Background

Short-term culture followed by MALDI-TOF MS is one of the most widely used methods for fast identification of microorganisms from blood cultures. The method identifies the vast majority of bloodstream infection pathogens in 2–6 h after positive blood culture. Transport time of blood culture bottles to laboratories is a major problem affecting total turnaround time. Therefore, many central laboratories establish satellite blood culture systems in other clinics and hospitals to allow blood culture bottles to be incubated immediately after sampling. However, positive blood culture bottles still need to be transported to the clinical microbiology laboratory for analysis. The aim of this study was to investigate how delayed analysis of positive blood culture bottles would affect the short-term culture followed by MALDI-TOF MS method.

Materials/methods

To simulate the effect of transportation and delayed analysis of blood culture bottles, 51 simulated blood culture bottles were incubated for 0, 2, 4 and 24 h at room temperature. After each time interval, a 2 to 4 h short-term culture followed by MALDI-TOF MS was performed. In addition, 257 prospective clinical positive blood culture bottles were analysed with the same method after a 24 h incubation at room temperature.

Results

In simulated samples, all (120/120) Gram-negative bacteria and 77/84 (91.6%) Gram-positive bacteria were accurately identified at species-level after a 2 h short-term culture, regardless of the duration of simulated transport time. In the clinical samples, 100/116 (86.2%) Gram-negative, and 44/141 (31.2%) Gram-positive bacteria were accurately identified at species-level after a 2 h short-term culture. After contaminants were excluded, 39/71 (54.9%) Gram-positive bacteria could be identified after 2 h. After a 4 h short-term culture, 112/116 (96.6%) Gram-negative, and 108/141 (76.6%) Gram-positive bacteria were accurately identified at species-level. Of the clinically relevant Gram-positive bacteria, 68/71 (95.8%) were identified at species-level after 4 h.

Conclusions

Short-term culture followed by MALDI-TOF MS can provide fast and accurate results for identification of clinically relevant bacteria, despite long transportation times from satellite laboratories. The present data shows that the method can be used for identification of microorganisms from positive blood cultures transported from satellite blood culture systems.

中文翻译：

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阳性血液培养物的延迟分析对随后MALDI-TOF MS的短期培养物性能的影响。

背景

短期培养后再进行MALDI-TOF MS分析是从血液培养物中快速鉴定微生物的最广泛使用的方法之一。该方法可在阳性血液培养后2–6小时内识别出绝大多数的血液感染病原体。血液培养瓶到实验室的运输时间是影响总周转时间的主要问题。因此，许多中央实验室在其他诊所和医院中都建立了卫星血液培养系统，以使血液培养瓶在取样后可以立即进行培养。但是，阳性血培养瓶仍需要运输到临床微生物学实验室进行分析。这项研究的目的是调查阳性血液培养瓶的延迟分析将如何影响采用MALDI-TOF MS方法进行的短期培养。

材料/方法

为了模拟运输和延迟分析血培养瓶的效果，将51个模拟血培养瓶在室温下孵育0、2、4和24小时。在每个时间间隔后，进行2至4小时的短期培养，然后进行MALDI-TOF MS。此外，在室温下孵育24小时后，使用相同的方法分析了257个预期的临床阳性血液培养瓶。

结果

在模拟样品中，无论经过模拟运输的时间长短，经过2 h短期培养后，所有物种（120/120）的革兰氏阴性菌和77/84（91.6％）的革兰氏阳性菌都可以在物种水平上准确识别。 。在临床样本中，经过2 h短期培养后，在物种水平上准确鉴定出100/116（86.2％）革兰氏阴性菌和44/141（31.2％）革兰氏阳性菌。排除污染物后，2小时后即可鉴定出39/71（54.9％）革兰氏阳性细菌。短期培养4小时后，在物种水平上准确鉴定出112/116（96.6％）革兰氏阴性菌和108/141（76.6％）革兰氏阳性菌。在临床相关的革兰氏阳性细菌中，4 h后在物种水平上鉴定出68/71（95.8％）。

结论

尽管卫星实验室的运输时间很长，但短期培养后再进行MALDI-TOF MS仍可提供快速准确的结果来鉴定临床相关细菌。本数据表明该方法可用于鉴定从卫星血液培养系统运送的阳性血液培养物中的微生物。