Okello Emmanuel, ElAshmawy Wagdy R, Williams Deniece R, Lehenbauer Terry W, Aly Sharif S
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, Tulare, CA, United States.
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA, United States.
Front Vet Sci. 2023 Jul 20;10:1132810. doi: 10.3389/fvets.2023.1132810. eCollection 2023.
The aim of this study was to evaluate the effect of dry cow therapy (DCT) on the antimicrobial resistance (AMR) profile of mastitis pathogens post-calving. A repository of isolates based on a DCT trial was utilized for the current study. A stratified random survey sample of cows from the trial were identified within the strata of season, herd, and trial treatment resulting in 382 cows. All isolates from the 382 cows were selected for the current study, which identified 566 isolates from milk samples collected at dry off (S1), post-calving (S2), and at the first clinical mastitis event up to 150 days in milk (S3). The AMR profiles were determined using broth microdilution method. Less than 10% of the coagulase-negative species (CNS) isolates ( = 421) were resistant to tetracycline, ceftiofur, penicillin/novobiocin or erythromycin, while higher proportions of resistance to sulfadimethoxine (72%) and penicillin (28%) were observed. All ( isolates ( = 4) were susceptible to all tested AMD except sulfadimethoxine, to which all isolates were resistant. Similarly, all spp. ( = 37) were susceptible to penicillin, penicillin/novobiocin, and ampicillin while resistant to tetracycline (17%). All coliforms ( = 21) were susceptible to ceftiofur, but resistance was recorded for sulfadimethoxine (70%), cephalothin (56%), and tetracycline (43%). The increased resistance percent from S1 to S2 was observed in CNS isolates from AMD-treated cows, with the highest increase recorded for penicillin (12.2%). Parametric survival interval regression models were used to explore the association between antimicrobial drug (AMD) therapy at dry off and the AMR phenotype post-calving. The accelerated failure-time metric was adopted to minimum inhibitory concentration measurements to permit interpretation of model exponentiated coefficients. Models for cows with CNS isolated at both S1 and S2 showed increased resistance against cephalothin, oxacillin, and ceftiofur in cows that received DCT from the same drug class, or a class with a shared resistance mechanism. In contrast, resistance of CNS isolates to tetracycline were associated with any AMD therapy at dry off. Resistance of CNS isolates to Penicillin decreased in CNS isolates in cows that received any AMD therapy at dry off compared to those that didn't. The study provided evidence that dry-cow IMM AMD was associated with AMR post-calving.
本研究的目的是评估干奶期治疗（DCT）对产犊后乳腺炎病原体抗菌药物耐药性（AMR）谱的影响。基于一项DCT试验的分离株储存库被用于当前研究。在季节、牛群和试验处理的分层中，从试验牛中确定了一个分层随机调查样本，共382头奶牛。本研究选取了这382头奶牛的所有分离株，这些分离株来自干奶期（S1）、产犊后（S2）以及产奶期达150天内首次临床乳腺炎事件时（S3）采集的牛奶样本，共鉴定出566株分离株。采用肉汤微量稀释法测定AMR谱。凝固酶阴性菌（CNS）分离株（n = 421）中，对四环素、头孢噻呋、青霉素/新生霉素或红霉素耐药的比例不到10%，而对磺胺二甲氧嘧啶（72%）和青霉素（28%）的耐药比例较高。所有金黄色葡萄球菌分离株（n = 4）对除磺胺二甲氧嘧啶外的所有测试抗菌药物敏感，所有分离株对磺胺二甲氧嘧啶均耐药。同样，所有无乳链球菌分离株（n = 37）对青霉素、青霉素/新生霉素和氨苄西林敏感，但对四环素耐药（17%）。所有大肠菌群（n = 21）对头孢噻呋敏感，但对磺胺二甲氧嘧啶（70%）、头孢噻吩（56%）和四环素（43%）耐药。在接受抗菌药物治疗的奶牛的CNS分离株中，观察到从S1到S2耐药百分比增加，其中青霉素的增加幅度最大（12.2%）。采用参数生存区间回归模型来探讨干奶期抗菌药物（AMD）治疗与产犊后AMR表型之间的关联。采用加速失效时间指标来衡量最低抑菌浓度测量值，以便解释模型指数系数。在S1和S2均分离出CNS的奶牛模型显示，接受来自同一药物类别或具有共同耐药机制类别的DCT的奶牛，对头孢噻吩、苯唑西林和头孢噻呋的耐药性增加。相比之下，CNS分离株对四环素的耐药性与干奶期的任何AMD治疗有关。与未接受任何AMD治疗的奶牛相比，接受干奶期任何AMD治疗的奶牛的CNS分离株对青霉素的耐药性降低。该研究提供了证据表明干奶期免疫AMD与产犊后的AMR有关。
