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Towards a better understanding of the epidemiology of naturally occurring Staphylococcus aureus intramammary infections.

机译：为了更好地了解自然发生的金黄色葡萄球菌乳房内感染的流行病学。

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摘要

Staphylococcus aureus (SA) is the most prevalent contagious mastitis pathogen on US dairies and contributes significantly to cow morbidity and mortality, and loss of revenue. Despite its prevalence, our understanding of the epidemiology of naturally occurring SA intramammary infections (IMI) is limited. The research described herein attempts to provide a basic understanding of the epidemiology of naturally occurring SA IMI.;Assuming a disease free status in quarters initially culture negative for SA and a disease positive status in quarters that were culture positive with ≥1cfu/0.01mL within the first 3 samples, the sensitivity and specificity of microbiologic culture was evaluated using 2 different inoculum volumes. Using samples collected during two studies examining shedding patterns of SA, we found that the sensitivity of microbiologic culture for detecting SA IMI using a 0.01mL inoculum was 91% and the specificity was 99.4%. Using a larger (0.1mL) inoculum the sensitivity increased to 96.8% and the specificity was 99.3%. This study demonstrated a clear benefit of using a larger inoculum volume (0.1mL) for culture in the microbiologic detection of SA IMI.;The first study evaluated daily shedding patterns of SA over three 21 day sample periods. It was demonstrated that the variability in shedding had little consequence on our ability to accurately detect a SA IMI. Although the amount of SA recovered from infected quarters varied tremendously, 97.7% of the samples were culture positive. There were no consistent patterns of shedding identified or a relationship between shedding of SA and SCC. Using pulse field gel electrophoresis (PFGE) to evaluate the association of strain type and shedding of SA, quarters grouped into PFGE pulsotype 1 shed at consistently higher levels and with comparatively little variability, (median cfu/0.01mL=100) while quarters placed in PFGE pulsotype 2 shed SA at consistently lower levels (median cfu/0.01mL=59, p 0.0001).;The second study examined naturally occurring SA IMI on 2 different dairies over an entire lactation further demonstrating a consistent recovery of SA from naturally infected quarters provided a large enough (0.1mL) inoculum was used. The sensitivity of culture was 95%, compared to 85% when using a smaller volume (0.01mL). Again, there were no consistent shedding patterns, other than that of consistently higher versus consistently lower. Quarters shedding consistently higher levels of SA were again grouped into PFGE pulsotype 1 further supporting the influence of strain type on either persistence or pathogenicity. Strains clustered into the PFGE type 1 had a median cfu/0.01mL of 83 while strains grouped into PFGE type 2 had a median cfu/0.01mL of 17.;The third study examined the effect of strain type on SA IMI cure rates. Evaluating cure by parity, 42% of the first lactation cows cured while only 10% of the multiparous cows cured. Unlike other published works, we found no significant difference (p=0.64) in cure rates in quarters with low quarter level SCC (200,000 cells/mL) and high SCC. Nor was there any significant difference (p = 0.35) when evaluating cure using composite test day information.;In conclusion, when using a larger inoculum volume, the influence of varied levels of bacterial shedding on the microbiological diagnosis of SA IMI is minimal providing a cost effective and efficient means by which to identify quarters with SA IMI. While there were no distinct shedding patterns or cycles identified in either bacterial or somatic cell count shedding, quarters infected with bacteria grouped into pulsotype 1 shed at significantly higher levels and experience fewer cures over the dry period. This finding highlights the potential application of pre-screening heifers prior to parturition for SA IMI and possible dry cow therapy providing the opportunities to cure a SA IMI before the heifer enters the milking parlor.
机译：金黄色葡萄球菌（SA）是美国奶牛场中最流行的传染性乳腺炎病原体，对奶牛的发病率和死亡率以及收入损失做出了重大贡献。尽管流行，但我们对自然发生的SA乳腺内感染（IMI）的流行病学了解有限。本文所述的研究旨在提供对自然发生的SA IMI流行病学的基本理解;假定最初SA培养阴性的地方为无病状态，而在≥1cfu/ 0.01mL的情况下培养阳性的地方为SA在前三个样品中，使用2种不同的接种量评估了微生物培养的敏感性和特异性。使用在两次研究SA脱落模式的研究中收集的样品，我们发现使用0.01mL接种物的微生物培养物检测SA IMI的敏感性为91％，特异性为99.4％。使用较大的（0.1mL）接种物，灵敏度提高到96.8％，特异性为99.3％。这项研究表明在SA IMI的微生物学检测中使用较大的接种量（0.1mL）进行培养具有明显的好处。第一项研究评估了在三个21天的采样期内SA的每日脱落模式。结果表明，脱落的变化对我们准确检测SA IMI的能力影响不大。尽管从感染区中回收的SA数量差异很大，但97.7％的样品为培养阳性。没有发现一致的脱落模式或SA与SCC脱落之间的关系。使用脉冲场凝胶电泳（PFGE）评估菌株类型与SA脱落的关联性，分组为PFGE pulsotype 1的四分之一始终保持较高水平，变异性相对较小（中位数cfu / 0.01mL = 100），而四分之一置于PFGE脉冲型2使SA的水平持续降低（中位cfu / 0.01mL = 59，p <0.0001）.;第二项研究检查了整个泌乳期在2个不同奶牛场上自然发生的SA IMI，进一步证明了SA从自然感染中持续恢复如果使用了足够大的（0.1mL）接种物，则需要四分之一的剂量。培养的灵敏度为95％，而使用较小体积（0.01mL）时为85％。再次，除了持续较高和持续较低的情况之外，没有持续的减少模式。持续释放较高水平SA的四分之一再次被归类为PFGE脉冲型1，进一步支持了菌株类型对持久性或致病性的影响。聚类为PFGE 1型的菌株的中位cfu / 0.01mL为83，而分组为PFGE 2型的菌株的中值cfu / 0.01mL为17。第三项研究考察了菌株类型对SA IMI治愈率的影响。按产值评估治愈率，有42％的第一头泌乳母牛治愈了，而只有10％的多头母牛治愈了。与其他已发表的作品不同，我们发现低四分之一水平的SCC（200,000细胞/ mL）和高SCC的季度的治愈率没有显着差异（p = 0.64）。使用综合测试日信息评估治愈情况时，也没有任何显着差异（p = 0.35）。总而言之，当使用更大的接种量时，不同水平的细菌脱落对SA IMI微生物诊断的影响极小。具有成本效益和高效的方式，可以通过SA IMI来识别住所。尽管在细菌或体细胞计数的减少中均未发现明显的脱落模式或周期，但被归类为脉冲型1的细菌感染的四分之一的脱落率明显较高，并且在干燥时期的治愈较少。这一发现突显了在分娩SA IMI之前对小母牛进行预筛查的潜在应用以及可能的干牛疗法，为在小母牛进入挤奶厅之前治愈SA IMI提供了机会。

著录项

  • 作者

    Walker, Jennifer B.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Agriculture Animal Pathology.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 180 p.
  • 总页数 180
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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