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Graduate student Anthony Pannullo passes PhD defense

Graduate successfully defended his PhD thesis entitled,  "Antimicrobial Sensing and Resistance in Clostridioides difficile" on Wednesday, January 25, 2023. Mentor Craig Ellermeier, PhD (left) is pictured with Anthony.   Craig Ellermeier and Anthony Pannullo image


Anthony was born just outside El Paso, Texas, to parents George and Helen Pannullo. After a series of moves, Anthony and his family ended up in Lincoln, Nebraska, where Anthony would eventually become (unfortunately for him) a devout Husker fan. Anthony spent most of his childhood being "that weird kid" who happened to know too many unnecessary animal facts for his own good.

Anthony attended the University of Nebraska-Lincoln for his undergraduate degree. He did not know exactly what he wanted to do with his life, but he watched many Crocodile Hunter growing up, so he decided to get a degree in Biology. It wasn't until his sophomore year that Anthony was introduced to the tiny wonders of the microbial world. As an undergraduate, Anthony joined Dr. Sydney Everhart's lab, where he studied the population genetics of the abundant fungal plant pathogen Sclerotinia sclerotiorum. In Dr. Everhart's lab, Anthony found an interest in molecular biology and a passion for taking beautifully complex biological systems and breaking them as much as possible.

Anthony wanted to extend his microbial interests to bacteria. Anthony decided to embark on the graduate school adventure and came here to the University of Iowa and joined the department of Microbiology and Immunology. Here, Anthony joined Craig Ellermeier's lab, where he began working on the unusual bacterial pathogen C. difficile. Anthony was excited to work with C. difficile as he was eager to get revenge for his hospitalization with a C. difficile infection. After over five years and untold liters of C. difficile, Anthony deems that the score has been settled. While in the lab, Anthony can usually be found surrounded by broken parts from the anaerobic chamber while trying to bargain with C. difficile to provide reasonable data for once.

While not in the lab, Anthony can be found bothering his friends to play D&D, enjoying the calming hobby of playing metal music on his guitar, or participating in philosophical conversations about the ocean's depth with his girlfriend, Lynnette.


Clostridioides difficile is a Gram-positive opportunistic pathogen that results in 250,000 infections, 12,000 deaths, and $1 billion in medical costs in the US each year. C. difficile infections are often difficult to treat due to C. difficile being resistant to a wide range of antibiotics. Even with successful treatments there is a 20% risk of recurrent infection. Because of this resistance, there have been recent investigations into alternative antibiotic therapies for use in treating C. difficile infections. There has been recent interest in using a daptomycin analog, Surotomycin, to treat C. difficile infections.

We identified a two-component system (TCS) HexRK and found that HexRK regulates a three gene operon of unknown function, hexSDF. We find that deletion of hexRK or hexSDF leads to decreased resistance to both daptomycin and bacitracin. Our data indicate that in the absence of HexSDF the phospholipid membrane composition is altered. In WT C. difficile the unique glycolipid, HNHDRG makes up ~16% of the lipids in the membrane. However, in a ∆hexSDF mutant, HNHDRG is completely absent.

We have also identified another TCS, DraRS. We find that when exposed to the lipid II inhibiting compounds daptomycin, vancomycin, bacitracin, and ramoplanin, activity of DraRS is increased. We also find that overproduction of the response regulator DraR leads to increased resistance to both daptomycin and bacitracin. We also found that DraRS partially regulates the previously mentioned hex locus.

Taken together, we have found two that work together to respond to a subset of lipid II interacting antimicrobial compounds. These systems also confer resistance to daptomycin and bacitracin, primarily through the production of the C. difficile unique glycolipid, HNHDRG.

Saturday, January 28, 2023