Robin M. Slawson

Use of Tetrahymena thermophila to study the role of protozoa in inactivation of viruses in water.

ABSTRACT The ability of a ciliate to inactivate bacteriophage was studied because these viruses are known to influence the size and diversity of bacterial populations, which affect nutrient cycling in natural waters and effluent quality in sewage treatment, and because ciliates are ubiquitous in aquatic environments, including sewage treatment plants. Tetrahymena thermophila was used as a representative ciliate; T4 was used as a model bacteriophage. The T4 titer was monitored on Escherichia coli B in a double-agar overlay assay. T4 and the ciliate were incubated together under different conditions and for various times, after which the mixture was centrifuged through a step gradient, producing a top layer free of ciliates. The T4 titer in this layer decreased as coincubation time increased, but no decrease was seen if phage were incubated with formalin-fixed Tetrahymena. The T4 titer associated with the pellet of living ciliates was very low, suggesting that removal of the phage by Tetrahymena inactivated T4. When Tetrahymena cells were incubated with SYBR gold-labeled phage, fluorescence was localized in structures that had the shape and position of food vacuoles. Incubation of the phage and ciliate with cytochalasin B or at 4°C impaired T4 inactivation. These results suggest the active removal of T4 bacteriophage from fluid by macropinocytosis, followed by digestion in food vacuoles. Such ciliate virophagy may be a mechanism occurring in natural waters and sewage treatment, and the methods described here could be used to study the factors influencing inactivation and possibly water quality.

Effect of gold nanoparticles and ciprofloxacin on microbial catabolism: a community‐based approach

The effect of gold nanoparticles (AuNPs) and ciprofloxacin on the catabolism of microbial communities was assessed. This was accomplished through an ex situ methodology designed to give a priori knowledge on the potential for nanoparticles, or other emerging contaminants, to affect the catabolic capabilities of microbial communities in the environment. Microbial communities from a variety of sources were incubated with 31 prespecified carbon sources and either National Institute of Standards and Technology reference material 10-nm AuNPs or ciprofloxacin on 96-well microtiter plates. From the ciprofloxacin study, dose-response curves were generated and exemplified how this method can be used to assess the effect of a toxicant on overall catabolic capabilities of microbial communities. With 10-nm AuNPs at concentrations ranging from 0.01 µg/mL to 0.5 µg/mL, rhizosphere communities from Typha roots were only slightly catabolically inhibited at a single concentration (0.05 µg/mL); no effects were seen on wetland water communities, and a minor positive (i.e., enhanced catabolic capabilities) effect was observed for loamy soil communities. This positive effect might have been because of a thin layer of citrate found on these AuNPs that initiated cometabolism with some of the carbon sources studied. Under the conditions considered, the possible adverse effects of AuNPs on the catabolic capabilities of microbial communities appears to be minimal.

Assessing levels of pathogenic contamination in a heavily impacted river used as a drinking-water source.

This paper describes initial results from a research program that aims to gain greater understanding of sources of pathogens and the environmental factors that influence their survival and transport in watersheds. An additional goal is to enhance the ability to predict potential levels of pathogenic microorganisms arriving at drinking-water treatment plant intakes. The objectives will be supported by an intensive monitoring program examining the temporal and spatial variability of pathogens in a test watershed (the Grand River Watershed, Ontario). As many as 500,000 people potentially receive at least part of their drinking water from the Grand River. The watershed has significant urban and agricultural use. Sampling for total coliforms, fecal coliforms, Escherichia coli, Escherichia coli O157:H7, and Campylobacter spp. began in July 2002. Although presumptive tests were occasionally positive, no Escherichia coli O157:H7 or Campylobacter spp. were confirmed to be present in water samples taken. Escherichia coli O157:H7 was, however, detected in a tributary of the Grand River during an initial investigation. Preliminary results did not show any statistically significant differences between coliform concentrations upstream and downstream of wastewater treatment plants. Data suggest that nonpoint sources may have a greater effect on routine stream coliform concentrations.

An Evaluation of Behavioral Health Compliance and Microbial Risk Factors on Student Populations within a High-Density Campus.

Abstract Objective: The aim of this Canadian study was to assess student behavioral response to disease transmission risk, while identifying high microbial deposition/transmission sites. Participants: A student survey was conducted during October 2009. Methods: The methods included a survey of students to assess use of health services, vaccination compliance, and hygiene along with a microbial analysis of potential transmission sites targeting specific residence buildings on campus. Results: Results indicated that most students maintained that they were worried about H1N1 and reported making changes in hygienic behavior, with the majority not planning to be vaccinated. The microbial analysis indicated contamination of fomites in co-ed residences to be higher than either male or female student residences. Conclusions: A consideration of physical space along with behavioral factors is required in order to properly assess risk pathways in the establishment of an evidence-based infection control plan for universities and their contiguous communities.