Mycobacterium avium is an opportunistic bacterial pathogen that is known to survive in drinking water systems. It has been reported that M. avium is able to infect the amoeba Acanthamoeba castellanii, but little is known about the environmental relevance of this interaction. The objectives of this research were: (i) to determine if M. avium is able to infect a range of acanthamoeba strains including recent environmental isolates; (ii) to assess the stability of infections; and (iii) to determine the effect of co-culture on disinfection efficacy of M. avium using the drinking water disinfectant monochloramine. Infections were monitored and quantified using staining and fluorescence microscopy as well as by culturing methods. In this work, we found that M. avium was able to maintain stable infections in the eight acanthamoeba strains tested, including four recent environmental isolates. M. avium persisted in acanthamoeba and were still culturable after four weeks of co-culture, even under nutrient-poor conditions. During exposure of cultures to the disinfectant monochloramine, intracellular M. avium was found to be more resistant to monochloramine than free-living M. avium. This suggests that acanthamoeba-associated growth may serve as a mechanism to protect bacteria from disinfectants in drinking water systems. To test the rate of acanthamoeba infection in complex biofilm communities, acanthamoeba were allowed to graze on multispecies bacterial communities which had been spiked with M. avium at percentages of 1, 10, 25, 50, and 75% of total bacteria. After a 60 hour period, infection rates of acanthamoeba were proportional to the abundance of M. avium in the biofilm, suggesting a density-dependent infection rate.

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Matthias Horn is Professor for Microbial Symbioses at the Deparment of Microbial Ecology, University of Vienna, and has extensive experience studying bacterial endosymbionts of free-living amoebae. He has applied a full cycle rRNA approach including 16S rRNA gene sequencing and fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes assigned to symbionts of Acanthamoeba spp. and Hartmannella sp., finding five different evolutionary lineages within the Proteobacteria, the Bacteroidetes, and the Chlamydiae, respectively. Several of these bacterial symbiont groups are most closely related to bacterial pathogens of humans, and it has been suggested that some of them should be considered potential emerging pathogens. Complete genome sequence analysis of a chlamydia-related symbiont of Acanthamoeba sp. showed that this endosymbiont uses similar mechanisms for interaction with its eukaryotic host cell as well known bacterial pathogens of humans. Furthermore, phylogenetic analysis suggested that these mechanisms have been invented by the ancestor of the amoeba symbionts in interplay with ancient unicellular eukaryotes. Currently, functional genomics of chlamydial symbionts, including global transcription and proteome analysis is a major research focus in Dr. Horn�s laboratory. Dr. Horn has 34 publications in peer-reviewed journals and eight book chapters and other publications. He has given 15 invited talks at university seminars and international conferences.

Lutgarde Raskin is a Professor of Environmental Engineering in the Department of Civil and Environmental Engineering at the University of Michigan. During the past 15 years, Professor Raskin has developed a leading edge and productive research program that is based on her expertise in molecular microbial ecology, environmental microbiology, and biological process engineering. A significant part of her work has focused on the development of molecular methods that allow for the quantification and visualization of microorganisms in complex microbial systems. Recent work has focused on techniques that can monitor growth and activity levels of microbial populations. Major applications of Professor Raskin's work have been in anaerobic waste treatment processes, filamentous foaming problems in activated sludge systems, and use of biologically active carbon to remove nitrate and perchlorate from drinking water. Her research has resulted in 80 refereed journal publications, one book, and six book chapters. She has presented over 50 invited lectures at university seminars and international conferences.

Michael Wagner is the head of the Department of Microbial Ecology, University of Vienna. He has experience discovering the identity and ecophysiology of microorganisms within selected environmental systems and to deciphering their interactions among each other and with eukaryotes, particularly through the development of novel molecular and microscope techniques. These studies are complemented by (eco-)genome, transcriptome, and proteome analyses of microbial key players. Dr. Wagner has 137 publications in peer-reviewed journals and 31 book chapters and other publications; the papers published during the last 10 years received 4,094 citations according to ISI Web of Science (rank 35 of all microbiologists). He also has given 88 invited talks at university seminars and international conferences.

Chuanwu Xi is an Assistant Professor in the Department of Environmental Health Sciences at the University of Michigan. He obtained his Ph.D. in molecular microbiology in 2000 from the University of Leuven, Belgium. He has extensive experience in microbial genetics, molecular biology, and flow cytometry. During his Ph.D. work, he constructed a bi-functional genetic tool containing gusA and gfp genes for studying gene expression and bacterial tracing simultaneously. More than 60 research groups around the world have requested this genetic tool. His Ph.D. and postdoctoral research have resulted in nine publications in highly ranked journals including two in the Proceedings of the National Academy of Sciences. He uses advanced imaging tools and nanotechnology to study biofilm development, the spread of antibiotic resistance, and control of biofilm-related infections. His research interests include the elucidation of molecular mechanisms of persistence and resistance of pathogens in natural, engineered and industrial environments.

Researchers should cite this work as follows:

• (2009), "Interactions of the bacterial pathogen Mycobacterium avium with amoebae," http://globalhub.org/resources/1768.

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