Modification of enrofloxacin treatment regimens for poultry experimentally infected with Salmonella enterica serovar Typhimurium DT104 to minimize selection of resistance

We hypothesized that higher doses of fluoroquinolones for a shorter duration could maintain efficacy (as measured by reduction in bacterial count) while reducing selection in chickens of bacteria with reduced susceptibility. Chicks were infected with Salmonella enterica serovar Typhimurium DT104 and treated 1 week later with enrofloxacin at the recommended dose for 5 days (water dose adjusted to give 10 mg/kg of body weight of birds or equivalence, i.e., water at 50 ppm) or at 2.5 or 5 times the recommended dose for 2 days or 1 day, respectively. The dose was delivered continuously (ppm) or pulsed in the water (mg/kg) or by gavage (mg/kg). In vitro in sera, increasing concentrations of 0.5 to 8 mu g/ml enrofloxacin correlated with increased activity. In vivo, the efficacy of the 1-day treatment was significantly less than that of the 2- and 5-day treatments. The 2-day treatments showed efficacy similar to that of the 5-day treatment in all but one repeat treatment group and significantly (P < 0.01) reduced the Salmonella counts. Dosing at 2.5x the recommended dose and pulsed dosing both increased the peak antibiotic concentrations in cecal contents, liver, lung, and sera as determined by high-pressure liquid chromatography. There was limited evidence that shorter treatment regimens (in particular the 1-day regimen) selected for fewer strains with reduced susceptibility. In conclusion, the 2-day treatment would overall require a shorter withholding time than the 5-day treatment and, in view of the increased peak antibiotic concentrations, may give rise to improved efficacy, in particular for treating respiratory and systemic infections. However, it would be necessary to validate the 2-day regimen in a field situation and in particular against respiratory and systemic infections to validate or refute this hypothesis.

Determination of the impact of continuous defoliation of Lolium perenne and Trifolium repens on bacterial and fungal community structure in rhizosphere soil

To determine the effects of defoliation on microbial community structure, rhizosphere soil samples were taken pre-, and post-defoliation from the root tip and mature root regions of Trifolium repens L. and Lolium perenne L. Microbial DNA isolated from samples was used to generate polymerase chain reaction-denaturing gradient gel electrophoresis molecular profiles of bacterial and fungal communities. Bacterial plate counts were also obtained. Neither plant species nor defoliation affected the bacterial and fungal community structures in both the root tip and mature root regions, but there were significant differences in the bacterial and fungal community profiles between the two root regions for each plant. Prior to defoliation, there was no difference between plants for bacterial plate counts of soils from the root tip regions; however, counts were greater in the mature root region of L. perenne than T. repens. Bacterial plate counts for T. repens were higher in the root tip than the mature root region. After defoliation, there was no effect of plant type, position along the root or defoliation status on bacterial plate counts, although there were significant increases in bacterial plate counts with time. The results indicate that a general effect existed during maturation in the root regions of each plant, which had a greater impact on microbial community structure than either plant type or the effect of defoliation. In addition there were no generic consequences with regard to microbial populations in the rhizosphere as a response to plant defoliation.

Use of an artificial root to examine the influence of 8-hydroxyquinoline on soil microbial activity and bacterial community structure

Invasive plant species have been shown to alter the microbial community composition of the soils they invade and it is suggested that this below-ground perturbation of potential pathogens, decomposers or symbionts may feedback positively to allow invasive success. Whether these perturbations are mediated through specific components of root exudation are not understood. We focussed on 8-hydroxyquinoline, a putative allelochemical of Centaurea diffusa (diffuse knapweed) and used an artificial root system to differentiate the effects of 8-hydroxyquinoline against a background of total rhizodeposition as mimicked through supply of a synthetic exudate solution. In soil proximal (0-10 cm) to the artificial root, synthetic exudates had a highly significant (P < 0.001) influence on dehydrogenase, fluorescein diacetate hydrolysis and urease activity. in addition, 8-hydroxyquinoline was significant (p = 0.003) as a main effect on dehydrogenase activity and interacted with synthetic exudates to affect urease activity (p = 0.09). Hierarchical cluster analysis of 16S rDNA-based DGGE band patterns also identified a primary affect of synthetic exudates and a secondary affect of 8-hydroxyquinoline on bacterial community structure. Thus, we show that the artificial rhizosphere produced by the synthetic exudates was the predominant effect, but, that the influence of the 8-hydroxyquinoline signal on the activity and structure of soil microbial communities could also be detected. (C) 2009 Elsevier Ltd. All rights reserved.

An extension of an over-dispersion test for count data

While over-dispersion in capture–recapture studies is well known to lead to poor estimation of population size, current diagnostic tools to detect the presence of heterogeneity have not been specifically developed for capture–recapture studies. To address this, a simple and efficient method of testing for over-dispersion in zero-truncated count data is developed and evaluated. The proposed method generalizes an over-dispersion test previously suggested for un-truncated count data and may also be used for testing residual over-dispersion in zero-inflation data. Simulations suggest that the asymptotic distribution of the test statistic is standard normal and that this approximation is also reasonable for small sample sizes. The method is also shown to be more efficient than an existing test for over-dispersion adapted for the capture–recapture setting. Studies with zero-truncated and zero-inflated count data are used to illustrate the test procedures.

Estimating the hidden number of scrapie affected holdings in great Britain using a simple, truncated count model allowing for heterogeneity.

None of the current surveillance streams monitoring the presence of scrapie in Great Britain provide a comprehensive and unbiased estimate of the prevalence of the disease at the holding level. Previous work to estimate the under-ascertainment adjusted prevalence of scrapie in Great Britain applied multiple-list capture–recapture methods. The enforcement of new control measures on scrapie-affected holdings in 2004 has stopped the overlapping between surveillance sources and, hence, the application of multiple-list capture–recapture models. Alternative methods, still under the capture–recapture methodology, relying on repeated entries in one single list have been suggested in these situations. In this article, we apply one-list capture–recapture approaches to data held on the Scrapie Notifications Database to estimate the undetected population of scrapie-affected holdings with clinical disease in Great Britain for the years 2002, 2003, and 2004. For doing so, we develop a new diagnostic tool for indication of heterogeneity as well as a new understanding of the Zelterman and Chao’s lower bound estimators to account for potential unobserved heterogeneity. We demonstrate that the Zelterman estimator can be viewed as a maximum likelihood estimator for a special, locally truncated Poisson likelihood equivalent to a binomial likelihood. This understanding allows the extension of the Zelterman approach by means of logistic regression to include observed heterogeneity in the form of covariates—in case studied here, the holding size and country of origin. Our results confirm the presence of substantial unobserved heterogeneity supporting the application of our two estimators. The total scrapie-affected holding population in Great Britain is around 300 holdings per year. None of the covariates appear to inform the model significantly.

Formulation of a live bacterial vaccine for stable room temperature storage results in loss of acid, bile and bile salt resistance

Live bacterial vaccines have great promise both as vaccines against enteric pathogens and as heterologous antigen vectors against diverse diseases. Ideally, room temperature stable dry formulations of live bacterial vaccines will allow oral vaccination without cold-chain storage or injections. Attenuated Salmonella can cross the intestinal wall and deliver replicating antigen plus innate immune activation signals directly to the intestinal immune tissues, however the ingested bacteria must survive firstly gastric acid and secondly the antimicrobial defences of the small intestine. We found that the way in which cells are grown prior to formulation markedly affects sensitivity to acid and bile. Using a previously published stable storage formulation that maintained over 10% viability after 56 days storage at room temperature, we found dried samples of an attenuated S. typhimurium vaccine lost acid and bile resistance compared to the same bacteria taken from fresh culture. The stable formulation utilised osmotic preconditioning in defined medium plus elevated salt concentration to induce intracellular trehalose accumulation before drying. Dried bacteria grown in rich media without osmotic preconditioning showed more resistance to bile, but less stability during storage, suggesting a trade-off between bile resistance and stability. Further optimization is needed to produce the ultimate room-temperature stable oral live bacterial vaccine formulation.

Formulation and delivery of the bacterial antagonist Bacillus subtilis for management of lentil vascular wilt caused by Fusarium oxysporum f. sp lentis

Different formulations of Bacillus subtilis were prepared using standard laboratory protocols. Bacillus subtilis survived in glucose and talc powders at 8.6 and 7.8 log(10) CFU/g, respectively, for 1 year of storage at room temperature compared with 3.5 log(10) CFU/g on a peat formulation. Glasshouse experiments using soil and seed treatments were conducted to test the efficacy of B. subtilis for protecting lentil against the wilt disease caused by Fusariumoxysporum f. sp. lentis. Seed treatments with formulations of B. subtilis on glucose, talc and peat significantly enhanced its biocontrol activity against Fusarium compared with a treatment in which spores were applied directly to seed. The formulations decreased disease severity by reducing colonization of plants by the pathogen, promoting their growth and increased the dry weight of lentil plants. Of these treatments the glucose and talc-based powder formulations were more effective than the peat formulation and the spore application without a carrier. It was shown that the B. subtilis spores applied with glucose were viable for longer than those applied with other carriers. Seed treatment with these formulated spores is an effective delivery system that can provide a conducive environment for B. subtilis to suppress vascular wilt disease on lentil and has the potential for utilization in commercial field application.

Factors affecting biological control effectiveness of Pasteuria penetrans in Meloidogyne javanica and the bacterial development in the nematode body

The invasion and infectivity of Meloidogyne javanica juveniles (J2) encumbered with spore of Pasteuria Penetrans were influenced by the temperature and the time J2 were in the soil before exposure to roots. The percentage of infected females decreased as the time juveniles spent in soil increased. When spore encumbered J2 were maintained at 30 degrees C the decrease in infection was greater than that at 18 degrees C. The thermal time requirements and the base temperature for P. penetrans development were estimated. The rate of development followed an exponential curve between 21 and 36 degrees C and the base temperature for development was estimated by extrapolation to be 18.5 degrees C. The effect of integrating a nematode resistant tomato cultivar with the biocontrol agent P. penetrans also was investigated. The ability of the biocontrol agent to reduce numbers of root-knot nematodes was dependent on the densities of the nematode and P. penetrans spores in the soil.

Antagonistic potential of bacterial isolates associated with entomopathogenic nematodes against tomato wilt caused by Fusarium oxysporum f.sp., Lycopersici under greenhouse conditions

Three concentrations of Xenorhabdus nematophila and Xenorhabdus spp., (4x10(5,) 4x10(6,) 4x10(7) cells/ml) were evaluated in the laboratory and in pot experiments to test their antagonistic effects on Fusarium oxysporum f.sp., lycopersici. All concentrations effectively inhibited its growth on agar plates. In soil under greenhouse conditions treatments with each bacterium at 4x10(7) cells/ml reduced the disease incidence of tomato by up to 40.38 and 47.54% respectively and there were significant increases of plant biomass by 198 and 211% respectively. The rhizosphere population of Fusarium oxysporum f.sp., lycopersici was reduced by 97%. The Xenorhabdus spp., was comparatively more effective than X. nematophila.

Susceptibility of different insect pupae to the bacterial symbiont, Xenorhabdus nematophila, isolated from the entomopathogenic nematode Steinernema carpocapsae

Cells of the bacterial symbiont Xenorhabdus nematophila from the entomopathogenic nematode, Steinernema carpocapsae entered the pupae of Plutella xylostella after 15 minutes treatment with suspensions containing the bacterial cells. Secretions of Xenorhabdus nematophila, in either broth or water, were found lethal to the pupae of P. xylostella when applied in moist sand. The bacterial symbiont Xenorhabdus nematophila was found lethal to the pupae of greater wax moth (Galleria mellonella), beet armyworm (Spodoptera exigua), diamondback moth (Plutella xylostella) and black vine weevil (Otiorhynchus sulcatus) in the absence of the nematode vector and the cells of X. nematophila entered the haemocoele of the pupae.

Mixture models for capture-recapture count data

The contribution investigates the problem of estimating the size of a population, also known as the missing cases problem. Suppose a registration system is targeting to identify all cases having a certain characteristic such as a specific disease (cancer, heart disease, ...), disease related condition (HIV, heroin use, ...) or a specific behavior (driving a car without license). Every case in such a registration system has a certain notification history in that it might have been identified several times (at least once) which can be understood as a particular capture-recapture situation. Typically, cases are left out which have never been listed at any occasion, and it is this frequency one wants to estimate. In this paper modelling is concentrating on the counting distribution, e.g. the distribution of the variable that counts how often a given case has been identified by the registration system. Besides very simple models like the binomial or Poisson distribution, finite (nonparametric) mixtures of these are considered providing rather flexible modelling tools. Estimation is done using maximum likelihood by means of the EM algorithm. A case study on heroin users in Bangkok in the year 2001 is completing the contribution.

On the question of proportionality of the count of observed Scrapie cases and the size of holding

Background: The present paper investigates the question of a suitable basic model for the number of scrapie cases in a holding and applications of this knowledge to the estimation of scrapie-ffected holding population sizes and adequacy of control measures within holding. Is the number of scrapie cases proportional to the size of the holding in which case it should be incorporated into the parameter of the error distribution for the scrapie counts? Or, is there a different - potentially more complex - relationship between case count and holding size in which case the information about the size of the holding should be better incorporated as a covariate in the modeling? Methods: We show that this question can be appropriately addressed via a simple zero-truncated Poisson model in which the hypothesis of proportionality enters as a special offset-model. Model comparisons can be achieved by means of likelihood ratio testing. The procedure is illustrated by means of surveillance data on classical scrapie in Great Britain. Furthermore, the model with the best fit is used to estimate the size of the scrapie-affected holding population in Great Britain by means of two capture-recapture estimators: the Poisson estimator and the generalized Zelterman estimator. Results: No evidence could be found for the hypothesis of proportionality. In fact, there is some evidence that this relationship follows a curved line which increases for small holdings up to a maximum after which it declines again. Furthermore, it is pointed out how crucial the correct model choice is when applied to capture-recapture estimation on the basis of zero-truncated Poisson models as well as on the basis of the generalized Zelterman estimator. Estimators based on the proportionality model return very different and unreasonable estimates for the population sizes. Conclusion: Our results stress the importance of an adequate modelling approach to the association between holding size and the number of cases of classical scrapie within holding. Reporting artefacts and speculative biological effects are hypothesized as the underlying causes of the observed curved relationship. The lack of adjustment for these artefacts might well render ineffective the current strategies for the control of the disease.