Samuelsen Orjan, Haukland Hanne Husom, Kahl Barbara C, von Eiff Christof, Proctor Richard A, Ulvatne Hilde, Sandvik Kjersti, Vorland Lars H
Department of Medical Microbiology, University Hospital of North Norway, Tromsø, Norway.
J Antimicrob Chemother. 2005 Dec;56(6):1126-9. doi: 10.1093/jac/dki385. Epub 2005 Nov 15.
To determine whether Staphylococcus aureus small colony variants (SCVs) are resistant to the antimicrobial peptide lactoferricin B. To assess if deficiency in transmembrane potential, a common characteristic of SCVs that are haemin- or menadione-auxotrophs, affects the uptake of the peptide into the bacterial cytoplasm.
A broth microdilution technique was used for susceptibility testing to determine the MIC of lactoferricin B for SCVs with three different auxotrophisms (haemin, menadione or thymidine) and their isogenic parent strains. Both clinical isolates and genetically defined mutants were used. The internalization of lactoferricin B in a hemB mutant and the respective parent strain was studied using transmission electron microscopy and immunogold labelling.
All SCVs showed reduced susceptibility to lactoferricin B irrespective of their auxotrophy compared with their isogenic parent strains. The MIC for all SCVs was >256 mg/L, whereas the MICs for the parent strains ranged from 16-256 mg/L. Surprisingly, the hemB mutant contained significantly more lactoferricin B intracellularly than the respective parent strain.
The resistance mechanism of SCVs towards the antimicrobial peptide lactoferricin B is presumably caused by the metabolic changes present in SCVs rather than by a changed transmembrane potential of SCVs or reduced uptake of the peptide.
确定金黄色葡萄球菌小菌落变异株（SCVs）是否对抗菌肽乳铁传递蛋白B耐药。评估跨膜电位缺陷（这是血红素或甲萘醌营养缺陷型SCVs的一个共同特征）是否会影响该肽进入细菌细胞质。
采用肉汤微量稀释技术进行药敏试验，以确定乳铁传递蛋白B对具有三种不同营养缺陷型（血红素、甲萘醌或胸苷）的SCVs及其同基因亲本菌株的最低抑菌浓度（MIC）。使用临床分离株和基因定义的突变体。利用透射电子显微镜和免疫金标记研究了乳铁传递蛋白B在hemB突变体及其亲本菌株中的内化情况。
与同基因亲本菌株相比，所有SCVs对乳铁传递蛋白B的敏感性均降低，无论其营养缺陷型如何。所有SCVs的MIC均>256 mg/L，而亲本菌株的MIC范围为16 - 256 mg/L。令人惊讶的是，hemB突变体细胞内的乳铁传递蛋白B含量明显高于相应的亲本菌株。
SCVs对抗菌肽乳铁传递蛋白B的耐药机制可能是由SCVs中存在的代谢变化引起的，而不是由SCVs跨膜电位的改变或该肽摄取减少所致。
