Gibreel Amera, Kos Veronica N, Keelan Monika, Trieber Cathy A, Levesque Simon, Michaud Sophie, Taylor Diane E
Department of Medical Microbiology and Immunology, 1-28 Medical Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2H7 Canada.
Antimicrob Agents Chemother. 2005 Jul;49(7):2753-9. doi: 10.1128/AAC.49.7.2753-2759.2005.
A collection of 23 macrolide-resistant Campylobacter isolates from different geographic areas was investigated to determine the mechanism and stability of macrolide resistance. The isolates were identified as Campylobacter jejuni or Campylobacter coli based on the results of the hippurate biochemical test in addition to five PCR-based genotypic methods. Three point mutations at two positions within the peptidyl transferase region in domain V of the 23S rRNA gene were identified. About 78% of the resistant isolates exhibited an A-->G transition at Escherichia coli equivalent base 2059 of the 23S rRNA gene. The isolates possessing this mutation showed a wide range of erythromycin and clarithromycin MICs. Thus, this mutation may incur a greater probability of treatment failure in populations infected by resistant Campylobacter isolates. Another macrolide-associated mutation (A-->C transversion), at E. coli equivalent base 2058, was detected in about 13% of the isolates. An A-->G transition at a position cognate with E. coli 23S rRNA base 2058, which is homologous to the A2142G mutation commonly described in Helicobacter pylori, was also identified in one of the C. jejuni isolates examined. In the majority of C. jejuni isolates, the mutations in the 23S rRNA gene were homozygous except in two cases where the mutation was found in two of the three copies of the target gene. Natural transformation demonstrated the transfer of the macrolide resistance phenotype from a resistant Campylobacter isolate to a susceptible Campylobacter isolate. Growth rates of the resulting transformants containing A-2058-->C or A-2059-->G mutations were similar to that of the parental isolate. The erythromycin resistance of six of seven representative isolates was found to be stable after successive subculturing in the absence of erythromycin selection pressure regardless of the resistance level, the position of the mutation, or the number of the mutated copies of the target gene. One C. jejuni isolate showing an A-2058-->G mutation, however, reverted to erythromycin and clarithromycin susceptibility after 55 subcultures on erythromycin-free medium. Investigation of ribosomal proteins L4 and L22 by sequence analysis in five representative isolates of C. jejuni and C. coli demonstrated no significant macrolide resistance-associated alterations in either the L4 or the L22 protein that might explain either macrolide resistance or enhancement of the resistance level.
对来自不同地理区域的23株大环内酯类耐药弯曲杆菌分离株进行了研究，以确定大环内酯类耐药的机制和稳定性。除了五种基于PCR的基因分型方法外，还根据马尿酸盐生化试验结果将这些分离株鉴定为空肠弯曲杆菌或结肠弯曲杆菌。在23S rRNA基因V结构域的肽基转移酶区域内的两个位置发现了三个点突变。约78%的耐药分离株在23S rRNA基因的大肠杆菌等效碱基2059处表现出A→G转换。具有这种突变的分离株表现出广泛的红霉素和克拉霉素最低抑菌浓度（MIC）。因此，这种突变可能会使耐药弯曲杆菌分离株感染人群中治疗失败的可能性更大。在约13%的分离株中检测到另一种与大环内酯相关的突变（A→C颠换），位于大肠杆菌等效碱基2058处。在一株检测的空肠弯曲杆菌分离株中还鉴定出与大肠杆菌23S rRNA碱基2058同源的位置发生A→G转换，该位置与幽门螺杆菌中常见的A2142G突变同源。在大多数空肠弯曲杆菌分离株中，23S rRNA基因中的突变是纯合的，只有两例在靶基因的三个拷贝中的两个中发现了突变。自然转化证明了大环内酯类耐药表型从耐药弯曲杆菌分离株转移到敏感弯曲杆菌分离株。含有A-2058→C或A-2059→G突变的所得转化体的生长速率与亲本分离株相似。在没有红霉素选择压力的情况下连续传代培养后，发现七株代表性分离株中的六株的红霉素耐药性是稳定的，无论耐药水平、突变位置或靶基因突变拷贝数如何。然而，一株表现出A-2058→G突变的空肠弯曲杆菌分离株在无红霉素培养基上传代55次后恢复了对红霉素和克拉霉素的敏感性。对五株空肠弯曲杆菌和结肠弯曲杆菌代表性分离株进行序列分析，研究核糖体蛋白L4和L22，结果表明L4或L22蛋白中没有明显的与大环内酯类耐药相关的改变，这些改变可能解释大环内酯类耐药或耐药水平的增强。
