SPARK: Seminar Series on Pathogens, Advancements, and Research Knowledge

Biofilm Aggregates and Antimicrobial Tolerance in Orthopedic Infections

Total joint arthroplasty (TJA) procedures are estimated to rise by over 300% by the year 2030.  Periprosthetic joint infection (PJI) is the most significant complication following TJA with healthcare costs exceeding $1.6 billion annually.  Treatment of PJI generally requires surgical intervention combined with a prolonged course of antibiotics costing $50,000 per patient.  Despite this aggressive treatment, treatment is only successful in half of patients. The leading cause of treatment failure in PJI is the formation of protective bacterial biofilms or communities of bacteria encased within an extracellular matrix which are tolerant to commercially available antibiotics.  The Gilbertie lab is investigating why these biofilms form within the synovial environment, how antimicrobial tolerance develops causing treatment failure, and new treatments that directly target these biofilms overcoming their inherent antimicrobial tolerance.  At the core of the Gilbertie lab, is the use of large animal models and a One Health approach to these questions

Jessica Gilbertie MS DVM PhD, Associate Professor of Microbiology, Department of Biomedical Sciences and Pathobiology, Virginia Maryland College of Veterinary Medicine

Virtual Seminar - https://virginiatech.zoom.us/j/89419666443

Fragmented Realities: Resisting the Binaries of Infectious Disease Discourse

During COVID-19, much of the discourse in the United States about perspectives of vaccines and of pandemic science was framed in terms of binaries: pro-science or anti-science, vaccine advocate or anti-vaxxer, responsible or selfish, trusting or mistrusting, reliable information or misinformation, etc. These dominant stories about how people think or what motivates them relative to trustworthy science overlook the complexity and nuance of people’s experiences and motivations, leading to stalemates in the promotion of infectious disease control and prevention behaviors. Antenarratives are a tool for understanding in situ and messy stories that do not follow a tidy beginning, middle and end. I will present antenarrative threads from an interview study with local Spanish-speaking residents to highlight non-linear strands of fear, myths, and resilience beneath the dominant COVID-19 story. In doing so, I will highlight the importance of narrative analysis, rhetoric, and thick description in understanding uptake of infectious disease control and prevention behaviors. 

Julie Gerdes, Assistant Professor, Department of English, Virginia Tech

Aspergillus fumigatus septins hold the key to unlock the cidal effect of the anti-cell wall drug caspofungin

Septins are a conserved family of GTP-binding proteins. In Aspergillus fumigatus, the etiological agent of invasive aspergillosis, septins participate in various roles, including asexual spore production, septation, and response to anti-cell wall stress. Previous studies indicate that the ∆aspB is more sensitive to anti-cell wall drugs. Nonetheless, how AspB contributes to the fungal response to anti-cell wall agents is unknown. Using cell viability staining post-caspofungin exposure, we found that the ∆aspA, ∆aspB, and ∆aspC strains are less viable than the wild-type strain. These results indicate that the septin cytoskeleton is important for A. fumigatus survival in the presence of caspofungin. Due to the potential for improved therapeutic outcomes, we tested if deleting aspB resulted in improved caspofungin treatment using a neutropenic murine model of invasive aspergillosis. Gene deletion of the aspB gene resulted in improved survival, reduced pulmonary inflammation, and reduced fungal burden when treated with caspofungin, compared to the wild-type or untreated ∆aspB strains. We identified four AspB-interacting protein candidates with possible roles in cell wall integrity using quantitative proteomics. Gene deletion of these candidate genes resulted in an increase in susceptibility to caspofungin and a moderate reduction in viability post-drug exposure. These data suggest that septin AspB contributes to the fungal response to caspofungin. 

"Chewing the fat: lipids as second messengers in Staphylococcus aureus signal transduction"

Two-component systems (TCSs) are the predominant signal transduction system in bacteria for monitoring their external environment. Typical TCSs contain a membrane histidine kinase with a large extracellular domain that binds a ligand. The resulting autophosphorylation and phosphoryl transfer to a response regulator DNA binding protein adjusts gene expression. We discovered a subclass of TCS histidine kinases in S. aureus that is responsive to the lipid composition of the bacterial phospholipid bilayer. In this seminar, I will discuss our efforts to combine classical genetic and biochemical techniques with native mass spectrometry and spatial lipidomics to understand the mechanism by which membrane lipids alter the activity of these histidine kinases. I'll also describe a new biosynthetic pathway we discovered for the synthesis of these lipids and the potential role of this pathway during infection.

Shaun R. Brinsmade, Ph.D. 
Associate Professor, Department of Biology
Associate Professor, Department of Microbiology & Immunology
Georgetown University College of Arts & Sciences

The bacterial pathogen Brucella: Communication, gene regulation, and virulence

  Brucella spp. are intracellular bacterial pathogens that primarily infect macrophages and cause abortions and sterility in a variety of wild and domesticated animals, as well as a chronic, debilitating flu-like illness in humans. Each year, Brucella infects approximately 2.1 million humans worldwide, and combating human Brucella infections is currently limited to an extensive course of antibiotics that is often not fully effective. Moreover, there is currently no safe and effective vaccine to protect humans against infection with Brucella.

Our laboratory is focused on identifying and characterizing systems in Brucella spp. that are critical for the ability of the bacteria to successful infect and colonize the host, and currently our group is concentrating on two important areas of Brucella biology: 1) a cellular communication system called quorum sensing, and 2) genetic regulatory pathways directed by small regulatory RNAs.

Historically, bacterial quorum sensing has been epitomized by group behaviors, such as bioluminescence and biofilm formation, but more recently, quorum sensing systems have been intimately linked to the biology of bacteria that do not exhibit classical group behaviors. Nonetheless, quorum sensing is extraordinarily important in these bacteria for the coordination of virulence factors and interactions with hosts. In Brucella, two transcriptional regulators are critical for sensing and responding to the quorum sensing molecule, C12-acyl-homoserine lactone (AHL), and our group is interested in the interplay between these two regulators, as well as the biosynthetic origin of AHL in Bucella.

The other major focus area of our group involves virulence pathways controlled by small regulatory RNAs (sRNAs), which are small (i.e., ~50-400 nt) discrete RNA molecules that interact with mRNAs through short stretches of limited complementarity to regulate gene expression. Exploratory work by members of our group have revealed the presence of more 20 sRNAs, and importantly, some of these sRNAs are required for the ability of Brucella to survive and replicate in macrophages and to colonize experimental infected animals. Ongoing efforts involve characterizing the molecular mechanisms of Brucella sRNAs, particularly in regards to the physiological consequences of sRNA-mediated gene expression as it relates to virulence.

Clay Caswell, PhD, Associate Professor, Department of Biomedical Sciences and Pathobiology, Virginia Tech

"Dissecting the virulence strategies of Acinetobacter baumannii"

Healthcare-associated infections (HAI) are often associated with the use of medical devices such as catheters and ventilators, surgical procedures, transmission between patients and healthcare workers, and overuse of antibiotics. Annually, approximately two million patients suffer from HAIs and nearly 100,000 patients are estimated to die in the US. Acinetobacter baumannii is a leading global cause of HAI. This bacterium is a known cause of medical device-associated infections like ventilator-associated pneumonia and catheter associated urinary tract infection (CAUTI), as well as nosocomial skin and soft tissue infections. These infections are severe in vulnerable patients, which can have high rates of morbidity and mortality. In the last few years, the frequency of multidrug resistance (MDR) in A. baumannii has skyrocketed and it is currently the Gram-negative bacterium displaying one of the highest rates of multidrug resistance worldwide. Reflecting its growing impact on global health, the WHO and CDC have classified the species as an urgent, high priority threat in need of new therapeutics. Within hospitals, infected patients act as bacterial sources for transmission, often through colonization of high-touch surfaces and equipment. Key unanswered questions are: how are new A. baumannii strains first introduced into hospitals to colonize these surfaces, and from where does the “patient zero” who initiates an A. baumannii outbreak contract their infection. In this talk I will present animal models developed in my lab for both, CAUTI and pneumonia, which are allowing us to uncover the strategies that A. baumannii employs to cause infections. I will discuss our novel findings on the intracellular lifestyle of A. baumannii and how this previously unappreciated aspect of A. baumannii can mediate resurgent infections. Finally, I will discuss our efforts to target colistin-resistant A. baumannii

Mario F. Feldman, PhD, Professor of Molecular Microbiology, School of Medicine

Host: Zhaomin Yang

Mentor Road Show

Kevin Edgar, Associate Dean, VT Graduate School

Molly Ryan, President, VTGrATE

Mentorship is an important element of the life of a graduate student. A grad student is mentored by their principal advisor, often by a thesis committee, and by more senior students, for example. In turn, grad students act as mentors, including to more junior grad students in their research group or on their project, or towards undergraduates with whom they teach or do research. Often in academia graduate students receive no formal training in how to manage or mentor people; that would of course include graduate students who go on to become faculty members. There are VERY few careers in which the ability to effectively mentor people is not of paramount importance; therefore we try to present the “Road Show” widely to faculty members, graduate students, and postdocs at Virginia Tech as just one element of trying to improve mentorship skills, at VT and beyond.

The Road Show is instructional to a small extent, and to a much larger extent is participatory. We present real life mentorship scenarios to the group for discussion; what went wrong, what could the participants do to improve or mitigate the situation, what is everyone’s responsibility. We find that the ensuing discussions are quite enlightening to all participants. Come ready to speak up, share your thoughts, and listen to your fellow students.

No CeZAP Seminar today. We encourage everyone to attend the Entomology Seminar https://www.ento.vt.edu/seminar.html

"Solving Mysteries of the Apicomplexan Cell Cycle"

Apicomplexan parasites are opportunistic intracellular pathogens of humans and animals. Apicomplexan cell divisions are remarkably versatile and vastly differ from the division mechanisms of their host cells. While most apicomplexans divide in a multinuclear fashion, Toxoplasma gondii tachyzoites divide in the traditional binary mode using an extended set of atypical regulators. Why does such seemly simple replication type require activity of five non-redundant Cdk-related kinases? Does apicomplexan cell cycle have Gap 2 period that segregates chromosome replication and segregation processes? What is the primary cell cycle mechanism of apicomplexan parasites? Our studies attempt to address these outstanding questions of biology of apicomplexan parasites. 

Elena S. Suvorova, Assistant Professor, Department of Internal Medicine, University of South Florida

Host: Raj Gaji

We wanted to inform you of a change to the speaker lineup for the CeZAP SPARK scheduled for Thursday, November 7. Unfortunately, Dr. Nikki Shariat will no longer be able to visit in person at this time. However, we are excited to announce that Dr. John Maurer, Professor, School of Animal Sciences will be stepping in as the new speaker this week.

“Salmonella Vs. The Intestinal Microbiome: How Microbial Communities Make Salmonella Behave”

Evidence of Bidirectional Cross-membrane Signaling in Bacterial Sensor Histidine Kinases

Membrane-embedded signaling histidine kinases (SKs) are central players in gene regulation of bacteria, fungi, and plants. The SK GacS is a global regulator of gene expression in the human pathogen Pseudomonas aeruginosa. GacS activation promotes biofilm formation to establish the chronic persistent infections that often befall Cystic Fibrosis patients. At the same time, GacS suppresses factors associated with dangerous acute infections, that are major complications of transplant patients and burn victims. My group studies the interactions between GacS and other SKs, as a model for exploring non-canonical crosstalk in multikinase networks that coordinate virulence gene expression in bacterial pathogens. Through a combination of structural modeling, biochemical and biophysical analyses, and functional assays, we have uncovered novel signaling mechanisms that facilitate crosstalk and shape extracellular signal perception. As such, our work establishes an important precedent that may broadly impact in vitro screening strategies for SKs ligands and inhibitors.

Tracking Salmonella in the food chain: “traditional” genomic epidemiology and educated guesses

Despite substantial progress in foodborne pathogen surveillance and control, Salmonella remains a leading cause of foodborne infections in the United States and worldwide. The past decade has seen a (genome) data-driven revolution in public health microbiology, making genomic epidemiology a routine practice for tracking Salmonella throughout the farm-to-fork continuum. The sustained exponential growth of Salmonella genomes keeps fueling data-intensive applications, including recent iterations of machine-learning models for Salmonella source attribution. In this talk, we will demonstrate how hypothesis-driven data mining under the established genomic epidemiology framework helped solve a decades-old mystery central to a continent-sweeping pandemic of Salmonella. We will also discuss if educated guesses by harnessing “the unreasonable effectiveness of data” could inform us about the environmental origins of Salmonella. 

Xiangyu Deng, Professor, Department of Food Science and Technology

Host: Jingqiu Liao

New paradigms for Campylobacter jejuni survival in the gut

The Centers for Disease Control and Prevention report that Campylobacter jejuni is the leading cause of bacterial diarrhea in the USA, and infection leads to high rates of morbidity and mortality, particularly in low-and-middle income countries (LMICs). C. jejuni is often transmitted to humans through consumption of undercooked or contaminated poultry products. In LMICs, the microbe is a major cause of illness in infants and has been associated with growth stunting and deficits in cognitive development. The majority of C. jejuni isolates express surface glycans mimicking human gangliosides that play a key role in triggering Guillain-Barré Syndrome through formation of anti-ganglioside antibodies that fix complement onto human neurons. For all these reasons, there has been interest in exploring methods to reduce C. jejuni burden in chickens and preventing infection of humans. This talk will describe our efforts in better understanding the surface composition of the microbe and the importance of these features in avoidance of phage predation and contribution to immune recognition in order to combat infection by this problematic pathogen. 

Dr. Christine Szymanski, Professor, Department of Microbiology, Complex Carbohydrate Research Center University of Georgia

Host: Birgit Scharf