Antimicrobial susceptibility of Salmonella and Escherichia coli from equids sampled in the NAHMS 2015-16 equine study and association of management factors with resistance

Several studies have investigated antimicrobial resistance (AMR) in Salmonella spp. and Escherichia coli isolated from hospitalized horses, but studies conducted on community-based populations of equids are limited. The factors associated with AMR in these bacteria in the general horse population are not well understood. The primary objective of our study was to estimate the prevalence of Salmonella and describe antimicrobial susceptibility of Salmonella and E. coli from equids across the United States. The second objective was to identify associations between health management and biosecurity practices and AMR. Fecal samples submitted from 1357 equids on 199 operations were tested for Salmonella, identifying 27 positive samples with 29 isolates belonging to 18 serotypes. Fecal sample and operation-level prevalence of Salmonella was 2.0% (27/1357) and 7.0% (14/199), respectively. Most (25/29) isolates were pan-susceptible while four isolates exhibited resistance, three of which were multidrug resistant. Of the 721 samples cultured for E. coli, 85% (613/721) were positive. Eighty-six percent of the E. coli isolates recovered were pan-susceptible (529/612). Ten isolates were intermediate to one antimicrobial drug and susceptible to all others. Seventy-three E. coli isolates (11.9%, SE=1.3) were resistant to one or more antimicrobials, corresponding to a 33.0% (64/194) operation-level prevalence. Resistance to sulfonamide drugs was most common with 63 isolates (10.3%) resistant to sulfisoxazole, 57 of which (9.3%) were resistant to trimethoprim-sulfamethoxazole. MDR in E. coli was rare (1.8%, SE=0.5). Univariate and multivariable regression were used to evaluate associations between health management and biosecurity questionnaire items and AMR in E. coli. The outcome modeled was resistance to any of the 14 tested antimicrobials. Depending on the operation type, operations with greater than 20 resident equids were significantly associated with resistance. In addition, performance operations were significantly associated with resistance when compared to farm/ranch operations. Operations with feed containers that prevent fecal contamination and those that had treated any equids for illness or injury were associated with a lower AMR. The study results suggest that equids in the general population appear to pose low risk of shedding antimicrobial resistant strains of Salmonella and E. coli, and therefore low transmission potential to other equids, animals, humans, or the environment. However, it is prudent to practice good hand hygiene to prevent spread of Salmonella as well as AMR, and to protect both animal and human health. Despite study limitations, potential management factors that may influence prevalence and prevent spread of AMR shed by equids were identified.

Comparative composition, diversity, and abundance of oligosaccharides in early lactation milk from commercial dairy and beef cows

Prebiotics are nondigestible dietary ingredients, usually oligosaccharides (OS), that provide a health benefit to the host by directly modulating the gut microbiota. Although there is some information describing OS content in dairy-source milk, no information is available to describe the OS content of beef-source milk. Given the different trait emphasis between dairy and beef for milk production and calf survivability, it is plausible that OS composition, diversity, and abundance differ between production types. The goal of this study was to compare OS in milk from commercial dairy and beef cows in early lactation. Early-lactation multiparous cows (5–12 d in milk) from 5 commercial Holstein dairy herds and 5 Angus or Angus hybrid beef herds were sampled once. Milk was obtained from each enrolled cow and frozen on the farm. Subsequently, each milk sample was assessed for total solids, pH, and OS content and relative abundance. Oligosaccharide diversity and abundance within and between samples was transformed through principal component analysis to reduce data complexity. Factors from principal component analysis were used to create similarity clusters, which were subsequently used in a multivariate logistic regression. In total, 30 OS were identified in early-lactation cow milk, including 21 distinct OS and 9 isomers with unique retention times. The majority of OS detected in the milk samples were present in all individual samples regardless of production type. Two clusters described distribution patterns of OS for the study sample; when median OS abundance was compared between the 2 clusters, we found that overall OS relative abundance was consistently greater in the cluster dominated by beef cows. For several of the structures, including those with known prebiotic effect, the difference in abundance was 2- to 4-fold greater in the beef-dominated cluster. Assuming that beef OS content in milk is the gold standard for cattle, it is likely that preweaning dairy calves are deprived of dietary-source OS. Although supplementing rations with OS is an approach to rectify this deficiency, understanding the health and productivity effects of improving OS abundance being fed to preweaning calves is a necessary next step before recommending supplementation. These studies should account for the observation that OS products are variable for both OS diversity and structural complexity, and some products may not be suitable as prebiotics.

A Randomized Clinical Trial Evaluating the Effects of Oligosaccharides on Transfer of Passive Immunity in Neonatal Dairy Calves

Background

Bacterial contamination of colostrum is common and can decrease IgG absorption in neonatal calves. Strategies that mitigate this situation without complicating colostrum management will benefit dairy calf health and survival.

Objectives

To evaluate the effects of supplementing colostrum with oligosaccharides (OS) on serum IgG concentration and apparent efficiency of absorption of IgG (AEA%) in calves fed unpasteurized colostrum and characterize these outcomes with respect to colostrum bacterial exposures.

Animals

One hundred twenty‐three neonatal dairy calves.

Methods

Randomized, blinded, controlled clinical trial conducted at a commercial dairy operation. Calves were enrolled at birth in 1 of 4 treatment groups. Data were complete for 123 calves, which were distributed across the treatment groups as follows: mannan‐oligosaccharides (MOS), n = 33; Saccharomyces galacto‐oligosaccharides (SGOS), n = 31; Bifidobacterium galacto‐oligosaccharides (BGOS), n = 28; and lactose control (CON), n = 31. A commercial radial immunodiffusion kit was used to determine colostrum and serum IgG concentrations. Conventional microbiology methods were used to enumerate colostrum bacterial counts.

Results

Bacterial counts were not significantly different among treatment groups. Total bacterial plate counts (TPC) were relatively low for the majority of colostrum samples, but TPC had a significant negative effect on serum IgG concentration and AEA% in the lactose‐supplemented control group but not the OS treatment groups.

Conclusions and Clinical Importance

These results suggest that a complement of OS structures may mitigate adverse effects of bacteria on transfer of passive immunity (TPI).

Nucleophosmin is a novel Bax chaperone that regulates apoptotic cell death

The proapoptotic B-cell lymphoma-2 family protein Bax is a key regulatory point in the intrinsic apoptotic pathway. However, the factors controlling the process of Bax activation and translocation to mitochondria have yet to be fully identified and characterized. We performed affinity chromatography using peptides corresponding to the mitochondrial-targeting region of Bax, which is normally sequestered within the inactive structure. The molecular chaperone nucleophosmin was identified as a novel Bax-binding protein by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Reciprocal co-immunoprecipitation and proximity assays confirmed the Bax-nucleophosmin protein-protein interaction and verified that nucleophosmin only bound to activated conformationally altered Bax. Confocal microscopy in a cell-based apoptosis model, demonstrated that nucleophosmin translocation from nucleolus to cytosol preceded Bax movement. Specific knockdown of nucleophosmin expression using RNAi attenuated apoptosis as measured by mitochondrial cytochrome c release and activation of the caspase cascade. In a mouse model of ischaemic stroke, subcellular fractionation studies verified that nucleophosmin translocation occurred within 3 h, at a time before Bax translocation but after Bax conformational changes have occurred. Thus, we have elucidated a novel molecular mechanism whereby Bax becomes activated and translocates to the mitochondria to orchestrate mitochondrial dysfunction and apoptotic cell death, which opens new avenues for therapeutic intervention.

Application of chemically induced dynamic nuclear polarization to the nitration of N-acetyltyrosine and to some reactions of peroxynitrite

By the observation of chemically induced dynamic nuclear polarization in (15)N NMR spectroscopy it has been shown that nitration of N-acetyltyrosine, even under acidic conditions, is largely a radical process. In the alkaline reaction of tyrosine with peroxynitrite the main products are nitrite and nitrate, both produced by a radical pathway, and tyrosine nitration is a minor reaction. It is suggested that tyrosine catalyzes the production of NO(*)(2) and HO(*) from peroxynitrite.

Interaction of cytochrome c with flavocytochrome b2

Flavocytochrome b2 from Saccharomyces cerevisiae couples L-lactate dehydrogenation to cytochrome c reduction. At 25 degrees C, 0.10 M ionic strength, and saturating L-lactate concentration, the turnover rate is 207 s-1 [per cytochrome c reduced; Miles, C. S., Rouviere, N., Lederer, F., Mathews, F. S., Reid, G. A., Black, M. T., & Chapman, S. K. (1992) Biochem. J. 285, 187-192]. The second-order rate constant for cytochrome c reduction in the pre-steady-state has been determined by stopped-flow spectrophotometry to be 34.8 (+/- 0.9) muM-1 s-1 in the presence of 10 mM L-lactate. This rate constant has been found to be dependent entirely on the rate of complex formation, the electron-transfer rate in the pre-formed complex being in excess of 1000 s-1. Inhibition of the pre-steady-state reduction of cytochrome c by either zinc-substituted cytochrome c or ferrocytochrome c has led to the estimation of a Kd for the catalytically competent complex of 8 microM, and from this the dissociation rate constant of 280 s-1, a value much less than the actual electron-transfer rate. The inhibition observed is only partial which indicates that electron transfer from the 1:1 complex to another cytochrome c can occur and that alternative electron transfer sites exist. The cytochrome c binding site proposed by Tegoni et al. [Tegoni, M., White, S. A., Roussel, A., Mathews, F. S. & Cambillau, C. (1993) Proteins 16, 408-422] has been tested using site-directed mutagenesis. Mutations designed to affect the complex stability and putative electron-transfer pathway had little effect, suggesting that the primary cytochrome c binding site on flavocytochrome b2 lies elsewhere. The combination of tight binding and multiple electron-transfer sites gives flavocytochrome b2 a low K(m) and a high kcat, maximizing its catalytic efficiency. In the steady-state, the turnover rate is therefore largely limited by other steps in the catalytic cycle, a conclusion which is discussed in the preceding paper in this issue [Daff, S., Ingledew, W. J., Reid, G. A., & Chapman, S. K. (1996) Biochemistry 35, 6345-6350].