School of Veterinary Science, University of Queensland, Gatton, QLD, 4343, Australia.
School of Veterinary Science, University of Queensland, Gatton, QLD, 4343, Australia.
J Dairy Sci. 2024 Feb;107(2):1151-1163. doi: 10.3168/jds.2023-23838. Epub 2023 Sep 26.
This study aimed to identify the pathogens isolated from the milk of cows with clinical mastitis in the subtropical region of Australia and to determine the antimicrobial susceptibility of these bacteria. Thirty dairy herds in the subtropical dairy region were asked to submit milk samples for the first 5 cases of clinical mastitis each month for 12 mo. Samples underwent aerobic culture, and isolates were identified via MALDI-TOF mass spectrometry. Antimicrobial susceptibility was determined for Escherichia coli, Enterococcus spp., Streptococcus agalactiae, Streptococcus uberis, Streptococcus dysgalactiae, Staphylococcus aureus, and non-aureus staphylococci and mammaliicocci (NASM). Between March 2021 and July 2022, 1,230 milk samples were collected. A positive culture result was recorded for 812 (66%) of the milk samples; from these samples, 909 isolates were obtained, including 49 isolates where no identification was possible. The remaining samples were classified as having no growth (16.8%) or as being contaminated (17.2%). The most common isolates with a MALDI-TOF diagnosis (n = 909) were Strep. uberis (23.6%), followed by the NASM group (15.0%). Farms enrolled in the study were in 3 distinct locations within the subtropical dairy region: North Queensland, Southeast Queensland, and Northern New South Wales. Some variation in isolate prevalence occurred between these 3 locations. We found lower odds of a sample being positive for E. coli in North Queensland (odds ratio [OR]: 0.25; 95% confidence interval [CI]: 0.07-0.87) and higher odds in Southeast Queensland (OR: 4.01; 95% CI: 1.96-8.20) compared with the reference, Northern New South Wales. We further found higher odds of Strep. dysgalactiae in North Queensland (OR: 5.69; 95% CI: 1.85-17.54) and Southeast Queensland compared with Northern New South Wales (OR: 3.99; 95% CI: 1.73-9.22). Although some seasonal patterns were observed, season was not significant for any of the analyzed isolates. Farm-level differences in pathogen profiles were obvious. Overall, clinical mastitis pathogens had low levels of resistance to the antimicrobials tested. This research demonstrates that Strep. uberis and the NASM bacterial group are the most common pathogens causing clinical mastitis in the subtropical dairy region. It highlights the importance of understanding pathogenic causes of mastitis at the farm and regional level for targeted control and therapy.
本研究旨在鉴定澳大利亚亚热带地区临床乳腺炎奶牛乳汁中分离的病原体，并确定这些细菌的抗菌药物敏感性。要求亚热带奶牛地区的 30 个奶牛场每月为前 5 例临床乳腺炎病例提交牛奶样本，持续 12 个月。样品进行有氧培养，使用 MALDI-TOF 质谱法进行分离物鉴定。对大肠杆菌、肠球菌属、无乳链球菌、乳房链球菌、停乳链球菌、金黄色葡萄球菌和非金黄色葡萄球菌（NASM）进行抗菌药物敏感性测定。在 2021 年 3 月至 2022 年 7 月期间，共采集了 1230 份牛奶样本。812 份（66%）牛奶样本的培养结果为阳性；从这些样本中获得了 909 个分离物，其中 49 个分离物无法鉴定。其余样本被归类为无生长（16.8%）或污染（17.2%）。MALDI-TOF 诊断最常见的分离物（n=909）是乳房链球菌（23.6%），其次是 NASM 组（15.0%）。参与研究的农场位于亚热带奶牛区的 3 个不同地点：北昆士兰、昆士兰东南部和新南威尔士北部。这 3 个地点的分离物流行率存在一些差异。与参考的新南威尔士北部相比，我们发现北昆士兰（优势比 [OR]：0.25；95%置信区间 [CI]：0.07-0.87）样本中大肠杆菌呈阳性的可能性较低，而昆士兰东南部（OR：4.01；95% CI：1.96-8.20）的可能性较高。我们还发现北昆士兰（OR：5.69；95% CI：1.85-17.54）和昆士兰东南部的停乳链球菌感染的可能性高于新南威尔士北部（OR：3.99；95% CI：1.73-9.22）。尽管观察到了一些季节性模式，但季节对任何分析的分离物都没有意义。农场层面的病原体谱差异明显。总的来说，临床乳腺炎病原体对测试的抗菌药物的耐药性较低。这项研究表明，乳房链球菌和 NASM 细菌群是亚热带奶牛区引起临床乳腺炎的最常见病原体。它强调了在农场和地区层面了解乳腺炎的致病原因对于有针对性的控制和治疗的重要性。
