Abstract

Intramammary bacterial infection, the most common cause of mastitis, is the most costly disease in dairy cattle in the US and reason for antibiotic usage. Ceftiofur, a third-generation cephalosporin, is generally used to treat such disease, but it has a high treatment failure rate. Though the reason is not known clearly, it is hypothesized that multiple factors are associated with the treatment failure. In this study, we analyzed 169 milk samples from cows with mastitis in two independent dairy farms (Farm A and B) in which 19.4% (Farm A) and 14.3% (Farm B) of the antibiotic treated cows were not cured. The prevalence of cephalosporin-resistant bacteria (CRB) in milk was 72.0% and 42.1% in Farm A and B, respectively. Nineteen and nine bacterial genera were identified in Farm A and B respectively, with the most abundant genus being Staphylococcus (27.1%; Farm A) and Bacillus (63.5%; Farm B). However, no strong relationship between the treatment failure rate and the CRB prevalence was observed. Furthermore, the metagenomic analysis showed no significant differences in the α- and β-diversities of microbiota in milk samples from cured and uncured cows, suggesting that antibiotic-resistant bacteria were not the sole reason for the antibiotic treatment failure.

Key Points

• The mastitic milk samples had high prevalence of cephalosporin-resistant bacteria (CRB).

• The CRB identified belong to diversified species.

• Antibiotic treatment failure was not solely caused by the abundance of CRB.

中文翻译：

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乳牛奶中多种β-内酰胺类抗生素耐药细菌和微生物群落

摘要

乳腺内细菌感染是乳腺炎的最常见原因，是美国奶牛中最昂贵的疾病，也是使用抗生素的原因。头孢噻呋，第三代头孢菌素，通常用于治疗这种疾病，但是其治疗失败率很高。尽管尚不清楚原因，但据推测是多种因素与治疗失败有关。在这项研究中，我们分析了两个独立的奶牛场（农场A和B）中有169例乳腺炎奶牛的牛奶样本，其中有19.4％（农场A）和14.3％（农场B）的抗生素未治愈。农场A和B中牛奶中的头孢菌素抗性细菌（CRB）的流行率分别为72.0％和42.1％。在农场A和B中分别鉴定出19个和9个细菌属，其中最丰富的属是金黄色葡萄球菌（27.1％;农场A）和芽孢杆菌（63.5％;农场B）。但是，未观察到治疗失败率与CRB患病率之间有很强的关系。此外，宏基因组学分析显示，在治愈和未治愈的奶牛的牛奶样品中，微生物群的α-和β-多样性没有显着差异，这表明抗药性细菌并不是导致抗生素治疗失败的唯一原因。

关键点

•乳脂样品中头孢菌素耐药菌（CRB）的患病率很高。

•确定的CRB属于多种物种。

•抗生素治疗失败不仅是由于CRB丰富引起的。