Ecology of Pathogenic Bacteria in the Environment
Pathogenic bacteria (such as those causing gastroenteritis, pneumonia, and other common diseases) are adapted to fluorish under the conditions within their hosts’ bodies. My colleagues (Joan Bernhard and Becky Gast) and I are interested in how these bacteria survive under conditions that are less favorable, such as marine and freshwater systems. The longer these bacteria survive in the environment, the greater the chance that they will infect humans and animals. Understanding the processes causing bacterial mortality, including both abiotic (UV light, desiccation) and biotic (bacterial grazers, viruses) factors, will allow us to better understand the fate of pathogens released into the environment through untreated human and animal waste.
Microbial Trojan Horses
Protists (e.g. ciliates, flagellates, and amoebae) are the main consumers of bacteria in the environment. Individual ciliates, for example, can ingest several hundred to several thousand bacteria per hour. However, not all bacteria that are ingested are digested. Certain pathogenic bacteria are capable of resisting protist digestion and can actually survive for extended periods within the cell body of bacterivorous protists. Within the host’s cell body, the bacteria are more resistant to both chlorination and antibiotics. The term ‘Trojan Horse’ describes how these pathogenic bacteria are concealed and protected in an innocuous host. The most notable example of such a relationship is Legionella pneumophila (the causative agent for Legionnaire’s disease) and its host, Acanthamoeba. Outbreaks of Legionnaire’s disease have been traced back to Legionella living within amoebae. Legionella can reproduce within their amoeboid hosts; amoebae are capable of releasing aggregates of live bacteria back into the environment. When these aggregates are aerosolized, they can be inhaled and infect Alveolar macrophages, the immune cells which normally ingest and destroy inhaled bacteria.
While the interactions between pathogenic bacteria and bacterivorous protists have been detailed in a few models (most notably Legionella and Acanthamoeba), it is unknown how the vast majority of protists will react when exposed to digestion-resistant pathogenic bacteria.
Metabolizing bacterial pathogens
Bacteria and their predators represent the most continuous predator-prey relationship on earth; they are found in almost every aqueous environment on the planet. My work is focused on expanding our knowledge of protists-pathogen interactions, with the hope that we can learn more about how common and abundant protists process and metabolize pathogens. For example, what conditions lead to the establishment of the intracellular bacterial symbiont? How long does the symbiotic bacteria persist? Are some protists capable of counteracting digestion resistance of pathogenic bacteria? Addressing these questions will shed light upon fundamentals of bacterial survival in the environment and microbial symbioses.
Oceanus article on Trojan horses
(See description of a recent talk at the Science Made Public Lecture Series)
PhD, Marine Sciences, University of Georgia, 2008 MS, Biology, University of Akron, 2002 BS, Biology, Ohio University, 1997