Multiple-Antibiotic Resistance of Enterococcus spp. Isolated from Commercial Poultry Production Environments

The potential impact of food animals in the production environment on the bacterial population as a result of antimicrobial drug use for growth enhancement continues to be a cause for concern. Enterococci from 82 farms within a poultry production region on the eastern seaboard were isolated to establish a baseline of susceptibility profiles for a number of antimicrobials used in production as well as clinical environments. Of the 541 isolates recovered, Enterococcus faecalis (53%) and E. faecium (31%) were the predominant species, while multiresistant antimicrobial phenotypes were observed among all species. The prevalence of resistance among isolates of E. faecalis was comparatively higher among lincosamide, macrolide, and tetracycline antimicrobials, while isolates of E. faecium were observed to be more frequently resistant to fluoroquinolones and penicillins. Notably, 63% of the E. faecium isolates were resistant to the streptogramin quinupristin-dalfopristin, while high-level gentamicin resistance was observed only among the E. faecalis population, of which 7% of the isolates were resistant. The primary observations are that enterococci can be frequently isolated from the poultry production environment and can be multiresistant to antimicrobials used in human medicine. The high frequency with which resistant enterococci are isolated from this environment suggests that these organisms might be useful as sentinels to monitor the development of resistance resulting from the usage of antimicrobial agents in animal production.     

THE FUNCTION OF CALL ALTERNATION IN ANURAN AMPHIBIANS: A TEST OF THREE HYPOTHESES

Males of many species of anurans alternate calls with those of their neighbors in a chorus. This pattern of calling reduces signal interference and may: 1) facilitate intermale spacing because males can better gauge the intensity of neighbors' calls if these calls do not overlap with their own; 2) help preserve species-specific temporal information in calls required to attract females; and/or 3) make it easier for females to localize males in the chorus. I tested these hypotheses with three species that exhibit call alternation, Hyla crucifer, H. versicolor, and H. microcephala. Males of all three species gave more aggressive calls to high-intensity synthetic stimuli that alternated with their calls than to those that overlapped their calls. These results support the first hypothesis. Results of four-speaker female choice experiments using alternating and overlapping calls indicate that preservation of signal integrity also is important in H. versicolor and H. microcephala, species that have fine-scale temporal information in their calls. However, the third hypothesis was not supported; females failed to discriminate among alternating and overlapping calls if the problem of signal disruption was eliminated or irrelevant.     

Arsenic inhibits CFTR-mediated chloride secretion by killifish (Fundulus heteroclitus) opercular membrane.

Killifish are euryhaline teleosts that normally experience rapid changes in the salinity of the swim water. Acclimation to seawater is mediated by cortisol, which by activating glucocorticoid receptors, upregulates CFTR mediated Cl- secretion in the gill and operculum. Arsenic, a toxic metalloid that naturally occurs in the aquatic environment, has been shown to disrupt glucocorticoid hormone-mediated regulation of genes. Because little is known about the effects of environmentally relevant levels of arsenic on ion channels and salt homeostasis, studies were conducted to examine the effects of arsenic on the ability of killifish to acclimate to increased salinity. Arsenic in the swim water or administered by intraperitoneal injection prevented acclimation. To determine if arsenic blocked acclimation by inhibiting CFTR mediated Cl- secretion (Isc), opercular membranes were isolated and mounted in Ussing chambers and the effects of arsenic on Isc were measured. Arsenic (24 hr exposure) reduced Isc in opercular membranes isolated from salt water acclimated killifish. In addition, arsenic acutely (5-10 minutes) and reversibly inhibited Isc with an IC50 = 4.1 microM (305 ppb) when applied to the apical (seawater) side of the operculum, but not when added to the basolateral side of the operculum. Arsenic (4 microM for 60 minutes) also reduced mitochondrial respiration. Thus, environmentally relevant levels of arsenic block acclimation to seawater in killifish by reversibly inhibiting CFTR-mediated Cl- secretion by the opercular membrane, in part by inhibiting mitochondrial respiration.     

In vitro chromatin self-association and its relevance to genome architecture.

Chromatin in a eukaryotic nucleus is condensed through 3 hierarchies: primary, secondary, and tertiary chromatin structures. In vitro, when induced with cations, chromatin can self-associate and form large oligomers. This self-association process has been proposed to mimic processes involved in the assembly and maintenance of tertiary chromatin structures in vivo. In this article, we review 30 years of studies of chromatin self-association, with an emphasis on the evidence suggesting that this in vitro process is physiologically relevant.     

In Vitro Processing of Herpes Simplex Virus Type 1 DNA Replication Intermediates by the Viral Alkaline Nuclease, UL12

Herpes simplex virus type 1 (HSV-1) DNA replication intermediates exist in a complex nonlinear structure that does not migrate into a pulsed-field gel. Genetic evidence suggests that the product of the UL12 gene, termed alkaline nuclease, plays a role in processing replication intermediates (R. Martinez, R. T. Sarisky, P. C. Weber, and S. K. Weller, J. Virol. 70:2075–2085, 1996). In this study we have tested the hypothesis that alkaline nuclease acts as a structure-specific resolvase. Cruciform structures generated with oligonucleotides were treated with purified alkaline nuclease; however, instead of being resolved into linear duplexes as would be expected of a resolvase activity, the artificial cruciforms were degraded. DNA replication intermediates were isolated from the well of a pulsed-field gel (“well DNA”) and treated with purified HSV-1 alkaline nuclease. Although alkaline nuclease can degrade virion DNA to completion, digestion of well DNA results in a smaller-than-unit-length product that migrates as a heterogeneous smear; this product is resistant to further digestion by alkaline nuclease. The smaller-than-unit-length products are representative of the entire HSV genome, indicating that alkaline nuclease is not inhibited at specific sequences. To further probe the structure of replicating DNA, well DNA was treated with various known nucleases; our results indicate that replicating DNA apparently contains no accessible double-stranded ends but does contain nicks and gaps. Our data suggest that UL12 functions at nicks and gaps in replicating DNA to correctly repair or process the replicating genome into a form suitable for encapsidation.     

Phosphodiesterase activity and the potentiation by theophylline of adrenocorticotrophin stimulated steroidogenesis and adenosine 3',5'-monophosphate levels in isolated rat adrenal cells

Corticosterone production and adenosine 3′,5′-monophosphate levels in collagenase prepared isolated rat adrenal cells have been measured in response to adrenocorticotrophin in the presence and absence of theophylline. Theophylline (1mM) was found to potentiate the steroidogenic effect of submaximal concentrations of adrenocorticotrophin. This concentration of theophylline was without effect on protein synthesis in this system. Potentiation of adrenocorticotrophin stimulated adenosine 3′,5′-monophosphate levels was also observed in the presence of theophylline (0.5 and 1.0mM). Phosphodiesterase activity in collagenase prepared adrenal cells was 67% of that in intact glands, while the activity in trypsin prepared cells was 37% of that in intact glands.     

Perinatal high fat diet and early life methyl donor supplementation alter one carbon metabolism and DNA methylation in the brain

One carbon metabolism is regulated by the availability of nutrients known as methyl donors, and disruption of this pathway can affect multiple physiological systems. DNA methylation, critical for the regulation of gene expression, is linked to one carbon metabolism, and can be altered by perinatal diet. In this study, dams (n  = 12/group) were fed HF or standard control (SC ) diet through pregnancy and lactation, and male and female offspring were then fed either SC or methyl donor‐supplemented diet (MDS ) between 3 and 6 weeks of age (n  = 20–26/group). Concentration of one carbon intermediates and other related metabolites were assessed within brain tissue (prefrontal cortex, PFC ) through the use of mass spectrometry at 6 weeks of age. In addition, the expression of target genes and enzymes that participate in DNA methylation or are relevant to one carbon metabolism were measured. We found that MDS increases the concentration of folate intermediates in the PFC , and that this increase is blunted in male offspring from dams fed a HF diet. In addition, perinatal HF diet increased the concentration of cysteine in the PFC of both male and female offspring, consistent with oxidative stress. Furthermore, both maternal HF diet and postnatal MDS altered global DNA methylation in the PFC in males but not females. Collectively, these data demonstrate sex differences in changes in one carbon metabolites in the prefrontal cortex in response to early life high fat diet and methyl donor supplementation.

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