Static behavioral effects on gonorrhea transmission dynamics in a MSM population

An SIS/SAS model of gonorrhea transmission in a population of highly active men-having-sex-with-men (MSM) is presented in this paper to study the impact of safe behavior on the dynamics of gonorrhea prevalence. Safe behaviors may fall into two categories—prevention and self-awareness. Prevention will be modeled via consistent condom use and self-awareness via STD testing frequency. Stability conditions for the disease free equilibrium and endemic equilibrium are determined along with a complete analysis of global dynamics. The control reproductive number is used as a means for measuring the effect of changes to model parameters on the prevalence of the disease. We also find that appropriate intervention would be in the form of a multifaceted approach at overall risk reduction rather than tackling one specific control individually.     

Role of the DinB Homologs Rv1537 and Rv3056 in Mycobacterium tuberculosis

The environment encountered by Mycobacterium tuberculosis during infection is genotoxic. Most bacteria tolerate DNA damage by engaging specialized DNA polymerases that catalyze translesion synthesis (TLS) across sites of damage. M. tuberculosis possesses two putative members of the DinB class of Y-family DNA polymerases, DinB1 (Rv1537) and DinB2 (Rv3056); however, their role in damage tolerance, mutagenesis, and survival is unknown. Here, both dinB1 and dinB2 are shown to be expressed in vitro in a growth phase-dependent manner, with dinB2 levels 12- to 40-fold higher than those of dinB1. Yeast two-hybrid analyses revealed that DinB1, but not DinB2, interacts with the β-clamp, consistent with its canonical C-terminal β-binding motif. However, knockout of dinB1, dinB2, or both had no effect on the susceptibility of M. tuberculosis to compounds that form N²-dG adducts and alkylating agents. Similarly, deletion of these genes individually or in combination did not affect the rate of spontaneous mutation to rifampin resistance or the spectrum of resistance-conferring rpoB mutations and had no impact on growth or survival in human or mouse macrophages or in mice. Moreover, neither gene conferred a mutator phenotype when expressed ectopically in Mycobacterium smegmatis. The lack of the effect of altering the complements or expression levels of dinB1 and/or dinB2 under conditions predicted to be phenotypically revealing suggests that the DinB homologs from M. tuberculosis do not behave like their counterparts from other organisms.The emergence and global spread of multi- and extensively drug-resistant strains of Mycobacterium tuberculosis have further complicated the already daunting challenge of controlling tuberculosis (TB) (15). The mechanisms that underlie the evolution of drug resistance in M. tuberculosis by chromosomal mutagenesis and their association with the conditions that tubercle bacilli encounter during the course of infection are poorly understood (6). It has been postulated that hypoxia, low pH, nutrient deprivation, and nitrosative and oxidative stress impose environmental and host immune-mediated DNA-damaging insults on infecting bacilli (64). In addition, the observed importance of excision repair pathways for the growth and survival of M. tuberculosis in murine models of infection (13, 55) and the upregulation of M. tuberculosis genes involved in DNA repair and modification in pulmonary TB in humans provide compelling evidence that the in vivo environment is DNA damaging (51).Damage tolerance constitutes an integral component of an organism''s response to genotoxic stress, preventing collapse of the replication fork at persisting, replication-blocking lesions through the engagement of specialized DNA polymerases that are able to catalyze translesion synthesis (TLS) across the sites of damage (19, 21, 60). Most TLS polymerases belong to the Y family, which comprises a wide range of structurally related proteins present in bacteria, archaea, and eukaryotes (44). Of these, the DinB subfamily of Y family polymerases, whose founder member is Escherichia coli Pol IV (63), is conserved among all domains of life (44). The association of Y family polymerases with inducible mutagenesis has implicated these enzymes in the adaptation of bacteria to environmental stress (17, 20, 39, 54, 58, 59, 66). Their key properties are exemplified in E. coli Pol IV: the polymerase catalyzes efficient and accurate TLS across certain N²-dG adducts (27, 28, 34, 40, 45, 67) and has been implicated in the tolerance of alkylation damage (4); furthermore, overexpression of Pol IV significantly increases mutation rates in E. coli (reviewed in references 21 and 26), and dinB is the only SOS-regulated gene required at induced levels for stress-induced mutagenesis in this organism (20). Furthermore, overproduction of E. coli Pol IV inhibits replication fork progression through replacement of the replicative polymerase to form an alternate replisome in which Pol IV modulates the rate of unwinding of the DnaB helicase (25) and also reduces colony-forming ability (61).The M. tuberculosis genome encodes two Y family polymerase homologs belonging to the DinB subfamily, designated herein as DinB1 (DinX, encoded by Rv1537) and DinB2 (DinP, encoded by Rv3056), as well as a third, distantly related homolog encoded by Rv3394c (see Fig. S1 in the supplemental material) (9). On the basis of sequence similarity with their counterparts from E. coli (63) and Pseudomonas aeruginosa (54), including the complete conservation of key acidic residues essential for catalysis, DinB1 and DinB2 may be functional DNA polymerases (see Fig. S1). In contrast, Rv3394c lacks these residues and as such is unlikely to have polymerase activity (see Fig. S1). Unlike most Y family polymerase-encoding genes investigated with other bacteria (17, 26, 54, 58), dinB1 and dinB2 expression in M. tuberculosis is not dependent on RecA, the SOS response, or the presence of DNA damage (5, 7, 52). That these genes are regulated by other mechanisms and so may serve distinct roles in DNA metabolism in M. tuberculosis is suggested by the observation that dinB1 is differentially expressed in pulmonary TB (51) and is a member of the SigH regulon (30), whereas expression of dinB2 is induced following exposure to novobiocin (5).In this study, we adopted a genetic approach to investigate the function of dinB1 and dinB2 in M. tuberculosis. Mutants with altered complements or expression levels of dinB1 and/or dinB2 were analyzed in vitro and in vivo under conditions predicted to be phenotypically revealing based on DinB function established with other model organisms. The lack of discernible phenotypes in any of the assays employed suggests that the DinB homologs from M. tuberculosis do not behave like their counterparts from other organisms.     

Synergistic effects of food and predators on annual reproductive success in song sparrows

The behaviour literature is full of studies showing that animals in every taxon balance the probability of acquiring food with the risk of being preyed upon. While interactions between food and predators clearly operate at an individual scale, population-scale studies have tended to focus on only one factor at a time. Consequently, interactive (or 'synergistic') effects of food and predators on whole populations have only twice before been experimentally demonstrated in mammals. We conducted a 2 x 2 experiment to examine the joint effects of food supply and predator pressure on the annual reproductive success of song sparrows (Melospiza melodia). Our results show that these two factors do not operate in an additive way, but instead have a synergistic effect on reproduction. Relative to controls, sparrows reared 1.1 more young when food was added and 1.3 more when predator pressure was low. When these treatments were combined 4.0 extra young were produced, almost twice as many as expected from an additive model. These results are a cause for optimism for avian conservation because they demonstrate that remedial actions, aimed at simultaneously augmenting food and reducing predators, can produce dramatic increases in reproductive success.     

Subzero nonfreezing cryopresevation of rat hearts using antifreeze protein I and antifreeze protein III

The purpose of the present study was to evaluate whether AFPs protect the heart from freezing and improve survival and viability in subzero cryopreservation. Hearts were subject to 5 preservation protocols; University of Wisconsin solution (UW) at 4 degrees C, UW at -1.3 degrees C without nucleation, UW at -1.3 degrees C with nucleation, UW AFP I (15 mg/cm(3)) at -1.3 degrees C with nucleation, and in UW AFP III (15 mg/cm(3)) at -1.3 degrees C with nucleation. Hearts were preserved for 24, 28, and 32 h, rewarmed and connected to the working isolated perfusion system. Data [heart rate (HR), coronary flow (CF), and developed pressure (dP)] was collected 30 and 60 min after reperfusion. Hearts preserved at -1.3 degrees C without AFPs froze, while hearts preserved with AFP did not freeze when nucleation was initiated and survived. Survival and dP of hearts preserved for 24h at -1.3 degrees C using AFP III was better than those preserved at 4 degrees C, (dP; 1.4 vs. 0.8, p<0.05). Four of six hearts and six of six hearts died when preserved at 4 degrees C for 28 and 32 h, respectively, all of the hearts that were preserved at -1.3 degrees C with or without AFPs survived after 28 h (n=18) and 32 h (n=18). CF was higher in UW -1.3 degrees C group without attempted nucleation than in AFP I and AFP III groups after 28 and 32 h (3.4 vs. 1.7, p<0.05, and 3.4 vs. 1.7, p<0.05, respectively). In conclusion, AFPs were found to protect the heart from freezing and improve survival and dP (AFP III) in prolonged subzero preservation.     

Conformation and self-assembly of a nystatin nitrobenzoxadiazole derivative in lipid membranes

Nystatin is a polyene (tetraene) macrolide antibiotic presenting antifungal activity that acts at the cellular membrane level. In the present study, we report the interaction of this antibiotic labelled at its amine group with 7-nitrobenz-2-oxa-1,3-diazole (NBD-Nys) with sterol-free and ergosterol- and cholesterol-containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) large unilamellar vesicles (LUV). The mean tetraene to NBD separating distance determined from fluorescence energy transfer measurements increased from 18 to 25.6 A upon antibiotic binding to the lipid vesicles, indicating that the monomeric labelled antibiotic adopts a more extended conformation in its lipid-bound state than in aqueous solution. The oligomeric state of membrane-bound NBD-Nys was also studied by resonance energy homotransfer between the NBD fluorophores. The decrease measured in its steady state fluorescence anisotropy upon increasing the surface concentration of the NBD-Nys is shown to be consistent with a random distribution of molecules on the surface of the liposomes. This data contradicts the sharp increase measured for nystatin mean fluorescence lifetime in the presence of 10 mol% ergosterol-containing POPC LUV within the same antibiotic concentration range and which is known to report nystatin oligomerization in the lipid vesicles. Therefore, we conclude that the amine group of nystatin is an essential requisite for the supramolecular organization/pore formation of this antibiotic.     

Dual roles for lipolysis and oxidation in peroxisome proliferation-activator receptor responses to electronegative low density lipoprotein

Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, including particle content and metabolism. One circulating subfraction, electronegative LDL (LDL(-)), which is increased in familial hypercholesterolemia and diabetes, is implicated in accelerated atherosclerosis. Cellular responses to LDL(-) remain poorly described. Here we demonstrate that LDL(-) increases tumor necrosis factor alpha (TNFalpha)-induced inflammatory responses through NF kappa B and AP-1 activation with corresponding increases in vascular cell adhesion molecule-1 (VCAM1) expression. LDL receptor overexpression increased these effects. In contrast, exposing LDL(-) to the key lipolytic enzyme lipoprotein lipase (LPL) reversed these responses, inhibiting VCAM1 below levels seen with TNFalpha alone. LPL is known to act on lipoproteins to generate endogenous peroxisomal proliferator-activated receptor alpha (PPAR alpha) ligand, thus limiting inflammation. These responses varied according to the lipoprotein substrate triglyceride content (very low density lipoprotein > LDL > high density lipoprotein). The PPAR alpha activation seen with LDL, however, was disproportionately high. We show here that MUT LDL activates PPAR alpha to an extent proportional to its LDL(-) content. As compared with LDL(-) alone, LPL-treated LDL(-) increased PPAR alpha activation 20-fold in either cell-based transfection or radioligand displacement assays. LPL-treated LDL(-) suppressed NF kappa B and AP-1 activation, increasing expression of the PPAR alpha target gene I kappa B alpha, although only in the genetic presence of PPAR alpha and with intact LPL hydrolysis. Mass spectrometry reveals that LPL-treatment of either LDL or LDL(-) releases hydroxy-octadecadienoic acids (HODEs), potent PPAR alpha activators. These findings suggest LPL-mediated PPAR alpha activation as an alternative catabolic pathway that may limit inflammatory responses to LDL(-).     

Expression of foreign LpxA acyltransferases in Neisseria meningitidis results in modified lipid A with reduced toxicity and retained adjuvant activity

A major problem in the development of vaccines against Gram-negative bacteria is the endotoxic -activity of lipopolysaccharide (LPS), which is determined by its lipid A moiety. Nevertheless, LPS would be an interesting vaccine component because of its immune-stimulating properties. In the present study, we have changed the fatty acid composition of Neisseria meningitidis LPS by replacing the lpxA gene of strain H44/76 with the Escherichia coli or Pseudomonas aeruginosa homologue. The majority of the O-linked 3-OH C12 in N. meningitidis lipid A was replaced by 3-OH C14 (strain HA01E) and 3-OH C10 (strain HA25P) respectively. Both strains, but most notably strain HA01E, had reduced amounts of LPS compared with the wild-type strain. In addition, growth was severely impaired for HA01E. The major outer membrane proteins were expressed normally. Outer membrane complexes of both strains normalized on their LPS content showed a 10-fold reduction in their ability to induce tumour necrosis factor (TNF)-alpha. Immunogenicity studies in BALB/c mice revealed that the adjuvant activity of the LPS was not affected. Thus, the replacement of the O-linked fatty acids in meningococcal lipid A results in immunogenic outer membranes with reduced endotoxic activity, more suitable for use in outer membrane vesicle vaccines.     

Evaluation of respiratory and cutaneous doses of chlorothalonil during re-entry in greenhouses

Five female workers were monitored for 5 consecutive days during re-entry into a greenhouse containing ornamental plants. Skin contamination (excluding hands) was evaluated with nine pads of filter paper placed on the skin. Hand contamination was assessed by washing with 95% ethanol. Respiratory exposure was evaluated by personal air sampling. The respiratory dose was based on a lung ventilation of 15 l/min. The doses absorbed were estimated assuming 10% skin absorption and 100% lung retention. Dislodgeable foliar residue was determined on days of re-entry to evaluate the decay of chlorothalonil. Chlorothalonil was analysed in the different matrices by GC-MS. Respiratory exposure was less than skin contamination, being 11.4+/-5.1% (mean+/-SD) of total exposure. The estimated total absorbed dose did not exceed the acceptable daily intake of 0.03 mg/kg body mass. The hands and unexposed skin of all workers were always found to be contaminated. Greater precautions are therefore needed to reduce skin exposure (clean gloves and suitable clean clothing every day).     

EAC细胞在3＇5＇－cAMP诱导下PKA－RⅡ移位入核与癌基因表达的动力学变化

Ｅｈｒｌｉｃｈ细胞在ｃＡＭＰ加茶碱的诱导下,于接种后５－７天,伴随着胞质内ｃＡＭＰ蛋白结合率上升的同时,依赖于ｃＡＭＰ的蛋白激酶Ⅱ型酶调节亚基（ＰＫＡ－ＲⅡ）从胞质向核移位,其表达强度在胞质和核内持续升高,此时癌基ｃ－ｍｙｃ,ｃ－ｆｏｓ,ｃ－Ｈ－ｒａｓ,ｃ－ｓｉｓ表达抑制。ｃＡＭＰ蛋白结合率与ＰＫＡ－ＲⅡ的移位入核呈显著的正相关,二者与癌基因表达抑制是显著的负相关,它们均从第７天最为显著。在癌龄晚期（按种后９－１１天）,当胞质内ｃＡＭＰ蛋白结合率下降（与对照组比较）时,ＰＫＡ－ＲⅡ则停止移位入核,癌基因又重新表达,如果用ｃＡＭＰ抑制剂人为阻断接种后第７天的癌细胞内ＰＫＡ信号通路时,ＰＫＡ－ＲＨ则停止移位入核,而癌基因仍呈强烈表达。对上述各结果之间的关系进行了分析与讨论。