Guangdong Provincial Key Laboratory of Gastroenterology, Department of Gastroenterology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
Divisions of Gastroenterology, Massachusetts.
Clin Infect Dis. 2020 Jun 10;70(12):2628-2633. doi: 10.1093/cid/ciz727.
Most Clostridioides difficile toxinogenic strains produce both toxins A and B (A+B+), but toxin A-negative, toxin B-positive (A-B+) variants also cause disease. We report the identification of a series of pathogenic clinical C. difficile isolates that produce high amounts of toxin A with low or nondetectable toxin B.
An ultrasensitive, quantitative immunoassay was used to measure toxins A and B in stool samples from 187 C. difficile infection (CDI) patients and 44 carriers. Isolates were cultured and assessed for in vitro toxin production and in vivo phenotypes (mouse CDI model).
There were 7 CDI patients and 6 carriers who had stools with detectable toxin A (TcdA, range 23-17 422 pg/mL; 5.6% of samples overall) but toxin B (TcdB) below the clinical detection limit (<20 pg/mL; median TcdA:B ratio 17.93). Concentrations of toxin A far exceeded B in in vitro cultures of all 12 recovered isolates (median TcdA:B ratio 26). Of 8 toxin A>>B isolates tested in mice, 4 caused diarrhea, and 3 of those 4 caused lethal disease. Ribotyping demonstrated strain diversity. TcdA-predominant samples were also identified at 2 other centers, with similar frequencies (7.5% and 6.8%).
We report the discovery of clinical pathogenic C. difficile strains that produce high levels of toxin A but minimal or no toxin B. This pattern of toxin production is not rare (>5% of isolates) and is consistently observed in vitro and in vivo in humans and mice. Our study highlights the significance of toxin A in human CDI pathogenesis and has important implications for CDI diagnosis, treatment, and vaccine development.
大多数艰难梭菌产毒株同时产生毒素 A 和 B（A+B+），但也有一些毒素 A 阴性、毒素 B 阳性（A-B+）的变体引起疾病。我们报告了一系列致病的临床艰难梭菌分离株的鉴定，这些分离株产生大量的毒素 A，但毒素 B 的量较低或无法检测到。
使用超灵敏定量免疫测定法检测了 187 例艰难梭菌感染（CDI）患者和 44 例携带者的粪便样本中的毒素 A 和 B。对分离株进行培养，并评估其体外毒素产生和体内表型（小鼠 CDI 模型）。
有 7 例 CDI 患者和 6 例携带者的粪便中可检测到毒素 A（TcdA，范围为 23-17422 pg/mL；总体样本的 5.6%），但毒素 B（TcdB）低于临床检测限（<20 pg/mL；TcdA:TcdB 比值中位数为 17.93）。在所有 12 株回收分离株的体外培养物中，毒素 A 的浓度远远超过 B（TcdA:TcdB 比值中位数为 26）。在 8 株毒素 A>>B 的分离株中，有 4 株在小鼠中引起腹泻，其中 3 株引起致死性疾病。核糖体分型显示出菌株的多样性。在另外 2 个中心也发现了 TcdA 优势样本，其频率相似（分别为 7.5%和 6.8%）。
我们报告了发现临床致病性艰难梭菌菌株，这些菌株产生高水平的毒素 A，但毒素 B 水平较低或无法检测到。这种毒素产生模式并不罕见（>5%的分离株），并且在体外和体内的人类和小鼠中都能观察到。我们的研究强调了毒素 A 在人类 CDI 发病机制中的重要性，对 CDI 的诊断、治疗和疫苗开发具有重要意义。
