Bacterial Cooperation Causes Systematic Errors in Pathogen Risk Assessment due to the Failure of the Independent Action Hypothesis

The Independent Action Hypothesis (IAH) states that pathogenic individuals (cells, spores, virus particles etc.) behave independently of each other, so that each has an independent probability of causing systemic infection or death. The IAH is not just of basic scientific interest; it forms the basis of our current estimates of infectious disease risk in humans. Despite the important role of the IAH in managing disease interventions for food and water-borne pathogens, experimental support for the IAH in bacterial pathogens is indirect at best. Moreover since the IAH was first proposed, cooperative behaviors have been discovered in a wide range of microorganisms, including many pathogens. A fundamental principle of cooperation is that the fitness of individuals is affected by the presence and behaviors of others, which is contrary to the assumption of independent action. In this paper, we test the IAH in Bacillus thuringiensis (B.t), a widely occurring insect pathogen that releases toxins that benefit others in the inoculum, infecting the diamondback moth, Plutella xylostella. By experimentally separating B.t. spores from their toxins, we demonstrate that the IAH fails because there is an interaction between toxin and spore effects on mortality, where the toxin effect is synergistic and cannot be accommodated by independence assumptions. Finally, we show that applying recommended IAH dose-response models to high dose data leads to systematic overestimation of mortality risks at low doses, due to the presence of synergistic pathogen interactions. Our results show that cooperative secretions can easily invalidate the IAH, and that such mechanistic details should be incorporated into pathogen risk analysis

A sample coordination method to monitor totals of environmental variables

A new sampling strategy for design-based environmental monitoring is proposed. It has the potential to produce superior estimators for totals of environmental variables and their changes over time. In the strategy, we combine two concepts known as spatially balanced sampling and coordination of samples. Spatially balanced sampling can provide superior estimators of totals, while coordination of samples over time is often used to improve estimators of change. Compared with reference strategies, we show that the new strategy can improve the precision of the estimators of totals and their change simultaneously. A forest inventory application is used to illustrate the new strategy and the results can be summarized as (i) using auxiliary information to spread the sample can improve the estimators of totals; (ii) a positive coordination of the samples reduced the variance of the estimator of change by more than 37% compared with independent samples; and (iii) a high overlap between successive samples does not guarantee a good estimator of change. The presented strategy can be used to develop more efficient environmental monitoring programs

An Arizona Guide to Water Quality and Uses

10 pp.Introduction: Adult human beings may drink up to two liters/day (approx. two quarts/day) of fresh water to stay alive. However, we can consume up to two quarts/hour of water, depending on the level of activity, ambient temperature, and humidity conditions (Born 2013). We also need fresh water to cook with and to clean ourselves. About 40% of our food production depends on irrigation (UN Water 2013) using water with low salinity and other contaminants. Climate scientists project increasing temperatures and possibly less rainfall in the Southwest now and into the near future, see Extension Publication #AZ1458 (Artiola et al. 2008). Thus, climate change is likely to stress the limited water resources of Arizona and affect water quality by concentrating contaminants and stressing water-dependent environments. This publication presents brief summaries of the types of water sources, their water quality, and possible uses in Arizona. Since the types and amounts of constituents found in water, whether nutrients, pathogens, contaminants or pollutants, help determine its possible uses, it is necessary to measure water quality to determine treatment options for a given use. To assist in this task, we present a triangle-shaped diagram (Figure 8) which divides water quality into three major groups: Pathogens, Salinity, and Specific Contaminants, placing major water sources in relation to the three groups. Home and well owners can use this diagram as a general aid to evaluate various sources of water, determine their likely water quality, and identify appropriate uses for them