University College Dublin, Belfield, Dublin, Ireland.
Irish Equine Centre, Johnstown, Naas, Co. Kildare Ireland.
Ir Vet J. 2015 Oct 6;68:23. doi: 10.1186/s13620-015-0051-4. eCollection 2015.
Rhodococcus equi is a gram positive, intracellular pathogen of foals worldwide. The aim of this study was to determine whether there was an increasing resistance occurring in Rhodococcus equi towards the antibiotics rifampin and erythromycin over a seven year period. The investigation was carried out with the use of E test strips (epsilometers) for rifampin and erythromycin in order to determine the Minimum Inhibitory Concentrations (MIC) values of Rhodococcus equi to these antibiotics.
The main results of this study found that the mean MICs were higher for erythromycin than for rifampin for every year analysed apart from 2008. The results highlight that 75 % (6/8) of the mean MICs for erythromycin were above the threshold of susceptibility of 0.5 μg/ml and one of the yearly mean MICs for rifampin (2008) was above the level of ≤ 1 μg/ml. Two soil samples analysed had high MIC values of 2 μg/ml and 3 μg/ml for rifampin and erythromycin respectively. These samples can be said to have acquired resistance as they are above 1 μg/ml.
The significance of these findings is that R. equi is already a problematic pathogen to treat and if the bacteria keeps gaining resistance to these antibiotics at rate that has been shown over the last decade, then a new form of treatment will have to be introduced. Further research into the genomics of Rhodococcus equi will, in time, shed more light on possible alternatives such as vaccines or new, more effective antimicrobials.
马红球菌是一种革兰氏阳性、细胞内病原体，存在于全世界的幼驹中。本研究的目的是确定在过去七年中，马红球菌对利福平（rifampin）和红霉素（erythromycin）这两种抗生素的耐药性是否有所增加。该研究使用 E 测试条（epsilometers）来测定利福平（rifampin）和红霉素（erythromycin）的最小抑菌浓度（Minimum Inhibitory Concentrations，MIC）值，以确定马红球菌对这两种抗生素的耐药性。
本研究的主要结果发现，除了 2008 年之外，每年的平均 MIC 值对于红霉素（erythromycin）都高于利福平（rifampin）。结果表明，75%（6/8）的红霉素（erythromycin）平均 MIC 值高于 0.5μg/ml 的药敏阈值，而利福平（rifampin）的一个年平均 MIC 值（2008 年）高于≤1μg/ml 的水平。分析的两个土壤样本的利福平（rifampin）和红霉素（erythromycin）的 MIC 值分别高达 2μg/ml 和 3μg/ml。可以说这些样本已经获得了耐药性，因为它们高于 1μg/ml。
这些发现的意义在于，马红球菌已经是一种难以治疗的病原体，如果细菌继续以过去十年所显示的速度对这些抗生素产生耐药性，那么就必须引入新的治疗方法。对马红球菌的基因组学进行进一步研究，将有助于及时发现疫苗或新的、更有效的抗菌药物等可能的替代方法。
