Automatic flushing of milking clusters between milking events is a control measure aimed at reducing transmission of mastitis pathogens from infectious milk to a subsequently milked cow. We evaluated the effect of flushing with cold water and flushing with water containing peracetic acid (PAA) on the concentration of Staphylococcus aureus in teat cup liners. Thirty-two clusters in a swing-over milking parlor (Dairymaster, Causeway, Ireland) were subjected to a simulated milking with S. aureus-contaminated milk. Sixteen clusters were not flushed (controls), whereas 8 clusters were flushed with cold water (966 ± 32 mL) and 8 clusters were flushed with water containing PAA (200 mL/mL). A random teat cup in each cluster was sampled by rinsing with a phosphate buffer. Teat cup samples were cultured on the day following collection on Baird-Parker plates to determine the concentration of S. aureus. In teat cup samples from control clusters, the mean concentration of S. aureus was 2.8 × 105 cfu/mL. The concentration of S. aureus was zero in teat cup samples from clusters flushed with cold water. In teat cup samples from clusters flushed with water containing PAA, the concentration of S. aureus was in general reduced compared with control clusters, but S. aureus was not removed completely. However, the automatic cluster flushing did not function properly when clusters were flushed with water containing PAA; thus, results reflected the effect of inadequate function rather than the effect of adding disinfectant to the flushing water. Before the main study, we conducted a pilot study to evaluate whether teat cup sampling with swabs and sample analysis with quantitative PCR were appropriate methods for the main study. Specifically, we evaluated the effect of swab sample mass on detection of S. aureus by quantitative PCR in the laboratory, Further, we compared PCR and bacterial culture on detection of S. aureus in a suspension following disinfection of the suspension with PAA. We sampled 20 identical S. aureus suspensions for culture and PCR by swabs before and after disinfection with PAA. Swab sample mass was determined by differential weighing and contributed to 46% of the variation observed in detection of S. aureus by PCR. Following disinfection with PAA, S. aureus remained detectable by PCR, although culturability ceased. Based on these results, we sampled teat cups in the main study with a buffer rinse and quantified S. aureus in the samples by bacterial culture. We concluded that automatic cluster flushing with cold water was effective in removing S. aureus from teat cup liners and that addition of PAA was therefore not necessary.

中文翻译：

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自动集群冲洗对奶杯杯衬中金黄色葡萄球菌浓度的影响。

在挤奶事件之间自动冲洗挤奶集群是一种控制措施，旨在减少乳腺炎病原体从传染性牛奶传播到随后挤奶的母牛。我们评估了用冷水冲洗和用含过氧乙酸（PAA）冲洗的水对奶杯杯衬中金黄色葡萄球菌浓度的影响。在隔间挤奶厅（Dairymaster，爱尔兰铜锣，爱尔兰）中的三十二个奶牛群受到金黄色葡萄球菌污染的牛奶进行了模拟挤奶。未冲洗（对照）16个簇，而用冷水（966±32 mL）冲洗8个簇，并用含PAA（200 mL / mL）的水冲洗8个簇。通过用磷酸盐缓冲液冲洗，在每个簇中随机抽取一个奶头杯。在收集后的第二天，将乳头杯样品在Baird-Parker板上培养，以确定金黄色葡萄球菌的浓度。在来自对照组的奶杯样品中，金黄色葡萄球菌的平均浓度为2.8×105 cfu / mL。在用冷水冲刷的乳头杯样品中，金黄色葡萄球菌的浓度为零。在用含PAA的水冲刷的乳头杯样品中，与对照组相比，金黄色葡萄球菌的浓度通常降低，但金黄色葡萄球菌并未完全去除。但是，当用含PAA的水冲洗簇时，自动簇冲洗功能将无法正常工作。因此，结果反映了功能不足的影响，而不是在冲洗水中添加消毒剂的影响。在学习之前 我们进行了一项初步研究，以评估使用棉签进行的奶杯采样以及采用定量PCR进行样品分析是否是主要研究的适当方法。具体而言，我们在实验室中通过定量PCR评估了拭子样品质量对金黄色葡萄球菌检测的影响。此外，我们比较了用PAA消毒悬浮液后，PCR和细菌培养对悬浮液中金黄色葡萄球菌检测的影响。在用PAA消毒之前和之后，我们取样了20个相同的金黄色葡萄球菌悬浮液，用于通过拭子进行培养和PCR。拭子样品质量通过差重称量确定，占通过PCR检测金黄色葡萄球菌时观察到的变异的46％。用PAA消毒后，尽管可培养性已停止，但通过PCR仍可检测到金黄色葡萄球菌。根据这些结果，在主要研究中，我们使用缓冲液冲洗对奶杯进行采样，并通过细菌培养对样品中的金黄色葡萄球菌进行了定量。我们得出的结论是，用冷水自动簇冲洗可以有效地从乳头杯衬套中去除金黄色葡萄球菌，因此不需要添加PAA。