The Lundquist Institute, Torrance, California, USA.
Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
Antimicrob Agents Chemother. 2022 Jun 21;66(6):e0025222. doi: 10.1128/aac.00252-22. Epub 2022 May 16.
Methicillin-resistant Staphylococcus aureus (MRSA) strains are a leading cause of many invasive clinical syndromes, and pose treatment difficulties due to their resistance to most β-lactams on standard laboratory testing. A novel phenotype frequently identified in MRSA strains, termed 'NaHCO-responsiveness', is a property whereby strains are susceptible to many β-lactams in the presence of NaHCO. Specific genotypes, repression of /PBP2a expression and perturbed maturation of PBP2a by NaHCO have all been associated with this phenotype. The aim of this study was to define the relationship between specific genotypes and PBP2a substitutions, on the one hand, with NaHCO-responsiveness . Mutations were made in the ribosomal binding site (RBS -7) and at amino acid position 246 of its coding region in parental strains MW2 (NaHCO-responsive) and C36 (NaHCO- nonresponsive) to generate 'swap' variants, each harboring the other's -RBS/coding region genotypes. Successful swaps were confirmed by both sequencing, as well as predicted swap of penicillin-clavulanate susceptibility phenotypes. MW2 swap variants harboring the nonresponsive genotypes became NaHCO-nonresponsive (resistant to the β-lactam, oxacillin [OXA]), in the presence of NaHCO. Moreover, these swap variants had lost NaHCO-mediated repression of /PBP2a expression. In contrast, C36 swap variants harboring the NaHCO-responsive genotypes remained NaHCO-nonresponsive phenotypically, and still exhibited nonrepressible /PBP2a expression. These data demonstrate that in addition to the genotype, NaHCO-responsiveness may also depend on strain-specific genetic backgrounds.
耐甲氧西林金黄色葡萄球菌（MRSA）菌株是许多侵袭性临床综合征的主要原因，由于其对标准实验室检测中大多数β-内酰胺类药物的耐药性，治疗困难。在 MRSA 菌株中经常发现一种新型表型，称为“碳酸氢钠反应性”，其特征是在存在碳酸氢钠的情况下，菌株对许多β-内酰胺类药物敏感。特定基因型、/PBP2a 表达的抑制以及碳酸氢钠对 PBP2a 成熟的干扰都与这种表型有关。本研究的目的是一方面定义特定基因型和 PBP2a 取代与碳酸氢钠反应性之间的关系。在亲本菌株 MW2（碳酸氢钠反应性）和 C36（碳酸氢钠非反应性）的核糖体结合位点（RBS-7）和其编码区的 246 位氨基酸处进行突变，产生“交换”变体，每个变体都携带另一个的 -RBS/编码区基因型。通过测序以及青霉素-克拉维酸药敏表型的预测交换成功确认了交换。在碳酸氢钠存在的情况下，携带非反应性基因型的 MW2 交换变体成为碳酸氢钠非反应性（对β-内酰胺类药物，即苯唑西林[OXA]耐药）。此外，这些交换变体失去了碳酸氢钠介导的 /PBP2a 表达抑制。相比之下，携带碳酸氢钠反应性基因型的 C36 交换变体在表型上仍保持碳酸氢钠非反应性，并且仍然表现出不可抑制的 /PBP2a 表达。这些数据表明，除了基因型外，碳酸氢钠反应性还可能取决于菌株特异性的遗传背景。
