Microbiologists at the University of Louisville study Yersinia pestis, the bacteria that causes bubonic plague, however, because it has the potential to be used as a bioweapon and it provides knowledge that may help defeat other bacteria. Through this work, they have made an important discovery about a molecule secreted by Y. pestis and other bacteria that helps defeat the host’s immune defenses, allowing the bacteria to infect its hosts.

Sarah Price, a doctoral student researcher, and her mentor, Matthew Lawrenz, associate professor of microbiology and immunology, have found that yersiniabactin, a small molecule secreted by Y. pestis, gathers zinc, a necessary element for bacterial replication. This discovery may have implications in other infections as well since bacteria causing pneumonia, sepsis and other illnesses also are known to release yersiniabactin.

“While yersiniabactin’s role in iron acquisition has been well known for over 30 years, we were surprised to see its significant impact on zinc acquisition during Y. pestis infection,” Price said “This is very exciting because it helps us understand how Y. pestis and other bacteria acquire nutrients that allow them to cause disease.”

Invading bacteria as well as the hosts they infect all require iron, zinc and other metals in order to grow. The host’s immune system employs a strategy called nutritional immunity to protect against these bacterial infections, sealing the metals away from the bacteria.

It has been known for many years that yersiniabactin defeats this defense by stealing away iron and delivering it into the bacterial cells. Price and Lawrenz have discovered that the molecule also is involved in securing zinc and perhaps even other metals to assist Y. pestis infection.

Yersiniabactin also is used by Escherichia coli, which causes a multitude of infections such as intestinal illness and kidney infections, and Klebsiella pneumoniae, which causes pneumonia and sepsis. These more common diseases can be life-threatening and multidrug-resistant infections. The new understanding may lead to additional strategies for controlling infection by all of these bacteria.

An article describing the research published Oct. 29 in  provides details about how the researchers determined that yersiniabactin was responsible for the collection of not only iron, but zinc. Price is first author on the publication, “.” Lawrenz is senior author and researchers from the University of Kentucky, Washington State University and the University of Illinois also contributed to these studies.

“With this understanding of the broader role of yersiniabactin in plague infection, we can explore further to understand its role in enabling other bacteria to infect a human or other host,” Lawrenz said. “If this mechanism holds true across these bacteria, it may be possible to develop a drug or vaccine that could inhibit yersiniabactin’s effectiveness, thus preventing all of these infections.”

Bubonic plague most often is transmitted to humans through the bite of an infected flea, usually carried by a rodent. By not handling animal carcasses, preventing flea bites and avoiding contact with bodily fluids of those infected, the spread of bubonic plague is largely controlled. However, since human-to-human transmission is possible, mortality from an infection ranges from 30-to-90% and no vaccine is available to prevent the infection, it remains an important pathogen for research. In addition, Y. pestis, has the potential for weaponization and is considered a bioterrorism threat.

Lawrenz, Price and their colleagues conduct research within the , which focuses on the development of prevention and treatment strategies for infectious diseases and other harmful pathogens. Its researchers utilize the Regional Biocontainment Laboratory, a member of the National Institute of Allergy and Infectious Diseases network of 12 regional and 2 national biocontainment laboratories for studying infectious agents. The lab includes Biosafety Level 3 facilities built to the most exacting federal safety and security standards to protect researchers and the public from exposure to the pathogens being investigated. 

The center’s researchers were called upon in early 2020 to develop tests and prevention and treatment strategies against SARS-CoV-2, the virus that causes COVID-19. This work continues.

Between Aug. 25 and Sept. 1, investigators from the tested nearly 3,000 Jefferson County residents for the to detect the presence of the virus in participants’ nasal swabs by the polymerase chain reaction (PCR) method and for the presence of antibodies against the virus in their blood.

The results showed that approximately 1.1% of all the participants tested positive for active coronavirus infections. Among vaccinated participants only 0.7% had an active infection, while nearly 5% of unvaccinated participants were actively infected. This number would roughly correspond to 7,260 active infections in the county, a nearly tenfold increase in infection rates over the rates measured in April, despite a sharp increase in vaccinated residents, as shown in Figure 1.

As in previous testing rounds, the team also tested for antibodies in participants. They found that independent of their vaccination status, in both the sampled and volunteer groups, nearly 16% of the participants had natural infection antibodies against the virus suggesting that they must have been infected by the virus in the recent past. These data indicate that in the last few months, at least 100,000 adults in Jefferson County have had COVID-19.

“These results highlight the steep rise in coronavirus infections in our community and provide a startling snapshot of the current state of the pandemic,” said Aruni Bhatnagar, director of the Envirome Institute. “Our estimates suggest that the number of infected individuals may be twice as high as that indicated in public records.

“Our work shows the vaccine is working as intended. Our population was almost 90% vaccinated, much higher than the 64% of fully vaccinated county residents. In the entire cohort, vaccinated people were over 12 times less likely to be infected compared with unvaccinated people. Though in our volunteer group, 65% of the active infections were in fully vaccinated individuals who had received the vaccine earlier this year. Most reported no or mild allergy-like symptoms and did not recognize that it may be a COVID infection thus did not think they needed to get tested.”

The study also provided estimates of where in Jefferson County the infections are most prevalent. To identify infection rates in different areas, the researchers classified the participants into neighborhood zones, as shown in Figure 2.

The highest rate of active infection was found in Zone 3A, or far southwestern Jefferson County. The highest rate of those recently having had an infection was found in Zone 3B, central southern Jefferson County, as shown in Figure 3.

Participants from Zone 3B also reported lower rates of vaccination, although vaccination rates were lowest in Zone 1B in western Jefferson County, as shown in Figure 4.

“Even though nearly 90% of the participants in the entire study population were vaccinated, we had areas that reported as low as 60% vaccination, and the persistence of infection in some geographical areas seems to be related to lower rates of reported vaccination,” said Rachel Keith, associate professor of environmental medicine at UofL who conducted the study. “Our results show that much work remains to be done and that knowing that rates of infection are high in their community may be an added incentive for some individuals to get vaccinated.

“Additionally, knowing that fully vaccinated individuals may still get an active infection allows those individuals to take additional precautions such as masking or testing which helps keep the community safe, including any young or immunocompromised friends and families who may need extra protection.”

“The vaccine is very effective. Nearly 96% of vaccinated individuals had detectable levels of antibodies against the virus in their blood. However, in a small number of people (less than 0.6%) the levels of antibodies were undetectable in our assay, even though these individuals were fully vaccinated,” Keith said. “The lack of a measurable response in some individuals even after vaccination may be due to their health and immune status. We are analyzing our results to find out more about why some rare individuals do not develop high antibody levels in response to vaccination.”

Using the data from more than 7,000 individuals tested over the past year, the team is trying to identify personal and environmental characteristics that increase the risk for coronavirus infection and how vaccination reduces this risk.

For this round of testing, the team collected samples at 13 locations across Jefferson County. Active coronavirus infections were analyzed by Bluewater Labs and antibodies against the virus were assayed at at the .

To randomly sample people from all parts of the city and to include proportional number of individuals of different age and race/ethnicity, researchers at UofL partnered with Westat to mail approximately 30,000 letters asking people to participate in the study. Nearly 1,000 people who responded to this invitation were tested and an additional 1,886 booked their own appointments after hearing about the study in the news or on social media.

This study was supported in part by a contract with the Centers for Disease Control and Prevention.

Researchers at the University of Louisville  are working at the forefront in combating these pathogens. The CPM has been testing the effectiveness of new drugs against P. aeruginosa under a contract with the National Institutes of Health since 2013, and a new contract from the U.S. Food and Drug Administration will expand the center’s work in testing new drugs against this pathogen. Under the new two-year, $933,606 contract, CPM will develop a validated model for screening antimicrobial drugs against P. aeruginosa.

“This model likely will play an important role in drug development pipelines leading to identification of new antimicrobial drugs,” said Matthew Lawrenz, PhD, associate professor of microbiology and immunology who is leading the research. “Researchers at UofL and from around the world will use the model to screen new antimicrobials against multi-drug resistant bacteria prior to clinical trials.”

Forest Arnold, DO, hospital epidemiologist for UofL Hospital and associate professor in the Division of Infectious Diseases in the UofL School of Medicine, said multi-drug resistant bacteria and XDR bacteria, those with resistance to all existing antibiotics, are evolving faster than the drugs to kill them.

“The germs get smarter as we make new drugs. If we are going to stay on top of them, we need new antibiotics, especially new classes of antibiotics — those with a new mechanism of action that the germ hasn’t seen before,” Arnold said.

Infections with MDR bacteria are particularly threatening for patients with weakened immune systems, those who have had multiple rounds of treatment with antibiotics, and in patients using devices such as ventilators and blood catheters. Since these bacteria are now resistant to many of the antibiotic drugs used to treat them, they can lead to severe infections and death.

“If you have an infection with a bacterium we don’t have an antibiotic to treat, it could kill you,” Arnold said.

P. aeruginosa is common in the environment and in otherwise healthy people, it may cause relatively minor of the ear, skin or eye. However, in people with weakened immune systems or in hospital settings, P. aeruginosa can cause serious, life-threatening infections of the blood, lungs, digestive tract or tissue. Infected wounds will have a green pus or discharge and a fruity smell.

The validated animal model, to be developed by UofL researchers with collaborators at the University of Kentucky and the University of Wisconsin, will be used to test new compounds developed by drug companies and research labs around the world against P. aeruginosa. This model will allow testing against multiple strains of pseudomonas and will give more detailed information about the effectiveness of the drugs being tested.

“The previous methods we used for testing the drugs provided basic information about a compound’s effectiveness. This new model will allow us to test anything from older classes of antibiotics to brand new classes and will provide information on dosing and scheduling. In addition, we will be able to test different strategies, such as immunomodulation – targeting the host to better respond to the infection as opposed to directly killing the bacteria,” Lawrenz said.

The CPM’s new contract with the FDA will take advantage of the sophisticated resources at the , located on the UofL ShelbyHurst Campus, which provide the environment necessary for this work.

“This new contract from the Food and Drug Administration supports the development of a model for understanding how bacteria build resistance to current commercially available antibiotics, which in turn, will lead to the discovery of new drugs or methods to combat a variety of infectious diseases,” said Robert Keynton, PhD, interim executive vice president for research and innovation at UofL. “The UofL Center for Predictive Medicine and the Regional Biocontainment Laboratory represents a significant investment in infrastructure, faculty and staff by the university in the field of emerging infectious diseases, which is one of our research and training strategic priorities.”