How Do Micro-organisms Evolve to Become Pathogens?

For August 14, 2019                Please share with your friends and neighbors.

Hi WN@TL Fans,

Microbes—bacteria, fungi, viruses, protists and other tiny critters—are everywhere.  They are in the soil, in the water, on the plants, in the rocks and even in the air.  They live urbi et orbi. They are ubiquitous. Yet they never quit.  They never quit adapting, never quit evolving, never quit amazing.

Nevertheless, most of them we don’t notice.

Some of them we wrangle and rope into doing our bidding:  brewing our beer, raising our bread, sharpening our cheese.  

Then there are those few, those maleficent few, that band of microbes that have taken great divots out of humanity, and that have served as grand pivots of history.   

How is it that microbes can go from ubiquitous and innocuous to infectious and deadly?  It is, to echo Churchill’s view of Russia, a riddle wrapped in a mystery inside an enigma.

This week (August 14) Caitlin Pepperell  of the Department of Medical Microbiology & Immunology, and also of the Department of Medicine, will pose and parse the question, “How Do Micro-organisms Evolve to Become Pathogens?” 

Here’s how she describes her talk:

A case study of bacterial pathogen emergence: Staphylococcus saprophyticus. Where do pathogens come from? Microbes are all around us, but infectious diseases arise from a tiny fraction of these diverse organisms. Research in my lab is aimed at uncovering the origin stories of pathogenic bacteria: the where, when, how and why of infectious disease emergence.

 “Bacteria occupy incredibly diverse niches and adapt by a multiplicity of mechanisms. Pathogen origin stories reflect this ecological and evolutionary diversity, with our work and others’ showing that there are numerous paths to virulence. 

“This presentation focuses on the origin story of a pathogen I started working on by accident, Staphylococcus saprophyticus. S. saprophyticus, which infects humans and animals, is able to move fluidly among diverse environments. This bacterium illustrates the intertwined ecologies of humans, animals, and the natural and built environments we share. In this presentation, I will share what we have learned about how S. saprophyticus evolved to cause disease.”

More at

About the Speaker:

Professor Pepperell graduated from McGill University in Montreal, attained her MD at Queen’s University in Kingston, Ontario, completed residency in Internal Medicine at the University of Toronto, and followed up with fellowships in infectious diseases at the University of Toronto and then at Stanford University. She joined the faculty at UW-Madison in 2011.  


Next week (August 21) I’ll be speaking on the saga of genetically engineered crops from the early days in the 1970’s, through the first field tests in the mid ‘80s (right here in Dane County), and on to commercialization in the mid ‘90s. Now, 25 years later, we face the questions of how CRISPR technologies will be viewed, used and regulated across the globe.

It is mid-August, and at long last this summer’s Tomato Tsunami is finally upon us.

It’s a good time to reflect on the pioneering transgenic tomato of a quarter century ago, and to ponder what range of genetic techniques might be applied to the tomato and its kin in the coming decade.

Hope to see you soon at Wednesday Nite @ The Lab.

Thanks again!


Tom Zinnen
Biotechnology Center & Division of Extension