Su Michelle, Davis Michelle H, Peterson Jessica, Solis-Lemus Claudia, Satola Sarah W, Read Timothy D
Division of Infectious Diseases, Department of Medicine, School of Medicine, Emory University, Atlanta, Georgia, USA.
Wisconsin Institute for Discovery and Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
PeerJ. 2021 Jul 13;9:e11764. doi: 10.7717/peerj.11764. eCollection 2021.
Vancomycin-intermediate (VISA) typically arises through accumulation of chromosomal mutations that alter cell-wall thickness and global regulatory pathways. Genome-based prediction of VISA requires understanding whether strain background influences patterns of mutation that lead to resistance. We used an iterative method to experimentally evolve three important methicillin-resistant (MRSA) strain backgrounds-(CC1, CC5 and CC8 (USA300)) to generate a library of 120 laboratory selected VISA isolates. At the endpoint, isolates had vancomycin MICs ranging from 4 to 10 μg/mL. We detected mutations in more than 150 genes, but only six genes (already known to be associated with VISA from prior studies) were mutated in all three background strains (). We found evidence of interactions between loci (e.g., and mutants were significantly negatively correlated) and and were more frequently mutated in one of the backgrounds. Increasing vancomycin resistance was correlated with lower maximal growth rates (a proxy for fitness) regardless of background. However, CC5 VISA isolates had higher MICs with fewer rounds of selection and had lower fitness costs than the CC8 VISA isolates. Using multivariable regression, we found that genes differed in their contribution to overall MIC depending on the background. Overall, these results demonstrated that VISA evolved through mutations in a similar set of loci in all backgrounds, but the effect of mutation in common genes differed with regard to fitness and contribution to resistance in different strains.
万古霉素中介耐药（VISA）通常是由于染色体突变积累导致细胞壁厚度和全局调控途径改变而产生的。基于基因组预测VISA需要了解菌株背景是否会影响导致耐药性的突变模式。我们采用迭代方法对三种重要的耐甲氧西林金黄色葡萄球菌（MRSA）菌株背景（CC1、CC5和CC8（USA300））进行实验性进化，以生成一个包含120株实验室筛选的VISA分离株的文库。在实验终点，分离株的万古霉素最低抑菌浓度（MIC）范围为4至10μg/mL。我们在150多个基因中检测到突变，但只有六个基因（先前研究已表明与VISA相关）在所有三种背景菌株中均发生了突变。我们发现基因座之间存在相互作用的证据（例如， 和 突变体呈显著负相关），并且 和 在其中一种背景中更频繁地发生突变。无论背景如何，万古霉素耐药性增加与最大生长速率降低（适应性的一个指标）相关。然而，CC5 VISA分离株在较少轮次的筛选下具有更高的MIC，并且与CC8 VISA分离株相比，适应性成本更低。使用多变量回归分析，我们发现不同基因对总体MIC的贡献因背景而异。总体而言，这些结果表明，在所有背景中，VISA都是通过一组相似的基因座突变进化而来的，但常见基因的突变在不同菌株的适应性和耐药性贡献方面存在差异。
