Rapid Resistance Development to Three Antistaphylococcal Therapies in Antibiotic-Tolerant Staphylococcus aureus Bacteremia. Staphylococcus aureus

Understating how antibiotic tolerance impacts subsequent resistance development in the clinical setting is important to identifying effective therapeutic interventions and prevention measures. This study describes a patient case of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia which rapidly developed resistance to three primary MRSA therapies and identifies genetic and metabolic changes selected in vivo that are associated with rapid resistance evolution. Index blood cultures displayed susceptibility to all (non-beta-lactam) antibiotics. One month after initial presentation, during the same encounter, blood cultures were again positive for MRSA, now displaying intermediate resistance to vancomycin and ceftaroline and resistance to daptomycin. Two weeks later, blood cultures were positive for a third time, still resistant to vancomycin and daptomycin but now ceftaroline-susceptible alongside a resistant-but-lower daptomycin MIC. Mutations in mprF and vraT were common to all multidrug resistant isolates whereas mutations in tagH, agrB and saeR and secondary mprF mutation emerged sequentially and transiently resulting in distinct in vitro phenotypes. The baseline mutation rate of the patient isolates was unremarkable ruling out the hypermutator phenotype as a contributor to the rapid emergence of resistance. However, the index isolates demonstrated pronounced tolerance to the antibiotic daptomycin, a phenotype that facilitates the subsequent development of resistance during antibiotic exposure. This study exemplifies the capacity of antibiotic-tolerant pathogens to rapidly develop both stable and transient genetic and phenotypic changes, over the course of a single patient encounter.

阐明抗生素耐受如何影响临床环境下后续耐药性的产生，对于确定有效的治疗干预手段与预防策略具有重要意义。本研究报道了1例耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus, MRSA）菌血症患者，其体内病原菌快速对三种主要的MRSA治疗方案产生耐药性；同时本研究鉴定了体内筛选出的、与快速耐药进化相关的遗传与代谢改变。首次血培养结果显示患者对所有（非β-内酰胺类）抗生素均敏感。初始就诊后1个月，同一次诊疗期间，血培养再次检出MRSA，此时该菌株对万古霉素、头孢他洛林呈中介耐药，对达托霉素耐药。两周后第三次血培养阳性，菌株仍对万古霉素和达托霉素耐药，但此时对头孢他洛林恢复敏感，同时达托霉素最低抑菌浓度（minimum inhibitory concentration, MIC）虽仍处于耐药范围但有所降低。所有多重耐药分离株均携带mprF与vraT基因突变；而tagH、agrB、saeR基因突变以及继发性mprF突变则依次、一过性出现，进而导致不同的体外表型。患者分离株的基础突变率并无异常，排除了高突变表型参与快速耐药出现的可能性。但首次分离株对达托霉素表现出显著的抗生素耐受特性，该表型可促进抗生素暴露过程中后续耐药性的产生。本研究证实了抗生素耐受病原菌可在单例患者的诊疗过程中，快速产生稳定及一过性的遗传与表型改变。