Department of Medical Microbiology, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway.
Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
PLoS One. 2022 Jul 8;17(7):e0270256. doi: 10.1371/journal.pone.0270256. eCollection 2022.
Thymine auxotrophic in vitro mutants of Escherichia coli were first reported in the mid-20th century. Later, thymine-dependent clinical strains of E. coli as well as other Enterobacterales, Enterococcus faecalis and Staphylococcus aureus have been recognized as the cause of persistent and recurrent infections.
The aim of this study was to characterize the phenotype and investigate the molecular basis of thymine auxotrophy in ten E. coli isolates obtained at different time points from a patient with recurrent bloodstream infection (BSI) due to a chronic aortic graft infection treated with Trimethoprim/sulfamethoxazole (TMP-SMX).
Clinical data was obtained from hospital records. Growth characterization and antimicrobial susceptibility testing to TMP-SMX was performed on M9 agar and in MH broth with different thymine concentrations (0.5, 2, 5, 10 and 20 μg/mL), on Mueller-Hinton (MH) and blood agar. Whole genome sequencing (WGS) was performed on all E. coli isolates.
E. coli were isolated from ten consecutive BSI episodes from a patient with chronic aortic graft infection. Six of these isolates were resistant to TMP-SMX when assayed on blood agar. Growth experiments with added thymine confirmed that these isolates were thymine-dependent (thy-), and revealed growth defects (slower growth rate and smaller colony size) in these isolates relative to thy+ isolates (n = 4). WGS indicated that all isolates were of the same clonal lineage of sequence type 7358. Genomic analysis revealed a G172C substitution in thyA in all TMP-SMX resistant isolates, while mutations affecting genes involved in the deoxyribose salvage pathway (deoB and deoC) were identified in eight isolates.
This case highlights the risk of resistance development to TMP-SMX, especially for long-term treatment, and the possible pitfalls in detection of growth-deficient subpopulations from chronic infections, which could lead to treatment failure.
20 世纪中叶首次报道了胸腺嘧啶营养缺陷型大肠杆菌体外突变株。后来，依赖胸腺嘧啶的大肠杆菌临床株以及其他肠杆菌科、粪肠球菌和金黄色葡萄球菌被认为是持续性和复发性感染的原因。
本研究旨在对从一名因慢性主动脉移植物感染接受甲氧苄啶/磺胺甲恶唑（TMP-SMX）治疗的患者反复血流感染（BSI）中获得的 10 株不同时间点的大肠杆菌分离株的表型进行特征描述，并研究其胸腺嘧啶营养缺陷的分子基础。
从医院记录中获取临床数据。在 M9 琼脂和含有不同胸腺嘧啶浓度（0.5、2、5、10 和 20μg/ml）的 MH 肉汤中，在 Mueller-Hinton（MH）和血琼脂上进行生长特征和 TMP-SMX 药敏试验。对所有大肠杆菌分离株进行全基因组测序（WGS）。
从一名慢性主动脉移植物感染患者的连续 10 次 BSI 中分离出大肠杆菌。这些分离株中有 6 株在血琼脂上检测到对 TMP-SMX 耐药。添加胸腺嘧啶的生长实验证实这些分离株是依赖胸腺嘧啶的（thy-），并且相对于 thy+分离株（n=4），这些分离株的生长缺陷（生长速度较慢和菌落较小）。WGS 表明所有分离株均为同一克隆谱系的 7358 型序列。基因组分析显示，所有 TMP-SMX 耐药分离株的 thyA 基因均存在 G172C 取代，而在 8 株分离株中发现了影响脱氧核糖核苷酸补救途径（deoB 和 deoC）相关基因的突变。
本案例强调了 TMP-SMX 耐药发展的风险，特别是对于长期治疗，以及在检测慢性感染中生长缺陷亚群时可能存在的陷阱，这可能导致治疗失败。
