Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA, USA.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, USA.
Vet Microbiol. 2019 May;232:74-78. doi: 10.1016/j.vetmic.2019.04.008. Epub 2019 Apr 6.
Rhodococcus equi causes severe pneumonia in foals and is most often recognized in people as an opportunistic pathogen. Longitudinal studies examining antimicrobial-resistant R. equi from environmental samples are lacking. We hypothesized that antimicrobial-resistant R. equi would be detectable in the ground (pasture soil or stall bedding) and air at breeding farms with previous documentation of foals infected with resistant isolates, and that concentrations of resistant isolates would increase over time during the foaling season. In this prospective cohort study, ground and air samples were collected from stalls and paddocks in January, March, May and July of 2018 at 10 horse-breeding farms with history of foal pneumonia attributed to macrolide- or Rifampicin-resistant R. equi. Environmental samples were cultured in the presence and absence of macrolides and Rifampicin to select for resistant organisms. Data were analyzed with linear mixed-effects and Hurdle models. Concentrations of total R. equi in bedding or air of stalls were significantly (P < 0.05) higher in January than other months. The proportion of resistant R. equi in soil samples from paddocks was significantly (P < 0.05) higher than stall bedding during all months. For each month, air samples from paddocks had a significantly (P < 0.05) higher proportion of resistant isolates than those from stalls. Fifty-five percent of resistant soil isolates and 34% of resistant air isolates were considered virulent by identification of the vapA gene. Concentrations of resistant R. equi isolates did not increase over time during the foaling season. Antimicrobial-resistant R. equi can persist in the environment at farms with a history of pneumonia caused by resistant R. equi infections, and exposure to resistant isolates in paddocks and stalls appears stable during the foaling season. Resistant isolates in the environment not only pose a risk for disease but also can serve as a repository for dissemination of resistance genes.
马红球菌引起驹肺炎，在人群中常被认为是机会性病原体。缺乏对环境样本中抗微生物药物耐药马红球菌的纵向研究。我们假设，在有先前记录表明驹感染耐药分离株的肺炎的繁殖农场，可在地面（牧场土壤或马厩垫料）和空气中检测到抗微生物药物耐药马红球菌，并且在产驹季节期间，耐药分离株的浓度会随时间增加。在这项前瞻性队列研究中，于 2018 年 1 月、3 月、5 月和 7 月，在 10 个有记录表明驹肺炎归因于大环内酯类或利福平耐药马红球菌的繁殖农场，从马厩和围场中采集地面和空气样本。环境样本在存在和不存在大环内酯类和利福平的情况下进行培养，以选择耐药生物体。使用线性混合效应和障碍模型分析数据。垫料或马厩空气的总马红球菌浓度在 1 月显著（P<0.05）高于其他月份。围场土壤样本中耐药马红球菌的比例在所有月份均显著（P<0.05）高于马厩垫料。对于每个月，围场的空气样本中的耐药分离株比例均显著（P<0.05）高于马厩样本。55%的耐药土壤分离株和 34%的耐药空气分离株通过 vapA 基因的鉴定被认为具有毒力。在产驹季节期间，耐药马红球菌分离株的浓度并未随时间增加。在有大环内酯类或利福平耐药马红球菌感染引起肺炎史的农场中，环境中可长期存在抗微生物药物耐药马红球菌，并且在产驹季节期间，围场和马厩中的耐药分离株的暴露似乎保持稳定。环境中的耐药分离株不仅构成疾病风险，而且还可以作为耐药基因传播的储存库。
