Fitness cost conferred by the novel erm(51) and rpoB mutation on environmental multidrug resistant-Rhodococcus equi.

Rhodococcus equi is a common cause of severe pneumonia in foals. Emergence of macrolide-resistant R. equi isolated from foals and their environment has been reported in the United States. A novel erm(51) gene was recently identified in R. equi in soil from horse farms in Kentucky. Our objective was to determine the effect of the erm(51) gene and associated rpoB mutation on the fitness of multidrug resistant-R. equi (MDR-R. equierm(51)+, rpoB+) under different nutrient conditions. Bacterial growth curves were generated for 3 MDR-R. equierm(51)+, rpoB+ isolates and 3 wild-type (WTN) R. equi isolates recovered from environmental samples of farms in central Kentucky. Growth was measured over 30.5 h in brain-heart infusion broth (BHI), minimal medium (MM), and minimal medium without iron (MM-I). All isolates had significantly (P < 0.05) higher growth in BHI compared to either MM or MM-I. MDR-R. equierm(51)+, rpoB+ exhibited significantly lower growth compared to WTN isolates in BHI (nutrient-rich condition), but not in either MM or MM-I (nutrient-restricted conditions). This study indicates that under nutrient-rich conditions fitness of MDR-R. equierm(51)+, rpoB+ is reduced relative to susceptible isolates; however, under nutrient-restricted conditions MDR-R. equierm(51)+, rpoB+ isolates grow similarly to susceptible isolates. These findings indicate that MDR-R. equierm(51)+, rpoB+ might be outcompeted by susceptible isolates in nature when practices to reduce antimicrobial pressure, such as reducing antimicrobial use in foals, are implemented. But it also raises the concern that these resistant genotypes might persist in the environment of horse-breeding farms in the face of selective pressures such as antimicrobials or nutrient restriction.

Systemic proliferative arteriopathy and hypophysitis in a cow with chronic ovine herpesvirus 2-induced malignant catarrhal fever.

Malignant catarrhal fever (MCF) is a severe, systemic, lymphoproliferative disease affecting domestic ruminants, caused by a group of MCF viruses in the genus Macavirus. Infection of cattle and bison with ovine herpesvirus 2 (OvHV2) is economically significant in North America. Sheep are the reservoir host of the virus, and only rarely manifest disease. Cattle and bison, however, frequently have lymphoproliferation, mucosal ulceration, and systemic vasculitis. OvHV2-induced MCF in cattle and bison is often fatal, with clinical recovery reported only rarely. Chronic cases are uncommon, but vascular changes of variable severity and ocular lesions have been described. Here we present a case of chronic MCF in a cow with proliferative arteriopathy, systemic vasculitis, and OvHV2-associated hypophysitis. We demonstrated OvHV2 nucleic acid in affected tissues with in situ hybridization.

Effect of gallium maltolate on a model of chronic, infected equine distal limb wounds.

Distal limb wounds are common injuries sustained by horses and their healing is fraught with complications due to equine anatomy, prevalence of infection, and challenges associated with wound management. Gallium is a semi-metallic element that has been shown to possess antimicrobial properties and aid in wound healing in various preclinical models. The effects of Gallium have not been studied in equine wound healing. Therefore, the objective of this study was to compare healing rates between gallium-treated and untreated wounds of equine distal limbs and to demonstrate the antimicrobial effects of gallium on wounds inoculated with S. aureus. Using an established model of equine wound healing we demonstrated beneficial effects of 0.5% topical gallium maltolate on equine wound healing. Specifically we documented reduced healing times, reduced bioburden, and reduced formation of exuberant granulation tissue in wounds treated with gallium maltolate as compared with untreated wounds. Gallium appeared to exert its beneficial effects via its well-described antimicrobial actions as well as by altering the expression of specific genes known to be involved in wound healing of horses and other animals. Specifically, gallium maltolate appeared to increase expression of transforming growth factor-ß in both infected and un-infected wounds. Further work is needed to document the effects of gallium on naturally occurring equine wounds and to compare the effects of gallium with other wound treatment options. These data, however, suggest that gallium may be an attractive and novel means of improving equine distal limb wound healing.