Department of Animal Health and Antimicrobial Strategies, Swedish Veterinary Agency, 751 89, Uppsala, Sweden.
Acta Vet Scand. 2024 Nov 5;66(1):58. doi: 10.1186/s13028-024-00781-7.
Bovine respiratory disease (BRD) is common in intensively raised cattle and is often treated with antibiotics. For practitioners, knowledge of the bacteria involved in an outbreak and their antibiotic susceptibility is warranted. To this end, samples from the upper or lower respiratory tract of calves can be submitted for bacteriological culture and susceptibility testing of relevant isolates. However, it is debated whether isolates from the upper respiratory tract are representative of bacteria causing infections in the lower respiratory tract. In this study, we used MALDI-TOF MS, multilocus sequence typing (MLST) and core-genome multilocus sequence typing (cgMLST) to compare culture results of 219 paired samples (sample pairs) of deep nasal swabs (DNS) and tracheobronchial lavage (TBL). The sample pairs came from 171 calves in 30 calf groups across 25 farms with 48 calves sampled twice.
The predominant bacterial pathogen was Pasteurella multocida, which was isolated from 37.4% of DNS and 22.4% of TBL. There was no statistically significant difference in isolation frequency of P. multocida between calves considered healthy and those suspected for BRD for DNS (P = 0.778) or TBL (P = 0.410). Among the 49 sample pairs where P. multocida was isolated from TBL, the same species was isolated from DNS in 29 sample pairs (59.2%). Isolates from 28 of these sample pairs were evaluated by MLST, and in 24 pairs (86.0%) P. multocida from DNS and TBL were of the same sequence type (ST). Moreover, cgMLST showed that the genetic distance between isolates within 21 of the 28 sample pairs (75.0%), was less than two alleles, and DNS and TBL isolates were considered identical. In seven sample pairs (25%), the genetic distance was greater, and DNS and TBL isolates were considered nonidentical.
Pasteurella multocida was readily isolated from DNS and in calves where this species was isolated also from TBL, DNS and TBL isolates were identical in 75% of the sample pairs. This suggests that during an outbreak of BRD, submission of DNS samples from 4 to 6 calves could be a convenient approach for practitioners seeking guidance on P. multocida present in the lower respiratory tract and their antibiotic susceptibility.
牛呼吸道疾病（BRD）在集约化饲养的牛群中很常见，通常用抗生素治疗。对于从业者来说，了解疫情中涉及的细菌及其抗生素敏感性是有必要的。为此，可以对犊牛的上呼吸道或下呼吸道样本进行细菌培养和相关分离物的药敏试验。然而，上呼吸道分离物是否能代表引起下呼吸道感染的细菌，这一点存在争议。在这项研究中，我们使用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）、多位点序列分型（MLST）和核心基因组多位点序列分型（cgMLST）对上呼吸道深鼻拭子（DNS）和气管支气管灌洗（TBL）的 219 对样本（样本对）的培养结果进行了比较。这些样本对来自 30 个牛群的 171 头犊牛，每个牛群有 48 头犊牛，其中 2 头犊牛被重复采样。
主要的病原菌是多杀性巴氏杆菌，从 37.4%的 DNS 和 22.4%的 TBL 中分离出来。对于被认为健康的犊牛和疑似 BRD 的犊牛，DNS 中分离出多杀性巴氏杆菌的分离频率没有统计学差异（P=0.778）或 TBL（P=0.410）。在 49 对 TBL 中分离出多杀性巴氏杆菌的样本中，有 29 对（59.2%）从 DNS 中分离出相同的物种。对其中 28 对样本进行 MLST 评估，24 对（86.0%）DNS 和 TBL 的多杀性巴氏杆菌为相同的序列型（ST）。此外，cgMLST 显示，在 28 对样本中的 21 对（75.0%），分离株之间的遗传距离小于两个等位基因，并且 DNS 和 TBL 分离株被认为是相同的。在 7 对样本（25%）中，遗传距离较大，DNS 和 TBL 分离株被认为是不同的。
多杀性巴氏杆菌很容易从 DNS 中分离出来，而且在这种细菌也从 TBL 中分离出来的犊牛中，75%的样本对中 DNS 和 TBL 分离株是相同的。这表明，在 BRD 爆发期间，从 4 到 6 头犊牛中采集 DNS 样本，对于寻求有关下呼吸道中多杀性巴氏杆菌及其抗生素敏感性的指导的从业者来说，可能是一种方便的方法。
