PhD candidate Alfa Herrera successfully defends thesis

Tuesday, June 28, 2016

On June 24, 2016, Alfa Herrera successfully defended her thesis titled, "Sphingomyelinase and DNA Biofilm Ligase Activities of Staphylococcus aureus β-toxin Promote Infective Endocarditis and Sepsis”. She worked under the supervision of her mentor Dr. Patrick Schlievert and Herrera is pictured with him. 

Staphylococcus aureus is a gram positive bacterium asymptomatically colonizing 30-40% of the human population.S. aureus causes a variety of infections including superficial skin lesions, toxic shock syndrome, and infective endocarditis (IE). There are 100,000 cases of IE each year in the United States. S. aureus is the most commonly identified pathogen in patients with IE. IE is a life-threatening infection of native/prosthetic valves and the lining of the heart. It is characterized by the formation of vegetations, “cauliflower-like” structures composed of bacteria and host factors. S. aureus produces a variety of cell surface and secreted virulence factors which are important in the microbe’s capacity to cause disease, including microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), cytolysins, and superantigens (SAgs). The mechanisms of how SAgs and cytolysins contribute to IE is not well understood. My research focuses on the role TSST-1 and β-toxin have in the development of IE.

My studies have determined both TSST-1 and β-toxin increase lethality in a rabbit model of IE and sepsis. I found both toxins utilize multiple mechanisms of action to exert their effects during the infection. Specifically for my studies in β-toxin, I identified important residues for its poorly characterized DNA biofilm ligase activity. I was able to determine this activity as well as the sphingomyelinase activity promote the growth of vegetations during IE. Furthermore, the ability of β-toxin to increase lethality can be attributed to its sphingomyelinase activity. Via in vitro studies I showed β-toxin can either suppress or activate the host immune system in a concentration dependent manner through the use of both of its activities.

Biographical Sketch

Alfa was raised in Rock Island, IL alongside her brother Oscar, by her parents Pedro and Lourdes. With her parents constantly imparting the value of education she was always a very studious child. She would come home with a backpack full of textbooks every day (breaking many backpacks through the years) and spent hours after school doing homework. Which probably would have taken her much less time, had she not done most of it during TV commercial breaks. Alfa enjoyed learning about anything and everything and took every opportunity to do so. While her family would be out shopping you could find her hidden away at the mall bookstore, reading.

After high school, Alfa enrolled at the University of Illinois at Urbana-Champaign as an MCB major on a pre-med track. She realized she did not want to pursue the medical profession and following graduation was unsure of which career path to pursue. So she joined the lab of Dr. Rachel Whitaker at UIUC the summer following graduation as a research technician. In this laboratory, she completed work on the archaeum S. islandicus, investigating the evolutionary processes of isolated populations from different geographical locations. Her work focused mainly on host-virus interactions through studies of the CRISPR system. This exposure to research fueled her fascination for microbiology and triggered her interest in its involvement in everyday life. After working there for three years and with lots of support and encouragement from her mentor she decided to pursue a doctorate in microbiology.

Alfa entered the Biosciences program at The University of Iowa in August of 2011, and joined the laboratory of Dr. Patrick Schlievert. Here she focused most of her doctoral work on the S. aureus cytolysin, β-toxin. She characterized the active site of a novel activity of β-toxin and determined how its different mechanisms of action contribute to infective endocarditis by looking at an animal model of infection and studying its effects on human aortic endothelial cells.

Following graduation Alfa will begin a post-doctoral position in the laboratory of Dr. Karla Satchell at Northwestern University. The lab focuses on studying the large MARTX toxins of V. cholera and V. vulnificusand the role of its effector domains in disease.

Outside of lab, Alfa enjoys spending time with her family and boyfriend, Julian, watching reality TV, shopping, playing with her cats, cooking, eating, and keeping up on the latest celebrity trash news.