The influence of host sex on the L3 to L4 molt of Brugia malayi

Immunocompetent male mice are more susceptible to experimental infection with Brugia spp. than are females. Because permissive male SCID mice (severe combined immunodeficient mice), which lack T and B cells, also possess higher worm burdens, the mechanism is not solely immune mediated. Recovery of fewer adult worms from the female SCID mouse suggests that females do not provide sufficient nutrients for larval growth. This study assessed the potential of the female SCID mouse to support the L3 to L4 molt of Brugia malayi. Unexpectedly, worms grown in females molted at earlier time points of recovery than those harvested from males. This suggests that the early stage of development of B. malayi is delayed in the male murine host. To determine whether the effect of host sex on molting may be similar in humans, worms were cultured in media supplemented with serum from male or female donors. Worms grown in serum obtained from female donors exhibited a significantly higher percentage of complete molts over those cultured with serum from males. Host-derived molecules required for the L3 to L4 molt may be more abundant in the female, perhaps allowing the worms to survive a vulnerable developmental stage in a less permissive environment.     

Detailed mapping of the nuclear export signal in the Rous sarcoma virus Gag protein

The Rous sarcoma virus (RSV) Gag polyprotein undergoes transient nuclear trafficking as an intrinsic part of the virus assembly pathway. Nuclear export of Gag is crucial for the efficient production of viral particles and is accomplished through the action of a leptomycin B (LMB)-dependent nuclear export signal (NES) in the p10 domain (L. Z. Scheifele, R. A. Garbitt, J. D. Rhoads, and L. J. Parent, Proc. Natl. Acad. Sci. USA 99:3944-3949, 2002). We have now mapped the nuclear export activity to the C-terminal portion of the p10 sequence and identified the four hydrophobic amino acids within this region that comprise a leucine-rich NES. Alteration of these hydrophobic residues resulted in the accumulation of Gag proteins within the nucleus and a budding defect greater than that obtained with LMB treatment of cells expressing the wild-type Gag protein (Scheifele et al., Proc. Natl. Acad. Sci. USA 99:3944-3949, 2002). In addition, export of Gag from the nucleus was found to be a rate-limiting step in virus-like particle production. Consistent with a role for the NES sequence in viral replication, this cluster of hydrophobic residues in p10 is conserved across a wide range of avian retroviruses. Furthermore, naturally occurring substitutions within this region in related viruses maintained nuclear export activity and remained sensitive to the activity of LMB. Using gain-of-function approaches, we found that the hydrophobic motif in p10 was sufficient to promote the nuclear export of a heterologous protein and was positionally independent within the Gag polyprotein. Finally, the export pathway was further defined by the ability of specific nucleoporin inhibitors to prevent the egress of Gag from the nucleus, thereby identifying additional cellular mediators of RSV replication.     

Extremely low-frequency electromagnetic fields do not affect DNA damage and gene expression profiles of yeast and human lymphocytes

We studied the effects of extremely low-frequency (50 Hz) electromagnetic fields (EMFs) on peripheral human blood lymphocytes and DBY747 Saccharomyces cerevisiae. Graded exposure to 50 Hz magnetic flux density was obtained with a Helmholtz coil system set at 1, 10 or 100 microT for 18 h. The effects of EMFs on DNA damage were studied with the single-cell gel electrophoresis assay (comet assay) in lymphocytes. Gene expression profiles of EMF-exposed human and yeast cells were evaluated with DNA microarrays containing 13,971 and 6,212 oligonucleotides, respectively. After exposure to the EMF, we did not observe an increase in the amount of strand breaks or oxidated DNA bases relative to controls or a variation in gene expression profiles. The results suggest that extremely low-frequency EMFs do not induce DNA damage or affect gene expression in these two different eukaryotic cell systems.     

Suspected secondary thiafentanil intoxication in a captive mountain lion (Puma concolor)

Inadvertent ingestion of thiafentanil oxalate by a captive adult female mountain lion (Puma concolor) caused a prolonged clinical syndrome that included sedation and depression, muscle tension, and myopathy that was incompletely antagonized by naltrexone HCl. A serum chemistry profile revealed markedly elevated creatinine phosphokinase (CK; 490,450 IU/l), alanine aminotransferase (ALT; 1,896 IU/l), and aspartate aminotransferase (AST; 4,321 IU/l) 2 days after onset. The affected animal's condition gradually improved over the next 15 days in response to supportive therapy that included diazepam (5 mg as needed), Normasol R (3 l/day), dexamethasone (tapering dose starting at 1 mg/kg), and ketoprofen (1 mg/kg). She eventually recovered completely. Based on these observations, carcasses of animals immobilized with thiafentanil should be marked and disposed of properly to preclude opportunities for secondary exposure and potential intoxication in scavenging species. In addition, caution is advised when using thiafentanil in animals that could be preyed upon before full metabolism of the drug.     

Modeling physiological resistance in bacterial biofilms

A mathematical model of the action of antimicrobial agents on bacterial biofilms is presented. The model includes the fluid dynamics in and around the biofilm, advective and diffusive transport of two chemical constituents and the mechanism of physiological resistance. Although the mathematical model applies in three dimensions, we present two-dimensional simulations for arbitrary biofilm domains and various dosing strategies. The model allows the prediction of the spatial evolution of bacterial population and chemical constituents as well as different dosing strategies based on the fluid motion. We find that the interaction between the nutrient and the antimicrobial agent can reproduce survival curves which are comparable to other model predictions as well as experimental results. The model predicts that exposing the biofilm to low concentration doses of antimicrobial agent for longer time is more effective than short time dosing with high antimicrobial agent concentration. The effects of flow reversal and the roughness of the fluid/biofilm are also investigated. We find that reversing the flow increases the effectiveness of dosing. In addition, we show that overall survival decreases with increasing surface roughness.