According to a study, published in the special edition of the journal Philosophical Transactions of the Royal Society B, the microbiome response may be a significant factor in vaccine effectiveness.
A human or animal’s microbiome is a collection of frequently advantageous microorganisms, like bacteria and fungi, that reside on or within a host organism. The microbiome of the host can play a crucial role in its overall immune response; however, it is unclear how vaccines against harmful pathogens affect the microbiome.
A recent study performed by Penn State researchers discovered that a novel vaccine against the dangerous chytrid fungus in frogs can change the microbiome’s composition, making frogs more resistant to exposure to the fungus in the future.
According to Gui Becker, associate professor of biology at Penn State and head of the research team, the microorganisms that make up an animal’s microbiome often help defend against diseases by creating beneficial compounds or by competing against the pathogens for space or nutrients. However, what occurs to the microbiome after receiving a vaccination is what the researchers wanted to explore, and for this investigation, they used frogs as their model system.
The Chytrid fungus
The chytrid fungus, which has caused the extinction of some species and drastic population decreases in hundreds of others, poses a threat to frogs and other amphibians. The fungus causes a skin condition that can occasionally be fatal in sensitive species.
Chytrid is one of the worst pathogens for wildlife conservation lately in history, and thus it is imperative to create tools to stop its spread, according to Becker, a member of Penn State’s One Health Microbiome Center and the Center for Infectious Disease Dynamics.
He added, that the team discovered that vaccines can occasionally cause a protective shift in the microbiome, which raises the possibility that modifying the microbiome could be utilized as a part of a larger approach to assist amphibians and perhaps other vertebrates in coping with new infections.
In this study, the tadpoles were given a vaccine by the researchers, which was composed of a non-lethal dose of a metabolic product made by the chytrid fungus. They tracked the microbiome’s makeup for five weeks, identifying specific bacterial species and their relative abundances.
Additionally, each type of bacteria was cultivated in the lab by the researchers, who then evaluated whether bacteria-specific products aided, hindered, or had no effect on chytrid growth. Results were added to and compared with data from a sizable database of this information.
Vaccine and microbiome shift
According to Samantha Siomko, who is the first author of the study and was a master’s student in the Becker Lab at the University of Alabama at the time of the research, when the amount and exposure duration to chytrid products were increased, the preventive measures significantly altered the composition of the microbiome so that there was a greater number of bacteria producing anti-chytrid substances. This protective change could mean an animal’s microbiome would be better equipped to combat the disease if it were exposed to the same fungus again.
Notably, only the makeup and relative proportions of species were altered, not the total number of species or diversity, inside the microbiome. The researchers see this as a good thing because it is well known that maintaining a diverse microbiome enables the community of bacterial and microbe species to respond to threats more dynamically and with higher functional redundancy. Furthermore, declines in the diversity of the frog microbiome can frequently result in illness or death.
According to the researchers, this alteration in microbiome composition, which they refer to as microbiome memory may be crucial to the effectiveness of vaccines. The research team intends to investigate the microbiome memory in adult frogs and other vertebrate species in the future, in addition to understanding the mechanisms underlying the transition.
Becker said that the team put into practice a prophylaxis method that depended on a chytrid fungus metabolic product. And the possibility that vaccines based on mRNA or live cells—like those frequently used to protect against bacterial or viral infections—may differently affect the microbiome is what the team is excited to explore.