Lake Erie | EPFL Graph Search

Lake Erie (ˈɪəri ) is the fourth-largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and also has the shortest average water residence time. At its deepest point Lake Erie is deep. Situated on the International Boundary between Canada and the United States, Lake Erie's northern shore is the Canadian province of Ontario, specifically the Ontario Peninsula, with the U.S. states of Michigan, Ohio, Pennsylvania, and New York on its western, southern, and eastern shores. These jurisdictions divide the surface area of the lake with water boundaries. The largest city on the lake is Cleveland, anchoring the third largest U.S. metro area in the Great Lakes region, after Greater Chicago and Metro Detroit. Other major cities along the lake shore include Buffalo, New York; Erie, Pennsylvani

Presence of sub-inhibitory concentrations of quaternary ammonium compounds in water: effects on bacteria and their inactivation by ozone and monochloramine

Margaux Océane Voumard

Disinfection agents have been present in our daily lives for several decades in detergents or in personal care products, where their role is to prevent the spread of pathogenic microor-ganisms. One of the largest class of disinfection agents is quaternary ammonium compounds (QACs). Within this class, cetyltrimethylammonium chloride (CTMA) and benzalkonium chlo-ride (BAC) are widely used. QACs have a broad-spectrum effect on bacteria, where they pri-marily target the membrane. After use, QACs are partially discharged to municipal wastewaters, where they are diluted to concentrations in the sub-inhibitory range. These low concentrations of QACs can trigger resistance mechanisms in bacteria, including membrane modifications and the expression of efflux pumps.The aim of this thesis was to investigate the consequences and the impact of the presence of low concentrations of QACs in wastewater and surface water on the survival of bacteria. It could be demonstrated that strains of P. aeruginosa long-term exposed to constant sub-inhibitory concentrations of either BAC or CTMA showed decreased susceptibility to both QACs, regardless of which QAC the bacteria had been exposed to. However, no resistance to selected antibiotics was found after this exposure. Investigations of the membrane using atomic force microscopy showed an increase in surface roughness following exposure to both BAC and CTMA, demonstrating that QACs affect bacterial membranes.QACs are poorly biodegradable and their presence, even at constant sub-inhibitory concen-trations, affect bacteria. QACs are poorly reactive with chemical oxidants commonly used for water disinfection, which aims to inactivate microorganisms. Therefore, QACs remain present during water and wastewater treatment. Several methods of disinfection exist, where ozona-tion and monochloramination are widely applied worldwide. The effect of a pre-exposure of E. coli to CTMA and of the presence of CTMA during disinfection with ozone (O3) and mono-chloramine (NH2Cl) were investigated. The pre-exposure to CTMA led to contrasting results: inactivation of E. coli was enhanced when using ozone but decreased when using monochlo-ramine. This result demonstrates the different modes of inactivation of bacteria for ozone and monochloramine. Moreover, the role of efflux pumps during inactivation was tested with two strains of E. coli, expressing different efflux pump systems. These two strains showed contrasting behaviors when treated with either ozone or monochloramine. Nevertheless, we were unable to resolve the role of efflux pumps in this system. The presence of CTMA en-hanced the inactivation when concentrations were higher than 2 mgL-1 for ozone and 2.25 mgL-1 for monochloramine.Standard methods to determine the minimum inhibitory concentration use ideal conditions for bacterial growth, which do not occur in natural water. Therefore, the susceptibility of E. coli to CTMA in PBS, lake water (Lake Geneva, Switzerland) and a wastewater effluent was investigated and compared to nutrient broth. It could be shown that E. coli was significantly more susceptible to CTMA in dilute aqueous solutions compared to broth. These results are relevant to assess the effect of CTMA and potentially other biocides on bacteria under realis-tic conditions, as it is probably overestimated using the current standard methods for MICs determination.

EPFL2021

Sources, Spreading and Fate of Antibiotic Resistance Genes and Resistant Bacteria in Vidy Bay, Lake Geneva, Switzerland

Nadine Czekalski

Increasing numbers of multiresistant bacterial pathogens cause severe health problems on a global scale. Large quantities of bacteria and their resistance genes are discharged into natural environments via human and animal waste. Not much is known so far about the fate and further spread of resistance determinants in the environment. There is evidence that aquatic environments may function as important compartments for preserving and exchanging antibiotic resistance genes (ARG) from sewage and drinking water. Lake Geneva is the largest fresh water reservoir of Western Europe and supplies the surrounding cities. At the same time these cities discharge sewage into the lake. Lausanne is the largest city in the lake’s catchment and discharges the highest amount of treated, as well as in case of heavy rain events, partly untreated waste waters. Also two rivers, Chambering and Flown, transport untreated sewage (bypass), in case of storm events. Only 3.4 km from the sewage discharge point lake water is pumped for drinking water preparation for Lausanne. Many studies have reported on contamination of the bay with heavy metals, inorganic nutrients, organic carbon and fecal indicator bacteria due to the sewage discharge. The present thesis aimed on investigating the sources, spreading and fate of antibiotic resistant bacteria and antibiotic resistance genes in the Vida bay, Lake Geneva. In the first part of this dissertation, a screening for antibiotic- and specifically multi-resistant bacteria was carried out as one of the first studies in a Swiss waste water stream and the receiving fresh water lake. For this purpose, a combined set of culture based (viable bacterial counts on nutrient media supplemented with antibiotics) and molecular tools (detection and quantitation of antibiotic resistance genes from environmental DNA-extracts using quantitative real-time PCR) was applied. Raw hospital and communal sewage, as well as partly treated/mixed sewage, which is discharged into the lake via an effluent pipe 700 m off shore, were taken into account. Furthermore lake water samples nearby the end of the waste water discharge pipe and the drinking water pump as well as close to the two river mouths were analyzed. Finally, the role of Lausannes WTP was evaluated for its potential to remove resistant and multiresistant bacteria, as well ARG. Results show highest levels of multiresistant bacteria and ARG in both hospital and communal sewage. Incidence was found that the WTP is a selective environment for multiresistant bacteria and resistance genes. Moreover, lake water and sediments nearby the end of the WTP discharge pipe and the two river mouths exhibited significantly higher levels of resistant determinants as compared to samples from the drinking water uptake. If the level of antibiotic resistance close to the drinking water uptake represents the natural background level of the lake or whether it is impacted by the WTP plume remained open during this first survey. The spatial distribution and persistence of ARG discharged via waste water into lake systems has been evaluated for the first time in the second part of this thesis. 22 sediment cores were sampled along two major transects (leading either into the deep lake or along the south-western shore line to the drinking water uptake) and in the vicinity of the WTP discharge pipe in the Vidy bay. A subset of samples was also analyzed for contamination with a “conventional” pollutant of sewage (mercury), for which a similar transport behavior (particle bound) as for bacteria and their resistance genes is assumed. The microbial community composition in all sediment as well as in waste water samples was analyzed using ARISA. Strong pollution with both ARG and mercury was detected in close proximity of the WTP discharge pipe and both contaminants significantly decreased along the transect into the deep lake. In general however, the spatial contamination of mercury and ARG was only moderately correlated. While the mercury contaminated sediment surface area tended to have a pollution tail in south eastern direction, ARG showed only a slow decrease along the south western transect. These findings imply differences in transport and fate of mercury and ARG in the bay, or additional sources of ARG contamination. Analysis of the microbial diversity in the samples support these hypotheses. This study revealed feasibility of qPCR as a tool to semi-quantitatively track spatial ARG contamination in fresh water lake sediments. Not much is known yet on the antibiotic resistance background level of fresh water lakes and how this may be influenced by anthropogenic activities in the surrounding catchment. Water samples from 21 Swiss lakes have been collected and were analyzed for the prevalence of different ARG (2 sulfonamide resistance genes sul1 & sul2, 3 tetracycline resistance genes tetB, tetM, tetW and one plasmid mediated fluoroquinolone resistance gene qnrA). In order to document the abundance of these genes in the bacterial populations, they were normalized to bacterial 16S rRNA gene copy numbers. The lakes differ in size, geographical position, land use pattern, and trophical status. The composition of the microbial community of all lakes was analyzed using ARISA. Sulfonamide resistance genes were detected in all investigated lakes (0.2-4%, sul1 and 0.01-0.3%, sul2), with highest levels in Lake Baldegger (21%). Lake Baldegger also contained all of the three tetracycline resistance genes, which were found in only 4 other lakes. None of the lakes was positive for qnrA. Important anthropogenic catchment activities linked to sul gene prevalence could not be identified based on our data and may require further analysis and an additional variables to complete our data set. However, our study demonstrates contamination of Swiss lakes with sulfonamide resistance genes and the potential of fresh water lakes preserve these genes, even remote from direct sources of pollution.

EPFL2013

Control of Waterborne Human Viruses by Indigenous Bacteria and Protists Is Influenced by Temperature, Virus Type, and Microbial Species

Anna Carratala Ripolles, Charles Zeng Gan, Tamar Kohn, Margot Ninon Lauren Olive

Human viruses are ubiquitous contaminants in surface waters, where they can persist over extended periods of time. Among the factors governing their environmental persistence, the control (removal or inactivation) by microorganisms remains poorly understood. Here we determined the contribution of indigenous bacteria and protists to the decay of human viruses in surface waters. Incubation of echovirus 11 (E11) in freshwater from Lake Geneva and seawater from the Mediterranean Sea led to a 2.5-log10 reduction in the infectious virus concentration within 48 hours at 22°C, whereas E11 was stable in sterile controls. The observed virus reduction was attributed to the action of both bacteria and protists in the biologically active matrices. The effect of microorganisms on viruses was temperature-dependent, with a complete inhibition of microbial virus control in lake water at temperatures ≤ 16°C. Among three protist isolates tested (Paraphysomonas sp., Uronema marinum and Caecitellus paraparvulus), Caecitellus paraparvulus was particularly efficient at controlling E11 (2.1-log10 reduction over four days with an initial protists concentration of 103 cells × ml-1). In addition, other viruses (human adenovirus type 2 and bacteriophage H6) exhibited different grazing kinetics compared to E11, indicating that the efficacy of antiviral action also depended on the type of virus. In conclusion, indigenous bacteria and protists in lake water and seawater can modulate the persistence of E11. These results pave the way for further research to understand how microorganisms control human viral pathogens in aquatic ecosystems and to exploit this process as a treatment solution to enhance microbial water safety.

2020