Ersoy Selvi C, Rose Warren E, Patel Robin, Proctor Richard A, Chambers Henry F, Harrison Ewan M, Pak Youngju, Bayer Arnold S
The Lundquist Institute, Torrance, CA 90502, USA.
School of Pharmacy, University of Wisconsin-Madison, Madison, WI 53705, USA.
Antibiotics (Basel). 2021 Sep 9;10(9):1089. doi: 10.3390/antibiotics10091089.
Antimicrobial susceptibility testing (AST) is routinely used to establish predictive antibiotic resistance metrics to guide the treatment of bacterial pathogens. Recently, a novel phenotype termed "bicarbonate (NaHCO)-responsiveness" was identified in a relatively high frequency of clinical MRSA strains, wherein isolates demonstrate in vitro "susceptibility" to standard β-lactams (oxacillin [OXA]; cefazolin [CFZ]) in the presence of NaHCO, and in vivo susceptibility to these β-lactams in experimental endocarditis models. We investigated whether a targeted phenotypic-genotypic screening of MRSA could rule in or rule out NaHCO susceptibility upfront. We studied 30 well-characterized clinical MRSA bloodstream isolates, including 15 MIC-susceptible to CFZ and OXA in NaHCO-supplemented Mueller-Hinton Broth (MHB); and 15 MIC-resistant to both β-lactams in this media. Using a two-tiered strategy, isolates were first screened by standard disk diffusion for susceptibility to a combination of amoxicillin-clavulanate [AMC]. Isolates then underwent genomic sequence typing: MLST (clonal complex [CC]); ; SCC; and promoter and coding region. The combination of AMC disk susceptibility testing plus and genotyping was able to predict MRSA strains that were more or less likely to be NaHCO-responsive in vitro, with a high degree of sensitivity and specificity. Validation of this screening algorithm was performed in six strains from the overall cohort using an ex vivo model of endocarditis. This ex vivo model recapitulated the in vitro predictions of NaHCO-responsiveness vs. nonresponsiveness above in five of the six strains.
抗菌药物敏感性试验（AST）通常用于建立预测性抗生素耐药指标，以指导细菌病原体的治疗。最近，在相对较高比例的临床耐甲氧西林金黄色葡萄球菌（MRSA）菌株中发现了一种新的表型，称为“碳酸氢盐（NaHCO）反应性”，其中分离株在存在NaHCO的情况下对标准β-内酰胺类药物（苯唑西林[OXA]；头孢唑林[CFZ]）表现出体外“敏感性”，并且在实验性心内膜炎模型中对这些β-内酰胺类药物表现出体内敏感性。我们研究了对MRSA进行有针对性的表型-基因型筛查是否可以预先判定或排除NaHCO敏感性。我们研究了30株特征明确的临床MRSA血流分离株，包括15株在补充了NaHCO的 Mueller-Hinton肉汤（MHB）中对CFZ和OXA的最低抑菌浓度（MIC）敏感的菌株；以及15株在该培养基中对两种β-内酰胺类药物均耐药的菌株。采用两级策略，首先通过标准纸片扩散法对分离株进行阿莫西林-克拉维酸[AMC]组合的敏感性筛查。然后对分离株进行基因组序列分型：多位点序列分型（MLST，克隆复合体[CC]）；葡萄球菌染色体盒式 mec（SCCmec）；以及青霉素结合蛋白2a（PBP2a）启动子和编码区。AMC纸片敏感性试验加上SCCmec和PBP2a基因分型的组合能够在体外预测MRSA菌株对NaHCO反应性的高低可能性，具有高度的敏感性和特异性。使用心内膜炎的体外模型对来自整个队列的6株菌株进行了这种筛查算法的验证。该体外模型在6株菌株中的5株中重现了上述体外对NaHCO反应性与无反应性的预测。
