Faculty of Sciences, Institute of Biochemistry and Microbiology, Universidad Austral de Chile, Valdivia, Chile.
FONDAP Centre, Interdisciplinary Centre for Aquaculture Research (INCAR), Concepción, Chile.
J Fish Dis. 2019 Dec;42(12):1645-1655. doi: 10.1111/jfd.13089. Epub 2019 Oct 7.
The aetiological agent of Piscirickettsiosis is Piscirickettsia salmonis, a Gram-negative intracellular pathogen, and high doses of antibiotics have regularly been employed to treat this infection. Seven florfenicol and/or oxytetracycline resistance genes (tet pump, tetE, Tclor/flor, Tbcr, TfloR, ompF and mdtN) were identified in strains by in silico genome analyses. Later, the number of single nucleotide polymorphisms (SNPs) and its relationship with the resistance to these antibiotics were identified and analysed, using the original LF-89 strain as reference. Trials to determine and compare the minimum inhibitory concentration (MIC) of oxytetracycline and florfenicol in each strain, as well as to quantify the gPCR transcripts levels in the selected genes, were performed. Therefore, variations in the resistance to both antibiotics were observed, where the strain with fewer SNPs showed the highest susceptibility. Consistently, the in silico 3D analyses of proteins encoded by the selected genes revealed structural changes, evident in the sequences with the highest number of SNPs. These results showed that the bacterial resistance to oxytetracycline was mainly linked to the presence of SNPs in relevant sites, antibiotic resistance genes and an OmpF porin, leading to important changes in the protein structure.
类立克次氏体病的病原体是鲑鱼立克次氏体，一种革兰氏阴性细胞内病原体，通常使用高剂量的抗生素来治疗这种感染。通过计算机基因组分析，在菌株中鉴定出了七种氟苯尼考和/或土霉素耐药基因（tet 泵、tetE、Tclor/flor、TbcR、TfloR、ompF 和 mdtN）。后来，使用原始 LF-89 菌株作为参考，鉴定并分析了单核苷酸多态性（SNP）的数量及其与这些抗生素耐药性的关系。然后，进行了确定和比较每个菌株中土霉素和氟苯尼考最小抑菌浓度（MIC）的试验，并对选定基因的 gPCR 转录本水平进行了定量分析。因此，观察到了对这两种抗生素的耐药性的变化，其中 SNP 数量较少的菌株表现出最高的敏感性。一致地，通过对选定基因编码的蛋白质进行计算机 3D 分析，揭示了结构变化，在具有最高 SNP 数量的序列中明显。这些结果表明，细菌对土霉素的耐药性主要与相关位点、抗生素耐药基因和 OmpF 孔蛋白中的 SNP 存在有关，导致蛋白质结构发生重要变化。
