Laxton Claire S, Allicock Orchid M, Peno Chikondi, Lin Tzu-Yi, Koelewijn Alidia M, Toekiran Femke L, Aguilar Luna, York Anna, Wyllie Anne L
Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA.
Microbiology (Reading). 2025 Aug;171(8). doi: 10.1099/mic.0.001585.
Non-encapsulated (NESp) represent up to 19% of circulating pneumococci and exhibit high rates of genetic exchange and antimicrobial resistance. Saliva is increasingly used as a pneumococcal carriage study specimen, and we recently developed a qPCR assay to enhance carriage surveillance and characterization of NESp in saliva. Previous work has established that pneumococci remain viable in unsupplemented saliva for extended periods under various conditions. However, these findings may not be applicable to NESp. Therefore, to ensure the robustness of NESp detection in saliva-based carriage studies, we evaluated the impact of transport and storage conditions of saliva samples on NESp detection. Six NESp strains from two clinically relevant NESp null-capsule clades (NCCs), NCC1 (carrying ) and NCC2 (carrying and ), were spiked into pneumococcus ()-negative saliva and incubated through various temperatures and freeze-thaw conditions. Endpoints were processed using either culture enrichment (CE) and DNA extraction (CE-DNA), or an extraction-free method without CE, before testing for using qPCR. Detection stability was assessed using linear regression modelling over temperature, time and freeze-thaws. Following CE-DNA, detection of NESp remained stable for ≤24 or ≤72 h when stored at room temperature or 4 °C, respectively, and over two freeze-thaw cycles (-80 °C), with glycerol supplementation providing slight benefits. Stability of detection when using CE-DNA depended on NCC; detection of NCC2 strains was lower and less stable than NCC1. Compared to CE-DNA, extraction-free detection was more stable, with no significant loss over 72 h at room temperature and over three freeze-thaw cycles, and negligible differences in detection between NCC1 and NCC2 strains. Additionally, extraction-free detection of NCC1, and less so NCC2, increased over the first 24 h when stored at 20-30 °C, suggesting growth of the NESp strains in saliva. Testing of and mutants revealed that these genes increased viability when cultured in broth but did not significantly alter competitive fitness during saliva CE. The NCC1 NESp strains tested exhibited similar stability patterns in unsupplemented saliva as encapsulated pneumococci. However, the NCC2 strains tested here were less resilient during CE, likely due to competition with other oral microbes. Therefore, recovery of NCC2 NESp may be impacted by transport and storage conditions, leading to an underestimation of carriage prevalence when tested using CE-based methods. For the reliable carriage surveillance of NESp, samples should be stored at 4 °C soon after collection and at -80 °C within 72 h. Methods which directly detect DNA without CE may provide a less biassed accounting of NCC2 strains.
非包膜肺炎球菌(NESp)占循环肺炎球菌的比例高达19%,并且表现出高频率的基因交换和抗菌耐药性。唾液越来越多地被用作肺炎球菌携带情况研究的标本,我们最近开发了一种定量聚合酶链反应(qPCR)检测方法,以加强对唾液中NESp的携带监测和特性分析。先前的研究已经证实,在各种条件下,肺炎球菌在未添加营养成分的唾液中可长时间保持存活。然而,这些发现可能不适用于NESp。因此,为确保基于唾液的携带情况研究中NESp检测的稳健性,我们评估了唾液样本的运输和储存条件对NESp检测的影响。将来自两个临床相关的NESp无荚膜分支(NCCs),即NCC1(携带 )和NCC2(携带 和 )的6株NESp菌株接种到肺炎链球菌( )阴性的唾液中,并在不同温度和冻融条件下进行培养。在使用qPCR检测 之前,终点样本采用培养富集(CE)和DNA提取(CE-DNA)处理,或者采用不进行CE的免提取方法处理。通过对温度、时间和冻融次数进行线性回归建模来评估检测稳定性。采用CE-DNA方法时,NESp在室温或4℃分别储存≤24小时或≤72小时以及经过两个冻融循环(-80℃)时检测结果保持稳定,添加甘油有轻微益处。使用CE-DNA时的检测稳定性取决于NCC;NCC2菌株的检测率低于NCC1且稳定性较差。与CE-DNA相比,免提取检测更稳定,在室温下72小时内以及经过三个冻融循环均无显著损失,NCC1和NCC2菌株之间的检测差异可忽略不计。此外,在20-30℃储存时,NCC1的免提取检测在最初24小时内增加,NCC2则较少,这表明NESp菌株在唾液中生长。对 和 突变体的检测表明,这些基因在肉汤中培养时可提高 活力,但在唾液CE过程中对竞争适应性没有显著影响。所检测的NCC1 NESp菌株在未添加营养成分的唾液中的稳定性模式与包膜肺炎球菌相似。然而,此处检测的NCC2菌株在CE过程中的恢复能力较差,可能是由于与其他口腔微生物竞争所致。因此,NCC2 NESp的回收率可能会受到运输和储存条件的影响,导致使用基于CE的方法检测时携带率被低估。为了可靠地监测NESp的携带情况,样本应在采集后尽快在4℃储存,并在72小时内储存于-80℃。直接检测DNA而不进行CE的方法可能对NCC2菌株的检测偏差较小。