Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Denmark; Infectious Diseases, Department of Animal Medicine, Faculty of Veterinary Medicine, Zagazig University, Zagazig City 44511, Sharkia Province, Egypt.
Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Denmark.
J Dairy Sci. 2013 Apr;96(4):2226-2233. doi: 10.3168/jds.2012-6059. Epub 2013 Feb 10.
Aseptic procedures for milk sample collection are considered crucial for bacterial culture to avoid misdiagnosis and subsequently unnecessary treatment or culling. The objective of this field study was to investigate the effect of presampling procedures on the PCR-positivity at cycle threshold value ≤ 37 of real-time PCR assay to detect Staphylococcus aureus from composite milk samples at routine milk recordings while accounting for known cow-level risk factors. A total of 1,199 dairy cows from 6 herds with conventional milking parlors were sampled and tested by PCR in 2011. Following the farmers' routine premilking preparations, 624 cows of the 1,199 cows were randomly selected for bacterial culture preceded by presampling procedures. These procedures were: cleaning of udder teats, removing the first streams of milk, and 70% alcohol teat disinfection. Data on parity, somatic cell counts, days in milk, daily milk yield, fat %, and protein % were extracted from the Danish Cattle Database, whereas energy-corrected milk was calculated based on the latter 3. The within-herd prevalence of intramammary infections with Staph. aureus was 31%, ranging from 16 to 48% in the 6 herds. Univariable analysis showed that the presampling procedures, somatic cell counts, energy-corrected milk, and days in milk were significantly associated with PCR-positivity, whereas parity was not significant. A multivariable model with herd as random effect showed that presampling procedures decreased the chance of being PCR-positive to 0.75 (95% CI; 0.58-0.97) compared with cows where the presampling procedures were not carried out. In conclusion, presampling procedures decreased the cow's chance of being PCR-positive to Staph. aureus. Presampling procedures appeared to improve the specificity of PCR for detection of Staph. aureus by reducing false positives through destruction of Staph. aureus bacteria colonizing or contaminating the teat skin, orifice, and canal. Random herd effects accounted for only 8.9%, indicating that the cluster effect due to herd management on the PCR positivity to Staph. aureus was virtually negligible.
无菌的牛奶样本采集程序对于细菌培养至关重要，以避免误诊和随后的不必要治疗或淘汰。本现场研究的目的是调查采样前程序对实时 PCR 检测金黄色葡萄球菌的循环阈值（Ct 值）≤37 的 PCR 阳性率的影响，同时考虑到已知的奶牛水平风险因素。2011 年，从 6 个常规挤奶厅的奶牛场采集了 1199 头奶牛的牛奶样本，并通过 PCR 进行了检测。在农民进行常规挤奶前准备后，从 1199 头奶牛中随机选择 624 头进行细菌培养，并进行采样前程序。这些程序是：清洗乳房乳头、去除最初的奶流、用 70%酒精消毒乳头。胎次、体细胞计数、泌乳天数、日产量、脂肪%和蛋白质%等数据从丹麦奶牛数据库中提取，而能量校正奶则基于后 3 项计算。金黄色葡萄球菌的乳腺炎感染的群内流行率为 31%，6 个牛场的范围为 16%至 48%。单变量分析表明，采样前程序、体细胞计数、能量校正奶和泌乳天数与 PCR 阳性显著相关，而胎次则不显著。以 herd 为随机效应的多变量模型表明，与未进行采样前程序的奶牛相比，采样前程序使奶牛 PCR 阳性的可能性降低到 0.75（95%CI；0.58-0.97）。总之，采样前程序降低了奶牛金黄色葡萄球菌 PCR 阳性的可能性。采样前程序通过破坏定植或污染乳头皮肤、孔口和导管的金黄色葡萄球菌细菌，似乎提高了 PCR 检测金黄色葡萄球菌的特异性，从而减少了假阳性。随机 herd 效应仅占 8.9%，表明由于 herd 管理对金黄色葡萄球菌 PCR 阳性的聚类效应几乎可以忽略不计。
