Effects of the naturally occurring food mycotoxin ochratoxin A on brain cells in culture.

The potential of ochratoxin A (OTA) to damage brain cells was studied by using a three-dimensional cell culture system as model for the developing brain. Aggregating cell cultures of foetal rat telencephalon were tested either during an early developmental period, or during a phase of advanced maturation, over a wide range of OTA concentrations (0.4 nM to 50 microM). By monitoring changes in activities of cell type-specific enzymes (ChAt and GAD, for cholinergic and GABAergic neurones, respectively, GS for astrocytes and CNP for oligodendrocytes), the concentration-dependent toxicity and neurodevelopmental effects of OTA were determined. OTA proved to be highly toxic, since a 10-day treatment at 50 nM caused a general cytotoxicity in both mature and immature cultures. At 10 nM of OTA, cell type-specific effects were observed: in immature cultures, a loss in neuronal and oligodendroglial enzyme activities, and an increase in the activity of the astroglial marker glutamine synthetase were found, Furthermore, at 2 and 10 nM of OTA, a clustering of microglial cells was observed. In mature cultures, OTA was somewhat less potent, but caused a similar pattern of toxic effects. A 24 h-treatment with OTA resulted in a concentration-dependent decrease in protein synthesis, with IC50 values of 25 nM and 33 nM for immature and mature cultures respectively. Acute (24 h) treatment at high OTA concentrations (10 to 50 microM) caused a significant increase in reactive oxygen species formation, as measured by the intracellular oxidation of 2',7'-dichlorofluorescin. These results suggest that OTA has the potential to be a potent toxicant to brain cells, and that its effects at nanomolar concentrations are primarily due to the inhibition of protein synthesis, whereas ROS seem not to be involved in the toxicity mediated by a chronic exposure to OTA at such low concentrations.

Evaluation of cumulative PCB exposure estimated by a job exposure matrix versus PCB serum concentrations.

Although polychlorinated biphenyls (PCBs) have been banned in many countries for more than three decades, exposures to PCBs continue to be of concern due to their long half-lives and carcinogenic effects. In National Institute for Occupational Safety and Health studies, we are using semiquantitative plant-specific job exposure matrices (JEMs) to estimate historical PCB exposures for workers (n = 24,865) exposed to PCBs from 1938 to 1978 at three capacitor manufacturing plants. A subcohort of these workers (n = 410) employed in two of these plants had serum PCB concentrations measured at up to four times between 1976 and 1989. Our objectives were to evaluate the strength of association between an individual worker's measured serum PCB levels and the same worker's cumulative exposure estimated through 1977 with the (1) JEM and (2) duration of employment, and to calculate the explained variance the JEM provides for serum PCB levels using (3) simple linear regression. Consistent strong and statistically significant associations were observed between the cumulative exposures estimated with the JEM and serum PCB concentrations for all years. The strength of association between duration of employment and serum PCBs was good for highly chlorinated (Aroclor 1254/HPCB) but not less chlorinated (Aroclor 1242/LPCB) PCBs. In the simple regression models, cumulative occupational exposure estimated using the JEMs explained 14-24% of the variance of the Aroclor 1242/LPCB and 22-39% for Aroclor 1254/HPCB serum concentrations. We regard the cumulative exposure estimated with the JEM as a better estimate of PCB body burdens than serum concentrations quantified as Aroclor 1242/LPCB and Aroclor 1254/HPCB.

NEW METHODS FOR DETECTION, SUSCEPTIBILITY TESTING AND BIOFILM ERADICATION OF DIFFICULT ORGANISMS

Aujourd'hui, les problèmes des maladies infectieuses concernent l'émergence d'infections difficiles à traiter, telles que les infections associées aux implants et les infections fongiques invasives chez les patients immunodéprimés. L'objectif de cette thèse était de développer des stratégies pour l'éradication des biofilms bactériens (partie 1), ainsi que d'étudier des méthodes innovantes pour la détection microbienne, pour l'établissement de nouveaux tests de sensibilité (partie 2). Le traitement des infections associées aux implants est difficile car les biofilms bactériens peuvent résister à des niveaux élevés d'antibiotiques. A ce jour, il n'y a pas de traitement optimal défini contre des infections causées par des bactéries de prévalence moindre telles que Enterococcus faecalis ou Propionibacterium acnés. Dans un premier temps, nous avons démontré une excellente activité in vitro de la gentamicine sur une souche de E. faecalis en phase stationnaire de croissance Nous avons ensuite confirmé l'activité de la gentamicine sur un biofilm précoce en modèle expérimental animal à corps étranger avec un taux de guérison de 50%. De plus, les courbes de bactéricidie ainsi que les résultats de calorimétrie ont prouvé que l'ajout de gentamicine améliorait l'activité in vitro de la daptomycine, ainsi que celle de la vancomycine. In vivo, le schéma thérapeutique le plus efficace était l'association daptomycine/gentamicine avec un taux de guérison de 55%. En établissant une nouvelle méthode pour l'évaluation de l'activité des antimicrobiens vis-à-vis de micro-organismes en biofilm, nous avons démontré que le meilleur antibiotique actif sur les biofilms à P. acnés était la rifampicine, suivi par la penicilline G, la daptomycine et la ceftriaxone. Les études conduites en modèle expérimental animal ont confirmé l'activité de la rifampicine seule avec un taux de guérison 36%. Le meilleur schéma thérapeutique était au final l'association rifampicine/daptomycine avec un taux de guérison 63%. Les associations de rifampicine avec la vancomycine ou la levofloxacine présentaient des taux de guérisons respectivement de 46% et 25%. Nous avons ensuite étudié l'émergence in vitro de la résistance à la rifampicine chez P. acnés. Nous avons observé un taux de mutations de 10"9. La caractérisation moléculaire de la résistance chez les mutant-résistants a mis en évidence l'implication de 5 mutations ponctuelles dans les domaines I et II du gène rpoB. Ce type de mutations a déjà été décrit au préalable chez d'autres espèces bactériennes, corroborant ainsi la validité de nos résultats. La deuxième partie de cette thèse décrit une nouvelle méthode d'évaluation de l'efficacité des antifongiques basée sur des mesures de microcalorimétrie isotherme. En utilisant un microcalorimètre, la chaleur produite par la croissance microbienne peut être-mesurée en temps réel, très précisément. Nous avons évalué l'activité de l'amphotéricine B, des triazolés et des échinocandines sur différentes souches de Aspergillus spp. par microcalorimétrie. La présence d'amphotéricine Β ou de triazole retardait la production de chaleur de manière concentration-dépendante. En revanche, pour les échinochandines, seule une diminution le pic de « flux de chaleur » a été observé. La concordance entre la concentration minimale inhibitrice de chaleur (CMIC) et la CMI ou CEM (définie par CLSI M38A), avec une marge de 2 dilutions, était de 90% pour l'amphotéricine B, 100% pour le voriconazole, 90% pour le pozoconazole et 70% pour la caspofongine. La méthode a été utilisée pour définir la sensibilité aux antifongiques pour d'autres types de champignons filamenteux. Par détermination microcalorimétrique, l'amphotéricine B s'est avéré être l'agent le plus actif contre les Mucorales et les Fusarium spp.. et le voriconazole le plus actif contre les Scedosporium spp. Finalement, nous avons évalué l'activité d'associations d'antifongiques vis-à-vis de Aspergillus spp. Une meilleure activité antifongique était retrouvée avec l'amphotéricine B ou le voriconazole lorsque ces derniers étaient associés aux échinocandines vis-à-vis de A. fumigatus. L'association échinocandine/amphotéricine B a démontré une activité antifongique synergique vis-à-vis de A. terreus, contrairement à l'association échinocandine/voriconazole qui ne démontrait aucune amélioration significative de l'activité antifongique. - The diagnosis and treatment of infectious diseases are today increasingly challenged by the emergence of difficult-to-manage situations, such as infections associated with medical devices and invasive fungal infections, especially in immunocompromised patients. The aim of this thesis was to address these challenges by developing new strategies for eradication of biofilms of difficult-to-treat microorganisms (treatment, part 1) and investigating innovative methods for microbial detection and antimicrobial susceptibility testing (diagnosis, part 2). The first part of the thesis investigates antimicrobial treatment strategies for infections caused by two less investigated microorganisms, Enterococcus faecalis and Propionibacterium acnes, which are important pathogens causing implant-associated infections. The treatment of implant-associated infections is difficult in general due to reduced susceptibility of bacteria when present in biofilms. We demonstrated an excellent in vitro activity of gentamicin against E. faecalis in stationary growth- phase and were able to confirm the activity against "young" biofilms (3 hours) in an experimental foreign-body infection model (cure rate 50%). The addition of gentamicin improved the activity of daptomycin and vancomycin in vitro, as determined by time-kill curves and microcalorimetry. In vivo, the most efficient combination regimen was daptomycin plus gentamicin (cure rate 55%). Despite a short duration of infection, the cure rates were low, highlighting that enterococcal biofilms remain difficult to treat despite administration of newer antibiotics, such as daptomycin. By establishing a novel in vitro assay for evaluation of anti-biofilm activity (microcalorimetry), we demonstrated that rifampin was the most active antimicrobial against P. acnes biofilms, followed by penicillin G, daptomycin and ceftriaxone. In animal studies we confirmed the anti-biofilm activity of rifampin (cure rate 36% when administered alone), as well as in combination with daptomycin (cure rate 63%), whereas in combination with vancomycin or levofloxacin it showed lower cure rates (46% and 25%, respectively). We further investigated the emergence of rifampin resistance in P. acnes in vitro. Rifampin resistance progressively emerged during exposure to rifampin, if the bacterial concentration was high (108 cfu/ml) with a mutation rate of 10"9. In resistant isolates, five point mutations of the rpoB gene were found in cluster I and II, as previously described for staphylococci and other bacterial species. The second part of the thesis describes a novel real-time method for evaluation of antifungals against molds, based on measurements of the growth-related heat production by isothermal microcalorimetry. Current methods for evaluation of antifungal agents against molds, have several limitations, especially when combinations of antifungals are investigated. We evaluated the activity of amphotericin B, triazoles (voriconazole, posaconazole) and echinocandins (caspofungin and anidulafungin) against Aspergillus spp. by microcalorimetry. The presence of amphotericin Β or a triazole delayed the heat production in a concentration-dependent manner and the minimal heat inhibition concentration (MHIC) was determined as the lowest concentration inhibiting 50% of the heat produced at 48 h. Due to the different mechanism of action echinocandins, the MHIC for this antifungal class was determined as the lowest concentration lowering the heat-flow peak with 50%. Agreement within two 2-fold dilutions between MHIC and MIC or MEC (determined by CLSI M38A) was 90% for amphotericin B, 100% for voriconazole, 90% for posaconazole and 70% for caspofungin. We further evaluated our assay for antifungal susceptibility testing of non-Aspergillus molds. As determined by microcalorimetry, amphotericin Β was the most active agent against Mucorales and Fusarium spp., whereas voriconazole was the most active agent against Scedosporium spp. Finally, we evaluated the activity of antifungal combinations against Aspergillus spp. Against A. jumigatus, an improved activity of amphotericin Β and voriconazole was observed when combined with an echinocandin. Against A. terreus, an echinocandin showed a synergistic activity with amphotericin B, whereas in combination with voriconazole, no considerable improved activity was observed.

Pregnancy Outcome Following Maternal Exposure To Statins: A Multicenter Prospective Study

Introduction: Statin use for the treatment of hypercholesterolemia in women of childbearing age is increasingly common. However, published data on pregnancy outcome after exposure to statins are scarce and conflicting. This contribution addresses the safety of exposure to statins during pregnancy.Method: In a multi-center (n = 11) observational, prospective study we compared the outcomes of 249 women exposed during the 1st trimester of pregnancy to simvastatin (n = 124), atorvastatin (n = 67), pravastatin (n = 32), rosuvastatin (n = 18), fluvastatin (n = 7) or cerivastatin (n = 1) with a control group exposed to agents known to be non-teratogenic (n = 249). The data were collected by members of the European Network of Teratology Information Services (ENTIS) during individual risk counseling between 1990 and 2009. Standardized procedures for data collection were used in each center.Results: The difference in the rate of major birth defects between the statin-exposed group and the control group was not statistically significant (4.0% vs. 2.7% OR 1.5; 95% CI 0.5-4.5, P = 0.44). The crude rate of spontaneous abortions (12.8% vs. 7.1%, OR 1.9, 95% CI 1.0-3.6, P = 0.04) was higher in the exposed group. However, after adjustment to maternal age and gestational age at initial contact, the difference became statistically insignificant. The rate of elective pregnancy-termination (8.8% vs. 4.4%, P = 0.05) was higher and the rate of deliveries resulting in live births was significantly lower in the statin exposed group (77.9% vs. 88.4%, P = 0.002). Prematurity was more frequent in exposed pregnancies (16.1% vs. 8.5%; OR 2.1, 95% CI 1.1-3.8, P = 0.02). Nonetheless, gestational age at birth (median 39 weeks, IQR 37-40 vs. 39 weeks, IQR 38-40, P = 0.27) and birth weight (median 3280 g, IQR 2835-3590 vs. 3250 g, IQR 2880-3600, P = 0.95) did not differ between exposed and non-exposed pregnancies.Conclusion: This study did not detect a clear teratogenic effect of statins. Its statistical power however is not sufficient to reverse the recommendation of treatment discontinuation during pregnancy. At most, the results are reassuring in case of inadvertent exposure.

Hand exposure in diagnostic nuclear medicine with 18F- and 99mTc-labelled radiopharmaceuticals - Results of the ORAMED project

Workers performing preparation and administration of radiopharmaceuticals in NM departments are likely to receive high local skin doses to the hands which may even surpass the dose limit of 500 mSv whenever radiation protection standards are insufficient. A large measurement campaign was organised within the framework of the ORAMED project to determine the dose distribution across the hands received during preparation and administration of 18F- and 99mTc-labelled radiopharmaceuticals. The final data, collected over almost 3 years, include 641 measurements from 96 workers in 30 NM departments from 6 European countries. Results have provided levels of reference doses for the considered standard NM diagnostic procedures (mean maximum normalised skin dose of 230 μSv/GBq, 430 μSv/GBq, 930 μSv/GBq and 1200 μSv/GBq for the administration of 99mTc, preparation of 99mTc, administration of 18F and preparation of 18F, respectively). Finger dose was analysed as a function of the potential parameters of influence showing that shielding is the most efficient means of radiation protection to reduce skin dose. An appropriate method for routine monitoring of the extremities is also proposed: the base of the index finger of the non-dominant hand is a suitable position to place the ring dosemeter, with its sensitive part oriented towards the palm side; its reading may be multiplied by a factor of 6 to estimate the maximum local skin dose. Finally, results were compared to earlier published data, which correspond mostly to individual works with a reduced number of workers and measurements.

Challenging recommended oral and intravenous voriconazole doses for improved efficacy and safety: population pharmacokinetics-based analysis of adult patients with invasive fungal infections.

BACKGROUND: Recommended oral voriconazole (VRC) doses are lower than intravenous doses. Because plasma concentrations impact efficacy and safety of therapy, optimizing individual drug exposure may improve these outcomes. METHODS: A population pharmacokinetic analysis (NONMEM) was performed on 505 plasma concentration measurements involving 55 patients with invasive mycoses who received recommended VRC doses. RESULTS: A 1-compartment model with first-order absorption and elimination best fitted the data. VRC clearance was 5.2 L/h, the volume of distribution was 92 L, the absorption rate constant was 1.1 hour(-1), and oral bioavailability was 0.63. Severe cholestasis decreased VRC elimination by 52%. A large interpatient variability was observed on clearance (coefficient of variation [CV], 40%) and bioavailability (CV 84%), and an interoccasion variability was observed on bioavailability (CV, 93%). Lack of response to therapy occurred in 12 of 55 patients (22%), and grade 3 neurotoxicity occurred in 5 of 55 patients (9%). A logistic multivariate regression analysis revealed an independent association between VRC trough concentrations and probability of response or neurotoxicity by identifying a therapeutic range of 1.5 mg/L (>85% probability of response) to 4.5 mg/L (<15% probability of neurotoxicity). Population-based simulations with the recommended 200 mg oral or 300 mg intravenous twice-daily regimens predicted probabilities of 49% and 87%, respectively, for achievement of 1.5 mg/L and of 8% and 37%, respectively, for achievement of 4.5 mg/L. With 300-400 mg twice-daily oral doses and 200-300 mg twice-daily intravenous doses, the predicted probabilities of achieving the lower target concentration were 68%-78% for the oral regimen and 70%-87% for the intravenous regimen, and the predicted probabilities of achieving the upper target concentration were 19%-29% for the oral regimen and 18%-37% for the intravenous regimen. CONCLUSIONS: Higher oral than intravenous VRC doses, followed by individualized adjustments based on measured plasma concentrations, improve achievement of the therapeutic target that maximizes the probability of therapeutic response and minimizes the probability of neurotoxicity. These findings challenge dose recommendations for VRC.

A toxicokinetic model to assess exposure to folpet fungicide from urinary biomarkers

Folpet is one of the most widely employed fungicides in agriculture. It is typically used in the culture of vegetables, fruits and ornamental plants. Once absorbed in the human body, it has been found to be very reactive, especially in acid conditions. According to various in vitro and in vivo experiments in animals, Folpet is first fractioned at the N-S link when in contact with aqueous solutions and thiol groups. From this non-enzymatic process a phthalimide (PI) molecule is formed, which may be used as a biomarker of exposure, along with the short-lived thiophosgene. We have built a human toxicokinetic model to account for the biotransformation of Folpet into PI and its subsequent excretion while accounting for other non-monitored metabolites. The mathematical parameters of the model were determined accordingly from best-fits to the time courses of PI in blood and urine of five volunteers administered orally 1 mg/kg and dermally 10 mg/kg of Folpet. In both cases, the mean elimination half-life of PI from the body (either through faeces, urine or metabolism) was found to be 31.6 h. The average final fractions of administered dose recovered in urine as PI were 0.025% and 0.002%, for oral and dermal administration, respectively after 96 h. According to the model, when orally administered, PI rapidly hydrolyzes to phthalamic and phthalic acids such that only 0.04% of the PI found in the gastrointestinal tract is absorbed into the blood stream. Likewise, after dermal application, model predicts that only 7.4% of the applied Folpet dose crosses the epidermis. In the model, the PI initial metabolite of Folpet is formed in the dermis and further metabolized prior to reaching systemic circulation, such that only 0.125% of PI formed at the site-of-entry reaches systemic blood. Our mathematical model is in accordance with both measures of blood (R2=0.57 for dermal and R2=0.66 for oral) and urine (R2 =0.98 for dermal and R2=0.99 for oral).

Self-Confidence, Overconfidence and Prenatal Testosterone Exposure: Evidence from the Lab

This paper examines whether the degree of confidence and overconfidence in one's ability is determined biologically. In articular, we study whether foetal testosterone exposure correlates with an incentive-compatible measure of confidence within an experimental setting. We find that men (rather than women) who were exposed to high testosterone levels in their mother's womb are less likely to overestimate their actual performance, which in turn helps them to gain higher monetary rewards. Men exposed to low prenatal testosterone levels, instead, set unrealistically high expectations which results in self-defeating behaviour. These results from the lab are able to reconcile hitherto disconnected evidence from the field, by providing a link between traders'overconfidence bias, long-term financial returns and prenatal testosterone exposure.

The effects of feeding Karlodinium veneficum (PLY # 103; Gymnodinium veneficum Ballantine) to the blue mussel Mytilus edulis

The effects of exposure to the type species for Karlodinium veneficum (PLY # 103) on immune function and histopathology in the blue mussel Mytilus edulis were investigated. Mussels from Whitsand Bay, Cornwall (UK) were exposed to K. veneficum (PLY # 103) for 3 and 6 days. Assays for immune function included total and differential cells counts, phagocytosis and release of extra cellular reactive oxygen species. Histology was carried out on digestive gland and mantle tissues. The toxin cell quota for K. veneficum (PLY #103) was measured by liquid chromatography-mass spectrometry detecting two separable toxins KvTx1 (11.6 ± 5.4 ng/ml) and KvTx2 (47.7 ± 4.2 ng/ml). There were significant effects of K. veneficum exposure with increasing phagocytosis and release of reactive oxygen species following 6 days exposure. There were no significant effects on total cell counts. However, differential cell counts did show significant effects after 3 days exposure to the toxic alga. All mussels produced faeces but not pseudofaeces indicating that algae were not rejected prior to ingestion. Digestive glands showed ingestion of the algae and hemocyte infiltration after 3 days of exposure, whereas mantle tissue did not show differences between treatments. As the effects of K. veneficum were not observed in the mantle tissue it can be hypothesized that the algal concentration was not high enough, or exposure long enough, to affect all the tissues. Despite being in culture for more than 50 years the original K. veneficum isolate obtained by Mary Parke still showed toxic effects on mussels.

Pathology and immune response of the blue mussel (Mytilus edulis L.) after an exposure to the harmful dinoflagellate Prorocentrum minimum

The harmful dinoflagellate Prorocentrum minimum has different effects upon various species of grazing bivalves, and these effects also vary with life-history stage. Possible effects of this dinoflagellate upon mussels have not been reported; therefore, experiments exposing adult blue mussels, Mytilus edulis, to P. minimum were conducted. Mussels were exposed to cultures of toxic P. minimum or benign Rhodomonas sp. in glass aquaria. After a short period of acclimation, samples were collected on day 0 (before the exposure) and after 3, 6, and 9 days of continuous-exposure experiment. Hemolymph was extracted for flow-cytometric analyses of hemocyte, immune-response functions, and soft tissues were excised for histopathology. Mussels responded to P. minimum exposure with diapedesis of hemocytes into the intestine, presumably to isolate P. minimum cells within the gut, thereby minimizing damage to other tissues. This immune response appeared to have been sustained throughout the 9-day exposure period, as circulating hemocytes retained hematological and functional properties. Bacteria proliferated in the intestines of the P. minimum-exposed mussels. Hemocytes within the intestine appeared to be either overwhelmed by the large number of bacteria or fully occupied in the encapsulating response to P. minimum cells; when hemocytes reached the intestine lumina, they underwent apoptosis and bacterial degradation. This experiment demonstrated that M. edulis is affected by ingestion of toxic P. minimum; however, the specific responses observed in the blue mussel differed from those reported for other bivalve species. This finding highlights the need to study effects of HABs on different bivalve species, rather than inferring that results from one species reflect the exposure responses of all bivalves.

Experimental exposure of the blue mussel (Mytilus edulis, L.) to the toxic dinoflagellate Alexandrium fundyense: Histopathology, immune responses, and recovery

Mussels (Mytilus edulis) were exposed to cultures of the toxic dinoflagellate Alexandrium fundyense or the non-toxic alga Rhodomonas sp. to evaluate the effects of the harmful alga on the mussels and to study recovery after discontinuation of the A. fundyense exposure. Mussels were exposed for 9 days to the different algae and then all were fed Rhodomonas sp. for 6 more days. Samples of hemolymph for hemocyte analyses and tissues for histology were collected before the exposure and periodically during exposure and recovery periods. Mussels filtered and ingested both microalgal cultures, producing fecal pellets containing degraded, partially degraded, and intact cells of both algae. Mussels exposed to A. fundyense had an inflammatory response consisting of degranulation and diapedesis of hemocytes into the alimentary canal and, as the exposure continued, hemocyte migration into the connective tissue between the gonadal follicles. Evidence of lipid peroxidation, similar to the detoxification pathway described for various xenobiotics, was found; insoluble lipofuchsin granules formed (ceroidosis), and hemocytes carried the granules to the alimentary canal, thus eliminating putative dinoflagellate toxins in feces. As the number of circulating hemocytes in A. fundyense-exposed mussels became depleted, mussels were immunocompromised, and pathological changes followed, i.e., increased prevalences of ceroidosis and trematodes after 9 days of exposure. Moreover, the total number of pathological changes increased from the beginning of the exposure until the last day (day 9). After 6 days of the exposure, mussels in one of the three tanks exposed to A. fundyense mass spawned; these mussels showed more severe effects of the toxic algae than non-spawning mussels exposed to A. fundyense. No significant differences were found between the two treatments during the recovery period, indicating rapid homeostatic processes in tissues and circulating hemocytes.

Catabolite repression in Pseudomonas aeruginosa PAO1 regulates the uptake of C4 -dicarboxylates depending on succinate concentration.

In Pseudomonas aeruginosa carbon catabolite repression (CCR) is exerted by the CbrA/B-CrcZ-Crc global regulatory system. Crc is a translational repressor that, in the presence of preferred carbon sources, such as C4 -dicarboxylates, impairs the utilization of less preferred substrates. When non-preferred substrates are present, the CrcZ sRNA levels increase leading to Crc capture, thereby allowing growth of the bacterium at the expense of the non-preferred substrates. The C4 -dicarboxylate transport (Dct) system in P. aeruginosa is composed of two main transporters: DctA, more efficient at mM succinate concentrations, and DctPQM, more important at μM. In this study, we demonstrate that the Dct transporters are differentially regulated by Crc, depending on the concentration of succinate. At high concentrations, Crc positively regulates the expression of the dctA transporter gene and negatively regulates dctPQM post-transcriptionally. The activation of dctA is explained by a Crc-mediated repression of dctR, encoding a transcriptional repressor of dctA. At low succinate concentrations, Crc regulation is impaired. In this condition, CrcZ levels are higher and therefore more Crc proteins are sequestered, decreasing the amount of Crc available to perform CCR on dctR and dctPQM. As a result, expression of dctA is reduced and that of dctPQM is increased.

Influence of short time exposure to an insect growth regulator, hexaflumuron, on mortality and adult emergence of vector mosquitoes

Hexaflumuron, an insect growth regulator (IGR), was found to greatly affect the development of immatures and emergence of adults of three species of vector mosquitoes, Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi, when larvae were subjected to short time exposure of < or = 1h. This IGR could completely prevent adult emergence even at a minimum exposure time of 10 min at 0.001, 0.01 and 0.1 mg/l. On treatment, larval and pupal mortality as well as varying degrees of morphogenetic abnormalities were induced in immatures and adults of the three species. Four weeks of control achieved in a slow moving sullage canal breeding Culex quinquefasciatus indicates that this IGR can be of use in such breeding habitats.