Showing papers by "Frederik Hammes published in 2010"

Cytometric methods for measuring bacteria in water: advantages, pitfalls and applications

Abstract: Rapid detection of microbial cells is a challenge in microbiology, particularly when complex indigenous communities or subpopulations varying in viability, activity and physiological state are investigated. Flow cytometry (FCM) has developed during the last 30 years into a multidisciplinary technique for analysing bacteria. When used correctly, FCM can provide a broad range of information at the single-cell level, including (but not limited to) total counts, size measurements, nucleic acid content, cell viability and activity, and detection of specific bacterial groups or species. The main advantage of FCM is that it is fast and easy to perform. It is a robust technique, which is adaptable to different types of samples and methods, and has much potential for automation. Hence, numerous FCM applications have emerged in industrial biotechnology, food and pharmaceutical quality control, routine monitoring of drinking water and wastewater systems, and microbial ecological research in soils and natural aquatic habitats. This review focuses on the information that can be gained from the analysis of bacteria in water, highlighting some of the main advantages, pitfalls and applications.

Cultivation-independent assessment of bacterial viability.

Abstract: Cultivation-independent assessment of bacterial viability is essential when (1) results are required fast and at high throughput, and/or (2) when the specific target or mode-of-action of a certain bactericidal process is of interest, and/or (3) when the organisms under investigation are regarded as "uncultivable". However, aside from cultivation, there exists no "silver bullet" method that demonstrates with absolute certainty whether an organism is alive or dead, and all currently available methods are prone to produce varying results with different organisms and in different environments. Here we discuss the fundamental concept of viability in bacteria, with specific focus on the main aspects that define it. It is argued that the presence of intact and functional nucleic acids, as well as an intact and polarized cytoplasmic membrane are essential components of cellular viability, while numerous other parameters and processes that are linked to viability are explored. Different methods/approaches are discussed with particular emphasis on the advantages and disadvantages of each approach, the applicability of the methods toward environmental samples, and the underlying link between the various viability parameters.

Assessing biological stability of drinking water without disinfectant residuals in a full-scale water supply system

Abstract: Biological stability refers to the inability of drinking water to support microbial growth. This phenomenon was studied in a full-scale drinking water treatment and distribution system of the city of Zurich (Switzerland). The system treats lake water with successive ozonation and biological filtration steps and distributes the water without any disinfectant residuals. Chemical and microbiological parameters, notably dissolved organic carbon (DOC), assimilable organic carbon (AOC), heterotrophic plate counts (HPC) and flow-cytometric total cell concentration (TCC), were measured over an 18-month period. We observed a direct correlation between changes in the TCC, DOC and AOC concentrations during treatment; an increase in cell concentration was always associated with a decrease in organic carbon. This pattern was, however, not discerned with the conventional HPC method. The treated water contained on average a TCC of 8.97 × 10 4 cells ml −1 , a DOC concentration of 0.78 mg l −1 and an AOC concentration of 32 μg l −1 , and these parameters hardly changed in the distribution network, suggesting that the treated water had a high level of biological stability. This study highlights the descriptive value of alternative parameters such as flow-cytometric TCC for drinking water analysis, and pinpoints some of the key aspects regarding biological stability in drinking water without disinfectant residuals.

Evaluating the Growth Potential of Pathogenic Bacteria in Water

Abstract: The degree to which a water sample can potentially support the growth of human pathogens was evaluated For this purpose, a pathogen growth potential (PGP) bioassay was developed based on the principles of conventional assimilable organic carbon (AOC) determination, but using pure cultures of selected pathogenic bacteria (Escherichia coli O157, Vibrio cholerae, or Pseudomonas aeruginosa) as the inoculum We evaluated 19 water samples collected after different treatment steps from two drinking water production plants and a wastewater treatment plant and from ozone-treated river water Each pathogen was batch grown to stationary phase in sterile water samples, and the concentration of cells produced was measured using flow cytometry In addition, the fraction of AOC consumed by each pathogen was estimated Pathogen growth did not correlate with dissolved organic carbon (DOC) concentration and correlated only weakly with the concentration of AOC Furthermore, the three pathogens never grew to the same final concentration in any water sample, and the relative ratio of the cultures to each other was unique in each sample These results suggest that the extent of pathogen growth is affected not only by the concentration but also by the composition of AOC Through this bioassay, PGP can be included as a parameter in water treatment system design, control, and operation Additionally, a multilevel concept that integrates the results from the bioassay into the bigger framework of pathogen growth in water is discussed The proposed approach provides a first step for including pathogen growth into microbial risk assessment

Critical evaluation of the volumetric "bottle effect" on microbial batch growth.

Abstract: We have analyzed the impact of surface-to-volume ratio on final bacterial concentrations after batch growth. We examined six bottle sizes (20 to 1,000 ml) using three independent enumeration methods to quantify growth. We found no evidence of a so-called volumetric bottle effect, thus contradicting numerous previous reports.