Search

Self-transmissible and mobilizable plasmids contribute to the emergence and spread of multidrug-resistant bacteria by enabling the horizontal transfer of acquired antibiotic resistance. The objective of this study was to capture and characterize self-transmissible and mobilizable resistance plasmids from a coastal wetland impacted by urban stormwater runoff and human wastewater during the rainy season. Four plasmids were captured, two self-transmissible and two mobilizable, using both mating and enrichment approaches. Plasmid genomes, sequenced with either Illumina or PacBio platforms, revealed representatives of incompatibility groups IncP-6, IncR, IncN3, and IncF. The plasmids ranged in size from 36 to 144 kb and encoded known resistance genes for most of the major classes of antibiotics used to treat Gram-negative infections (tetracyclines, sulfonamides, β-lactams, fluoroquinolones, aminoglycosides, and amphenicols). The mobilizable IncP-6 plasmid pLNU-11 was discovered in a strain of Citrobacter freundii enriched from the wetland sediments with tetracycline and nalidixic acid, and encodes a novel AmpC-like β-lactamase (blaWDC-1), which shares less than 62% amino acid sequence identity with the PDC class of β-lactamases found in Pseudomonas aeruginosa. Although the IncR plasmid pTRE-1611 was captured by mating wetland bacteria with P. putida KT2440 as recipient, it was found to be mobilizable rather than self-transmissible. Two self-transmissible multidrug-resistance plasmids were also captured: the small (48 kb) IncN3 plasmid pTRE-131 was captured by mating wetland bacteria with Escherichia coli HY842 where it is seemed to be maintained at nearly 240 copies per cell, while the large (144 kb) IncF plasmid pTRE-2011, which was isolated from a cefotaxime-resistant environmental strain of E. coli ST744, exists at just a single copy per cell. Furthermore, pTRE-2011 bears the globally epidemic blaCTX-M-55 extended-spectrum β-lactamase downstream of ISEcp1. Our results indicate that urban coastal wetlands are reservoirs of diverse self-transmissible and mobilizable plasmids of relevance to human health.

Juvenile tagging and escapement enumeration was conducted during 1985-1988 in nine streams within a 150-km section on the east coast of Vancouver Island. Fourteen coho salmon (Oncorhynchus kisutch) stocks of wild, hatchery, and mixed origin were monitored for ocean survival and exploitation patterns. Estimates of smolt-to-adult survival ranged from 0.5 to 23.1%. Survival rates were highly variable across years and stocks. No stock or stock type had consistently higher survival, but one hatchery stock exhibited consistently lower survival. Average exploitation rates were about 80% each year, and were as high as 96% for some stocks. Exploitation rates were not consistently higher or lower for any stock or stock type, but hatchery reared coho tended to be subject to higher exploitation. Log-linear models were used to assess the effects of various factors on survival and exploitation. Certain hatchery rearing practices had a large influence on survival. Genetic factors, run timing, and stream location had large influences on exploitation rates. An assessment of covariation in survival and exploitation rates showed no indication of a high level of similarity among stocks from adjacent streams or among stock types in this region.

Sustainable exploitation of renewable resources depends on the existence of a reproductive surplus, which is determined by the balance between births, deaths, and somatic growth. The reproductive surplus differs spatially and temporally as environmental conditions vary, and even in the absence of exploitation, change is the rule and constancy is the exception. Sustainable yields may be estimated by direct experimentation, observation of natural systems, or deduction from biological understanding. Each of these approaches has limitations, and for large-scale unique resources, the only way to determine the response of the population to harvesting is by direct exploitation. To find the maximum potential yield, the resource must be overexploited at some time, or very similar resources must have been overexploited. Temporal changes in environmental conditions mean that information on sustainability collected in the past may have limited applicability in the future. The unregulated dynamic of exploiters is to push the resources to overexploitation, and even when regulated, exploiters have been very successful at modifying their behavior so that regulations are less effective than anticipated. The most successful institutions at maintaining sustainability have been small-scale community or pri

The problem of robust estimation of optimal effort levels from surplus production models is considered. A variety of models are used to generate data, for the purpose of testing estimation schemes. The result of an estimation is an estimate of the optimal effort. These efforts are compared using the expected discounted value of a deterministic stock, which corresponds to the model used to generate the data. Such a criterion takes into account not only the loss due to bias in the estimated optimal effort, but also the loss due to the variance of the estimator. Estimation is difficult if there is a lack of informative variation in effort levels or stock sizes. In such cases, the estimation scheme which maximizes the criterion described above sacrifices realism in the representation of the stock-production relationship in order to reduce the variance of the estimate of optimal effort. We present a composite estimation scheme which performs acceptably in all the cases we have examined, and whose performance degrades slowly as the amount of information in the data decreases.

(1978). Initial impacts of experimental fish introductions on the macrozooplankton of small oligotrophic lakes. SIL Proceedings, 1922-2010: Vol. 20, No. 3, pp. 2003-2012.

The response of individuals to uncertainty is itself unpredictable. Some entrepreneurs thrive successfully in the most uncertain circumstances, and the existence of futures markets and insurance companies indicates that others are prepared to pay to avoid carrying the burden of uncertainty.

Fisheries management must face three types of uncertainties: environmental variations that will continue to be unpredictable, errors in production model parameter estimates and structures that can in principle be reduced over time, and persistent changes in parameters and structure due to a host of possible factors that are mostly unpredictable even in principle. Thus we must learn to live with continuing uncertainty as a basic feature of fisheries policy design. Uncertainties of the first type can be dealt with nicely without ever pretending to forecast responses accurately, by using robust feedback policies. Reduction in uncertainties of the second type depends fundamentally on what management policies are used, and here the idea of dual control or experimental policies appears very promising. Contrary to what some optimists have supposed, uncertainties of the third type cannot in general be sorted out through statistical procedures for adaptively reestimating parameters, since various effects are generally confounded with one another. Detailed process research and understanding may be of some help, but ultimately we may be forced to use the old scientific idea of replicated experimental units that are deliberately treated in different ways.

Imipramine in 25 mg. daily doses was found to be an effective agent for the control of enuresis. In a double-blind study, 17 of 23 (74%) severely enuretic boys showed marked improvement on the drug compared to the placebo when each medication was given for 20 days. Nightly incidence of enuresis was reduced from a mean of 70% to 47%. This difference is highly significant (P

Using theoretical arguments and a computer simulation model, we have concluded that in- creased yields may be obtained from some big game populations by harvesting only once every several years. Since productivity per female increases with age in most big game populations, and since hunting shifts the age distribution towards younger animals, annual harvest may result in lowered mean produc- tivity. Periodic harvest may help prevent changes in productivity. Computer simulation suggests that yield may be increased by 10 to 20 percent by periodic harvest and that the best interval between har- vests is usually 24 years. Abstract: Using theoretical arguments and a computer simulation model, we have concluded that in- creased yields may be obtained from some big game populations by harvesting only once every several years. Since productivity per female increases with age in most big game populations, and since hunting shifts the age distribution towards younger animals, annual harvest may result in lowered mean produc- tivity. Periodic harvest may help prevent changes in productivity. Computer simulation suggests that yield may be increased by 10 to 20 percent by periodic harvest and that the best interval between har