Bacterial Battle Armor: How a Frog Vaccine Alters Microbiome Against Deadly Fungus

A recent investigation by Penn State researchers suggests that the microbiome, a group of beneficial microorganisms living within a host, can be altered protectively by vaccines. This possible factor in vaccine efficiency has remained largely unexplored.

The study proposes that certain vaccines can cause a protective shift in the host organism’s resident microorganisms.

The role of a host organism’s microbiome, comprised of beneficial bacteria and fungi among other microorganisms, in its overall immune response is significant. Yet, the impact of vaccines designed to protect against harmful pathogens on this microbiome remains uncertain. The Penn State research team’s new study has found that a novel vaccine against the lethal chytrid fungus in frogs can change the microbiome composition. This change enhances the frogs’ resilience against future fungal exposures. The study, published in the journal Philosophical Transactions of the Royal Society B on June 12, posits that the overlooked microbiome response could be a key facet of vaccine efficacy.

Gui Becker, Associate Professor of Biology at Penn State and the lead researcher, explained that the microbiome helps in warding off pathogens through various means such as producing beneficial substances and competing for resources. However, the impact of vaccines on the microbiome remains a question. The team used frogs as a model to start probing this matter.

The chytrid fungus poses a severe threat to frogs and other amphibians, leading to species extinction and severe population reductions across continents. It causes a potentially deadly skin disease in susceptible species. Becker noted the pressing need for tools to control the fungus’s spread, one of the most significant wildlife pathogens. The study found that vaccines could induce a protective microbiome shift in certain cases, hinting at the potential of microbiome manipulation as a part of broader strategies to combat emerging pathogens.

The team exposed tadpoles to a non-lethal dosage of a metabolic product produced by the chytrid fungus as a vaccine. They then tracked the changes in the microbiome composition over five weeks, identifying bacterial species and their relative proportions. They further tested whether bacteria-specific products had any influence on chytrid growth by culturing each bacteria species.

Samantha Siomko, a master’s student in the Becker Lab at the University of Alabama at the time of the research and the paper’s primary author, stated that increasing the exposure to the chytrid product prophylaxis significantly shifted the microbiome composition towards bacteria that produce anti-chytrid substances. This shift could improve the microbiome’s defensive capabilities against the pathogen upon re-exposure.

Previous strategies to induce such a protective microbiome shift often involved adding potent antifungal bacteria, i.e., probiotics. However, these bacteria have to compete with other species in the microbiome to establish themselves, which is not always successful.

Becker noted the complexity and unpredictability of attempting to manipulate the microbiome community, like adding a bacterial probiotic. Yet, their research manipulated the entire bacterial community to improve its effectiveness against the fungal pathogen without introducing a living organism that would compete for survival resources.

While the number of species within the microbiome remained unaffected, their composition and relative proportions changed. The researchers found this to be a positive outcome, as reduced diversity in the frog microbiome can often cause sickness or death.

The team suggests this adaptive shift, termed “microbiome memory,” could have significant implications on vaccine efficacy. They aim to further understand this shift’s mechanisms and study microbiome memory in adult frogs and other vertebrates.

Becker stated that they employed a prophylaxis technique based on the chytrid fungus’s metabolic product. Vaccines using mRNA or live cells, like those used for bacterial or viral infections, might affect the microbiome differently. This possibility is a promising area for future research.

This research was a joint effort involving Becker, Siomko, Teagan McMahon from the University of Connecticut, Sasha Greenspan, Wesley Neely, and Stanislava Chtarbanova from the University of Alabama, Douglas Woodhams from the University of Massachusetts, and K. M. Barnett from Emory University. The work received support from the National Science Foundation, the National Institutes of Health, The University of Alabama, and The University of Tampa.

For reference: “Selection of an anti-pathogen skin microbiome following prophylaxis treatment in an amphibian model system” published on June 12, 2023, in Philosophical Transactions of the Royal Society B Biological Sciences. DOI: 10.1098/rstb.2022.0126

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More about Frog Vaccine and Microbiome Shift

• Penn State Study: [Link to the Penn State study](insert link here)
• Chytrid Fungus: [More information about the chytrid fungus](insert link here)
• Microbiome and Host Immune Response: [Understanding the role of the microbiome in the host immune response](insert link here)
• Vaccine Development in Other Species: [Exploring the potential implications for vaccine development in other species](insert link here)
• Manipulating the Microbiome: [Challenges and considerations in manipulating the microbiome](insert link here)
• Diversity of the Microbiome: [The importance of maintaining diversity in the microbiome](insert link here)