Michele Swanson, Ph.D.

Professor
734-647-7295

Areas of Interest

LEGIONELLA PNEUMOPHILA VIRULENCE AND ENVIRONMENTAL RESILIENCE

Legionella pneumophila is water-borne pathogen that replicates within fresh water amoebae and protozoa. When inhaled by vulnerable people, this gram-negative bacterium can colonize lung macrophages and cause a severe pneumonia, Legionnaires' disease. 

Metabolic cues govern virulence and resilience. To persist in the environment, L. pneumophila alternates between distinct cell types. Replicative cells grow within amoebae and macrophages, whereas a motile, infectious, transmissive form is equipped to escape a spent host and primed to invade a naive one. After prolonged starvation, L. pneumophila differentiates into a highly resilient Mature Infectious Form. By applying genetic, biochemical and cell biological methods, we have identified both metabolic cues and signal transduction pathways that govern the pathogen's complex lifecycle. By coupling cellular differentiation to its metabolic state, L. pneumophila swiftly acclimates to stresses encountered in host phagocytes or the environment, thereby enhancing the pathogen’s fitness in natural and engineered water systems.

Transmission to humans in water aerosols.  L. pneumophila can cause either sporadic disease or outbreaks of Legionnaires’ disease, as occurred in Flint, MI in 2014-2015.  Vulnerable humans become infected by inhaling contaminated water droplets generated by engineered devices, not other people.  Therefore, public health strategies focus on monitoring and eradicating L. pneumophila from built water systems.  To identify the mechanisms that equip this respiratory pathogen to persist in water and survive transmission in aerosols, we apply genetic, molecular, and microbiological techniques.  By identifying molecular markers of L. pneumophila virulence and resilience, we aim to guide microbial risk assessment approaches to keep public water systems safe.

Published Articles or Reviews

Flynn, K. J and M. S. Swanson.  Integrative Conjugative Element ICE-βox confers oxidative stress resistance to Legionella pneumophila in vitro and in macrophages.  mBio 5(3):e01091-14, 2014.

Abbott, Z. D., K. J. Flynn, B. G. Byrne, S. Makherjee, D. B. Kearns, M. S. SwansoncsrT represents a new class of csrA-like regulatory genes associated with Integrative Conjugative Elements of Legionella pneumophila.  J Bacteriol, 198(3):553-64, 2015.

Abbott, Z. D., H. Yakhnin, P. Babitzke, and M. S. SwansoncsrR, a paralog and direct target of CsrA, promotes Legionella pneumophila resilience in water.  mBio 6(3). pii: e00595-15, 2015

Byrne B. G., S. McColm, S. P. McElmurry, P. E. Kilgore, J. Sobeck, R. Sadler, N. G. Love, and M. S. Swanson:  Prevalence of infection-competent serogroup 6 Legionella pneumophila within premise plumbing in Southeast Michigan.  mBio 9(1): e00016-18, 2018.

Zahran, S., S. P. McElmurry, P. E. Kilgore, D. Mushinski, J. Press, N. G. Love, R. C. Sadler, M. S. Swanson:  Assessment of the Legionnaires’ Disease outbreak in Flint, Michigan.  PNAS 115(8):E1730-E1739, 2018.  Media: NPR All Things Considered, Michigan Radio Stateside, Weather.com, Wake Up with WURD

Konig L., C. Wentrup, F. Schulz, F. Wascher, S. Escolar, M. S. Swanson, C. Buchrieser, M. Horn:  Symbiont-mediated defense against Legionella pneumophila in amoebae. mBio 10(3). pii: e00333-19, 2019

Hughes, E. D., B. G. Bryne, and M. S. Swanson. A two-component system that modulates cyclic-di-GMP metabolism promotes Legionella pneumophila differentiation and viability in low-nutrient conditions. J Bacteriol, Jun 17, 2019. pii: JB.00253-19.