Rhodococcus equi (Prescottella equi) vaccines; the future of vaccine development

For decades researchers have been targeting prevention of Rhodococcus equi (Rhodococcus hoagui/Prescottella equi) by vaccination and the horse breeding industry has supported the ongoing efforts by researchers to develop a safe and cost effective vaccine to prevent disease in foals. Traditional vaccines including live, killed and attenuated (physical and chemical) vaccines have proved to be ineffective and more modern molecular‐based vaccines including the DNA plasmid, genetically attenuated and subunit vaccines have provided inadequate protection of foals. Newer, bacterial vector vaccines have recently shown promise for R. equi in the mouse model. This article describes the findings of key research in R. equi vaccine development and looks at alternative methods that may potentially be utilised.     

Efficacy of Gamithromycin for the Treatment of Foals with Mild to Moderate Bronchopneumonia

Background

Gamithromycin is active in vitro against the bacterial agents most commonly associated with bronchopneumonia in older foals. However, the clinical efficacy and safety of this drug have not been investigated.

Hypothesis

Gamithromycin is effective for the treatment of bronchopneumonia in foals.

Animals

One hundred and twenty‐one foals on a farm endemic for infections caused by Rhodococcus equi.

Methods

In a controlled, randomized, and double blinded clinical trial, foals with ultrasonographic evidence of pulmonary abscesses (abscess score 8.0–20 cm) were randomly allocated in 3 treatment groups: (1) gamithromycin IM q7 days (n = 40); (2) azithromycin with rifampin, PO q24h (n = 40); or (3) no antimicrobial treatment (controls; n = 41). Physical examination and thoracic ultrasonography were performed by individuals unaware of treatment group assignment. Foals that worsened were removed from the study.

Results

The proportion of foals that recovered without the need to be removed from the study was significantly higher for foals treated with gamithromycin (38 of 40) or azithromycin with rifampin (39 of 40) than for controls (32 of 41). Treatment with gamithromycin or with azithromycin‐rifampin resulted in a significantly faster decrease in the clinical score and abscess score compared to the controls. Adverse reactions characterized by colic (n = 18) and hind limb lameness (n = 14) were observed only in foals treated with gamithromycin.

Conclusion and Clinical Importance

Gamithromycin was noninferior to azithromycin with rifampin for the treatment of bronchopneumonia in the study population but had a higher frequency of adverse reactions.     

Rhodococcus equi occipital bone osteomyelitis,septic arthritis and meningitis in a neurological foal

This case report describes a 3‐month‐old female Thoroughbred foal that presented following the acute onset of apparent respiratory distress, abnormal head carriage and severe neurological deficits referable to the brainstem or cranial cervical spinal cord. Ultrasonography revealed an abscessing pneumonia. Radiographs did not show evidence of bony pathology at the atlanto‐occipital region, an area consistent with the observed neurological deficits. With magnetic resonance imaging, atlantal and occipital osteomyelitis, atlanto‐occipital septic arthritis, and atlanto‐axial synovitis were diagnosed. Brainstem meningitis and extradural compression were also revealed. Culture of the right occipitoatlantal joint and cerebrospinal fluid yielded a pure culture of Rhodococcus equi. These findings and multifocal R. equi abscessation were confirmed at necropsy.     

SONOGRAPHIC CHARACTERISTICS OF INTRAABDOMINAL ABSCESSATION AND LYMPHADENOPATHY ATTRIBUTABLE TO RHODOCOCCUS EQUI INFECTIONS IN FOALS

The sonographic characteristics of intraabdominal abscesses in 11 foals and intraabdominal lymphadenitis in five foals with Rhodococcus equi infections are presented. Intraabdominal abscesses were usually present in the ventral abdomen adjacent to the ventral body wall, well‐marginated, and contained a mixed or complex echo pattern. Lymphadenitis appeared as singular or multiple clusters of lymph nodes of mixed echogenicity adjacent to any portion of the gastrointestinal tract or body wall. Sonographic findings were supported by necropsy examinations, but sonographic measurements consistently underestimated the size of abscess.     

用红球菌生产类胡萝卜素的研究

从土壤中分离到一株黄色色素产生菌,经鉴定该菌为红球菌属（Rhodococcus)的一个种, 所产色素为类胡萝卜素。研究了pH、接种量、发酵周期、不同培养基、C源、N源种类等因素对该菌类胡萝卜素生成量的影响。结果表明,采用大米水解糖培养基、pH6.3、接种量为8%时色素产率最高。在最适条件下细胞生物量可达13.6 g/L,色素量为1.5 g/L。     

多菌灵降解菌XJ-D的分离鉴定及特性研究

为了进行多菌灵污染土壤的生物修复,笔者从长期施用多菌灵农药的葡萄园中分离筛选得到1株多菌灵降解菌XJ-D,经Biolog微生物自动分析系统和16S rDNA序列比对,以及系统聚类分析等鉴定菌株XJ-D为红串红球菌（Rhodococcus erythropolis）。多菌灵降解菌XJ-D可利用多菌灵为唯一碳源、氮源进行生长,将其接种在600 mg/L多菌灵的无机盐培养基中,11天时多菌灵的降解率达99.0%,平均降解能力为52.87 mg/(L?d)。     

喀什地区杏树吐伦球坚蚧经济阈值的初步研究

在喀什疏附县,初步研究了杏树重要害虫吐伦球坚蚧(Rhodococcus turanicus Arch.)种群密度与杏树产量的关系,初步探明了吐伦球坚蚧对杏树的为害损失率,通过回归分析,建立了杏树损失率与吐伦球坚蚧种群密度的回归模型为:y=15.724 Ln(X)+59.543(Y为产量损失率,X为吐伦球坚蚧种群密度,单位为头/cm2),相关系数(R2)为0.896;在此基础研究了在不同价格与不同药剂防治吐伦球坚蚧的经济阈值和投入产出比.     

Frequency of Rhodococcus equi in Feces of Mares in Central Kentucky

Rhodococcus equi (R equi) pneumonia is an important cause of disease and death in foals. Feces from mares can contain R equi, including virulent R equi, and thus may act as a source of the bacteria at horse breeding farms. A previous report documented that every mare at a farm in central Kentucky shed virulent R equi in at least one of four fecal samples collected serially during the periparturient period. The objective of this study was to assess the extent to which this high prevalence of fecal shedding could be replicated at other horse breeding farms. The frequency of detection of R equi and virulent R equi in fecal samples was studied among 131 mares from 24 farms in central Kentucky. The proportions of fecal samples from mares containing R equi and virulent R equi were 95% and 76%, respectively. These findings indicate that R equi and virulent R equi may be isolated with high frequency from feces of mares at breeding farms in central Kentucky, and that mares are a source of virulent R equi for the environment of their foals.     

响应面法优化紫红红球菌的发酵培养基

采用响应面法优化腈水合酶产生紫红红球菌的发酵培养基。以天冬酰胺、磷酸氢二钾、磷酸二氢钾、酵母抽提物、脲素、氯化钴为影响因子,以菌体干质量和酶活为响应值,进行多元二次响应回归分析,结果显示,最优培养基为:天冬酰胺含量0.04%、磷酸氢二钾0.05%、磷酸二氢钾0.03%、酵母抽提物(FM818)5.48%、脲素0.55%、氯化钴0.01%;在摇瓶中进行验证试验,优化条件下菌体干质量为33.98mg·mL-1、酶活为167.57U·mL-1;对照条件下菌体干质量26.6mg·mL-1、酶活为125.63U·mL-1,此优化培养基使干质量、酶活分别提高了27.74%和33.38%。     

腈水合酶产生菌的分离筛选和酶反应条件的优化

从化工废水处理厂的活性污泥中分离和筛选到一株腈水合酶产生菌HUST-1。经初步鉴定,菌株HUST-1属于红球菌属(Rhodococcus sp.)。对菌株(Rhodococcus sp.)HUST-1所产腈水合酶的反应条件进行研究,结果表明,该菌株的最优酶反应条件:丙烯腈加入量为5%,反应温度为28℃,pH值为7.0,反应时间为15min。在最优酶反应条件下,菌株(Rhodococcus sp.)HUST-1的最高比酶活可达119U·mg-1,比优化前提高24.5%。