Pereira Richard, Williams Deniece R, Rossitto Paul, Adaska John, Okello Emmanuel, Champagne John, Lehenbauer Terry W, Li Xunde, Chase Jennifer, Nguyen Tran, Pires Alda F A, Atwill Edward R, Aly Sharif S
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA, USA.
Veterinary Medicine Teaching and Research Center, University of California, Davis, Tulare, CA, USA.
PeerJ. 2019 Mar 21;7:e6546. doi: 10.7717/peerj.6546. eCollection 2019.
In this study cull dairy cows from six California dairy herds were sampled seasonally over the course of a year. The objectives were to determine the prevalence of antimicrobial resistant (AMR) spp. shed in cull cow feces, and the factors associated with fecal shedding of AMR and multidrug resistant (MDR) .
Six dairy farms located in the San Joaquin Valley of California were identified and enrolled as a convenience sample. On each dairy, and once during each of the four seasons, 10 cull cows were randomly selected for fecal sampling on the day of their removal from the herd. In addition, study personnel completed a survey based on responses of the herd manager to questions related to the previous 4 month's herd management and the specific cattle sampled. Fecal samples were submitted to the California Animal Health and Food Safety laboratory for isolation. Antimicrobial resistance was evaluated using broth microdilution method and a gram-negative assay plate following Clinical Laboratory Standards Institute (CLSI) guidelines and breakpoint references. All statistical models were survey adjusted for number of animals on sampling day.
A total of 62 were isolated from 60 of the 239 fecal samples collected. For 12% (95% confidence interval (CI) [3-20]) of fecal samples a multidrug resistant was isolated. The survey-weighted results for the two most common drug classes for which isolates were resistant were tetracycline (39%; 95% CI [27-51]) and ampicillin (18%; 95% CI [9-27]). An important finding was the identification of cephalosporin as the third most common drug class for which isolates were resistant, with ceftriaxone (10%; 95% CI [2-17]) being the most common drug associated with resistance in that class. At the cow-level, reason for culling, prior treatment with antimicrobial drugs as the reason for culling was associated with higher odds of isolating an AMR isolate. At the herd-level, percent of animals monthly culled on the farm as well as number of milking cows in the herd were associated with isolation of antimicrobial resistant in cull cows.
isolated from fecal samples from cull cows were resistant to important antimicrobials, such as ceftriaxone. The most common drug classes for which isolates were resistant were tetracyclines and beta-lactams, with ampicillin, ceftriaxone and ceftiofur being the three most common drugs within the latter. Cow and herd level factors were associated with isolating antimicrobial resistant that should be further investigated for their potential role in promoting occurrence of AMR . Our results also highlight the importance of monitoring dairy cattle sent to slaughter for shedding of resistant to medically important antimicrobial drugs.
在本研究中，对来自加利福尼亚州六个奶牛场的淘汰奶牛进行了为期一年的季节性采样。目的是确定淘汰奶牛粪便中抗菌药物耐药菌（AMR）的流行情况，以及与AMR和多重耐药菌（MDR）粪便排出相关的因素。
确定并纳入了位于加利福尼亚州圣华金谷的六个奶牛场作为便利样本。在每个奶牛场，在四个季节中的每个季节都进行一次，在淘汰奶牛离开牛群当天随机选择10头进行粪便采样。此外，研究人员根据牛群管理者对与前4个月牛群管理及所采样的特定奶牛相关问题的回答完成了一项调查。粪便样本被提交至加利福尼亚动物健康与食品安全实验室进行分离培养。按照临床实验室标准协会（CLSI）指南和折点参考，使用肉汤微量稀释法和革兰氏阴性菌检测平板评估抗菌药物耐药性。所有统计模型都针对采样日的动物数量进行了调查调整。
从收集的239份粪便样本中的60份中总共分离出62株菌。在12%（95%置信区间[CI][3 - 20]）的粪便样本中分离出了多重耐药菌。分离株耐药的两种最常见药物类别经调查加权后的结果为四环素（39%；95%CI[27 - 51]）和氨苄西林（18%；95%CI[9 - 27]）。一项重要发现是头孢菌素被确定为分离株耐药的第三大最常见药物类别，其中头孢曲松（10%；95%CI[2 - 17]）是该类别中与耐药相关的最常见药物。在奶牛层面，淘汰原因以及以抗菌药物先前治疗作为淘汰原因与分离出AMR菌株的较高几率相关。在牛群层面，农场每月淘汰动物的百分比以及牛群中泌乳奶牛的数量与淘汰奶牛中抗菌药物耐药菌的分离相关。
从淘汰奶牛粪便样本中分离出的菌株对重要抗菌药物如头孢曲松耐药。分离株耐药的最常见药物类别是四环素类和β - 内酰胺类，氨苄西林、头孢曲松和头孢噻呋是后者中的三种最常见药物。奶牛和牛群层面的因素与抗菌药物耐药菌的分离相关，应进一步研究它们在促进AMR发生中的潜在作用。我们的结果还强调了监测送往屠宰场的奶牛粪便中对医学上重要抗菌药物耐药菌排出情况的重要性。
