As a microbiologist who has studied bacteria in his lab for more than 30 years, Harry L. T. Mobley points out that most strains are good, and that many are necessary for basic biological functions in the human body, including digestion.

But, there is another group of bacteria that do bad things and are harmful to other strains of bacteria, and also to humans.

He points the finger specifically at Proteus mirabilis, a fascinating organism that is responsible for infections in humans. It can lead to the formation of kidney stones and is a leading cause of urinary tract infections, especially in the elderly.

Mobley also studies E. coli, the most common cause of these infections in otherwise healthy women.

“It is more important than ever that we understand how these things tick,” says Mobley, the Frederick G. Novy Distinguished University Professor of Microbiology and Immunology, and chair of the department. “Because we need to stop them.”

Mobley will discuss bacteria — good and bad — during his Distinguished University Professorship lecture, “Stones, Spears, and Bacterial Social Aggression at Its Worst” at 4 p.m. Tuesday in the Rackham Amphitheater.

In addition to chronicling a career that spans more than 30 years, he will share his perspective from sitting ringside for a fight that is being staged in Petri dishes, the smallest of battlefields.

He has watched through the microscope lens as strains of bacteria come together. Not content to simply coexist, they engage in a battle to the death, injecting each other with protein spears full of toxins. Usually only one strain emerges victorious; sometimes both bacterial strains die from the encounter. He calls this social aggression at its worst.

“They don’t like to mix it up with other strains because that disrupts their ability to swarm as a group. They want to keep other strains out of their territory,” says Mobley, who also holds the Frederick G. Novy Collegiate Professorship in Microbiology and Immunology. “So, they kill the other strains — they kill their neighbor.”

The survival of bad bugs has major implications for human health. Not only are they winning the battle of bacteria; they also are gaining ground in the disease war, often at great cost to humans.

“We are beginning to lose the battle with these bacteria using our traditional tools, like antibiotics,” he says. “Bacteria are becoming increasingly resistant to antibiotics, so we need to invent more tools — more vaccines and new antibiotics.”

Mobley joined the battle against disease in 1973 when he developed an interest in microbiology while playing soccer at Emory University in Atlanta. At the time, the Centers for Disease Control and Prevention were housed on campus. He quickly became interested in learning about how bacteria cause disease.

Now, Mobley is the seventh chair of the Department of Microbiology and Immunology, carrying on the legacy of Novy, the first leader of the oldest microbiology department in the country. Mobley has helped the department double the size of its faculty and students, and his unit will move into the top 10 in National Institutes of Health funding this year.

As humans look to gain ground in the war on life-threatening infections, Mobley says new research methods and faster data analysis will lead to more effective and more personalized treatments.

“When I started, we had to study one gene at a time in a test tube. Now we can look at the activity all of the genes in a bacterial strain at once during actual human infections,” he says. “Going forward, the same critical biological questions will be asked; but now, we will be able to answer them more quickly.”

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• Distinguished University Professors