Vaccine Induces Antibodies in Mice Exposed to Wastewater Salmonella

Salmonella might seem like a mild inconvenience to some, but for sensitive groups, it can prove dangerous or deadly. In fact, 26,500 people are hospitalized by the bacterial infection each year in the U.S., and 420 people die, according to the U.S. Centers for Disease Control and Prevention.

In a step toward combatting Salmonella infections, UF/IFAS microbiology researchers have published a study that they hope will lead to a vaccine against the disease.

In the U.S., about 1.35 million Salmonella infections are reported each year, according to the CDC. Salmonella infections are often caused by consuming contaminated food or water or touching infected animals or livestock or their feces, and result in severe diarrhea and even arthritis post-infection.

The findings of the UF study will help advance the development of a vaccine that protects against non-typhoidal strains of Salmonella, for which there are no current vaccines, said Mariola Ferraro, a study author and associate professor at the UF/IFAS microbiology and cell science department. Ferraro said they also highlight how important it is to address solutions for antibiotic-resistant strains of Salmonella, since resistant strains were found in Gainesville’s wastewater. 

Antibiotic resistant strains of Salmonella are especially dangerous and pose a distinct threat to children under 5, adults 65 and older, immunocompromised people and people taking certain medications such as stomach acid reducers, according to the CDC. Non-typhoidal Salmonella differs from typhoidal Salmonella, which causes typhoid fever and which has a vaccine. 

The UF/IFAS study, published in Infection and Immunity, looks at a new method to deliver a Salmonella vaccine, which was tested in mice. While a previous study tested this vaccine with lab-derived strains of Salmonella, this time the researchers used Salmonella bacteria from the local environment – the wastewater system of Gainesville, Florida – and used those environmental, real-world strains to test the effectiveness of the vaccine they created, she said.

The study found that when tested with real-world strains of Salmonella, the vaccine created antibodies against this microbe in the mice – which equips the animals with a defense mechanism against Salmonella, Ferraro said.

The vaccine, which was given to the mice through their noses, used an innovative approach of using small extracellular vesicles (sEVs) as a delivery method. The sEVs are tiny particles created by cells and are one of the ways by which cells communicate with one another. In this study, researchers devised sEVs to carry bacterial proteins, allowing their transfer between cells and causing a long-lasting immune response. Since no live bacteria are given to mice, the risk for complications is lower.

She said the study not only found that the vaccine was causing immune response against real-world infections but highlighted the importance of these sEVs in regulating immunity – an important step toward understanding the immune system more fully.

The next steps will be to figure out sEVs’ role in the immune system and why these nano-sized vesicles could be safer and more effective at creating an immune response than introducing the bacteria into the body directly.

Lisa Emerson, the first author of the study, tragically passed away from natural causes in September at just 29 years old. She was a driving force behind the success of this research. 

Ferraro said Emerson had a deep dedication to integrating public health into microbiology research, and her passion for public health was clear to those who worked with her both at UF as a doctoral student and at the CDC, where she worked after graduation on studying emerging respiratory viruses. 

“Lisa truly cared,” Ferraro said. “That’s why she chose to work at the CDC — because public health wasn’t just a field to her; it was a calling.”

UF now has a memorial scholarship in Emerson’s name for a student studying microbiology, preferably who is planning a career in public health. 

Reference: Emerson LE, Bhimani S, Rainey AL, Maurelli AT, Ferraro MJ. Evaluating small extracellular vesicle-based vaccination across heterologous Salmonella strains isolated from wastewater. Infect Immun. 2025:e0048524. doi: 10.1128/iai.00485-24

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