICAEN, CHU de CAEN Normandie, Normandie University, Caen, France.
Département de Microbiologie, Assistance Publique-Hôpitaux de Paris, Hôpital Henri Mondor, Unité de Bactériologie-Hygiène, Créteil, France.
Microb Drug Resist. 2020 Jul;26(7):727-731. doi: 10.1089/mdr.2019.0288. Epub 2020 Feb 7.
The aim of the study was to characterize phenotypically and genotypically an uncommon mechanism of resistance to macrolides, lincosamides, and streptogramins (MLS) in a group clinical isolate. The isolate UCN96 was recovered from an osteoradionecrosis wound, and was identified using the matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and the partial sequencing of the A gene. Antimicrobial susceptibility testing were carried out by the disk diffusion method and minimal inhibitory concentrations (MICs) were determined by the broth microdilution technique. PCR screening was performed for MLS resistance genes described in Gram-positive bacteria. Specific mutations in the ribosomal proteins L3-, L4-, and L22-encoding genes were also screened and those in domain V of the 23S rRNA gene (). The number of mutated copies of the gene was determined using amplification-refractory mutation system quantitative-polymerase chain reaction (qPCR) analysis. The clinical isolate UCN96 was unambiguously identified as . It was susceptible to all macrolides and lincosamides (ML) antibiotics except spiramycin (MIC >256 mg/L) while it was also resistant to streptogramins. Screening for all acquired resistance genes was negative and no mutation was found in genes coding for L3, L4, and L22 ribosomal proteins. Of interest, a single mutation, A2062C (according to numbering), was detected in the domain V of 23S rRNA. Mutations at the position 2062 of 23S rRNA have been detected once in , and not yet in other spp. This mechanism is very likely uncommon in Gram-positive bacteria because different copies of 23S rRNA operons should be mutated for development of such a resistance pattern.
本研究旨在对一株临床分离株中一种不常见的大环内酯类、林可酰胺类和链阳性菌素类（MLS）耐药表型和基因型特征进行分析。分离株 UCN96 来自放射性骨坏死伤口，通过基质辅助激光解吸电离飞行时间（MALDI-TOF）质谱和 A 基因部分测序进行鉴定。采用纸片扩散法进行抗菌药物敏感性试验，采用肉汤微量稀释法测定最小抑菌浓度（MIC）。对革兰氏阳性菌中描述的 MLS 耐药基因进行 PCR 筛选。还筛选了核糖体蛋白 L3、L4 和 L22 编码基因以及 23S rRNA 基因（）中结构域 V 的特定突变。使用扩增受阻突变系统定量聚合酶链反应（qPCR）分析确定 基因的突变拷贝数。临床分离株 UCN96 明确鉴定为 。除螺旋霉素（MIC >256mg/L）外，该分离株对所有大环内酯类和林可酰胺类（ML）抗生素均敏感，同时对链阳性菌素类耐药。对所有获得性耐药基因进行筛选均为阴性，未发现编码核糖体蛋白 L3、L4 和 L22 的基因发生突变。有趣的是，在 23S rRNA 的结构域 V 中检测到一个单一的突变，A2062C（根据 编号）。23S rRNA 2062 位的突变在 中仅检测到一次，在其他 spp 中尚未检测到。这种机制在革兰氏阳性菌中很可能不常见，因为要产生这种耐药模式，应该突变不同拷贝数的 23S rRNA 操纵子。
