Department of Microbiology and Molecular Genetics
3313 Bio Engineering Facility
Michigan State University
East Lansing, MI 48824
Phone: (517) 884-6971
The Hardy laboratory studies bacterial infections that affect children, exploiting multiple techniques of live animal, non-invasive imaging. These methods reveal the extent of infection, as well as the consequences to the host, over time in individual animals. The methods are non-invasive and require only mild anesthetics, permitting the dynamics of the diseases to be visualized, and revealing patterns not readily apparent to more classical methods. One of our most important tools is in vivo bioluminescence imaging (BLI), invented by Professor Christopher Contag, now of the Biomedical Engineering Department at Michigan State. This technique employs recombinant bacteria, eukaryotic cells, and/or transgenic animals that express luciferase enzymes. Luciferases emit light that permits their detection in individual living animals over time, using an ultrasensitive CCD camera.
We have imaged infections of several bacterial pathogens in live mice. Our mainstay is Listeria monocytogenes, a foodborne pathogen that preferentially infects pregnant women. This well-studied bacterium has provided much information regarding infectious disease, including the first demonstration of cellular immunity by Mackaness in 1962, and the discovery of actin-based intracellular motility by Tilney and Portnoy in 1989. We use BLI to image Listeria in mice, revealing unsuspected growth patterns. BLI demonstrated that Listeria replicates in the lumen of the gallbladder, a finding that was unexpected, because this pathogen usually grows within cells. In the gallbladder lumen, Listeria replicates to large numbers, without causing any distress to the animal and serving as an internal reservoir of the bacteria. Colonization of the gallbladder lumen by Listeria was subsequently demonstrated in humans. The only other documented case of such growth is in human asymptomatic carriers of typhoid fever, in which the causative agent, Salmonella enterica Serovar Typhi, is carried in the gallbladder for the life of the individual. We are actively seeking to characterize this unusual ability of Listeria, and to develop a mouse model of asymptomatic typhoid fever carriage in the gallbladder, using Salmonella.
Prenatal bacterial infection results in many consequences for the fetus including severe, life-threatening septicemia, meningitis and pneumonia. Listeria is especially dangerous for pregnant women and exhibits nearly 20% fetal mortality. We have developed a mouse model of this infection using multiple imaging techniques in addition to BLI, including ultrasound and MRI. These methods provide structural and functional information about prenatal infection and its consequences. One of the more interesting effects of prenatal infection on the offspring is a predisposition for schizophrenia and other neurodevelopmental disorders. We are exploiting the prenatal infection of mice with Listeria to reveal mechanisms of this process.
In addition to Listeria, we are engaged in imaging several other bacterial pathogens that affect children. Pseudomonas aeruginosa infects cystic fibrosis patients, colonizing the lung, where it resists antibiotic treatment and often proves lethal. We employ BLI to image Pseudomonas in mice, in combination with Positron Emission Tomography (PET) to advance imaging in humans with probes specific for bacteria, and to test alternatives to antibiotics. We also image Pseudomonas and Staphylococcus aureus in wounds, where novel treatments for abscesses and other persistent infections can be evaluated. Imaging provides unique tools to interrogate the dynamic process of bacterial infection and reveal aspects of the basic biology of pathogens. The Hardy laboratory is dedicated to exploiting these methods for the benefit of children and others who suffer from these devastating illnesses.